BACKGROUND

Genome editing via sequence-specific nucleases is known. See references 1, 2, and 3 hereby incorporated by reference in their entireties. A nuclease-mediated double-stranded DNA (dsDNA) break in the genome can be repaired by two main mechanisms: Non-Homologous End Joining (NHEJ), which frequently results in the introduction of non-specific insertions and deletions (indels), or homology directed repair (HDR), which incorporates a homologous strand as a repair template. See reference 4 hereby incorporated by reference in its entirety. When a sequence-specific nuclease is delivered along with a homologous donor DNA construct containing the desired mutations, gene targeting efficiencies are increased by 1000-fold compared to just the donor construct alone. See reference 5 hereby incorporated by reference in its entirety. Use of single stranded oligodeoxyribonucleotides (“ssODNs”) as DNA donors has been reported. See references 21 and 22 hereby incorporated by reference in their entireties.

Despite large advances in gene editing tools, many challenges and questions remain regarding the use of custom-engineered nucleases in human induced pluripotent stem cell (“hiPSC”) engineering. First, despite their design simplicity, Transcription Activator-Like Effectors Nucleases (TALENs) target particular DNA sequences with tandem copies of Repeat Variable Diresidue (RVD) domains. See reference 6 hereby incorporated by reference in its entirety. While the modular nature of RVDs simplifies TALEN design, their repetitive sequences complicate methods for synthesizing their DNA constructs (see references 2, 9, and 15-19 hereby incorporated by reference in their entireties) and also impair their use with lentiviral gene delivery vehicles. See reference 13 hereby incorporated by reference in its entirety.

In current practice, NHEJ and HDR are frequently evaluated using separate assays. Mismatch-sensitive endonuclease assays (see reference 14 hereby incorporated by reference in its entirety) are often used for assessing NHEJ, but the quantitative accuracy of this method is variable and the sensitivity is limited to NHEJ frequencies greater than ˜3%. See reference 15 hereby incorporated by reference in its entirety. HDR is frequently assessed by cloning and sequencing, a completely different and often cumbersome procedure. Sensitivity is still an issue because, while high editing frequencies on the order of 50% are frequently reported for some cell types, such as U2OS and K562 (see references 12 and 14 hereby incorporated by reference in their entireties), frequencies are generally lower in hiPSCs. See reference 10 hereby incorporated by reference in its entirety. Recently, high editing frequencies have been reported in hiPSC and hESC using TALENs (see reference 9 hereby incorporated by reference in its entirety), and even higher frequencies with the CRISPR Cas9-gRNA system (see references 16-19 hereby incorporated by reference in their entireties. However, editing rates at different sites appear to vary widely (see reference 17 hereby incorporated by reference in its entirety), and editing is sometimes not detectable at all at some sites (see reference 20 hereby incorporated by reference in its entirety).

Bacterial and archaeal CRISPR-Cas systems rely on short guide RNAs in complex with Cas proteins to direct degradation of complementary sequences present within invading foreign nucleic acid. See Deltcheva, E. et al. CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III.Nature471, 602-607 (2011); Gasiunas, G., Barrangou, R., Horvath, P. & Siksnys, V. Cas9-crRNA ribonucleoprotein complex mediates specific DNA cleavage for adaptive immunity in bacteria.Proceedings of the National Academy of Sciences of the United States of America109, E2579-2586 (2012); Jinek, M. et al. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity.Science337, 816-821 (2012); Sapranauskas, R. et al. TheStreptococcus thermophilusCRISPR/Cas system provides immunity inEscherichia coli. Nucleic acids research39, 9275-9282 (2011); and Bhaya, D., Davison, M. & Barrangou, R. CRISPR-Cas systems in bacteria and archaea: versatile small RNAs for adaptive defense and regulation.Annual review of genetics45, 273-297 (2011). A recent in vitro reconstitution of theS. pyogenestype II CRISPR system demonstrated that crRNA (“CRISPR RNA”) fused to a normally trans-encoded tracrRNA (“trans-activating CRISPR RNA”) is sufficient to direct Cas9 protein to sequence-specifically cleave target DNA sequences matching the crRNA. Expressing a gRNA homologous to a target site results in Cas9 recruitment and degradation of the target DNA. See H. Deveau et al., Phage response to CRISPR-encoded resistance inStreptococcus thermophilus. Journal of Bacteriology190, 1390 (February, 2008).

