Patent Application
20220145305
The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Feb. 10, 2020, is named ALA-002WO_SL.txt and is 135,245 bytes in size.
Genetic mutations are responsible for a plethora of defects, disorders, and disease conditions. Over 16,000 mutations, ranging from single base pair changes to large-scale chromosomal defects, are known to contribute to at least 6,000 different conditions. Duchenne muscular dystrophy, beta-thalassemia, hemophilia, sickle-cell disease, amyotrophic lateral sclerosis, familial hypercholesterolemia, cystic fibrosis, Usher syndrome, type II are a few of the more well known disease conditions caused by genetic mutations.
Cystic fibrosis (CF) is a lethal autosomal recessive disorder inherited in approximately 1 in 2,500 births. CF is the result of mutations in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene, a gene that is expressed in the apical membrane of all epithelial cells, thus affecting multiple organs. The primary cause of mortality in CF patients is bacterial infection of the airways, provoking chronic lung disease and, ultimately, respiratory failure.
Current CF treatments are not curative, being limited only to the reduction of clinical symptoms such as attacking chronic bacterial infections or alleviating airway blockages. The deleterious effects of a limited number of CFTR genetic mutations can be lessened by the use of recently developed small molecules such as CFTR correctors and potentiators. However, the success of potentiator treatment is strongly dependent upon residual CFTR protein, which is often very low and highly variable among patients. Moreover, the easing of symptoms through the use of current treatments brings only temporary alleviation to those suffering from CF; patients must undergo repeated cycles of discomfort and treatment followed by short-lived periods of relief. In addition, current treatments are associated with side effects that can be exacerbated by repeated administration.
Despite recent advances in gene therapy, little progress has been made towards a curative solution for CF and other genetically based disease conditions. In the case of CF, current gene therapies are based upon the delivery, typically via the lungs, of a functional copy of the CFTR gene to a patient in an attempt to compensate for the faulty CFTR gene. Such therapies are inefficient at best, hampered by poor lung transduction, transient and low levels of gene expression, the rapid turnover of pulmonary epithelial cells, and the disease symptoms which remain when the administered CFTR gene expression drops below a therapeutically effective level.
Mutations in the USH2A gene can cause Usher syndrome, type II. Usher syndrome, type II is characterized by hearing and vision loss. Treatment options for Usher syndrome, type II. Current treatments for Usher syndrome, type II are not curative. Instead, current treatments involve managing hearing and vision loss. Thus, there remains a significant need for new treatments and cures for cystic fibrosis, Usher syndrome, type II and other genetic diseases such as Duchenne muscular dystrophy, hemophilia, and amyotrophic lateral sclerosis.
The disclosure provides Cas12a guide RNA (gRNA) molecules engineered to contain a targeting sequence and a loop domain. The Cas12a gRNA molecules of the disclosure, in combination with Cas12a proteins, can be used, for example, to correct or modify aberrant splicing of a pre-mRNA molecule by editing a genomic DNA sequence encoding the pre-mRNA. The present disclosure is based, in part, on the discovery that allele specific repair of splicing mutations in the CFTR gene could be accomplished through the use of single Cas12a gRNAs targeting the vicinity of the splicing mutations. Unexpectedly, it was discovered that efficient correction of splicing errors resulting from splicing mutations in the CFTR gene does not require deletion or correction of the mutation itself when using Cas12a gRNAs as described herein. Instead, and without being bound by theory, it is believed that splicing corrections can be obtained from the deletion of nucleotides in or near the splicing regulatory elements close to the mutation rather than correction of the mutation. The deletion of nucleotides can result in removal or inactivation of splicing regulatory elements near the mutation, although in some instances the mutation itself can be deleted. Moreover, the strategy of using a single Cas12a gRNA to repair splicing mutations has been found surprisingly superior to the conventional approach of using Cas9 in combination with sgRNAs to induce genetic deletion. The genome editing approach exemplified with respect to the CFTR gene can be applied to correct splicing defects in various other genes associated with genetic diseases as well as applied to restore expression of functional protein, such as through exon skipping of exons having deleterious mutations such as premature stop codons.
Accordingly, the present disclosure provides Cas12a gRNA molecules that target genomic sequences that encode mutant splice sites. As illustrated in
In certain aspects, the Cas12a gRNAs have a targeting sequence corresponding to a target domain that includes a splice site (e.g., as shown schematically in
The splice site can be, for example, a cryptic splice site activated by or introduced by a mutation in the genomic DNA. The mutation in the genomic DNA can be within the target domain (e.g., as shown schematically in
Splicing of pre-mRNA molecules at cryptic splice sites can result in a disease phenotype, and reducing the activity of a cryptic splice site by editing the genomic DNA with a Cas12a gRNA in combination with a Cas12a protein can restore normal splicing. For example, CFTR mutations 3272-26A>G, 3849+10kbC>T, IVS11+194A>G, and IVS19+11505C>G result in cystic fibrosis, and Cas12a gRNAs of the disclosure can be used to restore normal CFTR splicing.
Including the mutation in the targeting sequence can allow for allele specific cleavage of the genomic DNA. The protospacer domain of most Cas12a proteins is typically 23 nucleotides in length, and as such, specific cleavage of the chromosome containing the mutation (as opposed to the wild-type allele) can be achieved by selecting a target domain that is 1 to 23 nucleotides away from a Cas12a PAM sequence.
The splice site can alternatively be a canonical splice site. Reducing the activity of a canonical splice site by editing the genomic DNA with a Cas12a gRNA in combination with a Cas12a protein can be used, for example, to cause exon skipping in a gene having a deleterious mutation (e.g., a mutation, for example in an exon, that results in a truncated protein). Generally, the mutation will be outside of the target domain. By skipping an exon, production of an altered, yet possibly still functional, protein can be achieved. For example, mutations in exon 50 of the DMD gene can cause premature truncation of the dystrophin protein encoded by the gene, but exon skipping of exon 51 can restore the reading frame and restore expression of functional dystrophin protein (see, Amoasii et al., 2017, Science Translational Medicine, 9(418):eaan8081). Cas12a gRNAs of the disclosure can be used, for example, to edit a DMD gene having mutations in exon 50 so that exon 51 is skipped, thereby restoring expression of functional dystrophin protein.
The activity of a splice site can be reduced by using a Cas12a gRNA designed so that upon introduction of the gRNA and the Cas12a protein into a cell containing the genomic sequence, the Cas12a protein cleaves the genomic DNA close to the splice site (e.g., up to 15 nucleotides from the splice site). Indels introduced during repair of the cleaved genomic DNA can reduce activity of the splice site (partially or completely). With knowledge of the PAM sequence recognized by a particular Cas12a protein (e.g., TTTV for AsCas12a), knowledge of where the Cas12a protein cuts (e.g. after the 19th base following the PAM sequence on the strand having the target domain sequence and after the 23rd base following the PAM sequence on the complementary strand for AsCas12a), and knowledge of the position of the splice site relative to the PAM sequence in the genomic DNA, a targeting sequence can be selected such that upon introduction of the gRNA and the Cas12a protein into a cell containing the genomic sequence, the Cas12a will cleave the genomic DNA up to 15 nucleotides from the splice site.
In some embodiments, the Cas12a gRNAs have a targeting sequence corresponding to a target domain adjacent to a Cas12a PAM sequence that is within 40 nucleotides (e.g., 4 to 38 nucleotides) of a splice site encoded by the genomic DNA sequence.
Exemplary features of genomic DNA that can be targeted and exemplary features of gRNA molecules of the disclosure are described in Sections 6.2 and 6.3 and numbered embodiments 1 to 283, infra. Exemplary Cas12a proteins which can be used in conjunction with gRNAs of the disclosure are described in Section 6.4, infra.
The disclosure further provides nucleic acids encoding gRNAs of the disclosure and cells containing the nucleic acids. Features of exemplary nucleic acids encoding gRNAs and exemplary cells are described in Section 6.5 and numbered embodiments 284 to 287 and 302 to 305, infra.
The disclosure further provides systems and particles containing Cas12a gRNAs of the disclosure. Exemplary systems and particles are described in Section 6.6 and numbered embodiments 296 to 301, infra.
The disclosure further provides methods of using the gRNAs, systems, and particles of the disclosure for altering cells. Methods of the disclosure can be used, for example, to treat subjects having a genetic disease, for example cystic fibrosis or muscular dystrophy. Exemplary methods of altering cells are described in Section 6.7 and numbered embodiments 306 to 376, infra.
It should be understood that the figures are exemplary and do not limit the scope of this disclosure.
The disclosure provides Cas12a guide RNA (gRNA) molecules, which in combination with Cas12a proteins, can be used, for example, to correct aberrant RNA splicing resulting from mutations in a genomic DNA sequence or, as another example, to prevent inclusion of an exon in a mature mRNA (e.g., where exon skipping would be advantageous).
In one aspect, a gRNA of the disclosure is engineered to comprise a protospacer domain containing a targeting sequence and a loop domain. The targeting sequence corresponds to a target domain in a genomic DNA sequence, and the target domain is adjacent to a protospacer-adjacent motif (PAM) of a Cas12a protein.
Exemplary features of genomic DNA that can be targeted and exemplary features of gRNA molecules of the disclosure are described in Sections 6.2 and 6.3. Exemplary Cas12a proteins which can be used in conjunction with gRNAs of the disclosure are described in Section 6.4.
The disclosure further provides nucleic acids encoding gRNAs of the disclosure and host cells containing the nucleic acids. Features of exemplary nucleic acids encoding gRNAs and exemplary host cells are described in Section 6.5.
The disclosure further provides systems and particles containing Cas12a gRNAs of the disclosure. Exemplary systems and particles are described in Section 6.6.
The disclosure further provides methods of using the gRNAs, systems, and particles of the disclosure for altering cells. Methods of the disclosure can be useful, for example, for treating a genetic disease. Exemplary methods of altering cells are described in Section 6.7.
Adjacent, when referring to two nucleotide sequences (e.g., a target domain and a PAM), means that the two nucleotide sequences are next to each other with no intervening nucleotides between the two sequences.
A Cas12a protein refers to a wild-type or engineered Cas12a protein. Cas12a proteins are also referred to in the art as Cpf1 proteins.
Corresponds to, when referring to a targeting sequence and a target domain, means that the targeting sequence is complementary to the complement of the target domain, with no more than 3 nucleotide mismatches. In some embodiments, the targeting sequence is complementary to the complement of the target domain, with no more than 2 nucleotide mismatches. In other embodiments, the targeting sequence is complementary to the complement of the target domain, with no more than 1 nucleotide mismatches. In other embodiments, the targeting sequence is complementary to the complement of the target domain, with no nucleotide mismatches.
Disrupted, in reference to a region of a genomic DNA sequence, means that the region has been altered by an indel.
Indels, in the context of this disclosure, refer to insertions and deletions in a genomic DNA sequence introduced during repair (e.g., by non-homologous end joining or homology-directed repair) of a genomic DNA sequence that has been cleaved by a Cas12a protein.
Loop domain is a component of a Cas12a gRNA of the disclosure comprising a stem-loop structure recognized by a Cas12a protein. Loop domains can comprise a nucleotide sequence of a naturally occurring stem-loop sequence recognized by a Cas12a protein or can comprise an engineered nucleotide sequence that forms a stem-loop structure recognized by a Cas12a protein. See, e.g., Zetsche et al., 2015, Cell 163:759-771.
Mutation, in the context of this disclosure, refers to an alteration of a wild-type genomic DNA sequence. A mutation can be an alteration at one or more nucleotides (e.g., a single nucleotide polymorphism (SNP)), a deletion, or an insertion relative to the wild-type genomic DNA sequence. A mutation which is a deletion or insertion can be, for example, a deletion or insertion from 1 to 106 nucleotides (e.g., 1 to 105 nucleotides, 1 to 104 nucleotides, 1 to 103 nucleotides, 1 to 100 nucleotides, or 1 to 10 nucleotides).
Protospacer domain refers to a region of a Cas12a gRNA molecule containing a targeting sequence. A protospacer domain is sometimes referred to as a crRNA.
Protospacer-adjacent motif (PAM), in the context of this disclosure, refers to a genomic DNA sequence, generally four nucleotides long, that is 5′ to a target domain in the genomic DNA sequence and which is required for cleavage of the genomic DNA by a Cas12a protein that recognizes the PAM. An exemplary PAM sequence is TTTV, which is the PAM sequence for wild-type AsCas12a and LbCas12a.
Splice site as used herein refers to an intron/exon junction in a precursor mRNA (pre-mRNA) molecule. A splice site can be a 5′ splice site (also referred to as a donor splice site), which is a splice site located at the 5′ end of an intron, or a 3′ splice site (also referred to as an acceptor splice site), which is a splice site located at the 3′ end of an intron. Splicing of pre-mRNA splicing at a canonical splice site is referred to herein as normal splicing. Pre-mRNA splicing that occurs at a cryptic splice site is referred to herein as aberrant splicing. Cryptic splice sites can be present in wild-type pre-mRNA molecules, but are generally dormant or used only at low levels unless activated by a mutation. Cryptic splice sites can also be created by a mutation.
Target Domain refers to a genomic DNA sequence targeted for cleavage by a Cas12a protein.
Targeting Sequence refers to a region of a Cas12a gRNA molecule corresponding to a target domain.
Wild-type, in reference to a genomic DNA sequence, refers to a genomic DNA sequence that predominates in a species, e.g., Homo sapiens.
Cas12a gRNAs of the disclosure can be designed to target, in combination with a Cas12a protein, eukaryotic genomic sequences, such as mammalian genomic sequences. Preferably, the targeted genomic sequences are human genomic sequences. Genomic sequences of interest are typically genomic sequences encoding a mutated gene whose expression results in a disease phenotype. For example, the disease phenotype can be a disease phenotype resulting from a mutation which causes aberrant splicing of pre-mRNA, or disease phenotype resulting from a mutation in an exon (e.g., a mutation that introduces a stop codon into mRNA encoded by the genomic sequence).
Exemplary genomic DNA sequences that can be targeted include variant Cystic Fibrosis Transmembrane conductance Regulator (CFTR) genes (e.g., which are associated with cystic fibrosis), variant dystrophin (DMD) genes (e.g., which are associated with muscular dystrophies such as Duchenne muscular dystrophy or Becker muscular dystrophy), variant hemoglobin subunit beta (HBB) genes (e.g., which are associated with beta-thalassemia), variant fibrinogen beta chain (FGB) genes (e.g., which are associated with afibrinogenemia), variant superoxide dismutase 1 (SOD1) genes (e.g., which are associated with amyotrophic lateral sclerosis), variant quinoid dihydropteridine reductase (QDPR) genes (e.g., which are associated with dihydropteridine reductase deficiency), variant alpha-galactosidase (GLA) genes (e.g., which are associated with Fabry disease), variant low density lipoprotein receptor (LDLR) genes (e.g., which are associated with familial hypercholesterolemia), variant BRCA1-interacting protein 1 (BRIP1) genes (e.g., which are associated with Fanconi anemia), variant coagulation factor IX (F9) genes (e.g., which are associated with hemophilia B), variant centrosomal protein of 290 kDa (CEP290) genes (e.g., which are associated with Leber congenital amaurosis), variant collagen, type II, alpha 1 (COL2A1) genes (e.g., which are associated with Stickler syndrome), variant usherin (USH2A) genes (e.g., which are associated with Usher syndrome, type II), and variant acid alpha-glucosidase (AAG) genes (e.g., which are associated with glycogen storage disease, type II). Exemplary target domains in different variants of these genes (and which can be used to design a Cas12a gRNA as described herein) are described in Section 6.3.4.
One constraint on the use of CRISPR systems in general (e.g., both CRISPR-Cas9 and CRISPR-Cas12a) is the requirement for the target domain to be in close proximity to a PAM sequence (e.g., adjacent to a PAM sequence). Cas12a proteins generate staggered cuts when cleaving genomic DNA; in the case of AsCas12a and LbCas12a, DNA cleavage of a target genomic sequence occurs after the 19th base following the PAM sequence on the strand having the target domain sequence and after the 23rd base following the PAM sequence on the complementary strand. Thus, design of Cas12a gRNAs is constrained by the location and availability of PAM sequences in genomic DNA. However, Cas12a variants recognizing PAM sequences which are different from the PAM sequences recognized by wild-type Cas12a proteins have been designed (see Section 6.4), expanding the number of genomic DNA sequences that can potentially be targeted for editing with Cas12a.
The PAM recognized by AsCas12a and LbCas12a is TTTV, where V is A, C, or G, while the PAM of FnCas12 is NTTN, where N is any nucleotide. Engineered Cas12a proteins recognizing alternative PAM sequences have been designed, for example which recognize one or more of TYCV, where Y is C or T and V is A, C, or G; CCCC; ACCC; TATV, where V is A, C, or G; and RATR. Cas12a proteins which recognize these PAM sequences are described in Section 6.4.
Cas12a gRNAs of the disclosure target genomic DNA sequences that are close to or include a splice site encoded by the genomic DNA. The splice site needs to be in close proximity to a Cas12a PAM sequence so that the genomic DNA can be cleaved by a Cas12a protein. For example, Cas12a gRNAs can be designed so that upon introduction of the gRNA and the Cas12a protein into a cell containing the genomic sequence, the Cas12a cleaves the genomic DNA up to 15 nucleotides (e.g., up to 10 nucleotides or 10-15 nucleotides) from a splice site encoded by the genomic DNA. Indels created during repair of the cleaved genomic DNA can cause a reduction (e.g., partial or complete) in the activity of the splice site, thereby altering the splicing of the pre-mRNA encoded by the genomic DNA. The splice site can be a cryptic splice site (e.g., one that results in a disease phenotype), or a canonical splice site (e.g., upstream of an exon containing a disease-causing mutation). The splice site (cryptic or canonical) can be a 5′ splice site or a 3′ splice site. Splice sites are described in greater detail in Section 6.3.2.
