Patent Application
20230407300
The instant application contains a Sequence Listing which has been submitted electronically in XML format and is hereby incorporated by reference in its entirety. Said XML copy, created on Aug. 31, 2023 is named 17023215US3 and is 852,062 bytes in size.
DNA molecules carry genetic information in the form of the sequence of the nucleotide bases that make up the DNA polymer. Only four nucleotide bases are utilized in DNA: adenine, guanine, cytosine, and thymine. This information, in the form of codons of three contiguous bases is transcribed into messenger RNA (mRNA), and then translated by transfer RNA (tRNA) and ribosomes to form proteins. Four nucleotide bases are utilized in RNA: adenine, guanine, cytosine, and uracil. The genetic code is the relation between a triplet codon and a particular amino acid. Sixty-four possible codon triplets form the genetic code, where three stop (also called terminating) codons, which provide a signal to the translation machinery (cellular ribosomes) to stop protein production at the particular codon. The other sixty-one triplets in the code correspond to one of the 20 standard amino acid. See
DNA is translated by ribosomes, causing each amino acid to be linked together one by one to form polypeptides, according to the genetic instructions specifically provided by the DNA. When the ribosome reaches a stop codon, the elongation of the protein terminates. The three stop codons are UAG (amber), UAA (ochre) and UGA (opal). Mutations that occur that change an amino acid-encoding codon to stop codon are called “nonsense mutations.” These nonsense mutations can result in a significant truncation/shortening of the polypeptide sequence, and can cause a profound change in genetic phenotype. Thus, even though a gene directing expression may be present, a crucial protein may not be produced because when the ribosome reaches the mutant stop signal, it terminates translation resulting in an unfinished protein.
Transfer RNAs translate mRNA into a protein on a ribosome. Each tRNA contains an “anti-codon” region that hybridizes with a complementary codon on the mRNA. A tRNA that carries its designated amino acid is called a “charged” tRNA. If the tRNA is one of the 61 amino-acid-associated (i.e., not a stop-signal-associated) tRNAs, it will normally attach its amino acid to the growing peptide. The structural gene of tRNA is about 72-90 nucleotides long and folds into a cloverleaf structure. tRNAs are transcribed by RNA polymerase III and contain their own intragenic split promoters that become a part of the mature tRNA coding sequence (Sharp S. J., Schaack J., Coolen L., Burke D. J. and Soll D., “Structure and transcription of eukaryotic tRNA genes”, Crit. Rev. Biochem, 19:107-144 (1985); Geiduschek E. O., and Tocchini-Valentini, “Transcription by RNA polymerase III, Annu. Rev. Biochem. 57:873-914 (1988)).
“Nonsense suppressors” are alleles of tRNA genes that contain an altered anticodon, such that instead of triggering a “stop” signal, they insert an amino acid in response to a termination codon. For example, an ochre mutation results in the creation of a UAA codon in an mRNA. An ochre suppressor gene produces tRNA with an AUU anticodon that inserts an amino acid at the UAA site, which permits the continued translation of the mRNA despite the presence of a codon that would normally trigger a stop in translation.
A number of nonsense suppressor tRNA alleles have been identified in prokaryotes and eukaryotes such as yeast and C. elegans. The different suppressor tRNAs vary in their suppression efficiency. In E. coli and other systems, the amber suppressors are relatively more efficient, ochre suppressors are less efficient while opal are the least, this suggests that the amber codons are used infrequently to terminate protein synthesis, while ochre and opal codons are more frequently used as natural termination signals.
Unwanted errors in the DNA blueprint can cause disease. For example, the occurrence of an unexpected “stop” signal in the middle of the protein, rather than at the end of the blueprint, results in the production of a truncated or shortened protein that has an altered function, or no function at all. Many human diseases, such as cystic fibrosis, muscular dystrophy, β-thalassemia and Liddle's syndrome result from unwanted stop signals in DNA reading frames for proteins that are important for proper lung, blood, muscle or kidney function, respectively.
Accordingly, there is a need to provide novel modified nonsense suppressor tRNAs that are stabilized as compared to corresponding unmodified nonsense suppressor tRNAs, and nonsense suppressor tRNAs that have an increased activity to suppress termination of genes associated with cystic fibrosis.
In certain embodiments, the present invention provides a modified transfer RNA (tRNA) comprising a T-arm, a D-arm, an anticodon arm and an acceptor arm, wherein the T-arm comprises a T-stem having nucleotides that interact with Elongation Factor 1-alpha 1 (EF1alpha). EF1alpha recruits aminoacyl-tRNA to the ribosome and protects the tRNA from being deacylated. Rational nucleotide replacement results in a tuned tRNA: EF1α interaction that enhances tRNA delivery to the ribosome and protection from deacylation.
In certain embodiments, the present invention provides a modified transfer RNA (tRNA) of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54 or 55, wherein the thymidines are replaced with uracils.
In certain embodiments, the present invention provides a modified transfer RNA (tRNA) of any one of SEQ ID NO: 1-538, wherein the thymidines are replaced with uracils.
In certain embodiments, the modified tRNA is any one of SEQ ID NOs: 56-60, 62-66, 84-86, 90-111, 113, 128-143, 147-149, 153-156, 161-174, 176, 178, 181, 184-186, 192, 196-197, 199-201, 205, 213-240, 246, 255-256, 258-285, 299, 305-312, 314, 318-332, 335-344, 346, 350-354, 357-360, 362, 365-370, 372-383, 388-390, 392, 394-401, 403-407, 414-416, 418, 422, 425, 428-433, 437, 444-445, 452, 455, 459-463, 470, 472-474, 476, 487-492, 525, 530-539, 545-550, 553-555, 561-563, and 567-579, wherein the thymidines are replaced with uracils.
In certain embodiments, the present invention provides a modified transfer RNA (tRNA) comprising a T-stem, a D-stem, an anticodon-loop and an acceptor stem, wherein (a) wherein the anticodon-arm comprises a tri-nucleotide anticodon, wherein the anticodon is 5′-UCA-3′ and recognizes TGA stop codons, and wherein the acceptor arm is operably linked to a arginine, tryptophan or glycine; (b) wherein the anticodon-arm comprises a tri-nucleotide anticodon, wherein the anticodon is 5′-UUA-3′ and recognizes TAA stop codons, and wherein the acceptor arm is operably linked to a glutamine or, glutamate; or (c) wherein the anticodon-arm comprises a tri-nucleotide anticodon, wherein the anticodon is 5′-CUA-3′ and recognizes TAG stop codons, and wherein the acceptor arm is operably linked to a tryptophan, glutamate or glutamine. In certain embodiments, the T-arm comprises rationally altered nucleotide sequences that tune the interaction with the EF1α, enhancing its suppression activity and thereby increasing its therapeutic potential. tRNAs with tuned interaction with the EF1alpha have enhanced nonsense suppression and provide enhanced therapeutic properties.
In certain embodiments, the present invention provides an oligonucleotide sequence that encodes the modified tRNA as described above, wherein the oligonucleotide has a total length of less than 150 nucleotides. In certain embodiments, the oligonucleotide is DNA.
In certain embodiments, the present invention provides an oligonucleotide comprising a first oligonucleotide sequence and a second oligonucleotide sequence, wherein the first and second oligonucleotide sequences independently encode a modified tRNA as described above, wherein the first and second oligonucleotides independently have a total length of less than 150 nucleotides, and wherein the two sequences are in tandem.
In certain embodiments, the present invention provides an expression cassette comprising a promoter and a nucleic acid encoding the modified tRNA or oligonucleotides as described above.
In certain embodiments, the present invention provides a vector comprising the oligonucleotide or the expression cassette described above.
In certain embodiments, the vector is a viral or plasmid vector.
In certain embodiments, the present invention provides a composition comprising a modified tRNA, an oligonucleotide, or a vector described above, and a pharmaceutically acceptable carrier.
In certain embodiments, the carrier is a liposome.
In certain embodiments, the invention provides a cell comprising the vector described above.
The present invention provides a method of treating a stop-codon-associated genetic disease, comprising administering the modified tRNA composition described above to a patient in need thereof.
In certain embodiments, the genetic disease associated with a premature stop codon is cystic fibrosis, muscular dystrophy, 0-thalassemia or Liddle's syndrome.
In certain embodiments, the present invention provides a method of restoring translation to a nucleotide sequence that includes a nonsense mutation in a cell, comprising introducing to the cell the composition described above.
In certain embodiments, the present invention provides a method of identifying anti-codon edited (ACE) tRNAs by high-throughput cloning and screening using suppression of a nonsense codon in luciferase enzymes including NanoLuc.
Over the years, researchers have identified hundreds of unique point mutations that resulted in nonsense codons being established in human genes. These types of mutations result, for example, in muscular dystrophy, xeroderma pigmentosum, cystic fibrosis, hemophilia, anemia, hypothyroidism, p53 squamal cell carcinoma, p53 hepatocellular carcinoma, p53 ovarian carcinoma, esophageal carcinoma, osteocarcinoma, ovarian carcinoma, esophageal carcinoma, hepatocellular carcinoma, breast cancer, hepatocellular carcinoma, fibrous histiocytoma, ovarian carcinoma, SRY sex reversal, triosephosphate isomerase-anemia, diabetes and rickets. The BRACA-1 and BRACA-2 genes associated with breast cancer also have similar mutations.
The nucleotide sequences encoding several hundred human tRNAs are known and generally available to those of skill in the art through sources such as Genbank. The structure of tRNAs is highly conserved and tRNAs are often functional across species. Thus, bacterial or other eukaryotic tRNA sequences are also potential sources for the oligonucleotides for the stabilized tRNAs of the invention. The determination of whether a particular tRNA sequence is functional in a desired mammalian cell can be ascertained through routine experimentation. Further additional potential tRNA sequences that are not yet known can be modified as described herein in order to be stabilized through routine experimentation.
tRNA genes have strong promoters that are active in all cell types. The promoters for eukaryotic tRNA genes are contained within the structural sequences encoding the tRNA molecule itself. Although there are elements that regulate transcriptional activity within the 5′ upstream region, the length of an active transcriptional unit may be considerably less than 500 base pairs and thus accommodation within a delivery vector is straightforward. Once they have been transcribed and processed, tRNAs have low rates of degradation. Finally, gene therapy with a nonsense suppressor maintains the endogenous physiological controls over the target gene that contains the nonsense codon.
Nonsense Mutations
Transfer RNA (tRNA) is a type of RNA molecule that functions in the decoding of a messenger RNA (mRNA) sequence into a protein. tRNAs function at specific sites in the ribosome during translation, which synthesizes a protein from an mRNA molecule. Nonsense mutations, also called Premature Termination Codons (PTCs), make up ˜10-15% of the single base pair mutations that cause human disease, and cystic fibrosis follows suit. (Peltz et al., Annu Rev Med., 64:407-25, 2013). In general, nonsense mutations have more serious ramifications than missense mutations because of the almost complete loss of gene expression and activity and with the possibility of dominant negative effects of truncated products. PTCs result in premature translation termination and accelerated mRNA transcript decay through the Nonsense Mediated Decay (NMD) pathway.
The current studies show that the specific site within an RNA transcript to which a tRNA delivers its amino acid can be changed through molecular editing of the anti-codon sequence within the tRNA. This approach allowed for a premature termination codon (PTC) to be effectively and therapeutically reverted back into the originally lost amino acid. Anticodon-edited tRNA (ACE-tRNA) form a new class of biological therapeutics.
Engineered tRNAs allow for “re-editing” of a disease-causing nonsense codon to a specific amino acid. These engineered tRNAs target only one type of stop codon, such as TGA over TAC or TAA. The small size of these tRNA molecules makes them amenable to ready expression, as the tRNA+the promoter is only ˜300 bp. Briefly, an oligonucleotide is synthesized that comprises the structural component of a tRNA gene functional in human cells. The sequence of this oligonucleotide is designed based upon the known sequence with substitutions made in the anticodon region of the tRNA causing the specific tRNA to recognize a nonsense or other specific mutation.
Several small molecule screens have been performed to suppress nonsense stop codons through interactions with the ribosome, the most outstanding molecules being G418, Gentamicin and PTC124. PTC124 or Ataluren has recently been relieved from Phase 3 clinical trials as use for a cystic fibrosis therapeutic. Ataluren and aminoglycosides promote read-through of each of the three nonsense codons by putting in a near cognate amino acid that turn a nonsense mutation into a missense mutation. (Roy et al., PNAS 2016 Nov. 1; 113(44):12508-12513)
Anticodon-Edited tRNA (ACE-tRNA)
tRNAs have a general four-arm structure comprising a T-arm, a D-arm, an anticodon-arm, and an acceptor arm (
The T-arm is made up of a “T-stem” and a “TψC loop.” In certain embodiments, the T-stem is modified to increase the stability of the tRNA. In certain embodiments, the ACE-tRNA has a modified T-stem that increases the biological activity to suppress stop sites relative to the endogenous T-stem sequence.
The present invention in one embodiment includes compositions comprising stabilized tRNAs, which can be used with higher effectiveness in order to treat a wide variety of nonsense mutation-associated diseases. The following sequences in Tables 1-8 are written as DNA, but as RNA (transcribed DNA) the “T: thymidine” is “U: uracil.” Therefore, tRNAs transcribed from the following sequences all contain uracils in place of the thymidines.
In certain embodiments, the tRNA has the following sequences (wherein the thymidines are replaced with uracils):
In one embodiment, the ACE-tRNA for nonsense suppression is as depicted in
According to the invention, human UAA, UAG, and UGA suppressor tRNAs have been designed. The screen has identified codon edited tRNA for the repair of Trp-TGA, Trp-TAG, Arg-TGA, Gln-TAG, Gln-TA, Glu-TAG, Glu-TAA. The tRNAs are approximately 100 nucleotides in length and can be introduced to cells to suppress nonsense codons mutations where the wild-type amino acid should be present. The oligonucleotides can be introduced directly to recipient cells or can be ligated in tandem to increase efficacy of the oligonucleotide.
Expression Cassettes and Vectors
In certain embodiments, the ACT-tRNA is encoded by an expression cassette. In yet another embodiment, the suppressor tRNA of the invention may be introduced to the cells using standard conventional genetic engineering techniques through use of vectors. Because of the internal promoter sequences of tRNA encoding sequences, the tRNA sequence need not be included in a separate transcription unit, although one may be provided.
In one embodiment of the present invention, the nucleotide expression system of the invention is included within an appropriate gene transfer vehicle which is then used to transduce cells to express the suppressor tRNA. The gene delivery vehicle can be any delivery vehicle known in the art, and can include naked DNA that is facilitated by a receptor and/or lipid mediated transfection, as well as any of a number of vectors. Such vectors include but are not limited to eukaryotic vectors, prokaryotic vectors (such as for example bacterial vectors) and viral vectors including, but not limited to, retroviral vectors, adenoviral vectors, adeno-associated viral vectors, lentivirus vectors (human and other including porcine), Herpes virus vectors, Epstein-Barr viral vectors, SV40 virus vectors, pox virus vectors, and pseudotyped viral vectors.
In certain embodiments, the ACT-tRNA (PTC) is encoded in a vector.
Retroviruses; Retroviral Vectors
The term “retrovirus” is used in reference to RNA viruses that utilize reverse transcriptase during their replication cycle. The retroviral genomic RNA is converted into double-stranded DNA by reverse transcriptase. This double-stranded DNA form of the virus is capable of being integrated into the chromosome of the infected cell; once integrated, it is referred to as a “provirus.” The provirus serves as a template for RNA polymerase II and directs the expression of RNA molecules that encode the structural proteins and enzymes needed to produce new viral particles. At each end of the provirus are structures called “long terminal repeats” or “LTRs.” The LTR contains numerous regulatory signals including transcriptional control elements, polyadenylation signals and sequences needed for replication and integration of the viral genome. There are several genera included within the family Retroviridae, including Cisternavirus A, Oncovirus A, Oncovirus B, Oncovirus C, Oncovirus D, Lentivirus, and Spumavirus. Some of the retroviruses are oncogenic (i.e., tumorigenic), while others are not. The oncoviruses induce sarcomas, leukemias, lymphomas, and mammary carcinomas in susceptible species. Retroviruses infect a wide variety of species, and may be transmitted both horizontally and vertically. They are integrated into the host DNA, and are capable of transmitting sequences of host DNA from cell to cell. This has led to the development of retroviruses as vectors for various purposes including gene therapy.
