CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present Application claims the benefit of U.S. Provisional App. No. 61/721 ,365 filed November 1 , 2012, and U.S. Provisional App. No. 61/779,987, filed March 13, 2013, each of which is hereby incorporated by reference in its entirety. This present application is related to U.S. Application No. 13/400,945, filed February 12, 2012.

STATEMENT REGARDING FEDERALLY SPONSORED R&D

[0002] This invention was made with government support under HHSN26120080000 IE awarded by the National Institutes of Health. The government has certain rights in the invention.

REFERENCE TO SEQUENCE LISTING, TABLE, OR COMPUTER PROGRAM LISTING

[0003] The present application is being filed along with a Sequence Listing in electronic format. The Sequence Listing is provided as a file

CALTE092WO_SEQLIST.TXT, created and last modified on October 30, 2013, which is 44,648 bytes in size. The information in the electronic format of the Sequence Listing is incorporated herein by reference in its entirety.

Field

[0004] Embodiments herein relate generally to inducible gene expression systems and methods expressing gene products.

SUMMARY

[0005] In some embodiments, an inducible expression system for gene products is provided. The system can comprise a first adeno-associated virus vector comprising a first ITR, a promoter positioned 3 ' to the first ITR, a first recombinase target site positioned 3 ' to the first ITR and 5 ' to a 3 ' end of the promoter, a second recombinase target site positioned 3 ' to a 5 ' end of the promoter, an insertion site positioned 3 ' to the promoter and 3 ' to the second recombinase target site, such that the promoter would be operably linked to at least an inserted polynucleotide, a third recombinase target site positioned 3 ' to the insertion site, and a second ITR positioned 3' to the third recombinase target site. In some embodiments, the first, second, and third recombinase target sites are oriented in the same direction. The system can include a source of a recombinase configured to induce recombination events between two or more of the recombinase target sites. In some embodiments, the source of recombinase comprises a second vector comprising a promoter operably linked to a recombinase polynucleotide encoding the recombinase. In some embodiments, the second vector comprises one of an adeno-associated virus vector, or an adenovirus vector. In some embodiments, the source of recombinase comprises a recombinase polypeptide fused to a cell-penetration peptide. In some embodiments, the first adeno-associated virus vector further comprises a WPRE positioned 3' to the insertion site and 5' to the second ITR, a fourth recombinase target site positioned 3 ' to the insertion site and 5' to a 3 ' end of the WPRE, a fifth recombinase target site positioned 3' to the fourth recombinase target site, and 3' to a 5' end of the WPRE, and a sixth recombinase target site positioned 3' of the first recombinase target site and 5' of the second recombinase target site. In some embodiments, the fourth, fifth, and sixth recombinase target sites are oriented in the same direction. In some embodiments, the third recombinase target site is positioned 3' to the WPRE and 5' to the second ITR. In some embodiments, the promoter comprises a synthetic intron comprising a splice donor, a transcriptional enhancer positioned 3 ' to the splice donor, and a splice acceptor positioned 3' to the splice donor, in which the first recombinase target and second recombinase target flank the synthetic intron. In some embodiments, the recombinase target sites of the AAV vector of the expression system comprise Lox sites and the recombinase comprises Cre. In some embodiments, the recombinase target sites of the AAV vector of the expression system comprise FRT sites and the recombinase comprises FLPase. In some embodiments, the first, second, and third recombinase target sites are identical to each other. In some embodiments, the fourth, fifth, and sixth recombinase target sites are identical to each other. In some embodiments, the first, second, third, fourth, fifth, and sixth recombinase target sites are identical to each other. In some embodiments, the first adeno-associated vector further comprises a cleavage polynucleotide positioned 3' to the third recombinase target site. In some embodiments, the WPRE comprises the polynucleotide sequence of SEQ ID NO: 27, SEQ ID NO: 28, or SEQ ID NO: 29. In some embodiments, the adeno-associated vector further comprises a polyadenylation sequence positioned 3 ' of the WPRE and 5' of the third recombinase target site. In some embodiments, the polyadenylation sequence comprises the polynucleotide sequence of SEQ ID NO: 26, or SEQ ID NO: 43. In some embodiments, the first, second, third, fourth, fifth, and sixth recombinase target sites are oriented in the same direction. In some embodiments, the first, second, and third recombinase target sites are oriented in a direction opposite the fourth, fifth, and sixth recombinase target sites. In some embodiments, the first adeno- associated virus vector further comprises a WPRE positioned 3 ' to the insertion site and 5 ' to the second ITR, a fourth recombinase target site positioned 3 ' to the first polynucleotide and 5' to a 3 ' end of the WPRE, a fifth recombinase target site positioned 3 ' to the fourth recombinase target site, and 3 ' to a 5 ' end of the WPRE. In some embodiments, the fourth and fifth recombinase target sites are oriented in the same direction. In some embodiments, the third recombinase target site is positioned 3 ' to the WPRE and 5 ' to the second ITR. In some embodiments, the first, second, third, fourth, and fifth recombinase target sites are oriented in the same direction.

[0006] In some embodiments, a method of conditionally expressing at least a first gene product in a mammal is provided. The method can comprise administering to the mammal a first adeno-associated virus vector comprising a first ITR, a promoter positioned 3 ' to the first ITR, a first recombinase target site positioned 3 ' to the first ITR and 5 ' to a 3 ' end of the promoter, a second recombinase target site positioned 3 ' to a 5' end of the promoter, and a first polynucleotide encoding a first gene product, in which the first polynucleotide is positioned 3 ' to the promoter and 3 ' to the second recombinase target site, and in which the promoter is operably linked to the first polynucleotide, a third recombinase target site positioned 3 ' to the first polynucleotide, and a second ITR positioned 3 ' to the third recombinase target site, in which the first, second, and third recombinase target sites are oriented in the same direction. After administration of the first adeno-associated virus vector, the first gene product can be expressed in the mammal. The method can further comprise administering a recombinase to the mammal, so that the recombinase induces recombination between at least two of the recombinase target sites after the first gene product is expressed, thus reducing expression of the first gene product. In some embodiments, administering the recombinase comprises administering a second vector to the mammal, in which the second vector comprises a promoter operably linked to a recombinase polynucleotide encoding the recombinase. In some embodiments, expression of the recombinase polynucleotide is induced after the first gene product is expressed, thus reducing expression of the first gene product. In some embodiments, the recombinase is administered after the first adeno-associated virus vector, thereby reducing expression of the first gene product. In some embodiments, administering the recombinase comprises contacting at least one cell of the mammal with the recombinase fused to a cell-penetration polypeptide. In some embodiments, the recombinase target sites comprise Lox sites and the recombinase comprises Cre. In some embodiments, the recombinase target sites comprise FRT sites and the recombinase comprises FLPase. In some embodiments, the first gene product comprises at least a heavy chain or a light chain of an immunoglobulin. In some embodiments, the first adeno-associated virus vector further comprises a cleavage polynucleotide positioned 3' of the first polynucleotide, and a second polynucleotide encoding a second gene product positioned 3' of the cleavage polynucleotide. In some embodiments, the first adeno-associated virus vector further comprises a WPRE positioned 3 ' to the insertion site and 5 ' to the second ITR, a fourth recombinase target site positioned 3' to the first polynucleotide and 5' to a 3 ' end of the WPRE, a fifth recombinase target site positioned 3' to the fourth recombinase target site, and 3' to a 5' end of the WPRE, and a sixth recombinase target site positioned 3 ' of the first recombinase target site and 5 ' of the second recombinase target site. In some embodiments, the fourth, fifth, and sixth recombinase target sites are oriented in the same direction. In some embodiments, the third recombinase target site is positioned 3 ' to the WPRE and 5' to the second ITR. In some embodiments, the recombinase induces recombination events involving the first, second, third, fourth, fifth, and sixth recombinase target sites, thereby excising at least a portion of the first adeno-associated virus vector. In some embodiments, the first adeno-associated virus vector further comprises a WPRE positioned 3 ' to the insertion site and 5 ' to the second ITR, a fourth recombinase target site positioned 3 ' to the first polynucleotide and 5 ' to a 3 ' end of the WPRE, a fifth recombinase target site positioned 3' to the fourth recombinase target site, and 3' to a 5' end of the WPRE. In some embodiments, the fourth and fifth recombinase target sites are oriented in the same direction. In some embodiments, the third recombinase target site is positioned 3 ' to the WPRE and 5' to the second ITR. In some embodiments, the recombinase induces recombination events involving the first, second, third, fourth, and fifth recombinase target sites, thereby excising at least a portion of the first adeno-associated virus vector.

[0007] In some embodiments, expression of the first gene product is reduced at least 10-fold. In some embodiments, the mammal is a mouse. In some embodiments, the mammal is a human

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A is a schematic diagram illustrating an adeno-associated vector for expressing a gene product of interest in accordance with some embodiments herein. Solid arrows indicate recombinase target sites and their relative orientations.

[0009] Figure IB is a schematic diagram illustrating promoter region for expressing a gene product of interest in accordance with some embodiments herein. Recombinase target sites (and relative orientations) are depicted as solid arrows.

[0010] Figure 2A is a schematic diagram of an adeno-associated vector for expressing a gene product of interest in accordance with some embodiments herein.