In one aspect, the disclosure provides an engineered Cas12a guide RNA (gRNA) molecule comprising a protospacer domain containing a targeting sequence and a loop domain. The targeting sequence corresponds to a target domain in a genomic DNA sequence, and the target domain is adjacent to a protospacer-adjacent motif (PAM) of a Cas12a protein.
In certain aspects, the Cas12a gRNAs have a targeting sequence corresponding to a target domain that includes a splice site (shown schematically in
The splice site can be, for example, a cryptic splice site activated or introduced by a mutation in the genomic DNA. Splicing of pre-mRNA molecules at cryptic splice sites can result in a disease phenotype, and reducing the activity of a cryptic splice site by editing the genomic DNA with a Cas12a gRNA in combination with a Cas12a protein can restore normal splicing. Including the mutation in the targeting sequence (e.g., where the mutation is 1 to 23 nucleotides from a Cas12a PAM sequence) can allow for allele specific cleavage of the genomic DNA. In some embodiments, the gRNA has a targeting sequence corresponding to a target domain having a mutation that is 1 to 20 nucleotides, 1 to 15 nucleotides, 1 to 10 nucleotides, 1 to 5 nucleotides, 5 to 15 nucleotides, 10 to 20 nucleotides, or 15 to 23 nucleotides from the PAM sequence.
The splice site can alternatively be a canonical splice site. Reducing the activity of a canonical splice site by editing the genomic DNA with a Cas12a gRNA in combination with a Cas12a protein can be used, for example, to cause exon skipping of an exon in a gene having a deleterious mutation (e.g., a mutation that introduces a stop codon or otherwise affects the open reading frame). Through exon skipping, production of an altered, yet possibly still functional protein, can be achieved.
Genomic DNA can be edited close to the splice site (e.g., so that the activity of the splice site is reduced partially or completely) by using a Cas12a gRNA designed so that upon introduction of the gRNA and the Cas12a protein into a cell containing the genomic sequence, the Cas12a protein cleaves the genomic DNA up to 15 nucleotides from the splice site (e.g., up to 10 nucleotides or 10-15 nucleotides from the splice site).
When a Cas12a protein cleaves genomic DNA, it produces staggered cuts. For example, AsCas12a and LbCas12a proteins cleave genomic DNA after the 19th base following the PAM sequence on the strand having the target domain sequence and after the 23rd base following the PAM sequence on the complementary strand. It should be understood that in connection with the expression “the Cas12a protein cleaves the genomic DNA up to 15 nucleotides from a splice site encoded by the genomic DNA” and similar phrases (e.g., reciting a different number of nucleotides), that counting of the nucleotides should be performed from the overhang closest to the splice site. Moreover, it should be understood that the expression “the Cas12a protein cleaves the genomic DNA up to 15 nucleotides from a splice site encoded by the genomic DNA” and similar phrases encompasses embodiments in which the Cas12a protein cleaves the genomic DNA at the splice site. Thus, the expression “the Cas12a protein cleaves the genomic DNA up to 15 nucleotides from a splice site encoded by the genomic DNA” encompasses embodiments in which the Cas12a protein cleaves the genomic DNA at the splice site, 1 nucleotide from the splice site, 2 nucleotides from the splice site, 3 nucleotides from the splice site, 4 nucleotides from the splice site, 5 nucleotides from the splice site, 6 nucleotides from the splice site, 7 nucleotides from the splice site, 8 nucleotides from the splice site, 9 nucleotides from the splice site, 10 nucleotides from the splice site, 11 nucleotides from the splice site, 12 nucleotides from the splice site, 13 nucleotides from the splice site, 14 nucleotides from the splice site, or 15 nucleotides from the splice site.
With knowledge of the PAM sequence recognized by a particular Cas12a protein (e.g., TTTV for AsCas12a), knowledge of where the Cas12a protein cuts (e.g. 19 and 23 nucleotides after the PAM for AsCas12a), and knowledge of the position of a splice site relative to the PAM sequence in the genomic DNA, a targeting sequence can be selected such that upon introduction of the gRNA and the Cas12a protein into a cell containing the genomic sequence, the Cas12a protein will cleave the genomic DNA up to 15 nucleotides from the splice site. For example, when designing a gRNA for use with AsCas12a protein, the splice site can be after the 4th nucleotide following a TTTV sequence to after the 38th nucleotide following a TTTV sequence.
In some embodiments, the disclosure provides Cas12a gRNAs whose targeting sequence corresponds to a target domain adjacent to a PAM sequence that is within 40 nucleotides (e.g., 4 to 38 nucleotides, 5 to 35 nucleotides, 5 to 25 nucleotides, 5 to 15 nucleotides, 5 to 10 nucleotides, 10 to 35 nucleotides, 10 to 25 nucleotides, 10 to 20 nucleotides, 10 to 15 nucleotides, 15 to 35 nucleotides, 15 to 25 nucleotides, 20 to 35 nucleotides, 20 to 30 nucleotides, or 25 to 35 nucleotides) of a splice site.
Cas12a gRNAs of the disclosure are generally 40-44 nucleotides long (e.g., 40 nucleotides, 41 nucleotides, 42 nucleotides, or 43 nucleotides), but gRNAs of other lengths are also contemplated. For example, extending the 5′ end of a gRNA (e.g., as described in Park et al., 2018, Nature Communications, 9:3313) can be helpful for enhancing gene editing efficacy. Additionally, Cas12a gRNAs of the disclosure can optionally be chemically modified, which can be useful, for example, to enhance serum stability of a gRNA (see, e.g., Park et al., 2018, Nature Communications, 9:3313).
The gRNAs of the disclosure comprise a protospacer domain containing a targeting sequence. In some embodiments, the sequence of the protospacer domain and the targeting sequence are the same. In other embodiments, the sequence of the protospacer domain and the targeting sequence are different (e.g., where the protospacer domain comprises one or more nucleotides 5′ and/or 3′ to the targeting sequence).
The protospacer domain can in some embodiments be 17 to 26 nucleotides in length (e.g., 17-20 nucleotides, 17-23 nucleotides, 20-26 nucleotides, or 20-24 nucleotides). In some embodiments, the protospacer domain is 17 nucleotides in length. In other embodiments, the protospacer domain is 18 nucleotides in length. In other embodiments, the protospacer domain is 19 nucleotides in length. In other embodiments, the protospacer domain is 20 nucleotides in length. In other embodiments, the protospacer domain is 21 nucleotides in length. In other embodiments, the protospacer domain is 22 nucleotides in length. In other embodiments, the protospacer domain is 23 nucleotides in length. In other embodiments, the protospacer domain is 24 nucleotides in length. In other embodiments, the protospacer domain is 25 nucleotides in length. In other embodiments, the protospacer domain is 26 nucleotides in length.
The targeting sequence corresponds to a target domain in a genomic DNA sequence. There are preferably no mismatches between the targeting sequence and the complement of the target domain, although embodiments with a small number of mismatches (e.g., 1 or 2) are envisioned. The targeting sequence can in some embodiments be 17 to 26 nucleotides in length (e.g., 20-24 nucleotides in length). In some embodiments, the targeting sequence is 17 nucleotides in length. In other embodiments, the targeting sequence is 18 nucleotides in length. In other embodiments, the targeting sequence is 19 nucleotides in length. In other embodiments, the targeting sequence is 20 nucleotides in length. In other embodiments, the targeting sequence is 21 nucleotides in length. In other embodiments, the targeting sequence is 22 nucleotides in length. In other embodiments, the targeting sequence is 23 nucleotides in length. In other embodiments, the targeting sequence is 24 nucleotides in length. In other embodiments, the targeting sequence is 25 nucleotides in length. In other embodiments, the targeting sequence is 26 nucleotides in length. In some embodiments, the sequence of the protospacer domain and the targeting sequence are the same.
The targeting sequence can, but does not necessarily, correspond to a target domain having a mutation (e.g., a single nucleotide polymorphism). In some embodiments, a Cas12a gRNA of the disclosure has a targeting sequence corresponding to a target domain having a mutation 1 to 23 nucleotides 3′ of a Cas12a PAM sequence (e.g., 1 to 20 nucleotides, 1 to 15 nucleotides, 1 to 10 nucleotides, 1 to 5 nucleotides, 5 to 15 nucleotides, 10 to 20 nucleotides, or 15 to 23 nucleotides from a Cas12a PAM sequence). Cas12a gRNAs having a targeting sequence corresponding to a target domain having a mutation can have allele specificity such that a Cas12a/Cas12a gRNA complex can preferentially cleave the mutant allele over the wild-type allele, thereby resulting in genome editing of only the mutant allele.
Without being bound by theory, it is believed that deletion, correction or other alteration of a mutation during repair of the genomic DNA following cleavage is not necessary to reduce the activity of a splice site. Thus, gRNAs of the disclosure can be effective to reduce the activity of a splice site even when introduction of the gRNA and a Cas12a protein into a cell containing the genomic sequence does not result in deletion, correction or other alteration of the mutation. Thus, in some embodiments, upon introduction of a gRNA of the disclosure and a Cas12a protein into a population cells containing the genomic sequence, cleavage of the genomic DNA by the Cas12a protein may not necessarily delete, correct, or otherwise alter the mutation in all of the resulting indels. For example, the mutation may be deleted, corrected or otherwise altered in 50% or fewer (e.g., 10% to 50%, 10% to 40%, 10% to 30%, or 10% to 20%) of the resulting indels.
6.3.2.1. Cryptic Splice Sites
A cryptic splice site is a non-canonical splice site having the potential for interacting with the spliceosome. Mutations (e.g., splice site mutations) in the DNA encoding mRNA or errors during transcription can create or activate a cryptic splice site in part of the transcript that usually is not spliced. Creation or activation of a cryptic splice site can result in aberrant splicing and, in some cases, a disease phenotype. Thus, in some embodiments, Cas12a gRNAs of the disclosure target a cryptic splice site. In some embodiments, the target domain includes the cryptic splice site. In other embodiments, the target domain does not include the cryptic splice site. The cryptic splice site can be a 5′ cryptic splice site or a 3′ cryptic splice site.
In some embodiments, the cryptic splice is one that is created or activated by a mutation in a genomic DNA sequence. The mutation can be, for example, a single nucleotide polymorphism, an insertion (e.g., 1 to 10 nucleotides or 1 to 100 nucleotides), or a deletion (e.g., 1 to 10 nucleotides or 1 to 100 nucleotides). In some embodiments, the mutation is a single nucleotide polymorphism.
Upon introduction of a Cas12a gRNA and a Cas12a protein into a cell having the genomic DNA sequence encoding the cryptic splice site, the genomic DNA can be edited so that normal splicing is restored. For example, when the Cas12a gRNA is introduced with a Cas12a protein into a population of cells having the genomic DNA sequence (e.g., in vitro), normal splicing can be restored in a portion of the cells, e.g., at least 10% of the cells (e.g., 10% to 20% of the cells), at least 20% of the cells (e.g., 20% to 30% of the cells), at least 30% of the cells (e.g., 30% to 40% of the cells), at least 40% of the cells (e.g., 40% to 50% of the cells), at least 50% of the cells (e.g., 50% to 60% of the cells), at least 60% of the cells (e.g., 60% to 70% of the cells), or at least 70% of the cells (e.g., 70% to 80% of the cells or 70% to 90% of the cells). Without being bound by theory, it is believed that restoration of normal splicing in even a minority of cells can be advantageous for treating some genetic diseases, such as CF, familial hypercholesterolemia type 2, spinal muscular atrophy, hemophilia, and Duchenne muscular dystrophy. For example, it is believed that for a subject having CF, restoring normal splicing in as few as 10% of the subject's lung cells would be sufficient to alleviate the patient's symptoms.
6.3.2.1.1. Cryptic 3′ Splice Sites
A cryptic splice site targeted by a gRNA of the disclosure can be a cryptic 3′ splice site, for example, a splice site which is created by or activated by a mutation. Cryptic 3′ splice sites can be, for example, upstream of a 3′ canonical splice site or upstream of a 5′ cryptic splice site.
When the cryptic 3′ splice site is upstream of a 3′ canonical splice site, splicing at the cryptic 3′ splice site rather than the 3′ canonical splice site results in an elongated exon (shown schematically in
When the cryptic 3′ splice site is upstream of a 5′ cryptic splice site, splicing at the cryptic 3′ splice site and the cryptic 5′ splice site results in the inclusion of a pseudo-exon in the mature mRNA (shown schematically in
Reducing the activity of a cryptic 3′ splice site can be achieved, for example, by disrupting the splice site, disrupting the branch site upstream of the cryptic 3′ splice site (referred to herein as the “branch site of the cryptic 3′ splice site”), or disrupting the polypyrimidine tract upstream of the cryptic 3′ splice site (referred to herein as the “polypyrimidine tract of the cryptic 3′ splice site”). Thus, reducing the activity of a cryptic 3′ splice site can be achieved by using a Cas12a gRNA targeting, for example, the splice site, the branch site, or the polypyrimidine tract.
6.3.2.1.2. Cryptic 5′ Splice Sites
A cryptic splice site targeted by a gRNA of the disclosure can be a cryptic 5′ splice site, for example which has been created or activated by a mutation. Cryptic 5′ splice sites can be, for example, downstream of a cryptic 3′ splice site or downstream of a 5′ canonical splice site.
When the cryptic 5′ splice site is downstream of a cryptic 3′ splice site, splicing at the cryptic 3′ splice site and the cryptic 5′ splice site results in the inclusion of a pseudo-exon in the mature mRNA (shown schematically in
Reducing the activity of a cryptic 5′ splice site can be achieved, for example, by disrupting the cryptic 5′ splice site or surrounding sequence (e.g., from the three nucleotides 5′ of the cryptic splice site to the eight nucleotides 3′ of the cryptic 5′ splice site).
6.3.2.2. Canonical Splice Sites
A Cas12a gRNA of the disclosure can target a canonical splice site. A targeted canonical splice site can be a canonical 3′ splice site or a 5′ canonical splice site.
Reducing the activity of a canonical 3′ splice site or a 5′ canonical splice site can be used to cause exon skipping. Targeting of a canonical 3′ splice site is shown schematically in
Reducing the activity of a canonical 3′ splice site can be achieved, for example, by disrupting the splice site, disrupting the branch site upstream of the canonical 3′ splice site (referred to herein as the “branch site of the canonical 3′ splice site”), or disrupting the polypyrimidine tract upstream of the canonical 3′ splice site (referred to herein as the “polypyrimidine tract of the canonical 3′ splice site”). Reducing the activity of a canonical 5′ splice site can be achieved, for example, by disrupting the canonical 5′ splice site or surrounding sequence (e.g., from the three nucleotides 5′ of the canonical splice site to the eight nucleotides 3′ of the canonical 5′ splice site).
Cas12a is a single gRNA-guided endonuclease where the gRNA comprises a single loop domain having a direct repeat sequence, e.g., a loop domain 20 nucleotides in length. Cas12a proteins recognize the Cas12a gRNA via a combination of structural and sequence-specific features of the loop domain. Loop domains of gRNAs of the disclosure are typically at least 16 nucleotides in length, e.g., 16-20 nucleotides, 16-18 nucleotides, 18-20 nucleotides, 16 nucleotides, 17 nucleotides, 18 nucleotides, 19 nucleotides, or 20 nucleotides in length. In some embodiments, the loop domain is 20 nucleotides in length. Typically, the loop domain will be 5′ to the protospacer domain of a Cas12a gRNA.
Loop domains can comprise a stem-loop sequence that associates with a wild-type Cas12a protein or a variant thereof. See, e.g., Zetsche, et. al, 2015, Cell, 163:759-771, incorporated herein by reference in its entirety, which describes stem-loop sequences of various loop domains capable of associating with Cas12a proteins. Exemplary loop domains include loop domains comprising a nucleotide sequence selected from UCUACUGUUGUAGA (SEQ ID NO: 1), UCUACUGUUGUAGAU (SEQ ID NO: 2), UCUGCUGUUGCAGA (SEQ ID NO: 3), UCUGCUGUUGCAGAU (SEQ ID NO: 4), UCCACUGUUGUGGA (SEQ ID NO: 5), UCCACUGUUGUGGAU (SEQ ID NO: 6), CCUACUGUUGUAGG (SEQ ID NO: 7), CCUACUGUUGUAGGU (SEQ ID NO: 8), UCUACUAUUGUAGA (SEQ ID NO: 9), UCUACUAUUGUAGAU (SEQ ID NO: 10), UCUACUGCUGUAGAU (SEQ ID NO: 11), UCUACUGCUGUAGAUU (SEQ ID NO: 12), UCUACUUUCUAGAU (SEQ ID NO: 13), UCUACUUUCUAGAUU (SEQ ID NO: 14), UCUACUUUGUAGA (SEQ ID NO: 15), UCUACUUUGUAGAU (SEQ ID NO: 16), UCUACUUGUAGA (SEQ ID NO: 17), and UCUACUUGUAGAU (SEQ ID NO: 18).
