The text of the computer readable sequence listing filed herewith, titled “STDU2_41203_601_SequenceListing_Updated_20240716”, created Jul. 16, 2024, having a file size of 668,877 bytes, is hereby incorporated by reference in its entirety.
The foregoing applications, and all documents cited therein or during their prosecution (“appln cited documents”) and all documents cited or referenced in the appln cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention. More specifically, all referenced documents are incorporated by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.
The present invention relates to RNA-guided recombineering-editing systems using phage recombination enzymes as well as methods, vectors, nucleic acid compositions, and kits thereof.
The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system, originally found in bacteria and archaea as part of the immune system to defend against invading viruses, forms the basis for genome editing technologies that can be programmed to target specific stretches of a genome or other DNA for editing at precise locations. While various CRISPR-based tools are available, the majority are geared towards editing short sequences. Long-sequence editing is highly sought after in the engineering of model systems, therapeutic cell production and gene therapy. Prior studies have developed technologies to improve Cas9-mediated homology-5 directed repair (HDR) (K. S. Pawelczak, et al., ACS Chem. Biol. 13, 389-396 (2018)), and tools leveraging nucleic acid modification enzymes with Cas9, e.g., prime-editing (A. V. Anzalone, et al., Nature. 576, 149-157 (2019)) that demonstrated editing up to 80 base-pairs (bp) in length. Despite these progresses, there are continued demands for large-scale mammalian genome engineering with high efficiency and fidelity.
Provided herein are systems and methods that facilitate nucleic acid editing in a manner that allows large-scale nucleic acid editing with high accuracy and low off-target errors. These systems and methods employ a combination of recombination components with CRISPR recombination components.
For example, disclosed herein are systems comprising a protein, a nucleic acid molecule comprising a guide RNA sequence that is complementary to a target DNA sequence, and a recombination protein. A recombination protein may comprise an exonuclease, a single stranded DNA binding protein (SSB), a single stranded DNA annealing protein (SSAP), or functional fragment or activity thereof. A recombination protein may comprise or be engineered to comprise a two or more of the activities. In certain embodiments, recombination proteins are cooperative. In certain embodiments the recombination protein comprises a microbial recombination protein, for example a bacterial or bacteriophage protein, including but not limited to, RecE, RecT, lambda exonuclease (Exo), Bet protein (betA, redB), exonuclease gp6, single-stranded DNA-binding protein gp2.5, or a derivative or variant thereof. In certain embodiments the recombination protein comprises a eukaryotic or mammalian recombination protein. A certain non-limiting embodiments, a eukaryotic recombination protein or system comprises RAD52 or a homolog thereof which binds ssDNA, and mediates annealing of complementary ssDNA, including RPA-bound complementary ssDNA. In some embodiments, the system further comprises donor DNA. In some embodiments, the target DNA sequence is a genomic DNA sequence in a host cell.
In certain embodiments, the invention provides a system comprising one, two, three, or more recombination proteins of SEQ ID NO:166 to SEQ ID NO:491 or a recombination protein at least 85%, at least 90%, at least 95% identical, or higher thereto. In certain embodiments, the recombination protein has at least 85% identity to a recombination protein of Table 9. In certain embodiments, the recombination protein has at least 85% identity to SEQ ID NO:179, SEQ ID NO: 185, SEQ ID NO:205, SEQ ID NO:321, SEQ ID NO: 353, SEQ ID NO:359, SEQ ID NO:366, SEQ ID NO:424, or SEQ ID NO:479.
In certain embodiments, the recombination protein has at least 95% identity to SEQ ID NO: 166, SEQ ID NO: 168, SEQ ID NO: 169, SEQ ID NO: 170, SEQ ID NO: 171, SEQ ID NO:241, SEQ ID NO:253, SEQ ID NO:290, SEQ ID NO:408, SEQ ID NO:411, or SEQ ID NO:442.
In some embodiments, the system further comprises a recruitment system comprising at least one aptamer sequence and an aptamer binding protein functionally linked to the recombination protein as part of a fusion protein. In some embodiments, the aptamer sequence is an RNA aptamer sequence or a peptide aptamer sequence. In some embodiments, the RNA aptamer sequence is part of the nucleic acid molecule. In some embodiments, the nucleic acid molecule comprises two RNA aptamer sequences. In some embodiments, the recombination protein is functionally linked to the aptamer binding protein as a fusion protein. In some embodiments, the binding protein comprises a MS2 coat protein, a lambda N22 peptide, or a functional derivative, fragment, or variant thereof. In some embodiments, the fusion protein further comprises a linker and/or a nuclear localization sequence.
Without being bound by theory, the recruitment system serves to localize one or more recombination proteins to the location of a Cas protein/gRNA complex and via interaction between recombinase and a template nucleic acid promote HDR at a selected target while not promoting off-target Cas protein function.
The recruitment system is adaptable to a multitude of combinations and configurations of recombination proteins. For example, by selecting and incorporating multiple nucleic acid aptamers, the system can comprise multiple recombination proteins, which may be the same or different and in various ratios. In certain embodiments, the system comprises an exonuclease. In certain embodiments, the system comprises an SSAP. In certain embodiments, the system comprises an SSB. In certain embodiments, the system comprises an exonuclease and an SSAP.
In certain embodiments, the system comprises an exonuclease and an SSB. In certain embodiments, the system comprises an SSAP and an SSB. In certain embodiments, the system comprises an exonuclease and an SSAP and does not comprise an SSB. In certain embodiments, the system comprises an exonuclease and an SSB and does not comprise an SSAP. In certain embodiments, the system comprises an SSAP and an SSB and does not comprise an exonuclease. In certain embodiments, the system comprises an exonuclease, an SSAP, and an SSB.
Disclosed herein are compositions comprising a nucleic acid sequence encoding a fusion protein comprising a recombination protein functionally linked to an aptamer binding protein. The recombination protein may be a microbial recombination protein, including but not limited to RecE, RecT, lambda exonuclease (Exo), Bet protein (betA, redB), exonuclease gp6, single-stranded DNA-binding protein gp2.5, or a derivative or variant thereof. The compositions may further comprise one or both of a polynucleotide comprising a nucleic acid sequence encoding a Cas protein and a nucleic acid molecule comprising a guide RNA sequence that is complementary to a target DNA sequence. In some embodiments, the nucleic acid molecule further comprises at least one RNA aptamer sequence. In some embodiments, the polynucleotide comprising a nucleic acid sequence encoding a Cas protein further comprises a sequence encoding at least one peptide aptamer sequence.
Also disclosed herein are vectors comprising a nucleic acid sequence encoding a fusion protein comprising a recombination protein functionally linked to an aptamer binding protein. A microbial recombination protein may comprise RecE, RecT, lambda exonuclease (Exo), Bet protein (betA, redB), exonuclease gp6, single-stranded DNA-binding protein gp2.5, or a derivative or variant thereof. The vectors may further comprise one or both of a polynucleotide comprising a nucleic acid sequence encoding a Cas protein and a nucleic acid molecule comprising a guide RNA sequence that is complementary to a target DNA sequence. In some embodiments, the nucleic acid molecule further comprises at least one RNA aptamer sequence. In some embodiments, the polynucleotide comprising a nucleic acid sequence encoding a Cas protein further comprises a sequence encoding at least one peptide aptamer sequence.
In certain embodiments, the fusion protein comprises a recombination protein comprising an amino acid sequence at least 75% similar, or at least 75% identical to a recombination protein of SEQ ID NO:166 to SEQ ID NO:491. In certain embodiments the fusion protein comprises a recombination protein comprising a sequence having at least 80%, at least 85%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 98.5%, at least 99%, at least 99.5%, or 100% similarity or identity to a recombination protein of SEQ ID NO:166 to SEQ ID NO: 491.
In certain embodiments, systems comprising a recombination protein of the invention are capable of editing efficiency equal to or greater than systems comprising EcRecT, for example, without limitation, 1.2×, 1.5×, 1.7×, 2×, 2.5×, 3×, or more compared to EcRecT.
In certain embodiments, systems comprising a recombination protein of the invention provide cell viability equal to or greater than systems comprising EcRecT, for example, without limitation, 1.1×, 1.2×, 1.3×, 1.5×, 1.7×, 2×, 2.5×, 3×, or more compared to EcRecT.
In some embodiments, the Cas protein is Cas9 or Cas12a. In some embodiments, the Cas protein is a catalytically dead. In some embodiments, the Cas9 protein is wild-type Streptococcus pyogenes Cas9 or a wild type Staphylococcus aureus Cas9. In some embodiments, the Cas9 protein is a Cas9 nickase (e.g., wild-type Streptococcus pyogenes Cas9 with an amino acid substation at position 10 of D10A).
Also disclosed is a eukaryotic cell comprising the systems or vectors disclosed herein.
Further disclosed herein are methods of altering a target genomic DNA sequence in a host cell. The methods comprise contacting the systems, compositions, or vectors described herein with a target DNA sequence (e.g., introducing the systems, compositions, or vectors described herein into a host cell comprising a target genomic DNA sequence). Kits containing one or more reagents or other components useful, necessary, or sufficient for practicing any of the methods are also disclosed herein.
Accordingly, it is an object of the invention not to encompass within the invention any previously known product, process of making the product, or method of using the product such that Applicants reserve the right and hereby disclose a disclaimer of any previously known product, process, or method. It is further noted that the invention does not intend to encompass within the scope of the invention any product, process, or making of the product or method of using the product, which does not meet the written description and enablement requirements of the USPTO (35 U.S.C. § 112, first paragraph) or the EPO (Article 83 of the EPC), such that Applicants reserve the right and hereby disclose a disclaimer of any previously described product, process of making the product, or method of using the product. It may be advantageous in the practice of the invention to be in compliance with Art. 53 (c) EPC and Rule 28 (b) and (c) EPC. All rights to explicitly disclaim any embodiments that are the subject of any granted patent(s) of applicant in the lineage of this application or in any other lineage or in any prior filed application of any third party is explicitly reserved. Nothing herein is to be construed as a promise.
It is noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like; and that terms such as “consisting essentially of” and “consists essentially of” have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.
These and other embodiments are disclosed or are obvious from and encompassed by the following Detailed Description.
Other aspects and embodiments of the disclosure will be apparent in light of the following detailed description and accompanying figures.
Current genome editing technology is limited by the low efficiency and accuracy for precision editing leading to very unreliable ability for using current tools such as CRISPR systems to introduce accurate replacement, deletion, or insertion in mammalian cells. The usual process involves delivery of gene editing tool (like CRISPR) and DNA repair template for introducing desirable changes to genome sequence. However, the DNA delivered into the cell can insert non-specifically into off-target genomic loci or unintended targets, a major challenge for ensuring safe, accurate gene editing for therapeutic purposes.
The present disclosure is directed to a system and the components for DNA editing. In particular, the disclosed system based on CRISPR targeting and homology directed repair by phage recombination enzymes. The system results in superior recombination efficiency and accuracy at a kilobase scale.
The invention features RNA as a molecular entity to mediate gene editing, and includes designed and validated components of systems and methods to apply RNA as template (donor) to insert, delete, replace, or control genomic DNA sequences, mediated through the activity of a recombination protein such as a SSAP (single-strand annealing protein, exemplified by RccT, lambda Red, T7gp2.5).
In certain embodiments, the invention provides efficient gene editing through the process of delivering three components into a cell: (1) local DNA cleavage, nicking, or R-loop-formation using the CRISPR system comprising a CRISPR enzyme (including but not limited to Cas9/Cas9n/dCas9 or Cas12a/nCas12a/dCas12a respectively for cleavage/nick/R-loop-formation), and a guide RNA, where the guide RNA contains an aptamer (such as MS2, or PP7, or BoxB) to recruit SSAP protein; (2) an RNA sequence bearing the desirable DNA changes with one or more homology arm (HA) region(s) that is either fused/linked to the guide RNA in (1), or fused/linked to a second guide RNA. The HA region is at least 20 bp and provides a homology region next to the editing site for SSAP-mediated editing. If using a second guide RNA, this second guide RNA will bind to a nearby genomic site, located between 0 bp to 150 bp away from the guide RNA in (1). This second guide RNA forms a complex with a CRISPR enzyme (such as Cas9/nCas9/dCas9 and Cas12a/nCas12a/dCas12a), is recruited to the target genomic loci, and serves to provide RNA template/donor for the editing. The enzymes can be either fully active CRISPR enzymes, nickases, or deactivated CRISPR enzymes (dCas9, dCas12a, etc.) that only bind to target loci. The guide may be regular guide RNA or shorter guide RNA (typically 2˜6 bp shorter than the regular guide RNA, so 14 bp to 18 bp) to allow efficient binding but not cleavage of targets. (3) SSAP protein fused to an RNA-aptamer-binding protein (RBP) via linker. The RBP can be, without limitation, MS2 coat protein (MCP), PP7 coat protein (PCP), or BoxB binding peptide from lambda phage (lambda N22 peptide). For this component, we also identified an additional factor that could enhance this RNA-templated SSAP gene-editing: if we fuse a reverse transcriptase (RT) to the SSAP protein via a long peptide linker, making this third component RBP-SSAP-RT, or RBP-RT-SSAP (-represent linkers), this further enhance editing efficiencies.
In other embodiments, the Cas9/nCas9/dCas9 or Cas12a/nCas12a/dCas12a protein is fused via linker to a reverse transcriptase (RT), this design is comparable to the prime-editing. The guide RNA in this design optionally comprises a primer-binding-site (PBS) of at least 14-bp or more, which is complementary to a region at the editing site. This PBS promotes initiation of RT activity. Alternatively, another design is to use the same guide RNA as in the first embodiment, and to initiate RT activity by supplying to the cell a short oligo DNA (length is 14 bp or more) that is complementary to a region at the editing site. This oligo DNA can initiate RT activity and allow SSAP-mediated gene-editing.
In other embodiments, the Cas9/nCas9/dCas9 or Cas12a/nCas12a/dCas12a protein is fused via linker to a reverse transcriptase (RT) from a retron system. The guide RNA in this design has a msr/msd sequence from retron, and also one or more homology arm (HA) region(s), which is complementary to a region at the editing site. The msr/msd sequence helps to initiate RT activity. While the HA region help to mediate SSAP gene-editing.
The compositions and methods of the invention herein provide novel RNA-mediated/RNA-templated gene editing in eukaryotic/mammalian cells. By designing cleavable RNA template using endogenous tRNA, ribozyme, or the direct repeat from Cas 12a system, we also achieve multiple-target gene editing using RNA as template.
The invention provides at least the following 5 advantages of our RNA-templated SSAP gene editing system: (1) reduced off-target or toxicity due to RNA being less immunogenic compared with DNA used in existing gene editing process, and that RNA cannot integrated directly into unintended genomic DNA sites or off-target DNA sites; (2) case of multiplexing the precision gene editing methods by using cleavable RNA template in our methods; (3) simplicity of RNA delivery into cells, it is easier to manufacture, potentially cheaper to scale up for clinical usage (4) RNA has a lot of engineering potential by combining other regulatory or combinatorial payload/components via chemical linkage or biochemical coupling, to enable more efficiency delivery, editing, or synergistic action of RNA-templated gene editing with other type of gene editing or therapeutic modalities; and (5) the efficiency of RNA-templated gene editing can be enhanced via RNA and protein factors and is orthogonal to regular DNA-repair pathways that may be critical for health of target cells.
To facilitate an understanding of the present technology, a number of terms and phrases are defined below. Additional definitions are set forth throughout the detailed description.
The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.
For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.
Unless otherwise defined herein, scientific, and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. For example, any nomenclature used in connection with, and techniques of, cell and tissue culture, molecular biology, immunology, microbiology, genetics and protein and nucleic acid chemistry and hybridization described herein are those that are well known and commonly used in the art. The meaning and scope of the terms should be clear; in the event, however of any latent ambiguity, definitions provided herein take precedent over any dictionary or extrinsic definition. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.
The terms “complementary” and “complementarity” refer to the ability of a nucleic acid to form hydrogen bond(s) with another nucleic acid sequence by either traditional Watson-Crick base-paring or other non-traditional types of pairing. The degree of complementarity between two nucleic acid sequences can be indicated by the percentage of nucleotides in a nucleic acid sequence which can form hydrogen bonds (e.g., Watson-Crick base pairing) with a second nucleic acid sequence (e.g., 50%, 60%, 70%, 80%, 90%, and 100% complementary). Two nucleic acid sequences are “perfectly complementary” if all the contiguous nucleotides of a nucleic acid sequence will hydrogen bond with the same number of contiguous nucleotides in a second nucleic acid sequence. Two nucleic acid sequences are “substantially complementary” if the degree of complementarity between the two nucleic acid sequences is at least 60% (e.g., 65%, 70%, 75%, 80%, 85%, 90%, 95%. 97%, 98%, 99%, or 100%) over a region of at least 8 nucleotides (e.g., 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 35, 40, 45, 50, or more nucleotides), or if the two nucleic acid sequences hybridize under at least moderate, preferably high, stringency conditions. Exemplary moderate stringency conditions include overnight incubation at 37° C. in a solution comprising 20% formamide, 5×SSC (150 mM NaCl, 15 mM trisodium citrate), 50 mM sodium phosphate (pH 7.6), 5×Denhardt's solution, 10% dextran sulfate, and 20 mg/ml denatured sheared salmon sperm DNA, followed by washing the filters in 1×SSC at about 37-50° C., or substantially similar conditions, e.g., the moderately stringent conditions described in Sambrook et al., infra. High stringency conditions are conditions that use, for example (1) low ionic strength and high temperature for washing, such as 0.015 M sodium chloride/0.0015 M sodium citrate/0.1% sodium dodecyl sulfate (SDS) at 50° C., (2) employ a denaturing agent during hybridization, such as formamide, for example, 50% (v/v) formamide with 0.1% bovine serum albumin (BSA)/0.1% Ficoll/0.1% polyvinylpyrrolidone (PVP)/50 mM sodium phosphate buffer at pH 6.5 with 750 mM sodium chloride and 75 mM sodium citrate at 42° C., or (3) employ 50% formamide, 5×SSC (0.75 M NaCl, 0.075 M sodium citrate), 50 mM sodium phosphate (pH 6.8), 0.1% sodium pyrophosphate, 5×Denhardt's solution, sonicated salmon sperm DNA (50 μg/ml), 0.1% SDS, and 10% dextran sulfate at 42° C., with washes at (i) 42° C. in 0.2×SSC, (ii) 55° C. in 50% formamide, and (iii) 55° C. in 0.1×SSC (preferably in combination with EDTA). Additional details and an explanation of stringency of hybridization reactions are provided in, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd ed., Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (2001); and Ausubel et al., Current Protocols in Molecular Biology, Greene Publishing Associates and John Wiley & Sons, New York (1994).
A cell has been “genetically modified,” “transformed,” or “transfected” by exogenous DNA, e.g., a recombinant expression vector, when such DNA has been introduced inside the cell. The presence of the exogenous DNA results in permanent or transient genetic change. The transforming DNA may or may not be integrated (covalently linked) into the genome of the cell. In prokaryotes, yeast, and mammalian cells for example, the transforming DNA may be maintained on an episomal element such as a plasmid. With respect to eukaryotic cells, a stably transformed cell is one in which the transforming DNA has become integrated into a chromosome so that it is inherited by daughter cells through chromosome replication. This stability is demonstrated by the ability of the eukaryotic cell to establish cell lines or clones that comprise a population of daughter cells containing the transforming DNA. A “clone” is a population of cells derived from a single cell or common ancestor by mitosis. A “cell line” is a clone of a primary cell that is capable of stable growth in vitro for many generations.
As used herein, a “nucleic acid” or a “nucleic acid sequence” refers to a polymer or oligomer of pyrimidine and/or purine bases, preferably cytosine, thymine, and uracil, and adenine and guanine, respectively. The present technology contemplates any deoxyribonucleotide, ribonucleotide, or peptide nucleic acid component, and any chemical variants thereof, such as methylated, hydroxymethylated, or glycosylated forms of these bases, and the like. The polymers or oligomers may be heterogenous or homogenous in composition and may be isolated from naturally occurring sources or may be artificially or synthetically produced. In addition, the nucleic acids may be DNA or RNA, or a mixture thereof, and may exist permanently or transitionally in single-stranded or double-stranded form, including homoduplex, heteroduplex, and hybrid states. In some embodiments, a nucleic acid or nucleic acid sequence comprises other kinds of nucleic acid structures such as, for instance, a DNA/RNA helix, peptide nucleic acid (PNA), morpholino nucleic acid (scc, e.g., Braasch and Corey, Biochemistry, 41 (14): 4503-4510 (2002)) and U.S. Pat. No. 5,034,506, incorporated herein by reference), locked nucleic acid (LNA; see Wahlestedt et al., Proc. Natl. Acad. Sci. U.S.A., 97:5633-5638 (2000), incorporated herein by reference), cyclohexenyl nucleic acids (scc Wang, J. Am. Chem. Soc., 122:8595-8602 (2000), incorporated herein by reference), and/or a ribozyme. Hence, the term “nucleic acid” or “nucleic acid sequence” may also encompass a chain comprising non-natural nucleotides, modified nucleotides, and/or non-nucleotide building blocks that can exhibit the same function as natural nucleotides (e.g., “nucleotide analogs”); further, the term “nucleic acid sequence” as used herein refers to an oligonucleotide, nucleotide or polynucleotide, and fragments or portions thereof, and to DNA or RNA of genomic or synthetic origin, which may be single or double-stranded, and represent the sense or antisense strand. The terms “nucleic acid,” “polynucleotide,” “nucleotide sequence,” and “oligonucleotide” are used interchangeably. They refer to a polymeric form of nucleotides of any length, either deoxyribonucleotides or ribonucleotides, or analogs thereof.