SUMMARY

Aspects of the present disclosure are directed to the use of modified Transcription Activator-Like Effector Nucleases (TALENs) for genetically modifying a cell, such as a somatic cell or a stem cell. TALENs are known to include repeat sequences. Aspects of the present disclosure are directed to a method of altering target DNA in a cell including introducing into a cell a TALEN lacking repeat sequences 100 bp or longer wherein the TALEN cleaves the target DNA and the cell undergoes nonhomologous end joining to produce altered DNA in the cell. According to certain aspects, repeat sequences of desired length have been removed from a TALEN. According to certain aspects, the TALEN is devoid of repeat sequences of certain desired length. According to certain aspects, a TALEN is provided with repeat sequences of desired length removed. According to certain aspects, a TALEN is modified to remove repeat sequences of desired length. According to certain aspects, a TALEN is engineered to remove repeat sequences of desired length.

Aspects of the present disclosure include methods of altering target DNA in a cell including combining within a cell a TALEN lacking repeat sequences 100 bp or longer and a donor nucleic acid sequence wherein the TALEN cleaves the target DNA and the donor nucleic acid sequence is inserted into the DNA in the cell. Aspects of the present disclosure are directed to a virus including a nucleic acid sequence encoding a TALEN lacking repeat sequences 100 bp or longer. Aspects of the present disclosure are directed to a cell including a nucleic acid sequence encoding a TALEN lacking repeat sequences 100 bp or longer. According to certain aspects described herein, the TALEN lacks repeat sequences 100 bp or longer, 90 bp or longer, 80 bp or longer, 70 bp or longer, 60 bp or longer, 50 bp or longer, 40 bp or longer, 30 bp or longer, 20 bp or longer, 19 bp or longer, 18 bp or longer, 17 bp or longer, 16 bp or longer, 15 bp or longer, 14 bp or longer, 13 bp or longer, 12 bp or longer, 11 bp or longer, or 10 bp or longer.

Aspects of the present disclosure are directed to making a TALE including combining an endonuclease, a DNA polymerase, a DNA ligase, an exonuclease, a plurality of nucleic acid dimer blocks encoding repeat variable diresidue domains and a TALE-N/TF backbone vector including an endonuclease cutting site, activating the endonuclease to cut the TALE-N/TF backbone vector at the endonuclease cutting site to produce a first end and a second end, activating the exonuclease to create a 3′ and a 5′ overhang on the TALE-N/TF backbone vector and the plurality of nucleic acid dimer blocks and to anneal the TALE-N/TF backbone vector and the plurality of nucleic acid dimer blocks in a desired order, activating the DNA polymerase and the DNA ligase to connect the TALE-N/TF backbone vector and the plurality of nucleic acid dimer blocks. One of skill in the art will readily based on the present disclosure be able to identify suitable endonucleases, DNA polymerases, DNA ligases, exonucleases, nucleic acid dimer blocks encoding repeat variable diresidue domains and TALE-N/TF backbone vectors.

Aspects of the present disclosure are directed to a method of altering target DNA in a stem cell expressing an enzyme that forms a co-localization complex with RNA complementary to the target DNA and that cleaves the target DNA in a site specific manner including (a) introducing into the stem cell a first foreign nucleic acid encoding an RNA complementary to the target DNA and which guides the enzyme to the target DNA, wherein the RNA and the enzyme are members of a co-localization complex for the target DNA, introducing into the stem cell a second foreign nucleic acid encoding a donor nucleic acid sequence, wherein the RNA and the donor nucleic acid sequences are expressed, wherein the RNA and the enzyme co-localize to the target DNA, the enzyme cleaves the target DNA and the donor nucleic acid is inserted into the target DNA to produce altered DNA in the stem cell.