In some embodiments, the loop domain comprises or consists of a nucleotide sequence selected from UAAUUUCUACUGUUGUAGAU (SEQ ID NO: 19), AGAAAUGCAUGGUUCUCAUGC (SEQ ID NO: 20), AAAAUUACCUAGUAAUUAGGU (SEQ ID NO: 21), GGAUUUCUACUUUUGUAGAU (SEQ ID NO: 22), AAAUUUCUACUUUUGUAGAU (SEQ ID NO: 23), CGCGCCCACGCGGGGCGCGAC (SEQ ID NO: 24), UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25), GAAUUUCUACUAUUGUAGAU (SEQ ID NO: 26), GAAUCUCUACUCUUUGUAGAU (SEQ ID NO: 27), UAAUUUCUACUUUGUAGAU (SEQ ID NO: 28), AAAUUUCUACUGUUUGUAGAU (SEQ ID NO: 29), GAAUUUCUACUUUUGUAGAU (SEQ ID NO: 30), UAAUUUCUACUAAGUGUAGAU (SEQ ID NO: 31), UAAUUUCUACUAUUGUAGAU (SEQ ID NO: 32), UAAUUUCUACUUCGGUAGAU (SEQ ID NO: 33), and UAAUUUCUACUAUUGUAGAU (SEQ ID NO: 32). In some embodiments, the loop domain comprises or consists of UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25), which is the loop domain sequence associated with AsCas12a. In some embodiments, the loop domain comprises or consists of UAAUUUCUACUAAGUGUAGAU (SEQ ID NO: 31), which is the loop domain sequence associated with LbCas12a.
Additional stem-loop sequences that associate with Cas12a proteins and which can be used in loop domains of the Cas12a gRNAs of the disclosure are described in Feng, et. al, 2019, Genome Biology, 20:15, incorporated herein by reference in its entirety. Exemplary nucleotide sequences described in Feng, et. al, 2019, Genome Biology, 20:15 and which can be included in loop domains of the Cas12a gRNAs of the disclosure include AUUUCUACUAGUGUAGAU (SEQ ID NO: 34), AUUUCUACUGUGUGUAGA (SEQ ID NO: 35), AUUUCUACUAUUGUAGAU (SEQ ID NO: 36), and AUUUCUACUUUGGUAGAU (SEQ ID NO: 37).
Loop domains having a nucleotide sequence varying from the nucleotide sequences described above can also be used. For example, mutations in a loop domain sequence that preserve the RNA duplex of the loop domain can be used. See, e.g., Zetsche, et. al, 2015, Cell, 163:759-771.
Cas12a gRNAs having targeting sequences corresponding to target domains in various genes can be designed as described herein. For example, a target domain can be in a variant CFTR gene, a variant DMD gene, a variant HBB gene, a variant FGB gene, a variant SOD1 gene, a variant QDPR gene, a variant GLA gene, a variant LDLR gene, a variant BRIP1 gene, a variant F9 gene, a variant CEP290 gene, a variant COL2A1 gene, a variant USH2A gene, or a variant GAA gene. The target domains described below can be used, for example, to design a Cas12a gRNA of the disclosure (e.g., a Cas12a gRNA comprising a targeting sequence corresponding to a target domain described below and a loop domain as described in Section 6.3.3). Such Cas12a gRNAs can be used, for example, together with an appropriate Cas12a protein to restore normal splicing of mRNA. Additional details regarding the specific mutations described in this section can be found in the DBASS database (www.dbass.org.uk).
In some embodiments, the target domain is in a CFTR gene, for example, a CFTR gene having a 3272-26A>G mutation, a 3849+10kbC>T mutation, a IVS11+194A>G mutation, or a IVS19+115050>G mutation. The 3272-26A>G mutation causes aberrant splicing at a cryptic 3′ splice site, whereas the 3849+10kbC>T mutation, IVS11+194A>G mutation, and IVS19+115050>G mutation each cause aberrant splicing at a cryptic 5′ splice site. Each of these mutations is associated with cystic fibrosis.
An exemplary Cas12a gRNA for editing a CFTR gene having a 3272-26A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CATAGAAAACACTGCAAATAACA (SEQ ID NO: 38).
An exemplary Cas12a gRNA for editing a CFTR gene having a 3849+10kbC>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AGGGTGTCTTACTCACCATTTTA (SEQ ID NO: 39).
An exemplary Cas12a gRNA for editing a CFTR gene having a IVS11+194A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TACTTGAGATGTAAGTAAGGTTA (SEQ ID NO: 40). Another exemplary Cas12a gRNA for editing a CFTR gene having a IVS11+194A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence ATAGTAACCTTACTTACATCTCA (SEQ ID NO: 41).
An exemplary Cas12a gRNA for editing a CFTR gene having a IVS19+115050>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AAATTCCATCTTACCAATTCTAA (SEQ ID NO: 42). Another exemplary Cas12a gRNA for editing a CFTR gene having a IVS19+115050>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AACGTTAAAATTCCATCTTACCA (SEQ ID NO: 43).
In other embodiments, the target domain is in a DMD gene, for example a DMD gene having a IVS9+468060>T mutation, a IVS62+62296A>G mutation, a IVS1+36947G>A mutation, a IVS1+36846G>A mutation, a IVS2+5591T>A mutation or a IVS8-15A>G mutation. The IVS1+36947G>A mutation, IVS1+36846G>A mutation, IVS2+5591T>A mutation and IVS8-15A>G mutation each cause aberrant splicing at a cryptic 3′ splice site, whereas the IVS9+468060>T mutation and IVS62+62296A>G mutation each cause aberrant splicing at a cryptic 5′ splice site. Each of these mutations is associated with muscular dystrophy.
An exemplary Cas12a gRNA for editing a DMD gene having a IVS9+468060>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGACCTTTGGTAAGTCATCTAAT (SEQ ID NO: 44). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS9+46806C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CCTTTGTGACCTTTGGTAAGTCA (SEQ ID NO: 45).
An exemplary Cas12a gRNA for editing a DMD gene having a IVS62+62296A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTGATCACATAACAAGGTCAGTT (SEQ ID NO: 46). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS62+62296A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence ATCACATAACAAGGTCAGTTTAT (SEQ ID NO: 47). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS62+62296A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AGTTATGATAAACTGACCTTGTT (SEQ ID NO: 48). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS62+62296A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGATAAACTGACCTTGTTATGTG (SEQ ID NO: 49).
An exemplary Cas12a gRNA for editing a DMD gene having a IVS1+36947G>A mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TCTTCCTTGGTTTTGCAGCTTCT (SEQ ID NO: 50). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS1+36947G>A mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTGGTTTTGCAGCTTCTCGAGTT (SEQ ID NO: 51). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS1+36947G>A mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CTCTTTCTCTTCCTTGGTTTTGC (SEQ ID NO: 52).
An exemplary Cas12a gRNA for editing a DMD gene having a IVS2+5591T>A mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CTTGTTTCTCTACATAGGTTGAA (SEQ ID NO: 53).
An exemplary Cas12a gRNA for editing a DMD gene having a IVS8-15A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TCCTCTCTATCCACCTCCCCCAG (SEQ ID NO: 54). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS8-15A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CCTCCCCCAGACCCTTCTCTGCA (SEQ ID NO: 55). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS8-15A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CCCCTCCTCTCTATCCACTCCCC (SEQ ID NO: 56). Another exemplary Cas12a gRNA for editing a DMD gene having a IVS8-15A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CCTCCTCTCTATCCACCTCCCCC (SEQ ID NO: 57).
An exemplary Cas12a gRNA for editing for causing exon skipping of exon 51 in a DMD gene having a mutation in exon 50 of DMD can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CAAAAACCCAAAATATTTTAGCT (SEQ ID NO: 58). Another exemplary Cas12a gRNA for causing exon skipping of exon 51 of a DMD gene having a mutation in exon 50 of DMD can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CTTTTTGCAAAAACCCAAAATAT (SEQ ID NO: 59). Another exemplary Cas12a gRNA for causing exon skipping of exon 51 of a DMD gene having a mutation in exon 50 of DMD can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTTTTGCAAAAACCCAAAATATT (SEQ ID NO: 60). Another exemplary Cas12a gRNA for causing exon skipping of exon 51 of a DMD gene having a mutation in exon 50 of DMD can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGTCACCAGAGTAACAGTCTGAG (SEQ ID NO: 61). Another exemplary Cas12a gRNA for causing exon skipping of exon 51 of a DMD gene having a mutation in exon 50 of DMD can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence GCTCCTACTCAGACTGTTACTCT (SEQ ID NO: 62).
In other embodiments, the target domain is in a HBB gene, for example a HBB gene having a IVS2+645C>T mutation, a IVS2+705T>G mutation, or a IVS2+745C>G mutation. Each of these mutations causes aberrant splicing at a 5′ cryptic splice site and is associated with beta-thalassemia.
An exemplary Cas12a gRNA for editing a HBB gene having a IVS2+645C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGGGTTAAGGTAATAGCAATATC (SEQ ID NO: 63). Another exemplary Cas12a gRNA for editing a HBB gene having a IVS2+645C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TATGCAGAGATATTGCTATTACC (SEQ ID NO: 64). Another exemplary Cas12a gRNA for editing a HBB gene having a IVS2+645C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CTATTACCTTAACCCAGAAATTA (SEQ ID NO: 65). Another exemplary Cas12a gRNA for editing a HBB gene having a IVS2+645C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CAGAGATATTGCTATTACCTTAA (SEQ ID NO: 66).
An exemplary Cas12a gRNA for editing a HBB gene having a IVS2+705T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGCATATAAATTGTAACTGAGGT (SEQ ID NO: 67). Another exemplary Cas12a gRNA for editing a HBB gene having a IVS2+705T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AATTGTAACTGAGGTAAGAGGTT (SEQ ID NO: 68). Another exemplary Cas12a gRNA for editing a HBB gene having a IVS2+705T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AAACCTCTTACCTCAGTTACAAT (SEQ ID NO: 69). Another exemplary Cas12a gRNA for editing a HBB gene having a IVS2+705T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence GCAATATGAAACCTCTTACCTCA (SEQ ID NO: 70).
An exemplary Cas12a gRNA for editing a HBB gene having a IVS2+745C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CTAATAGCAGCTACAATCCAGGT (SEQ ID NO: 71).
In other embodiments, the target domain is in a FGB gene, for example a FGB gene having a IVS6+13C>T mutation. This mutation causes aberrant splicing at cryptic 5′ splice site and is associated with afibrinogenemia. An exemplary Cas12a gRNA for editing a FGB gene having a IVS6+13C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTTTGCATACCTGTTCGTTACCT (SEQ ID NO: 72). Another exemplary Cas12a gRNA for editing a FGB gene having a IVS6+13C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AAATAGAATGATTTTATTTTGCA (SEQ ID NO: 73).
In other embodiments, the target domain is in a SOD1 gene, for example a SOD1 gene having a IVS4+792C>G mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with amyotrophic lateral sclerosis. An exemplary Cas12a gRNA for editing a SOD1 gene having a IVS4+792C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGGTAAGTTACACTAACCTTAGT (SEQ ID NO: 74).
In other embodiments, the target domain is in a QDPR gene, for example a QDPR gene having a IVS3+2552A>G mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with dihydropteridine reductase deficiency. An exemplary Cas12a gRNA for editing a QDPR gene having a QDPR a IVS3+2552A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TCATCTGTAAAATAAGAGTAAAA (SEQ ID NO: 75).
In other embodiments, the target domain is in a GLA gene, for example a GLA gene having a IVS4+919G>A mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with Fabry disease. An exemplary Cas12a gRNA for editing a GLA gene having a IVS4+919G>A mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CCATGTCTCCCCACTAAAGTGTA (SEQ ID NO: 76).
In other embodiments, the target domain is in a LDLR gene, e.g., a LDLR gene having a IVS12+11C>G mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with familial hypercholesterolemia. An exemplary Cas12a gRNA for editing a LDLR gene having a IVS12+11C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AGGTGTGGCTTAGGTACGAGATG (SEQ ID NO: 77).
In other embodiments, the target domain is in a BRIP1 gene, for example a BRIP1 gene having a IVS11+2767A>T mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with Fanconi anemia. An exemplary Cas12a gRNA for editing a BRIP1 gene having a IVS11+2767A>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TAAAATTCTTACATACCTTTGAA (SEQ ID NO: 78).
In other embodiments, the target domain is in a F9 gene, for example a F9 gene having a IVS5+13A>G mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with hemophilia B. An exemplary Cas12a gRNA for editing a F9 gene having a IVS5+13A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AAAAATCTTACTCAGATTATGAC (SEQ ID NO: 79). Another exemplary Cas12a gRNA for editing for a F9 gene having a IVS5+13A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTTAAAAAATCTTACTCAGATTA (SEQ ID NO: 80).
In other embodiments, the target domain is in a CEP290 gene, for example a CEP290 gene having a IVS26+1655A>G mutation. This mutation causes aberrant splicing at a cryptic 5′ splice site and is associated with Leber congenital amaurosis. An exemplary Cas12a gRNA for editing a CEP290 gene having a VS26+1655A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AGTTGTAATTGTGAGTATCTCAT (SEQ ID NO: 81).
In other embodiments, the target domain is in a COL2A1 gene, for example a COL2A1 gene having a IVS23+135G>A mutation. This mutation causes aberrant splicing at a cryptic 3′ splice site and is associated with Stickler syndrome An exemplary Cas12a gRNA for editing a COL2A1 gene having a IVS23+135G>A mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TCCATCCACACCGCAGGGAGAG (SEQ ID NO: 82).
In other embodiments, the target domain is in a USH2A gene, for example a USH2A gene having a IVS40-8C>G mutation, a IVS66+39C>T mutation, or a c.7595-2144A>G mutation. The IVS40-8C>G mutation causes aberrant splicing at a cryptic 3′ splice site and is associated with Usher syndrome, type II. The IVS66+39C>T mutation is associated with Usher syndrome and causes aberrant splicing at a cryptic 5′ splice site. The c.7595-2144A>G mutation is deep intronic mutation associated with Usher syndrome, type II and causes aberrant splicing at a cryptic 5′ splice site and a cryptic 3′ splice site.
An exemplary Cas12a gRNA for editing a USH2A gene having a IVS40-8C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGGATTTATTTTAGTTTACAGAA (SEQ ID NO: 83). Another exemplary Cas12a gRNA for editing a USH2A gene having a IVS40-8C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTTTAGTTTACAGAACCTGGACC (SEQ ID NO: 84). Another exemplary Cas12a gRNA for editing a USH2A gene having a IVS40-8C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CAAGAGGTCTGACTTTCTGGATT (SEQ ID NO: 85). Another exemplary Cas12a gRNA for editing a USH2A gene having a IVS40-8C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AGAGGTCTGACTTTCTGGATTTA (SEQ ID NO: 86). Another exemplary Cas12a gRNA for editing a USH2A gene having a IVS40-8C>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence GGTTCTGTAAACTAAAATAAATC (SEQ ID NO: 87).
An exemplary Cas12a gRNA for editing a USH2A gene having a IVS66+39C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TATGTCTGTACACATACCTTGTT (SEQ ID NO: 88). Another exemplary Cas12a gRNA for editing a USH2A gene having a IVS66+39C>T mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence ATATGTCTGTACACATACCTTGT (SEQ ID NO: 89).
An exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TTAAAGATGATCTCTTACCTTGG (SEQ ID NO: 90). Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence CCAAGGTAAGAGATCATCTTTAA (SEQ ID NO: 91). Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AAATTGAACACCTCTCCTTTCCC (SEQ ID NO: 92). Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AAGATGATCTCTTACCTTGGGAA (SEQ ID NO: 93). The sequences identified in this paragraph can be used to edit the USH2A gene close to the cryptic 5′ splice site.
Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence AGCTGCTTTCAGCTTCCTCTCCAG (SEQ ID NO: 94). Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGGAGAGGAAGCTGAAAGCAGCT (SEQ ID NO: 95). Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGTGATTCTGGAGAGGAAGCTGA (SEQ ID NO: 96). Another exemplary Cas12a gRNA for editing a USH2A gene having a c.7595-2144A>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence ACTTGTGTGATTCTGGAGAGGAA (SEQ ID NO: 97). The sequences identified in this paragraph can be used to edit the USH2A gene close to the cryptic 3′ splice site.
In other embodiments, the target domain is in a GAA gene, for example a GAA gene having a IVS1-13T>G mutation or a IVS6-22T>G mutation. Both of these mutations cause aberrant splicing at cryptic 3′ splice sites, and are associated with glycogen storage disease, type II.
An exemplary Cas12a gRNA for editing a GAA gene having a IVS1-13T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TGCTGAGCCCGCTTGCTTCTCCC (SEQ ID NO: 98). Another exemplary Cas12a gRNA for editing a GAA gene having a IVS1-13T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of GCCTCCCTGCTGAGCCCGCTTGC (SEQ ID NO: 99). Another exemplary Cas12a gRNA for editing a GAA gene having a IVS1-13T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of TCCCGCCTCCCTGCTGAGCCCGC (SEQ ID NO: 100).
An exemplary Cas12a gRNA for editing a GAA gene having a IVS6-22T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of the sequence TCCTCCCTCCCTCAGGAAGTCGG (SEQ ID NO: 101). Another exemplary Cas12a gRNA for editing a GAA gene having a IVS6-22T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of AAGGCTCCCTCCTCCCTCCCTCA (SEQ ID NO: 102). Another exemplary Cas12a gRNA for editing a GAA gene having a IVS6-22T>G mutation can have a targeting sequence corresponding to a target domain comprising or consisting of TCCCTCAGGAAGTCGGCGTTGGC (SEQ ID NO: 103).