A “peptide” or “polypeptide” is a linked sequence of two or more amino acids linked by peptide bonds. The peptide or polypeptide can be natural, synthetic, or a modification or combination of natural and synthetic. Polypeptides include proteins such as binding proteins, receptors, and antibodies. The proteins may be modified by the addition of sugars, lipids or other moieties not included in the amino acid chain. The terms “polypeptide” and “protein,” are used interchangeably herein.
As used herein, the term “percent sequence identity” refers to the percentage of nucleotides or nucleotide analogs in a nucleic acid sequence, or amino acids in an amino acid sequence, that is identical with the corresponding nucleotides or amino acids in a reference sequence after aligning the two sequences and introducing gaps, if necessary, to achieve the maximum percent identity. Hence, in case a nucleic acid according to the technology is longer than a reference sequence, additional nucleotides in the nucleic acid, that do not align with the reference sequence, are not taken into account for determining sequence identity. Methods and computer programs for alignment are well known in the art, including BLAST, Align 2, and FASTA.
The term “percent sequence similarity” takes into account conservative amino acid substitutions. Conservative substitution tables providing functionally similar amino acids are well known in the art. The following five groups each contain amino acids that are conservative substitutions for one another: Aliphatic: Glycine (G), Alanine (A), Valine (V), Leucine (L), Isoleucine (I); Aromatic: Phenylalanine (F), Tyrosine (Y), Tryptophan (W); Sulfur-containing: Methionine (M), Cysteine (C); Basic: Arginine (R), Lysine (K), Histidine (H); Acidic: Aspartic acid (D), Glutamic acid (E), Asparagine (N), Glutamine (Q). In addition, individual substitutions, deletions, or additions which alter, add, or delete a single amino acid or a small percentage of amino acids in an encoded sequence are also “conservatively modified variations.” Means for making this adjustment are well known to those of skill in the art. Typically this involves scoring a conservative substitution as a partial rather than a full mismatch, thereby increasing the percentage sequence identity. Thus, for example, where an identical amino acid is given a score of 1 and a non-conservative substitution is given a score of zero, a conservative substitution is given a score between zero and 1. The scoring of conservative substitutions is calculated, e.g., as implemented in the program PC/GENE (Intelligenetics, Mountain View, California).
It will be understood that sequences identified as having greater than a given percent similarity to a reference sequence include as a subset the sequences having greater than the given percent identity to the reference sequence. Thus, recitations herein to sequences having greater than a given percent similarity include the subset of sequences having greater than a given percent identity.
A “vector” or “expression vector” is a replicon, such as plasmid, phage, virus, or cosmid, to which another DNA segment, e.g., an “insert,” may be attached or incorporated so as to bring about the replication of the attached segment in a cell.
The term “wild-type” refers to a gene or a gene product that has the characteristics of that gene or gene product when isolated from a naturally occurring source. A wild-type gene is that which is most frequently observed in a population and is thus arbitrarily designated the “normal” or “wild-type” form of the gene. In contrast, the term “modified,” “mutant,” or “polymorphic” refers to a gene or gene product that displays modifications in sequence and or functional properties (e.g., altered characteristics) when compared to the wild-type gene or gene product. It is noted that naturally occurring mutants can be isolated; these are identified by the fact that they have altered characteristics when compared to the wild-type gene or gene product.
In bacteria and archaea, CRISPR/Cas systems provide immunity by incorporating fragments of invading phage, virus, and plasmid DNA into CRISPR loci and using corresponding CRISPR RNAs (“crRNAs”) to guide the degradation of homologous sequences. Each CRISPR locus encodes acquired “spacers” that are separated by repeat sequences. Transcription of a CRISPR locus produces a “pre-crRNA,” which is processed to yield crRNAs containing spacer-repeat fragments that guide effector nuclease complexes to cleave dsDNA sequences complementary to the spacer. Three different types of CRISPR systems are known, type I, type II, or type III, and classified based on the Cas protein type and the use of a proto-spacer-adjacent motif (PAM) for selection of proto-spacers in invading DNA. The endogenous type II systems comprise the Cas9 protein and two noncoding crRNAs: trans-activating crRNA (tracrRNA) and a precursor crRNA (pre-crRNA) array containing nuclease guide sequences (also referred to as “spacers”) interspaced by identical direct repeats (DRs). tracrRNA is important for processing the pre-crRNA and formation of the Cas9 complex. First, tracrRNAs hybridize to repeat regions of the pre-crRNA. Second, endogenous RNaseIII cleaves the hybridized crRNA-tracrRNAs, and a second event removes 5′ end of each spacer, yielding mature crRNAs that remain associated with both the tracrRNA and Cas9. Third, each mature complex locates a target double stranded DNA (dsDNA) sequence and cleaves both strands using the nuclease activity of Cas9.
CRISPR/Cas gene editing systems have been developed to enable targeted modifications to a specific gene of interest in eukaryotic cells. CRISPR/Cas gene editing systems are commonly based on the RNA-guided Cas9 nuclease from the type II prokaryotic clustered regularly interspaced short palindromic repeats (CRISPR) adaptive immune system. Engineering CRISPR/Cas systems for use in eukaryotic cells typically involves reconstitution of the crRNA-tracrRNA-Cas9 complex. In human cells, for example, the Cas9 amino acid sequence may be codon-optimized and modified to include an appropriate nuclear localization signal, and the crRNA and tracrRNA sequences may be expressed individually or as a single chimeric molecule via an RNA polymerase II promoter. Typically, the crRNA and tracrRNA sequences are expressed as a chimera and are referred to collectively as “guide RNA” (gRNA) or single guide RNA (sgRNA). Thus, the terms “guide RNA,” “single guide RNA,” and “synthetic guide RNA,” are used interchangeably herein and refer to a nucleic acid sequence comprising a tracrRNA and a pre-crRNA array containing a guide sequence. The terms “guide sequence,” “guide,” and “spacer,” arc used interchangeably herein and refer to the about 20 nucleotide sequence within a guide RNA that specifies the target site. In CRISPR/Cas9 systems, the guide RNA contains an approximate 20-nucleotide guide sequence followed by a protospacer adjacent motif (PAM) that directs Cas9 via Watson-Crick base pairing to a target sequence.
In some embodiments, the disclosure provides a system for RNA-guided recombineering utilizing tools from CRISPR gene editing systems. The system comprises: a Cas protein, a nucleic acid molecule comprising a guide RNA sequence that is complementary to a target DNA sequence and a recombination protein. In certain embodiments, the recombination protein comprises a microbial recombination protein. In certain embodiments, the recombination protein comprises a viral recombination protein. In certain embodiments, the recombination protein comprises a eukaryotic recombination protein. In certain embodiments, the recombination protein comprises a mitochondrial recombination protein.
Cas protein families are described in further detail in, e.g., Haft et al., PLOS Comput. Biol., 1 (6): c60 (2005), incorporated herein by reference. The Cas protein may be any Cas endonucleases. In some embodiments, the Cas protein is Cas9 or Cas 12a, otherwise referred to as Cpf1. In one embodiment, the Cas9 protein is a wild-type Cas9 protein. The Cas9 protein can be obtained from any suitable microorganism, and a number of bacteria express Cas9 protein orthologs or variants. In some embodiments, the Cas9 is from Streptococcus pyogenes or Staphylococcus aureus. Cas9 proteins of other species are known in the art (see, e.g., U.S. Patent Application Publication 2017/0051312, incorporated herein by reference) and may be used in connection with the present disclosure. The amino acid sequences of Cas proteins from a variety of species are publicly available through the GenBank and UniProt databases.
In some embodiments, the Cas9 protein is a Cas9 nickase (Cas9n). Wild-type Cas9 has two catalytic nuclease domains facilitating double-stranded DNA breaks. A Cas9 nickase protein is typically engineered through inactivating point mutation(s) in one of the catalytic nuclease domains causing Cas9 to nick or enzymatically break only one of the two DNA strands using the remaining active nuclease domain. Cas9 nickases are known in the art (see, e.g., U.S. Patent Application Publication 2017/0051312, incorporated herein by reference) and include, for example, Streptococcus pyogenes with point mutations at D10 or H840. In select embodiments, the Cas9 nickase is Streptococcus pyogenes Cas9n (D10A).
In some embodiments, the Cas protein is a catalytically dead Cas. For example, catalytically dead Cas9 is essentially a DNA-binding protein due to, typically, two or more mutations within its catalytic nuclease domains which renders the protein with very little or no catalytic nuclease activity. Streptococcus pyogenes Cas9 may be rendered catalytically dead by mutations of D10 and at least one of E762, H840, N854, N863, or D986, typically H840 and/or N863 (see, e.g., U.S. Patent Application Publication 2017/0051312, incorporated herein by reference). Mutations in corresponding orthologs are known, such as N580 in Staphylococcus aureus Cas9. Oftentimes, such mutations cause catalytically dead Cas proteins to possess no more than 3% of the normal nuclease activity.
In some embodiments, the system comprises a nucleic acid molecule comprising a guide RNA sequence complementary to a target DNA sequence. The guide RNA sequence, as described above, specifies the target site with an approximate 20-nucleotide guide sequence followed by a protospacer adjacent motif (PAM) that directs Cas9 via Watson-Crick base pairing to a target sequence.
The terms “target DNA sequence,” “target nucleic acid,” “target sequence,” and “target site” are used interchangeably herein to refer to a polynucleotide (nucleic acid, gene, chromosome, genome, etc.) to which a guide sequence (e.g., a guide RNA) is designed to have complementarity, wherein hybridization between the target sequence and a guide sequence promotes the formation of a Cas9/CRISPR complex, provided sufficient conditions for binding exist. In some embodiments, the target sequence is a genomic DNA sequence. The term “genomic,” as used herein, refers to a nucleic acid sequence (e.g., a gene or locus) that is located on a chromosome in a cell. The target sequence and guide sequence need not exhibit complete complementarity, provided that there is sufficient complementarity to cause hybridization and promote formation of a CRISPR complex. A target sequence may comprise any polynucleotide, such as DNA or RNA. Suitable DNA/RNA binding conditions include physiological conditions normally present in a cell. Other suitable DNA/RNA binding conditions (e.g., conditions in a cell-free system) are known in the art; see, e.g., Sambrook, referenced herein and incorporated by reference. The strand of the target DNA that is complementary to and hybridizes with the DNA-targeting RNA is referred to as the “complementary strand” and the strand of the target DNA that is complementary to the “complementary strand” (and is therefore not complementary to the DNA-targeting RNA) is referred to as the “noncomplementary strand” or “non-complementary strand.”
The target genomic DNA sequence may encode a gene product. The term “gene product,” as used herein, refers to any biochemical product resulting from expression of a gene. Gene products may be RNA or protein. RNA gene products include non-coding RNA, such as tRNA, rRNA, micro RNA (miRNA), and small interfering RNA (siRNA), and coding RNA, such as messenger RNA (mRNA). In some embodiments, the target genomic DNA sequence encodes a protein or polypeptide.
In some embodiments, for instance, when the system includes a Cas9 nickase or a catalytically dead Cas 9, two nucleic acid molecules comprising a guide RNA sequence may be utilized. The two nucleic acid molecules may have the same or different guide RNA sequences, thus complementary to the same or different target DNA sequence. In some embodiments, the guide RNA sequences of the two nucleic acid molecules are complementary to a target DNA sequences at opposite ends (e.g., 3′ or 5′) and/or on opposite strands of the insert location.
In some embodiments, the system further comprises a recruitment system comprising at least one aptamer sequence and an aptamer binding protein functionally linked to the recombination protein as part of a fusion protein.
In some embodiments, the aptamer sequence is an RNA aptamer sequence. In some embodiments, the nucleic acid molecule comprising the guide RNA also comprises one or more RNA aptamers, or distinct RNA secondary structures or sequences that can recruit and bind another molecular species, an adaptor molecule, such as a nucleic acid or protein. Several CRISPR systems are compatible with guide RNA insertions and extensions, including but not limited to SpCas9, SaCas9, and LbCas12a (aka Cpf1). The RNA aptamers can be naturally occurring or synthetic oligonucleotides that have been engineered through repeated rounds of in vitro selection or SELEX (systematic evolution of ligands by exponential enrichment) to bind to a specific target molecular species. In some embodiments, the nucleic acid comprises two or more aptamer sequences. The aptamer sequences may be the same or different and may target the same or different adaptor proteins. In select embodiments, the nucleic acid comprises two aptamer sequences.
Any RNA aptamer/aptamer binding protein pair known may be selected and used in connection with the present disclosure (see, e.g., Jayasena, S. D., Clinical Chemistry, 1999. 45 (9): p. 1628-1650; Gelinas, et al., Current Opinion in Structural Biology, 2016. 36: p. 122-132; and Hasegawa, H., Molecules, 2016; 21 (4): p. 421, incorporated herein by reference).
A number of RNA aptamer binding, or adaptor, proteins exist, including a diverse array of bacteriophage coat proteins. Examples of such coat proteins include but are not limited to: MS2, QB, F2, GA, fr, JP501, M12, R17, BZ13, JP34, JP500, KU1, M11, MX1, TW18, VK, SP, FI, ID2, NL95, TW19, AP205, ϕCb5, ϕCb8r, ϕCb12r, ϕCb23r, 7s and PRR1. In some embodiments, the RNA aptamer binds MS2 bacteriophage coat protein or a functional derivative, fragment, or variant thereof. MS2 binding RNA aptamers commonly have a simple stem-loop structure, classically defined by a 19 nucleotide RNA molecule with a single bulged adenine on 5′ leg of the stem (Witherall G. W., et al., (1991) Prog. Nucleic Acid Res. Mol. Biol., 40, 185-220, incorporated herein by reference). However, a number of vastly different primary sequences were found to be able to bind the MS2 coat protein (Parrott A M, et al., Nucleic Acids Res. 2000; 28 (2): 489-497, Buenrostro J D, et al. Natura Biotechnology 2014; 32, 562-568, and incorporated herein by reference). Any of the RNA aptamer sequence known to bind the MS2 bacteriophage coat protein may be utilized in connection with the present disclosure to bind to fusion proteins comprising MS2. In select embodiments, the MS2 RNA aptamer sequence comprises: AACAUGAGGAUCACCCAUGUCUGCAG (SEQ ID NO:145), AGCAUGAGGAUCACCCAUGUCUGCAG (SEQ ID NO:146), or AGCGUGAGGAUCACCCAUGCCUGCAG (SEQ ID NO:147).
N-proteins (Nut-utilization site proteins) of bacteriophages contain arginine-rich conserved RNA recognition motifs of ˜20 amino acids, referred to as N peptides. The RNA aptamer may bind a phage N peptide or a functional derivative, fragment, or variant thereof. In some embodiments, the phage N peptide is the lambda or P22 phage N peptide or a functional derivative, fragment, or variant thereof.
In select embodiments, the N peptide is lambda phage N22 peptide, or a functional derivative, fragment, or variant thereof. In some embodiments, the N22 peptide comprises an amino acid sequence with at least 70% similarity to the amino acid sequence GNARTRRRERRAEKQAQWKAAN (SEQ ID NO:149). N22 peptide, the 22 amino acid RNA-binding domain of the 2 bacteriophage antiterminator protein N (AN-(1-22) or AN peptide), is capable of specifically binding to specific stem-loop structures, including but not limited to the BoxB stem-loop. See, for example Cilley and Williamson, RNA 1997; 3 (1): 57-67, incorporated herein by reference. A number of different BoxB stem-loop primary sequences are known to bind the N22 peptide and any of those may be utilized in connection with the present disclosure. In some embodiments, the N22 peptide RNA aptamer sequence comprises a nucleotide sequence with at least 70% similarity to an RNA sequence selected from the group consisting of GCCCUGAAAAAGGGC (SEQ ID NO:150), GCCCUGAAGAAGGGC (SEQ ID NO:151), GCGCUGAAAAAGCGC (SEQ ID NO:152), GCCCUGACAAAGGGC (SEQ ID NO:153), and GCGCUGACAAAGCGC (SEQ ID NO:154). In some embodiments, the N22 peptide RNA aptamer sequence is selected from the group consisting of SEQ ID NOs: 150-154.
In select embodiments, the N peptide is the P22 phage N peptide, or a functional derivative, fragment, or variant thereof. A number of different BoxB stem-loop primary sequences are known to bind the P22 phage N peptide and variants thereof and any of those may be utilized in connection with the present disclosure. See, for example Cocozaki, Ghattas, and Smith, Journal of Bacteriology 2008; 190 (23): 7699-7708, incorporated herein by reference. In some embodiments, the P22 phage N peptide comprises an amino acid sequence with at least 70% similarity to the amino acid sequence GNAKTRRHERRRKLAIERDTI (SEQ ID NO:155). In some embodiments, the P22 phage N peptide RNA aptamer sequence comprises a sequence with at least 70% similarity to an RNA sequence selected from the group consisting of GCGCUGACAAAGCGC (SEQ ID NO:156) and CCGCCGACAACGCGG (SEQ ID NO:157).
In some embodiments, the P22 phage N peptide RNA aptamer sequence is selected from the group consisting of SEQ ID NOs: 156-157, UGCGCUGACAAAGCGCG (SEQ ID NO:158) or ACCGCCGACAACGCGGU (SEQ ID NO:159).
In certain embodiments, different aptamer/aptamer binding protein pairs can be selected to bring together a combination of recombination proteins and functions.
In some embodiments, the aptamer sequence is a peptide aptamer sequence. The peptide aptamers can be naturally occurring or synthetic peptides that are specifically recognized by an affinity agent. Such aptamers include, but are not limited to, a c-Myc affinity tag, an HA affinity tag, a His affinity tag, an S affinity tag, a methionine-His affinity tag, an RGD-His affinity tag, a 7×His tag, a FLAG octapeptide, a strep tag or strep tag II, a V5 tag, or a VSV-G epitopc. Corresponding aptamer binding proteins are well-known in the art and include, for example, primary antibodies, biotin, affimers, single domain antibodies, and antibody mimetics.
An exemplary peptide aptamer includes a GCN4 peptide (Tanenbaum et al., Cell 2014; 159 (3): 635-646, incorporated herein by reference). Antibodies, or GCN4 binding protein can be used as the aptamer binding proteins.
In some embodiments, the peptide aptamer sequence is conjugated to the Cas protein. The peptide aptamer sequence may be fused to the Cas in any orientation (e.g., N-terminus to C-terminus, C-terminus to N-terminus, N-terminus to N-terminus). In select embodiments, the peptide aptamer is fused to the C-terminus of the Cas protein.
In some embodiments, between 1 and 24 peptide aptamer sequences may be conjugated to the Cas protein. The aptamer sequences may be the same or different and may target the same or different aptamer binding proteins. In select embodiments, 1 to 24 tandem repeats of the same peptide aptamer sequence are conjugated to the Cas protein. In preferred embodiments between 4 and 18 tandem repeats are conjugated to the Cas protein. The individual aptamers may be separated by a linker region. Suitable linker regions are known in the art. The linker may be flexible or configured to allow the binding of affinity agents to adjacent aptamers without or with decreased steric hindrance. The linker sequences may provide an unstructured or linear region of the polypeptide, for example, with the inclusion of one or more glycine and/or serine residues. The linker sequences can be at least about 2, 3, 4, 5, 6, 7, 8, 9, 10 or more amino acids in length.
In some embodiments, the fusion protein comprises a recombination protein functionally linked to an aptamer binding protein. In some embodiments, the recombination protein comprises a microbial recombination protein. In some embodiments, the recombination protein comprises a recombinase. In certain embodiments, the recombination protein comprises 5′-3′ exonuclease activity. In certain embodiments, the recombination protein comprises 3′-5′ exonuclease activity. In certain embodiments, the recombination protein comprises ssDNA binding activity. In certain embodiments, the recombination protein comprises ssDNA annealing activity.
The bacteriophage A-encoded genetic recombination machinery, named the λ red system, comprises the exo and bet genes, assisted by the gam gene, together designated λ red genes. Exo is a 5′-3′ exonuclease which targets dsDNA and Bet is a ssDNA-binding protein. Bet functions include protecting ssDNA from degradation and promoting annealing of complementary ssDNA strands. Another bacteriophage system found in E. coli is the Rac prophage system, comprising recE and recT genes which are functionally similar to exo and bet. In some embodiments, the microbial recombination protein may be RecE, RecT, lambda exonuclease (Exo), Bet protein (betA, redB), exonuclease gp6, single-stranded DNA-binding protein gp2.5, or a derivative or variant thereof.
Recombination proteins and functional fragments thereof useful in the invention include nucleases, ssDNA-binding proteins (SSBs), and ssDNA annealing proteins (SSABs). Among microbial proteins, these include, without limitation, E. coli proteins such as ExoI (xonA; sbcB), ExoIII (xthA), ExoIV (orn), ExoVII (xseA, xseB), ExoIX (ygdG), ExoX (exoX), DNA poll 5′ Exo (ExoVI) (polA), DNA Pol I 3′ Exo (ExoII) (polA), DNA Pol II 3′ Exo (polB), DNA Pol III 3′ Exo (dnaQ, mutD), RecBCD (recB, recC, recD), and RecJ (recJ) and their functional fragments.