[0011] Figure 2B is a graph illustrating luciferase activity in 293T cells with adeno-associated virus (AAV) constructs according to some embodiments herein. The AAV constructs were based on the vector of Figure 2A and contained one loxP site. Luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0012] Figure 2C is a schematic diagram illustrating the position of the loxP site for each of the constructs used in the experiment depicted in Figure 2B. For each experiment (e.g. each pair of bars) in Figure 2B, the corresponding construct schematic is shown in Figure 2C to the right of the bars. LoxP sites (and relative orientations) are depicted as solid arrows.

[0013] Figure 3A is a schematic diagram of an adeno-associated vector for expressing a gene product of interest in accordance with some embodiments herein. [0014] Figure 3B is a graph illustrating luciferase activity in 293T cells transfected with AAV constructs according to some embodiments herein. The constructs were based on the vector of Figure 3A, and contained two loxP sites. The luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0015] Figure 3C is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 3B. For each experiment (e.g. each pair of bars) in Figure 3B, the corresponding construct schematic is shown in Figure 3C to the right of the bars. LoxP sites (and relative orientations) are depicted as solid arrows.

[0016] Figure 4A is a graph illustrating luciferase activity in 293T cells transfected with AAV constructs according to some embodiments herein. The constructs contained three loxP sites, and luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0017] Figure 4B is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 4A. For each experiment (e.g. each pair of bars) in Figure 4 A, the corresponding construct schematic is shown in Figure 4B to the right of the bars. LoxP sites (and relative orientations) are depicted as solid arrows.

[0018] Figure 5A is a schematic diagram of an adeno-associated vector for expressing a gene product of interest in accordance with some embodiments herein.

[0019] Figure 5B is a graph illustrating luciferase activity in 293T cells transfected with AAV constructs according to some embodiments herein. The constructs were based on the vector of Figure 5A and contained four loxP sites. Luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0020] Figure 5C is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 5B. For each experiment (e.g. each pair of bars) in Figure 5B, the corresponding construct schematic is shown in Figure 5C to the right of the bars. LoxP sites (and relative orientations) are depicted as solid arrows.

[0021] Figure 6A is a graph illustrating luciferase activity in 293T cells transfected with AAV constructs according to some embodiments herein. Each construct contained five loxP sites. Luciferase activity for each construct was observed in the absence of CPvE (i.e., pUC) and the presence or CRE.

[0022] Figure 6B is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 6A. For each experiment (e.g. each pair of bars) in Figure 6 A, the corresponding construct schematic is shown in Figure 6B to the right of the bars. LoxP sites (and relative orientations) are depicted as solid arrows.

[0023] Figure 7A is a schematic diagram of an adeno-associated vector for expressing a gene product of interest in accordance with some embodiments herein.

[0024] Figure 7B is a graph illustrating luciferase activity in 293T cells transfected with AAV constructs according to some embodiments herein. The AAV constructs were based on the vector of Figure 7A, and contained six loxP sites. Luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0025] Figure 7C is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 7B. For each experiment (e.g. each pair of bars) in Figure 7B, the corresponding construct schematic is shown in Figure 7C to the right of the bars. LoxP sites (and relative orientations) are depicted as solid arrows.

[0026] Figure 8A is a graph illustrating luciferase activity in 293T cells transfected with shortened AAV constructs according to some embodiments herein. The constructs contained five loxP sites. Luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0027] Figure 8B is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 8A. For each experiment (e.g. each pair of bars) in Figure 8 A, the corresponding construct schematic is shown in Figure 8B to the right of the bars. Certain elements of the constructs are depicted, include a WPRE, WPRE (No X), WPRE (Short), SV40 PolyA sequence, and a synthetic PolyA sequence. LoxP sites (and relative orientations) are depicted as solid arrows.

[0028] Figure 9A is a graph illustrating luciferase activity in 293T cells transfected with shortened AAV constructs according to some embodiments herein. The constructs contained five loxP sites. Luciferase activity for each construct was observed in the absence of CRE (i.e., pUC) and the presence or CRE.

[0029] Figure 9B is a schematic diagram illustrating the position of the loxP sites for each of the constructs used in the experiment depicted in Figure 9A. For each experiment (e.g. each pair of bars) in Figure 9 A, the corresponding construct schematic is shown in Figure 9B to the right of the bars. Certain elements of the constructs are depicted, include a WPRE, WPRE (No X), WPRE (Short), SV40 PolyA sequence, and a synthetic PolyA sequence. LoxP sites (and relative orientations) are depicted as solid arrows.

[0030] Figure 10 is a schematic diagram illustrating an experimental protocol for reversibly expressing gene products encoded by AAV vector according to some embodiments herein.

[0031] Figure 11 is a series of photographs illustrating Xenogen imaging of mice injected with AAV (AAV) vectors in accordance with some embodiments herein. Each mouse was injected with the indicated adeno-associated vector encoding luciferase. Mice 1 and 2 (from left) were injected with a mixture of AAV vector encoding luciferase and AAV vector encoding ZsGreen. Mice 3 and 4 (from left) were injected with a mixture of AAV vector encoding luciferase and AAV vector encoding Cre. The images of Figure 11 were taken one week after administering the Cre. Figure HA illustrates the results for vector 1594, Figure 11B illustrates the results for vector 1784, Figure 11C illustrates the results for vector 1799, Figure 11D illustrates the results for vector 1605, Figure HE illustrates the results for vector 1785, Figure 11F illustrates the results for vector 1800, Figure 11G illustrates the results for vector 1782, Figure 11H illustrates the results for vector 1797, Figure HI illustrates the results for vector 1806, Figure 11 J illustrates the results for vector 1490, Figure HK illustrates the results for vector 1783, Figure 11L illustrates the results for vector 1798, and Figure 11M illustrates the results for vector 1180.

[0032] Figure 12 is a series of photographs illustrating Xenogen imaging of mice injected with AAV vectors in accordance with some embodiments herein. Each mouse was injected with the indicated adeno-associated vector encoding luciferase. Mice 1 and 2 (from left) were injected with a mixture of AAV vector encoding luciferase and AAV vector encoding ZsGreen. Mice 3 and 4 (from left) were injected with a mixture of AAV vector encoding luciferase and AAV vector encoding Cre. The images of Figure 12 were taken four weeks after administering the CRE. Figure 12A illustrates the results for vector 1594, Figure 12B illustrates the results for vector 1784, Figure 12C illustrates the results for vector 1799, Figure 12D illustrates the results for vector 1605, Figure 12E illustrates the results for vector 1785, Figure 12F illustrates the results for vector 1800, Figure 12G illustrates the results for vector 1782, Figure 12H illustrates the results for vector 1797, Figure 121 illustrates the results for vector 1806, Figure 12 J illustrates the results for vector 1490, Figure 12K illustrates the results for vector 1783, Figure 12L illustrates the results for vector 1798, and Figure 12M illustrates the results for vector 1180.

[0033] Figure 13 is a graph illustrating a comparison of luciferase expression 18 weeks after transfecting mice with the indicated AAV vector encoding luciferase according to some embodiments herein. For each vector, a bar is shown for a mice co-transfected with ZsGreen and mice co-transfected with nlsCre2.

[0034] Figure 14 is a series of photographs and schematics illustrating Xenogen imaging of mice injected with AAV vectors in accordance with some embodiments herein. The Xenogen images were taken 10 weeks after administration of the indicated vectors. Figure 14A illustrates a schematic vector encoding luciferase, but without Lox sites, and a Xenogen image of the detected luciferase expression for mice co-transfected with ZsGreen (no Cre; mice 1-2 from left) or Cre (mice 3-4 from left). Figure 14B illustrates a schematic vector encoding luciferase with Lox sites and their relative orientations indicated by solid arrows, and a Xenogen image of the detected luciferase expression for mice co-transfected with ZsGreen (no Cre; mice 1-2 from left) or Cre (mice 3-4 from left).

[0035] Figure 15 is a series of photographs and schematics illustrating Xenogen imaging of mice injected with AAV vectors in accordance with some embodiments herein. The Xenogen images were taken 18 weeks after administration of the indicated vectors. Figure 15A illustrates a schematic vector encoding luciferase, but without Lox sites, and a Xenogen image of the detected luciferase expression for mice co-transfected with ZsGreen (no Cre; mice 1-2 from left) or Cre (mice 3-4 from left). Figure 15B illustrates a schematic vector encoding luciferase, with Lox sites and their relative orientations indicated by solid arrows, and a Xenogen image of the detected luciferase expression for mice co-transfected with ZsGreen (no Cre; mice 1-2 from left) or Cre (mice 3-4 from left). [0036] Figure 16 is a graph illustrating luciferase activity in mice at various timepoints after infection with AAV vectors according to some embodiments herein. Shown is luciferase activity for mice injected with vector 1490, encoding AAV and luciferase (but no Lox sites; see, e.g., Figures 14A and 15 A), and cotransfected with either ZsGreen (no Cre) or Cre. Shown is luciferase activity for mice transfected with vector 1806, encoding luciferase and comprising six LoxP sites {see, e.g., Figures 14B and 15B), and cotransfected with either ZsGreen (no Cre) or Cre.

[0037] Figure 17 is a schematic diagram illustrating an experimental protocol for reversibly expressing gene products encoded by AAV vector according to some embodiments herein.

[0038] Figure 18 is a series of photographs and schematics illustrating Xenogen imaging of mice injected with various amounts of AAV vector in accordance with some embodiments herein. Mice were injected with 5uL (shown in Figure 18A), lOuL (shown in Figure 18B), 20uL (shown in Figure 18C) or 40uL (shown in Figure 18D) of solution containing 5x10 ¹⁰ GC vector 1806 (Luc-LoxP). The Xenogen images were taken 20 weeks after administration of vector 1806.