Cas12a proteins have been isolated from a number of bacterial species, e.g., Alicyclobacillus acidoterrestris, Bacillus thermoamylovorans, Lachnospiraceae bacterium (e.g., LbCas12a, NCBI Reference Sequence WP_051666128.1), Acidaminococcus sp. BV3L6 (e.g., AsCas12a, NCBI Reference Sequence WP_021736722.1), Arcobacter butzleri L348 (e.g., AbCas12a, GeneBank ID: JAIQ01000039.1), Agathobacter rectalis strain 2789STDY5834884 (e.g., ArCas12a, GeneBank ID: CZAJ01000001.1), Bacteroidetes oraltaxon 274 str. F0058 (e.g., BoCas12a, GeneBank ID: NZ_GG774890.1), Butyrivibrio sp. NC3005 (e.g., BsCas12a, GeneBank ID: NZ_AUKC01000013.1), Candidate division WS6 bacterium GW2011_GWA2_37_6 US52_C0007 (e.g., C6Cas12a, GeneBank ID: LBTH01000007.1), Helcococcus kunzii ATCC 51366 (e.g., HkCas12a, GeneBank ID: JH601088.1/AGEI01000022.1), Lachnospira pectinoschiza strain 2789STDY5834836 (e.g., LpCas12a, GeneBank ID: CZAK01000004.), Oribacterium sp. NK2B42 (e.g., OsCas12a, GeneBank ID: NZ_KE384190.1), Pseudobutyrivibrio ruminis CF1b (e.g., PrCas12a, GeneBank ID: NZ_KE384121.1), Proteocatella sphenisci DSM 23131 (e.g., PsCas12a, GeneBank ID: NZ_KE384028.1), Pseudobutyrivibrio xylanivorans strain DSM 10317 (e.g., PxCas12a, GeneBank ID: FMWK01000002.1), Sneathia amnii strain SN35 (e.g., SaCas12a, GeneBank ID: CP011280.1), Francisella novicida, and Leptotrichia shahii. The Cas12a protein used in the systems, particles, and methods of the disclosure can be, for example, a wild-type Cas12a protein, for example AsCas12a, LbCas12a, or another wild-type Cas12a protein described herein. In some embodiments, the Cas12a protein is AsCas12a. In other embodiments, the Cas12a protein is LbCas12a.
The success of gene editing by CRSIPR-Cas systems relies, at least in part, upon the specificity of the Cas protein for the target sequence with the fewest off-target effects, e.g., editing of non-targeting DNA. Cas12a proteins can be engineered to exhibit increased specificity relative to wild-type proteins by, for example, the introduction of one or more mutations in amino acid residues involved with directing contact of the Cas12a protein with the DNA backbone of either the target or non-target DNA. Reducing the binding affinity of a Cas12a protein to DNA can improve Cas12a protein fidelity by increasing the ability of the Cas12a protein to discriminate against non-target DNA sequences. In some embodiments, the Cas12a protein used in the systems, particles, and methods of the disclosure can be, for example, an engineered Cas12a protein, e.g., an engineered LbCas12a or engineered AsCas12a having one or more amino acid substitutions compared to the wild-type protein.
Exemplary engineered LbCas12a proteins are described in US Patent Application Publication No. 2018/0030425, the contents of which are incorporated herein by reference in their entirety. Engineered LbCas12a proteins can include, but are not limited to, the amino acid sequence of SEQ ID NO:1 (corresponding to NCBI Reference Sequence WP_051666128.1) or SEQ ID NO:10 of US 2018/0030425, optionally comprising mutations, for example, replacement of a native amino acid with a different amino acid, e.g., alanine, glycine, or serine, at one or more positions in the sequence of SEQ ID NO:10 of US 2018/0030425, e.g., at position S186, e.g., at position N256, e.g., at position N260, e.g., at position K272, e.g., at position K349, e.g., at position K514, e.g., at position K591, e.g., at position K897, e.g., at position Q944, e.g., at position K945, e.g., at position K948, e.g., at position K984, or e.g., at position S985, or any combination thereof, or at positions analogous thereto in SEQ ID NO:1 of US 2018/0030425, e.g., at position S202, e.g., at position N274, e.g., at position N278, e.g., at position K290, e.g., at position K367, e.g., at position K532, e.g., at position K609, e.g., at position K915, e.g., at position Q962, e.g., at position K963, e.g., at position K966, e.g., at position K1002, or e.g., at position S1003 of SEQ ID NO:1 US 2018/0030425; or any combination thereof. In some embodiments, an engineered LbCas12a comprises mutations G532R/K595R and G532R/K538V/Y542R.
Exemplary engineered AsCas12a proteins are described in US Patent Application Publication No. 2018/0030425, the contents of which are incorporated herein by reference in their entirety. Engineered AsCas12a proteins include, but are not limited to, the amino acid sequence of SEQ ID NO:2 (corresponding to NCBI Reference Sequence WP_021736722.1) or SEQ ID NO:8 of US 2018/0030425, optionally comprising mutations, for example, replacement of a native amino acid with a different native amino acid, e.g., alanine, glycine, or serine, at one or more positions in the sequence of SEQ ID NO:2 of US 2018/0030425, e.g., at position N178, e.g., at position S186, e.g., at position N278, e.g., at position N282, e.g., at position R301, e.g., at position T315, e.g., at position S376, e.g., at position N515, e.g., at position K523, e.g., at position K524, e.g., at position K603, e.g., at position K965, e.g., at position Q1013, e.g., at position Q1014, or e.g., at position K1054 of SEQ ID NO:2, or a combination thereof.
Additional engineered LbCas12a and AsCas12a proteins are described in US Patent Application Publication No. 2019/0010481, the contents of which are incorporated herein by reference in their entirety. Such engineered Cas12a proteins can comprise, for example, an amino acid sequence that is at least 80% or at least 95% identical to the amino acid sequence of wild-type LbCas12a or wild-type AsCas12a. Engineered Cas12a proteins can include one or more of the mutations described in US Patent Application Publication No. 2019/0010481.
Engineered Cas12a proteins can be a fusion protein, for example, comprising a heterologous functional domain, e.g., a transcriptional activation domain, a transcriptional silencer or transcriptional repression domain, an enzyme that modifies the methylation state of DNA, an enzyme that modifies a histone subunit, a deaminase that modifies cytosine DNA bases, a deaminase that modifies adenosine DNA bases, an enzyme, domain, or peptide that inhibits or enhances endogenous DNA repair or base excision repair (BER) pathways, or a biological tether, as described in US Patent Application Publication No. 2019/0010481.
The success of gene editing by CRISPR-Cas systems also relies, at least in part, upon the specificity of the Cas protein for its PAM sequence(s). Wild-type LbCas12a and AsCas12a proteins recognize the PAM sequence TTTV, where V is A, C or G. Engineered AsCas12a proteins having S542R/K607R (RR Cas12a) and S542R/K548V/N552R (RVR Cas12a) mutations are described in Gao et. al, 2017, Nat Biotechnol., 35(8):789-792, and have altered PAM specificities compared to wild-type Cas12a. Table 1 shows PAM sequences recognized by various Cas12a proteins. See also Feng, et. al, 2019, Genome Biology, 20:15.
The disclosure provides nucleic acids (e.g., DNA or RNA) encoding the Cas12a gRNAs of the disclosure. A nucleic acid encoding a Cas12a gRNA can be, for example, a plasmid or a virus genome (e.g., a lentivirus, retrovirus, adenovirus, or adeno-associated virus genome modified to encode the Cas12a gRNA). Plasmids can be, for example, plasmids for producing virus particles, e.g., lentivirus particles, or plasmids for propagating the Cas12a gRNA coding sequence in bacterial (e.g., E. coli) or eukaryotic (e.g., yeast) cells.
A nucleic acid encoding a gRNA can, in some embodiments, further encode a Cas12a protein, e.g., a Cas12a protein described in Section 6.4. An exemplary plasmid that can be used to encode a Cas12a gRNA of the disclosure and a Cas12a protein is pY108 lentiAsCas12a (Addgene Plasmid 84739), which encodes AsCas12a. Those of skill in the art will appreciate that plasmids encoding a Cas12a protein can be modified to encode a different Cas12a protein, e.g., a Cas12a variant as described in Section 6.4 or a Cas12a protein from a different species such as Lachnospiraceae bacterium or Francisella novicida.
Nucleic acids encoding a Cas12a protein can be codon optimized, e.g., where at least one non-common codon or less-common codon has been replaced by a codon that is common in a host cell. For example, a codon optimized nucleic acid can direct the synthesis of an optimized messenger mRNA, e.g., optimized for expression in a mammalian expression system.
Nucleic acids of the disclosure, e.g., plasmids, can comprise one or more regulatory elements such as promoters, enhancers, and other expression control elements (e.g., transcription termination signals, such as polyadenylation signals and poly-U sequences). Such regulatory elements are described, for example, in Goeddel, 1990, GENE EXPRESSION TECHNOLOGY: METHODS IN ENZYMOLOGY 185, Academic Press, San Diego, Calif. Regulatory elements include those that direct constitutive expression of a nucleotide sequence in many types of host cell and those that direct expression of the nucleotide sequence only in certain host cells (e.g., tissue-specific regulatory sequences). A tissue-specific promoter may direct expression primarily in a desired tissue of interest, such as muscle, neuron, bone, skin, blood, specific organs (e.g., liver, pancreas), or in particular cell types (e.g., lymphocytes). Regulatory elements may also direct expression in a temporal-dependent manner, such as in a cell-cycle dependent or developmental stage-dependent manner, which may or may not also be tissue or cell-type specific. In some embodiments, a nucleic acid of the disclosure comprises one or more pol III promoter (e.g., 1, 2, 3, 4, 5, or more pol III promoters), one or more pol II promoters (e.g., 1, 2, 3, 4, 5, or more pol II promoters), one or more pol I promoters (e.g., 1, 2, 3, 4, 5, or more pol I promoters), or combinations thereof, e.g., to express a Cas12a gRNA and a Cas12a protein separately. Examples of pol III promoters include, but are not limited to, U6 and H1 promoters. Examples of pol II promoters include, but are not limited to, the retroviral Rous Sarcoma virus (RSV) LTR promoter (optionally with the RSV enhancer), the cytomegalovirus (CMV) promoter (optionally with the CMV enhancer) (see, e.g., Boshart et al, Cell, 1985, 41:521-530), the SV40 promoter, the dihydrofolate reductase promoter, the β-actin promoter, the phosphoglycerol kinase (PGK) promoter, and the EF1α promoter. Exemplary enhancer elements include WPRE; CMV enhancers; the R-U5′ segment in LTR of HTLV-I; SV40 enhancer; and the intron sequence between exons 2 and 3 of rabbit β-globin. It will be appreciated by those skilled in the art that the design of an expression vector can depend on such factors as the choice of the host cell, the level of expression desired, etc.
The disclosure also provides a host cell comprising a nucleic acid of the disclosure.
Such host cells can be used, for example, to produce virus particles encoding a Cas12a gRNA of the disclosure and, optionally, a Cas12a protein. Host cells can also be used to make vesicles containing a Cas12a gRNA and, optionally, a Cas12a protein (e.g., by adapting the methods described in Montagna et al., 2018, Molecular Therapy: Nucleic Acids, 12:453-462 to make vesicles comprising a Cas12a gRNA and a Cas12a protein rather than a Cas9 sgRNA and a Cas9 protein). Exemplary host cells include eukaryotic cells, e.g., mammalian cells. Exemplary mammalian host cells include human cell lines such as BHK-21, BSRT7/5, VERO, WI38, MRCS, A549, HEK293, HEK293T, Caco-2, B-50 or any other HeLa cells, HepG2, Saos-2, HuH7, and HT1080 cell lines. Host cells can be engineered host cells, for example, host cells engineered to express a DNA binding protein such a repressor (e.g., TetR), to regulate virus or vesicle production (see Petris et al., 2017, Nature Communications, 8:15334).
Host cells can also be used to propagate the Cas12a gRNA coding sequences of the disclosure. The host cell can be a eukaryote or prokaryote and includes, for example, yeast (such as Pichia pastoris or Saccharomyces cerevisiae), bacteria (such as E. coli or Bacillus subtilis), insect Sf9 cells (such as baculovirus-infected SF9 cells) or mammalian cells (such as Human Embryonic Kidney (HEK) cells, Chinese hamster ovary cells, HeLa cells, human 293 cells and monkey COS-7 cells).
The disclosure further provides systems comprising a Cas12a gRNA of the disclosure and a Cas12a protein. The systems can comprise a ribonucleoprotein particle (RNP) in which the Cas12a gRNA as described herein is complexed with a Cas12a protein. The Cas12a protein can be, for example, a Cas12a protein described in Section 6.4. Systems of the disclosure can further comprise genomic DNA complexed with the Cas12a gRNA and the Cas12a protein. Accordingly, the disclosure provides a system comprising a Cas12a gRNA of the disclosure comprising a targeting sequence, a genomic DNA comprising a corresponding target domain and a Cas12a PAM, and the Cas12a protein that recognizes PAM, all complexed with one another.
The systems of the disclosure can exist within a cell (whether the cell is in vivo, ex vivo, or in vitro) or outside a cell.
The disclosure further provides particles comprising a Cas12a gRNA of the disclosure. The particles can further comprise a Cas12a protein, e.g., a Cas12a protein described in Section 6.4. Exemplary particles include liposomes, vesicles, and gold nanoparticles. In some embodiments, a particle contains only a single species of gRNA.
The disclosure further provides cells and populations of cells (e.g., a population comprising 10 or more, 50 or more 100 or more, 1,000 or more, or 100,000 thousand or more cells) comprising a Cas12a gRNA of the disclosure. Such cells and populations can further comprise a Cas12a protein. In some embodiments, such cells and populations are isolated, e.g., isolated from cells not containing the Cas12a gRNA.
The cell populations of the disclosure can be cells in which gene editing by the systems of the disclosure has taken place, or cells in which the components of a system of the disclosure have been expressed but gene editing has not taken place, or a combination thereof. A cell population can comprise, for example, a population in which at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, or at least 70% of the cells have undergone gene editing by a system of the disclosure.
In the systems, particles, cells and cell populations of the disclosure comprising a Cas12a protein, the Cas12a protein should be a Cas12a protein capable of recognizing a PAM adjacent to the target domain to which the targeting sequence of the Cas12a gRNA corresponds. For example, when the PAM sequence adjacent to the target domain is TTTV, the Cas12a protein can be, for example, a wild-type AsCas12a or a wild-type LbCas12a. As another example, when the PAM sequence is TYCV, CCCC, or ACCC, the Cas12a protein can be AsCas12a RR. As yet another example, when the PAM sequence is TATV or RATR, the Cas12a protein can be AsCas12a RVR.
The disclosure further provides methods of altering a cell comprising contacting the cell with a system or particle of the disclosure.
The cell can be contacted with a system or particle of the disclosure or encoding nucleic acid(s) in vitro, ex vivo, or in vivo.
Contacting a cell with a system or particle of the disclosure can result in editing of the genomic DNA of the cell so that the activity of a splice site encoded by the genomic DNA is reduced. Reducing the activity of a splice site can reduce aberrant splicing and restore normal splicing in the cell, for example, when the splice site is a cryptic splice site, or promote exon skipping, for example, when the splice site is a canonical splice site.
The term “contacting,” as used herein, refers to either contacting the cell directly with an assembled system or particle of the disclosure, by introducing into the cell one or more components of a system of the disclosure (or encoding nucleic acid that is expressed in the cell so that the system is assembled in situ), for example by introducing one or more encoding plasmids into the cell or contacting the cell with one or more viral particles capable of being taken up by the cell, or a combination thereof. When the components of the system are introduced as nucleic acids, preferably included are control elements that allow the nucleic acids to be expressed and assembled into a system of the disclosure in the cell.
Accordingly, contacting a cell with a system of the disclosure can comprise, for example, introducing the system to the cell by a physical delivery method, a vector delivery method (e.g., plasmid or virus), or a non-viral delivery method. Exemplary physical delivery methods include microinjection (e.g., by injecting a plasmid encoding a Cas12a gRNA and a Cas12a protein into the cell, injecting the Cas12a gRNA and mRNA encoding the Cas12a protein into the cell, or injecting a RNP comprising the Cas12a gRNA and Cas12a protein into the cell), electroporation (e.g., to introduce a plasmid encoding a Cas12a gRNA and a Cas12a protein into the cell or to introduce mRNA encoding a Cas12a protein and a Cas12a gRNA into the cell), and hydrodynamic delivery (e.g., using high pressure injection to introduce a plasmid encoding a Cas12a gRNA and a Cas12a protein into the cell or RNP comprising the Cas12a gRNA and Cas12a protein into the cell). Exemplary viral delivery methods include contacting the cell with a virus encoding the Cas12a gRNA and a Cas12a protein (e.g., an adeno-associated virus, an adenovirus, or a lentivirus). Exemplary non-viral delivery methods comprise contacting the cell with a particle containing the system, e.g., a particle as described in Section 6.6. Various methods for delivering a Cas12a gRNA and Cas12a protein to a cell or tissue of interest are described in U.S. Pat. No. 9,790,490, the contents of which are incorporated herein by reference in their entirety. See also, Lino et al., 2018, Drug Delivery, 25(1):1234-1257, which reviews several in vitro, ex vivo, and in vivo techniques for delivering CRISPR/Cas9 systems to cells in vitro, ex vivo, and in vivo. Such techniques can be adapted for delivering the Cas12a gRNAs and Cas12a proteins of the disclosure (e.g., by substituting a Cas12a system of the disclosure for the Cas9 gRNA and Cas9 protein).