While double-stranded DNA contains genetic information, use of the information involves single-stranded intermediates. Whereas the single-stranded intermediates form secondary structures and are sensitive to chemical and nucleolytic degradation, cells encode ssDNA binding proteins (SSBs) that bind to and stabilize ssDNA. Useful SSBs include, without limitation, SSBs of prokaryotes, bacteriophage, eukaryotes, mammals, mitochondria, and viruses. While SSBs are found in every organism, the proteins themselves share surprisingly little sequence similarity, and may differ in subunit composition and oligomerization states. SSB proteins may comprise certain structural features. One is use of oligonucleotide/oligosaccharide-binding (OB) domains to bind ssDNA through a combination of electrostatic and base-stacking interactions with the phosphodiester backbone and nucleotide bases. Another feature is oligomerization that brings together DNA-binding OB folds. Eukaryotic SSBs are regulated by phosphorylation on serine and threonine residues. Tyrosine phosphorylation of microbial SSBs is observed in taxonomically distant bacteria and substantially increases affinity for ssDNA. The human mitochondrial ssDNA-binding protein is structurally similar to SSB from Escherichia coli (EcoSSB), but lacks the C-terminal disordered domain. Eukaryotic replication protein A (RPA) shares function, but not sequence homology with bacterial SSB. The herpes simplex virus (HSV-1) SSB, ICP8, is a nuclear protein that, along other replication proteins is required for viral DNA replication.
Without being bound by theory, it is thought that exonuclease activities and ssDNA binding activities of the recombination proteins of the invention uncover and protect single stranded regions of template and target DNAs, thereby facilitating recombination. Also, targeting can be cooperative, involving target directed CRISPR-mediated nicking of chromosomal DNA coordinated with recombination directed by homology arms designed into template DNAs. In certain embodiments of the invention, off-target effects are minimized. For example, whereas targeted recombination involves coordinated CRISPR and recombination functions, at off-target sites, homology with the HR template DNA is absent and nick repair may be favored.
Single stranded DNA annealing proteins (SSAPs) also are ubiquitous among organisms with diverse sequences and have been classified into families and superfamilies by bioinformatics and experimental analysis. Moreover, phage encoded SSAPs are recognized to encode their own SSAP recombinases which substitute for classic RecA proteins while functioning with host proteins to control DNA metabolism. Steczkiewiz classified SSAPs into seven families (RecA, Gp2.5, RecT/RedB, Erf, Rad52/22, Sak3, and Sak4) organized into three superfamilies including prokaryotes, eukaryotes, and phage (Steczkiewicz et al., 2021, Front. Microbiol 12:644622). Non-limiting examples of SSAPs that can be used according to the invention are provided in Table 5. Any one or more of the SSAPs can be employed in the invention.
In certain embodiments, a microbial recombination protein is RecE or RecT, or a derivative or variant thereof. Derivatives or variants of RecE and RecT are functionally equivalent proteins or polypeptides which possess substantially similar function to wild type RecE and RecT. RecE and RecT derivatives or variants include biologically active amino acid sequences similar to the wild-type sequences but differing due to amino acid substitutions, additions, deletions, truncations, post-translational modifications, or other modifications. In some embodiments, the derivatives may improve translation, purification, biological half-life, activity, or eliminate or lessen any undesirable side effects or reactions. The derivatives or variants may be naturally occurring polypeptides, synthetic or chemically synthesized polypeptides or genetically engineered peptide polypeptides. RecE and RecT bioactivities are known to, and easily assayed by, those of ordinary skill in the art, and include, for example exonuclease and single-stranded nucleic acid binding, respectively.
The RecE or RecT may be from a number of microbial organisms, including Escherichia coli, Pantoea breeneri, Type-F symbiont of Plautia stali, Providencia sp. MGF014, Shigella sonnei, Pseudobacteriovorax antillogorgiicola, among others. Other non-limiting sources include Desulfotalea psychrophila, Lactococcus lactis, Flavobacterium psychrophilum, Mycobacterium smegmatis, Lactobacillus rhamnosus, Psychrobacter arcticus, Psychrobacter cryohalolentis, Psychromonas ingrahamii, Photobacterium profundum, Psychroflexus torquis, and Caulobacter crescentus. In certain embodiments, the RecE and RecT protein is derived from Escherichia coli.
In some embodiments, the fusion protein comprises RecE, or a derivative or variant thereof. The RecE, or derivative or variant thereof, may comprise an amino acid sequence selected from the group consisting of SEQ ID NOs: 1-8. The RecE, or derivative or variant thereof, may comprise an amino acid sequences with at least 70% (e.g., 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%) similarity to amino acid sequences selected from the group consisting of SEQ ID NOs: 1-8. In select embodiments, the RecE, or derivative or variant thereof, comprises an amino acid sequences with at least 90% similarity to amino acid sequences selected from the group consisting of SEQ ID NOs: 1-8. In exemplary embodiments, the RecE, or derivative or variant thereof, comprises an amino acid sequences with at least 90% similarity to amino acid sequences selected from the group consisting of SEQ ID NOs: 1-3.
In some embodiments, the fusion protein comprises RecT, or a derivative or variant thereof. The RecT, or derivative or variant thereof, may comprise an amino acid sequence selected from the group consisting of SEQ ID NOs: 9-14. The RecT, or derivative or variant thereof, may comprise an amino acid sequences with at least 70% (e.g., 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%) similarity to amino acid sequences selected from the group consisting of SEQ ID NOs: 9-14. In select embodiments, the RecT, or derivative or variant thereof, comprises an amino acid sequences with at least 90% similarity to amino acid sequences selected from the group consisting of SEQ ID NOs: 9-14. In exemplary embodiments, the RecT, or derivative or variant thereof, comprises an amino acid sequences with at least 90% similarity to amino acid sequences selected from the group consisting of SEQ ID NO:9.
In certain embodiments, the fusion protein comprises a recombination protein comprising an amino acid sequence at least 75% similar, or at least 75% identical to a recombination protein of SEQ ID NO: 166 to SEQ ID NO:491, a recombination protein of Table 9, a recombination protein of SEQ ID NO: 179, SEQ ID NO: 185, SEQ ID NO:205, SEQ ID NO:321, SEQ ID NO:353, SEQ ID NO:359, SEQ ID NO: 366, SEQ ID NO:424, or SEQ ID NO:479, or a recombination protein of SEQ ID NO:166, SEQ ID NO:168, SEQ ID NO:169, SEQ ID NO:170, SEQ ID NO: 171, SEQ ID NO:241, SEQ ID NO:253, SEQ ID NO:290, SEQ ID NO:408, SEQ ID NO: 411, or SEQ ID NO:442. In certain embodiments the fusion protein comprises a recombination protein comprising a sequence having at least 80%, at least 85%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 98.5%, at least 99%, at least 99.5%, or 100% similarity or identity to the above referenced recombination proteins.
In certain embodiments, the fusion protein comprises a truncated recombination protein of SEQ ID NO:166 to SEQ ID NO:491. Truncations may be from either the C-terminal or N-terminal ends, or both. For example, as demonstrated in Example 6 below, a diverse set of truncations from either end or both provided a functional product. In some embodiments, one or more (2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 or more) amino acids may be truncated from the C-terminal, N-terminal ends as compared to the wild-type sequence. The invention includes guidance as to suitability of truncations, substitutions, deletions, and insertions, for example with reference to
The invention provides recombination proteins capable of improved gene editing activity. In certain embodiments, systems comprising a recombination protein of the invention are capable of editing efficiency equal to or greater than systems comprising EcRecT, for example, without limitation, 1.2×, 1.5×, 1.7×, 2×, 2.5×, 3×, or more compared to EcRecT. In certain embodiments, systems comprising a recombination protein of the invention provide cell viability equal to or greater than systems comprising EcRecT, for example, without limitation, 1.1×, 1.2×, 1.3×, 1.5×, 1.7×, 2×, 2.5×, 3×, or more compared to EcRecT.
In some embodiments, the recombination protein comprises a tyrosine recombinase or functional fragment thereof. In some embodiments, the recombination protein comprises a serine recombinase or functional fragment thereof. In some embodiments, the recombination protein comprises an integrase, resolvase, or invertase, or functional fragment thereof. In some embodiments, the recombinase protein comprises a site-specific recombinase protein or functional fragment thereof. In some embodiments, the recombination protein comprises an exonuclease or functional fragment thereof. In some embodiments, the recombination protein comprises an ssDNA-binding protein or functional fragment thereof. In certain embodiments, the fusion protein comprises without limitation, Hin, Gin, Tn3, β/six, CinH, Min, ParA, γδ, Bxb1, ϕC31, TP901-1, TGI, Wβ, ϕ370.1, ϕK38, ϕBT1, R4, ϕRV1, ϕFC1, MR11, A118, U153, Bxz2, gp29, Cre, Dre, Vika, Flp, Kw, SprA, HK022, P22, L1, or L5 or a homolog of any of such proteins or functional fragment thereof. Such recombinases, which may be classified in the art as integrases, resolvases, or invertases, may share substructures and activities with exonucleases and SSBs and be used according to the invention.
In the fusion protein, the microbial recombination protein may be linked to cither terminus of the aptamer binding protein in any orientation (e.g., N-terminus to C-terminus, C-terminus to N-terminus, N-terminus to N-terminus). In select embodiments, the microbial recombination protein N-terminus is linked to the aptamer binding protein C-terminus. Thus, the overall fusion protein from N- to C-terminus comprises the aptamer binding protein (N- to C-terminus) linked to the microbial recombination protein (N- to C-terminus).
In some embodiments, the fusion protein further comprises a linker between the microbial recombination protein and the aptamer binding protein. The linkers may comprise any amino acid sequence of any length. The linkers may be flexible such that they do not constrain either of the two components they link together in any particular orientation. The linkers may essentially act as a spacer. In select embodiments, the linker links the C-terminus of the microbial recombination protein to the N-terminus of the aptamer binding protein. In select embodiments, the linker comprises the amino acid sequence of the 16-residue XTEN linker, SGSETPGTSESATPES (SEQ ID NO:15) or the 37-residue EXTEN linker, SASGGSSGGSSGSETPGTSESATPESSGGSSGGSGGS (SEQ ID NO:148).
In some embodiments, the fusion protein further comprises a nuclear localization sequence (NLS). The nuclear localization sequence may be at any location within the fusion protein (e.g., C-terminal of the aptamer binding protein, N-terminal of the aptamer binding protein, C-terminal of the microbial recombination protein). In select embodiments, the nuclear localization sequence is linked to the C-terminus of the microbial recombination protein. A number of nuclear localization sequences are known in the art (see, e.g., Lange, A., et al., J Biol Chem. 2007; 282 (8): 5101-5105, incorporated herein by reference) and may be used in connection with the present disclosure. The nuclear localization sequence may be the SV40 NLS, PKKKRKV (SEQ ID NO:16); the Ty1 NLS, NSKKRSLEDNETEIKVSRDTWNTKNMRSLEPPRSKKRIH (SEQ ID NO:17); the c-Myc NLS, PAAKRVKLD (SEQ ID NO:18); the biSV40 NLS, KRTADGSEFESPKKKRKV (SEQ ID NO:19); and the Mut NLS, PEKKRRRPSGSVPVLARPSPPKAGKSSCI (SEQ ID NO:20). In select embodiments, the nuclear localization sequence is the SV40 NLS, PKKKRKV (SEQ ID NO:16).
The Cas protein and the fusion protein are desirably included in a single composition alone, in combination with each other, and/or the polynucleotide(s) (e.g., a vector) comprising the guide RNA sequence and the aptamer sequence. The Cas protein and/or the fusion protein may or may not be physically or chemically bound to the polynucleotide. The Cas protein and/or the microbial recombination protein can be associated with a polynucleotide using any suitable method for protein-protein linking or protein-virus linking known in the art.
The disclosure further provides compositions and vectors comprising a polynucleotide comprising a nucleic acid sequence encoding a fusion protein comprising a microbial recombination protein functionally linked to an RNA aptamer binding protein.
The compositions or vectors may further comprise at least one or both of a polynucleotide comprising a nucleic acid sequence encoding a Cas protein and a nucleic acid molecule comprising a guide RNA sequence that is complementary to a target DNA sequence. In some embodiments, the nucleic acid molecule comprising a guide RNA sequence further comprises at least one RNA aptamer sequence. In some embodiments, the polynucleotide comprising a nucleic acid sequence encoding a Cas protein further comprises a sequence encoding at least one peptide aptamer sequence.
Descriptions of the nucleic acid molecule comprising a guide RNA sequence, the aptamer sequences, the Cas proteins, the microbial recombination proteins, and the aptamer binding proteins set forth above in connection with the inventive system also are applicable to the polynucleotides of the recited compositions and vectors.
The nucleic acid sequence encoding the Cas protein and/or the nucleic acid sequence encoding a fusion protein comprising a microbial recombination protein functionally linked to an aptamer binding protein can be provided to a cell on the same vector (e.g., in cis) as the nucleic acid molecule comprising the guide RNA sequence and/or the RNA aptamer sequence. In such embodiments, a unidirectional promoter can be used to control expression of each nucleic acid sequence. In another embodiment, a combination of bidirectional and unidirectional promoters can be used to control expression of multiple nucleic acid sequences.
In other embodiments, a nucleic acid sequence encoding the Cas protein, the nucleic acid sequence encoding a fusion protein comprising a microbial recombination protein functionally linked to an aptamer binding protein, and the nucleic acid molecule comprising the guide RNA sequence and/or the RNA aptamer sequence can be provided to a cell on separate vectors (e.g., in trans). Each of the nucleic acid sequences in each of the separate vectors can comprise the same or different expression control sequences. The separate vectors can be provided to cells simultaneously or sequentially.
The vector(s) comprising the nucleic acid sequences encoding the Cas protein and encoding a fusion protein comprising a microbial recombination protein functionally linked to an aptamer binding protein can be introduced into a host cell that is capable of expressing the polypeptide encoded thereby, including any suitable prokaryotic or eukaryotic cell. As such, the disclosure provides an isolated cell comprising the vector or nucleic acid sequences disclosed herein. Preferred host cells are those that can be easily and reliably grown, have reasonably fast growth rates, have well characterized expression systems, and can be transformed or transfected easily and efficiently. Examples of suitable prokaryotic cells include, but are not limited to, cells from the genera Bacillus (such as Bacillus subtilis and Bacillus brevis), Escherichia (such as E. coli), Pseudomonas, Streptomyces, Salmonella, and Endivia. Suitable eukaryotic cells are known in the art and include, for example, yeast cells, insect cells, and mammalian cells. Examples of suitable yeast cells include those from the genera Kluyveromyces, Pichia, Rhino-sporidium, Saccharomyces, and Schizosaccharomyces. Exemplary insect cells include Sf-9 and HIS (Invitrogen, Carlsbad, Calif.) and are described in, for example, Kitts et al., Biotechniques, 14:810-817 (1993); Lucklow, Curr. Opin. Biotechnol., 4:564-572 (1993); and Lucklow et al., J. Virol., 67:4566-4579 (1993), incorporated herein by reference. Desirably, the host cell is a mammalian cell, and in some embodiments, the host cell is a human cell. A number of suitable mammalian and human host cells are known in the art, and many are available from the American Type Culture Collection (ATCC, Manassas, Va.). Examples of suitable mammalian cells include, but are not limited to, Chinese hamster ovary cells (CHO) (ATCC No. CCL61), CHO DHFR-cells (Urlaub et al., Proc. Natl. Acad. Sci. USA, 97:4216-4220 (1980)), human embryonic kidney (HEK) 293 or 293T cells (ATCC No. CRL1573), and 3T3 cells (ATCC No. CCL92). Other suitable mammalian cell lines are the monkey COS-1 (ATCC No. CRL1650) and COS-7 cell lines (ATCC No. CRL1651), as well as the CV-1 cell line (ATCC No. CCL70). Further exemplary mammalian host cells include primate, rodent, and human cell lines, including transformed cell lines. Normal diploid cells, cell strains derived from in vitro culture of primary tissue, as well as primary explants, are also suitable. Other suitable mammalian cell lines include, but are not limited to, mouse neuroblastoma N2A cells, HeLa, HEK, A549, HepG2, mouse L-929 cells, and BHK or HaK hamster cell lines. Methods for selecting suitable mammalian host cells and methods for transformation, culture, amplification, screening, and purification of cells are known in the art.
The disclosure also provides a method of altering a target DNA. In some embodiments, the method alters genomic DNA sequence in a cell, although any desired nucleic acid may be modified. When applied to DNA contained in cells, the method comprises introducing the systems, compositions, or vectors described herein into a cell comprising a target genomic DNA sequence. Descriptions of the nucleic acid molecule comprising a guide RNA sequence, the Cas proteins, the microbial recombination proteins, the recruitment systems, and polynucleotides encoding thereof, the cell, the target genomic DNA sequence, and components thereof, set forth above in connection with the inventive system are also applicable to the method of altering a target genomic DNA sequence in a cell. The systems, composition or vectors may be introduced in any manner known in the art including, but not limited to, chemical transfection, electroporation, microinjection, biolistic delivery via gene guns, or magnetic-assisted transfection, depending on the cell type.
Upon introducing the systems described herein into a cell comprising a target genomic DNA sequence, the guide RNA sequence binds to the target genomic DNA sequence in the cell genome, the Cas protein associates with the guide RNA and may induce a double strand break or single strand nick in the target genomic DNA sequence and the aptamer recruits the microbial recombination proteins to the target genomic DNA sequence through the aptamer binding protein of the fusion protein, thereby altering the target genomic DNA sequence in the cell. When introducing the compositions, or vectors described herein into the cell, the nucleic acid molecule comprising a guide RNA sequence, the Cas9 protein, and the fusion protein are first expressed in the cell.
In some embodiments, the cell is in an organism or host, such that introducing the disclosed systems, compositions, vectors into the cell comprises administration to a subject. The method may comprise providing or administering to the subject, in vivo, or by transplantation of ex vivo treated cells, systems, compositions, vectors of the present system.
A “subject” may be human or non-human and may include, for example, plants or animal strains or species used as “model systems” for research purposes, such a mouse model as described herein. Likewise, subject may include either adults or juveniles (e.g., children). Moreover, subject may mean any living organism, preferably a mammal (e.g., human or non-human) that may benefit from the administration of compositions contemplated herein. Examples of mammals include, but are not limited to, any member of the Mammalian class: humans, non-human primates such as chimpanzees, and other apes and monkey species; farm animals such as cattle, horses, sheep, goats, swine; domestic animals such as rabbits, dogs, and cats; laboratory animals including rodents, such as rats, mice, and guinea pigs, and the like. Examples of non-mammals include, but are not limited to, birds, fish and the like. In one embodiment of the methods and compositions provided herein, the mammal is a human. Plants include without limitation sugar cane, corn, wheat, rice, oil palm fruit, potatoes, soybeans, vegetables, cassava, sugar beets, tomatoes, barley, bananas, watermelon, onions, sweet potatoes, cucumbers, apples, seed cotton, oranges, and the like.
As used herein, the terms “providing”, “administering,” “introducing,” are used interchangeably herein and refer to the placement of the systems of the disclosure into a subject by a method or route which results in at least partial localization of the system to a desired site. The systems can be administered by any appropriate route which results in delivery to a desired location in the subject.
The phrase “altering a DNA sequence,” as used herein, refers to modifying at least one physical feature of a DNA sequence of interest. DNA alterations include, for example, single or double strand DNA breaks, deletion, or insertion of one or more nucleotides, and other modifications that affect the structural integrity or nucleotide sequence of the DNA sequence. The modifications of a target sequence in genomic DNA may lead to, for example, gene correction, gene replacement, gene tagging, transgene insertion, nucleotide deletion, gene disruption, gene mutation, gene knock-down, and the like.
In some embodiments, the systems and methods described herein may be used to correct one or more defects or mutations in a gene (referred to as “gene correction”). In such cases, the target genomic DNA sequence encodes a defective version of a gene, and the system further comprises a donor nucleic acid molecule which encodes a wild-type or corrected version of the gene. Thus, in other words, the target genomic DNA sequence is a “disease-associated” gene. The term “disease-associated gene,” refers to any gene or polynucleotide whose gene products are expressed at an abnormal level or in an abnormal form in cells obtained from a disease-affected individual as compared with tissues or cells obtained from an individual not affected by the disease. A disease-associated gene may be expressed at an abnormally high level or at an abnormally low level, where the altered expression correlates with the occurrence and/or progression of the disease. A disease-associated gene also refers to a gene, the mutation or genetic variation of which is directly responsible or is in linkage disequilibrium with a gene(s) that is responsible for the etiology of a disease. Examples of genes responsible for such “single gene” or “monogenic” diseases include, but are not limited to, adenosine deaminase, α-1 antitrypsin, cystic fibrosis transmembrane conductance regulator (CFTR), β-hemoglobin (HBB), oculocutaneous albinism II (OCA2), Huntingtin (HTT), dystrophia myotonica-protein kinase (DMPK), low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), neurofibromin 1 (NF1), polycystic kidney disease 1 (PKD1), polycystic kidney disease 2 (PKD2), coagulation factor VIII (F8), dystrophin (DMD), phosphate-regulating endopeptidase homologue, X-linked (PHEX), methyl-CpG-binding protein 2 (MECP2), and ubiquitin-specific peptidase 9Y, Y-linked (USP9Y). Other single gene or monogenic diseases are known in the art and described in, e.g., Chial, H. Rare Genetic Disorders: Learning About Genetic Disease Through Gene Mapping, SNPs, and Microarray Data, Nature Education 1 (1): 192 (2008), incorporated herein by reference; Online Mendelian Inheritance in Man (OMIM); and the Human Gene Mutation Database (HGMD).