[0039] Figure 19 is a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. Mice were injected with 5uL (shown Figure 19A), lOuL (shown in Figure 19B), 20uL (shown in Figure 19C) or 40uL (shown in Figure 19D) solution containing 5xl0 ¹⁰ GC vector 1806 (Luc-LoxP), and 20 weeks later, injected with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre). The Xenogen images were taken 3 days after administration of the second AAV vector.

[0040] Figure 20 is a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. Mice were injected with 5uL (shown Figure 20A), lOuL (shown in Figure 20B), 20uL (shown in Figure 20C) or 40uL (shown in Figure 20D) of solution containing 5xl0 ¹⁰ GC vector 1806 (Luc-LoxP), and 20 weeks later, injected with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre). The Xenogen images were taken 7 days after administration of the second AAV vector.

[0041] Figure 21 is a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. Mice were injected with 5uL (shown Figure 21A), lOuL (shown in Figure 21B), 20uL (shown in Figure 21C) or 40uL (shown in Figure 21D) solution containing 5xl0 ¹⁰ GC vector 1806 (Luc-LoxP), and 20 weeks later, injected with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre). The Xenogen images were taken 14 days after administration of the second AAV vector.

[0042] Figures 22A-D are a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector according to the dosages shown in Figure 21, and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. The Xenogen images were taken 21 days after administration of the second AAV vector.

[0043] Figures 23A-D are a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector according to the dosages shown in Figure 21, and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. The Xenogen images were taken 28 days after administration of the second AAV vector.

[0044] Figures 24A-D are a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector according to the dosages shown in Figure 21, and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. The Xenogen images were taken 56 days after administration of the second AAV vector.

[0045] Figures 25A-D are a series of photographs illustrating Xenogen imaging of mice injected with various amounts of AAV vector according to the dosages shown in Figure 21, and subsequently injected with AAV vector encoding Cre or ZsGreen in accordance with some embodiments herein. The Xenogen images were taken 84 days after administration of the second AAV vector. [0046] Figure 26 is a graph illustrating luciferase activity in mice (total body) at various timepoints after injection with various quantities of vector 1806 encoding luciferase, 20 weeks later, injection with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre) in accordance with some embodiments herein. Figure 26 summarizes the results of the whole body Xenogen imaging shown in Figure 19-23.

[0047] Figure 27 is a graph illustrating luciferase activity in mice (liver) at various timepoints after injection with various quantities of vector 1806 encoding luciferase, 20 weeks later, injection with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre) in accordance with some embodiments herein. Figure 27 summarizes the results of the liver Xenogen imaging shown in Figure 19-23.

[0048] Figure 28 is a graph illustrating luciferase activity in mice (leg) at various timepoints after injection with various quantities of vector 1806 encoding luciferase, 20 weeks later, injection with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre) in accordance with some embodiments herein. Figure 28 summarizes the results of the leg Xenogen imaging shown in Figure 19-23.

[0049] Figure 29 is a graph illustrating luciferase activity in mice (leg) at various timepoints after intramuscular injection with AAV vector 1806 (encoding luciferase) and seven weeks later, were injected with either AAV vector 1787 (encoding GFP) or AAV vector 1742 (encoding Cre) in accordance with some embodiments herein.

[0050] Figure 30 is a graph illustrating expression levels of AC50 antibody ^g/mL) at various timepoints after infection with AAV vectors in the presence or absence of Cre, in accordance with some embodiments herein. Mice received intramuscular injection of either 2xl0 ¹⁰ GC of vector 1677 encoding the heavy chain and light chain of antibody AC50, but lacking loxP sites, or 2xl0 ¹⁰ GC of vector 1834 encoding the heavy chain and light chain of antibody AC50, and containing loxP sites in accordance with embodiments herein. 7

12

weeks later, the mice were injected intramuscularly with either 2.5x10 GC of vector 1787

(encoding GFP) or 2.5x10 12 GC of vector 1742 (encoding Cre). Antibody expression was measured by a sandwich ELISA, and although initial antibody expression levels were comparable, antibody expression was substantially decreased for the combination of vector 1834 (LoxP sites) and vector 1742 (Cre) in comparison to the other vectors. [0051] Figure 31A is a vector map illustrating an AAV vector according to some embodiments herein. Depicted is vector pAAVLiLo-CASLIL-Luc2-LW oX-LSV40 (vector 1806)(SEQ ID NO: 1).

[0052] Figure 3 IB is a vector map illustrating an AAV vector according to some embodiments herein. Depicted is vector pAAVLiLo-CASLIL-B12ABK-LWNoX-LSV40 (vector 1833)(SEQ ID NO: 2).

[0053] Figure 31C is a vector map illustrating an AAV vector according to some embodiments herein. Depicted is vector pAAVLiLo-CASLIL-VRCOl ABK-LWNoX-LSV40 (vector 1834)(SEQ ID NO: 3).

[0054] Figure 3 ID is a vector map illustrating an AAV vector according to some embodiments herein. Depicted is vector pAAVLiLo-CASLIL-VRC07ABK-LWNoX-LSV40 (1835)(SEQ ID NO: 4).

DETAILED DESCRIPTION

[0055] According to some embodiments herein, reversible adeno-associated virus (AAV)-based gene expression systems are provided. The AAV gene expression systems can be useful for reversible gene expression in a mammal, for example for gene therapy applications. AAV is a non-integrating vector, and as such, does not modify the host cell genome. As AAV can stably exist in a host for a long time, it can be useful to turn-off gene expression from the AAV after a period of time. On the other hand, other types of vectors for gene expression, for example adenovirus, a typically short-lived, and thus would seldom benefit from additional mechanisms for turning-off gene expression. An AAV vector can encode a gene product of interest, and can contain a promoter region comprising a plurality of recombinase target sites, preferably positioned in the same orientation, although in some embodiments, different recombinase sites can be positioned in different orientations. One or more of the recombinase sites can be positioned between the promoter and the sequence encoding the gene product of interest. Upon insertion of the AAV vector into a mammal, the gene product of interest can be expressed. In some embodiments, at least some gene expression can be controllably turned-off using recombination. A recombinase can act upon two or more of the recombinase target sites of the inserted construct, inducing removal of sequences downstream of the promoter, and optionally at least a portion of the promoter. The removal of such sequences can reduce or eliminate expression of the gene product of interest. In some embodiments, the recombinase is encoded in a second AAV vector. In some embodiments, the recombinase is encoded in an adenoviral vector. In some embodiments, a cell-penetration-peptide-recombinase fusion polypeptide (for example Tat- Cre) is provided. Since AAV vectors do not integrate into the host genome, there is minimal danger of the recombinase inducing rearrangements in the host genome. In contrast, if multiple copies of an integrating vector (e.g. lentivirus) were to be integrated into a host genome, the recombinase could cause rearrangements.

[0056] As used herein, the term "vector" refers to a polynucleotide construct, typically a plasmid or a virus, used to transmit genetic material to a host cell. Vectors can be, for example, viruses, plasmids, cosmids, or phage. A vector as used herein can be composed of either DNA or R A. In some embodiments, a vector is composed of DNA. An "expression vector" is a vector that is capable of directing the expression of a protein encoded by one or more genes carried by the vector when it is present in the appropriate environment. Vectors are preferably capable of autonomous replication. Typically, an expression vector comprises a transcription promoter, a gene, and a transcription terminator. Gene expression is usually placed under the control of a promoter, and a gene is said to be "operably linked to" the promoter.

[0057] As used herein, the term "operably linked" is used to describe the connection between regulatory elements and a gene or its coding region. Typically, gene expression is placed under the control of one or more regulatory elements, for example, without limitation, constitutive or inducible promoters, tissue-specific regulatory elements, and enhancers. A gene or coding region is said to be "operably linked to" or "operatively linked to" or "operably associated with" the regulatory elements, meaning that the gene or coding region is controlled or influenced by the regulatory element. For instance, a promoter is operably linked to a coding sequence if the promoter effects transcription or expression of the coding sequence.

[0058] As used herein "upstream" refers to positions 5 ' of a location on a polynucleotide, and positions toward the N-terminus of a location on a polypeptide. As used herein "downstream" refers to positions 3 ' of a location on nucleotide and toward the C- terminus of a location on a polypeptide. [0059] The term "construct," as used herein, refers to a recombinant nucleic acid that has been generated for the purpose of the expression of a specific nucleotide sequence(s), or that is to be used in the construction of other recombinant nucleotide sequences.

[0060] As used herein, the terms "nucleic acid" and "polynucleotide" are interchangeable and refer to any nucleic acid, whether composed of phosphodiester linkages or modified linkages such as phosphotriester, phosphoramidate, siloxane, carbonate, carboxymethylester, acetamidate, carbamate, thioether, bridged phosphoramidate, bridged methylene phosphonate, bridged phosphoramidate, bridged phosphoramidate, bridged methylene phosphonate, phosphorothioate, methylphosphonate, phosphorodithioate, bridged phosphorothioate or sultone linkages, and combinations of such linkages. The terms "nucleic acid" and "polynucleotide" also specifically include nucleic acids composed of bases other than the five biologically occurring bases (adenine, guanine, thymine, cytosine and uracil).