Retroviruses, including human foamy virus (HFV) and human immunodeficiency virus (HIV) have gained much recent attention, as their target cells are not limited to dividing cells and their restricted host cell tropism can be readily expanded via pseudotyping with vesicular stomatitis virus G (VSV-G) envelope glycoproteins (See e.g., J. C. Burns et al., Proc. Natl. Acad. Sci. USA 90:8033-8037 [1993]; A. M. L. Lever, Gene Therapy. 3:470-471 [1996]; and D. Russell and A. D. Miller, J. Virol., 70:217-222 [1996]).
Vector systems generally have a DNA vector containing a small portion of the retroviral sequence (the viral long terminal repeat or “LTR” and the packaging or “psi” signal) and a packaging cell line. The gene to be transferred is inserted into the DNA vector. The viral sequences present on the DNA vector provide the signals necessary for the insertion or packaging of the vector RNA into the viral particle and for the expression of the inserted gene. The packaging cell line provides the viral proteins required for particle assembly (D. Markowitz et al., J. Virol., 62:1120 [1988]). In one embodiment of the present invention, an FIV system employing a three-plasmid transfection production method in 293T cells was used (Johnston et al., J Virol. 1999 73:4991-5000). Replication incompetent virus was successfully produced.
The vector DNA is introduced into the packaging cell by any of a variety of techniques (e.g., calcium phosphate coprecipitation, lipofection, electroporation). The viral proteins produced by the packaging cell mediate the insertion of the vector sequences in the form of RNA into viral particles, which are shed into the culture supernatant.
For cells that are naturally dividing, or are stimulated to divide by growth factors, simple retroviruses like murine leukemia virus (MLV) vectors are suitable delivery systems. A major limitation in the use of many commonly used retroviral vectors in gene transfer, however, is that many of the vectors are restricted to dividing cells. If a non-dividing cell is the target cell, then a lentivirus, which is capable of infecting non-dividing cells, may be used.
As used herein, the term “lentivirus” refers to a group (or genus) of retroviruses that give rise to slowly developing disease. Viruses included within this group include HIV (human immunodeficiency virus; including HIV type 1, and HIV type 2), the etiologic agent of the human acquired immunodeficiency syndrome (AIDS); visna-maedi, that causes encephalitis (visna) or pneumonia (maedi) in sheep, the caprine arthritis-encephalitis virus, which causes immune deficiency, arthritis, and encephalopathy in goats; equine infectious anemia virus, which causes autoimmune hemolytic anemia, and encephalopathy in horses; feline immunodeficiency virus (FIV), which causes immune deficiency in cats; bovine immune deficiency virus (BIV), which causes lymphadenopathy, lymphocytosis, and possibly central nervous system infection in cattle; and simian immunodeficiency virus (SIV), which cause immune deficiency and encephalopathy in sub-human primates. Diseases caused by these viruses are characterized by a long incubation period and protracted course. Usually, the viruses latently infect monocytes and macrophages, from which they spread to other cells. HIV, FIV, and SIV also readily infect T lymphocytes (i.e., T-cells).
Lentiviruses including HIV, SIV, FIV and equine infectious anemia virus (EIAV) depend on several viral regulatory genes in addition to the simple structural gag-pol-env genes for efficient intracellular replication. Thus, lentiviruses use more complex strategies than classical retroviruses for gene regulation and viral replication, with the packaging signals apparently spreading across the entire viral genome. These additional genes display a web of regulatory functions during the lentiviral life cycle. For example, upon HIV-1 infection, transcription is up-regulated by the expression of Tat through interaction with an RNA target (TAR) in the LTR. Expression of the full-length and spliced mRNAs is then regulated by the function of Rev, which interacts with RNA elements present in the gag region and in the env region (RRE) (S. Schwartz et al., J. Virol., 66:150-159 [1992]). Nuclear export of gag-pol and env mRNAs is dependent on the Rev function. In addition to these two essential regulatory genes, a list of accessory genes, including vif, vpr, vpx, vpu, and nef, are also present in the viral genome and their effects on efficient virus production and infectivity have been demonstrated, although they are not absolutely required for virus replication (K. and F. Wong-Staal, Microbiol. Rev., 55:193-205 (1991]; R. A. Subbramanian and E. A. Cohen, J. Virol. 68:6831-6835 [1994]; and D. Trono, Cell 82:189-192 [1995]). A detailed description of the structure of an exemplary lentivirus, HIV-1, is given in U.S. Pat. No. 6,531,123.
A “source” or “original” retrovirus is a wild-type retrovirus from which a pseudotyped retrovirus is derived, or is used as a starting point, during construction of the packaging or transgene vector, for the preparation of one or more of the genetic elements of the vector. The genetic element may be employed unchanged, or it may be mutated (but not beyond the point where it lacks a statistically significant sequence similarity to the original element). A vector may have more than one source retrovirus, and the different source retroviruses may be, e.g., MLV, FIV, HIV-1 and HIV-2, or HIV and SIV. The term “genetic element” includes but is not limited to a gene.
A cognate retrovirus is the wild-type retrovirus with which the vector in question has the greatest percentage sequence identity at the nucleic acid level. Normally, this will be the same as the source retrovirus. However, if a source retrovirus is extensively mutated, it is conceivable that the vector will then more closely resemble some other retrovirus. It is not necessary that the cognate retrovirus be the physical starting point for the construction; one may choose to synthesize a genetic element, especially a mutant element, directly, rather than to first obtain the original element and then modify it. The term “cognate” may similarly be applied to a protein, gene, or genetic element (e.g., splice donor site or packaging signal). When referring to a cognate protein, percentage sequence identities are determined at the amino acid level.
The term “cognate” retrovirus may be difficult to interpret in the extreme case, i.e., if all retroviral genetic elements have been replaced with surrogate non-lentiviral genetic elements. In this case, the source retrovirus strain mentioned previously is arbitrarily considered to be the cognate retrovirus.
The term “replication” as used herein in reference to a virus or vector, refers not to the normal replication of proviral DNA in a chromosome as a consequence of cell reproduction, or the autonomous replication of a plasmid DNA as a result of the presence of a functional origin of replication. Instead “replication” refers to the completion of a complete viral life cycle, wherein infectious viral particles containing viral RNA enter a cell, the RNA is reverse transcribed into DNA, the DNA integrates into the host chromosome as a provirus, the infected cell produces virion proteins and assembles them with full length viral genomic RNA into new, equally infectious particles.
The term “replication-competent” refers to a wild-type virus or mutant virus that is capable of replication, such that replication of the virus in an infected cell result in the production of infectious virions that, after infecting another, previously uninfected cell, causes the latter cell to likewise produce such infectious virions. The present invention contemplates the use of replication-defective virus.
As used herein, the term “attenuated virus” refers to any virus (e.g., an attenuated lentivirus) that has been modified so that its pathogenicity in the intended subject is substantially reduced. The virus may be attenuated to the point it is nonpathogenic from a clinical standpoint, i.e., that subjects exposed to the virus do not exhibit a statistically significant increased level of pathology relative to control subjects.
The present invention contemplates the preparation and use of a modified retrovirus. In some embodiments, the retrovirus is an mutant of murine leukemia virus, human immunodeficiency virus type 1, human immunodeficiency virus type 2, feline immunodeficiency virus, simian immunodeficiency virus, visna-maedi, caprine arthritis-encephalitis virus, equine infectious anemia virus, and bovine immune deficiency virus, or a virus comprised of portions of more than one retroviral species (e.g., a hybrid, comprised of portions of MLV, FIV, HIV-1 and HIV-2, or HIV-1 and/or SIV).
A reference virus is a virus whose genome is used in describing the components of a mutant virus. For example, a particular genetic element of the mutant virus may be said to differ from the cognate element of the reference virus by various substitutions, deletions or insertions. It is not necessary that the mutant virus actually be derived from the reference virus.
The preferred reference FIV sequence is found in Talbott et al., Proc Natl Acad Sci USA. 1989 86:5743-7; Genbank access #NC_001482. In certain embodiments, a three-plasmid transient transfection method can be used to produce replication incompetent pseudotyped retroviruses (e.g., FIV). General methods are described in Wang et al., J Clin Invest. 1999 104:R55-62 and Johnston et al., J Virol. 1999 73:4991-5000.
Retroviral Vector System
The present invention contemplates a retroviral gene amplification and transfer system comprising a transgene vector, one or more compatible packaging vectors, an envelope vector, and a suitable host cell. The vectors used may be derived from a retrovirus (e.g., a lentivirus). Retrovirus vectors allow (1) transfection of the packaging vectors and envelope vectors into the host cell to form a packaging cell line that produces essentially packaging-vector-RNA-free viral particles, (2) transfection of the transgene vector into the packaging cell line, (3) the packaging of the transgene vector RNA by the packaging cell line into infectious viral particles, and (4) the administration of the particles to target cells so that such cells are transduced and subsequently express a transgene.
Either the particles are administered directly to the subject, in vivo, or the subject's cells are removed, infected in vitro with the particles, and returned to the body of the subject.
The packaging vectors and transgene vectors of the present invention will generate replication-incompetent viruses. The vectors chosen for incorporation into a given vector system of the present invention are such that it is not possible, without further mutation of the packaging vector(s) or transgene vector, for the cotransfected cells to generate a replication-competent virus by homologous recombination of the packaging vector(s) and transgene vector alone. The envelope protein used in the present system can be a retroviral envelope, a synthetic or chimeric envelope, or the envelope from a non-retroviral enveloped virus (e.g., baculovirus).
Packaging Signal
As used herein, the term “packaging signal” or “packaging sequence” refers to sequences located within the retroviral genome or a vector that are required for, or at least facilitate, insertion of the viral or vector RNA into the viral capsid or particle. The packaging signals in an RNA identify that RNA as one that is to be packaged into a virion. The term “packaging signal” is also used for convenience to refer to a vector DNA sequence that is transcribed into a functional packaging signal. Certain packaging signals may be part of a gene, but are recognized in the form of RNA, rather than as a peptide moiety of the encoded protein.
The key distinction between a packaging vector and a transgene vector is that in the packaging vector, the major packaging signal is inactivated, and, in the transgene vector, the major packaging sign al is functional. Ideally, in the packaging vector, all packaging signals would be inactivated, and, in the transgene vector, all packaging signals would be functional. However, countervailing considerations, such as maximizing viral titer, or inhibiting homologous recombination, may lend such constructs less desirable.
Packaging System; Packaging Vectors; Packaging Cell Line
A packaging system is a vector, or a plurality of vectors, which collectively provide in expressible form all of the genetic information required to produce a virion that can encapsidate suitable RNA, transport it from the virion-producing cell, transmit it to a target cell, and, in the target cell, cause the RNA to be reverse transcribed and integrated into the host genome in a such a manner that a transgene incorporated into the aforementioned RNA can be expressed. However, the packaging system must be substantially incapable of packaging itself. Rather, it packages a separate transgene vector.
In the present invention, the packaging vector will provide functional equivalents of the gag and pol genes (a “GP” vector). The env gene(s) will be provided by the envelope vector. In theory, a three vector system (“G”, “P”, and “E” vectors) is possible if one is willing to construct distinct gag and pol genes on separate vectors, and operably link them to different regulatable promoters (or one to a regulatable and the other to a constitutive promoter) such that their relative levels of expression can be adjusted appropriately.
A packaging cell line is a suitable host cell transfected by a packaging system that, under achievable conditions, produces viral particles. As used herein, the term “packaging cell lines” is typically used in reference to cell lines that express viral structural proteins (e.g., gag, pol and env), but do not contain a packaging signal. For example, a cell line has been genetically engineered to carry at one chromosomal site within its genome, a 5′-LTR-gag-pol-3′-LTR fragment that lacks a functional psi+ sequence (designated as Δ-psi), and a 5′-LTR-env-3′-LTR fragment that is also Δ-psi located at another chromosomal site. While both of these segments are transcribed constitutively, because the psi+ region is missing and the viral RNA molecules produced are less than full-size, empty viral particles are formed.
If a host cell is transfected by the packaging vector(s) alone, it produces substantially only viral particles without the full-length packaging vector. In one example, less than 10% of the viral particles produced by the packaging cell contain full length packaging vector-derived RNA. However, since the packaging vector lacks a functional primer-binding site, even if these particles infect a new cell, the packaging vector RNA will not be reverse transcribed back into DNA and therefore the new cell will not produce virion. Thus, by itself, the packaging vector is a replication-incompetent virus.
In some embodiments, the packaging cell and/or cell line contains a transgene vector. The packaging cell line will package the transgene vector into infectious particles. Such a cell line is referred to herein as a “transgenic virion production cell line.”
It is contemplated that packaging may be inducible, as well as non-inducible. In inducible packaging cells and packaging cell lines, retroviral particles are produced in response to at least one inducer. In non-inducible packaging cell lines and packaging cells, no inducer is required in order for retroviral particle production to occur.
The packaging vectors necessarily differ from wild-type, replication-competent retroviral genomes by virtue of the inactivation of at least one packaging signal of the cognate wild-type genome. More than one packaging signal may be inactivated. In one example, only the retroviral genes provided by the packaging vector are those encoding structural, or essential regulatory, proteins.
Transgene Vectors
A transgene vector is an expression vector that bears an expressible non-retroviral gene of interest and includes at least one functional retroviral packaging signal, so that, after the transgene vector is transfected into a packaging cell line, the transgene vector is transcribed into RNA, and this RNA is packaged into an infectious viral particle. These particles, in turn, infect target cells, their RNA is reverse transcribed into DNA, and the DNA is incorporated into the host cell genome as a proviral element, thereby transmitting the gene of interest to the target cells.
As used herein, the term “transduction” refers to the delivery of a gene(s) using a viral or retroviral vector by means of infection rather than by transfection. In certain embodiments, retroviral vectors are transduced. Thus, a “transduced gene” is a gene that has been introduced into the cell via retroviral or vector infection and provirus integration. In certain embodiments, viral vectors (e.g., “transgene vectors”) transduce genes into “target cells” or host cells. The, present invention encompasses transgene vectors that are suitable for use in the present invention that are linked to any gene of interest (or a “marker gene” or “reporter gene,” used to indicate infection or expression of a gene).
As used herein, the term “long-term transduction” refers to vectors that are capable of remaining transduced in host or target cells for time periods that are longer than those observed with other vectors. For example, the present invention provides retroviral vectors that are capable of remaining transduced for at least 120 days, at least one year, or for the life of the subject or the necessary time course of treatment. The duration of expression is a function of the choice of promoter and the target cell type, more so than the choice of vector.
The term “stable transduction” or “stably transduced” refers to the introduction and integration of foreign DNA into the genome of the transducted cell. The term “stable transductant” refers to a cell that has stably integrated foreign DNA into the genomic DNA.
The term “transient transduction” or “transiently transduced” refers to the introduction of foreign DNA into a cell where the foreign DNA fails to integrate into the genome of the transducted cell. The foreign DNA persists in the nucleus of the transducted cell for several days. During this time the foreign DNA is subject to the regulatory controls that govern the expression of endogenous genes in the chromosomes. The term “transient transductant” refers to cells that have taken up foreign DNA but have failed to integrate this DNA.
In some embodiments, the target and/or host cells of the present invention are “non-dividing” cells. These cells include cells such as neuronal cells that do not normally divide. However, it is not intended that the present invention be limited to non-dividing cells (including, but not limited to muscle cells, white blood cells, spleen cells, liver cells, eye cells, epithelial cells).
In some embodiments, the vector and the vector progeny are capable of transducing a plurality of target cells so as to achieve vector titers of at least 105 cfu/ml. The multiplicity of infection (MOI) may be at least one (i.e., one hit on average per cell), or even at least two.
Expression Cassettes and Vectors
The present invention also provides an expression cassette comprising a sequence encoding ACE-tRNA.
In certain embodiments, the expression cassette further contains a promoter. In certain embodiments, the promoter is a regulatable promoter. In certain embodiments, the promoter is a constitutive promoter. In certain embodiments, the promoter is a PGK, CMV, RSV, H1 or U6 promoter (Pol II and Pol III promoters).