Cells can come from a subject having a genetic disease (e.g., a stem cell) or derived from a subject having a genetic disease (e.g., an induced pluripotent stem (iPS) cell derived from a cell of the subject).
For example, the cell can be a human cell having a mutation in the CFTR gene, e.g., a 3272-26A>G mutation, a 3849+10kbC>T mutation, a IVS11+194A>G mutation, or a IVS19+11505C>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a DMD gene, e.g., a IVS9+46806C>T mutation, a IVS62+62296A>G mutation, a IVS1+36947G>A mutation, a IVS2+5591T>A mutation, or a IVS8-15A>G mutation, or a mutation in exon 50. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a HBB gene, e.g., a IVS2+645C>T mutation, a IVS2+705T>G mutation, or a IVS2+745C>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a FGB gene, e.g., a IVS6+13C>T mutation, a IVS4+792C>G mutation, or a IVS3+2552A>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a GLA gene, e.g., a IVS4+919G>A mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a LDLR gene, e.g., a IVS12+11C>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a BRIP1 gene, e.g., a IVS11+2767A>T mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a F9 gene, e.g., a IVS5+13A>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a CEP290 gene, e.g., a IVS26+1655A>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a COL2A1 gene, e.g., a IVS23+135G>A mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a USH2A gene, e.g., a IVS40-8C>G mutation, a IVS66+39C>T mutation, or a c.7595-2144A>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
As another example, the cell can be a human cell having a mutation in a GAA gene, e.g., a IVS1-13T>G mutation or a IVS6-22T>G mutation. Exemplary gRNAs for incorporation into a system useful for correcting the foregoing mutations are described in Section 6.3.4.
Contacting of a cell with a system or particle of the disclosure can be performed in vitro, ex vivo or can be performed in vivo (e.g., to treat a subject having a genetic disease in need of treatment for such disease). When performed in vitro or ex vivo, the methods of the disclosure can further comprise a step of introducing the contacted cell to a subject, for example to treat a subject in need of treatment for a genetic disease.
A system can be delivered via any suitable delivery vehicle. Examples of delivery vehicles include viruses (lentivirus, adenovirus) and particles (nanospheres, liposomes, quantum dots, nanoparticles, microparticles, nanocapsules, vesicles, polyethylene glycol particles, hydrogels, and micelles).
Exemplary viral delivery vehicles can include adeno associated virus (AAV), lentivirus, retrovirus, adenovirus, herpes simplex virus I or II, parvovirus, reticuloendotheliosis virus, and or other viral vector types, for example, using formulations and doses from, U.S. Pat. No. 8,454,972 (formulations, doses for adenovirus), U.S. Pat. No. 8,404,658 (formulations, doses for AAV) and U.S. Pat. No. 5,846,946 (formulations, doses for DNA plasmids) and from clinical trials and publications regarding the clinical trials involving lentivirus, AAV and adenovirus. The viruses can infect and transduce the cell in vivo, in vitro, or ex vivo.
Viral delivery vehicles can also be used in ex vivo and in vitro delivery methods, and the transduced cells can be administered to a subject in need of therapy. For ex vivo and in vitro applications, the transduced cells can be stem cells obtained or generated from (e.g., induced pluripotent stem cells generated from fibroblasts of) the subject in need of therapy.
The delivery vehicles can alternatively be particles. Particle delivery systems within the scope of the present disclosure may be provided in any form, including but not limited to solid, semi-solid, emulsion, or colloidal particles. It will be appreciated that reference made herein to particles or nanoparticles can be interchangeable, where appropriate. Cas12a protein mRNA and Cas12a gRNA may be delivered simultaneously using particles or lipid envelopes; for instance, a Cas12a gRNA and a Cas12a protein, e.g., as a complex, can be delivered via a particle as in Dahlman et al., WO2015089419 A2 and documents cited therein.
Delivery of a Cas12a gRNA and a Cas12a protein 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). 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, 2011, Journal of Drug Delivery, vol. 2011, Article ID 469679, doi:10.1155/2011/469679 for review).
For administration to a subject, the systems, delivery vehicles and transduced cells can be administered by intravenously, parenterally, intraperitoneally, subcutaneously, intramuscular injection, transdermally, intranasally, mucosally, by direct injection, stereotaxic injection, by minipump infusion systems, by convection, catheters, or other delivery methods to a cell, tissue, or organ of a subject in need. Such delivery may be either via a single dose, or multiple doses.
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 saline), a pharmaceutically-acceptable excipient, and/or other compounds known in the art. 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.
Frequency of administration is within the ambit of the medical or veterinary practitioner (e.g., physician, veterinarian), depending on usual factors including the age, sex, general health, other conditions of the patient or subject and the particular disease, condition or symptoms being addressed.
Specific cell types and delivery methods for use in the methods of the disclosure can be selected, for example, based upon the specific gene to be edited. For example, DMD is a genetic disorder characterized by progressive muscle degeneration and weakness and caused by splicing defects that inactivate the dystrophin protein. Recombinant AAV whose genome is engineered to encode gRNAs of the disclosure suitable for correcting splicing defects in the dystrophin gene (such as the gRNAs whose sequences are exemplified in Example 7) under the control of the muscle creatine kinase and desmin promoters, which can achieve high levels of expression in skeletal muscle (see, e.g., Naso et al., 2017, BioDrugs. 31(4): 317-334), can be delivered intramuscularly to subjects suffering from DMD. Below are illustrative embodiments for using the gRNA molecules of the disclosure to treat subjects suffering from cystic fibrosis.
Cystic fibrosis affects epithelial cells, and in some embodiments, the cell being contacted in the method can be an epithelial cell from a subject having a CFTR mutation, e.g., a pulmonary epithelial cell, e.g., a bronchial epithelial cell or an alveolar epithelial cell. The contacting can be performed ex vivo and the contacted cell can be returned to the subject's body after the contacting step. In other embodiments, the contacting step can be performed in vivo.
Cells from a subject having cystic fibrosis can be harvested from, for example, the epidermis, pulmonary tree, hepatobiliary tree, gastrointestinal tract, reproductive tract, or other organ. In an embodiment, the cell is reprogrammed to an induced pluripotent stem (iPS) cell. In an embodiment, the iPS cell is differentiated into airway epithelium, pulmonary epithelium, submucosal glands, submucosal ducts, biliary epithelium, gastrointestinal epithelium, pancreatic duct cells, reproductive epithelium, epidydimal cells, and/or cells of the hepatobiliary tree, e.g., clara cells, e.g., ciliated cells, e.g., goblet cells, e.g., basal cells, e.g., acinus cells, e.g., bronchioalveolar stem cell e.g., lung epithelial cells, e.g., nasal epithelial cells, e.g., tracheal epithelial cells, e.g., bronchial epithelial cells, e.g., enteroendocrine cells, e.g., Brunner's gland cells, e.g., epididymal epithelium. In an embodiment, the CFTR gene in the cell is corrected with a method described herein. In an embodiment, the cell is re-introduced into an appropriate location in the subject, e.g., airway, pulmonary tree, bile duct system, gastrointestinal tract, pancreas, hepatobiliary tree, and/or reproductive tract.
In some embodiments, an autologous stem cell can be treated ex vivo, differentiated into airway epithelium, pulmonary epithelium, submucosal glands, submucosal ducts, biliary epithelium, gastrointestinal epithelium, pancreatic duct cells, reproductive epithelium, epidydimal cells, and/or cells of the hepatobiliary tree, e.g., clara cells, e.g., ciliated cells, e.g., goblet cells, e.g., basal cells, e.g., acinus cells, e.g., bronchioalveolar stem cell e.g., lung epithelial cells, e.g., nasal epithelial cells, e.g., tracheal epithelial cells, e.g., bronchial epithelial cells, e.g., enteroendocrine cells, e.g., Brunner's gland cells, e.g., epididymal epithelium, and transplanted into the subject. In other embodiments, a heterologous stem cell can be treated ex vivo and differentiated into airway epithelium, pulmonary epithelium, submucosal glands, submucosal ducts, biliary epithelium, gastrointestinal epithelium, pancreatic duct cells, reproductive epithelium, epidydimal cells, and/or cells of the hepatobiliary tree, e.g., clara cells, e.g., ciliated cells, e.g., goblet cells, e.g., basal cells, e.g., acinus cells, e.g., bronchioalveolar stem cell e.g., lung epithelial cells, e.g., nasal epithelial cells, e.g., tracheal epithelial cells, e.g., bronchial epithelial cells, e.g., enteroendocrine cells, e.g., Brunner's gland cells, e.g., epididymal epithelium, and transplanted into the subject.
In some embodiments, the method described herein comprises delivery of the Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) to a subject having cystic fibrosis, by inhalation, e.g., via a nebulizer. In other embodiments, the method described herein comprises delivery of a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) by intravenous administration. In some embodiments, the method described herein comprises delivery of a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) by intraparenchymal injection into lung tissue. In other embodiments, the method described herein comprises delivery of a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) by intraparenchymal, intralveolar, intrabronchial, intratracheal injection into the trachea, bronchial tree and/or alveoli. In some embodiments, the method described herein comprises delivery of a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) by intravenous, intraparenchymal or other directed injection or administration to any of the following locations: the portal circulation, liver parenchyma, pancreas, pancreatic duct, bile duct, jejunum, ileum, duodenum, stomach, upper intestine, lower intestine, gastrointestinal tract, epididymis, or reproductive tract.
In some embodiments, a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) are delivered, e.g., to a subject having cystic fibrosis, by an AAV, e.g., via a nebulizer, or via nasal spray or inhaled, with or without accelerants to aid in absorption. In some embodiments, a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) are delivered, e.g., to a subject, by Sendai virus, adenovirus, lentivirus or other modified or unmodified viral delivery particle.
In some embodiments, a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) are delivered, e.g., to a subject, via a nebulizer or jet nebulizer, nasal spray, or inhalation. In some embodiments, a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein), are formulated in an aerosolized cationic liposome, lipid nanoparticle, lipoplex, non-lipid polymer complex or dry powder, e.g., for delivery via nebulizer, with or without accelerants to aid in absorption.
In some embodiments, a Cas12a gRNA and a Cas12a protein (or one or more nucleic acid(s) encoding the Cas12a gRNA and Cas12a protein) are delivered, e.g., to a subject having cystic fibrosis, via liposome GL67A. GL67A is described, e.g., at www.cfgenetherapy.org.uk/clinical/article/GL67A_pGM169_Our_first_clinical_trial_product; Eastman et al., 1997, Hum Gene Ther. 8(6):765-73.
The CFTR 3242-26A>G mutation is a point mutation that creates a new acceptor splice site causing the abnormal inclusion of 25 nucleotides within exon 20 of the CTFR gene. The resulting mRNA contains a frameshift in CFTR, producing a premature termination codon and consequent expression of a truncated, non-functional CFTR protein. A genome editing strategy using AsCas12a in combination with various Cas12a gRNAs to correct the splicing mutation was examined.
6.8.1.1. Materials and Methods
6.8.1.1.1. Oligonucleotides: Guide RNAs
AsCas12a gRNAs targeting a CFTR gene having a 3272-26A>G splicing mutation were designed with protospacer domains corresponding, with no mismatches, to the target domains set forth in Table 2. Each gRNA was designed to have a loop domain consisting of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25). The gRNAs are referred to in this Example according to their protospacer domains, e.g., crRNA+11.
#PAM sequence is underlined;
6.8.1.1.2. Other Oligonucleotides
Oligonucleotides for PCR, RT-PCR, cloning, site-directed mutagenesis, and sequencing were designed and prepared. These oligonucleotides are listed in Table 3.
6.8.1.1.3. Preparation of WT and Minigene Plasmids for CFTR 3272-26A>G Mutation
Minigene plasmid models were generated to mimic the splicing pattern of the CFTR gene corresponding to the region encompassing exons 19, 20 and intron 19. Plasmid pMG3272-26WT contained the wild-type allele; plasmid pMG3272-26A>G contained the mutated allele (see
A wild-type minigene representing the CFTR 3272-26 locus was cloned into plasmid pcDNA3 (Invitrogen®). Primers 1f, 2f, and 3r were used to PCR amplify CFTR DNA of the wild-type sequence of exons 19, 20 and intron 19 from the genome of HEK293T cells. The amplified DNA was cloned into plasmid pcDNA3 (Invitrogen®) to generate plasmid pMG3272-26WT containing the wild-type allele of exons 19, 20 and intron 19. Primers 4mf and 5mr were used to carry out site-directed mutagenesis of the wild-type minigene housed in pMG3272-26WT to generate the 3272-26A>G mutation, creating plasmid pMG3272-26A>G.
Sequences coding for guide RNAs were cloned into a commercially available plasmid, pY108 lentiAsCas12a (Addgene Plasmid 84739), using BsmBI restriction sites as previously described (Shalem, O., et al., 2014, Science, 343:84-87). The lenti virus-based plasmids allow for simultaneous delivery of the RNA-guided Cas12a protein and the gRNA to target cells in a single viral particle (see
6.8.1.1.4. Cell Lines
Human colorectal adenocarcinoma cells (Caco-2), human embryonic kidney cells HEK293T, and HEK293 cells were obtained from the American Type Culture Collection.
6.8.1.1.5. Transfection
Caco-2, HEK293T, and HEK293 cells stably expressing pMG3272-26WT (cell line HEK293/pMG3272-26WT) or 3272-26A>G (cell line HEK293/pMG3272-26A>G) were prepared. Cells were cultured in Dulbecco's modified Eagle's medium (DMEM; Life Technologies) supplemented with 10% fetal bovine serum (FBS; Life Technologies), 10 U/ml antibiotics (PenStrep, Life Technologies), and 2 mM L-glutamine at 37° C. in a 5% CO2 humidified atmosphere.
Cells were seeded at 1.5×105 cells/well in 24 well plates and transfected with 100 ng of Bgl-II linearized minigene plasmids pMG3272-26WT or pMG3272-26A>G complexed with polyethylenimine (PEI) and with 700 ng of plasmid pY108 lentiAsCas12a encoding both the AsCas12a protein and gRNA sequences. After 16 hours incubation, the cell medium was changed. Selection was carried out by exposing the transfected Caco-2 cells to 10 μg/ml puromycin; transfected HEK293T or HEK293 cells were selected by exposure to 2 μg/ml puromycin. Plasmid integration was selected for by the addition of 500 μg/ml of G418 added approximately 48 h after transfection. Single cell clones were isolated and characterized for the expression of the minigene constructs. Transfected cells were collected three days post-transfection.
6.8.1.1.6. Lentiviral Vector Production
Lentiviral particles were produced in HEK293T cells at 80% confluency in 10 cm plates. Ten μg of transfer vector pY108 lentiAsCas12a plasmid, 3.5 μg of VSV-G, and 6.5 μg of Δ8.91 packaging plasmid were transfected into the cells using PEI. After an overnight incubation, the medium was replaced with complete DMEM. The supernatant containing the viral particles was collected after 48 hours and filtered through a 0.45 μm PES filter. The lentiviral particles were concentrated and purified by ultracentrifugation for 2 hours at 4° C. and 150000×g with a 20% sucrose cushion. Pellets of lentivirus particles were resuspended in OptiMEM and aliquots stored at −80° C. Vector titres were measured as Reverse Transcriptase Units (RTU) using the SG-PERT method (see Casini, A., et al., 2015, J. Virol. 89:2966-2971).
6.8.1.1.7. Transduction
For transduction studies, HEK293/pMG3272-26WT, HEK293/pMG3272-26A>G and Caco-2 cells were seeded at a density of 3×105 cells/well in 12 well plates. Following an overnight incubation, the cells were transduced with 3 RTU of lentiviral vectors. Forty-eight hours later, the cells were selected with puromycin (2 μg/ml for HEK293 or 10 μg/ml for Caco-2 cells) and collected 10 days from transduction.
6.8.1.1.8. Transcript Analysis
The splicing pattern produced by the mutated or wild-type minigenes in transfected HEK293T cells, either altered or correct respectively, was evaluated by RT-PCR and sequencing analyses (see Beck, S., et al., 1999, Hum. Mutat., 14:133-144). RNA was extracted from the collected cells using TRIzol™ Reagent (Invitrogen®) and resuspended in DEPC-ddH2O. cDNA was obtained from 500 ng of RNA using RevertAid Reverse Transcriptase (Thermo Scientific) according to the manufacturer's protocol. Target regions were amplified by PCR with Phusion High Fidelity DNA Polymerase (Thermo Fisher).
6.8.1.1.9. Detection of Nuclease Induced Genomic Mutations
Genomic DNA was extracted using QuickExtract DNA extraction solution (Epicentre) and the target locus amplified by PCR using Phusion High Fidelity DNA Polymerase (Thermo Fisher). In order to evaluate any indels resulting from the cleavage of a single gRNA, the purified PCR products were sequenced and analyzed using TIDE (see Table 3 primers 7f and 8r; Brinkman, E. K., et al., 2014, Nucleic Acids Res., 42: 1-8) or SYNTHEGO ICE software (see Hsiau, T., et al., 2018, bioRxiv, January 20, 1-14). In some studies, DNA editing was also measured using a T7 Endonuclease 1 (T7E1) assay (New England BioLabs) following manufacturer's instructions and as previously described (see Petris, G., et al., 2017, Nat. Commun. 8:1-9).