[0061] As used herein, the term "promoter" is a nucleotide sequence that permits binding of RNA polymerase and directs the transcription of a gene. Typically, a promoter is located in the 5' non-coding region of a gene, proximal to the transcriptional start site of the gene. Sequence elements within promoters that function in the initiation of transcription are often characterized by consensus nucleotide sequences. Examples of promoters include, but are not limited to, promoters from bacteria, yeast, plants, viruses, and mammals (including humans). A promoter can be inducible, repressible, and/or constitutive. Inducible promoters initiate increased levels of transcription from DNA under their control in response to some change in culture conditions, such as a change in temperature.

[0062] As used herein, the term "enhancer" refers to a type of regulatory element that can modulate the efficiency of transcription, regardless of the distance or orientation of the enhancer relative to the start site of transcription.

[0063] As used herein, the term "antibody" is used in the broadest sense and specifically covers human, non-human (e.g., murine) and humanized monoclonal antibodies (including full-length monoclonal antibodies), polyclonal antibodies, multi-specific antibodies (e.g., bispecific antibodies), and antibody fragments so long as they exhibit the desired biological activity. Various antibodies can be expressed using the system and method disclosed herein. "Antibodies" and "immunoglobulins" are usually heterotetrameric glycoproteins, composed of two identical light (L) chains and two identical heavy (H) chains. Each light chain is linked to a heavy chain by a disulfide bond. The number of disulfide linkages varies among the heavy chains of different immunoglobulin isotypes. Each heavy chain comprises a variable domain (V _H ) followed by a number of constant domains. Each light chain comprises a variable domain at one end (V _L ) and a constant domain at its other end. The constant domain of the light chain is aligned with the first constant domain of the heavy chain, and the light- chain variable domain is aligned with the variable domain of the heavy chain. While antibodies exhibit binding specificity to a specific antigen, immunoglobulins include both antibodies and other antibody-like molecules that lack antigen specificity. Polypeptides of the latter kind are, for example, produced at low levels by the lymph system and at increased levels by myelomas.

[0064] As used herein, the term "variant" refers to a polynucleotide (or polypeptide) having a sequence substantially similar to a reference polynucleotide (or polypeptide). In the case of a polynucleotide, a variant can have deletions, substitutions, additions of one or more nucleotides at the 5 ' end, 3 ' end, and/or one or more internal sites in comparison to the reference polynucleotide. Similarities and/or differences in sequences between a variant and the reference polynucleotide can be detected using conventional techniques known in the art, for example polymerase chain reaction (PCR) and hybridization techniques. Variant polynucleotides also include synthetically derived polynucleotides, such as those generated, for example, by using site-directed mutagenesis. Generally, a variant of a polynucleotide, including, but not limited to, a DNA, can have at least about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99% or more sequence identity to the reference polynucleotide as determined by sequence alignment programs known by skilled artisans. In the case of a polypeptide, a variant can have deletions, substitutions, additions of one or more amino acids in comparison to the reference polypeptide. Similarities and/or differences in sequences between a variant and the reference polypeptide can be detected using conventional techniques known in the art, for example Western blot. Generally, a variant of a polypeptide, can have at least about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 91 %, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99% or more sequence identity to the reference polypeptide as determined by sequence alignment programs known by skilled artisans.

[0065] As used herein, the term "transfection" refers to the introduction of a nucleic acid into a host cell, such as by contacting the cell with a recombinant AAV vector as described herein.

AAV vectors

[0066] AAV vectors are a class of relatively compact vector that can be used to stably introduce a transgene into a host cell without integrating into the host genome. As such, AAV vectors can introduce a transgene without disruption host genomic sequences, and expression of a transgene from an AAV vector can persist for a long time, for example months or years. AAV vectors are described in detail in U.S. Pub. No. 2012/0232133, the entirety of which is incorporated by reference herein. AAV is a replication-deficient parvovirus, the single-stranded DNA genome of which is about 4.7 kb in length including 145 nucleotide inverted terminal repeat (ITRs). The ITRs can play a role in integration of the AAV DNA into the host cell genome. However, in the absence of the rep gene, integration by AAV vectors is negligible. It is contemplated that integration of AAV's comprising recombinase target sites into a host genome can create a risk of the recombinase inducing rearrangements of the host genome. For example if a first AAV integrates at a first genomic location, and a second AAV integrates at a second genomic location, and each AAV comprises a recombinase target site, the recombinase can induce recombination between the two AAVs, and thus rearrange portions of the host genome. Accordingly, preferably the AAV vectors in accordance with embodiments herein are configured not to integrate with the host genome. In some embodiments, the AAV vectors lack a functional rep gene. In some embodiments, the rep gene is deleted from the AAV vectors. In some embodiments, the ITRs of the AAVs are configured to minimize or eliminate integration.

[0067] Accounting for the ITR's (about 0.3kb), AAV's can typically contain up to about 4.4kb of nucleic acid sequence of interest. As such, AAV's are much more compact than adenovirus vectors, which can typically contain up to about 7.5kb of nucleic acid sequence of interest. When AAV infects a host cell, the viral genome integrates into the host's chromosome resulting in latent infection of the cell. In a natural system, a helper virus (for example, adenovirus or herpesvirus) provides genes that allow for production of AAV vector in the infected cell. In the case of adenovirus, genes El A, E1B, E2A, E4 and VA provide helper functions. Upon infection with a helper virus, the AAV provirus is rescued and amplified, and both AAV and adenovirus are produced. In the instances of recombinant AAV vectors having no Rep and/or Cap genes, the AAV can be non-integrating.

[0068] AAV vectors that comprise coding regions of one or more proteins of interest, for example proteins that are more than 500 amino acids in length, are provided. The AAV vector can include a 5 ' inverted terminal repeat (ITR) of AAV, a 3 ' AAV ITR, a promoter, and a restriction site downstream of the promoter to allow insertion of a polynucleotide encoding one or more proteins of interest, wherein the promoter and the restriction site are located downstream of the 5 ' AAV ITR and upstream of the 3 ' AAV ITR. In some embodiments, the recombinant AAV vector includes a posttranscriptional regulatory element downstream of the restriction site and upstream of the 3 ' AAV ITR. In some embodiments, the AAV vectors disclosed herein can be used as AAV transfer vectors carrying a transgene encoding a protein of interest for producing recombinant AAV vectors that can express the protein of interest in a host cell.

[0069] Generation of the viral vector can be accomplished using any suitable genetic engineering techniques well known in the art, including, without limitation, the standard techniques of restriction endonuclease digestion, ligation, transformation, plasmid purification, and DNA sequencing, for example as described in Sambrook et al. (Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory Press, N.Y. (1989)).

[0070] The viral vector can incorporate sequences from the genome of any known organism. The sequences can be incorporated in their native form or can be modified in any way to obtain a desired activity. For example, the sequences can comprise insertions, deletions or substitutions.

[0071] The viral vectors described herein can include a prokaryotic replicon (that is, a DNA sequence having the ability to direct autonomous replication and maintenance of the recombinant DNA molecule extrachromosomally in a prokaryotic host cell), such as a bacterial host cell, transformed therewith. Such replicons are well known in the art. In addition, vectors that include a prokaryotic replicon may also include a gene whose expression confers a detectable marker such as a drug resistance. Typical bacterial drug resistance genes are those that confer resistance to ampicillin or tetracycline.

Additional Vectors

[0072] Additional exemplary vectors for use in eukaryotic cells that can be used in accordance with some embodiments herein, for example to deliver recombinase to the host cell, include, but are not limited to: pSVL and pKSV-10 available from Pharmacia; pBPV- l/pML2d (International Biotechnologies, Inc.); pCDNA and pTDTl (ATCC, #31255); viral vectors based on vaccinia virus, poliovirus, adenovirus, herpes simplex virus, a lentivirus; vectors derived from retroviruses such as Rous Sarcoma Virus, Harvey Sarcoma Virus, avian leukosis virus, human immunodeficiency virus, myeloproliferative sarcoma virus, and mammary tumor virus); and the like. Additional examples of suitable eukaryotic vectors include bovine papilloma virus-based vectors, Epstein-Barr virus-based vectors, SV40, 2- micron circle, pcDNA3.1 , pcDNA3.1/GS, pYES2/GS, pMT, p IND, pIND(Spl), pVgRXR (Invitrogen), and the like, or their derivatives. In some embodiments, one of these vectors is used to deliver recombinase to the host cell. In some embodiments, one of these vectors is used to deliver a second gene product of interest to the host cell, for example a gene product in which reversible expression is not desired. In some embodiments, one of these vectors encodes a gene product of interest and comprises sequences for reversible expression of the gene product of interest as described herein.

Cell-penetrating peptides

[0073] Cell-penetrating peptides can be fused to a polypeptide of interest, and facilitate entry of the polypeptide of interest into a cell. According to some embodiments, polypeptides, for example recombinase polypeptides, are delivered to a cell through use of a cell penetration peptide. As discussed in more detail below, concurrently with, or following administration of an AAV vector for reversible expression of a gene product of interest to a host organism or cell, a recombinase polypeptide fused to a cell-penetration peptide can be administered to the host organism or cell, so that the recombinase enters the cell or cells of the host organism, and provides recombinase activity therein. [0074] Various cell penetration peptides are known in the art, for example Hiv- 1 - Tat and derivatives thereof. HIV-1 Tat

(MEPVDPRLEPWKHPGSQPKTACTNCYCKKCCFHCQVCFITKALGISYGRKK RQRR RAHQNSQTHQASLSKQPTSQPRGDPTGPKE; SEQ ID NO: 5) has been shown to facilitate entry of a peptide comprising this sequence into a eukaryotic cell (see, e.g., Lundberg et al. (2002) A brief introduction to cell-penetrating peptides, J. Mol. Recognit. 16: 227-233, hereby incorporated by reference in its entirety). Various Tat derivatives fused to polypeptides of interest have been shown to mediate cell entry. For example, residues 47-57 of TAT (YGRKKRRQRRR; SEQ ID NO: 6) are sufficient to mediate cellular entry by a target polypeptide fused thereto. Additional exemplary cell-penetrating peptides are shown in Table 1, below. It is noted that several of the peptides identified in Table 1 include C- terminal amidation or cysteamide modification to facilitate cell-penetrating-peptide activity. In some embodiments, a cell penetrating peptide is fused to a C-terminus of a polypeptide of interest, for example a recombinase, so that the polypeptide of interest can be internalized by a cell. In some embodiments, the cell penetrating peptide is fused to an N-terminus of a polypeptide of interest. In some embodiments, the cell penetrating peptide is fused internally to a polypeptide of interest. In some embodiments, a cell-penetrating peptide comprising at least about 80% identity to a cell-penetrating polypeptide listed in Table 1 , for example 80%, 81%, 82%, 83%, 84%, 85%, 86, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity is fused to a polypeptide of interest.