The present invention provides a vector containing the expression cassette described above. In certain embodiments, the vector is a viral vector. In certain embodiments, the viral vector is an adenoviral, lentiviral, adeno-associated viral (AAV), poliovirus, HSV, or murine Maloney-based viral vector.
“Expression cassette” as used herein means a nucleic acid sequence capable of directing expression of a particular nucleotide sequence in an appropriate host cell, which may include a promoter operably linked to the nucleotide sequence of interest that may be operably linked to termination signals. It also may include sequences required for proper translation of the nucleotide sequence. The coding region usually codes for a protein of interest. The expression cassette including the nucleotide sequence of interest may be chimeric. The expression cassette may also be one that is naturally occurring but has been obtained in a recombinant form useful for heterologous expression. The expression of the nucleotide sequence in the expression cassette may be under the control of a constitutive promoter or of a regulatable promoter that initiates transcription only when the host cell is exposed to some particular stimulus. In the case of a multicellular organism, the promoter can also be specific to a particular tissue or organ or stage of development.
“Operably-linked” refers to the association of nucleic acid sequences on single nucleic acid fragment so that the function of one of the sequences is affected by another. For example, a regulatory DNA sequence is said to be “operably linked to” or “associated with” a DNA sequence that codes for an RNA or a polypeptide if the two sequences are situated such that the regulatory DNA sequence affects expression of the coding DNA sequence (i.e., that the coding sequence or functional RNA is under the transcriptional control of the promoter). Coding sequences can be operably-linked to regulatory sequences in sense or antisense orientation.
Adeno Associated Virus (AAV)
Adeno associated virus (AAV) is a small nonpathogenic virus of the parvoviridae family. AAV is distinct from the other members of this family by its dependence upon a helper virus for replication. In the absence of a helper virus, AAV may integrate in a locus specific manner into the q arm of chromosome 19. The approximately 5 kb genome of AAV consists of one segment of single stranded DNA of either plus or minus polarity. The ends of the genome are short inverted terminal repeats that can fold into hairpin structures and serve as the origin of viral DNA replication. Physically, the parvovirus virion is non-enveloped and its icosohedral capsid is approximately 20 nm in diameter.
To date, numerous serologically distinct AAVs have been identified, and more than a dozen have been isolated from humans or primates. The genome of AAV2 is 4680 nucleotides in length and contains two open reading frames (ORFs). The left ORF encodes the non-structural Rep proteins, Rep 40, Rep 52, Rep 68 and Rep 78, which are involved in regulation of replication and transcription in addition to the production of single-stranded progeny genomes. Furthermore, two of the Rep proteins have been associated with the preferential integration of AAV genomes into a region of the q arm of human chromosome 19. Rep68/78 has also been shown to possess NTP binding activity as well as DNA and RNA helicase activities. The Rep proteins possess a nuclear localization signal as well as several potential phosphorylation sites. Mutation of one of these kinase sites resulted in a loss of replication activity.
The ends of the genome are short inverted terminal repeats (ITR) which have the potential to fold into T-shaped hairpin structures that serve as the origin of viral DNA replication. Within the ITR region two elements have been described which are central to the function of the ITR, a GAGC repeat motif and the terminal resolution site (trs). The repeat motif has been shown to bind Rep when the ITR is in either a linear or hairpin conformation. This binding serves to position Rep68/78 for cleavage at the trs, which occurs in a site- and strand-specific manner. In addition to their role in replication, these two elements appear to be central to viral integration. Contained within the chromosome 19 integration locus is a Rep binding site with an adjacent trs. These elements have been shown to be functional and necessary for locus specific integration.
The AAV virion is a non-enveloped, icosohedral particle approximately 25 nm in diameter, consisting of three related proteins referred to as VP1, VP2 and VP3. The right ORF encodes the capsid proteins VP1, VP2, and VP3. These proteins are found in a ratio of 1:1:10 respectively and are all derived from the right-hand ORF. The capsid proteins differ from each other by the use of alternative splicing and an unusual start codon. Deletion analysis has shown that removal or alteration of VP1 which is translated from an alternatively spliced message results in a reduced yield of infections particles. Mutations within the VP3 coding region result in the failure to produce any single-stranded progeny DNA or infectious particles. An AAV particle is a viral particle comprising an AAV capsid protein. An AAV capsid polypeptide can encode the entire VP1, VP2 and VP3 polypeptide. The particle can be a particle comprising AAV2 and other AAV capsid proteins (i.e., a chimeric protein, such as AAV1 and AAV2). Variations in the amino acid sequence of the AAV2 capsid protein are contemplated herein, as long as the resulting viral particle comprises the AAV2 capsid remains antigenically or immunologically distinct from AAV1, as can be routinely determined by standard methods. Specifically, for example, ELISA and Western blots can be used to determine whether a viral particle is antigenically or immunologically distinct from AAV1. Furthermore, the AAV2 viral particle preferably retains tissue tropism distinct from AAV1.
An AAV2 particle is a viral particle comprising an AAV2 capsid protein. An AAV2 capsid polypeptide encoding the entire VP1, VP2, and VP3 polypeptide can overall have at least about 63% homology (or identity) to the polypeptide having the amino acid sequence encoded by nucleotides set forth in NC_001401 (nucleotide sequence encoding AAV2 capsid protein). The capsid protein can have about 70% homology, about 75% homology, 80% homology, 85% homology, 90% homology, 95% homology, 98% homology, 99% homology, or even 100% homology to the protein encoded by the nucleotide sequence set forth in NC_001401. The capsid protein can have about 70% identity, about 75% identity, 80% identity, 85% identity, 90% identity, 95% identity, 98% identity, 99% identity, or even 100% identity to the protein encoded by the nucleotide sequence set forth in NC_001401. The particle can be a particle comprising another AAV and AAV2 capsid protein, i.e., a chimeric protein. Variations in the amino acid sequence of the AAV2 capsid protein are contemplated herein, as long as the resulting viral particle comprising the AAV2 capsid remains antigenically or immunologically distinct from AAV4, as can be routinely determined by standard methods. Specifically, for example, ELISA and Western blots can be used to determine whether a viral particle is antigenically or immunologically distinct from AAV1. Furthermore, the AAV2 viral particle preferably retains tissue tropism distinction from AAV1, such as that exemplified in the examples herein, though an AAV2 chimeric particle comprising at least one AAV2 coat protein may have a different tissue tropism from that of an AAV2 particle consisting only of AAV2 coat proteins.
In certain embodiments, the invention further provides an AAV2 particle containing, i.e., encapsidating, a vector comprising a pair of AAV2 inverted terminal repeats. The nucleotide sequence of AAV2 ITRs is known in the art. Furthermore, the particle can be a particle comprising both AAV1 and AAV2 capsid protein, i.e., a chimeric protein. Moreover, the particle can be a particle encapsidating a vector comprising a pair of AAV inverted terminal repeats from other AAVs (e.g., AAV1-AAV9 and AAVrh10). The vector encapsidated in the particle can further comprise an exogenous nucleic acid inserted between the inverted terminal repeats.
The following features of AAV have made it an attractive vector for gene transfer. AAV vectors have been shown in vitro to stably integrate into the cellular genome; possess a broad host range; transduce both dividing and non-dividing cells in vitro and in vivo and maintain high levels of expression of the transduced genes. Viral particles are heat stable, resistant to solvents, detergents, changes in pH, temperature, and can be concentrated on CsCl gradients or by other means. The present invention provides methods of administering AAV particles, recombinant AAV vectors, and recombinant AAV virions. For example, an AAV2 particle is a viral particle comprising an AAV2 capsid protein, or an AAV1 particle is a viral particle comprising an AAV1 capsid protein. A recombinant AAV2 vector is a nucleic acid construct that comprises at least one unique nucleic acid of AAV2. A recombinant AAV2 virion is a particle containing a recombinant AAV2 vector. To be considered within the term “AAV2 ITRs” the nucleotide sequence must retain one or both features described herein that distinguish the AAV2 ITR from the AAV1 ITR: (1) three (rather than four as in AAV1) “GAGC” repeats and (2) in the AAV2 ITR Rep binding site the fourth nucleotide in the first two “GAGC” repeats is a C rather than a T.
The promoter to drive expression of the sequence encoding the tRNA to be delivered can be any desired promoter, selected by known considerations, such as the level of expression of a nucleic acid functionally linked to the promoter and the cell type in which the vector is to be used. Promoters can be an exogenous or an endogenous promoter. Promoters can include, for example, known strong promoters such as SV40 or the inducible metallothionein promoter, or an AAV promoter, such as an AAV p5 promoter. Additional examples of promoters include promoters derived from actin genes, immunoglobulin genes, cytomegalovirus (CMV), adenovirus, bovine papilloma virus, adenoviral promoters, such as the adenoviral major late promoter, an inducible heat shock promoter, respiratory syncytial virus, Rous sarcomas virus (RSV), etc. Additional examples include regulated promoters.
The AAV vector can further comprise an exogenous (heterologous) nucleic acid functionally linked to the promoter. By “heterologous nucleic acid” is meant that any heterologous or exogenous nucleic acid can be inserted into the vector for transfer into a cell, tissue or organism. The nucleic acid can encode a tRNA, for example. By “functionally linked” is meant such that the promoter can promote expression of the heterologous nucleic acid, as is known in the art, such as appropriate orientation of the promoter relative to the heterologous nucleic acid. Furthermore, the heterologous nucleic acid preferably has all appropriate sequences for expression of the nucleic acid, as known in the art, to functionally encode, i.e., allow the nucleic acid to be expressed. The nucleic acid can include, for example, expression control sequences, such as an enhancer. The nucleic acid can encode more than one gene product, limited only by the size of nucleic acid that can be packaged.
An AAV1 particle is a viral particle comprising an AAV1 capsid protein. Variations in the amino acid sequence of the AAV1 capsid protein are contemplated herein, as long as the resulting viral particle comprising the AAV1 capsid remains antigenically or immunologically distinct from other AAV capsids, as can be routinely determined by standard methods. Specifically, for example, ELISA and Western blots can be used to determine whether a viral particle is antigenically or immunologically distinct from other AAV serotypes.
The term “polypeptide” as used herein refers to a polymer of amino acids and includes full-length proteins and fragments thereof. Thus, “protein” and “polypeptide” are often used interchangeably herein.
The present method provides a method of delivering a nucleic acid to a cell comprising administering to the cell an AAV particle containing a vector comprising the nucleic acid inserted between a pair of AAV inverted terminal repeats, thereby delivering the nucleic acid to the cell. Administration to the cell can be accomplished by any means, including simply contacting the particle, optionally contained in a desired liquid such as tissue culture medium, or a buffered saline solution, with the cells. The particle can be allowed to remain in contact with the cells for any desired length of time, and typically, the particle is administered and allowed to remain indefinitely. For such in vitro methods, the virus can be administered to the cell by standard viral transduction methods, as known in the art and as exemplified herein. Titers of virus to administer can vary, particularly depending upon the cell type, but will be typical of that used for AAV transduction in general. Additionally the titers used to transduce the particular cells in the present examples can be utilized. The cells can include any desired cell in humans as well as other large (non-rodent) mammals, such as primates, horse, sheep, goat, pig, and dog.
The present invention further provides a method of delivering a nucleic acid to a cell in a subject comprising administering to the subject an AAV particle comprising the nucleic acid inserted between a pair of AAV inverted terminal repeats, thereby delivering the nucleic acid to a cell in the subject.
Certain embodiments of the present disclosure provide a cell comprising a viral vector as described herein.
AAV Vectors
In one embodiment, a viral vector of the disclosure is an AAV vector. An “AAV” vector refers to an adeno-associated virus, and may be used to refer to the naturally occurring wild-type virus itself or derivatives thereof. The term covers all subtypes, serotypes and pseudotypes, and both naturally occurring and recombinant forms, except where required otherwise. As used herein, the term “serotype” refers to an AAV, which is identified by, and distinguished from other AAVs based on capsid protein reactivity with defined antisera, e.g., there are eight known serotypes of primate AAVs, AAV-1 to AAV-9 and AAVrh10. For example, serotype AAV2 is used to refer to an AAV, which contains capsid proteins encoded from the cap gene of AAV2 and a genome containing 5′ and 3′ ITR sequences from the same AAV2 serotype. As used herein, for example, rAAV1 may be used to refer an AAV having both capsid proteins and 5′-3′ ITRs from the same serotype or it may refer to an AAV having capsid proteins from one serotype and 5′-3′ ITRs from a different AAV serotype, e.g., capsid from AAV serotype 2 and ITRs from AAV serotype 5. For each example illustrated herein, the description of the vector design and production describes the serotype of the capsid and 5′-3′ ITR sequences. The abbreviation “rAAV” refers to recombinant adeno-associated virus, also referred to as a recombinant AAV vector (or “rAAV vector”).
An “AAV virus” or “AAV viral particle” refers to a viral particle composed of at least one AAV capsid protein (preferably by all of the capsid proteins of a wild-type AAV) and an encapsidated polynucleotide. If the particle comprises heterologous polynucleotide (i.e., a polynucleotide other than a wild-type AAV genome such as a transgene to be delivered to a mammalian cell), it is typically referred to as “rAAV”.
In one embodiment, the AAV expression vectors are constructed using known techniques to at least provide as operatively linked components in the direction of transcription, control elements including a transcriptional initiation region, the DNA of interest and a transcriptional termination region. The control elements are selected to be functional in a mammalian cell. The resulting construct which contains the operatively linked components is flanked (5′ and 3′) with functional AAV ITR sequences.
By “adeno-associated virus inverted terminal repeats” or “AAV ITRs” is meant the art-recognized regions found at each end of the AAV genome which function together in cis as origins of DNA replication and as packaging signals for the virus. AAV ITRs, together with the AAV rep coding region, provide for the efficient excision and rescue from, and integration of a nucleotide sequence interposed between two flanking ITRs into a mammalian cell genome.
The nucleotide sequences of AAV ITR regions are known. As used herein, an “AAV ITR” need not have the wild-type nucleotide sequence depicted, but may be altered, e.g., by the insertion, deletion or substitution of nucleotides. Additionally, the AAV ITR may be derived from any of several AAV serotypes, including without limitation, AAV1, AAV2, AAV3, AAV4, AAV5, AAV7, etc. Furthermore, 5′ and 3′ ITRs which flank a selected nucleotide sequence in an AAV vector need not necessarily be identical or derived from the same AAV serotype or isolate, so long as they function as intended, i.e., to allow for excision and rescue of the sequence of interest from a host cell genome or vector, and to allow integration of the heterologous sequence into the recipient cell genome when AAV Rep gene products are present in the cell.
In one embodiment, AAV ITRs can be derived from any of several AAV serotypes, including without limitation, AAV1, AAV2, AAV3, AAV4, AAV5, AAV7, etc. Furthermore, 5′ and 3′ ITRs which flank a selected nucleotide sequence in an AAV expression vector need not necessarily be identical or derived from the same AAV serotype or isolate, so long as they function as intended, i.e., to allow for excision and rescue of the sequence of interest from a host cell genome or vector, and to allow integration of the DNA molecule into the recipient cell genome when AAV Rep gene products are present in the cell.
In one embodiment, AAV capsids can be derived from AAV2. Suitable DNA molecules for use in AAV vectors will be less than about 5 kilobases (kb), less than about 4.5 kb, less than about 4 kb, less than about 3.5 kb, less than about 3 kb, less than about 2.5 kb in size and are known in the art.
In one embodiment, the selected nucleotide sequence is operably linked to control elements that direct the transcription or expression thereof in the subject in vivo. Such control elements can comprise control sequences normally associated with the selected gene. Alternatively, heterologous control sequences can be employed. Useful heterologous control sequences generally include those derived from sequences encoding mammalian or viral genes. Examples include, but are not limited to, the SV40 early promoter, mouse mammary tumor virus LTR promoter; adenovirus major late promoter (Ad MLP); a herpes simplex virus (HSV) promoter, a cytomegalovirus (CMV) promoter such as the CMV immediate early promoter region (CMVIE), a rous sarcoma virus (RSV) promoter, pol II promoters, pol III promoters, synthetic promoters, hybrid promoters, and the like. In addition, sequences derived from non-viral genes, such as the murine metallothionein gene, will also find use herein. Such promoter sequences are commercially available from, e.g., Stratagene (San Diego, Calif.).