Aspects of the present disclosure are directed to a stem cell including a first foreign nucleic acid encoding for an enzyme that forms a co-localization complex with RNA complementary to target DNA and that cleaves the target DNA in a site specific manner.

Aspects of the present disclosure are directed to a cell including a first foreign nucleic acid encoding for an enzyme that forms a co-localization complex with RNA complementary to target DNA and that cleaves the target DNA in a site specific manner and including an inducible promoter for promoting expression of the enzyme. In this manner, expression can be regulated, for example, it can be started and it can be stopped.

Aspects of the present disclosure are directed to a cell including a first foreign nucleic acid encoding for an enzyme that forms a co-localization complex with RNA complementary to target DNA and that cleaves the target DNA in a site specific manner, wherein the first foreign nucleic acid is removable from genomic DNA of the cell using a removal enzyme, such as a transposase.

Aspects of the present disclosure are directed to a method of altering target DNA in a cell expressing an enzyme that forms a co-localization complex with RNA complementary to the target DNA and that cleaves the target DNA in a site specific manner including (a) introducing into the cell a first foreign nucleic acid encoding a donor nucleic acid sequence, introducing into the cell from media surrounding the cell an RNA complementary to the target DNA and which guides the enzyme to the target DNA, wherein the RNA and the enzyme are members of a co-localization complex for the target DNA, wherein the donor nucleic acid sequence is expressed, wherein the RNA and the enzyme co-localize to the target DNA, the enzyme cleaves the target DNA and the donor nucleic acid is inserted into the target DNA to produce altered DNA in the cell.

Aspects of the present disclosure are directed to the use of an RNA guided DNA binding protein for genetically modifying a stem cell. In one aspect, the stem cell has been genetically modified to include a nucleic acid encoding for the RNA guided DNA binding protein and the stem cell expresses the RNA guided DNA binding protein. According to a certain aspect, donor nucleic acids for introducing specific mutations are optimized for genome editing using either the modified TALENs or the RNA guided DNA binding protein.

Aspects of the present disclosure are directed to the modification of DNA, such as multiplex modification of DNA, in a stem cell using one or more guide RNAs (ribonucleic acids) to direct an enzyme having nuclease activity expressed by the stem cell, such as a DNA binding protein having nuclease activity, to a target location on the DNA (deoxyribonucleic acid) wherein the enzyme cuts the DNA and an exogenous donor nucleic acid is inserted into the DNA, such as by homologous recombination. Aspects of the present disclosure include cycling or repeating steps of DNA modification on a stem cell to create a stem cell having multiple modifications of DNA within the cell. Modifications may include insertion of exogenous donor nucleic acids.

Multiple exogenous nucleic acid insertions can be accomplished by a single step of introducing into a stem cell, which expresses the enzyme, nucleic acids encoding a plurality of RNAs and a plurality of exogenous donor nucleic acids, such as by co-transformation, wherein the RNAs are expressed and wherein each RNA in the plurality guides the enzyme to a particular site of the DNA, the enzyme cuts the DNA and one of the plurality of exogenous nucleic acids is inserted into the DNA at the cut site. According to this aspect, many alterations or modification of the DNA in the cell are created in a single cycle.