6.8.1.1.10. GUIDE-seq
Approximately 2×105 HEK293T cells were transfected using Lipofectamine 3000 transfection reagent (Invitrogen) with 1 μg lenti Cas12a plasmid pY108 and 10 pmol of dsODNs designed according to the original GUIDE-seq protocol (see Tsai, S. Q., et al., 2015, Nat. Biotechnol., 33:187-198). One day post transfection, the cells were detached and selected with 2 μg/ml puromycin. Four days post transfection, the cells were collected and genomic DNA extracted using DNeasy Blood and Tissue kit (Qiagen) following manufacturer's instructions. The isolated genomic DNA was sonicated and sheared to an average length of 500 bp using a Bioruptor Pico sonication device (Diagenode). Library preparation, sequencing, and analysis was carried out using methods known to those of skill in the art (see, for example, Montagna, C., et al., 2018, Mol. Ther. Nucleic Acids, 12:453-462; Casini, A., et al., 2018, Nat. Biotechnol., 36:265-271).
6.8.1.1.11. Targeted Deep Sequencing
The locus of interest (3272-26A>G/4218insT) was amplified from genomic DNA extracted from the transfected cells 14 days after transduction with lentiAsCas12a-crRNA+11 or a control (CTR) using Phusion high-fidelity polymerase (Thermo Scientific) and primers 7f and 8r. Amplicons were indexed by PCR using Nextera indexes (Illumina), quantified with the Qubit dsDNA High Sensitivity Assay kit (Invitrogen), pooled in near-equimolar concentrations, and sequenced on an Illumina Miseq system using an Illumina Miseq Reagent kit V3-150 cycles (150 bp single read). Raw sequencing data (FASTQ files) were analyzed using CRISPResso online tool (see Pinello, L., et al., 2016, Nat. Biotechnol., 34:695-697; windows size=3, minimum average read quality (phred33 scale)=30, minimum single bp quality (phred33 scale)=10).
6.8.1.2. Results
The splicing pattern of pMG3272-26A>G was evaluated after its co-transfection with the designed gRNAs. Increased levels of correctly spliced product resulted after editing by AsCas12a in combination with various gRNAs (
To further validate the activity of AsCas12a with selected gRNAs within a more physiological chromatin context, the splicing correction of CFTR intron 19 in HEK293 cells stably transfected with the pMG3272-26A>G minigene (HEK293/3272-26A>G) was tested. AsCas12a-crRNA+11 resulted in the formation of numerous correct transcripts, >60%, from the pMG3272-26A>G transgene (
TIDE analysis of the integrated minigenes, following editing with AsCas12a-crRNA+11, revealed a heterogeneous pool of deletions (
A large majority of CF patients are compound heterozygous for the 3272-26A>G mutation. As such, it was important to evaluate potential off-target effects of AsCas12a-crRNA+11, for example, potential modification within the wild-type allele. The cleavage properties of the AsCas12a-crRNA+11 were analyzed in stable cell lines expressing either pMG3272-26WT or pMG3272-26A>G (HEK293/3272-26WT and HEK293/3272-26A>G cells respectively). As shown in
The specificity of the AsCas12a-crRNA+11 delivered by lentiviral vectors towards the wild-type intron was further confirmed in Caco-2 epithelial cells endogenously expressing the wild-type CFTR gene. Long term nuclease expression (10 days after transduction), which has been demonstrated to highly favor non-specific cleavages (Petris, G., et al., 2017, Nat. Commun. 8:1-9), did not generate any unspecific CFTR editing above TIDE background levels (about 1%; see Brinkman, E. K., et al., 2014, Nucleic Acids Res. 42:1-8); whereas AsCas12a-crRNA+11/wt efficiently edited the CFTR gene (more than 80%;
To exclude splicing alterations following potential wild-type intronic cleavages, the splicing pattern was evaluated in HEK293/3272-26WT and Caco-2 cells. No major alterations were observed following AsCas12a treatment in combination with either crRNA+11/wt or crRNA+11 (
The specificity of the AsCas12a-crRNA+11 editing was also tested in terms of off-target cleavages by a genome-wide survey, GUIDE-seq (Nissim-Rafinia, M. et al., 2000, Hum. Mol. Genet. 9:1771-1778, Kashima, T. et al., 2007, Hum. Mol. Genet. 16, 3149-3159). Off-target profiling of AsCas12a-crRNA+11 genome editing in HEK293/3272-26A>G cells (Tsai, S. Q., et al., 2015, Nat. Biotechnol. 33:187-198; Kleinstiver, B. P., et al., 2016, Nat. Biotechnol. 34:869-874) showed very high specificity, as demonstrated by exclusive editing of the 3272-26A>G CFTR locus, while no non-specific cleavages in the second allele, or any other genomic loci, could be detected (
6.8.2. Example 2: CRISPR-Cas12a Correction of 3272-26A>G Splicing Mutation in Organoids
Human organoids represent a near-physiological model for translational research (Fatehullah, A., et al., 2016, Nat. Cell Biol., 18:246-254). Intestinal organoids from CF patients are valuable tools to evaluate CFTR activity and functional recovery (Dekkers, J. F., et al., 2013, Nat. Med., 19:939-945; Dekkers, J. F., et al., 2016, Sci. Transl. Med. 8:344ra84; Sato, T., et al., 2011, Gastroenterology, 141:1762-1772).
The rescue potential of the CF phenotype by AsCas12a-crRNA+11 in human intestinal organoids compound heterozygous for the 3272-26A>G mutation (3272-26A>G/4218insT) was examined.
6.8.2.1. Materials and Methods
6.8.2.1.1. Human Intestinal Organoids Culture and Transduction
Human intestinal organoids of human cystic fibrosis subjects determined to be compound heterozygous for the 3272-26A>G splicing mutation (3272-26A>G/4218insT; n=1, CF-86) were cultured (see Dekkers, J. F., et al., 2013, Nat. Med., 19:939-945).
Cultured organioids were separated into single cells using trypsin 0.25% EDTA (Gibco). Approximately 3 to 4×104 single cells were resuspended with 25 μl of lentiviral vector (0.25-1 RTU) and incubated for 10 min at 37° C. (see Vidovic, D., et al., 2016, Am. J. Respir. Crit. Care Med., 193:288-298). An equal volume of Matrigel (Corning) was added to the cell and vector solution and the mix plated in a 96-well plate. After polymerisation of the Matrigel drops at 37° C. for 7 minutes, the cells were covered with 100 μl of complete organoid medium (Dekkers, J. F., et al., 2013, Nat. Med., 19:939-945) containing 10 μM of Rock inhibitor (Y-27632 2HCI, Sigma Aldrich, Y0503) for three days to ensure optimal outgrowth of single stem cells (see Sato, T., et al., 2011, Gastroenterology, 141:1762-1772). The medium was replaced every 2-3 days until the day of organoid analysis.
6.8.2.1.2. Forskolin Induced Swelling (FIS) Assay and Analysis of CFTR Activity in Intestinal Organoids
Fourteen days after viral vector transduction, the organoids were incubated for 30 minutes with 0.5 μM calcein-green (Invitrogen, C3-100MP) and analysed by live cell confocal microscopy with a 5× objective (LSM800, Zeiss; Zen Blue software, version 2.3). The steady-state area of the organoids was determined by calculating the absolute area (xy plane, μm2) of each organoid using ImageJ software through the Analyse Particle algorithm. Organoid particles with an area less than 1500 μm were considered defective and were excluded from the analysis. Data were averaged for each different run and plotted in a box plot representing means±SD.
The FIS assay was performed by stimulation of the organoids with 5 μM of forskolin. The effect of the forskolin on the organoids was analysed by live cell confocal microscopy at 37° C. for 60 min, with one image taken every 10 min. The area of each organoid (xy plane) at each time point was calculated using ImageJ, as described above. Statistical analyses were performed by ordinary one-way analysis of variance (ANOVA) in GraphPad Prism version 6. Differences in the size of the organoids were considered statistically different at P<0.05.
6.8.2.2. Results
The splicing pattern of CFTR intron 19 in the crRNA control and untreated organoids showed two transcript variants (
Deep sequencing analysis revealed 40.25% indels in the CFTR locus (39.77% within the 3272-26A>G allele and 0.48% within the other allele,
In agreement with previous reports (van Overbeek, M., et al., 2016, Mol. Cell, 63, 63:633-646) and despite the heterogeneity of the editing observed, the repair events in patient's organoids were largely similar to those observed in the pMG3272-26A>G model, with the 18 nucleotide deletion being the most frequent repair observed (compare
Lumen formation in intestinal organoids (swelling) depends on the activity of the CFTR anion channel (Dekkers, J. F., et al., 2013, Nat. Med. 19, 939-945; schematized in
Another assay used to evaluate CFTR activity is the Forskolin Induced Swelling (FIS) assay (Dekkers, J. F., et al., 2013, Nat. Med., 19, 939-945;
The AsCas12a-crRNA+11 modifications of the 3272-26A>G defect in CFTR organoids results in the efficient repair of the intron 19 splicing defect, leading to the full recovery of endogenous CFTR protein.
The CFTR 3849+10kbC>T mutation creates a novel donor splice site inside intron 22 of the CFTR gene, leading to the insertion of the new cryptic exon of 84 nucleotides which results in an in-frame stop codon and consequent production of a truncated non-functional CFTR protein. A genome editing strategy using AsCas12a in combination with various Cas12a gRNAs to correct the splicing mutation was examined.
6.8.3.1. Materials and Methods
6.8.3.1.1. Oligonucleotides: Guide RNAs
An AsCas12a gRNA targeting a CTFR gene having a 3849+10KbC>T splicing mutation was designed with a protospacer domains corresponding, with no mismatches, to the target domain set forth in Table 4. An AsCas12a gRNA targeting the wild-type sequence was also designed. Each gRNA was designed to have a loop domain consisting of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25). The gRNAs are referred to in this Example according to their protospacer domains, e.g., crRNA+14.
ACCATTTTA
GCCATTTTA
#PAM is underlined;
6.8.3.1.2. Other Oligonucleotides
Oligonucleotides for PCR, RT-PCR, cloning, site-directed mutagenesis, and sequencing were designed and prepared. These oligonucleotides are listed in Table 5.
6.8.3.1.3. Preparation of WT and Minigene Plasmids for CFTR 3849+10KbC>T Mutation
Minigene plasmid models were generated to mimic the splicing pattern of the CFTR gene corresponding to the region encompassing exons 22, 23 and part of intron 22. Plasmid pMG3849+10 kbWT contained the wild-type allele; plasmid pMG3849+10kbC>T contained the mutated allele (
A wild-type minigene representing the CFTR 3849+10 kb locus was cloned into plasmid pcDNA3 (Invitrogen). Primers 9f, 10f, 11f, 12r, 13r and 14r were used to PCR amplify CFTR DNA of the wild-type sequence of exons 22, 23 and part of intron 22 from the genome of HEK293T cells. The amplified DNA was cloned into plasmid pcDNA3 to generate plasmid pMG3849+10 kbWT containing the wild-type allele of exons 22, 23 and part of intron 22. Primers 15mf and 16mr were used to carry out site-directed mutagenesis of the wild-type minigene housed in pMG3849+10 kbWT to generate the 3849+10kbC>T mutation, creating plasmid pMG3849+10kbC>T.
Sequences coding for guide RNAs (Table 4) were cloned into a commercially available plasmid to generate pY108 lentiAsCas12a (Addgene Plasmid 84739) using BsmBI restriction sites as described above (see
6.8.3.1.4. Cell Lines
Human colorectal adenocarcinoma cells (Caco-2), and human embryonic kidney cells HEK293T, and HEK293 cells were obtained from the American Type Culture Collection.
6.8.3.1.5. Transfection
Caco-2, HEK293T, and HEK293 cells stably expressing pMG3849+10 kbWT (cell line HEK293/pMG3849+10 kbWT) or 3849+10kbC>T (cell line HEK293/pMG3849+10kbC>T) were prepared and cultured as described in Example 1
Cells were seeded at 1.5×105 cells/well in 24 well plates and transfected with 100 ng of Bgl-II linearized minigene plasmids pMG3849+10 kbWT or pMG3849+10kbC>T complexed with polyethylenimine (PEI) and with 700 ng of plasmid pY108 lentiAsCas12a encoding both the Cas nuclease and gRNA sequences. Cell culture, transfection, and selection for plasmid integration was carried out as described in Example 1. Single cell clones were isolated and characterized for the expression of the minigene construct. Transfected cells were collected three days post-transfection.
6.8.3.1.6. Lentiviral Vector Production
Lentiviral particles were produced in HEK293T cells as described in Example 1.
6.8.3.1.7. Transduction
For transduction studies, HEK293/pMG3849+10 kbWT, HEK293/pMG3849+10kbC>T and Caco-2 cells were seeded at a density of 3×105 cells/well in 12 well plates and transduced as described in Example 1.
6.8.3.1.8. Transcript Analysis
The splicing pattern produced by the mutated or wild-type minigenes, either altered or correct respectively, was evaluated by RT-PCR and sequencing analyses in transfected HEK293T cells (see Beck, S., et al., 1999, Hum. Mutat., 14:133-144). RNA was extracted and target regions were amplified by RT-PCR as previously described. Oligonucleotides are listed in Table 5.
6.8.3.1.9. Detection of Nuclease Induced Genomic Mutations
Genomic DNA was extracted and the target locus amplified by PCR as described in Example 1. The purified PCR products were sequenced and analyzed using TIDE (see Table 4 primers 18f and 19r; Brinkman, E. K., et al., 2014, Nucleic Acids Res., 42: 1-8) or SYNTHEGO ICE software (see Hsiau, T., et al., 2018, bioRxiv, January 20, 1-14). In some studies, DNA editing was also measured using a T7 Endonuclease 1 (T7E1) assay (New England BioLabs) following manufacturer's instructions and as previously described (see Petris, G., et al., 2017, Nat. Commun. 8:1-9).
6.8.3.1.10. GUIDE-seq
Approximately 2×105 HEK293T cells were transfected using Lipofectamine 3000 transfection reagent (Invitrogen) with 1 μg lenti Cas12a plasmid pY108 and 10 pmol of dsODNs designed according to the original GUIDE-seq protocol (see Tsai, S. Q., et al., 2015, Nat. Biotechnol., 33:187-198). Cell culture, genomic DNA extractions and shearing, library construction, sequencing, and analysis was carried out using methods known to those of skill in the art (see Example 1; also Montagna, C., et al., 2018, Mol. Ther. Nucleic Acids, 12:453-462; Casini, A., et al., 2018, Nat. Biotechnol., 36:265-271).
6.8.3.1.11. Targeted Deep Sequencing
The locus of interest, 3849+10Kb C>T/F508, was amplified from genomic DNA extracted from human intestinal organoids 14 days after transduction with lentiAsCas12a-crRNA+14 or a control (CTR) using Phusion high-fidelity polymerase (Thermo Scientific) and primers 18f and 19r. Amplicons were indexed by PCR, quantified, pooled, sequenced on an Illumina Miseq system, and raw sequencing data (FASTQ files) were analysed as described in Example 1.
6.8.3.2. Results
The minigene model containing exon 22, part of intron 22 and exon 23 (pMG3849+10kbWT and pMG3849+10kbC>T; see
To further verify AsCas12a-crRNA+14 specificity, and to examine genome-wide off-target activity, GUIDE-seq analysis was performed in HEK293T cells. The studies revealed a complete absence of sequence reads in the CFTR locus or in any other off-target site; all 631 sequencing reads corresponding to spontaneous DNA breaks were indicative of the proper execution of the GUIDE-seq assay (
The rescue potential of the CF phenotype by AsCas12a-crRNA+14 in human intestinal organoids compound heterozygous for the 3849+10kbC>T mutation (3849+10kbC>T/ΔF508) was examined.
6.8.4.1. Materials and Methods
6.8.4.1.1. Human Intestinal Organoids Culture and Transduction
Human intestinal organoids of human cystic fibrosis subjects determined to be compound heterozygous for the 3849+10Kb C>T mutation (3849+10Kb C>T/F508, n=1, CF-110) were cultured (see Dekkers, J. F., et al., 2013, Nat. Med., 19:939-945). Cultured organoids were treated and transduced as previously described in Example 2.
6.8.4.1.2. Forskolin Induced Swelling (FIS) Assay and Analysis of CFTR Activity in Intestinal Organoids
Fourteen days after viral vector transduction, the organoids were incubated for 30 minutes with 0.5 μM calcein-green (Invitrogen, C3-100MP) and analyzed by live cell confocal microscopy with a 5× objective (LSM800, Zeiss; Zen Blue software, version 2.3). The steady-state area of the organoids was determined by calculating the absolute area (xy plane, μm2) of each organoid using ImageJ software through the Analyse Particle algorithm. Organoid particles with an area less than 3000 μm were considered defective and were excluded from the analysis. Data were averaged for each different run and plotted in a box plot representing means±SD. The FIS assay was performed by stimulation of the organoids and analysis carried out by live cell confocal microscopy and statistical analyses performed as described above.
6.8.4.2. Results
Efficient and precise correction of the CFTR 3849+10kbC>T splicing defect was obtained by using AsCas12a combined with a single allele specific crRNA in patient organoids. Lentiviral delivery of AsCas12a-crRNA+14 produced 31% indels in the CFTR locus (
CRISPR-Cas9 has been the traditional system of choice for gene editing and it was of interest to compare the ability of a SpCas9 system, utilizing multiple sgRNAs, with the AsCas12a system, utilizing single gRNAs, to edit the CFTR 3272-26A>G mutation.