In one embodiment, both heterologous promoters and other control elements, such as tissue-specific and inducible promoters, enhancers and the like, will be of particular use. Examples of heterologous promoters include the CMV promoter. Examples of inducible promoters include DNA responsive elements for ecdysone, tetracycline, hypoxia and aufin.
In one embodiment, the AAV expression vector that harbors the DNA molecule of interest bounded by AAV ITRs, can be constructed by directly inserting the selected sequence(s) into an AAV genome, which has had the major AAV open reading frames (“ORFs”), excised therefrom. Other portions of the AAV genome can also be deleted, so long as sufficient portions of the ITRs remain to allow for replication and packaging functions. Such constructs can be designed using techniques well known in the art.
Alternatively, AAV ITRs can be excised from the viral genome or from an AAV vector containing the same and fused 5′ and 3′ of a selected nucleic acid construct that is present in another vector using standard ligation techniques. For example, ligations can be accomplished in 20 mM Tris-Cl pH 7.5, 10 mM MgCl2, 10 mM DTT, 33 μg/ml BSA, 10 mM-50 mM NaCl, and either 40 μM ATP, 0.01-0.02 (Weiss) units T4 DNA ligase at 0° C. (for “sticky end” ligation) or 1 mM ATP, 0.3-0.6 (Weiss) units T4 DNA ligase at 14° C. (for “blunt end” ligation). Intermolecular “sticky end” ligations are usually performed at 30-100 μg/ml total DNA concentrations (5-100 nM total end concentration). AAV vectors which contain ITRs.
Additionally, chimeric genes can be produced synthetically to include AAV ITR sequences arranged 5′ and 3′ of one or more selected nucleic acid sequences. The complete chimeric sequence is assembled from overlapping oligonucleotides prepared by standard methods.
In order to produce rAAV virions, an AAV expression vector is introduced into a suitable host cell using known techniques, such as by transfection. A number of transfection techniques are generally known in the art. See, e.g., Sambrook et al. (1989) Molecular Cloning, a laboratory manual, Cold Spring Harbor Laboratories, New York. Particularly suitable transfection methods include calcium phosphate co-precipitation, direct micro-injection into cultured cells, electroporation, liposome mediated gene transfer, lipid-mediated transduction, and nucleic acid delivery using high-velocity microprojectiles.
In one embodiment, suitable host cells for producing rAAV virions include microorganisms, yeast cells, insect cells, and mammalian cells, that can be, or have been, used as recipients of a heterologous DNA molecule. The term includes the progeny of the original cell that has been transfected. Thus, a “host cell” as used herein generally refers to a cell that has been transfected with an exogenous DNA sequence. Cells from the stable human cell line, 293 (readily available through, e.g., the American Type Culture Collection under Accession Number ATCC CRL1573) can be used in the practice of the present disclosure. Particularly, the human cell line 293 is a human embryonic kidney cell line that has been transformed with adenovirus type-5 DNA fragments, and expresses the adenoviral E1a and E1b genes. The 293 cell line is readily transfected, and provides a particularly convenient platform in which to produce rAAV virions.
By “AAV rep coding region” is meant the art-recognized region of the AAV genome which encodes the replication proteins Rep 78, Rep 68, Rep 52 and Rep 40. These Rep expression products have been shown to possess many functions, including recognition, binding and nicking of the AAV origin of DNA replication, DNA helicase activity and modulation of transcription from AAV (or other heterologous) promoters. The Rep expression products are collectively required for replicating the AAV genome. Suitable homologues of the AAV rep coding region include the human herpesvirus 6 (HHV-6) rep gene which is also known to mediate AAV-2 DNA replication.
By “AAV cap coding region” is meant the art-recognized region of the AAV genome that encodes the capsid proteins VP1, VP2, and VP3, or functional homologues thereof. These Cap expression products supply the packaging functions, which are collectively required for packaging the viral genome.
In one embodiment, AAV helper functions are introduced into the host cell by transfecting the host cell with an AAV helper construct either prior to, or concurrently with, the transfection of the AAV expression vector. AAV helper constructs are thus used to provide at least transient expression of AAV rep and/or cap genes to complement missing AAV functions that are necessary for productive AAV infection. AAV helper constructs lack AAV ITRs and can neither replicate nor package themselves. These constructs can be in the form of a plasmid, phage, transposon, cosmid, virus, or virion. A number of AAV helper constructs have been described, such as the commonly used plasmids pAAV/Ad and pIM29+45 that encode both Rep and Cap expression products. A number of other vectors have been described that encode Rep and/or Cap expression products.
Methods of delivery of viral vectors include injecting the AAV into the subject. Generally, rAAV virions may be introduced into cells using either in vivo or in vitro transduction techniques. If transduced in vitro, the desired recipient cell will be removed from the subject, transduced with rAAV virions and reintroduced into the subject. Alternatively, syngeneic or xenogeneic cells can be used where those cells will not generate an inappropriate immune response in the subject.
Suitable methods for the delivery and introduction of transduced cells into a subject have been described. For example, cells can be transduced in vitro by combining recombinant AAV virions with cells e.g., in appropriate media, and screening for those cells harboring the DNA of interest can be screened using conventional techniques such as Southern blots and/or PCR, or by using selectable markers. Transduced cells can then be formulated into pharmaceutical compositions, described more fully below, and the composition introduced into the subject by various techniques, such as by grafting, intramuscular, intravenous, subcutaneous and intraperitoneal injection.
In one embodiment, pharmaceutical compositions will comprise sufficient genetic material to produce a therapeutically effective amount of the nucleic acid of interest, i.e., an amount sufficient to reduce or ameliorate symptoms of the disease state in question or an amount sufficient to confer the desired benefit. The pharmaceutical compositions will also contain a pharmaceutically acceptable excipient. Such excipients include any pharmaceutical agent that does not itself induce the production of antibodies harmful to the individual receiving the composition, and which may be administered without undue toxicity. Pharmaceutically acceptable excipients include, but are not limited to, sorbitol, Tween80, and liquids such as water, saline, glycerol and ethanol. Pharmaceutically acceptable salts can be included therein, for example, mineral acid salts such as hydrochlorides, hydrobromides, phosphates, sulfates, and the like; and the salts of organic acids such as acetates, propionates, malonates, benzoates, and the like. Additionally, auxiliary substances, such as wetting or emulsifying agents, pH buffering substances, and the like, may be present in such vehicles. A thorough discussion of pharmaceutically acceptable excipients is available in Remington's Pharmaceutical Sciences (Mack Pub. Co., N.J. 1991).
It should be understood that more than one transgene could be expressed by the delivered viral vector. Alternatively, separate vectors, each expressing one or more different transgenes, can also be delivered to the subject as described herein. Furthermore, it is also intended that the viral vectors delivered by the methods of the present disclosure be combined with other suitable compositions and therapies.
As is apparent to those skilled in the art in view of the teachings of this specification, an effective amount of viral vector that must be added can be empirically determined. Administration can be effected in one dose, continuously or intermittently throughout the course of treatment. Methods of determining the most effective means and dosages of administration are well known to those of skill in the art and will vary with the viral vector, the composition of the therapy, the target cells, and the subject being treated. Single and multiple administrations can be carried out with the dose level and pattern being selected by the treating physician.
In certain embodiments, the rAAV is administered at a dose of about 0.3-2 ml of 1×105-1×1016 vg/ml. In certain embodiments, the rAAV is administered at a dose of about 1-3 ml of 1×107-1×1014 vg/ml. In certain embodiments, the rAAV is administered at a dose of about 1-2 ml of 1×108-1×1013 vg/ml.
Formulations containing the rAAV particles will contain an effective amount of the rAAV particles in a vehicle, the effective amount being readily determined by one skilled in the art. The rAAV particles may typically range from about 1% to about 95% (w/w) of the composition, or even higher or lower if appropriate. The quantity to be administered depends upon factors such as the age, weight and physical condition of the animal or the human subject considered for treatment. Effective dosages can be established by one of ordinary skill in the art through routine trials establishing dose response curves. The subject is treated by administration of the rAAV particles in one or more doses. Multiple doses may be administered as is required to maintain adequate enzyme activity.
Vehicles including water, aqueous saline, artificial CSF, or other known substances can be employed with the subject invention. To prepare a formulation, the purified composition can be isolated, lyophilized and stabilized. The composition may then be adjusted to an appropriate concentration, optionally combined with an anti-inflammatory agent, and packaged for use.
The present invention provides a method of increasing the level of a target protein in a cell by introducing a protein, or nucleic acid molecule encoding a protein described above into a cell in an amount sufficient to increase the level of the target protein in the cell. In certain embodiments, the accumulation of target protein is increased by at least 10%. The accumulation of target protein is increased by at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% 95%, or 99%. 39
Nucleic Acids Encoding Therapeutic Agents
The term “nucleic acid” refers to deoxyribonucleotides or ribonucleotides and polymers thereof in either single- or double-stranded form, composed of monomers (nucleotides) containing a sugar, phosphate and a base that is either a purine or pyrimidine. Unless specifically limited, the term encompasses nucleic acids containing known analogs of natural nucleotides that have similar binding properties as the reference nucleic acid and are metabolized in a manner similar to naturally occurring nucleotides.
A “nucleic acid fragment” is a portion of a given nucleic acid molecule. The term “substantial identity” of polynucleotide sequences means that a polynucleotide comprises a sequence that has at least 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, or 79%, or at least 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or 89%, or at least 90%, 91%, 92%, 93%, or 94%, or even at least 95%, 96%, 97%, 98%, or 99% sequence identity, compared to a reference sequence using one of the alignment programs described using standard parameters.
Methods for Introducing Genetic Material into Cells
The exogenous genetic material (e.g., a DNA encoding one or more therapeutic ACE-tRNAs) is introduced into the cell in vivo by genetic transfer methods, such as transfection or transduction, to provide a genetically modified cell. Various expression vectors (i.e., vehicles for facilitating delivery of exogenous genetic material into a target cell) are known to one of ordinary skill in the art.
As used herein, “transfection of cells” refers to the acquisition by a cell of new genetic material by incorporation of added DNA. Thus, transfection refers to the insertion of nucleic acid into a cell using physical or chemical methods. Several transfection techniques are known to those of ordinary skill in the art including: calcium phosphate DNA co-precipitation; DEAE-dextran; electroporation; cationic liposome-mediated transfection; and tungsten particle-facilitated microparticle bombardment. Strontium phosphate DNA co-precipitation is another possible transfection method.
In contrast, “transduction of cells” refers to the process of transferring nucleic acid into a cell using a DNA or RNA virus. A RNA virus (i.e., a retrovirus) for transferring a nucleic acid into a cell is referred to herein as a transducing chimeric retrovirus. Exogenous genetic material contained within the retrovirus is incorporated into the genome of the transduced cell. A cell that has been transduced with a chimeric DNA virus (e.g., an adenovirus carrying a cDNA encoding a therapeutic agent), will not have the exogenous genetic material incorporated into its genome but will be capable of expressing the exogenous genetic material that is retained extrachromosomally within the cell.
Typically, the exogenous genetic material includes the heterologous gene (usually in the form of a cDNA comprising the exons coding for the therapeutic protein) together with a promoter to control transcription of the new gene. The promoter characteristically has a specific nucleotide sequence necessary to initiate transcription. Optionally, the exogenous genetic material further includes additional sequences (i.e., enhancers) required to obtain the desired gene transcription activity. For the purpose of this discussion, an “enhancer” is simply any non-translated DNA sequence that works contiguous with the coding sequence (in cis) to change the basal transcription level dictated by the promoter. The exogenous genetic material may introduced into the cell genome immediately downstream from the promoter so that the promoter and coding sequence are operatively linked so as to permit transcription of the coding sequence. A retroviral expression vector may include an exogenous promoter element to control transcription of the inserted exogenous gene. Such exogenous promoters include both constitutive and inducible promoters.
Naturally-occurring constitutive promoters control the expression of essential cell functions. As a result, a gene under the control of a constitutive promoter is expressed under all conditions of cell growth. Exemplary constitutive promoters include the promoters for the following genes that encode certain constitutive or “housekeeping” functions: hypoxanthine phosphoribosyl transferase (HPRT), dihydrofolate reductase (DHFR), adenosine deaminase, phosphoglycerol kinase (PGK), pyruvate kinase, phosphoglycerol mutase, the actin promoter, and other constitutive promoters known to those of skill in the art. In addition, many viral promoters function constitutively in eucaryotic cells. These include the early and late promoters of SV40; the long terminal repeats (LTRs) of Moloney Leukemia Virus and other retroviruses; and the thymidine kinase promoter of Herpes Simplex Virus, among many others. Accordingly, any of the above-referenced constitutive promoters can be used to control transcription of a heterologous gene insert.
Genes that are under the control of inducible promoters are expressed only or to a greater degree, in the presence of an inducing agent, (e.g., transcription under control of the metallothionein promoter is greatly increased in presence of certain metal ions). Inducible promoters include responsive elements (REs) which stimulate transcription when their inducing factors are bound. For example, there are REs for serum factors, steroid hormones, retinoic acid and cyclic AMP. Promoters containing a particular RE can be chosen in order to obtain an inducible response and in some cases, the RE itself may be attached to a different promoter, thereby conferring inducibility to the recombinant gene. Thus, by selecting the appropriate promoter (constitutive versus inducible; strong versus weak), it is possible to control both the existence and level of expression of a therapeutic agent in the genetically modified cell. If the gene encoding the therapeutic agent is under the control of an inducible promoter, delivery of the therapeutic agent in situ is triggered by exposing the genetically modified cell in situ to conditions for permitting transcription of the therapeutic agent, e.g., by intraperitoneal injection of specific inducers of the inducible promoters which control transcription of the agent. For example, in situ expression by genetically modified cells of a therapeutic agent encoded by a gene under the control of the metallothionein promoter, is enhanced by contacting the genetically modified cells with a solution containing the appropriate (i.e., inducing) metal ions in situ.
Accordingly, the amount of therapeutic agent that is delivered in situ is regulated by controlling such factors as: (1) the nature of the promoter used to direct transcription of the inserted gene, (i.e., whether the promoter is constitutive or inducible, strong or weak); (2) the number of copies of the exogenous gene that are inserted into the cell; (3) the number of transduced/transfected cells that are administered (e.g., implanted) to the patient; (4) the size of the implant (e.g., graft or encapsulated expression system); (5) the number of implants; (6) the length of time the transduced/transfected cells or implants are left in place; and (7) the production rate of the therapeutic agent by the genetically modified cell. Selection and optimization of these factors for delivery of a therapeutically effective dose of a particular therapeutic agent is deemed to be within the scope of one of ordinary skill in the art without undue experimentation, taking into account the above-disclosed factors and the clinical profile of the patient.
In addition to at least one promoter and at least one heterologous nucleic acid encoding the therapeutic agent, the expression vector may include a selection gene, for example, a neomycin resistance gene, for facilitating selection of cells that have been transfected or transduced with the expression vector. Alternatively, the cells are transfected with two or more expression vectors, at least one vector containing the gene(s) encoding the therapeutic agent(s), the other vector containing a selection gene. The selection of a suitable promoter, enhancer, selection gene and/or signal sequence (described below) is deemed to be within the scope of one of ordinary skill in the art without undue experimentation.
Disease Conditions and Methods of Treatment
The present invention in one embodiment includes compositions and methods for treating cystic fibrosis by reversing the effects of mutations present that are associated with nonsense mutations through introduction of the synthetic oligonucleotide suppressor tRNAs of the invention.
Certain embodiments of the present disclosure provide a method of treating a disease in a mammal comprising administering a protein or vector encoding a therapeutic agent (e.g., a modified and/or stabilized ACE-tRNA) as described herein to the mammal. In certain embodiments, the mammal is human.
Certain embodiments of the present disclosure provide a use of a therapeutic agent or vector encoding a therapeutic agent as described herein to prepare a medicament useful for treating disease in a mammal. In certain embodiments, the disease is cystic fibrosis.
The present disclosure also provides a mammalian cell containing a vector described herein. The cell may be human.