Multiple exogenous nucleic acid insertions can be accomplished in a cell by repeated steps or cycles of introducing into a stem cell, which expresses the enzyme, one or more nucleic acids encoding one or more RNAs or a plurality of RNAs and one or more exogenous nucleic acids or a plurality of exogenous nucleic acids wherein the RNA is expressed and guides the enzyme to a particular site of the DNA, the enzyme cuts the DNA and the exogenous nucleic acid is inserted into the DNA at the cut site, so as to result in a cell having multiple alterations or insertions of exogenous DNA into the DNA within the stem cell. According to one aspect, the stem cell expressing the enzyme has been genetically altered to express the enzyme such as by introducing into the cell a nucleic acid encoding the enzyme and which can be expressed by the stem cell. In this manner, aspects of the present disclosure include cycling the steps of introducing RNA into a stem cell which expresses the enzyme, introducing exogenous donor nucleic acid into the stem cell, expressing the RNA, forming a co-localization complex of the RNA, the enzyme and the DNA, enzymatic cutting of the DNA by the enzyme, and insertion of the donor nucleic acid into the DNA. Cycling or repeating of the above steps results in multiplexed genetic modification of a stem cell at multiple loci, i.e., a stem cell having multiple genetic modifications.

According to certain aspects, DNA binding proteins or enzymes within the scope of the present disclosure include a protein that forms a complex with the guide RNA and with the guide RNA guiding the complex to a double stranded DNA sequence wherein the complex binds to the DNA sequence. According to one aspect, the enzyme can be an RNA guided DNA binding protein, such as an RNA guided DNA binding protein of a Type II CRISPR System that binds to the DNA and is guided by RNA. According to one aspect, the RNA guided DNA binding protein is a Cas9 protein.

This aspect of the present disclosure may be referred to as co-localization of the RNA and DNA binding protein to or with the double stranded DNA. In this manner, a DNA binding protein-guide RNA complex may be used to cut multiple sites of the double stranded DNA so as to create a stem cell with multiple genetic modifications, such as multiple insertions of exogenous donor DNA.

According to certain aspects, a method of making multiple alterations to target DNA in a stem cell expressing an enzyme that forms a co-localization complex with RNA complementary to the target DNA and that cleaves the target DNA in a site specific manner is provided including (a) introducing into the stem cell a first foreign nucleic acid encoding one or more RNAs complementary to the target DNA and which guide the enzyme to the target DNA, wherein the one or more RNAs and the enzyme are members of a co-localization complex for the target DNA, introducing into the stem cell a second foreign nucleic acid encoding one or more donor nucleic acid sequences, wherein the one or more RNAs and the one or more donor nucleic acid sequences are expressed, wherein the one or more RNAs and the enzyme co-localize to the target DNA, the enzyme cleaves the target DNA and the donor nucleic acid is inserted into the target DNA to produce altered DNA in the stem cell, and repeating step (a) multiple times to produce multiple alterations to the DNA in the stem cell.

According to one aspect, the RNA is between about 10 to about 500 nucleotides. According to one aspect, the RNA is between about 20 to about 100 nucleotides.

According to one aspect, the one or more RNAs is a guide RNA. According to one aspect, the one or more RNAs is a tracrRNA-crRNA fusion.

According to one aspect, the DNA is genomic DNA, mitochondrial DNA, viral DNA, or exogenous DNA.

According to one aspect, a cell may be genetically modified to reversibly include a nucleic acid encoding a DNA binding enzyme using a vector which can be easily removed using an enzyme. Useful vectors methods are known to those of skill in the art and include lentivirus, adeno associated virus, nuclease and integrase mediated tarteget insertion methods and transposon mediated insertion methods. According to one aspect, the nucleic acid encoding a DNA binding enzyme that has been added, such as by using a cassette or vector can be removed in its entirety along with the cassette and vector and without leaving a portion of such nucleic acid, cassette or vector in the genomic DNA, for example. Such removal is referred to in the art as “scarless” removal, as the genome is the same as it was before addition of the nucleic acid, cassette or vector. One exemplary embodiment for insertion and scarless removal is a PiggyBac vector commercially available from System Biosciences.

Further features and advantages of certain embodiments of the present invention will become more fully apparent in the following description of embodiments and drawings thereof, and from the claims.