Table 1

pISL 14 RVIRVWFQNKRCKDKK-amide

(R) ₇ 15 RRRRRRR

Pep- 1 16 KETWWETWWTEWSQPKKKRKV (C-terminally modified with a cysteamide group)

Mouse PrP (l -28) 17 MANLGYWLLALFVTMWTDVGLCKKRPKP

[0075] As discussed herein, cell-penetration peptides can be fused to a recombinase, and the recombinase can be administered to a host cell or host organism when reduction or elimination of gene expression from the AAV vector is desired.

Recombinases and recombinase target sites

[0076] Recombination systems can mediate recombination between recombinase target sites, and depending on the orientation of the recombinase target sites, can either excise or flip sequences flanked by the recombinase target sites. According to some embodiments herein, recombinase target sites in the same orientation can flank portions of AAV vectors as described herein, so that upon addition of a recombinase, portions of the AAV vector can be removed, reducing or silencing expression of gene products encoded by these vectors. In some embodiments, an AAV vector encoding at least one gene product of interest and comprising recombinase target sites positioned as described herein is administered to a subject, so that the gene product or products of interest are expressed in the subject, and a recombinase is then administered to the subject (or recombinase activity is induced in the subject) to induce recombination in the AAV vector, so as to eliminate or reduce expression of the gene product or products of interest in the subject.

[0077] A variety of recombinases and corresponding recombinase target sites can be used in accordance with embodiments herein. "Recombinases," as used herein, refer to gene products and synthetic analogs thereof that catalyze recombination between a first and second polynucleotide. It is noted that recombinases typically can catalyze recombination between polynucleotide sequences in cis (i.e. on the same polynucleotide strand) or in trans (i.e. on different polynucleotide strands). "Recombinase target sites" refer to polynucleotide sequences on which recombinases specifically act to induce recombination. A particular recombinase may have specificity for a single nucleic acid sequence, or a plurality of nucleic acid sequences. Such a plurality of sequences can be described by a consensus sequence. In some embodiments, a recombinase polypeptide is provided. In some embodiments, a polynucleotide encoding a recombinase polypeptide (a "recombinase polynucleotide") is provided. Exemplary recombinases and recombinase target sites that can be used in accordance with embodiments herein include, but are not limited to, Cre-lox and FLP-FRT.

[0078] The Cre-lox system, derived from bacteriophage PI , is a well- characterized recombinase and recombinase target site system (see, e.g. , Lakso et al , 1992, Proc. Natl. Acad. Sci. USA 89: 6232-6236; Orban et al , 1992, Proc. Natl. Acad. Sci. USA 89: 6861-6865, each of which is incorporated by reference herein in its entirety) that can be used in accordance with some embodiments herein. Cre recombinase catalyzes site-specific recombination, which can excise or invert an intervening target sequence or transgene located between lox sequences. Canonically, loxP sequences are targets for Cre recombinase. A loxP sequence comprises a 34 base pair polynucleotide sequence of SEQ ID NO: 18 (ATAACTTCGTATAGCATACATTATACGAAGTTAT). It is appreciated that variants loxP sequences, for example lox2272 and l ΌχΝ can also be used as Cre recombinase target in accordance with embodiments herein (see Livet et al. (2007), Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system, Nature 450: 56- 63). Lox2272 comprises the polynucleotide sequence of SEQ ID NO: 19 (ATAACTTCGTATAAAGTATCCTATACGAAGTTAT). LoxN comprises the polynucleotide sequence of SEQ ID NO: 20

(ATAACTTCGTATAGTATACCTTATACGAAGTTAT). Without being limited to any particular theory, Cre recombinase can work on any of the loxP or variant lox sites described herein. While Cre recombinase can induce recombination between a pair of identical lox sites (e.g. two loxP sites, or two lox2272 sites), Cre recombinase typically cannot induce recombination between a pair of non-identical lox sites (e.g. cannot induce recombination between a loxP and a lox2272 site, or a loxN and a lox2272 site). As such, according to some embodiments herein, for each lox sequence in the AAV vector, there is at least one additional identical lox sequence in the vector.

[0079] The orientation of lox sequences can determine whether the intervening transgene is excised or inverted when Cre recombinase is present (Abremski et al , 1984, J. Biol. Chem. 259: 1509-1514). Cre can catalyze the excision of the transgene when the lox sequences are oriented as direct repeats (e.g. in the same orientation on the same strand) and catalyzes inversion of the transgene when lox sequences are oriented as inverted repeats (e.g. in opposite orientations on the strand. As such, in some embodiments, two or more lox sequences are oriented in the same direction on a polynucleotide strand. In some embodiments, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, or 20 lox sequences are oriented in the same direction on a polynucleotide strand. In some embodiments, all of the lox sequences on a strand are oriented in the same direction.

[0080] The FLP recombinase system, derived from of Saccharomyces cerevisiae (see, e.g. , O'Gorman et al , 1991 , Science 251 : 1351-1355; PCT publication WO 92/15694, each of which is incorporated by reference herein in its entirety) can be used to generate in vivo site-specific genetic recombination, similar to the Cre-lox system. In some embodiments a FLP recombinase target (FRT) site comprises the sequence of SEQ ID NO: 21 (GAAGTTCCTATTCTCTAGAAAGTATAGGAACTTC). A number of functional variant FRTs are known in the art, for example SEQ ID NO: 22 (GAAGTTCCTATTCCGAAGTTCCTATTCTCTAGAAAGTATAGGAACTTC).

Accordingly, in some embodiments, a variant FRT site is used. Without being limited by any particular theory, FLPase recombinase can work on any of the FRT or variant FRT sites described herein. While FLP recombinase can induce recombination between a pair of identical FLP sites, it typically cannot induce recombination between a pair of non-identical FRT sites. Similar to Cre, FLP recombinase can catalyze the excision of a sequence positioned between two FRT sites in the same orientation, and can catalyze the inversion of a sequence positioned between two FRT sites in opposite orientations. Accordingly, in some embodiments, at least two FRT sequences are oriented in the same direction on a polynucleotide strand. In some embodiments, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, or 20 FRT sequences are oriented in the same direction on a polynucleotide strand. In some embodiments, all of the FRT sequences on a strand are oriented in the same direction.

[0081] It is noted that while orienting a plurality identical recombinase target sites (e.g. loxP sites or FRT sites) in different directions could still result in excision of sequences, depending on which sites paired with each other, a combination of inversion and recombination events could occur, yielding different final sequences from AAV vector to AAV vector (e.g. if a vector included loxPl > hxP2> <loxP3 <loxP4, with arrows indicating orientation, recombinase could excise the sequences between loxPl and loxP2, and also the sequences between loxP3 and loxP4, but could also result in an inversion between loxPl and loxP3, and a subsequent excision of sequences between loxP2 and loxP2, which would then be oriented in the same direction; the skilled artisan will appreciate that such an arrangement could also lead to a variety of other outcomes). Thus, preferably, all of the recombinase target sites that can recombine with each other (e.g. identical recombinase target sites) are oriented in the same direction.

[0082] While all of recombinase target sites that can recombine with each other are preferably oriented in the same orientation, in some embodiments, the AAV vector can comprise recombinase target sites in different orientations. In some embodiments, two or more of a first recombinase target site (e.g. a loxP site) are oriented in one direction flanking a first sequence, and two or more of a second, different, recombinase target site (e.g. an FRT site) are oriented in the other direction, flanking a second sequence. The addition of Cre can induce recombination between the loxP sites to excise the first sequence, while the addition of FLR can induce recombination between the FRT sites to excise the second sequence. Accordingly in some embodiments, recombinase target sites can be provided in different orientations, for example of two or more of a first recombinase target site are oriented in a first orientation, and two or more of a different, second recombinase target site are oriented in a second orientation, in which the first recombinase target sites are different from the second recombinase target sites, so that recombination events cannot be induced between the first and second sites.