In another embodiment, the target genomic DNA sequence can comprise a gene, the mutation of which contributes to a particular disease in combination with mutations in other genes. Diseases caused by the contribution of multiple genes which lack simple (e.g., Mendelian) inheritance patterns are referred to in the art as a “multifactorial” or “polygenic” disease. Examples of multifactorial or polygenic diseases include, but are not limited to, asthma, diabetes, epilepsy, hypertension, bipolar disorder, and schizophrenia. Certain developmental abnormalities also can be inherited in a multifactorial or polygenic pattern and include, for example, cleft lip/palate, congenital heart defects, and neural tube defects.
In another embodiment, the method of altering a target genomic DNA sequence can be used to delete nucleic acids from a target sequence in a cell by cleaving the target sequence and allowing the cell to repair the cleaved sequence in the absence of an exogenously provided donor nucleic acid molecule. Deletion of a nucleic acid sequence in this manner can be used in a variety of applications, such as, for example, to remove disease-causing trinucleotide repeat sequences in neurons, to create gene knock-outs or knock-downs, and to generate mutations for disease models in research.
The term “donor nucleic acid molecule” refers to a nucleotide sequence that is inserted into the target DNA (e.g., genomic DNA). As described above the donor DNA may include, for example, a gene or part of a gene, a sequence encoding a tag or localization sequence, or a regulating element. The donor nucleic acid molecule may be of any length. In some embodiments, the donor nucleic acid molecule is between 10 and 10,000 nucleotides in length. For example, between about 100 and 5,000 nucleotides in length, between about 200 and 2,000 nucleotides in length, between about 500 and 1,000 nucleotides in length, between about 500 and 5,000 nucleotides in length, between about 1,000 and 5,000 nucleotides in length, or between about 1,000 and 10,000 nucleotides in length,
The disclosed systems and methods overcome challenges encountered during conventional gene editing, including low efficiency and off-target events, particularly with kilobase-scale nucleic acids. In some embodiments, the disclosed systems and methods improve the efficiency of gene editing. For example, the disclosed systems and methods can have a 2- to 10-fold increase in efficiency over conventional CRISPR-Cas9 systems and methods, as shown in Examples 2, 3, and 5. In some embodiments, the improvement in efficiency is accompanied by a reduction in off-target events. The off-target events may be reduced by greater than 50% compared to conventional CRISPR-Cas9 systems and methods, for example, a reduction of off-target events by about 90% is shown in Example 3. Another aspect of increasing the overall accuracy of a gene editing system is reducing the on-target insertion-deletions (indels), a byproduct of HDR editing. In some embodiments, the disclosed systems and methods reduce the on-target indels by greater than 90% compared to conventional CRISPR-Cas9 systems and methods, as shown in Example 3.
The disclosure further provides kits containing one or more reagents or other components useful, necessary, or sufficient for practicing any of the methods described herein. For example, kits may include CRISPR reagents (Cas protein, guide RNA, vectors, compositions, etc.), recombineering reagents (recombination protein-aptamer binding protein fusion protein, the aptamer sequence, vectors, compositions, etc.) transfection or administration reagents, negative and positive control samples (e.g., cells, template DNA), cells, containers housing one or more components (e.g., microcentrifuge tubes, boxes), detectable labels, detection and analysis instruments, software, instructions, and the like.
The RNAs may be delivered using adeno associated virus (AAV), lentivirus, adenovirus or other viral vector types, or combinations thereof. The RNAs can be packaged into one or more viral vectors. In some embodiments, the viral vector is delivered to the tissue of interest by, for example, an intramuscular injection, while other times the viral delivery is via intravenous, transdermal, intranasal, oral, mucosal, or other delivery methods. Such delivery may be either via a single dose, or multiple doses. One skilled in the art understands that the actual dosage to be delivered herein may vary greatly depending upon a variety of factors, such as the vector chose, the target cell, organism, or tissue, the general condition of the subject to be treated, the degree of transformation/modification sought, the administration route, the administration mode, the type of transformation/modification sought, etc.
Such a dosage may further contain, for example, a carrier (water, saline, ethanol, glycerol, lactose, sucrose, calcium phosphate, gelatin, dextran, agar, pectin, peanut oil, sesame oil, etc.), a diluent, a pharmaceutically-acceptable carrier (e.g., phosphate-buffered salinc), a pharmaceutically-acceptable excipient, and/or other compounds known in the art. Such a dosage formulation is readily ascertainable by one skilled in the art. The dosage may further contain one or more pharmaceutically acceptable salts such as, for example, a mineral acid salt such as a hydrochloride, a hydrobromide, a phosphate, a sulfate, etc.; and the salts of organic acids such as acetates, propionates, malonates, benzoates, etc. Additionally, auxiliary substances, such as wetting or emulsifying agents, pH buffering substances, gels or gelling materials, flavorings, colorants, microspheres, polymers, suspension agents, etc. may also be present herein. In addition, one or more other conventional pharmaceutical ingredients, such as preservatives, humectants, suspending agents, surfactants, antioxidants, anticaking agents, fillers, chelating agents, coating agents, chemical stabilizers, etc. may also be present, especially if the dosage form is a reconstitutable form. Suitable exemplary ingredients include microcrystalline cellulose, carboxymethylcellulose sodium, polysorbate 80, phenylethyl alcohol, chlorobutanol, potassium sorbate, sorbic acid, sulfur dioxide, propyl gallate, the parabens, ethyl vanillin, glycerin, phenol, parachlorophenol, gelatin, albumin, and a combination thereof. A thorough discussion of pharmaceutically acceptable excipients is available in REMINGTON'S PHARMACEUTICAL SCIENCES (Mack Pub. Co., N.J. 1991) which is incorporated by reference herein.
In an embodiment herein the delivery is via an adenovirus, which may be at a single booster dose containing at least 1×105 particles (also referred to as particle units, pu) of adenoviral vector. In an embodiment herein, the dose preferably is at least about 1×106 particles (for example, about 1×106-1×1012 particles), more preferably at least about 1×1010 particles, more preferably at least about 1×108 particles (e.g., about 1×108-1×1011 particles or about 1×108-1×1012 particles), and most preferably at least about 1×100 particles (e.g., about 1×109-1×1010 particles or about 1×109-1×1012 particles), or even at least about 1×1010 particles (e.g., about 1×1010-1×1012 particles) of the adenoviral vector. Alternatively, the dose comprises no more than about 1×1014 particles, preferably no more than about 1×1013 particles, even more preferably no more than about 1×1012 particles, even more preferably no more than about 1×1011 particles, and most preferably no more than about 1×1010 particles (e.g., no more than about 1×109 articles). Thus, the dose may contain a single dose of adenoviral vector with, for example, about 1×106 particle units (pu), about 2×106 pu, about 4×106 pu, about 1×107 pu, about 2×107 pu, about 4×107 pu, about 1×108 pu, about 2×108 pu, about 4×108 pu, about 1×109 pu, about 2×109 pu, about 4×109 pu, about 1×1010 pu, about 2×1010 pu, about 4×1010 pu, about 1×1011 pu, about 2×1011 pu, about 4×1011 pu, about 1×1012 pu, about 2×1012 pu, or about 4×1012 pu of adenoviral vector. See, for example, the adenoviral vectors in U.S. Pat. No. 8,454,972 B2 to Nabel, et. al., granted on Jun. 4, 2013; incorporated by reference herein, and the dosages at col 29, lines 36-58 thereof. In an embodiment herein, the adenovirus is delivered via multiple doses.
In an embodiment herein, the delivery is via an AAV. A therapeutically effective dosage for in vivo delivery of the AAV to a human is believed to be in the range of from about 20 to about 50 ml of saline solution containing from about 1×1010 to about 1×1010 functional AAV/ml solution. The dosage may be adjusted to balance the therapeutic benefit against any side effects. In an embodiment herein, the AAV dose is generally in the range of concentrations of from about 1×105 to 1×1050 genomes AAV, from about 1×108 to 1×1020 genomes AAV, from about 1×1010 to about 1×1016 genomes, or about 1×1011 to about 1×1016 genomes AAV. A human dosage may be about 1×1013 genomes AAV. Such concentrations may be delivered in from about 0.001 ml to about 100 ml, about 0.05 to about 50 ml, or about 10 to about 25 ml of a carrier solution. Other effective dosages can be readily established by one of ordinary skill in the art through routine trials establishing dose response curves. See, for example, U.S. Pat. No. 8,404,658 B2 to Hajjar, et al., granted on Mar. 26, 2013, at col. 27, lines 45-60.
In an embodiment herein the delivery is via a plasmid. In such plasmid compositions, the dosage should be a sufficient amount of plasmid to elicit a response. For instance, suitable quantities of plasmid DNA in plasmid compositions can be from about 0.1 to about 2 mg, or from about 1 μg to about 10 μg.
The doses herein are based on an average 70 kg individual. The frequency of administration is within the ambit of the medical or veterinary practitioner (e.g., physician, veterinarian), or scientist skilled in the art. Mice used in experiments are about 20 g. From that which is administered to a 20 g mouse, one can extrapolate to a 70 kg individual.
Lentiviruses are complex retroviruses that have the ability to infect and express their genes in both mitotic and post-mitotic cells. The most commonly known lentivirus is the human immunodeficiency virus (HIV), which uses the envelope glycoproteins of other viruses to target a broad range of cell types.
Lentiviruses may be prepared as follows. After cloning pCasES10 (which contains a lentiviral transfer plasmid backbone), HEK293FT at low passage (p=5) were seeded in a T-75 flask to 50% confluence the day before transfection in DMEM with 10% fetal bovine serum and without antibiotics. After 20 hours, media was changed to OptiMEM (serum-free) media and transfection was done 4 hours later. Cells were transfected with 10 μg of lentiviral transfer plasmid (pCasES10) and the following packaging plasmids: 5 μg of pMD2. G (VSV-g pseudotype), and 7.5 ug of psPAX2 (gag/pol/rev/tat). Transfection was done in 4 mL OptiMEM with a cationic lipid delivery agent (50 uL Lipofectamine 2000 and 100 uL Plus reagent). After 6 hours, the media was changed to antibiotic-free DMEM with 10% fetal bovine serum.
Lentivirus may be purified as follows. Viral supernatants were harvested after 48 hours. Supernatants were first cleared of debris and filtered through a 0.45 um low protein binding (PVDF) filter. They were then spun in an ultracentrifuge for 2 hours at 24,000 rpm. Viral pellets were resuspended in 50 ul of DMEM overnight at 4 C. They were then aliquotted and immediately frozen at −80 C.
In another embodiment, minimal non-primate lentiviral vectors based on the equine infectious anemia virus (EIAV) are also contemplated, especially for ocular gene therapy (see, e.g., Balagaan, J Genc Med 2006; 8:275-285, Published online 21 Nov. 2005 in Wiley Interscience; available at the website: interscience.wiley.com. DOI: 10.1002/jgm.845). In another embodiment, RetinoStat®, an equine infectious anemia virus-based lentiviral gene therapy vector that expresses angiostatic proteins endostain and angiostatin that is delivered via a subretinal injection for the treatment of the web form of age-related macular degeneration is also contemplated (see, e.g., Binley et al., HUMAN GENE THERAPY 23:980-991 (September 2012)) may be modified for the system of the present invention.
Lentiviral vectors have been disclosed as in the treatment for Parkinson's Disease, see, e.g., US Patent Publication No. 20120295960 and U.S. Pat. Nos. 7,303,910 and 7,351,585. Lentiviral vectors have also been disclosed for the treatment of ocular diseases, see e.g., US Patent Publication Nos. 20060281180, 20090007284, US20110117189; US20090017543; US20070054961, US20100317109. Lentiviral vectors have also been disclosed for delivery to the brain, scc, e.g., US Patent Publication Nos. US20110293571; US20110293571, US20040013648, US20070025970, US20090111106 and U.S. Pat. No. 7,259,015.
Several types of particle delivery systems and/or formulations are known to be useful in a diverse spectrum of biomedical applications. In general, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties. Particles are further classified according to diameter Coarse particles cover a range between 2,500 and 10,000 nanometers. Fine particles are sized between 100 and 2,500 nanometers. Ultrafine particles, or nanoparticles, are generally between 1 and 100 nanometers in size. The basis of the 100-nm limit is the fact that novel properties that differentiate particles from the bulk material typically develop at a critical length scale of under 100 nm.
As used herein, a particle delivery system/formulation is defined as any biological delivery system/formulation which includes a particle in accordance with the present invention. A particle in accordance with the present invention is any entity having a greatest dimension (e.g., diameter) of less than 100 microns (μm). In some embodiments, inventive particles have a greatest dimension of less than 10 In some embodiments, inventive particles have a greatest dimension of less than 2000 nanometers (nm). In some embodiments, inventive particles have a greatest dimension of less than 1000 nanometers (nm). In some embodiments, inventive particles have a greatest dimension of less than 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm. Typically, inventive particles have a greatest dimension (e.g., diameter) of 500 nm or less. In some embodiments, inventive particles have a greatest dimension (e.g., diameter) of 250 nm or less. In some embodiments, inventive particles have a greatest dimension (e.g., diameter) of 200 nm or less. In some embodiments, inventive particles have a greatest dimension (e.g., diameter) of 150 nm or less. In some embodiments, inventive particles have a greatest dimension (e.g., diameter) of 100 nm or less. Smaller particles, e.g., having a greatest dimension of 50 nm or less are used in some embodiments of the invention. In some embodiments, inventive particles have a greatest dimension ranging between 25 nm and 200 nm.
Particle characterization (including e.g., characterizing morphology, dimension, etc.) is done using a variety of different techniques. Common techniques are electron microscopy (TEM, SEM), atomic force microscopy (AFM), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF), ultraviolet-visible spectroscopy, dual polarization interferometry and nuclear magnetic resonance (NMR). Characterization (dimension measurements) may be made as to native particles (i.e., preloading) or after loading of the cargo (herein cargo refers to one or more RNAs and/or vectors encoding the same, and may include additional components, carriers and/or excipients) to provide particles of an optimal size for delivery for any in vitro, ex vivo and/or in vivo application of the present invention. In certain preferred embodiments, particle dimension (e.g., diameter) characterization is based on measurements using dynamic laser scattering (DLS).
Particles delivery systems within the scope of the present invention may be provided in any form, including but not limited to solid, semi-solid, emulsion, or colloidal particles. As such any of the delivery systems described herein, including but not limited to, e.g., lipid-based systems, liposomes, micelles, microvesicles, exosomes, or gene gun may be provided as particle delivery systems within the scope of the present invention.
In terms of this invention, it is preferred to have one or more components of the system delivered using nanoparticles or lipid envelopes. CRISPR enzyme mRNA and guide RNA may be delivered simultaneously using nanoparticles or lipid envelopes. Other delivery systems or vectors may be used in conjunction with the nanoparticle aspects of the invention.
In general, a “nanoparticle” refers to any particle having a diameter of less than 1000 nm. In certain preferred embodiments, nanoparticles of the invention have a greatest dimension (e.g., diameter) of 500 nm or less. In other preferred embodiments, nanoparticles of the invention have a greatest dimension ranging between 25 nm and 200 nm. In other preferred embodiments, nanoparticles of the invention have a greatest dimension of 100 nm or less. In other preferred embodiments, nanoparticles of the invention have a greatest dimension ranging between 35 nm and 60 nm.
Nanoparticles encompassed in the present invention may be provided in different forms, e.g., as solid nanoparticles (e.g., metal such as silver, gold, iron, titanium), non-metal, lipid-based solids, polymers), suspensions of nanoparticles, or combinations thereof. Metal, dielectric, and semiconductor nanoparticles may be prepared, as well as hybrid structures (e.g., core-shell nanoparticles). Nanoparticles made of semiconducting material may also be labeled quantum dots if they are small enough (typically sub 10 nm) that quantization of electronic energy levels occurs. Such nanoscale particles are used in biomedical applications as drug carriers or imaging agents and may be adapted for similar purposes in the present invention.
Semi-solid and soft nanoparticles have been manufactured, and are within the scope of the present invention. A prototype nanoparticle of semi-solid nature is the liposome. Various types of liposome nanoparticles are currently used clinically as delivery systems for anticancer drugs and vaccines. Nanoparticles with one half hydrophilic and the other half hydrophobic are termed Janus particles and are particularly effective for stabilizing emulsions. They can self-assemble at water/oil interfaces and act as solid surfactants.
For example, Su X, Fricke J, Kavanagh D G, Irvine D J (“In vitro and in vivo mRNA delivery using lipid-enveloped pH-responsive polymer nanoparticles” Mol Pharm. 2011 Jun. 6; 8 (3): 774-87. doi:10.1021/mp100390w. Epub 2011 Apr. 1) describes biodegradable core-shell structured nanoparticles with a poly(β-amino ester) (PBAE) core enveloped by a phospholipid bilayer shell. These were developed for in vivo mRNA delivery. The pH-responsive PBAE component was chosen to promote endosome disruption, while the lipid surface layer was selected to minimize toxicity of the polycation core. Such are, therefore, preferred for delivering RNA of the present invention.
In one embodiment, nanoparticles based on self-assembling bioadhesive polymers are contemplated, which may be applied to oral delivery of peptides, intravenous delivery of peptides and nasal delivery of peptides, all to the brain. Other embodiments, such as oral absorption and ocular deliver of hydrophobic drugs are also contemplated. The molecular envelope technology involves an engineered polymer envelope which is protected and delivered to the site of the disease (see, e.g., Mazza, M. et al. ACSNano, 2013. 7 (2): 1016-1026; Siew, A., et al. Mol Pharm, 2012. 9 (1): 14-28; Lalatsa, A., et al. J Contr Rel, 2012. 161 (2): 523-36; Lalatsa, A., et al., Mol Pharm, 2012. 9 (6): 1665-80; Lalatsa, A., et al. Mol Pharm, 2012. 9 (6): 1764-74; Garrett, N. L., et al. J Biophotonics, 2012. 5 (5-6): 458-68; Garrett, N. L., et al. J Raman Spect, 2012. 43 (5): 681-688; Ahmad, S., et al. J Royal Soc Interface 2010. 7: S423-33; Uchegbu, I. F. Expert Opin Drug Deliv, 2006. 3 (5): 629-40; Qu, X., et al. Biomacromolecules, 2006. 7 (12): 3452-9 and Uchegbu, I. F., et al. Int J Pharm, 2001. 224:185-199). Doses of about 5 mg/kg are contemplated, with single or multiple doses, depending on the target tissue.
In one embodiment, nanoparticles that can deliver RNA to a cancer cell to stop tumor growth developed by Dan Anderson's lab at MIT may be used/and or adapted to the CRISPR Cas system of the present invention. In particular, the Anderson lab developed fully automated, combinatorial systems for the synthesis, purification, characterization, and formulation of new biomaterials and nanoformulations. Sec, e.g., Alabi et al., Proc Natl Acad Sci USA. 2013 Aug. 6; 110 (32): 12881-6; Zhang et al., Adv Mater. 2013 Sep. 6; 25 (33): 4641-5; Jiang et al., Nano Lett. 2013 Mar. 13; 13 (3): 1059-64; Karagiannis et al., ACS Nano. 2012 Oct. 23; 6 (10): 8484-7; Whitehead et al., ACS Nano. 2012 Aug. 28; 6 (8): 6922-9 and Lee et al., Nat Nanotechnol. 2012 Jun. 3; 7 (6): 389-93.
U.S. patent application No. 20110293703 relates to lipidoid compounds are also particularly useful in the administration of polynucleotides, which may be applied to deliver the CRISPR Cas system of the present invention. In one aspect, the aminoalcohol lipidoid compounds are combined with an agent to be delivered to a cell or a subject to form microparticles, nanoparticles, liposomes, or micelles. The agent to be delivered by the particles, liposomes, or micelles may be in the form of a gas, liquid, or solid, and the agent may be a polynucleotide, protein, peptide, or small molecule. The minoalcohol lipidoid compounds may be combined with other aminoalcohol lipidoid compounds, polymers (synthetic or natural), surfactants, cholesterol, carbohydrates, proteins, lipids, etc. to form the particles. These particles may then optionally be combined with a pharmaceutical excipient to form a pharmaceutical composition.