6.8.5.1. Materials and Methods
SpCas9 sgRNAs targeting a CFTR gene having a 3272-26A>G splicing mutation were designed. Target domains are shown in Table 6.
GGtta
AGaat
Gact
Gtac
AGtgt
AGaaa
Gaaa
AGgca
#PAM is underlined;
Sequences encoding sgRNAs were cloned into lentiCRISPR v1 plasmid (Addgene Plasmid 49535), which expresses SpCas9, using BsmBI restriction sites. Lentiviral particle production, transduction, and CFTR gene editing analysis was performed as in Example 1.
6.8.5.2. Results
The splicing pattern of the pMG3272-26A>G was evaluated after its co-transfection with the designed sgRNAs in combination with SpCas9 (
Unexpectedly, when the splicing correction of CFTR intron 19 in HEK293 cells stably transfected with the pMG3272-26A>G minigene (HEK293/3272-26A>G) was tested, all of the SpCas9-sgRNA pairs failed to correct the splicing defect, suggesting inefficient cleavage at the chromosomal level (
The ability of a SpCas9 system, utilizing multiple sgRNAs, with the AsCas12a system, utilizing single gRNAs, to edit the CFTR 3849+10KbC>T mutation in cells and organoids was compared.
6.8.6.1. Materials and Methods
SpCas9 sgRNAs targeting a CFTR gene having a 3849+10KbC>T splicing mutation were designed. Target domains are shown in Table 7.
TGGatc
AGGtga
TGGtac
#PAM is underlined;
Sequences encoding sgRNAs were cloned into lentiCRISPR v1 plasmid (Addgene Plasmid 49535). Lentiviral particle production, transduction, cell-based CFTR gene editing studies, and organoid studies were performed as in Examples 3 and 4.
6.8.6.2. Results
The more conventional strategy to delete the 3849+10kbC>T mutation by SpCas9 with two sgRNAs was carried out in HEK293 and Caco-2 cells (
In patient-derived organoids, the sgRNA-95/+119 appeared to be the best sgRNA pair to obtain efficient intron deletion and splicing correction. Nevertheless, in patient organoids up to 33% of the CFTR 3849+10 kb locus deletion induced an increase of the area of the organoids, which is significantly lower than the area measured after lentiviral delivery of the wild-type CFTR cDNA. (
In contrast, the correction of the CFTR 3849+10kbC>T splicing defect was efficiently and precisely obtained by using AsCas12a combined with a single allele specific crRNA in patient organoids (Example 4), similarly to the splicing repair of the 3272-26A>G variant (Example 2). The AsCas12a strategy proved superior to the conventional SpCas9 induced genetic deletion obtained in combination with multiple sgRNAs.
6.8.7.1. Materials and Methods
6.8.7.1.1. gRNA Design
The CEP290 IVS26+1655A>G mutation is associated with Leber congenital amaurosis (LCA). A Cas12a gRNA molecule having a targeting sequence corresponding to a target domain in a CEP290 gene having the IVS26+1655A>G mutation is designed (Table 8), with no mismatches between the between the targeting sequence and the complement of the target domain. The loop domain, 5′ to the target domain in the Cas12a gRNA molecule, consists of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25).
CCCCAGTTGTAAT
Using standard golden-gate assembly, a DNA sequence encoding the Cas12a gRNA is cloned into a pY108 lentiAsCas12a plasmid engineered to encode AsCas12a RR to provide a plasmid encoding AsCas12a RR and the Cas12a gRNA. A pY108 lentiAsCas12a plasmid encoding ASCas12a RR and a scramble-truncated gRNA is also prepared for use as a control.
6.8.7.1.2. Minigene Generation
PCR with primers located in CEP290 introns 25 (forward GGGGACAAGTTTGTACAAAAAAGCAGGCTTCGGCCGCTCTTTCTCAAAAGTGGC) (SEQ ID NO: 168) and 27 (reverse GGGGACCACTTTGTACAAGAAAGCTGGGTGCTTGGTGGGGTTAAGTACAGG) (SEQ ID NO: 169) is performed on genomic DNA from a healthy individual and the PCR product is cloned into a pDONR vector using the Gateway system. Via site-directed mutagenesis, the c.2991+1655A>G mutation is introduced using primers mut for (CACCTGGCCCCAGTTGTAATTGTGAGTATCTCATACCTATCCC) (SEQ ID NO: 170) and mut rev (GGGATAGGTATGAGATACTCACAATTACAACTGGGGCCAGGTG) (SEQ ID NO: 171). Both pDONR vectors (mutant and wild-type (WT)) are sequenced and cloned into the destination vector pCi-Neo-Rho-Splicing vector, which allows the cloning of the CEP290 fragment of interest between exons 3 and 5 of RHO under the control of the cytomegalovirus immediate-early promoter as previously described (Shafique, S. et al., 2014, PLoS One, 9:e100146), generating pMG CEP290 WT IVS26+1655A or pMG CEP290 LCA IVS26+1655A>G minigene constructs, as described in Garanto, et al., 2015, Int J Mol Sci, 16(3):5285-5298.
6.8.7.1.3. Cell Culture
HEK293T and HEK293 cells are obtained from American Type Culture Collection (ATCC; www.atcc.org). HEK293T cells and HEK293 cells stably expressing pMG CEP290 WT IVS26+1655A or pMG CEP290 LCA IVS26+1655A>G are cultured in Dulbecco's modified Eagle's medium (DMEM; Life Technologies) supplemented with 10% fetal bovine serum (FBS; Life Technologies), 10 U/ml antibiotics (PenStrep, Life Technologies) and 2 mM L-glutamine at 37° C. in a 5% CO2 humidified atmosphere.
IVS26 patient fibroblasts as described in Burnight, et al., 2014, Gene Ther. 21:662-672 and in Maeder et al., 2019, Nature Medicine, doi: 10.1038/s41591-018-0327-9 are obtained and maintained in Gibco DMEM/F12+glutamax (Thermofisher), supplemented with 1% penicillin/streptomycin, 1% non-essential amino acids and 15% fetal bovine serum.
6.8.7.1.4. Transfection and Transduction
Transfection of HEK293T cells
Transfection is performed in HEK293T cells seeded (150,000 cells/well) in a 24 well plate. Cells are transfected using PEI (polyethylenimine) with 100 ng of minigene plasmids and 700 ng of the plasmid encoding for AsCas12a RR and the Cas12a gRNA.
Stable minigene cell lines (HEK293/CEP290 WT IVS26+1655A and HEK293/CEP290 LCA IVS26+1655A>G) are produced by transfection with linearized minigene plasmids (pMG CEP290 WT IVS26+1655A or pMG CEP290 LCA IVS26+1655A>G) in HEK293 cells. Cells are selected with 500 μg/ml of G418, 48 h after transfection. Single cell clones are isolated and characterized for the expression of the minigene construct.
Lentiviral particles are produced in HEK293T cells at 80% confluency in 10 cm plates. 10 μg of transfer vector (pY108 lentiAsCas12a RR) plasmid, 3.5 μg of VSV-G and 6.5 μg of Δ8.91 packaging plasmid are transfected using PEI. After over-night incubation, the medium is replaced with complete DMEM. The viral supernatant is collected after 48 h and filtered through a 0.45 μm PES filter. Lentiviral particles are concentrated and purified with a 20% sucrose cushion by ultracentrifugation for 2 hours at 4° C. and 150,000×g. Pellets are resuspended in an appropriate volume of OptiMEM. Aliquots are stored at −80° C. Vector titers are measured as Reverse Transcriptase Units (RTU) by SG-PERT method (see Casini, A., et al., 2015, J. Virol. 89:2966-2971). For transduction studies, HEK293 cells stably expressing the minigene constructs and IVS26 patient fibroblast cells are seeded (300,000 cells/well) in a 12 well plate, and the day after seeding the cells are transduced with 1-5 RTU of lentiviral vectors. Approximately 48 hours later, cells are selected with puromycin (2-10 μg/ml) and collected 10-14 days from transduction.
6.8.7.1.5. RT-PCR and Transcriptional Analysis
RNA is extracted using TRIzol™ Reagent (Invitrogen) and resuspended in DEPC-ddH2O. cDNA is obtained using 500 ng of RNA and RevertAid Reverse Transcriptase (Thermo Scientific), according to the manufacturer's protocol. Target regions are amplified by PCR with Phusion High Fidelity DNA Polymerase (Thermo Fisher) using primers ex26 for (TGCTAAGTACAGGGACATCTTGC (SEQ ID NO: 172)) and ex27rev (AGACTCCACTTGTTCTTTTAAGGAG (SEQ ID NO: 173)) for the CEP290 minigene. PCR products are separated on a 1-2% agarose gel. Fragments representing correctly and aberrantly spliced CEP290 are excised from the gel, purified using Nucleospin Extract II isolation kit (MACHEREY-NAGEL) and sequenced.
6.8.7.2. Results
Minigene transcripts are analyzed two to three days after transfection and exhibit correct and aberrant splicing for the pMG CEP290 WT IVS26+1655A and the plasmids, respectively. Abundant inclusion of the 128 bp cryptic exon is also observed in control cells treated with pY108 lentiAsCas12a RR having a scramble-truncated gRNA, while this aberrant splicing is decreased in transfected cells treated with the CEP290 gRNA. These results are reproduced in HEK293 cells stably transfected with the pMG CEP290 LCA IVS26+1655A>G minigene and transduced with the CEP290 gRNA/AsCas12a lentiviral vector, showing a splicing correction proportional to the gene editing efficiency. CEP290 mRNA transcripts are analyzed 10-14 days after transduction of IVS26+1655A>G and primary patient fibroblasts show that the wild-type transcript is significantly increased and the mutant transcript is decreased relative to the control.
6.8.8.1. Materials and Methods
6.8.8.1.1. gRNA Design
The USH2A c.7595-2144A>G mutation is a deep intronic mutation that causes aberrant splicing at a cryptic 5′ splice site and a cryptic 3′ splice site. The mutation is associated with Usher syndrome, Type II (Slijkerman et al., 2016, Mol. Ther. Nucleic Acids, 5(10):e381). Cas12a gRNA molecules having targeting sequences corresponding to the target domains in USH2A shown in Table 9 are designed, with no mismatches between the between the targeting sequence and the complement of the target domain. The Cas12a gRNAs in this example are designed to edit the USH2A gene near the cryptic 5′ splice site (the top four target domains listed in Table 9) or the cryptic 3′ spice site (the bottom four target domains listed in Table 9). The loop domain, 5′ to the target domain in the Cas12a gRNA molecules, consists of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25).
tttc-ttaaagatgatctcttacCTTGG
TTTC-
ATTG-
ctta-
atta-
ATTC-
CTTG-
TTTA-
Using standard golden-gate assembly, DNA sequences encoding the Cas12a gRNAs are cloned into pY108 lentiAsCas12a plasmids engineered to encode AsCas12a RR, AsCas12a RVR, or other Cas12a proteins recognizing the PAM sequences upstream of the target domains to provide plasmids encoding a Cas12a protein and a single Cas12a gRNA. pY108 lentiAsCas12a plasmids encoding a Cas12a protein and a scramble-truncated gRNA are also prepared for use as controls.
6.8.8.1.2. Minigene Generation
A plasmid containing the genomic region of RHO encompassing exons 3-5 cloned into the EcoRI/SalI sites in the pCI-NEO vector (Gamundi, et al., 2008, Hum Mutat 29:869-878) is adapted to the Gateway cloning system, as previously described (Yariz, et al., 2012, Am J Hum Genet, 91:872-882). Gateway cloning technology is used to insert the 152 bp human USH2A pseudoexon 40 (PE40, wild-type and mutant) together with 722 bp of 5′-flanking and 636 bp of 3′-flanking intronic sequences to obtain pMG USH2A-PE40 wt and pMG USH2A-PE40A>G as described in Slijkerman et al., 2016, Mol. Ther. Nucleic Acids, 5(10):e381.
6.8.8.1.3. Cell Culture
HEK293T and HEK293 cells are obtained from American Type Culture Collection (ATCC; www.atcc.org). HEK293T cells and HEK293 cells stably expressing pMG USH2A-PE40 wt or pMG USH2A-PE40A>G are cultured in Dulbecco's modified Eagle's medium (DMEM; Life Technologies) supplemented with 10% fetal bovine serum (FBS; Life Technologies), 10 U/ml antibiotics (PenStrep, Life Technologies) and 2 mM L-glutamine at 37° C. in a 5% CO2 humidified atmosphere.
Primary fibroblasts of an USH2 patient with compound heterozygous USH2A mutations are cultured in DMEM (Sigma-Aldrich D0819) supplemented with 20% fetal bovine serum (Sigma-Aldrich F7524), 1% sodium pyruvate (Sigma-Aldrich S8636) and 1% penicillin-streptomycin (Sigma-Aldrich P4333).
6.8.8.1.4. Transfection and Transduction
Transfection is performed in HEK293T cells seeded (150,000 cells/well) in a 24 well plate. Cells are transfected using PEI (polyethylenimine) with 100 ng of minigene plasmids and 700 ng of the plasmids encoding for the Cas12a proteins and the Cas12a gRNAs.
Stable minigene cell lines (HEK293/pMG USH2A-PE40 wt and HEK293/pMG USH2A-PE40A>G) are produced by transfection of linearized minigene plasmids (pMG USH2A-PE40 wt or pMG USH2A-PE40A>G) in HEK293 cells. Cells are selected with 500 μg/ml of G418 48 h after transfection. Single cell clones are isolated and characterized for the expression of the minigene constructs.
Lentiviral particles are produced in HEK293T cells at 80% confluency in 10 cm plates. Ten μg of transfer vector plasmid (pY108 lentiAsCas12a plasmids encoding the Cas12a proteins and the Cas12a gRNAs), 3.5 μg of VSV-G and 6.5 μg of Δ8.91 packaging plasmid are transfected into HEK293T cells using PEI. After over-night incubation the medium is replaced with complete DMEM. The viral supernatants are collected after 48 h and filtered through a 0.45 μm PES filter. Lentiviral particles are concentrated and purified with a 20% sucrose cushion by ultracentrifugation for 2 hours at 4° C. and 150,000×g. Pellets are resuspended in an appropriate volume of OptiMEM. Aliquots are stored at −80° C. Vector titers are measured as Reverse Transcriptase Units (RTU) by SG-PERT method (see Casini, A., et al., 2015, J. Virol. 89:2966-2971). For transduction studies, HEK293 cells stably expressing the minigene constructs and USH2 patient fibroblast cells are seeded (300,000 cells/well) in a 12 well plate, and the day after seeding the cells are transduced with 1-5 RTU of the lentiviral vectors. Approximately 48 hours later, cells are selected with puromycin (2-10 μg/ml) and collected 10-14 days from transduction.
6.8.8.1.5. RT-PCR and Transcriptional Analysis
RNA is extracted using TRIzol™ Reagent (Invitrogen) and resuspended in DEPC-ddH2O. cDNA is obtained using 500 ng of RNA and RevertAid Reverse Transcriptase (Thermo Scientific), according to the manufacturer's protocol. Target regions are amplified by PCR with Phusion High Fidelity DNA Polymerase (Thermo Fisher) using primers minigene-USH2A forward (CGGAGGTCAACAACGAGTCT) (SEQ ID NO: 184) and reverse (AGGTGTAGGGGATGGGAGAC (SEQ ID NO: 185)). For the splicing correction experiments in fibroblasts, part of the USH2A cDNA is amplified under standard PCR conditions using Q5 polymerase and primers 5′-GCTCTCCCAGATACCAACTCC-3′ (SEQ ID NO: 186) and 5′-GATTCACATGCCTGACCCTC-3′ (SEQ ID NO: 187) designed for exons 39 and 42, respectively. PCR products are separated on a 1-2% agarose gel. Fragments representing correctly and aberrantly spliced USH2A are excised from the gel, purified using Nucleospin Extract II isolation kit (MACHEREY-NAGEL) and sequenced.
6.8.8.2. Results
Minigene transcripts are analyzed two to three days after transfection and exhibit correct and aberrant splicing for the pMG USH2A-PE40 wt or pMG USH2A-PE40A>G plasmids, respectively. Abundant inclusion of the 152 bp PE40 cryptic exon is also observed in control cells treated with a Cas12a protein and a scramble-truncated gRNA, while this aberrant splicing is decreased in cells treated with at least some of the USH2A PE40 targeting gRNAs. Results are confirmed in HEK293T cells stably transfected with the pMG USH2A-PE40A>G minigene and transduced with USH2A PE40 targeting gRNA/AsCas12a protein lentiviral vectors, showing a splicing correction proportional to the gene editing efficiency. USH2A mRNA transcripts are analyzed 10-14 days after transduction of USH2 patient fibroblast cells and show that the wild-type transcript is significantly increased and the mutant transcript is decreased relative to the control.
6.8.9.1. Materials and Methods
6.8.9.1.1. gRNA Design
Mutations in exon 50 of the DMD gene can cause premature truncation of the dystrophin protein. Exon skipping of exon 51 can restore the reading frame and restore expression of a functional dystrophin protein (see, Amoasii et al., 2017, Science Translational Medicine, 9(418):eaan8081). Cas12a gRNA molecules having targeting sequences corresponding to the target domains in DMD shown in Table 10 are designed, with no mismatches between the between the targeting sequence and the complement of the target domain. The loop domain, 5′ to the target domain in the Cas12a gRNA molecules, consists of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25).
tttq-
tttc-
ttcc-
GTTG-
ttta-
Using standard golden-gate assembly, DNA sequences encoding the Cas12a gRNAs are cloned into pY108 lentiAsCas12a plasmids engineered to encode AsCas12a RR, AsCas12a RVR, or other Cas12a proteins recognizing the PAM sequences upstream of the target domains to provide plasmids encoding a Cas12a protein and a single Cas12a gRNA. pY108 lentiAsCas12a plasmids encoding a Cas12a protein and a scramble-truncated gRNA are also prepared for use as controls.