Certain aspects of the disclosure relate to polynucleotides, polypeptides, vectors, and genetically engineered cells (modified in vivo), and the use of them. In particular, the disclosure relates to a method for gene therapy that is capable of both systemic delivery of a therapeutically effective dose of the therapeutic agent.
According to one aspect, a cell expression system for expressing a therapeutic agent in a mammalian recipient is provided. The expression system (also referred to herein as a “genetically modified cell”) comprises a cell and an expression vector for expressing the therapeutic agent. Expression vectors include, but are not limited to, viruses, plasmids, and other vehicles for delivering heterologous genetic material to cells. Accordingly, the term “expression vector” as used herein refers to a vehicle for delivering heterologous genetic material to a cell. In particular, the expression vector is a recombinant adenoviral, adeno-associated virus, or lentivirus or retrovirus vector.
The expression vector further includes a promoter for controlling transcription of the heterologous gene. The promoter may be an inducible promoter (described herein). The expression system is suitable for administration to the mammalian recipient. The expression system may comprise a plurality of non-immortalized genetically modified cells, each cell containing at least one recombinant gene encoding at least one therapeutic agent.
The cell expression system is formed in vivo. According to yet another aspect, a method for treating a mammalian recipient in vivo is provided. The method includes introducing an expression vector for expressing a heterologous gene product into a cell of the patient in situ, such as via intravenous administration. To form the expression system in vivo, an expression vector for expressing the therapeutic agent is introduced in vivo into the mammalian recipient i.v.
According to yet another aspect, a method for treating a mammalian recipient in vivo is provided. The method includes introducing the target therapeutic agent into the patient in vivo.
The expression vector for expressing the heterologous gene may include an inducible promoter for controlling transcription of the heterologous gene product. Accordingly, delivery of the therapeutic agent in situ is controlled by exposing the cell in situ to conditions, which induce transcription of the heterologous gene.
The present disclosure provides methods of treating a disease in a mammal by administering an expression vector to a cell or patient. For the gene therapy methods, a person having ordinary skill in the art of molecular biology and gene therapy would be able to determine, without undue experimentation, the appropriate dosages and routes of administration of the expression vector used in the novel methods of the present disclosure.
According to one embodiment, the cells are transformed or otherwise genetically modified in vivo. The cells from the mammalian recipient are transformed (i.e., transduced or transfected) in vivo with a vector containing exogenous genetic material for expressing a heterologous (e.g., recombinant) gene encoding a therapeutic agent and the therapeutic agent is delivered in situ.
As used herein, “exogenous genetic material” refers to a nucleic acid or an oligonucleotide, either natural or synthetic, that is not naturally found in the cells; or if it is naturally found in the cells, it is not transcribed or expressed at biologically significant levels by the cells. Thus, “exogenous genetic material” includes, for example, a non-naturally occurring nucleic acid that can be transcribed into a tRNA.
The above-disclosed therapeutic agents and conditions amenable to gene therapy are merely illustrative and are not intended to limit the scope of the instant disclosure. The selection of a suitable therapeutic agent for treating a known condition is deemed to be within the scope of one of ordinary skill of the art without undue experimentation.
In certain embodiments, the therapy has potential use for the treatment/management of diseases that are caused by Premature Termination Codons (PTCs), including, but not limited to, cystic fibrosis, muscular dystrophy, β-thalassemia and Liddle's syndrome. This therapy is advantageous in that it provides improved stop codon suppression specificity. The therapeutic ACE-tRNAs of the present invention target a specific stop-codon, TGA for instance, thus reducing off-target effects at stop-codons unrelated to disease. The present therapy is also advantageous in that it provides amino-acid specificity. The expressed tRNA is engineered to specifically replace the amino acid that was lost via insertion of the disease stop codon, thus negating any spurious effects on protein stability, folding and trafficking.
In certain embodiments, the present system is modular, and thus can be “personalized” to every possible disease PTC. For instance, there are nine individual tryptophan tRNAs in the human genome that are recognized by the Trp synthetase, all of which suppress the mRNA UGG codon. Thus, each of these nine Trp tRNA provides an opportunity for codon re-editing tolerance (UGG→UGA). Additionally, given their proximity to stop codons in the genetic code, the mutation of arginine codons to PTC nonsense codons are common in disease. There are over thirty Arg tRNA that could be tested for codon editing tolerance and suppression efficacy.
A further advantage of the present invention is that it provides facile expression and cell specific delivery, because the entire system (tRNA+promoter sequence) is compact.
Dosages, Formulations and Routes of Administration of the Agents of the Invention
The agents of the invention are administered so as to result in a reduction in at least one symptom associated with a genetic disease (e.g., cystic fibrosis). The amount administered will vary depending on various factors including, but not limited to, the composition chosen, the particular disease, the weight, the physical condition, and the age of the mammal, and whether prevention or treatment is to be achieved. Such factors can be readily determined by the clinician employing animal models or other test systems that are well known to the art.
The present invention envisions treating genetic disease (e.g., cystic fibrosis) by the administration of an agent, e.g., ACE-tRNA, an expression vector, or a viral particle of the invention. Administration of the therapeutic agents in accordance with the present invention may be continuous or intermittent, depending, for example, upon the recipient's physiological condition, whether the purpose of the administration is therapeutic or prophylactic, and other factors known to skilled practitioners. The administration of the agents of the invention may be essentially continuous over a preselected period of time or may be in a series of spaced doses. Both local and systemic administration is contemplated.
One or more suitable unit dosage forms having the therapeutic agent(s) of the invention, which, as discussed below, may optionally be formulated for sustained release (for example using microencapsulation), can be administered by a variety of routes including parenteral, including by intravenous and intramuscular routes, as well as by direct injection into the diseased tissue. The formulations may, where appropriate, be conveniently presented in discrete unit dosage forms and may be prepared by any of the methods well known to pharmacy. Such methods may include the step of bringing into association the therapeutic agent with liquid carriers, solid matrices, semi-solid carriers, finely divided solid carriers or combinations thereof, and then, if necessary, introducing or shaping the product into the desired delivery system.
When the therapeutic agents of the invention are prepared for administration, they may be combined with a pharmaceutically acceptable carrier, diluent or excipient to form a pharmaceutical formulation, or unit dosage form. The total active ingredients in such formulations include from 0.1 to 99.9% by weight of the formulation. A “pharmaceutically acceptable” is a carrier, diluent, excipient, and/or salt that is compatible with the other ingredients of the formulation, and not deleterious to the recipient thereof. The active ingredient for administration may be present as a powder or as granules; as a solution, a suspension or an emulsion.
Pharmaceutical formulations containing the therapeutic agents of the invention can be prepared by procedures known in the art using well-known and readily available ingredients. The therapeutic agents of the invention can also be formulated as solutions appropriate for parenteral administration, for instance by intramuscular, subcutaneous or intravenous routes.
The pharmaceutical formulations of the therapeutic agents of the invention can also take the form of an aqueous or anhydrous solution or dispersion, or alternatively the form of an emulsion or suspension.
Thus, the therapeutic agent may be formulated for parenteral administration (e.g., by injection, for example, bolus injection or continuous infusion) and may be presented in unit dose form in ampules, pre-filled syringes, small volume infusion containers or in multi-dose containers with an added preservative. The active ingredients may take such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. Alternatively, the active ingredients may be in powder form, obtained by aseptic isolation of sterile solid or by lyophilization from solution, for constitution with a suitable vehicle, e.g., sterile, pyrogen-free water, before use.
It will be appreciated that the unit content of active ingredient or ingredients contained in an individual aerosol dose of each dosage form need not in itself constitute an effective amount for treating the particular indication or disease since the necessary effective amount can be reached by administration of a plurality of dosage units. Moreover, the effective amount may be achieved using less than the dose in the dosage form, either individually, or in a series of administrations.
The pharmaceutical formulations of the present invention may include, as optional ingredients, pharmaceutically acceptable carriers, diluents, solubilizing or emulsifying agents, and salts of the type that are well-known in the art. Specific non-limiting examples of the carriers and/or diluents that are useful in the pharmaceutical formulations of the present invention include water and physiologically acceptable buffered saline solutions such as phosphate buffered saline solutions pH 7.0-8.0 and water.
Disease state: For the purposes of the present invention, a “disease state” or “disease phenotype” is a characteristic of a mammalian cell that results from a stop codon within the coding region of a gene inside the cell (e.g., that results from a nonsense mutation). For example, an increasing number of human genetic diseases are thought to be caused by nonsense mutations (see, for example, Atkinson et al., Nuc. Acids Res. 22:1327, 1994). To give but a few examples, β-thalessemia, Duchenne muscular dystrophy, xeroderma pigmentosum, Fanconi's anemia, and cystic fibrosis can all be caused by nonsense mutations in identified genes.
Endogenous tRNA synthetase: A tRNA synthetase is considered to be “endogenous” to a cell if it is present in the cell into which a tRNA is introduced according to the present invention. As will be the apparent to those of ordinary skill in the art, a tRNA synthetase may be considered to be endogenous for these purposes whether it is naturally found in cells of the relevant type, or whether the particular cell at issue has been engineered or otherwise manipulated by the hand of man to contain or express it.
Suppressor tRNA: A “suppressor tRNA” is one whose anti-codon is complementary with a codon that would otherwise terminate translation, so that detectable read-through occurs under the conditions of the experiment. Standard termination codons are amber (UAG), ochre (UAA), and opal (UGA) codons. However, non-standard termination codons (e.g., 4-nucleotide codons) have also been employed in the literature (see, for example, Moore et al., J. Mol. Biol. 298:195, 2000; Hohsaka et al., J. Am. Chem. Soc. 121:12194, 1999).
The invention is now illustrated by the following non-limiting Examples.
The genetic code uses four nucleotides that in turn form triplet codons, which form the basis for DNA to protein translation. There are 64 codons in total, 61 of which are used to encode amino acids, and three (TAG, TGA and TAA) of which encode protein termination “stop” or “nonsense” codons.
Five to ten percent of cystic fibrosis cases are caused by “nonsense” mutations that lead to premature truncation of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. An example of this “class 1” mutation is p.Trp1282X, a premature termination codon (PTC) which causes a loss of CFTR function and severe cystic fibrosis phenotypes. Some compounds, such as ataluren, promote stop read-through of disease producing nonsense mutations but have been only modestly successful as therapeutics due to a number of caveats, including poor stop-codon specificity and unexpectedly low efficiency of codon skipping in vivo. However, the widespread use of these compounds and the discovery that endogenous stop-codon read-through is common in metazoans, suggests that assisted suppression could be viable if delivered to a subset of cell types, i.e., airway epithelium. Yet, when therapeutically assisted stop-codon read-through is successful, the nonselective incorporation of an amino acid at the location of the nonsense codon has the potential to affect protein folding, trafficking and function (as is the case with CFTR 1282X); and thus, requires additional therapeutic intervention. Thus, there is an acute unmet need to understand the nature of disease PTCs and potentially therapeutic suppressors and generally, more effective treatments of PTC diseases.
This Example characterizes anticodon edited (ACE) Trp-tRNA for the rescue of CFTR p.Trp1282X channels. Such tRNAs are engineered to ‘suppress’ the disease-causing TGA stop codon and incorporate the original amino acid, Trp at p.Trp1282X CFTR, in effect, genetically reconstructing the wild-type CFTR protein. Data demonstrate that this general approach (nonsense suppression) produces robust rescue of transcripts that carry in-frame stop codons, through either transient transfection of a tRNA and its cognate synthetase in adherent cells, or their virus-based delivery to more native airway cell-types, such as A549 airway cells. This approach offers a number of significant benefits over existing strategies: 1) Improved codon specificity—the expressed tRNA may be directed towards a specific stop-codon, thus reducing off-target effects at stop-codons unrelated to disease. 2) Amino-acid specificity—the expressed tRNA and/or synthetase can be engineered to replace the amino acid that was lost via insertion of the disease stop codon, thus negating any spurious effects on CFTR stability, folding and trafficking. 3) Tunability—the system can be theoretically personalized for each type of tRNA and PTC mutation. 4) Facile expression—the entire system is compact (<1 kb) and can be easily packaged and expressed transiently or via nanoparticle delivery of tRNA. 5) Proof of principle for a general strategy—in-frame stop codons are a major cause of human disease and few treatment options exist; the experiments performed here on p.Trp1282X are expected to lead to insights into the mechanisms of other CFTR nonsense codons.
Data shows that ACE-tRNA stop-codon suppressor tRNA are efficient at “rescuing” transcripts which contain introduced stop-sites (
Results
We questioned if it might be possible to express eukaryotic tRNA that had been anticodon edited to suppress stop sites, TGA for instance, and not its designated codon. This was tested in five human tryptophan tRNA on a test construct consisting of a fluorescent protein (cherry) in frame with eGFP sequence that are separated by a linker containing a TGA site. To indicate the production of the full-length protein an HA epitope was added to the C-terminus of the eGFP reading frame. This test system is useful because visual appearance of the cherry signal indicates plasmid delivery and expression and in combination with the eGFP rescue shows TGA suppression. Data in
Methods
The Trp tRNA were examined for codon editing tolerance (TGG→TGA) and their ability to suppress a targeted TGA test site in a transiently transfected tandem-fluorophore (mCherry-TGA-GFP) and CFTR Trp1282X. Initial screening of 5/9 Trp tRNA discovered an anticodon edited Trp-tRNA that was transiently transfected in HEK cells and has ‘stand alone’ functionality to rescue a cherry-TGA-eGFP-HA test construct,
The remaining four Trp-tRNA are functionally examined for tolerance of anticodon editing from TAA to TGA suppressors. These anticodon edited tRNA are tested for their ability to rescue the cherry-TGA-eGFPHA clone. Biochemical (western blot) data are obtained for cherry and eGFP signals as well as HA epitopes. Here, cherry expression serves as the positive transfection control. Confocal imaging verifies cherry and eGFP fluorescence at the single cell level.
The fidelity of endogenous Trp synthetases to charge ACE-Trp tRNA with the tryptophan amino acid is determined by mass spectroscopic analysis of tryptic fragments of purified rescued cherry-Trp-eGFPHAprotein. Predicted mass for the tryptic fragment generated from the linker between the cherry and eGFP reading frames is: KPINQWPANTHER (SEQ ID NO: 648) with a predicted mass of 1590.8135; bold W indicates incorporation site,
Rescue of transiently transfected CFTR 1282X channels by ACE-tRNA identified above are assessed by standard biochemical methods for full maturation of the B and C glycosylated CFTR bands 20. Thus, the channel has been repaired with the wildtype amino acid, is fully functional and successfully trafficked to the plasma membrane.
The next step is to functionally characterize CFTR Trp1282X channels rescued with ACE-tRNA systems identified above using electrophysiological (single cell patch clamp and Ussing chamber) and biochemical approaches. The efficacy of expressed tRNA to diminish nonsense-mediated decay (NMD) of 1282X mRNA would be assessed with quantitative rtPCR. Reprogramed human airway cells are used to test expressed codon edited Trp-tRNA rescue of native 1282X CFTR channels.
It is demonstrated that anticodon editing is tolerated in an identified human Trp tRNA and this 75-base pair transfer RNA is capable of suppressing an in-frame TGA codon within a test construct. These experiments extrapolate this discovery to characterize the ability of this ACE-tRNA to interact with CFTR 1282TGA mRNA and produce functional CFTR channels in model cells (FRT and A549) as well as p. 1282X human reprogrammed airway cells.
Biochemical determination of rescue levels in transiently expressed CFTR 1282X channels as well as those in reprogrammed airway cells. Antibody M3A7 is used to recognize the rescued (epitope is aa 1370-1380) and to detect all CFTR, rescued and non-rescued, antibody binding to the N-terminus likeMM13-4 (epitope aa 25-36), available through EMD Millipore. Alternatively, L12B4 (epitope aa 386-412, EMD Millipore) or 660 (epitope aa 576-585,) are available through Cystic Fibrosis Foundation Therapeutics.
Surface functionality is examined through electrophysiological approaches, patch-clamp and Ussing chamber recording. 1282X mRNA stability and abundance is assayed by quantitative rtPCR of RNA extracts from transiently expressing cells and reprogrammed airway cells.