US Patent Publication No. 0110293703 also provides methods of preparing the aminoalcohol lipidoid compounds. One or more equivalents of an amine are allowed to react with one or more equivalents of an epoxide-terminated compound under suitable conditions to form an aminoalcohol lipidoid compound of the present invention. In certain embodiments, all the amino groups of the amine are fully reacted with the epoxide-terminated compound to form tertiary amines. In other embodiments, all the amino groups of the amine are not fully reacted with the epoxide-terminated compound to form tertiary amines thereby resulting in primary or secondary amines in the aminoalcohol lipidoid compound. These primary or secondary amines are left as is or may be reacted with another electrophile such as a different epoxide-terminated compound. As will be appreciated by one skilled in the art, reacting an amine with less than excess of epoxide-terminated compound will result in a plurality of different aminoalcohol lipidoid compounds with various numbers of tails. Certain amines may be fully functionalized with two epoxide-derived compound tails while other molecules will not be completely functionalized with epoxide-derived compound tails. For example, a diamine or polyamine may include one, two, three, or four epoxide-derived compound tails off the various amino moieties of the molecule resulting in primary, secondary, and tertiary amines. In certain embodiments, all the amino groups are not fully functionalized. In certain embodiments, two of the same types of epoxide-terminated compounds are used. In other embodiments, two or more different epoxide-terminated compounds are used. The synthesis of the aminoalcohol lipidoid compounds is performed with or without solvent, and the synthesis may be performed at higher temperatures ranging from 30-100 C., preferably at approximately 50-90 C. The prepared aminoalcohol lipidoid compounds may be optionally purified. For example, the mixture of aminoalcohol lipidoid compounds may be purified to yield an aminoalcohol lipidoid compound with a particular number of epoxide-derived compound tails. Or the mixture may be purified to yield a particular stereo- or regioisomer. The aminoalcohol lipidoid compounds may also be alkylated using an alkyl halide (e.g., methyl iodide) or another alkylating agent, and/or they may be acylated.
US Patent Publication No. 0110293703 also provides libraries of aminoalcohol lipidoid compounds prepared by the inventive methods. These aminoalcohol lipidoid compounds may be prepared and/or screened using high-throughput techniques involving liquid handlers, robots, microtiter plates, computers, etc. In certain embodiments, the aminoalcohol lipidoid compounds are screened for their ability to transfect polynucleotides or other agents (e.g., proteins, peptides, small molecules) into the cell.
US Patent Publication No. 20130302401 relates to a class of poly(beta-amino alcohols) (PBAAs) has been prepared using combinatorial polymerization. The inventive PBAAs may be used in biotechnology and biomedical applications as coatings (such as coatings of films or multilayer films for medical devices or implants), additives, materials, excipients, non-biofouling agents, micropatterning agents, and cellular encapsulation agents. When used as surface coatings, these PBAAs elicited different levels of inflammation, both in vitro and in vivo, depending on their chemical structures. The large chemical diversity of this class of materials allowed us to identify polymer coatings that inhibit macrophage activation in vitro. Furthermore, these coatings reduce the recruitment of inflammatory cells, and reduce fibrosis, following the subcutaneous implantation of carboxylated polystyrene microparticles. These polymers may be used to form polyelectrolyte complex capsules for cell encapsulation. The invention may also have many other biological applications such as antimicrobial coatings, DNA or siRNA delivery, and stem cell tissue engineering. The teachings of US Patent Publication No. 20130302401 may be applied to the system of the present invention.
In another embodiment, lipid nanoparticles (LNPs) are contemplated. In particular, an antitransthyretin small interfering RNA encapsulated in lipid nanoparticles (see, e.g., Coelho et al., N Engl J Med 2013; 369:819-29) may be applied to the system of the present invention. Doses of about 0.01 to about 1 mg per kg of body weight administered intravenously are contemplated. Medications to reduce the risk of infusion-related reactions are contemplated, such as dexamethasone, acetaminophen, diphenhydramine or cetirizine, and ranitidine are contemplated. Multiple doses of about 0.3 mg per kilogram every 4 weeks for five doses are also contemplated. Lipids include, but are not limited to, DLin-KC2-DMA4, C12-200 and colipids disteroylphosphatidyl choline, cholesterol, and PEG-DMG may be formulated RNA instead of siRNA (see, e.g., Novobrantseva, Molecular Therapy—Nucleic Acids (2012) 1, e4; doi:10.1038/mtna.2011.3) using a spontaneous vesicle formation procedure. The component molar ratio may be about 50/10/38.5/1.5 (DLin-KC2-DMA or C12-200/disteroylphosphatidyl choline/cholesterol/PEG-DMG). The final lipid: siRNA weight ratio may be ˜12:1 and 9:1 in the case of DLin-KC2-DMA and C12-200 lipid nanoparticles (LNPs), respectively. The formulations may have mean particle diameters of ˜80 nm with >90% entrapment efficiency. A 3 mg/kg dose may be contemplated.
LNPs have been shown to be highly effective in delivering siRNAs to the liver (see, e.g., Tabernero et al., Cancer Discovery, April 2013, Vol. 3, No. 4, pages 363-470) and are therefore contemplated for delivering CRISPR Cas to the liver. A dosage of about four doses of 6 mg/kg of the LNP (or RNA of the CRISPR-Cas) every two weeks may be contemplated. Tabernero et al. demonstrated that tumor regression was observed after the first 2 cycles of LNPs dosed at 0.7 mg/kg, and by the end of 6 cycles the patient had achieved a partial response with complete regression of the lymph node metastasis and substantial shrinkage of the liver tumors. A complete response was obtained after 40 doses in this patient, who has remained in remission and completed treatment after receiving doses over 26 months. Two patients with RCC and extrahepatic sites of disease including kidney, lung, and lymph nodes that were progressing following prior therapy with VEGF pathway inhibitors had stable disease at all sites for approximately 8 to 12 months, and a patient with PNET and liver metastases continued on the extension study for 18 months (36 doses) with stable disease.
However, the charge of the LNP must be taken into consideration. As cationic lipids combined with negatively charged lipids to induce nonbilayer structures that facilitate intracellular delivery. Because charged LNPs are rapidly cleared from circulation following intravenous injection, ionizable cationic lipids with pKa values below 7 were developed (see, e.g., Rosin et al, Molecular Therapy, vol. 19, no. 12, pages 1286-220 December 2011). Negatively charged polymers such as siRNA oligonucleotides may be loaded into LNPs at low pH values (e.g., pH 4) where the ionizable lipids display a positive charge. However, at physiological pH values, the LNPs exhibit a low surface charge compatible with longer circulation times. Four species of ionizable cationic lipids have been focused upon, namely 1,2-dilineoyl-3-dimethylammonium-propane (DLinDAP), 1,2-dilinolcyloxy-3-N,N-dimethylaminopropane (DLinDMA), 1,2-dilinoleyloxy-keto-N,N-dimethyl-3-aminopropane (DLinKDMA), and 1,2-dilinoleyl-4-(2-dimethylaminocthyl)-[1,3]-dioxolane (DLinKC2-DMA). It has been shown that LNP siRNA systems containing these lipids exhibit remarkably different gene silencing properties in hepatocytes in vivo, with potencies varying according to the series DLinKC2-DMA>DLinKDMA>DLinDMA>>DLinDAP employing a Factor VII gene silencing model (see, e.g., Rosin et al, Molecular Therapy, vol. 19, no. 12, pages 1286-220 December 2011). A dosage of 1 μg/ml levels may be contemplated, especially for a formulation containing DLinKC2-DMA. Preparation of LNPs and CRISPR Cas encapsulation may be used/and or adapted from Rosin et al, Molecular Therapy, vol. 19, no. 12, pages 1286-220 December 2011). The cationic lipids 1,2-dilincoyl-3-dimethylammonium-propane (DLinDAP), 1,2-dilinoleyloxy-3-N,N-dimethylaminopropane (DLinDMA), 1,2-dilinolcyloxykcto-N,N-dimethyl-3-aminopropanc (DLinK-DMA), 1,2-dilinoleyl-4-(2-dimethylaminocthyl)-[1,3]-dioxolane (DLinKC2-DMA), (3-0-[2″-(methoxypolyethyleneglycol 2000) succinoyl]-1,2-dimyristoyl-sn-glycol (PEG-S-DMG), and R-3-[(w-methoxy-poly(ethylene glycol) 2000) carbamoyl]-1,2-dimyristyloxlpropyl-3-amine (PEG-C-DOMG) may be provided by Tekmira Pharmaceuticals (Vancouver, Canada) or synthesized. Cholesterol may be purchased from Sigma (St Louis, Mo.). The specific CRISPR Cas RNA may be encapsulated in LNPs containing DLinDAP, DLinDMA, DLinK-DMA, and DLinKC2-DMA (cationic lipid: DSPC: CHOL: PEGS-DMG or PEG-C-DOMG at 40:10:40:10 molar ratios). When required, 0.2% SP-DiOC18 (Invitrogen, Burlington, Canada) may be incorporated to assess cellular uptake, intracellular delivery, and biodistribution. Encapsulation may be performed by dissolving lipid mixtures comprised of cationic lipid: DSPC: cholesterol: PEG-c-DOMG (40:10:40:10 molar ratio) in ethanol to a final lipid concentration of 10 mmol/1. This ethanol solution of lipid may be added dropwise to 50 mmol/1 citrate, pH 4.0 to form multilamellar vesicles to produce a final concentration of 30% ethanol vol/vol. Large unilamellar vesicles may be formed following extrusion of multilamellar vesicles through two stacked 80 nm Nuclepore polycarbonate filters using the Extruder (Northern Lipids, Vancouver, Canada). Encapsulation may be achieved by adding RNA dissolved at 2 mg/ml in 50 mmol/l citrate, pH 4.0 containing 30% ethanol vol/vol drop-wise to extruded preformed large unilamellar vesicles and incubation at 31° C. for 30 minutes with constant mixing to a final RNA/lipid weight ratio of 0.06/1 wt/wt. Removal of ethanol and neutralization of formulation buffer were performed by dialysis against phosphate-buffered saline (PBS), pH 7.4 for 16 hours using Spectra/Por 2 regenerated cellulose dialysis membranes. Nanoparticle size distribution may be determined by dynamic light scattering using a NICOMP 370 particle sizer, the vesicle/intensity modes, and Gaussian fitting (Nicomp Particle Sizing, Santa Barbara, Calif.). The particle size for all three LNP systems may be ˜70 nm in diameter. siRNA encapsulation efficiency may be determined by removal of free siRNA using VivaPureD MiniH columns (Sartorius Stedim Biotech) from samples collected before and after dialysis. The encapsulated RNA may be extracted from the eluted nanoparticles and quantified at 260 nm. siRNA to lipid ratio was determined by measurement of cholesterol content in vesicles using the Cholesterol E enzymatic assay from Wako Chemicals USA (Richmond, Va.). PEGylated liposomes (or LNPs) can also be used for delivery.
Preparation of large LNPs may be used/and or adapted from Rosin et al, Molecular Therapy, vol. 19, no. 12, pages 1286-220 December 2011. A lipid premix solution (20.4 mg/ml total lipid concentration) may be prepared in ethanol containing DLinKC2-DMA, DSPC, and cholesterol at 50:10:38.5 molar ratios. Sodium acetate may be added to the lipid premix at a molar ratio of 0.75:1 (sodium acetate: DLinKC2-DMA). The lipids may be subsequently hydrated by combining the mixture with 1.85 volumes of citrate buffer (10 mmol/1, pH 3.0) with vigorous stirring, resulting in spontaneous liposome formation in aqueous buffer containing 35% ethanol. The liposome solution may be incubated at 37° C. to allow for time-dependent increase in particle size. Aliquots may be removed at various times during incubation to investigate changes in liposome size by dynamic light scattering (Zetasizer Nano ZS, Malvern Instruments, Worcestershire, UK). Once the desired particle size is achieved, an aqueous PEG lipid solution (stock=10 mg/ml PEG-DMG in 35% (vol/vol) ethanol) may be added to the liposome mixture to yield a final PEG molar concentration of 3.5% of total lipid. Upon addition of PEG-lipids, the liposomes should their size, effectively quenching further growth. RNA may then be added to the empty liposomes at an siRNA to total lipid ratio of approximately 1:10 (wt:wt), followed by incubation for 30 minutes at 37° C. to form loaded LNPs. The mixture may be subsequently dialyzed overnight in PBS and filtered with a 0.45-μm syringe filter.
Spherical Nucleic Acid (SNA™) constructs and other nanoparticles (particularly gold nanoparticles) are also contemplated as a means to delivery CRISPR/Cas system to intended targets. Significant data show that AuraSense Therapeutics' Spherical Nucleic Acid (SNA™) constructs, based upon nucleic acid-functionalized gold nanoparticles, are superior to alternative platforms based on multiple key success factors, such as:
High in vivo stability. Due to their dense loading, a majority of cargo (DNA or siRNA) remains bound to the constructs inside cells, conferring nucleic acid stability and resistance to enzymatic degradation.
Deliverability. For all cell types studied (e.g., neurons, tumor cell lines, etc.) the constructs demonstrate a transfection efficiency of 99% with no need for carriers or transfection agents.
Therapeutic targeting. The unique target binding affinity and specificity of the constructs allow exquisite specificity for matched target sequences (i.e., limited off-target effects).
Superior efficacy. The constructs significantly outperform leading conventional transfection reagents (Lipofectamine 2000 and Cytofectin).
Low toxicity. The constructs can enter a variety of cultured cells, primary cells, and tissues with no apparent toxicity.
No significant immune response. The constructs elicit minimal changes in global gene expression as measured by whole-genome microarray studies and cytokine-specific protein assays.
Chemical tailorability. Any number of single or combinatorial agents (e.g., proteins, peptides, small molecules) can be used to tailor the surface of the constructs.
This platform for nucleic acid-based therapeutics may be applicable to numerous disease states, including inflammation and infectious disease, cancer, skin disorders and cardiovascular disease.
Citable literature includes: Cutler et al., J. Am. Chem. Soc. 2011 133:9254-9257, Hao et al., Small. 2011 7:3158-3162, Zhang et al., ACS Nano. 2011 5:6962-6970, Cutler et al., J. Am. Chem. Soc. 2012 134:1376-1391, Young et al., Nano Lett. 2012 12:3867-71, Zheng et al., Proc. Natl. Acad. Sci. USA. 2012 109:11975-80, Mirkin, Nanomedicine 2012 7:635-638 Zhang et al., J. Am. Chem. Soc. 2012 134:16488-1691, Weintraub, Nature 2013 495: S14-S16, Choi et al., Proc. Natl. Acad. Sci. USA. 2013 110 (19): 7625-7630, Jensen et al., Sci. Transl. Med. 5, 209ra152 (2013) and Mirkin, et al., Small, doi.org/10.1002/smll.201302143.
Self-assembling nanoparticles with siRNA may be constructed with polyethyleneimine (PEI) that is PEGylated with an Arg-Gly-Asp (RGD) peptide ligand attached at the distal end of the polyethylene glycol (PEG), for example, as a means to target tumor neovasculature expressing integrins and used to deliver siRNA inhibiting vascular endothelial growth factor receptor-2 (VEGF R2) expression and thereby tumor angiogenesis (see, e.g., Schiffelers et al., Nucleic Acids Research, 2004, Vol. 32, No. 19). Nanoplexes may be prepared by mixing equal volumes of aqueous solutions of cationic polymer and nucleic acid to give a net molar excess of ionizable nitrogen (polymer) to phosphate (nucleic acid) over the range of 2 to 6. The electrostatic interactions between cationic polymers and nucleic acid resulted in the formation of polyplexes with average particle size distribution of about 100 nm, hence referred to here as nanoplexes. A dosage of about 100 to 200 mg of CRISPR Cas is envisioned for delivery in the self-assembling nanoparticles of Schiffelers et al.
The nanoplexes of Bartlett et al. (PNAS, Sep. 25, 2007, vol. 104, no. 39) may also be applied to the present invention. The nanoplexes of Bartlett et al. are prepared by mixing equal volumes of aqueous solutions of cationic polymer and nucleic acid to give a net molar excess of ionizable nitrogen (polymer) to phosphate (nucleic acid) over the range of 2 to 6. The electrostatic interactions between cationic polymers and nucleic acid resulted in the formation of polyplexes with average particle size distribution of about 100 nm, hence referred to here as nanoplexes. The DOTA-siRNA of Bartlett et al. was synthesized as follows: 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono(N-hydroxysuccinimide ester) (DOTA-NHSester) was ordered from Macrocyclics (Dallas, Tex.). The amine modified RNA sense strand with a 100-fold molar excess of DOTA-NHS-ester in carbonate buffer (pH 9) was added to a microcentrifuge tube. The contents were reacted by stirring for 4 h at room temperature. The DOTA-RNAsense conjugate was ethanol-precipitated, resuspended in water, and annealed to the unmodified antisense strand to yield DOTA-siRNA. All liquids were pretreated with Chelex-100 (Bio-Rad, Hercules, Calif.) to remove trace metal contaminants. Tf-targeted and nontargeted siRNA nanoparticles may be formed by using cyclodextrin-containing polycations. Typically, nanoparticles were formed in water at a charge ratio of 3 (+/−) and an siRNA concentration of 0.5 g/liter. One percent of the adamantane-PEG molecules on the surface of the targeted nanoparticles were modified with Tf (adamantane-PEG-Tf). The nanoparticles were suspended in a 5% (wt/vol) glucose carrier solution for injection.
Davis et al. (Nature, Vol 464, 15 Apr. 2010) conducts a siRNA clinical trial that uses a targeted nanoparticle-delivery system (clinical trial registration number NCT00689065). Patients with solid cancers refractory to standard-of-care therapies are administered doses of targeted nanoparticles on days 1, 3, 8 and 10 of a 21-day cycle by a 30-min intravenous infusion. The nanoparticles consist of a synthetic delivery system containing: (1) a linear, cyclodextrin-based polymer (CDP), (2) a human transferrin protein (TF) targeting ligand displayed on the exterior of the nanoparticle to engage TF receptors (TFR) on the surface of the cancer cells, (3) a hydrophilic polymer (polyethylene glycol (PEG) used to promote nanoparticle stability in biological fluids), and (4) siRNA designed to reduce the expression of the RRM2 (sequence used in the clinic was previously denoted siR2B+5). The TFR has long been known to be upregulated in malignant cells, and RRM2 is an established anti-cancer target. These nanoparticles (clinical version denoted as CALAA-01) have been shown to be well tolerated in multi-dosing studies in non-human primates. Although a single patient with chronic myeloid leukemia has been administered siRNA by liposomal delivery, Davis et al.'s clinical trial is the initial human trial to systemically deliver siRNA with a targeted delivery system and to treat patients with solid cancer. To ascertain whether the targeted delivery system can provide effective delivery of functional siRNA to human tumors, Davis et al. investigated biopsies from three patients from three different dosing cohorts; patients A, B and C, all of whom had metastatic melanoma and received CALAA-01 doses of 18, 24 and 30 mg m−2 siRNA, respectively. Similar doses may also be contemplated for the CRISPR Cas system of the present invention. The delivery of the invention may be achieved with nanoparticles containing a linear, cyclodextrin-based polymer (CDP), a human transferrin protein (TF) targeting ligand displayed on the exterior of the nanoparticle to engage TF receptors (TFR) on the surface of the cancer cells and/or a hydrophilic polymer (for example, polyethylene glycol (PEG) used to promote nanoparticle stability in biological fluids).
Delivery or administration according to the invention can be performed with liposomes. Liposomes are spherical vesicle structures composed of a uni- or multilamellar lipid bilayer surrounding internal aqueous compartments and a relatively impermeable outer lipophilic phospholipid bilayer. Liposomes have gained considerable attention as drug delivery carriers because they are biocompatible, nontoxic, can deliver both hydrophilic and lipophilic drug molecules, protect their cargo from degradation by plasma enzymes, and transport their load across biological membranes and the blood brain barrier (BBB) (see, e.g., Spuch and Navarro, Journal of Drug Delivery, vol. 2011, Article ID 469679, 12 pages, 2011. doi:10.1155/2011/469679 for review).
Liposomes can be made from several different types of lipids; however, phospholipids are most commonly used to generate liposomes as drug carriers. Although liposome formation is spontaneous when a lipid film is mixed with an aqueous solution, it can also be expedited by applying force in the form of shaking by using a homogenizer, sonicator, or an extrusion apparatus (see, e.g., Spuch and Navarro, Journal of Drug Delivery, vol. 2011, Article ID 469679, 12 pages, 2011. doi:10.1155/2011/469679 for review).
Several other additives may be added to liposomes in order to modify their structure and properties. For instance, either cholesterol or sphingomyelin may be added to the liposomal mixture in order to help stabilize the liposomal structure and to prevent the leakage of the liposomal inner cargo. Further, liposomes are prepared from hydrogenated egg phosphatidylcholine or egg phosphatidylcholine, cholesterol, and dicetyl phosphate, and their mean vesicle sizes were adjusted to about 50 and 100 nm. (see, e.g., Spuch and Navarro, Journal of Drug Delivery, vol. 2011, Article ID 469679, 12 pages, 2011. doi:10.1155/2011/469679 for review).
Conventional liposome formulation is mainly comprised of natural phospholipids and lipids such as 1,2-distearoryl-sn-glycero-3-phosphatidyl choline (DSPC), sphingomyelin, egg phosphatidylcholines and monosialoganglioside. Since this formulation is made up of phospholipids only, liposomal formulations have encountered many challenges, one of the ones being the instability in plasma. Several attempts to overcome these challenges have been made, specifically in the manipulation of the lipid membrane. One of these attempts focused on the manipulation of cholesterol. Addition of cholesterol to conventional formulations reduces rapid release of the encapsulated bioactive compound into the plasma or 1,2-diolcoyl-sn-glycero-3-phosphoethanolamine (DOPE) increases the stability (see, e.g., Spuch and Navarro, Journal of Drug Delivery, vol. 2011, Article ID 469679, 12 pages, 2011. doi:10.1155/2011/469679 for review).