Promoters and associated sequences

[0083] Various promoters can be operably linked with a nucleic acid comprising the coding region of the gene product of interest in the vectors to drive expression of the gene product of interest in accordance with embodiments herein. In some embodiments, the promoter can drive the expression of the protein of interest in a cell infected with a virus derived from the viral vector, such as a target cell. The promoter can be naturally-occurring or non-naturally occurring. [0084] Examples of promoters, include, but are not limited to, viral promoters, plant promoters and mammalian promoters. Examples of viral promoters include, but are not limited to cytomegalovirus (CMV) immediate early promoter, CAG promoter (which is a combination of the CMV early enhancer element and chicken beta-actin promoter, described in Alexopoulou et al. BMC Cell Biology 9:2, (2008)), simian virus 40 (SV40) promoter, the 35S R A and 19S RNA promoters of cauliflower mosaic virus (CaMV) described in Brisson et al., Nature 1984, 310:51 1-514, the coat protein promoter to tobacco mosaic virus (TMV), and any variants thereof. Examples of plant promoters include, but are not limited to, heat shock promoters, such as soybean hspl7.5-E or hspl7.3-B described in Gurley et al., Mol. Cell. Biol. 1986, 6:559-565, and any variants thereof. Examples of mammalian promoters include, but are not limited to, human elongation factor la-subunit (EFl-la) promoter, human ubiquitin C (UCB) promoter, murine phosphoglycerate kinase- 1 (PGK) promoter, and any variants thereof.

[0085] In some embodiments, the promoter is a synthetic CASI promoter. The synthetic CASI promoter contains a portion of the CMV enhancer, a portion of the chicken beta-actin promoter, and a portion of the UBC enhancer. In some embodiments, the UBC enhancer is positioned in a synthetic intron, for example flanked by an upstream splice donor and downstream splice acceptor. An exemplary portion of the chicken beta-actin promoter that can be used in CASI promoters in conjunction with embodiments herein includes SEQ ID NO: 23

(TGGTCGAGGTGAGCCCCACGTTCTGCTTCACTCTCCCCATCTCCCCCCCCTCCCC ACCCCCAATTTTGTATTTATTTATTTTTTAATTATTTTGTGCAGCGATGGGGGCGG GGGGGGGGGGGGGGCGCGCGCCAGGCGGGGCGGGGCGGGGCGAGGGGCGGGG CGGGGCGAGGCGGAGAGGTGCGGCGGCAGCCAATCAGAGCGGCGCGCTCCGAA AGTTTCCTTTTATGGCGAGGCGGCGGCGGCGGCGGCCCTATAAAAAGCGAAGCG CGCGGCGGGCGGGAGTCGCTGCGCGCTGCCTTCGCCCCGTGCCCCGCTCCGCCGC CGCCTCGCGCCGCCCGCCCCGGCTCTGACTGACCGCGTTACT), as well as polynucleotides with at least about 80% identity thereto, for example 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and 99%. An exemplary portion of the UBC enhancer that can be used in CASI promoters in conjunction with embodiments herein includes SEQ ID NO: 24 (GCCTCCGCGCCGGGTTTTGGCGCCTCCCGCGGGCGCCCCCCTCCTCACGGCGAG CGCTGCCACGTCAGACGAAGGGCGCAGCGAGCGTCCTGATCCTTCCGCCCGGAC GCTCAGGACAGCGGCCCGCTGCTCATAAGACTCGGCCTTAGAACCCCAGTATCA GCAGAAGGACATTTTAGGACGGGACTTGGGTGACTCTAGGGCACTGGTTTTCTTT CCAGAGAGCGGAACAGGCGAGGAAAAGTAGTCCCTTCTCGGCGATTCTGCGGAG GGATCTCCGTGGGGCGGTGAACGCCGATG), as well as polynucleotides with at least about 80% identity thereto, for example 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and 99%. In some embodiments, the CASI promoter is modified. In some embodiments, the CASI promoter comprises a first recombinase target site upstream of the splice donor and a second recombinase target site upstream of the splice acceptor. In some embodiments, the CASI promoter comprises a first recombinase target site upstream of the splice donor and a second recombinase target site downstream of the splice acceptor. In some embodiments, the CASI promoter comprises a first recombinase target site downstream of the splice donor and a second recombinase target site upstream of the splice acceptor. In some embodiments, the CASI promoter comprises a first recombinase target site downstream of the splice donor and a second recombinase target site downstream of the splice acceptor.

[0086] An exemplary modified CASI promoter that can be used in accordance with some embodiments herein is illustrated in Figure IB. Such a promoter can comprise, from 5' to 3 ', a CMV enhancer fragment, beta-actin promoter fragment, splice donor, UBC enhancer fragment, splice acceptor, in which a first pair of loxP sites flank the splice donor, and a second pair of loxP site flank the splice acceptor, and in which all four of the loxP sites are in the same orientation. Such promoter can comprise a nucleic acid sequence having at least about 80%, at least about 85%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more, sequence identity to SEQ ID NO: 25 (GGAGTTCCGCGTTACATAACTTACGGTAAATGGCCCGCCTGGCTGACCGCCC AACGACCCCCGCCCATTGACGTCAATAATGACGTATGTTCCCATAGTAACGCCAA TAGGGACTTTCCATTGACGTCAATGGGTGGAGTATTTACGGTAAACTGCCCACTT GGCAGTACATCAAGTGTATCATATGCCAAGTACGCCCCCTATTGACGTCAATGAC GGTAAATGGCCCGCCTGGCATTATGCCCAGTACATGACCTTATGGGACTTTCCTA

CTTGGCAGTACATCTACGTATTAGTCATCGCTATTACCATGGTCGAGGTGAGCCC

CACGTTCTGCTTCACTCTCCCCATCTCCCCCCCCTCCCCACCCCCAATTTTGTATTT

ATTTATTTTTTAATTATTTTGTGCAGCGATGGGGGCGGGGGGGGGGGGGGGGCGC

GCGCCAGGCGGGGCGGGGCGGGGCGAGGGGCGGGGCGGGGCGAGGCGGAGAG

GTGCGGCGGCAGCCAATCAGAGCGGCGCGCTCCGAAAGTTTCCTTTTATGGCGA

GGCGGCGGCGGCGGCGGCCCTATAAAAAGCGAAGCGCGCGGCGGGCGGGAGTC

GCTGCGCGCTGCCTTCGCCCCGTGCCCCGCTCCGCCGCCGCCTCGCGCCGCCCGC

CCCGGCTCTGACTGACCGCGTTACTAAAACAGGTAAGTCCATAACTTCGTATAGC

ATACATTATACGAAGTTATGGCCTCCGCGCCGGGTTTTGGCGCCTCCCGCGGGCG

CCCCCCTCCTCACGGCGAGCGCTGCCACGTCAGACGAAGGGCGCAGCGAGCGTC

CTGATCCTTCCGCCCGGACGCTCAGGACAGCGGCCCGCTGCTCATAAGACTCGGC

CTTAGAACCCCAGTATCAGCAGAAGGACATTTTAGGACGGGACTTGGGTGACTC

TAGGGCACTGGTTTTCTTTCCAGAGAGCGGAACAGGCGAGGAAAAGTAGTCCCT

TCTCGGCGATTCTGCGGAGGGATCTCCGTGGGGCGGTGAACGCCGATGATATAA

CTTCGTATAGCATACATTATACGAAGTTATGCCTCTACTAACCATGTTCATGTTTT

CTTTTTTTTTCTACAGGTCCTGGGTGACGAACAG).

[0087] To increase expression from the promoter in vectors in accordance with embodiments herein, the promoter can comprise a transcriptional enhancer. In some embodiments, the transcriptional enhancer comprises a UBC enhancer. In some embodiments, the transcriptional enhancer is positioned in a synthetic intron. For example, the transcriptional enhancer can be positioned downstream of a splice acceptor, and upstream of a splice donor.

[0088] In some embodiments, the promoter is operably linked to a polynucleotide encoding one or more polypeptides of interest. In some embodiments, the promoter is operably linked with a polynucleotide encoding the heavy chain and/or the light chain of an antibody of interest, or a portion thereof (such as the heavy and light variable region of the antibody). In some embodiments, the promoter is operably linked to a polynucleotide encoding the heavy chain and the light chain of an antibody of interest to allow multicistronic expression of the heavy and light chain genes. In some embodiments, a cleavage site (for example a 2A sequence) or IRES element is positioned between the coding region of the heavy chain variable region and the coding region of the light chain variable region in the vector to facilitate equivalent expression of each subunit. Alternatively, polynucleotides encoding the heavy and light chains can be introduced separately into the target cell, each in an appropriate viral vector.

[0089] The size of the promoter can vary. Because of the limited packaging capacity of AAV, it is preferred to use a promoter that is small in size, but at the same time allows high level production of the protein(s) of interest in host cells. For example, in some embodiments the promoter is at most about 1.5 kb, at most about 1.4 kb, at most about 1.35 kb, at most about 1.3 kb, at most about 1.25 kb, at most about 1.2 kb, at most about 1.15 kb, at most about 1.1 kb, at most about 1.05 kb, at most about 1 kb, at most about 800 base pairs, at most about 600 base pairs, at most about 400 base pairs, at most about 200 base pairs, or at most about 100 base pairs.