Bioinformatic analysis of RNA transcriptome data from human airway cells identifies abundance, context and identity of TGA codon containing transcripts. The top 10 expressing transcripts using TGA for their normal stop sites are followed up at the level of individual transcript with protein biochemistry before and after ACE-tRNA expression. Biochemical and immunohistological probes of cellular apoptosis are also used to examine the impact of ACE-tRNA in cell death.
In conclusion, the data show that ion channel genes with in-frame stop sites are amenable to this type of “rescue” (
Several different nonsense mutations cause CF, thus underlying roughly 10% of all CF disease.
Screening studies were first performed to identify the best ACE-tRNA Candidates from tryptophan and glycine. 125 ng of sequence verified miniprep cDNA of NanoLuc reporter plasmid with ACE-tRNA was transfected into HEK cells using calcium phosphate. HEK cells were plated in 96 well plates at 4×104 the day prior. 24 hrs after transfection the media was replaced with 20 ul of PBS and 15 ul of NanoGlo reagent (Promega) was added. Plates were read on a SpectraMax i3 (Molecular Devices). Data are of replicates of 3 or greater.
To assess is these novel tRNA could rescue CFTR channels harboring nonsense codons, they were co-expressed in mammalian HEK cells with a CFTR W1282X cDNA plasmid. The cellular preparations were analyzed by standard biochemical approaches via Western blot assessment of CFTR protein. This method is highly advantageous for this purpose because the CFTR protein displays a multi-banded pattern that is well-established. Specifically, the “B” and “C” bands represent the full-length and fully mature, post-translationally proceeded CFTR protein at the cell surface, respectively. In this case, both rescue with Trpchr17.trna39 and Glychr19.trna2 ACT-tRNAs produce robust populations of ‘B’ and ‘C’ CFTR immunopositive (antibody MA37) bands, indicating the promotion by said tRNA of the full-length, successfully trafficked ion channel protein.
T-stem modification significantly improves nonsense suppression.
In order to enable the identification of the nucleotide composition and functional ability to suppress nonsense codons by new types of tRNA, an All-In-One Plasmid With A One Pot Cloning Reaction was invented for High Throughput Cloning
The ‘one-pot’ cloning and expression system described in
Engineered Transfer RNAs for Suppression of Premature Termination Codons
Abstract
Premature termination codons (PTCs) are responsible for 10-15% of all inherited disease. PTC suppression during translation offers a promising approach to treat a variety of genetic disorders, yet small molecules that promote PTC read-through have yielded mixed performance in clinical trials. A high-throughput, cell-based assay is presented to identify anticodon engineered transfer RNAs (ACE-tRNA) that can effectively suppress in-frame PTCs and faithfully encode their cognate amino acid. In total, ACE-tRNA were identified with a high degree of suppression activity targeting the most common human disease-causing nonsense codons. Genome-wide transcriptome ribosome profiling of cells expressing ACE-tRNA at levels which repair PTC indicate that there are limited interactions with translation termination codons. These ACE-tRNAs display high suppression potency in mammalian cells, Xenopus oocytes and mice in vivo, producing PTC repair in multiple genes, including disease causing mutations within the cystic fibrosis transmembrane conductance regulator (CFTR).
Introduction
Premature termination codons (PTCs) arise from single nucleotide mutations that convert a canonical triplet nucleotide codon into one of three stop codons, e.g., TAG, TGA, or TAA. PTCs are often more deleterious than missense mutations because they result in the loss of protein expression. Additionally, mRNA abundance is reduced through nonsense-mediated decay (NMID) and in some cases, truncated proteins may have a dominant negative function1-3. Therefore, it is not surprising that PTCs are associated with many severe disease phenotypes, including cystic fibrosis4, Duchenne muscular dystrophy, spinal muscular atrophy5, infantile neuronal ceroid lipofuscinosis6, β-thalessemia7, cystinosis8, X-linked nephrogenic diabetes insipidus9, Hurler syndrome10, Usher syndrome11, and polycystic kidney disease. Additionally, nonsense mutations occur within the tumor suppressor genes p53 and ATM12, further implicating their role in disease. Amino acid codons most vulnerable to PTC conversion are those with a single nucleotide substitution from a stop codon: tryptophan, tyrosine, cysteine, glutamic acid, lysine, glutamine, serine, leucine, arginine, and glycine (
Small molecules, such as aminoglycosides14 dipeptides15, and oxadiazoles16 promote the “read-through” or “suppression” of nonsense mutations. These compounds are effective in model organisms17, 18, mammalian cell lines19 and some animal disease models16, 20. However, this approach results in the encoding of a near-cognate amino acid21, effectively generating a missense mutation at the PTC, which itself may have deleterious effects on protein folding, trafficking, and function. Furthermore, aminoglycosides are oto- and nephrotoxic22 and the first-in-class oxadiazole, Ataluren, displayed unexpectedly low efficacy in patient populations (ACT DMD Phase 3 clinical trial, NCT01826487; ACT CF, NCT02139306), thus limiting their utility as PTC therapeutics. Recent and ongoing advances in CRISPR/Cas9-mediated genome editing provides potentially a permanent solution for diseases resulting from nonsense mutations. However, aspects of this technology impart hurdles for its rapid use as a therapeutic23, 24. This is not limited to the requirement of “precision” or “personalized” diagnostics for each mutation based on the context of each patient's genetic variability.
A PTC repair approach was identified that displays the versatility of small molecules and the precision of gene editing. tRNAs were investigated to fulfill these criteria, whereby their anticodons have been engineered via mutagenesis to recognize and suppress UGA, UAA or UAG PTC codons. In order to be effective, the anticodon edited tRNAs, aka ACE-tRNAs, should still be recognized by the endogenous translation cellular machinery, including the aminoacyl-tRNA synthetase for charging the ACE-tRNA with their cognate amino acid and the eukaryotic elongation factor 1a (eEF-1α) for delivery of the charged tRNA to the ribosome,
Here it is shown that an anti-codon editing approach is generalizable to multiple tRNA gene families, indicating that many annotated tRNA are biologically viable. Further, it is demonstrate that anti-codon edited suppressor tRNA encode their cognate amino acid, lack significant interactions with termination stop codons and are efficacious in vivo to suppress PTC. In total, the data support the possibility that such engineered tRNA satisfy the broad requirement for coverage of disease-causing PTCs and thus represent a promising new class of RNA therapeutic agent.
Results
The rationale of this study is rooted in the observation that there are multiple tRNA genes with unique sequences (isodecoders) for a given cognate amino acid (isoacceptors), leading to >400 tRNAs annotated in the human genome (http:lowelab.ucsc.edu/GtRNAdb/)28, 29. First, tRNA genes were examined to identify individual ACE-tRNAs that retain suppression efficacy of PTCs in mammalian cells. In order to maximize sequence coverage, an all-in-one cDNA plasmid was generated that supports both high-throughput cloning (HTC) of ACE-tRNAs and quantitative measurement of PTC suppression using luminescence following delivery to mammalian cells,
Next, performed screens were performed on codon-edited tRNA for the each of the possible single nucleotide mutations which could produce a disease-causing PTCs: Arg-tRNAUGA, Gln-tRNAUAA, Gln-tRNAUAG Trp-tRNAUGA, Trp-tRNAUAG, Glu-tRNAUAA, Glu-tRNAUAG, Cys-tRNAUGA, Tyr-tRNAUAG, Tyr-tRNAUAA, Ser-tRNAUAG, Leu-tRNAUAG, Leu-tRNAUAA, Lys-tRNAUAG, Lys-tRNAUGA and Ser-tRNAUAG. The enzymatic activity of NLuc was not significantly influenced by the introduced amino acid (
Next it was established whether ACE-tRNAs identified in the screen were functionalized at the expense of aminoacylation stringency by the cognate aminoacyl-tRNA synthetase. To this end, mass spectrometry was used to examine PTC suppression in a model soluble protein, histidinol dehydrogenase (HDH),
The question was raised whether ACE-tRNAs that show efficacious suppression of premature stop codons may also induce global readthrough of native stop codons. To address this potential “off target” suppression, a transcriptome-wide quantitative profile of actively engaged ribosomes on all cellular transcripts was obtained by generating libraries of ribosome footprints from HEK293 cells expressing exogenous ACE-tRNAs or a control mock plasmid (puc57GG). Streptomycin was removed from the growth media to prevent readthrough artifacts. For comparison, the ribosome footprint library was also generated from cells in the presence or absence of G418 (150 μM, 48 h).
Multiple in-frame stop codons are frequently found at the end of genes 37-39 and may cause a minor difference in overall 3′UTR ribosome density for ACE-tRNA and G418 treatment. Ribosome occupancy was examined at each nucleotide in the 3′UTR within a 60 nt region downstream of the stop codons.
PTCs cause a multitude of human diseases and there are no established therapeutic options for their therapeutic management. The high-throughput cloning and identification, characterization and functional analysis of anticodon-edited tRNA that display efficacious PTC reversion in eukaryotic cells and mouse skeletal muscle is reported herein. Notably, the screen identifies ACE-tRNA, in total, with the ability to repair a vast majority of known human disease-causing PTC. The engineered tRNA faithfully encode their cognate amino acid, thus abrogating spurious effects on downstream protein stability, folding, and trafficking, and consequently negating the need for tandem therapies involving protein folding or trafficking agents. When transfected as cDNA, ACE-tRNAs rescued multiple full-length proteins via PTC suppression; a NLuc luciferase reporter, a model protein HDH, and two disease nonsense mutations in CFTR. Potent and stable in vivo PTC suppression in mouse skeletal muscle was displayed by an ACE-tRNAArg cDNA, suggesting a particularly high level of cellular tolerance for ACE-tRNA activity. The identification of an active ACE-tRNA for arginine in muscle is relevant for the treatment of dystrophinopathies caused by nonsense mutations. Following suit with most genetic diseases, greater than 10 percent of dystrophinopathies are caused by nonsense mutations43, where CGA->TGA mutations are most prevalent43. Efficient suppression was also achieved with ACE-tRNAs delivered as synthetic RNA transcripts, thus enabling the development of nanoparticle formulations. Future studies will be needed to assess ideal tRNA delivery strategies for each tissue and disease type, where efforts will likely benefit from rapidly expanding technologies for nucleic acid delivery.
Agents that suppress PTCs have the potential to also produce readthrough of native stop codons. The RNA profiling data presented herein suggest this is, generally, not the case in the cells and for the codon-edited tRNA that were tested. While detectable readthrough was found with Arg-tRNAUGA and Gln-tRNAUAA no significant effect on global translation termination was measured with Glu-tRNAUAG, UGA-Gly-tRNAUGA and Trp-tRNAUGA. This behavior did not obviously segregate with stop codon type, or the intrinsic PTC suppression activity of the tRNA. One potential reason that ACE-tRNA ineffectually promote readthrough at real stop codons may be due to the contextual sequence landscapes near translation terminations44. This possibility is supported by the finding that the composition of termination complexes at PTCs differ from those at native stops45, 46 However, in cases where lower level readthrough occurs, there are multiple cellular mechanisms in place to limit both normal stop read-through and damaging effects thereof. Multiple in-frame stop codons are frequently found at the end of genes37-39 and specialized ubiquitin ligases47 and ribosome associated pathways48 are known to identify and degrade proteins with erroneous translation termination. Nonetheless, despite the limited impact seen here in mammalian cells, similar ribosomal profiling experiments should be performed in the desired cell or tissue type for ACE-tRNA delivery and expression.
Previous studies have shown that the surrounding mRNA sequence influences inherent stop codon suppression efficacy of aminoglycosides and Ataluren PTC49-52, and ACE-tRNA may be similarly affected. Further, while gene addition strategies to replace a PTC containing gene, via viral or non-viral delivery, have achieved short term benefit in some settings, it may be difficult to regulate transgene expression levels. In contrast, the abundance of protein rescue via ACE-tRNA suppression is coupled to native cellular RNA levels, and thus upper levels of expression will be intrinsically regulated. The biological purpose remains unknown for a majority of the variable isoacceptor tRNA sequences in the human genome, and almost half these genes have been speculated to be transcriptionally silent pseudogenes53, however the data here suggest many annotated tRNA are viable. Consistent with this possibility, a suppression approach has been used to identify functional isodecoder tRNAs within Ser and Leu isoacceptor families54. The data presented here further demonstrate that the majority of tRNA gene sequences support viable activity when removed from the genomic context, further deepening the mystery for the biological need for a plurality of tRNA, and codon usage. Thus, the high-throughput suppression strategy described here will be useful to identify new types of tRNA sequences with unique suppression properties, and such studies have the potential to produce new RNA reagents as well as advance the molecular understanding tRNA expression and suppression.
Materials and Methods
Nonsense Reporter HTC Plasmid
The parent plasmid used was pcDNA3.1(+). The cDNA encoding pNLuc was Gibson Assembled (New England Biolabs, USA) into restriction sites HindIII and XhoI. A glycine (codon gga), tryptophan (tgc), amber (tag), opal (tga) and ochre (taa), were added to amino acid position 160 during cDNA pcr. The pcDNA3.1(+) polyA sequence was replaced for one with no BbsI restriction sites using pcr based Gibson Assembly. The high throughput ACE-tRNA Golden Gate cloning site was generated by first inserting the 5′ leader sequence of the human tRNATyr gene (bold) with a T7 promoter sequence upstream (italics)
GTTTTTCTGTGCTGAACCTCAGGGGACG
CCGACACACGTACACGTC
(Ye et al., 2008) followed by two BbsI restriction sites (bold italics) (TAGTCTTCGG (SEQ ID NO: 650) (ccdB cassette) AAGAAGACCG (SEQ ID NO: 651)) and 3′ termination sequence (bold) followed by a reverse T3 primer sequence (italics)
HTC of ACE-tRNA Library
tRNA gene sequences were obtained from the tRNA database tRNAscan-SE (http://gtrnadb.ucsc.edu/index.html; PMID: 26673694). Sequences of all tRNA genes used in this study are numbered in
HTS of ACE-tRNA Library
The day before transfection, HEK293 cells (<40 passages) were plated at 1.4×104 cells/well in 96 well cell culture treated plates in Dulbecco's Modified Essential Medium (DMEM) supplemented with 10% FBS, 1% Pen/Step and 2 mM L-Glutamine (Thermofisher, USA). The all-in-one nonsense reporter with ACE-tRNA genes were transfected in triplicate/plate using Calfectin (Signagen, USA). 16 hrs post-transfection, the media was aspirated and 20 ul of PBS was added to each well. 15 ul of lytic Nano-Glo® Luciferase Assay Reagent was added to each well (1:50 reagent to buffer; Promega, USA). The plates were incubated for 2 min after rotational shaking and read using a SpectraMax i3 plate reader (Molecular Devices, USA; integration time, 200 ms; All wavelengths collected in endpoint mode). Luminescence was averaged across three wells for each experiment and all ACE-tRNAs were repeated >3 times in this fashion. Each plate also contained in triplicate wells transfected with the all-in-one nonsense reporter with no ACE-tRNA to server as control for transfection efficiency and baseline PTC readthrough. All values are reported as ratios of ACE-tRNA luminescence over baseline PTC readthrough luminescence ±SEM. One-way ANOVAs were performed with Tukey's post-hoc analysis across all ACE-tRNAs in a given amino acid family.