In a particularly advantageous embodiment, Trojan Horse liposomes (also known as Molecular Trojan Horses) are desirable and protocols may be found at cshprotocols.cshlp.org/content/2010/4/pdb.prot5407.long. These particles allow delivery of a transgene to the entire brain after an intravascular injection. Without being bound by limitation, it is believed that neutral lipid particles with specific antibodies conjugated to surface allow crossing of the blood brain barrier via endocytosis. Applicant postulates utilizing Trojan Horse Liposomes to deliver the CRISPR family of nucleases to the brain via an intravascular injection, which would allow whole brain transgenic animals without the need for embryonic manipulation. About 1-5 g of nucleic acid molecule, e.g., DNA, RNA, may be contemplated for in vivo administration in liposomes.
In another embodiment, the system may be administered in liposomes, such as a stable nucleic-acid-lipid particle (SNALP) (see, e.g., Morrissey et al., Nature Biotechnology, Vol. 23, No. 8, August 2005). Daily intravenous injections of about 1, 3 or 5 mg/kg/day of a specific CRISPR Cas targeted in a SNALP are contemplated. The daily treatment may be over about three days and then weekly for about five weeks. In another embodiment, a specific CRISPR Cas encapsulated SNALP) administered by intravenous injection to at doses of abpit 1 or 2.5 mg/kg are also contemplated (see, e.g., Zimmerman et al., Nature Letters, Vol. 441, 4 May 2006). The SNALP formulation may contain the lipids 3-N-[(wmethoxypoly(ethylene glycol) 2000) carbamoyl]-1,2-dimyristyloxy-propylamine (PEG-C-DMA), 1,2-dilinoleyloxy-N,N-dimethyl-3-aminopropane (DLinDMA), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol, in a 2:40:10:48 molar percent ratio (see, e.g., Zimmerman et al., Nature Letters, Vol. 441, 4 May 2006).
In another embodiment, stable nucleic-acid-lipid particles (SNALPs) have proven to be effective delivery molecules to highly vascularized HepG2-derived liver tumors but not in poorly vascularized HCT-116 derived liver tumors (see, e.g., Li, Gene Therapy (2012) 19, 775-780). The SNALP liposomes may be prepared by formulating D-Lin-DMA and PEG-C-DMA with distcaroylphosphatidylcholine (DSPC), Cholesterol and siRNA using a 25:1 lipid/siRNA ratio and a 48/40/10/2 molar ratio of Cholesterol/D-Lin-DMA/DSPC/PEG-C-DMA. The resulted SNALP liposomes are about 80-100 nm in size.
In yet another embodiment, a SNALP may comprise synthetic cholesterol (Sigma-Aldrich, St Louis, Mo., USA), dipalmitoylphosphatidylcholine (Avanti Polar Lipids, Alabaster,
Ala., USA), 3-N-[(w-methoxy poly(ethylene glycol) 2000) carbamoyl]-1,2-dimyrestyloxypropylamine, and cationic 1,2-dilinoleyloxy-3-N,Ndimethylaminopropane (scc, e.g., Geisbert et al., Lancet 2010; 375:1896-905). A dosage of about 2 mg/kg total CRISPR Cas per dose administered as, for example, a bolus intravenous infusion may be contemplated.
In yet another embodiment, a SNALP may comprise synthetic cholesterol (Sigma-Aldrich), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC; Avanti Polar Lipids Inc.), PEG-cDMA, and 1,2-dilinolcyloxy-3-(N;N-dimethyl)aminopropane (DLinDMA) (scc, e.g., Judge, J. Clin. Invest. 119:661-673 (2009)). Formulations used for in vivo studies may comprise a final lipid/RNA mass ratio of about 9:1.
Other cationic lipids, such as amino lipid 2,2-dilinoleyl-4-dimethylaminoethyl-[1,3]-dioxolane (DLin-KC2-DMA) may be utilized to encapsulate CRISPR Cas similar to SiRNA (scc, e.g., Jayaraman, Angew. Chem. Int. Ed. 2012, 51, 8529-8533). A preformed vesicle with the following lipid composition may be contemplated: amino lipid, di stearoylphosphatidylcholine (DSPC), cholesterol and (R)-2,3-bis(octadecyloxy) propyl-1-(methoxy poly(ethylene glycol) 2000) propylcarbamate (PEG-lipid) in the molar ratio 40/10/40/10, respectively, and a FVII siRNA/total lipid ratio of approximately 0.05 (w/w). To ensure a narrow particle size distribution in the range of 70-90 nm and a low polydispersity index of 0.11_0.04 (n=56), the particles may be extruded up to three times through 80 nm membranes prior to adding the CRISPR Cas RNA. Particles containing the highly potent amino lipid 16 may be used, in which the molar ratio of the four lipid components 16, DSPC, cholesterol and PEG-lipid (50/10/38.5/1.5) which may be further optimized to enhance in vivo activity.
Any element of any suitable CRISPR/Cas gene editing system known in the art can be employed in the systems and methods described herein, as appropriate. CRISPR/Cas gene editing technology is described in detail in, for example, U.S. Patent Application Publication 2014/0068797; U.S. Pat. Nos. 8,697,359; 8,771,945; and 8,945,839; US2010/0076057; US2011/0189776; US2011/0223638; US2013/0130248; WO/2008/108989; WO/2010/054108; WO/2012/164565; WO/2013/098244; WO/2013/176772; US20150050699; US20150045546; US20150031134; US20150024500; US20140377868; US20140357530; US20140349400; US20140335620; US20140335063; US20140315985; US20140310830; US20140310828; US20140309487; US20140304853; US20140298547; US20140295556; US20140294773; US20140287938; US20140273234; US20140273232; US20140273231; US20140273230; US20140271987; US20140256046; US20140248702; US20140242702; US20140242700; US20140242699; US20140242664; US20140234972; US20140227787; US20140212869; US20140201857; US20140199767; US20140189896; US20140186958; US20140186919; US20140186843; US20140179770; US20140179006; and US20140170753, incorporated herein by reference.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims.
The present invention will be further illustrated in the following Examples which are given for illustration purposes only and are not intended to limit the invention in any way.
RecE/T Homolog Screening RefSeq non-redundant protein database was downloaded from NCBI on Oct. 29, 2019. The database was searched with E. coli Rac prophage RecT (NP_415865.1) and RecE (NP_415866.1) as queries using position-specific iterated (PSI)-BLAST1 to retrieve protein homologs. Hits were clustered with CD-HIT2 and representative sequences were selected from each cluster for multiple alignment with MUSCLE3. Then, FastTree4 was used for maximum likelihood tree reconstruction with default parameters. A diverse set of RecET homologs were selected, synthesized by GenScript, and cloned into pMPH_MCP vectors for testing.
Plasmids construction pX330, pMPH and pU6-(BbsI)_CBh-Cas9-T2A-BFP plasmids were obtained from Addgene. Tested effector DNA fragments were ordered from IDT, Genewiz, and GenScript. The fragments were Gibson assembled into the backbones using NEBuilder HiFi DNA Assembly Master Mix (New England BioLabs). All sgRNAs (Table 1) were inserted into backbones using Golden Gate cloning. All constructs were sequence-verified with Sanger sequencing of prepped plasmids.
Cell culture Human Embryonic Kidney (HEK) 293T, HeLa and HepG2 were maintained in Dulbecco's Modified Eagle's Medium (DMEM, Life Technologies), with 10% fetal bovine serum (FBS, HyClone), 100 U/mL penicillin, and 100 μg/mL streptomycin (Life Technologies) at 37° C. with 5% CO2.
hES-H9 cells were maintained in mTeSR1 medium (StemCell Technologies) at 37° C. with 5% CO2. Culture plates were pre-coated with Matrigel (Corning) 12 hours prior to use, and cells were supplemented with 10 μM Y27632 (Sigma) for the first 24 hours after passaging. Culture media was changed every 24 hours.
Transfection HEK293T cells were seeded into 96-well plates (Corning) 12-24 hours prior to transfection at a density of 30,000 cells/well, and 250 ng of total DNA was transfected per well. HeLa and HepG2 cells were seeded into 48-well plates (Corning) one day prior to transfection at a density of 50,000 and 30,000 cells/well respectively, and 400 ng of total DNA was transfected per well. Transfections were performed with Lipofectamine 3000 (Life Technologies) following the manufacturer's instructions.
Electroporation For hES-H9 related transfection experiments, P3 Primary Cell 4D-Nucleofector™ X Kit S (Lonza) was used following the manufacturer's protocol. For each reaction, 300,000 cells were nucleofected with 4 μg total DNA using the DC100 Nucleofector Program.
Fluorescence-activated cell sorting (FACS) mKate knock-in efficiency was analyzed on a CytoFLEX flow cytometer (Beckman Coulter; Stanford Stem Cell FACS Core). 72 hours after transfection, cells were washed once with PBS and dissociated with TrypLE Express Enzyme (Thermo Fisher Scientific). Cell suspension was then transferred to a 96-well U-bottom plate (Thermo Fisher Scientific) and centrifuged at 300×G for 5 minutes. After removing the supernatant, pelleted cells were resuspended with 50 μl 4% FBS in PBS, and cells were sorted within 30 minutes of preparation.
RFLP HEK293T cells were transfected with plasmid DNA and PCR templates and harvested after 72 hours for genomic DNA using the QuickExtract DNA Extraction Solution (Biosearch Technologies) following the manufacturer's protocol. The target genomic region was amplified using specific primers outside of the homology arms of the PCR template. PCR products were purified with Monarch PCR & DNA Cleanup Kit (New England BioLabs). 300 ng of purified product was digested with BsrGI (EMX1, New England BioLabs) or XbaI (VEGFA, NEB), and the digested products were analyzed on a 5% Mini-PROTEAN TBE gel (Bio-Rad).
Next-Generation Sequencing Library Preparation 72 hours after transfection, genomic DNA was extracted using QuickExtract DNA Extraction Solution (Biosearch Technologies). 200 ng total DNA was used for NGS library preparation. Genes of interest were amplified using specific primers (Table 2) for the first round PCR reaction. Illumina adapters and index barcodes were added to the fragments with a second round PCR using the primers listed in Table 2. Round 2 PCR products were purified by gel electrophoresis on a 2% agarose gel using the Monarch DNA Gel Extraction Kit (NEB). The purified product was quantified with Qubit dsDNA HS Assay Kit (Thermo Fisher) and sequenced on an Illumina MiSeq according to the manufacturer's instructions.
CCATCTCATCCCTGCGTGTCTCCAGAAGA
CCTCTCTATGGGCAGTCGGTGATgAGCAG
CCATCTCATCCCTGCGTGTCTCCCAGCGT
CCTCTCTATGGGCAGTCGGTGATgTTGGA
CCATCTCATCCCTGCGTGTCTCCACAAAA
CCTCTCTATGGGCAGTCGGTGATgGCTGA
CCATCTCATCCCTGCGTGTCTCCACACAC
CCTCTCTATGGGCAGTCGGTGATgAATGT
CCATCTCATCCCTGCGTGTCTCCGGCTAC
CCTCTCTATGGGCAGTCGGTGATgAGGAC
CCATCTCATCCCTGCGTGTCTCCGCAGGC
CCTCTCTATGGGCAGTCGGTGATgCCCTC
CCATCTCATCCCTGCGTGTCTCCGGAGG
CCTCTCTATGGGCAGTCGGTGATgCAAAT
CCATCTCATCCCTGCGTGTCTCCTGAGCG
CCTCTCTATGGGCAGTCGGTGATgGCCAG
High-throughput Sequencing Data Analysis Processed (demultiplexed, trimmed, and merged) sequencing reads were analyzed to determine editing outcomes using CRISPPResso25 by aligning sequenced amplicons to reference and expected HDR amplicons. The quantification window was increased to 10 bp surrounding the expected cut site to better capture diverse editing outcomes, but substitutions were ignored to avoid inclusion of sequencing errors. Only reads containing no mismatches to the expected amplicon were considered for HDR quantification; reads containing indels that partially matched the expected amplicons were included in the overall reported indel frequency.
Statistical Analysis Unless otherwise stated, all statistical analysis and comparison were performed using t-test, with 1% false-discovery-rate (FDR) using two-stage step-up method of Benjamini, Krieger and Yekutieli (Benjamini, Y., et. al, Biometrika 93, 491-507 (2006), incorporated herein by reference). All experiments were performed in triplicates unless otherwise noted to ensure sufficient statistical power in the analysis.
Determination of editing at predicted Cas9 off-target sites To evaluate RecT/RecE off-target editing activity at known Cas9 off-target sites, same genomic DNA extracts for knock-in analysis were used as template for PCR amplification of top predicted off-targets sites (high scored as predicted CRISPOR, a web-based analysis tool) for the EMX1, VEGFA guides, primer sequences are listed in Table 2.
iGUIDE Off-target Analysis Genome-wide, unbiased off-target analysis was performed following the iGUIDE pipeline (Nobles, C. L., et al. Genome Biol 20, 14 (2019), incorporated herein by reference) based on Guide-seq invented previously (Tsai, S., et al. Nat Biotechnol 33, 187-197 (2015), incorporated herein by reference). HEK293T cells were transfected in 20 uL Lonza SF Cell Line Nucleofector Solution on a Lonza Nucleofector 4-D with program DS-150 according to the manufacturer's instructions. 300 ng of gRNA-Cas9 plasmids (or 150 ng of each gRNACas9n plasmid for the double nickase), 150 ng of the effector plasmids, and 5 pmol of double stranded oligonucleotides (dsODN) were transfected. Cells were harvested after 72 hrs for genomic DNA using Agencourt DNAdvance reagent kit. 400 ng of purified gDNA which was then fragmented to an average of 500 bp and ligated with adaptors using NEBNext Ultra II FS DNA Library Prep kit following manufacturer's instructions. Two rounds of nested anchored PCR from the oligo tag to the ligated adaptor sequence were performed to amplify targeted DNA, and the amplified library was purified, size-selected, and sequenced using Illumina Miseq V2 PE300. Sequencing data was analyzed using the published iGUIDE pipeline, with the addition of a downsampling step which ensures an unbiased comparison across samples.
In contrast to mammals, convenient recombineering-edit tools are available for bacteria, e.g., the phage lambda Red and RecE/T. Microbial recombineering has two major steps: template DNA is chewed back by exonucleases (Exo), then the single-strand annealing protein (SSAP) supports homology directed repair by the template, optionally facilitated by nuclease inhibitor. A system for RNA-guided targeting of RecE/T recombineering activities was developed and achieved kilobase (kb) human gene-editing without DNA cutting.
Candidate microbial systems with recombineering activities were surveyed. Two lines of reasoning guided the search: 1) Orthogonality: prioritizing proteins with minimal resemblance to mammalian repair enzymes; 2) Parsimony: focusing on systems with fewest interdependent components. Three protein families were identified: lambda Red, RecE/T, and phage T7 gp6 (Exo) and gp2.5 (SSAP) recombination machinery. Based on phylogenetic reconstruction, RecE/T proteins were determined to be the most distant from eukaryotic recombination proteins and among the most compact (
The NCBI protein database was systematically searched for RecE/T homologs. To develop a portable tool, evolutionary relationships and lengths were examined (
The top 12 candidates were codon-optimized and MS2 coat protein (MCP) fusions were constructed to recruit these RecE/T homologs, hereafter termed “recombinator”, to wild-type Streptococcus pyogenes Cas9 (wtCas9) via MS2 RNA aptamers. To understand their respective molecular effects as Exo and SSAP, each was tested independently (
To validate RecE/T recombineering in human cells, homology directed repair (HDR) was measured at five genomic sites with two templates. While the RecE variants (RecE_587, RecE_CTD) demonstrated variable increases in knock-in efficiency, RecT significantly enhanced HDR in all cases, replacing ˜16 bp sequences at EMX1 and VEGFA, and knocking-in ˜1 kb cassette at HSP90AA1, DYNLT1, AAVS1 (
Three tests on REDITv1 were performed to explore: 1) activity across cell types, 2) optimal designs of HDR template, and 3) specificity. REDITv1 activity was robust across multiple genomic sites in HEK, A549, HepG2, and HeLa cells (
To alleviate unwanted edits, a version of REDIT with non-cutting Cas9 nickases (Cas9n) was assessed. A similar strategy was previously employed (Ran, F. A., et al., Cell (2013), 154:1380-1389, incorporated herein by reference) to address off-target issues but had low HDR efficiency. REDIT was tested to determine if this system could overcome the limitation of endogenous repair and promote nicking-mediated recombination. Indeed, the nickase version demonstrated higher efficiencies, with the best results from Cas9n (D10A) with single- and double-nicking. This Cas9n (D10A) variant was designated REDITv2N (
The off-target activity of REDITv2N was investigated using GUIDE-seq. Results showed minimal off-target cleavage and a reduction of OTSs by ˜90% compared to REDITv1 (
Another byproduct of HDR editing is on-target insertion-deletions (indels). They could drastically lower yields of gene-editing, especially for long sequences. Indel formation was measured in an EMX1 knock-in experiment using deep sequencing. REDITv2N increased HDR to the same efficiency as its counterpart using wtCas9 (
Concepts from GUIDE-seq, LAM-PCR, and TLA were used to develop an NGS-based assay to identify genome-wide insertion sites (GIS), or GIS-seq (
REDIT was examined for long sequence editing ability in the absence of any nicking/cutting of the target DNA. Remarkably, when using catalytically dead Cas9 (dCas9) to construct REDITv2D, an exact genomic knock-in of a kilobase cassette was observed in human cells (
Microscopy analysis revealed incomplete nuclei-targeting of REDITv1, particularly REDITv1_RecT (
Finally, REDITv3 was utilized in hESCs to engineer kilobase knock-in alleles in human stem cells. REDITv3N single- and double-nicking designs resulted in 5-fold and 20-fold increased HDR efficiencies over no-recombinator controls, respectively (
To further investigate RecT and RecE_587 variants, both RecT and RecE_587 were truncated at various lengths as shown in
The truncated versions of both RecT and RecE_587 retained significant recombineering activity when used with different Cas9s. In particular, compared with the full-length RecT (1-269aa), the new truncated versions such as RecT (93-264aa) are over 30% smaller yet they preserved essentially the full activities of RecT in stimulating recombination in eukaryotic cells. Similarly, compared with the full-length RecE (1-280aa), truncated versions such as RecE_587 (120-221aa) and RecE_587 (120-209aa) are over 60% smaller but still retained high recombination activities in human cells. These truncated versions demonstrated the potential to further engineer minimal-functional recombineering enzymes using RecE and RecT protein variants, but also provide valuable compact recombineering tools for human genome editing that is ideal for in vitro, ex vivo, and in vivo delivery given their small size.
Overall, REDIT harnessed the specificity of CRISPR genome-targeting with the efficiency of RecE/RecT recombineering. The disclosed high-efficiency, low-error system makes a powerful addition to existing CRISPR toolkits. The balanced efficiency and accuracy of REDITv3N makes it an attractive therapeutic option for knock-in of large cassette in immune and stem cells.
The reconstructed RecE and RecT phylogenetic trees with eukaryotic recombination enzymes from yeast and human (
Three exonuclease proteins were used: the exonuclease from phage Lambda, the RecE587 core domain of E. coli RecE protein, and the exonuclease (gene name gp6) from phage T7 (
Similar measurements were made testing the genome editing efficiencies of three single-strand DNA annealing proteins (SSAPs) from the same three species of microbes as the exonucleases, namely Bet protein from phage Lambda, RecT protein from E. coli, and SSAP (gene name gp2.5) from phage T7 (
From these results, the genome recombineering activities of all three major family of phage/microbial recombination systems was systematically measured and validated in eukaryotic cells (lambda phage exonuclease and beta proteins; E. coli prophase RecE and RecT proteins, T7 phage exonuclease gp6 and single-strand binding gp2.5 proteins). All six proteins from three systems achieved efficient gene editing to knock-in kilobase-long sequences into mammalian genome across two genomic loci. Overall, the exonucleases showed ˜3-fold higher recombination efficiency (up to 4% mKate genome knock-in) when compared with no-recombinator controls. The single-strand annealing proteins (SSAP) showed higher activities, with 4-fold to 8-fold higher gene-editing activities over the control groups. This demonstrated the general applicability and validity that microbial recombination proteins in the exonuclease and SSAP families could be engineered via the Cas9-based fusion protein system to achieve highly efficient genome recombination in mammalian cells.
In order to demonstrate the generalizability of REDIT protein design, alternative recruitment systems were developed and tested. For a more compact REDIT system, the REDIT recombinator proteins were fused to N22 peptide and at the same time the sgRNA included boxB, the short cognizant sequence of N22 peptide, replacing MCP within the sgRNA (
A REDIT system using SunTag recruitment, a protein-based recruitment system, was developed (
mKate knock-in experiments (
In order to demonstrate the generalizability of REDIT protein design and develop versatile REDIT system applicable to a range of CRISPR enzymes, Cpf1/Cas12a based REDIT system using the SunTag recruitment design was developed (
These results showed that the microbial recombination proteins (exonuclease and single-strand annealing proteins) could be engineered using alternative designs such as the SunTag recruitment system to perform genome editing in eukaryotic cells. These protein-based recruitment system does not require the usage of RNA aptamers or RNA-binding proteins, instead, they took advantage of fusion protein domains directly connecting to the CRISPR enzymes to recruit REDIT proteins.