6.8.9.1.2. Minigene Generation
Plasmid pCI (Alanis et al., 2012, Hum. Mol. Genet. 21:2389-2398) is used to clone a minigene of DMD Δex50. The minigene is obtained by PCR amplification and cloning of target exons 49 to 52 of DMD from muscle cells or HEK293 cells, excluding exon 50 and including about 200 bp of introns 49, 50 and 51 flanking exons 49, 51, 52 included from the DMD gene. Primers pairs useful for PCR amplification of the genetic regions required for the final minigene assembly (excluding sequences for standard cloning sites used for golden gate assembly) are: 1) exon 49 for GAAACTGAAATAGCAGTTCAAGCTAAACAACC (SEQ ID NO: 194) and intron 49 rev GCCTTAAGATCACAATATATAAATAGGATATGCTG (SEQ ID NO: 195); 2) intron 50 for TGAATCTTTTCATTTTCTACCATGTATTGCT (SEQ ID NO: 196) and intron 51 rev CTTTTTAATGTATGGCTACTTTTGTTATTTGCA (SEQ ID NO: 197); 3) intron 51 for TGAAATATTTTTGATATCTAAGAATGAAACATATTTCCTGT (SEQ ID NO: 198) and exon 52 rev TTCGATCCGTAATGATTGTTCTAGCCTCT (SEQ ID NO: 199).
6.8.9.1.3. Cell Culture
HEK293T and HEK293 cells are obtained from American Type Culture Collection (ATCC; www.atcc.org). HEK293T cells are cultured in Dulbecco's modified Eagle's medium (DMEM; Life Technologies) supplemented with 10% fetal bovine serum (FBS; Life Technologies), 10 U/ml antibiotics (PenStrep, Life Technologies) and 2 mM L-glutamine at 37° C. in a 5% CO2 humidified atmosphere.
6.8.9.1.4. Transfection
Transfection is performed in HEK293T cells seeded (150,000 cells/well) in a 24 well plate. Cells are transfected using PEI (polyethylenimine) with 100 ng of minigene plasmids and 700 ng of the plasmids encoding for Cas12a and the Cas12a gRNAs.
6.8.9.2. Results
Minigene transcripts analyzed two to three days after transfection show the expected splicing pattern including exon 51 in control cells. Decreased exon 51 inclusion is observed in cells transfected with plasmids encoding gRNAs having a targeting sequence corresponding to a target domain in close proximity to or including the intron50-exon51 junction.
6.8.10.1. Materials and Methods
Cas12a gRNA molecules having targeting sequences corresponding to the target domains shown in Table 11 are designed, with no mismatches between the between the targeting sequence and the complement of the target domain. The loop domain, 5′ to the target domain in the Cas12a gRNA molecules, consists of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25). The mutations shown in Table 11 are associated with various genetic diseases (see Section 6.3.4).
TTTGTGACCTTTGgt
GTTACCTTTGTGAC
ATTATTGATCACAT
ATTGATCACATAAC
cttcagttatgataaactgac
gttatgataaactgacCTT
tttctcttccttggttttgcagC
ttccttggttttgcagCTTC
attactctttctcttccttggtttt
tttccttgtttctctacatagG
cccctcctctctatccacctc
tttccccctcctctctatccact
tccacctcccccagaccctt
tccccctcctctctatccacct
tttg-
tttc-
ttcc-
GTTG-
ttta-
tttattttgcatacctgttcgtta
tttcaaatagaatgattttatttt
tccatggtaagttacactaa
TTTCTGGGTTAAGgt
tttatatgcagagatattgcta
attgctattacCTTAACC
tatgcagagatattgctatta
TTTCTGCATATAAA
TATAAATTGTAACT
tatgaaacctcttacCTCA
attagcaatatgaaacctctt
ATTGCTAATAGCAG
TATGTACTTGAGAT
gtaagtaaggtta
attgatagtaaccttacttac
gttaaaattccatcttacCA
attgaacgttaaaattccatc
TTTGTCATCTGTAA
GTTACCATGTCTCC
TTTGAGgtgtggcttagg
gttataaaattcttacatacC
tttaaaaaatcttactcagatt
tttctttaaaaaatcttactca
CCCCAGTTGTAATT
tttctccatccacaccgcag
tttctggatttattttagtttaca
tttccaagaggtctgactttct
tccaagaggtctgactttctg
TCCAGGTTctgtaaact
tttattttagtttacagAACC
ttca-
gttc-
tttc-
TTTC-
ATTG-
ctta-
atta-
ATTC-
CTTG-
TTTA-
tccc-
tccc-
cccc-
tccc-
cccc-
tccc-
Lentivirus particles encoding single Cas12a gRNAs and Cas12a proteins are produced according to methods similar to those described in Example 1. Stable minigene cell lines expressing the wild-type and mutant mini-genes corresponding to the genes listed in Table 11 are produced in a manner similar to Example 1, and transduced with the lentivirus particles. Approximately 10 days after transduction, cells are collected and DNA and RNA are extracted from the cells. DNA is analyzed for Cas12a induced genome editing, and RNA is analyzed for corrected splicing, similar to Example 1.
Organoids from subjects having the mutations described in Table 11 are transduced with the lentivirus particles using procedures similar to the procedure described in Example 2. Fourteen days after transduction organoids are analyzed for reversion of disease phenotype.
6.8.10.2. Results
Cas12a proteins in combination with single Cas12a gRNAs correct splicing defects caused by the mutations identified in Table 11 in minigene models and restores dystrophin expression in a minigene model of a deleterious mutation in exon 50 of DMD. In the organoids, Cas12a proteins in combination with single Cas12a gRNAs reverse the disease phenotypes.
6.8.11.1. Materials and Methods
6.8.11.1.1. gRNA Design
Cas12a gRNA molecules having targeting sequences corresponding to the target domains in USH2A shown in Table 12 were designed, with no mismatches between the targeting sequence and the complement of the target domain. The Cas12a gRNAs in this example were designed to edit the USH2A gene near the cryptic 5′ splice site (the top two target domains listed in Table 12) or the cryptic 3′ spice site (the bottom target domain listed in Table 12). The loop domain, 5′ to the target domain in the Cas12a gRNA molecules, consists of the sequence UAAUUUCUACUCUUGUAGAU (SEQ ID NO: 25) (AsCas12a) or UAAUUUCUACUAAGUGUAGAU (SEQ ID NO: 31) (LbCas12a). A schematic representation of the positions of the selected target domains is reported in
tttc-ttaaagatgatctcttacCTTGG
TTTC-CCAAGgtaagagatcatctttaa
TTTA-
Using standard golden-gate assembly, DNA sequences encoding the Cas12a gRNAs were cloned into the pY108 (Addgene plasmid number 84739, encoding AsCas12a) or pY109 (Addgene plasmid number 84740, encoding LbCas12a) lentiviral vectors. These vectors were engineered to encode Cas12a proteins together with their respective gRNAs in order to recognize the PAM sequences upstream of the selected target domains. pY108 and pY109 plasmids encoding the AsCas12a and LbCas12a proteins, respectively, together with a scramble-truncated gRNA were also prepared for use as controls. The oligonucleotides used to generate the above described vectors are reported in Table 13.
6.8.11.1.1. Minigenes Generation
Minigene models were generated to mimic the splicing pattern of the wild-type USH2A gene and its mutated counterpart. USH2A exon 40 and exon 41, together with the genomic region corresponding to PE40 were amplified from genomic DNA extracted from HEK293T cells using the primers listed in Table 14. The amplicon corresponding to exon 40 includes additional 208 bp of the 5′-end of intron 40; the amplicon corresponding to exon 41 further includes 248 bp of the 3′-end of intron 40; the amplicon corresponding to PE40 further includes portions of intron 40 up to 722 bp upstream and 622 bp downstream of the pseudoexon itself. These fragments were then assembled using golden-gate assembly and cloned into the KpnI and BglII sites of a previously published pcDNA3 vector (Cesaratto et al., 2015, J. Biotechnol. 212:159-166) to allow expression under the control of a CMV promoter. The construct also included two protein tags, a V5-tag and a roTag (Petris et al., 2014, PLoS One, 9(5):e96700) respectively, at the 5′- and 3′-end of the minigene to aid its expression. The minigene containing the USH2A c.7595-2144A>G mutation was obtained from the wild-type minigene through standard procedures of site-directed mutagenesis using the primers reported in Table 14 (oligonucleotides USH2A_mutA2144G_F and USH2A_mutA2144G_R). A schematic representation of the minigene construct is reported in
6.8.11.1.1. Cell Culture
HEK293T and HEK293 cells were obtained from the American Type Culture Collection (ATCC; www.atcc.org). Cells were cultured in Dulbecco's modified Eagle's medium (DMEM; Life Technologies) supplemented with 10% fetal bovine serum (FBS; Life Technologies), 10 U/ml antibiotics (PenStrep, Life Technologies) and 2 mM L-glutamine at 37° C. in a 5% CO2 humidified atmosphere.
HEK293 cells stably expressing USH2A wild-type and mutated minigenes were generated by stable transfection of linearized minigene plasmids. Cells were selected with 600 μg/ml of G418 (Invivogen) starting from 48 h after transfection. Single cell clones were isolated and characterized for the minigenes copy number and the expression of the minigene constructs. Stable clones were maintained in culture as indicated above with the additional supplementation of 500 μg/ml of G418.
6.8.11.1.1. Determination of Minigene Copy Number in HEK293 Stable Clones
Determination of minigene copy number was performed by qPCR analysis on genomic DNA extracted using the NucleoSpin Tissue kit (Macherey-Nagel). Genomic DNA was diluted to 86.2 ng/μl and qPCR was performed using primers reported in Table 15. GAPDH was used as control to determine the relative copy number. Standard curves for both the minigene and GAPDH were obtained with serial dilutions of the minigene plasmids or pcDNA3-GAPDH-fragment, respectively. The pcDNA3-GAPDH-fragment construct was obtained by blunt-end cloning of a GAPDH fragment amplified using the GAPDH_CN_For and GAPDH_CN_Rev primers reported in Table 15, which were the same primers used for GAPDH qPCR amplification.
6.8.11.1.1. Transfection and Transduction
Transfections were performed in HEK293 cells seeded (100,000 cells/well) in a 24 well plate. 24 hours after seeding, cells were transfected with 100 ng of minigene plasmids and 700 ng of the plasmids encoding for the Cas12a proteins and the Cas12a gRNAs targeting USH2A using TransIT-LT1 (Mirus Bio) according to manufacturer's instructions. Cells were split at confluence and collected 6 days post-transfection. Pellets were subsequently divided into two for DNA and RNA extraction to compare editing efficiency and splicing correction within the same samples.
Lentiviral particles were produced in HEK293T cells at 80% confluency in 10 cm plates. Briefly, 10 μg of transfer vector plasmid (pY108 or pY109 plasmids, encoding the Cas12a proteins and the Cas12a gRNAs), 3.5 μg of a VSV-G expressing plasmid (pMD2.G, Addgene plasmid number 12259) and 6.5 μg of a lentiviral packaging plasmid (pCMV-dR8.91) were transfected into HEK293T cells using the polyethyleneimine method (PEI) (see Casini A et al., 2015, J. Virol. 89: 2966-2971). After over-night incubation the medium was replaced with complete DMEM. The viral supernatants were collected after 48 h and filtered through a 0.45 μm PES filter. Aliquots were stored at −80° C. until use. Vector titers were measured as Reverse Transcriptase Units (RTU) by the SG-PERT method (see Casini, A., et al., 2015, J. Virol. 89:2966-2971). For transduction studies, HEK293 cells stably expressing the minigene constructs were seeded (100,000 cells/well) in a 24 well plate, and the day after seeding the cells were transduced with 1 RTU of the lentiviral vectors by centrifuging vector-containing medium on the cells for 2 hours at 1600×g 25° C. Approximately 48 hours later, cells were selected with puromycin (1 μg/ml) and collected at 10 days from transduction.
6.8.11.1.1. RT-PCR and Transcriptional Analysis
RNA was extracted using NucleoZOL Reagent (Macherey-Nagel) and resuspended in RNase free-ddH2O. cDNA was obtained from 1 μg of RNA using the RevertAid RT Reverse Transcription kit (Thermo Scientific), according to the manufacturer's protocol. Target regions were amplified by PCR with the HOT FIREPol MultiPlex Mix (Solis Biodyne) using primers V5tag_For and TEVsite_Rev (reported in Table 13). PCR products were run on 1.5% agarose gel and images were obtained with the UVIdoc HD5 system (Uvitec Cambridge). Bands quantification was performed using the Uvitec Alliance Software (Uvitec Cambridge).
6.8.11.1.1. Evaluation of Indel Formation
Genomic DNA was extracted from cell pellets using the QuickExtract solution (Lucigen) according to manufacturer's instructions. The HOT FIREPol MultiPlex Mix (Solis Biodyne) was used to amplify the integrated USH2A minigene using primers TIDE-USH2A-PE40-F (reported in Table 16) and TEVsite_Rev (reported in Table 16), specifically detecting the integrated USH2A minigene. The amplicon pools were Sanger sequenced (Mix2seq kits, Eurofins Genomics) and the indel levels were evaluated using the TIDE webtool (tide.deskgen.com/) or the Synthego ICE webtool (ice.synthego.com/).
6.8.11.2.
6.8.11.3. Results
6.8.11.3.1. Design of Minigenes to Recapitulate USH2A c.7595-2144A>G Splicing
A minigene to recapitulate the aberrant USH2A c.7595-2144A>G splicing was generated by cloning the human genomic regions coding for USH2A exon 40 and exon 41, as well as portions of USH2A intron 40 corresponding to the pseudoexon 40 (PE40), into a CMV-driven mammalian expression vector based on pcDNA3 (Cesaratto et al., J. Biotechnol. 212, 159-166, 2015). In addition, to preserve important splicing regulatory sequences, the minigene included also parts of USH2A intron 40 immediately downstream and upstream of exons 40 and 41, respectively. A schematic representation of minigene design is reported in
6.8.11.3.1. Correction of USH2A c.7595-2144A>G Splicing Using Cas12a-Mediated Genome Editing
Cas12a guide RNAs targeting the 5′ and 3′-cryptic splice sites promoting the inclusion of PE40 in the USH2A transcript were designed for both AsCas12a and LbCas12a. While guide 1 and guide 2 span the 3′ cryptic splice site and the c.7595-2144A>G mutation, guide 3 is positioned at the level of the 5′ cryptic splice site, at the beginning of the sequence corresponding to PE40 (
The levels of splicing correction promoted by AsCas12a and LbCas12a in combination with the 3 designed gRNAs were first tested by transient transfection of HEK293 cells with each nuclease-gRNA pair together with the USH2A minigene bearing the c.7595-2144A>G mutation. A scramble non-targeting gRNA (scr) was included in the studies as a control. Cells were collected at 6 days post transfection and USH2A splicing pattern was analyzed by RT-PCR on total extracted mRNA. As shown in
To further confirm the efficiency of the correction strategy, HEK293 clones stably expressing the c.7595-2144A>G USH2A mutated minigene and its wild-type counterpart were generated and characterized for copy number using a qPCR assay. Three clones were selected for subsequent studies: two clones expressing the mutated minigene (clone 4, bearing 2 copies of the mutated minigene; clone 6, bearing 1 copy of the mutated minigene) and a single clone (clone 1) characterized by 5 copies of the wild-type minigene. In addition, only LbCas12a in combination with guide 1 and guide 3 was further tested since those resulted to be the best performing combinations in transient transfection studies. Lentiviral vectors encoding LbCas12a and either guide 1, guide 3 or a scramble non-targeting gRNA were produced. HEK293 clones bearing the mutated minigenes were transduced with each of the three lentiviral vectors and kept for 10 days under puromycin selection to isolate transduced cells. The levels of USH2A splicing correction were then assessed by RT-PCR on total extracted RNA, revealing the restoration of the corrected transcript with both gRNAs (
The levels of indel formation on both the wild-type and mutated minigenes generated by the different LbCas12a-gRNA combinations were also evaluated in order to assess their allele-specificity. Genomic DNA extracted from the same samples employed for transcript evaluation was PCR amplified, Sanger sequenced and analyzed using the TIDE web tool (
The present disclosure is exemplified by the specific embodiments below.
While various specific embodiments have been illustrated and described, it will be appreciated that various changes can be made without departing from the spirit and scope of the disclosure(s).
All publications, patents, patent applications and other documents cited in this application are hereby incorporated by reference in their entireties for all purposes to the same extent as if each individual publication, patent, patent application or other document were individually indicated to be incorporated by reference for all purposes. In the event that there is an inconsistency between the teachings of one or more of the references incorporated herein and the present disclosure, the teachings of the present specification are intended.
This application claims the priority benefit of U.S. provisional application No. 62/804,591, filed Feb. 12, 2019 the contents of which are incorporated herein in their entireties by reference thereto.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/051089 | 2/11/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62804591 | Feb 2019 | US |