CFTR, HDH-his-Strep and 4×ACE-tRNA Expression Plasmids
For expression in mammalian cells, the cDNA for the coding region and 200 base-pair of the 3′ untranslated region (UTR) of human CFTR was ligated into pcDNA3.1(+) (Promega, USA) using the KpnI and XbaI restriction enzymes. The G542tga and W1282tga mutations were introduced using QuickChange XL II (Stratagene, USA). For expression in Xenopus laevis oocytes, the cDNA for the coding region and 140 base-pair of the 5′ and 244 base-pair 3′ UTR of human CFTR was ligated into pGEM-HE (Promega, USA). Bothe the G542tga and W1282tga mutations were introduced using QuickChange XL II. The cDNA encoding the E. coli histidinol dehydrogenase was codon optimized for Mus musculus and synthesized (BioBasic Inc, Canada) with a c-terminal 8×His-Strep-tag (“8×His” disclosed as SEQ ID NO: 647) for protein purification from mammalian cells. The synthesized cDNA was ligated into pcDNA3.1(+) using EcoRI and XhoI restriction sites. The nonsense mutations tag, taa and tga were introduced using QuickChange XL II. To generate multiplexed ACE-tRNA expression plasmids, a novel parent Golden Gate pUC57(amp) plasmid was generated by inserting a BbsI “multiple cloning site” (5′-GAATTCTTCCCGAGACGTTCCAAGTCTTCATGAAGACTACAGGCGTCTCCCAGGAAG CT-3′ (SEQ ID NO: 653); directional BbsI recognition sequences are italicized and unique four base-pair overhangs for ligation are bolded) between the EcoRI and HindIII restriction sites. pUC57(amp) was chosen as a parent plasmid because it is relatively small in size and lacks backbone BbsI restriction sites and T7 and T3 promoter sequence. A feature included in the HTS plasmid is T7 and T3 promoter sequence flanking the ACE-tRNA cassette, giving universal primer binding sequences with comparable melting temperatures (Tm), ideal for pcr amplification. Using the NEB Golden Gate Assembly Tool (https://goldengate.neb.com/editor) pcr primers were generated that annealed to the T7 and T3 flanking sequence and created unique four base-pair overhangs following cleavage of distal BbsI recognition sequence. The end result was the generation of four ACE-tRNA pcr products using universal pcr primers that could be “daisy-chained” through complementary four base-pair overhangs and ligated into the puc57 Golden Gate plasmid using a one-pot Golden Gate reaction. All clones were sequence verified.
Cell Culture, Protein Expression and Western Blot
HEK293T cells (ATCC, USA) were grown in standard grown media containing (% in v/v) 10% FBS (HiClone, USA), 1% Pen Strep, 1% L-Glut in high glucose DMEM (Gibco, USA) at 37° C., 5% CO2. cDNA was transfected at 75% confluency using Calfectin according to standard protocols (SignaGen Laboratories, USA). Following 36 hrs the cells were scraped and pelleted at 7,000 g for 8 min at 4° C. in PBS supplemented with 0.5 μg/ml pepstatin, 2.5 μg/ml aprotinin, 2.5 μg/ml leupeptin, 0.1 mM PMSF, 0.75 mM benzamidine. For CFTR expressing cells, the cell pellet was vigorously dounced in 100 mM sucrose, 150 mM NaCl, 1 mM DTT, 0.5 μg/ml pepstatin, 2.5 μg/ml aprotinin, 2.5 μg/ml leupeptin, 0.1 mM PMSF, 0.75 mM benzamidine, 50 mM Tris-HCL ph 7.4 and centrifuged at 100,000 g to separate total membranes from the soluble cytosolic proteins. Pellets were solubilized in a buffer containing 1% triton, 250 mM NaCl, 50 mM tris-HCl pH 7.4, and 0.5 μg/ml pepstatin, 2.5 μg/ml aprotinin, 2.5 μg/ml leupeptin, 0.1 mM PMSF, 0.75 mM benzamidine. Equal cell-lysate was loaded on a 3-15% separating gradient SDS-page with 4% stacking gel in the presence of 1% 2-mercaptoethanol, separated at 55 V O/N and transferred to 0.45 μM LF PVDF (Bio-Rad, USA). PVDF was immunoblotted using anti-CFTR antibody M3A7(1:1000; Millipore, USA) in 2% non-fat milk and imaged on LI-COR Odyssey Imaging System (LI-COR, USA). For HDH-His-Strep expressing cells, the cell pellet was vigorously dounce homogenized in 100 mM sucrose, 1 mM DTT, 1 mM EDTA, 20 mM tris-HCl pH 8.0, 0.5 μg/ml pepstatin, 2.5 μg/ml aprotinin, 2.5 μg/ml leupeptin, 0.1 mM PMSF and 0.75 mM benzamidine. The lysate was centrifuged at 100,000 g for 30 min at 4° C. The supernatant (soluble cellular protein) was separated on 4-12% Bis-Tris SDS-page acrylamide gels (ThermoFisher, USA) in the presence of 1% 2-mercaptoethanol, transferred to 0.22 μM LF PVDF (Bio-Rad, USA) and immunoblotted using anti-Strep antibody (1:5000; iba, Germany) in 2% non-fat milk and imaged on LI-COR Odyssey Imaging System (LI-COR, USA).
Mass Spectrometry
Fragmentation data on purified HDH-His-Strep protein were obtained at the University of Iowa Proteomics Facility. Briefly, HDH-His-Strep protein from the soluble fraction of the high-speed spin was passed through StrepTrap HP columns (GE Healthcare, Sweden) and washed with 5 column volumes of 100 mM sucrose, 1 mM DTT, 1 mM EDTA, 20 mM tris-HCl pH 8.0, 0.5 μg/ml pepstatin, 2.5 μg/ml aprotinin, 2.5 μg/ml leupeptin, 0.1 mM PMSF and 0.75 mM benzamidine. The protein was eluted in wash buffer supplemented with 10 mM d-desthbiotin and concentrated in 30 kDA cutoff Amicon-Ultra filtration columns (Millipore, USA). The concentrated protein was loaded on NuPage 4-12% Bis-Tris precast gels (Invitrogen, USA) and separated at 150V for 1.5 hrs. The gel was stained using a Pierce mass spec compatible silver stain kit (ThermoFisher Scientific, USA).
In-gel Trypsin Digestion. Briefly, the targeted protein bands from SDS-PAGE gel were manually excised, cut into 1 mm3 pieces, and washed in 100 mM ammonium bicarbonate:acetonitrile (1:1, v/v) and 25 mM ammonium bicarbonate/acetonitrile (1:1, v/v), respectively to achieve complete destaining. The gel pieces were further treated with ACN, and dried via speed vac. After drying, gel pieces were reduced in 50 μl of 10 mM DTT at 56° C. for 60 min and then alkylated by 55 mM IAM for 30 min at room temperature. The gel pieces were washed with 25 mM ammonium bicarbonate:acetonitrile (1:1, v/v) twice to removed excess DTT and IAM. After drying, the gel pieces were placed on ice in 50 μL of trypsin solution at 10 ng/μL in 25 mM ammonium bicarbonate and incubated on ice for 60 min. Then, digestion was performed at 37° C. for 16 h. Peptide extraction was performed twice for 0.5 h with 100 μl 50% acetonitrile/0.2% formic acid. The combined extracts were concentrated in a Speed Vac to ˜15 μl.
LC-MS/MS. The mass spectrometry data were collected using an Orbitrap Fusion Lumos mass spectrometer (Thermo Fisher Scientific, San Jose, CA) coupled to an Eksigent Ekspert™ nanoLC 425 System (Sciex). A Trap-Elute Jumper Chip (P/N:800-00389) and a coupled to a 1/16″ 10 port Valco directed loading performed by the gradient 1 pump and final elution (by the gradient 2 pump). The column assembly was designed as two tandem 75 μm×15 cm columns (ChromXP C18-CL, 3 m 120 A, Eksigent part of AB SCIEX) mounted in the Ekspert™ cHiPLC system. For each injection, an estimated 0.5 μg of total digest was loaded. Peptides were separated in-line with the mass spectrometer using a 120 min gradient composed of linear and static segments wherein Buffer A is 0.1% formic acid and B is 95% ACN, 0.1% Formic acid. The gradient begins first holds at 4% for 3 min then makes the following transitions (% B, min): (26, 48), (35, 58), (35, 64), (50, 72), (50, 78), (94, 84), (94, 96), (4, 100), (4, 120).
Tandem mass spectrometry on the LUMOS Orbitrap. Scan sequences began with a full survey (m/z 350-1500) acquired on an Orbitrap Fusion Lumos mass spectrometer (Thermo) at a resolution of 60,000 in the off axis Orbitrap segment (MS1). Every 3 seconds of the gradient MS1 scans were acquired during the 120 min gradient described above. The most abundant precursors were selected among 2-8 charge state ions at a 2.0E5 threshold. Ions were dynamically excluded for 30 seconds if they were targeted twice in the prior 30 sec. Selected ions were isolated by a multi-segment quadrupole with a mass window on m/z 2, then sequentially subjected to both CID and HCD activation conditions in the IT and the ioin routing multipole respectively. The AGC target for CID was 4.0E04, 35% collision energy, an activation Q of 0.25 and a 100 milliseconds maximum fill time. Targeted precursors were also fragmented by high energy collision-induced dissociation (HCD) at 40% collision energy, and an activation Q of 0.25. HCD fragment ions were analyzed using the Orbitrap (AGC 1.2E05, maximum injection time 110 ms, and resolution set to 30,000 at 400 Th). Both MS2 channels were recorded as centroid and the MS1 survey scans were recorded in profile mode.
Proteomic Searches. Initial spectral searches were performed with Proteome Discoverer version 2.1.1.21 (ThermoFisher Scientific, USA) using Sequest HT. Spectra were also searched with Byonic search engine (Protein Metrics) ver. 2.8.2. Search databases were composed of the Uniprot KB for species 9606 (Human) downloaded 10/24/2016 containing 92645 sequences and Uniprot KB for taxonomy 562 (E. coli) downloaded on 11/08/2016 containing 10079 sequences. For Byonic searches, these two data bases were directly concatenated. In either search an equal number of decoy entries were created and searched simultaneously by reversing the original entries in the Target databases.
In vitro cRNA transcription. G542XUGA, W1282XUGA, and WT CFTR pGEMHE (Mense et al., 2006; PMID:1703051) plasmids were linearized by 10× excess of NheI-HF restriction enzyme (site positioned 3′ of coding region)(New England BioLabs, USA) for 3 hrs at 37° C. and purified using standard cDNA precipitation methods. All cRNAs were transcribed using the mMessage mMachine T7 Kit (ThermoFisher Scientific, USA). Purification of the cRNA from the transcription reaction was conducted on columns from the RNeasy Mini Kit (Qiagen, Germany). Concentration was determined by absorbance measurements at 260 nn and quality was confirmed on a 1% agarose gel (RNase-free). All cRNA was queued to 1 μg/ml before use and all results were generated from ≥2 cRNA preparations.
In vitro tRNA transcription. Trpchr17.trna39 and Glychr19.trna2, the top performing Trp and Gly ACE-tRNAs, were transcribed in vitro using CellScript T7-Scribe Standard RNA IVT Kit (CELLSCRIPT, USA). Equimolar concentration of T7 oligo (5′-taatacgactcactata-3′) (SEQ ID NO: 656) was annealed to ACE-tRNA PAGE-purified Ultramers (20 μg; Integrated DNA Technologies, Coralville, IA) coding for the ACE-tRNA and preceded by a T7 promoter (italics). Importantly, the three terminal nucleotides containing CCA were included (bold).
TGGTGACCCCGACGTGATTTGAACACGC
TCGTATTA
TGGTGCGTTGGCCGGGAATCGAACCCGG
TATTA
The total reaction volume was adjusted to 100 μl and the kit reagents were added in the following amounts: 10 μl of 10× T7-Scribe transcription buffer, 7.5 μl of each nucleotide (100 mM stocks), 10 μl of 100 mM Dithiothreitol, 2.5 μl ScriptGuard RNase Inhibitor, 10 μl T7-Scribe enzyme solution. After the reaction was incubated for 4-5 hr at 37° C., the DNA template was digested with 5 μl DNase (1 U/μl) provided with the kit for 30-60 min. The ACE-tRNA was extracted from the reaction with acidic phenol chloroform (5:1, pH 4.5) and precipitated with ethanol. The precipitates ACE-tRNA was pelleted, washed, dried and resuspended in 100 μl DEPC-treated water and further purified with Chroma Spin-30 columns (Clontech, USA). The procedure yielded roughly 100 μl of ˜5 μq/μl ACE-tRNA. ACE-tRNAs were re-pelleted in 20 ug aliquots, washed, lyophilized and stored at −80° C. until use. All results were generated from ≥2 ACE-tRNA preparations.
Ribosome Footprint Profiling Library preparation. HEK293 cells transiently transfected with ACE-tRNAs and control plasmid (puc57GG) were grown in standard grown media in the absence of Pen-Strep for 48 h. Libraries were prepared as described55, with a few modifications. Briefly, cells were rapidly cooled by addition of ice-cold PBS, lysed in lysis buffer (20 mM Tris-HCl/pH7.4, 150 mM NaCl, 5 mM MgCl2, 1 mM DTT, 1% (v/v) Triton X-100, and 25 U ml−1 Turbo DNase I) for 10 min on ice, and triturated with ten times through a 26-G needle. After clearance by centrifugation at 16,000 g for 10 min at 4° C., the lysates were digested with 100 U RNase I (Ambion, USA) per A260 lysate at room temperature for 45 min with gentle agitation prior to adding 200 U RiboLock RNase Inhibitor (Thermo Scientific). Ribosome protected mRNA fragments were then isolated by loading lysates onto a 1M sucrose cushion prepared in modified polysome buffer (20 mM Tris-HCl/pH7.4, 150 mM NaCl, 8.5 mM MgCl2, 0.5 mM DTT, 20 U ml−1 RiboLock RNase Inhibitor) and centrifugated at 70,000 rpm at 4° C. for 2 h using a Beckmen TLA-110 rotor. Ribosome pellets containing mRNA footprints were extracted using TRIzol and separated on a denaturing 12% polyacrylamide gel containing 8M urea. RNA fragments with sizes ranging from 26 to 34 nt were manually excised from the gel stained with SYBR Gold (Invitrogen) and isolated to generate the ribosome-protected fragment library. Contaminating rRNA fragments depleted using a Ribo-Zero kit (Illumina). 3′ Oligonucleotide adaptor ligation, reverse transcription, circularization, and secondary rRNA depletion using biotinylated rRNA depletion oligos (Table 9) were performed as described5. Libraries were barcoded using indexing primers for each sample during PCR amplification. Barcoded libraries were then pooled with 3% PhiX (Illumina) and sequenced in an Illumina NextSeq 500 as per manufacturer protocol to typically generate 18-27 million reads per sample.
Ribosome Footprint Data analysis. Data files for each barcoded sample (minus adaptor sequence at 3′ end) were first mapped to four rRNA sequences (RNA5S1; NR_023363, RNA5-8SN5; NR_003285, RNA18SN5; NR_003286, and RNA28SN5; NR_003287) using HISAT 2.0.356 to eliminate rRNA contaminant reads. The remaining reads were aligned to the sense stands of the longest transcript variant of each human gene (UCSC RefSeq GRCh38). Transcripts with 3′UTR length of at least 75 nt (18,101 sequences) were used for subsequence analysis. A maximum of two mismatches at the 5′end of reads was allowed. All multi-mapped reads were discarded. Fragment reads with lengths between 26 to 34 nt were defined as ribosome footprints and used for analysis. The 5′ end nucleotide from each footprint was annotated and mapped on each transcript. Position of the ribosome A-site occupying the 16th-18th nucleotides of each footprint57,58 was used to infer the position of the ribosome on each transcript. RPKM (footprint Reads Per Kilobase of transcript per total Million-mapped reads) on each individual transcript (18,101 sequences) was calculated. Only transcripts with a minimum threshold of 5 RPKM in the coding sequence and 0.5 RPKM in 3′UTR region in two replicate libraries (254 transcripts in G418 and 495-748 transcripts in ACE-tRNAs) were included for analysis in
Generation of stable NLuc reporter cell lines. The cDNAs encoding pNLuc with tag, taa and tga stop codons at amino acid position 160 were inserted into AgeI and NotI restriction sites within the multiple cloning site of the retroviral vector pQCXIP (Clontech, USA) using Gibson Assembly (New England Biolabs, USA). PhoenixGP cells (PMID: 7690960) were co-transfected with pNLuc-STOP-pQCXIP and cmv-VSV-G (VSV-G envelope pseudotyping) plasmids using Calfectin (SignaGen Laboratories, USA) and placed in a 33° C. CO2-controlled (5%) cell incubator for 48 hr. The culture media (20 mls) containing retroviral particles was chilled to 4° C. and spun at 10,000 g to remove cell debris and filtered through a 0.45 um MCE-membrane syringe filter (Millipore, USA) onto two 10 cm dishes seeded with low-passage HEK293 cells at 30% confluency. Cell culture dishes were sealed with Parafilm and spun for 90 minutes at 3,500 g at 24° C. and placed in a 37° C. CO2 controlled (5%) cell culture incubator. Cells were selected 24 hr later with puromycin (1 ug/ml) until the control dish (no infection) showed complete cell death. Cells were monodispersed into 96-well plates using FACS and clonal populations were subsequently. Puromycin was not used to maintain selected clones during experimentation and standard DMEM media (DMEM-Dulbecco's Modified Eagle Medium-high glucose with L-glutamine supplemented with 10% FBS, 1% Pen/Step and 2 mM L-Glutamine; ThermoFisher, USA) was used in all studies.