In addition to the flexibility in recruitment system design, these results using Cpf1/Cas 12a-type CRISPR enzymes also demonstrated the general adaptability of REDIT proteins to various CRISPR systems for genome recombination. Cpf1/Cas12a enzymes have different catalytic residues and DNA-recognition mechanisms from the Cas9 enzymes. Hence, the REDIT recombination proteins (exonucleases and single-strand annealing proteins) could function independent from the specific choices of the CRISPR enzyme components (Cas9, Cpf1/Cas12a, and others). This proved the generalizability of the REDIT system and open up possibility to use additional CRISPR enzymes (known and unknown) as components of REDIT system to achieve accurate genome editing in eukaryotic cells.
15 different species of microbes having RecE/RecT proteins were selected for a screen of various RecE and RecT proteins across the microbial kingdom (Table 3). Each protein was codon-optimized and synthesized. As previously described for E. coli RecE/RecT based REDIT systems, each protein was fused via E-XTEN linker to the MCP protein with additional nuclear localization signal. mKate knock-in gene-editing assay was used to measure efficiencies at DYNLT1 locus (
Pantoea stewartii
Pantoea stewartii
Pantoea brenneri
Pantoea brenneri
Pantoea dispersa
Pantoea dispersa
Providencia stuartii
Providencia stuartii
Providencia sp. MGF014
Providencia sp. MGF014
Providencia alcalifaciens DSM 30120
Providencia alcalifaciens DSM 30120
Shewanella putrefaciens
Shewanella putrefaciens
Bacillus sp. MUM 116
Bacillus sp. MUM 116
Shigella sonnei
Shigella sonnei
Salmonella enterica
Salmonella enterica
Acetobacter
Acetobacter
Salmonella enterica subsp. enterica
Salmonella enterica subsp. enterica
Pseudobacteriovorax antillogorgiicola
Pseudobacteriovorax antillogorgiicola
Photobacterium sp. JCM 19050
Photobacterium sp. JCM 19050
Next, to benchmark the RecT-based REDIT design, it was compared with three categories of existing HDR-enhancing tools (
The effect of template HA lengths on the editing efficiency of REDIT was quantified when using the canonical HDR donor bearing HAs of at least 100 bp on each side (
The knock-in cells were clonally isolated and the target genomic region was amplified using primers binding completely outside of the donor DNAs for colony Sanger sequencing (
Furthermore, the efficiencies of REDIT and Cas9 were compared when making different lengths of editing. For longer edits, 2-kb knock-in cassettes were used (
The sensitivity of REDIT's ability to promote HDR in the presence or absence of two distinctive pharmacological inhibitors of RAD51, B02 and RI-1 (
Mirin, a potent chemical inhibitor of DSB repair, which has also been shown to prevent MRN complex formation, MRN-dependent ATM activation, and inhibit Mre11 exonuclease activity was also used. When treating cells with Mrining, only the editing efficiencies of Cas9 reference experiments were affected by the Miring treatment, whereas the REDIT versions were essentially the same as vehicle-treated groups across all genomic targets (
To test if cell cycle inhibition affected recombination, cells were chemically synchronized at the G1/S boundary using double Thymidine blockage (DTB). REDIT versions had reduced editing efficiencies under DTB treatment, though it maintained higher editing efficiencies under DNA repair pathway inhibition, compared with Cas9 reference experiments, when Miring RI-1, or B02 were combined with DTB treatment (
To validate REDIT in different contexts, REDIT was applied in human embryonic stem cells (hESCs) to test their ability to engineer long sequences in non-transformed human cells. Robust stimulation of HDR was observed across all three genomic sites (HSP90AA1, ACTB, OCT4/POU5F1) using REDIT and REDITdn (
In vivo use of dCas9-EcRecT (SAFE-dCas9) was tested using cleavage free dCas9 editor via hydrodynamic tail vein injection. The gene editing vectors and template DNA used are shown in
At approximately seven days after injection, the perfused mice livers were dissected. The lobes of the liver were homogenized and processed to extract liver genomic DNA from the primary hepatocytes. The extracted genomic DNA was used for three different downstream analyses: 1) PCR using knock-in-specific primers and agarose gel electrophoresis (
In addition, in vivo use was tested using adeno-associated virus (AAV) delivery into LTC mice lungs. LTC mice include three genome alleles: 1) Lkb1 (flox/flox) allele allows Lkb1-KO when expressing Cre; 2) R26 (LSL-TdTom) allele allows detection of AAV-transduced cells via TdTom red fluorescent protein; and 3) H11 (LSL-Cas9) allele allows expression of Cas9 in AAV-transduced cells. Schematics of the REDI gene editing vector and Cas9 control vectors are shown in
Approximately fourteen weeks after the AAV injection, perfused mice lungs were dissected. Fixed lung tissue was used for imaging analysis to identify tumor formation from successful gene-editing (
Escherichia coli RecE amino acid sequence
Escherichia coli RecE_587 amino acid sequence
Escherichia coli CTD_RecE amino acid sequence
Pantoea brenneri RecE amino acid sequence
Providencia sp. MGF014 RecE amino acid
Shigella sonnei RecE amino acid sequence
Pseudobacteriovorax antillogorgiicola RecE
Escherichia coli RecT amino acid sequence
Pantoea brenneri RecT amino acid sequence
Providencia sp. MGF014 RecT amino acid
Shigella sonnei RecT amino acid sequence
Pseudobacteriovorax antillogorgiicola RecT
CTGAAGCAGGCTGGAGACGTGGAGGAGAACCCTGGACCTgccacc
atggtgagcgagctgattaaggagaacatgcacatgaagctgtac
atggagggcaccgtgaacaaccaccacttcaagtgcacatccgag
ggcgaaggcaagccctacgagggcacccagaccatgagaatcaag
gcggtcgagggcggccctctccccttcgccttcgacatcctggct
accagcttcatgtacggcagcaaaaccttcatcaaccacacccag
ggcatccccgacttctttaagcagtccttccccgagggcttcaca
tgggagagagtcaccacatacgaagatgggggcgtgctgaccgct
acccaggacaccagcctccaggacggctgcctcatctacaacgtc
aagatcagaggggtgaacttcccatccaacggccctgtgatgcag
aagaaaacactcggctgggaggcctccaccgagacactgtacccc
gctgacggcggcctggaaggcagagccgacatggccctgaagctc
gtggggggggccacctgatctgcaaccttaagaccacatacagat
ccaagaaacccgctaagaacctcaagatgcccggcgtctactatg
tggacaggagactggaaagaatcaaggaggccgacaaagagacat
acgtcgagcagcacgaggtggctgtggccagatactgcgacctcc
ctagcaaactggggcacaaacttaattccTAACCaGCtGTCCtGC
GAAGCAGGCTGGAGACGTGGAGGAGAACCCTGGACCTgtgagcga
gctgattaaggagaacatgcacatgaagctgtacatggagggcac
cgtgaacaaccaccacttcaagtgcacatccgagggcgaaggcaa
gccctacgagggcacccagaccatgagaatcaaggcggtcgaggg
ggccctctccccttcgccttcgacatcctggctaccagcttcatg
tacggcagcaaaaccttcatcaaccacacccagggcatccccgac
ttctttaagcagtccttccccgagggcttcacatgggagagagtc
accacatacgaagatgggggcgtgctgaccgctacccaggacacc
agcctccaggacggctgcctcatctacaacgtcaagatcagaggg
gtgaacttcccatccaacggccctgtgatgcagaagaaaacactc
ggctgggaggcctccaccgagacactgtaccccgctgacggcggc
ctggaaggcagagccgacatggccctgaagctcgtgggcgggggc
cacctgatctgcaaccttaagaccacatacagatccaagaaaccc
gctaagaacctcaagatgcccggcgtctactatgtggacaggaga
ctggaaagaatcaaggaggccgacaaagagacatacgtcgagcag
cacgaggtggctgtggccagatactgcgacctccctagcaaactg
gggcacaaacttaattccTAaATCTgTGGCTGAGGGATGACTTAC
agatctggcagcggaGGAAGCGGAGCTACTAACTTCAGCCTGCTG
AAGCAGGCTGGAGACGTGGAGGAGAACCCTGGACCTgtgagcgag
ctgattaaggagaacatgcacatgaagctgtacatggagggcacc
gtgaacaaccaccacttcaagtgcacatccgagggcgaaggcaag
ccctacgagggcacccagaccatgagaatcaaggcggtcgagggc
ggccctctccccttcgccttcgacatcctggctaccagcttcatg
tacggcagcaaaaccttcatcaaccacacccagggcatccccgac
ttctttaagcagtccttccccgagggcttcacatgggagagagtc
accacatacgaagatgggggcgtgctgaccgctacccaggacacc
agcctccaggacggctgcctcatctacaacgtcaagatcagaggg
gtgaacttcccatccaacggccctgtgatgcagaagaaaacactc
ggctgggaggcctccaccgagacactgtaccccgctgacggcggc
ctggaaggcagagccgacatggccctgaagctcgtgggcgggggc
cacctgatctgcaaccttaagaccacatacagatccaagaaaccc
gctaagaacctcaagatgcccggcgtctactatgtggacaggaga
ctggaaagaatcaaggaggccgacaaagagacatacgtcgagcag
cacgaggtggctgtggccagatactgcgacctccctagcaaactg
gggcacaaacttaattccTAaactaggacaggattggtgacaga
CTAACTTCAGCCTGCTGAAGCAGGCTGGAGACGTGGAGGAGAACC
CTGGACCTgccaccatggtgagcgagctgattaaggagaacatgc
acatgaagctgtacatggagggcaccgtgaacaaccaccacttca
agtgcacatccgagggcgaaggcaagccctacgagggcacccaga
ccatgagaatcaaggcggtcgagggcggccctctccccttcgcct
tcgacatcctggctaccagcttcatgtacggcagcaaaaccttca
tcaaccacacccagggcatccccgacttctttaagcagtccttcc
ccgagggcttcacatgggagagagtcaccacatacgaagatgggg
gcgtgctgaccgctacccaggacaccagcctccaggacggctgcc
tcatctacaacgtcaagatcagaggggtgaacttcccatccaac
ggccctgtgatgcagaagaaaacactcggctgggaggcctccac
cgagacactgtaccccgctgacggcggcctggaaggcagagccg
acatggccctgaagctcgtggggggggccacctgatctgcaacc
ttaagaccacatacagatccaagaaacccgctaagaacctcaag
atgcccggcgtctactatgtggacaggagactggaaagaatcaag
gaggccgacaaagagacatacgtcgagcagcacgaggtggctgtg
gccagatactgcgacctccctagcaaactggggcacaaacttaat
tccTAaTGACTAGGAATGGGGGACAGGGGGAGGGGAGGAGCTAGG
Pantoea stewartii RecT DNA
Pantoea stewartii RecE DNA
Pantoea brenneri RecT DNA
Pantoea brenneri RecE DNA
Pantoea dispersa RecT DNA
Pantoea dispersa RecE DNA
Providencia stuartii RecT DNA
Providencia stuartii RecE DNA
Providencia sp. MGF014 RecT DNA
Providencia sp. MGF014 RecE DNA
Shewanella putrefaciens RecT DNA
Shewanella putrefaciens RecE DNA
Bacillus sp. MUM 116 RecT DNA
Bacillus sp. MUM 116 RecE DNA
Shigella sonnei RecT DNA
Salmonella enterica RecT DNA
Salmonella enterica RecE DNA
Acetobacter RecT DNA
Acetobacter RecE DNA
Salmonella enterica subsp. enterica serovar
Javiana str. 10721 RecT DNA
Salmonella enterica subsp. enterica serovar
Javiana str. 10721 RecE DNA
Pseudobacteriovorax antillogorgiicola RecT DNA
Pseudobacteriovorax antillogorgiicola RecE DNA
Photobacterium sp. JCM 19050 RecT DNA
Photobacterium sp. JCM 19050 RecE DNA
Providencia alcalifaciens DSM 30120 RecE DNA
Pantoea stewartii RecT Protein
Pantoea stewartii RecE Protein
Pantoea brenneri RecT Protein
Pantoea brenneri RecE Protein
Pantoea dispersa RecT Protein
Pantoea dispersa RecE Protein
Providencia stuartii RecT Protein
Providencia stuartii RecE Protein
Providencia sp. MGF014 RecT Protein
Providencia sp. MGF014 RecE Protein
Shewanella putrefaciens RecT Protein
Shewanella putrefaciens RecE Protein
Bacillus sp. MUM 116 RecT Protein
Bacillus sp. MUM 116 RecE Protein
Shigella sonnei RecT Protein
Shigella sonnei RecE Protein
Salmonella enterica RecT Protein
Salmonella enterica RecE Protein
Acetobacter RecT Protein
Acetobacter RecE Protein
Salmonella enterica subsp. enterica serovar
Javiana str. 10721 RecT Protein
Salmonella enterica subsp. enterica serovar
Javiana str. 10721 RecE Protein
Pseudobacteriovorax antillogorgiicola RecT
Pseudobacteriovorax antillogorgiicola RecE
Photobacterium sp. JCM 19050 RecT Protein
Photobacterium sp. JCM 19050 RecE Protein
Providencia alcalifaciens DSM 30120 RecT Protein
Providencia alcalifaciens DSM 30120 RecE Protein
The structure of E. coli RecT (EcRecT) alone (
322 new SSAP proteins were identified from sequence data, synthesized, and screened for activity with Cas9 and dCas9. Gene editing activities are shown below in Table 5, followed by amino acid sequences of the proteins.
Exemplified by CRISPR-Cas9 systems, gene editing has become a powerful tool for probing the mechanisms of human health and diseases. Cas9 editing can cause DNA damage at on- and off-target sites and rely on the endogenous DNA repair mechanisms that are error-prone. These features often lead to unwanted mutations and safety concerns, which can be exacerbated when we alter long sequences. Building on prior studies that mammalian genome DNA becomes transiently accessible upon dCas9 DNA-unwinding and R-loop formation, we hypothesized that microbial single-strand annealing proteins (SSAPS) could stimulate DNA strand exchange for gene-editing when coupled to dCas9-guideRNA complex. Thus, we developed a cleavage-free gene-editing tool using the catalytically-dead dCas9 for knock-in long sequences. Our data demonstrated that this dCas9-based editor had very low editing errors at target loci, minimal detectable off-target effect, and higher overall accuracy than Cas9 editors. Meanwhile, dCas9-SSAP editor had comparable efficiencies as Cas9 editors, with robust performances across human cell lines and stem cells. This dCas9-SSAP editor was effective for inserting sequences of variable lengths, up to kilobase scale. In experiments where we chemically inhibited DNA repair enzymes, dCas9-SSAP editing demonstrated notable independence from endogenous mammalian repair pathways. For convenient viral delivery of the dCas9-SSAP editor for challenging cell types, we performed truncation and aptamer engineering to minimize its size to fit into a single AAV vector for future applications. Overall, this tool opens opportunities towards safer genome engineering in mammalian cells.
Since the initial demonstration of CRISPR-Cas9 gene-editing, significant efforts have improved and expanded gene-editing technologies for studying genome function, modeling biological processes, and gene therapies. New generations of gene-editing tools, such as base editing and prime editing, substantially improved the efficiency and fidelity of gene editing and are powerful for altering relatively short sequences. Most gene-editing tools work by cleaving genome DNA to induce single-strand nicks (SSNs) or double-stranded breaks (DSBs) that facilitate targeted editing. These DNA modifications are often repaired by error-prone endogenous pathways such as non-homologous end-joining (NHEJ). This process often leads to unwanted mutations and off-target effects, which could result in toxicity and raise safety concerns. Such editing errors and off-target effects would become increasingly and sometimes prohibitively severe when engineering long genomic sequences (>=100 bp). These unwanted effects limit the application of gene-editing to engineering large-scale genomic knock-in or in vivo gene-editing.
Available CRISPR-based methods for long-sequence editing, such as homology-directed repair (HDR) or microhomology-mediated end-joining (MMEJ), rely on Cas9 cutting and often trigger random indel formation within the genome. Many recent efforts have enhanced precision long-sequence editing, such as chemical enhancers, fusion of enhancement domains, and modified donor DNAs. Nicking-based HDR has been shown to reduce editing errors but could lead to lower efficiency. Thus, there remains a need for efficient, safer CRISPR editing tools for long-sequence alterations.
Bacteriophages evolved enzymes that take advantage of accessible replicating genome DNA to perform precise recombination. We reasoned that the key enzyme for microbial recombination, the single-strand annealing protein (SSAP), could be useful for gene editing in mammalian cells, would not rely on DNA cleavage, and not trigger the error-prone pathways involved in Cas9 editing. Motivated by this hypothesis and our prior work showing its ability to stimulate genomic recombination, we developed a gene-editing tool using the deactivated Cas9 (dCas9, or catalytically dead Cas9) and microbial SSAPs. This dCas9 editor uses the SSAP for knock-in editing when supplied with a donor DNA, without the need for genomic DNA cleavage. We termed it dCas9-SSAP editor (dCas9-SSAP).
To optimize dCas9-SSAP, we performed a metagenomic search of SSAPs focusing on RecT homologs, and identified EcRecT as the most efficient one for human genome knock-in. For validation, we conducted a series of genome engineering and chemical perturbation experiments. Our data showed that dCas9-SSAP had comparable knock-in efficiencies to wild-type Cas9 references, with efficiencies significantly higher than Cas9 nickase editors. dCas9-SSAP achieved up to 12% knock-in efficiency without selection, across multiple genomic targets and cell lines, for kilobase-scale sequence editing. More importantly, our data showed that this new tool generates nearly zero on- and off-target errors. In an assay for 1 kb-sequence knock-in, dCas9-SSAP had less than 0.3% editing errors across all cells, while Cas9 editors had similar yields but an additional 10%-16% incorrectly-edited cells. Across loci tested, dCas9-SSAP had 90%-99.6% editing accuracies, while Cas9 editors' accuracy ranges from 10% to 38% (
Further, we probed the mechanism of dCas9-SSAP editing via inhibiting several DNA repair enzymes and performing cell cycle synchronization. In these experiments, dCas9-SSAP demonstrated less dependence on the endogenous DNA repair pathways, as opposed to Cas9 editing. Results of our cell cycle assays supported our hypothetical mechanism of dCas9 editor; they are consistent with the known biophysical, biochemical properties of dCas9.
Finally, to help with delivery of dCas9-SSAP for future applications, we optimize its molecular design using structural-guided truncation, and obtain a minimized dSaCas9-mSSAP, achieving over 50% reduction in size and retaining similar levels of efficiency. This minimal dCas9 editor would allow convenient delivery using viral vectors such as adeno-associated virus (AAV), potentially useful for hard-to-transfect cell types or in vivo applications. Overall, the dCas9-SSAP editor is capable of efficient, accurate knock-in genome engineering. With space for further improvement, it has potential research and therapeutic values as a cleavage-free gene-editing tool for mammalian cells.
Using Phage SSAPs for dCas9 Knock-In Gene Editing
Most CRISPR-based editors capable of long-sequence knock-in require SSNs or DSBs, which can trigger the competing, error-prone NHEJ pathways, resulting in variable efficiency and accuracy. In contrast, bacteriophages evolved DNA-modifying enzymes to integrate themselves into the genomes of host bacteria via sequence homology, e.g., Lambda Red. Such precise phage integration relies on a major homology-directed step: recombination between genomic and donor DNA is stimulated by the SSAPs, e.g., Lambda Bet or its functional homolog, RecT. From prior studies, we reasoned that phage SSAPs may not rely on DNA cleavage thanks to its unusual ATP-independent activity, in contrast to the ATP-dependent RAD51 protein in human cells. Phage SSAPs' high affinity for single- and double-stranded DNAs may allow attachment to donor templates when multiple SSAPs are recruited to genomic targets via RNA-guided dCas9. It could then promote genomic-donor DNA exchange without cleavage, as target DNA strands become transiently accessible during dCas9-mediated DNA-unwinding and R-loop formation.
Based on this hypothesis, we designed a system to recruit SSAPs to catalytically-dead Cas9 (dCas9) (
Development of dCas9-SSAP as a Mammalian Gene-Editing Tool
We conducted metagenomic mining to identify the best SSAP for mammalian gene-editing. We focused on RecT homologs and sought to maximize evolutionary diversity via a phylogenetic analysis. We systematically searched the NCBI non-redundant sequence database for RecT homologs, and identified 2,071 initial candidates. Then we built phylogenetic trees, filtered out proteins with high sequence homology, and subsampled the evolutionary branches, obtaining 16 highly diverse SSAP candidates (
We examined the SSAP candidates by knock-in screening and evaluating their editing efficiencies across three genomic loci: HSP90AA1, DYNLT1, and ACTB (
Characterizing the Accuracy of dCas9-SSAP Gene-Editing
The motivation for developing dCas9-SSAP is to perform potentially safer, cleavage-free dCas9 editing with the help of SSAP. Thus, we experimentally evaluated the accuracy of dCas9-SSAP for knock-in editing where the target sequence is ˜1 kb in length. We measured the on-target error, off-target insertion, cell fitness effect, and editing yields of dCas9-SSAP, in comparison with Cas9 references.
On-target error analysis. There are two types of on-target errors: (1) on-target indel formation, whose occurrence means that knock-in is unsuccessful; (2) knock-in errors, which means that knock-in happens but is imperfect, and that junction indels occur.