Regulatory Elements

[0090] Vectors according to some embodiments herein, for example AAV vectors, can include various regulatory elements, such as a transcription initiation region and/or a transcriptional termination region. Examples of transcription termination region include, but are not limited to, polyadenylation signal sequences. Examples of polyadenylation signal sequences include, but are not limited to, Bovine growth hormone (BGH) poly(A), SV40 late poly(A), rabbit beta-globin (RBG) poly(A), thymidine kinase (TK) poly(A) sequences, and any variants thereof. In some embodiments, the transcriptional termination region is located downstream of the posttranscriptional regulatory element. In some embodiments, the transcriptional termination region is a polyadenylation signal sequence. In some embodiments, the transcriptional termination region comprises a SV40 late poly(A) sequence, for example the polynucleotide sequence of SEQ ID NO: 26 (TTCGAGCAGACATGATAAGATACATTGATGAGTTTGGACAAACCACAACTAGAA TGCAGTGAAAAAAATGCTTTATTTGTGAAATTTGTGATGCTATTGCTTTATTTGTA ACCATTATAAGCTGCAATAAACAAGTTAACAACAACAATTGCATTCATTTTATGT TTCAGGTTCAGGGGGAGATGTGGGAGGTTTTTTAAAGCAAGTAAAACCTCTACA AATGTGGTAAAATC) or a polynucleotides with at least about 80% identity thereto, for example 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and 99% identity. In some embodiments, the transcriptional termination region comprises a synthetic poly(A) sequence. In some embodiments, the transcriptional termination region comprises a synthetic poly(A) sequence, for example the polynucleotide sequence of SEQ ID NO: 43

(AATAAAATATCTTTATTTTCATTACATCTGTGTGTTGGTTTTTTGTGTG), or a polynucleotides with at least about 80% identity thereto, for example 80%, 81 %, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and 99% identity.

[0091] Various posttranscriptional regulatory elements can be used in the viral vectors, for example to increase expression level of the protein of interest in a host cell. In some embodiments, the posttranscriptional regulatory element can be a viral posttranscriptional regulatory element. Non-limiting examples of viral posttranscriptional regulatory element include woodchuck hepatitis virus posttranscriptional regulatory element (WPRE), hepatitis B virus posttranscriptional regulatory element (HBVPRE), RNA transport element (RTE), and any variants thereof.

[0092] A variety of WPRE's can be used in accordance with embodiments herein. In some embodiments, the WPRE is "full-length" (see, e.g., Figures 8B and 9B), comprising the nucleic acid sequence of SEQ ID NO: 27 (TAATCAACCTCTGGATTACAAAATTTGTGAAAGATTGACTGGTATTCTTAACTAT GTTGCTCCTTTTACGCTATGTGGATACGCTGCTTTAATGCCTTTGTATCATGCTAT TGCTTCCCGTATGGCTTTCATTTTCTCCTCCTTGTATAAATCCTGGTTGCTGTCTCT TTATGAGGAGTTGTGGCCCGTTGTCAGGCAACGTGGCGTGGTGTGCACTGTGTTT GCTGACGCAACCCCCACTGGTTGGGGCATTGCCACCACCTGTCAGCTCCTTTCCG GGACTTTCGCTTTCCCCCTCCCTATTGCCACGGCGGAACTCATCGCCGCCTGCCTT GCCCGCTGCTGGACAGGGGCTCGGCTGTTGGGCACTGACAATTCCGTGGTGTTGT CGGGGAAATCATCGTCCTTTCCTTGGCTGCTCGCCTGTGTTGCCACCTGGATTCTG CGCGGGACGTCCTTCTGCTACGTCCCTTCGGCCCTCAATCCAGCGGACCTTCCTTC CCGCGGCCTGCTGCCGGCTCTGCGGCCTCTTCCGCGTCTTCGCCTTCGCCCTCAGA CGAGTCGGATCTCCCTTTGGGCCGCCTCCCCGCCT). It is contemplated herein that to increase cloning capacity of adeno-associated viral vectors, in some embodiments, a shorter WPRE is used. As shown in Figures 8-9, a variety of shorter WPREs can function comparably to the full-length WPRE to mediate gene expression. It has been observed that under some circumstances, an "X" polypeptide can be expressed from a portion of the WPRE sequence. To avoid expression of an "X" polypeptide, a portion of the WPRE can be removed, while still retaining posttranscriptional regulatory function (e.g. a "no X" WPRE).

In some embodiments a "no X" WPRE is used, for example a WPRE of SEQ ID NO: 28

(TAATCAACCTCTGGATTACAAAATTTGTGAAAGATTGACTGGTATTCTTAACTAT

GTTGCTCCTTTTACGCTATGTGGATACGCTGCTTTAATGCCTTTGTATCATGCTAT

TGCTTCCCGTATGGCTTTCATTTTCTCCTCCTTGTATAAATCCTGGTTGCTGTCTCT

TTATGAGGAGTTGTGGCCCGTTGTCAGGCAACGTGGCGTGGTGTGCACTGTGTTT

GCTGACGCAACCCCCACTGGTTGGGGCATTGCCACCACCTGTCAGCTCCTTTCCG

GGACTTTCGCTTTCCCCCTCCCTATTGCCACGGCGGAACTCATCGCCGCCTGCCTT

GCCCGCTGCTGGACAGGGGCTCGGCTGTTGGGCACTGACAATTCCGTGGTGTTGT

CGGGGAAATCATCGTCCTTTCC)(see, e.g., Figures 8B and 9B). In some embodiments, a "short WPRE" is used, for example SEQ ID NO: 29

(TAATCAACCTCTGGATTACAAAATTTGTGAAAGATTGACTGGTATTCTTAACTAT

GTTGCTCCTTTTACGCTATGTGGATACGCTGCTTTAATGCCTTTGTATCATGCTAT

TGCTTCCCGTATGGCTTTCATTTTCTCCTCCTTGTATAAATCCTGGTTGCTGTCTCT

TTATGAGGAGTTGTGGCCCGTTGTCAGGCAACGTGGCGTGGTGTGCACTGTGTTT

GCTGACGCAACCCCCACTGGTTGGGGCATTGCCACCACCTGTCAGCTCCTTTCCG

GGACTTTCGCTTTCCCCCTCCCTATTGCCACGGCGGAACTCATCGCCGCCTGCCTT

GCCCGCTGCTGGACAGGGGCTCGGCTGTTGGGCACTGACAATTCCGTGGTGTTGT

CGGGGAAATCATCGTCCTTTCCTTGGCTGCTCGCCTGTGTTGCCACCTGGATTCTG

CGCGGGACGTCCTTCTGCTACGTCCCTTCGGCCCTCAATCCAGCGGACCTTCCTTC

CCG). In some embodiments, a variant of one of the listed WPREs is used. It is noted that the "no X" WPRE is about 69% identical (41 1/592 bases) to the "full-length" WPRE, while the "short" WPRE is about 85% identical (504/592 bases) to the "full-length" WPRE.

Accordingly, in some embodiments, the adeno-associated vector comprises a WPRE with at least about 69% identity to the full-length WPRE, for example, at least about 69%, 70%,

71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%,

87%, 88%, 89%, 90%, 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical, including ranges between any two of the listed values. In some embodiments, the WPRE is at least about 69% identical to the "short" WPRE or "no X" WPRE, for example, at least about 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical, including ranges between any two of the listed values.

[0093] The RTE can comprise a rev response element (RRE), for example, a lentiviral RRE. A non-limiting example is bovine immunodeficiency virus rev response element (RRE). In some embodiments, the RTE is a constitutive transport element (CTE). Examples of CTE include, but are not limited to Mason-Pfizer Monkey Virus CTE and Avian Leukemia Virus CTE.

[0094] In some embodiments, the AAV vector includes a gene for a selectable marker that is effective in a eukaryotic cell, such as a drug resistance selection marker. This selectable marker gene can encode a factor necessary for the survival or growth of transformed host cells grown in a selective culture medium. Host cells not transformed with the vector containing the selection gene will not survive in the culture medium. Typical selection genes encode proteins that confer resistance to antibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate, kanamycin, gentamycin, Zeocin, or tetracycline, complement auxotrophic deficiencies, or supply critical nutrients withheld from the media.

[0095] The viral vectors disclosed herein can also include one or more A nucleotides immediately after an insertion site downstream of the promoter, where the insertion site allows the insertion of a polynucleotide encoding the protein(s) of interest. For example, one or more A nucleotides are located immediately after the TAA stop codon of the protein of interest after the insertion of the polynucleotide encoding the protein of interest into the vector. In some embodiments, one A nucleotide, two A nucleotides, three A nucleotides, or more are located immediately after the restriction site. In some embodiments, one A nucleotide, two A nucleotides, three A nucleotides, or more are located immediately after the TAA stop codon of the protein of interest.

[0096] In some embodiments, the viral vectors can include additional sequences that make the vectors suitable for replication and integration in eukaryotes. In other embodiments, the viral vectors disclosed herein can include a shuttle element that makes the vectors suitable for replication and integration in both prokaryotes and eukaryotes. In some embodiments, the viral vectors can include additional transcription and translation initiation sequences, such as promoters and enhancers; and additional transcription and translation terminators, such as polyadenylation signals.

[0097] In some embodiments, the viral vectors can include a regulatory sequence that allows, for example, the translation of multiple proteins from a single mRNA. Non- limiting examples of such regulatory sequences include internal ribosome entry site (IRES) and "cleavage polynucleotides" encoding cleavage sites such as 2A self-processing sequence. In some embodiments, the 2A sequence is a 2A peptide site from foot-and-mouth disease virus (F2A sequence). In some embodiments, the F2A sequence has a standard furin cleavage site. For example, the F2A sequence having a standard furin cleavage site can include a nucleotide sequence having at least about 90%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more, sequence identity to SEQ ID NO: 30

(CGGGCTAAGAGAGCACCGGTGAAACAGACTTTGAATTTTGACCTTCTCAAGTTG GCGGGAGACGTGGAGTCCAACCCAGGGCCC). In some embodiments, the F2A sequence has a modified furin cleavage site. For example, the F2A sequence having a modified furin cleavage site can include a nucleotide sequence having at least about 90%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more, sequence identity to SEQ ID NO: 31 (CGAAAAAGAAGATCAGGTTCGGGTGCGCCAGTAAAGCAGACATTAAACTTTGA TTTGCTGAAACTTGCAGGTGATGTAGAGTCAAATCCAGGTCCA).