RNA transfection. HEK293 cells stably expressing pNLuc-UGA were plated at 1.4×104 cells/well in 96 well cell culture treated plates in Dulbecco's Modified Essential Medium (DMEM) supplemented with 10% FBS, 1% Pen/Step and 2 mM L-Glutamine (Thermofisher, USA). 16-24 hr later the cells were transfected with ACE-tRNAs using lipofectamine 2000 (ThermoFisher Scientific, USA). Briefly, 3 μg of ACE-tRNA were suspended in 150 μl of OptiMEM and 12 μl of Lipofectamine 2000 was mixed with 150 ul of OptiMEM. The volumes were combined, thoroughly mixed and incubated for 10 mins at RT. 75 ul of the transfection complex was added to each well. PTC suppression by ACE-tRNA transcripts was quantified as described above.
Expression in Xenopus laevis oocytes. Xenopus laevis oocytes (stage V and VI) were purchased from Ecocyte (Austin, TX). Prior to injection, each ACE-tRNA pellet was resuspended in 2 μl of ddH2O and debris was pelleted at 21,000×g, 4° C. for 25 min. To determine dose response of ACE-tRNAs on CFTR channel rescue, serial dilutions were generated of ACE-tRNA aliquots (200, 100, 50, 25, 12.5, 6.25, 3.125 and 1.562 ng/oocyte) balanced in volume with ddH2O. In all experiments 25 ng of CFTR cRNA was injected per oocyte and injection volumes were 50 μl. ddH2O was used in no ACE-tRNA background control experiments. After injection, oocytes were kept in OR-3 (50% Leibovitz's medium, 250 mg/l gentamycin, 1 mM L-glutamine, 10 mM HEPES (pH 7.6)) at 18° C. for 36 hr.
Two-electrode voltage clamp (TEVC) recordings. CFTR Cl− currents were recorded in ND96 bath solution that contained (in mM): 96 NaCl, 2 KCl, 1 MgCl2, and 5 HEPES (pH 7.5) in the presence of a maximal CFTR activation cocktail, forskolin (10 μM; adenylate cyclase activator) and 3-isobutyl-1-methylxanthine (1 mM; phosphodiesterase inhibitor). Glass microelectrodes backfilled with 3 M KCl had resistances of 0.5-2 MO. Data were filtered at 1 kHz and digitized at 10 kHz using a Digidata 1322 A controlled by the pClamp 9.2 software (Molecular Devices, USA). CFTR currents were elicited using 5 mV voltage steps from −60 to +35 mV using an OC-725C voltage clamp amplifier (Warner Instruments, USA). Oocytes where the CFTR Cl− current reversed positive of −20 mV were discarded. Clampfit 9.2 software was used for current analysis. All values are presented as mean±SEM.
Animals and in vivo imaging. Nu/J mice were purchased from Jackson labs. Animal experiments were approved by the Institutional Animal Care and Use Committee at the Wistar Institute (protocol number: 112762). Mice were treated by injecting 10-20 ug of DNA resuspended in 30 ul of water into the tibialis anterior muscle followed by electroporation. 10 ug pNano-TGA+10 ug Arg ACE-tRNA (right tibialis anterior) or 10 ug pNano-TGA+10 ug empty pUC57 (left tibialis anterior) were injected into 3 mice. As controls 3 other mice were injected with 10 ug pNano-WT (right tibialis anterior; positive control) or water (left tibialis anterior; negative control). The DNA was formulated with 333 IU/ml of hyaluronidase (Sigma). One minute after DNA injection, electroporation with CELLECTRA 3P device (Inovio Pharmaceuticals) was performed. Nanoluciferase activity was imaged in mice by injecting 100 ul of furimazine (40x dilution of Nano-Glo substrate) intraperitoneally and imaged mice on an IVIS Spectrum (Perkin Elmer) 5 minutes after injection. Imaging was with open filter and images were acquired at 40 seconds. The images were analyzed using Living Image Software (Perkin Elmer).
TrpTGAchr17.trna39
TrpTGAchr17.trna10
TrpTGAchr6.trna171
TrpTGAchr12.trna6
TrpTGAchr7.trna3
TrpTAGchr17.trna39
TrpTAGchr17.trna10
TrpTAGchr6.trna171
TrpTAGchr12.trna6
TrpTAGchr7.trna3
GlyTGAchr19.trna2
GlyTGAchr1.trna107
GlyTGAchr17.trna9
ArgTGAchr3.trna8
ArgTGAchr6.trna115
ArgTGAchr17.trna21
ArgTGAchr17.trna16
ArgTGAchr17.trna19
ArgTGAchr16.trna3
ArgTGAchr7.trna5
ArgTGAchr16.trna13
ArgTGAchr15.trna4
ArgTGAchr6.trna4
ArgTGAchr17.trna17
ArgTGAchr6.trna3
ArgTGAchr6.trna125
ArgTGAchr9.trna5
ArgTGAchr1.trna10
ArgTGAchr1.trna10/
nointron
ArgTGAchr17.trna3
ArgTGAchr17.trna3/
nointron
ArgTGAchr9.trna6
ArgTGAchr9.trna6/
nointron
ArgTGAchr11.trna3
ArgTGAchr6.trna52/
nointron
GlnTAGchr12.trna3
GlnTAGchr5.trna23
GlnTAGchr6.trna147
GlnTAGchr1.trna17
GlnTAGchr1.trna101
GlnTAGchr6.trna42
GlnTAGchr6.trna132
GlnTAGchr1.trna23
GlnTAGchr1.trna111
GlnTAGchr1.trna24
GlnTAGchr19.trna4
GlnTAGchr17.trna14
GlnTAGchr6.trna63
GlnTAGchr6.trna175
GlnTAGchr6.trna82
GlnTAGchr2.trna26
GlnTAAnmt-tRNA-Gln
chr10.trna6
GlnTAAnmt-tRNA-Gln
chrX.trna1
GlnTAAnmt-tRNA-
Glnc_hr7.trna32
GlnTAAnmt-tRNA-Gln
chr7.trna7
GlnTAAnmt-tRNA-Gln
chr12.trna15
GlnTAAnmt-tRNA-Gln
chr2.trna21
GlnTAAnmt-tRNA-
Glnchr2.trna9
GlnTAAchr6.trna147
GlnTAAchr1.trna17
GlnTAAchr1.trna101
GlnTAAchr6.trna42
GlnTAAchr6.trna132
GlnTAAchr1.trna23
GlnTAAchr1.trna111
GlnTAAchr1.trna24
GlnTAAchr19.trna4
GlnTAAchr17.trna14
GlnTAAchr6.trna63
GlnTAAchr6.trna175
GlnTAAchr6.trna82
GlnTAAchr2.trna26
GluTAAchr1.trna106
GluTAAchr1.trna55
GluTAAchr2.trna18
GluTAAchr13.trna2
GluTAAchr1.trna5
GluTAAchr1.trna123
GluTAGchr1.trna106
GluTAGchr2.trna18
GluTAGchr1.trna92
GluTAGchr13.trna2
GluTAGchr1.trna5
GluTAGchr1.trna86
ctacttcctcagtaggagacGTCCTTAGGtTGCTGGT
TyrTAAchr6.trna14
TyrTAAchr6.trna14/
nointron
TyrTAA_chr7.trna12
TyrTAAchr7.trna28
TyrTAAchr15.trna6
TyrTAA_chr2.trna2
TyrTAAchr2.trna2/n
ointron
TyrTAAchr6.trna16
TyrTAAchr6.trna16/
nointron
TyrTAAchr14.trna19
TyrTAAchr14.trna19
/nointron
TyrTAAchr8.trna2
TyrTAAchr8.trna2/n
ointron
TyrTAAchr8.trna3
TyrTAAchr8.trna3/n
ointron
TyrTAAchr14.trna20
TyrTAAchr14.trna20/
nointron
TyrTAAchr14.trna17
TyrTAAchr14.trna17/
nointron
TyrTAAchr14.trna5
TyrTAAchr14.trna5/
nointron
TyrTAAchr6.trna17
TyrTAAchr6.trna17/
nointron
TyrTAAchr14.trna18
TyrTAAchr14.trna18/
nointron
TyrTAAchr6.trna15
TyrTAAchr6.trna15/
nointron
TyrTAAchr7.trna1
TyrTAGchr1.trna52
TyrTAGchr11.trna9
TyrTAGchr6.trna14
TyrTAGchr6.trna14/
nointron
TyrTAGchr7.trna12
TyrTAGchr7.trna28
TyrTAGchr15.trna6
TyrTAGchr2.trna2
TyrTAGchr2.trna2/n
ointron
TyrTAGchr6.trna16
TyrTAGchr6.trna16/
nointron
TyrTAGchr14.trna19
TyrTAG
chr14.trna19/
nointron
TyrTAGchr8.trna2
TyrTAGchr8.trna2/
nointron
TyrTAGchr8.trna3
TyrTAGchr8.trna3/
nointron
TyrTAGchr14.trna20
TyrTAGchr14.trna20/
nointron
TyrTAGchr14.trna17
TyrTAGchr14.trna17/
nointron
TyrTAGchr14.trna5
TyrTAGchr14.trna5/
nointron
TyrTAGchr6.trna17
TyrTAGchr6.trna17/
nointron
TyrTAGchr14.trna18
TyrTAGchr14.trna18/
nointron
TyrTAGchr6.trna15
TyrTAGchr6.trna15/
nointron
LeuTAAnmtchrX.
trna2
LeuTAAchr6.trna100
/nointron
LeuTAAchr6.trna73
LeuTAAchr6.trna73/
nointron
LeuTAAchr6.trna141
LeuTAAchr6.trna141
/nointron
LeuTAAchr6.trna142
LeuTAAchr6.trna142
/nointron
LeuTAAchr1.trna54
LeuTAAchr11.trna1
LeuTAAchr6.trna81
LeuTAAchr6.trna135
LeuTAAchr11.trna4
LeuTAAchr6.trna156
LeuTAAchr6.trna79
LeuTAAchr1.trna9
LeuTAAchr11.trna12
LeuTAAchr17.trna42
LeuTAAchr14.trna2
LeuTAAchr16.trna27
LeuTAAchr14.trna16
LeuTAGchr4.trna2
LeuTAGnmtchrX.trna
2
LeuTAGchr6.trna77
LeuTAGchr6.trna127
LeuTAGchr5.trna20
LeuTAGchr6.trna100
LeuTAGchr6.trna100
/nointron
LeuTAGchr6.trna73
LeuTAGchr6.trna73/
nointron
LeuTAGchr6.trna141
LeuTAGchr6.trna141
/nointron
LeuTAGchr6.trna142
LeuTAGchr6.trna142
/nointron
LeuTAGchr1.trna54
LeuTAGchr11.trna1
LeuTAGchr9.trna7
LeuTAGchr6.trna81
LeuTAGchr6.trna135
LeuTAGchr11.trna4
LeuTAGchr6.trna156
LeuTAGchr6.trna79
LeuTAGchr1.trna9
LeuTAGchr17.trna42
LeuTAGchr14.trna2
LeuTAGchr16.trna27
LeuTAGchr14.trna16
LeuTGAchr6.trna77
LeuTGAchr6.trna100
LeuTGAchr6.trna100
/nointron
LeuTGAchr6.trna73
LeuTGAchr6.trna73/
nointron
LeuTGAchr6.trna141
LeuTGAchr6.trna141
/nointron
LeuTGAchr6.trna142
LeuTGAchr6.trna142
/nointron
LeuTGAchr1.trna54
LeuTGAchr6.trna81
LeuTGAchr6.trna135
LeuTGAchr11.trna4
LeuTGAchr6.trna156
LeuTGAchr6.trna79
LeuTGAchr1.trna9
LeuTGAchr11.trna12
LeuTGAchr17.trna42
LeuTGAchr14.trna2
LeuTGAchr16.trna27
SerTAGnmtchr2.trna
7
SerTAGchr6.trna148
SerTAGchr6.trna50
SerTAGchr6.trna146
SerTAGchr7.trna15
SerTAGchr11.trna10
SerTAGchr11.trna8
SerTAGchr17.trna41
SerTAGchr6.trna34
SerTAGchr6.trna138
SerTAGchr12.trna2
SerTAGchr6.trna30
SerTAGchr6.trna43
SerTAGchr11.trna6
SerTAGchr6.trna61
SerTAGchr6.trna176
SerTAGchr10.trna2
SerTAGchr6.trna51
SerTAGchr6.trna173
SerTAGchr6.trna149
SerTGAchr6.trna148
SerTGAchr6.trna50
SerTGAchr6.trna146
SerTGAchr11.trna10
SerTGAchr17.trna41
SerTGAchr6.trna34
SerTGAchr6.trna138
SerTGAchr12.trna2
SerTGAchr6.trna30
SerTGAchr6.trna43
SerTGAchr11.trna6
SerTGAchr6.trna61
SerTGAchr10.trna2
SerTGAchr6.trna51
SerTGAchr6.trna173
SerTGAchr6.trna149
SerTAAchr6.trna148
SerTAAchr6.trna50
SerTAAchr6.trna146
SerTAAchr17.trna41
SerTAAchr6.trna34
SerTAAchr6.trna138
SerTAAchr12.trna2
SerTAAchr6.trna30
SerTAAchr6.trna43
SerTAAchr11.trna6
SerTAAchr6.trna61
SerTAAchr6.trna176
SerTAAchr10.trna2
SerTAAchr6.trna51
SerTAAchr6.trna173
SerTAAchr6.trna149
LysTAAchr19.trna6
LysTAAchr16.trna31
LysTAAchr16.trna11
LysTAAchr16.trna30
LysTAAchr16.trna6
LysTAAchr16.trna23
LysTAAchr19.trna8
LysTAAchr2.trna15
LysTAAchr11.trna11
LysTAAchr6.trna144
LysTAAchr11.trna5
LysTAAchr6.trna150
LysTAAchr6.trna70
LysTAAchr6.trna53
LysTAGchr19.trna6
LysTAGchr16.trna31
LysTAGchr16.trna11
LysTAGchr16.trna23
LysTAGchr19.trna8
LysTAGchr11.trna11
LysTAGchr6.trna144
LysTAGchr11.trna5
LysTAGchr6.trna150
LysTAGchr6.trna70
CysTGAchr7.trna8
CysTGAchr7.trna24
CysTGAchr7.trna20
CysTGAchr7.trna29
CysTGAchr7.trna13
CysTGAchr7.trna23
CysTGAchr17.trna27
CysTGAchr15.trna3
CysTGAchr3.trna6
CysTGAchr14.trna9
CysTGAchr3.trna5
Although the foregoing specification and examples fully disclose and enable the present invention, they are not intended to limit the scope of the invention, which is defined by the claims appended hereto.
All publications, patents and patent applications are incorporated herein by reference. While in the foregoing specification this invention has been described in relation to certain embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein may be varied considerably without departing from the basic principles of the invention.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
This application is a divisional of U.S. patent application Ser. No. 16/761,205, filed May 1, 2020, which is a 35 U.S.C. § 371 application of International Application Serial No. PCT/US2018/059065, filed Nov. 2, 2018; which claims the benefit of U.S. Provisional Application Ser. No. 62/580,887, filed Nov. 2, 2017 and U.S. Provisional Application Ser. No. 62/687,015, filed Jun. 19, 2018. The entire content of the applications referenced above are hereby incorporated by reference herein.
This invention was made with government support under R01 GM106569 awarded by the National Institutes of Health. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62580887 | Nov 2017 | US | |
| 62687015 | Jun 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16761205 | May 2020 | US |
| Child | 18137942 | US |