To evaluate type (1), we used deep sequencing to measure the on-target indel formation of dCas9 editor. We used the nested PCR design with an initial primer binding outside the donor DNA to avoid template contamination (
To evaluate type (2), we benchmarked the knock-in errors of dCas9-SSAP and measured junction indels. We clonally isolated edited cells, and then amplified the knock-in genomic loci using a similar 2-step nested PCR design to avoid contamination (
Off-target error analysis. We evaluated the off-target knock-in error of dCas9-SSAP editing via a genome-wide transgene insertion assay (
Cell fitness effect and editing yield analysis. We also compared the fitness of cells that went through Cas9/dCas9-based editing. We experimented with two target sites and our data suggests that dCas9 editing in general leads to higher cell fitness than Cas9 editing (
For the full picture, we summarized editing yields for dCas9-SSAP with comparison to Cas9 references. We tabulated the percentage of accurate knock-ins, percentage of knock-ins with errors, and the percentage of on-target indels without knock-ins, where the sum of latter two is the total on-target errors (
Benchmarking the Efficiency of dCas9-SSAP Editing with Cas9 Editing
Having established that dCas9-SSAP has higher accuracy for knock-in editing, we further validated its efficiencies and usages. We benchmarked its editing efficiency across different cell lines. For benchmarks, we experimented with both wild-type and nicking-based Cas9 (nCas9) editors, including three HDR-enhancing tools. We examined their 1-kb knock-in activities across the three genome targets in human HEK293T cells. Results from this comparison demonstrated that dCas9-SSAP achieved higher efficiencies than the Cas9, nCas9, and nCas9-hRAD51 nickase editors, with comparable efficiencies as Cas9-HE and Cas9-GEM, two published HDR-enhancing editors (
Next, we evaluated the editing efficiencies of dCas9-SSAP with different donor DNA designs (
Lastly, we tested if dCas9-SSAP editor has robust activities across genomic targets, and if it is applicable in more challenging cases beyond one model cell line. We selected four additional endogenous loci from house-keeping genes (BCAP31, HISTIH2BK, CLTA, RAB11A) in addition to the three previously tested ones (DYNLT1, HSP90AA1, ACTB) (
Chemical Perturbations Suggest dCas9-SSAP Gene-Editing has Less Dependence on Endogenous DNA Repair Pathways
Recall our model that dCas9-SSAP performs gene editing without DNA cleavage or dependence on an endogenous repair pathway. To better understand the nature of dCas9-SSAP editing, we used three orthogonal chemical perturbations to probe its mechanism (
First, we investigate if the dCas9-SSAP editing depends on the DSB repair pathway as Cas9 editing docs (
Second, we investigated the dependence of dCas9-SSAP on the HDR pathways. We used two small-molecule inhibitors of the HDR enzyme RAD51, RI-1 and B02, to block this rate-limiting step. Our data showed that blocking RAD51 activity via these two inhibitors significantly reduced Cas9 editing efficiencies at all genomic targets, but it did not have a significant effect on dCas9-SSAP editing (
Third, we investigated how cell cycling affects the dCas9-SSAP editor. Cell cycling has been shown to facilitate the accessibility of mammalian genomes. More specifically, the genome replication (during S phase) may provide a favorable environment for the dCas9 to unwind DNAs and allow SSAP-mediated recombination (
Taken together, our data supported the hypothetical mechanism of dCas9-SSAP editing: RNA-guided dCas9 binds to genomic targets and makes them accessible to the SSAP, so SSAP would promote homology-directed recombination without generating any DNA break (
Minimization of dCas9-SSAP Gene-Editing Tool for Convenient Delivery
Finally, to optimize the dCas9-SSAP editor for potential future applications, we sought to develop a minimal version compatible with the size limitations of viral vectors such as AAV. We designed 14 different truncated EcRecT variants based on its secondary structure prediction (
We next integrated this short RecT variant with the more compact SaCas9 system and the smaller N22-BoxB aptamer design to build a minimal-functional dSaCas9-mSSAP editor (
Overall, the dCas9-SSAP editor harmonizes the RNA-guided programmability of CRISPR genome-targeting with the SSAP activity of phage enzyme RecT. It enables long-sequence editing with minimal DNA damage and provides research and therapeutic possibilities for addressing some of the currently intractable diseases involving large disease-causing variants, delivering therapeutic genes in vivo where selection methods are limited, or minimizing undesirable modifications during gene-editing. Compared with other long-sequence editing methods that depend on endogenous repair pathways following DNA cleavage, dCas9-SSAP and its mini-version facilitate homology-mediated gene editing via non-cutting dCas9s. This efficient, low-error technology offers a new and complementary approach to existing CRISPR editing tools.
Human codon optimized DNA fragments were ordered from Genescript, Genewiz and IDT DNA. The fragments encoding the recombination enzymes were Gibson assembled into backbones (addgene plasmid #61423) using Q5® High-Fidelity 2× Master Mix (New England BioLabs). The amino acids sequence for these SSAP could be found in the Table 8. All sgRNAs were inserted into backbones (dCas9-SSAP and dSaCas9-SSAP plasmids) using Golden Gate cloning. dCas9-SSAP plasmids bearing BbsI (dSpCas9) and BsaI (dSaCas9) sites as gRNA backbones were sequence-verified (Eton and Genewiz). The sgRNA sequence used in this research could be found in the Table 6. All dCas9-SSAP plasmids will be deposited to Addgene for open access.
Human Embryonic Kidney (HEK) 293T, Hela, HepG2 and U2OS cells were maintained in Dulbecco's Modified Eagle's Medium (DMEM, Life Technologies), with 10% fetal bovine serum (FBS, BenchMark), 100 U/mL penicillin, and 100 μg/mL streptomycin (Life Technologies) at 37° C. with 5% CO2. HEK 293T, Hela, HepG2 and U2OS cells were obtained from American Type Culture Collection (ATCC). The identity of the cell line is authenticated regularly by short tandem repeat (STR) assay and routinely tested for the presence of Mycoplasma using qPCR assay.
hES-H9 cells were maintained in mTeSR1 medium (StemCell Technologies) at 37° C. with 5% CO2. Culture plates were pre-coated with Matrigel (Corning) 12 hours prior to use. 10 μM Rho Kinase inhibitor Y27632 (Sigma) was added for the first 24 hours after each passaging. Culture media was changed every 24 hours.
HEK293T, Hela, HepG2 and U2OS cells were seeded into 96-well plates (Corning) 12-24 hours prior to transfection at a density of 30,000 cells/well, and 250 ng of total DNA was transfected per well. Cells were transfected with Lipofectamine 3000 (Life Technologies) following the manufacturer's instructions when the cell are ˜70% confluence. In brief, we used 250 ng total DNA, 0.4 ul Lip3000 reagent, mixed with 10 ul of Opti-MEM per well. For the 250 ng DNA, we used 160 ng of dCas9-SSAP guide RNA plasmids (for double sgRNAd design, use equal amount of the two guide RNA plasmids, e.g., 80 ng each), 60 ng of pMCP-RecT or GFP control plasmid (addgene #64539) and 30 ng of PCR template DNA (the PCR primer could be found in Table 7, the template sequence could be found in Supplementary Sequences). Three days later, the cells were analyzed using FACS.
For hES-H9 transfection, P3 Primary Cell 4D-Nucleofector™ X Kit S (Lonza) was used following the manufacturer's protocol. In brief, the hES-H9 cells were resuspended using Accutase (Innovative Cell Technology) and washed with PBS twice before the electroporation. For each reaction, 300,000 cells were nucleofected with 4 μg total DNA mixed in 20 ul electroporation buffer using the DC100 Nucleofector Program. For the 4 ug DNA, we used 2.6 μg of dCas9-SSAP guide RNA plasmids (for double sgRNAd design, use equal amount of the two guide RNA plasmids, e.g., 1.3 ug each), 1 μg of pMCP-RecT or GFP control plasmid and 0.4 ug of PCR template DNA (the PCR primer could be found in Table 7, the template sequence could be found in Supplementary Sequences). After electroporation, the cells were seeded into 12-well plates with 1 mL of mTeSR1 media added with 10 uM Y27632. Culture media was changed every 24 hours. Four days later, the cells were analyzed using FACS.
mKate knock-in efficiency was analyzed on a CytoFLEX flow cytometer (Beckman Coulter; Stanford Stem Cell FACS Core). 72 hours after transfection or 96 hours after electroporation, cells were washed twice with PBS and dissociated with TrypLE Express Enzyme (Thermo Fisher Scientific). Cell suspension was then transferred to a 96-well U-bottom plate (Thermo Fisher Scientific) and centrifuged at 300 g for 5 minutes. After removing the supernatant, pelleted cells were resuspended with 50 μl 4% FBS in PBS, and cells were analyzed within 30 minutes after preparation.
HEK293T cells transfected with plasmid DNA and HDR templates were harvested 72 hours after transfection. The genomic DNA of these cells were extracted using the QuickExtract DNA Extraction Solution (Biosearch Technologies) following the manufacturer's protocol. The target genomic region was amplified using specific primers outside of the homology arms of the HDR template. The primers used for Sanger sequencing or NGS analysis could be found in the Table 7. PCR products were purified with Monarch PCR & DNA Cleanup Kit (New England BioLabs). 100 ng of purified product was sent for Sanger sequencing with target-specific primers (EtonBio or Genewiz).
Treatment with HR and Cell Cycle Inhibitor
All inhibitors were ordered from Sigma-Aldrich. For different inhibitor assays, the cells were pretreated with Mirin (Sigma, M9948-5 MG, 25 uM), B02 (Sigma, SML0364, 10 uM),) or RI-1 (Sigma, 553514-10 MG-M, 1 uM) for 16 hours. For cell cycle test, the cells were pretreated with Thymidine (Sigma, T9250-1G, 2 mM) for 18 hours, then remove thymidine, culture the cells using normal D10 without thymidine for 9 hours, add the second round of thymidine to a final concentration of 2 mM for another 18 hours. After the inhibitor and thymidine, the cells were transfected with dCas9-SSAP using Lipofectamine 3000 following the manufacturer's instruction. 3 days later, the cells were analyzed on a CytoFLEX flow cytometer and genomic DNA were also harvested for sequencing validation as above.
72 hours after transfection, genomic DNA was extracted using QuickExtract DNA Extraction Solution (Biosearch Technologies). 200 ng total DNA was used for NGS library preparation. Genes of interest were amplified using specific primers (Table 7) for the first round PCR reaction. Illumina adapters and index barcodes were added to the fragments with a second round PCR using the primers listed in Table 7. Round 2 PCR products were purified by gel electrophoresis on a 2% E-gel using the Monarch DNA Gel Extraction Kit (New England BioLab). The purified product was quantified with Qubit dsDNA HS Assay Kit (Thermo Fisher) and sequenced on an Illumina MiSeq system using paired-end PE300 kits. All sequencing data will be deposited to NCBI SRA archive.
Total of 250 ng genomic DNA was used for the TOPO cloning experiments. The knock-in events were amplified using specific TA colony primers targeted to DYNLT1 or HSP90AA1 locus (Table 7) using Phusion Flash High-Fidelity PCR Master Mix (ThermoScientific, F-548L). Purify the targeted PCR products using Gel extraction kit (New England BioLabs, T1020L) following the manufacturer's instructions. Add a-tail to the PCR products using Taq polymerase (New England BioLabs, M0273S) through incubate at 72 C for 30 minutes. Set up the TOPO cloning reaction and transformation following the manufacturer's instructions (Thermo Scientific, K457501). Send the colony plates for RCA/colony sequencing using M13F (5′-GTAAAACGACGGCCAG-3′) [SEQ ID NO: 560] and M13R (5′-CAGGAAACAGCTATGAC-3′) [SEQ ID NO: 561] primers. The sequence results were analyzed using SnapGene software.
Processed (demultiplexed, trimmed, and merged) sequencing reads were analyzed to determine editing outcomes using CRISPPResso2 by aligning sequenced amplicons to reference and expected HDR amplicons. The quantification window was increased to 10 bp surrounding the expected cut site to better capture diverse editing outcomes, but substitutions were ignored to avoid inclusion of sequencing errors. Only reads containing no mismatches to the expected amplicon were considered for HDR quantification; reads containing indels that partially matched the expected amplicons were included in the overall reported indel frequency. The computation work was supported by the SCG cluster hosted by the Genetics Bioinformatics Service Center (GBSC) at the Department of Genetics of Stanford. All customized scripts for data analysis will be deposited to Github under Cong Lab and made available for download.
We are using a process that was previously developed (GIS-seq) and adapted for the genome-wide, unbiased off-target analysis of mKate knock-in, following the similar protocol in our previous study. Briefly, we harvest the HEK293T cells 3 days after transfection. The genomic DNA was size-selected to avoid the template contamination in the following step via the DNAdvance genomic DNA kit (A48705, Beckman Coulter). 400 ng of purified genomic DNA was fragmented to an average of 500 bp using NEB Fragmentase, ligated with adaptors, and size-selected using NEBNext Ultra II FS DNA Library Prep kit following manufacture's instruction. Following two rounds of nested anchored PCR to amplify targeted DNA (from the end of the knock-in sequence to the ligated adaptor sequence), and do a size-selected purification following the NEBNext Ultra II FS DNA library Prep kit protocol. The libraries were sequenced using Illumina Miseq V3 PE600 kits. Sequencing data was analyzed to determine off-target insertion events with all analysis code deposited to Github (github.com/cong-lab).
Unless otherwise stated, all statistical analysis and comparison were performed using t-test, with 1% false-discovery-rate (FDR) using a two-stage step-up method of Benjamini, Krieger and Yekutieli. All experiments were performed in triplicates unless otherwise noted to ensure sufficient statistical power in the analysis.
For initial SSAP screening, we identified the three major family of phage recombination enzymes from Bacteriophage lambda, E. coli Rac prophage, and bacteriophage T7, and extracted the primary enzyme sequences as listed in supplementary sequences.
For RecT-like SSAP mining. RefSeq non-redundant protein database was downloaded from NCBI on Oct. 29, 2019. We systematically searched the NCBI non-redundant sequence database for RecT homologs. Our search follows two guidelines: 1) Closely-related candidates are less likely to have differential activities; 2) Microbial enzymes that function well when heterologous expressed in eukaryotic cells are difficult to predict, thus sampling diverse evolutionary branches of RecT homologs would be ideal. After identifying a large set of 2,071 candidates, we built phylogenetic trees and selected representative candidates after filtering out proteins with high sequence homology. Then, we used a threshold of at least 10% sequence divergence and sizes up to 300-aa (to avoid extremely large proteins that are hard to synthesize and less portable) to refine the hits, and randomly sampled the evolutionary branches to obtain a final list of 16 SSAPs (
The multiple sequence alignment between RecT homologs used online tool (T-Coffee: tcoffcc.crg.cat/apps/tcoffee/do: regular).
Donor Design Test Comparing Cas9 HDR, Cas9 MMEJ, and dCas9-SSAP
As shown in
Firstly, for the NHEJ donors without any HAs (highlighted box in
Secondly, dCas9-SSAP benefited from successively longer HA within the donor, regardless of whether the HAs are for HDR-type or MMEJ-type, in contrast to Cas9 editor that showed a boost of knock-in efficiencies when using the MMEJ donors (
Further, while the focus of this work is long-sequence engineering, we also tested dCas9-SSAP for shorter sequence editing (
In summary, dCas9-SSAP editing becomes most efficient when using HDR donors, and longer homology arms in general make editing efficiency higher.
Step-by-Step Gene-Editing Protocol Using dCas9-SSAP Plasmids
This step is the same as standard Cas9 experiments. Briefly, based on the Cas9 enzyme used, target sequence (usually 20-bp) near the knock-in or editing sites can be selected next to the protospacer adjacent motif (PAM). For SpCas9 use “NGG” and for SaCas9 use “NNGRRT”. We usually append extra “G” base to the beginning of the guide sequence to facilitate U6/Pol-III transcription initiation if the first base of the guide sequence is not “G”. Two DNA oligos could be ordered based on selected guides, with golden gate cloning overhangs, as shown below.
N denotes the guide sequences. Standard desalting oligos are sufficient for this cloning. The two oligos above will be annealed to form the insert fragments in the next step.
B. Annealing of Two DNA Oligos for Each Guide RNA Target. Perform Phosphorylation and Annealing of Each Pair of Oligos Via Reaction Setup Below.
Anneal in a thermocycler using the following parameters:
C1. Golden Gate Cloning of Annealed Oligos into sgRNA/dspCas9 (dCas9-SSAP) Plasmid
For wild-type Cas9 test, one guide RNA is needed and the backbone vectors for the cloning will bear BbsI cloning sites matching the annealed oligos from Step B. The wild-type Cas9 plasmids for this step will be: pCas9-MS2-BB_BbsI (see list of plasmids at end of protocol)
This protocol uses a minimal amount of enzyme and could be scaled up as needed. After setting up the golden gate reaction (on ice), immediately move the reaction into Thermocycler and perform the golden gate reaction using the following parameters:
After the reaction, perform bacterial transformation as per standard protocol of the competent cells used in the lab.
C2. Golden Gate Cloning of Annealed Oligos into sgRNA/dspCas9 (dCas9-SSAP) Plasmid
For dCas9-SSAP using dSpCas9, one or two guide RNAs can be used with double guide RNAs providing slightly better efficiency of editing. The backbone vectors for the cloning will bear BbsI cloning sites matching the annealed oligos from Step B. The dCas9-SSAP plasmids for this step will be: pdCas9-SSAP-MS2-BB_BbsI (see list of plasmids at end of protocol)
Golden Gate reaction setup and transformation steps are similar as above.
Please refer to Supplementary Sequences for template used in the study and examples of template designs are illustrated as in FIG. 38. We recommend using a dsDNA template with at least 200 bp of homology arms on each end of the insertion/replacement sequences (the edited portion of the template). We suggest cloning the template into simple plasmids such as pUC19, then, restriction digestion of plasmids or standard PCR (using primers such as listed in the Table 7) could be employed for generating large amounts of dsDNA templates.
E. Perform Gene-Editing Via Delivery of dCas9-SSAP Plasmids and Template DNA
With previous steps, the three components of dCas9-SSAP editing method are ready for experiments: the guide RNA/Cas9 plasmid (cloned in step A-C), the template DNA (from step D), and the SSAP plasmid (pMCP-RecT, can be obtained from Addgene). For delivery into cells in vitro, routine transfection or electroporation could be performed following the recommended conditions by the reagent or equipment manufacturer and selected based on the cell types. For HEK293T cells as an example, a typical transfection condition is described below:
Sequences for gRNAs are provided in Table 6. Annotations of the guide RNA names are: guides starting with sp indicate SpCas9 guide RNA targets, and guides starting with dsp indicate dSpCas9 guide RNA targets.
Table 7 provides Primer Sequences.
Sequences for primers used for DNA template generation, targeted sequencing, and NGS assays are listed below. All NGS adapter sequences are shown underscored color.
Table 8 provides sequence for certain SSAP tested in this Example.
Annotations of the replaced or inserter editing sequences are detailed below with each of the templates. Unless otherwise noted, when different homology arms are used in the Example, we used primers listed in Table 7 to obtain templates with different homology arm lengths.
Arrayed SSAP library screening on endogenous genome targets (ACTB. HSP90AA1) using mKate knock-in assay.
SSAP-encoding plasmids were purified and quantified.
Each SSAP encoding plasmid was tested in duplicate, including a negative control (same plasmid encoding Flag_HA which is not expected to promote gene editing). Transfections were in 96-well plates and transfection efficiency was estimated to be 50%.
Three days after transfection, mKate positive cells and cell viability were quantified across all replicates, along with positive (original RecT SSAP) and negative (Flag-HA control protein) controls. Higher frequency of mKate+ cells indicates a candidate SSAP is more active (i.e., has higher ability to mediate precision knock-in editing of the kilobase-scale transgene). At the same time, the cell viability was measured by live cell counts via flow cytometry, to help quantify the fitness effect of SSAP on mammalian cells.
Alignments and phylogenic trees depicting related proteins and sequence alignments for several of the top targets are provided in
Top scoring SSAP proteins are shown in Table 9. The table shows editing efficiency as the normalized average of two targets (HSP90 and ACTB), absolute editing efficiency, and cell viability. SSAP proteins are identified by Uniparc deposit number and SEQ ID NO. Alignment numbers correspond to SSAPs in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Having thus described in detail preferred embodiments of the present invention, it is to be understood that the invention defined by the above paragraphs is not to be limited to particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope of the present invention.
This application is a national phase application under 35 U.S.C. § 371 of PCT International Application No.: PCT/US2022/075850, filed on Sep. 1, 2022, which claims the benefit of priority from U.S. Patent Application Ser. No. 63/239,732 filed Sep. 1, 2021, the contents of which are incorporated herein by reference in their entireties. Reference is made to U.S. Patent Application Ser. No. 62/984,618, filed Mar. 3, 2020, U.S. Patent Application Ser. No. 63/146,447, filed Feb. 5, 2021, and PCT/US2021/020513, filed Mar. 2, 2021.
Filing Document | Filing Date | Country | Kind |
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PCT/US22/75850 | 9/1/2022 | WO |
Number | Date | Country | |
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63239732 | Sep 2021 | US |