[0098] The viral vectors can also, in some embodiments, have one or more restriction site(s) located near the promoter sequence to provide for the insertion of nucleic acid sequences encoding one or more proteins of interest and other protein(s).

Insertion sites

[0099] In some embodiments, the AAV vector includes one or more insertion sites. An insertion site can be positioned for the insertion of a polynucleotide in a desired location on the AAV vector. In some embodiments, the insertion site is for inserting a polynucleotide encoding a desired gene product in a desired location. In some embodiments, the insertion site includes at least one cleavage polynucleotide (for example a 2A polynucleotide) positioned between a site for inserting a first polynucleotide encoding a gene product and a site for inserting a second polynucleotide encoding a gene product.

[0100] In some embodiments, an insertion site can be positioned in an AAV vector to facilitate insertion of a polynucleotide encoding a gene product of interest that is operative ly linked to the promoter of the AAV vector. The insertion site can be positioned 3 ' to the promoter, for example about lObp, 20, 30, 40, 50, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1 100, 1200, 1500, or 2000bp 3 ' to the promoter.

[0101] In some embodiments, the insertion site is configured for the insertion of a first polynucleotide encoding a first gene product of interest and a second polynucleotide encoding a second gene product of interest. The insertion site can comprise a cleavage polynucleotide positioned 3 ' of a site in which the first polynucleotide can be inserted, and can be configured to be in-frame with the coding sequence of the first polynucleotide. The cleavage polynucleotide can be positioned 5' of a site in which the second polynucleotide can be inserted, and can be configured to be in-frame with the coding sequence of the second polynucleotide. In some embodiments, the cleavage polynucleotide encodes a 2A sequence or 2A variant as described herein.

[0102] In some embodiments, the insertion site comprises one or more restriction endonuclease sites. In some embodiments, the insertion site comprises a multiple cloning site (MCS). In some embodiments, the insertion site comprises a GATEWAY destination site.

Cleavage Sites

[0103] As used herein "cleavage site" refers to a sequence that mediates the separation of a first polypeptide that would otherwise be in cis to a second polypeptide. Accordingly, for simplicity, "cleavage," "cleavage site," and the like as used herein refer to the separation of any two polypeptides that are encoded by a single polynucleotide in cis. Thus, "cleavage" and "cleavage site," can, but do not necessarily refer to proteolytic sites and events, and can also refer to other mechanisms for mediating the separation of polypeptides, for example ribosomal skipping. As used herein "cleavage polynucleotide" refers to a polynucleotide encoding a cleavage site. In some embodiments, a cleavage site mediates the separation via an intra-ribosomal, translational termination-and-restart event during the synthesis of the nascent polypeptide chains so that a peptide bond is not formed between an upstream amino acid residue and a downstream amino acid residue. For example, such a cleavage site can include a 2A polypeptide as described herein. Exemplary cleavage sites are listed in Table 2. For example, such a cleavage site can comprise a translation termination sequence (e.g. a stop codon) upstream of an internal ribosome entry site. In some embodiments, a cleavage site includes a protease target site. For example, such a protease target site can comprise a furin cleavage site (Arg-X-X-Arg, preferably Arg-X- Lys/Arg-Arg; SEQ ID NO: 32). As used herein, "cleavage polynucleotide" refers to a polynucleotide that encodes a cleavage site.

[0104] As used herein, 2A sequences or elements refer to small peptides introduced as a linker between two proteins, allowing autonomous intraribosomal self- processing of polyproteins (See e.g. , de Felipe. Genetic Vaccines and Ther. 2: 13 (2004); deFelipe et al. Traffic 5:616-626 (2004)). These short peptides allow co-expression of multiple proteins from a single vector. Many 2A elements are known in the art. Examples of 2A sequences that can be used in the methods and system disclosed herein, without limitation, include 2A sequences from the foot-and-mouth disease virus (F2A), equine rhinitis A virus (E2A), Thosea asigna virus (T2A), and porcine tescho virus- 1 (P2A) as described in U.S. Patent Publication No. 2007/01 16690. In some embodiments, a cleavage site comprises a 2A polypeptide. In some embodiments, the 2A polypeptide comprises a wild-type 2A polypeptide from foot-and-mouth disease virus ("F2A"; QLLNFDLLKL AGD VE SNPGP ; SEQ ID NO: 33). In some embodiments, the 2A polypeptide is selected from Table 1. In some embodiments, the 2A polypeptide is a variant of a 2A polypeptide from Table 1. Variants can include polypeptide sequences having at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 99%, or more, sequence identity to a 2A polypeptide disclosed herein. Variants can include a deletion of at least one N-terminal amino acid from the 2A polypeptide of SEQ ID NO: 33, for example a deletion of 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids, including ranges between any two of the listed values. Variants can include a deletion of at least one C-terminal amino acid from the 2 A polypeptide of SEQ ID NO: 33, for example a deletion of 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids. [0105] Depending on the desired stoichiometry between two gene products encoded in a single transcript, a cleavage site of desired activity can be selected. In some embodiments, a polynucleotide encoding the 2A polypeptide is selected based on its relative activity. In some embodiments, F2A(wt)(QLLNFDLLKLAGDVESNPGP; SEQ ID NO: 34); F2A(-2) (LNFDLLKLAGDVESNPGP; SEQ ID NO: 35), and F2A(-1) (LLNFDLLKL AGD VE SNPGP ; SEQ ID NO: 36) are relatively high activity 2A polypeptides. In some embodiments, F2A(-7) (LKLAGDVESNPGP; SEQ ID NO: 37), F2A(19) (QLLNFDLLKLAGDVESNPAP; SEQ ID NO: 38), I2A(0) (TRAEIEDELIRRGIESNPGP; SEQ ID NO: 39), I2A(1) (TRAEIEDELIRAGIE SNPGP ; SEQ ID NO: 40), I2A(2) (TRAEIEDELIRRGIESNPGP; SEQ ID NO: 41), and I2A(3) (TRAEIEDELIRRGIESNPAP; SEQ ID NO: 42) are relatively low activity 2A polypeptides.

Gene products of interest

[0106] As used herein "gene product of interest," also referred to as "desired gene product" refers to a gene product, for example a polypeptide or polynucleotide (such as a ribosomal RNA, ribozyme, dsRNA, antisense-polynucleotide, siRNA, or the like) that can be inducibly expressed in a host cell or host organism.

[0107] It can be useful to express an antibody directly in a host organism. For example, vectored immunoprophylaxis can be an effective strategy to prevent HIV infection in humanized mice, and involves continuous production of antibody proteins at protective doses to function. Regulation systems that require the addition of exogenous drugs to maintain gene expression are not amenable to prophylaxis strategies due to difficulty of achieving patient compliance for drugs that could prevent infection such as HAART. As such, in some embodiments, the gene product of interest comprises an antibody.

[0108] It can be useful to replace or supplement a defective gene product through gene therapy. However, in some instances, it can be useful to subsequently silence expression of a gene product in gene therapy. For example in the context of clinical trials for a gene therapy product, it can be useful to have the option to reduce or eliminate transgene expression. For example, if a transgene construct in clinical trials may produce undesired side effects, or if an improved transgene construct is developed subsequent to the clinical trials, it can be useful to reduce or eliminate expression from the earlier transgene, so as to minimize or end the undesired side effects, or to deactivate the earlier transgene if favor of a later-generation transgene.

AAV vectors

[0109] Various vectors can be used to express gene products of interest in mammals or mammalian cells as described herein, for example, for gene therapy. In some embodiments, the vector comprises an AAV vector. A variety of AAV vectors can be used in inducible expression systems in accordance with embodiments herein. In some embodiments, an AAV vector comprises a first ITR, and a promoter positioned downstream (3 ') of the first ITR. The vector can comprise a first recombinase target site downstream (3 ') of the first ITR, and upstream (5') of the 3 ' end of promoter. The vector can comprise an insertion site downstream (3 ') of the promoter such that the promoter is operably linked to any polypeptide (for example, a polypeptide encoding a gene product of interest) that is inserted in the insertion site. The vector can comprise a second recombinase target site positioned downstream (3 ') of the 5' end of the promoter and upstream (5') of the insertion site. The vector can comprise a third recombinase target site positioned downstream (3 ') of the insertion site and upstream (5 ') of a second ITR. All three of the recombinase sites can be oriented in the same direction. The inducible expression system can also comprise a source of recombinase that can act on the recombination target sites.

[0110] In some embodiments, the vector also include a WPRE positioned downstream (3 ') of the insertion site and upstream (5') of a second ITR. The vector can also include a fourth recombinase target site positioned downstream (3 ') of the insertion site and upstream (5 ') of a 3 ' end of the WPRE. The vector can also include a fifth recombinase target site positioned downstream (3 ') of a 5' end of the WPRE. The vector can also include a sixth recombinase target site positioned downstream (3 ') of the WPRE and upstream (5') of the second ITR. All six recombinase target sites can all be oriented in the same direction.

[0111] In some embodiments, the AAV vector comprises at least three recombinase target sites, more preferably, four recombinase target sites, more preferably five recombinase target sites, more preferably six recombinase target sites. In some embodiments, the AAV vector comprises at least three recombinase target sites, for example 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, or 20 recombinase target sites, including ranges between any two of the listed values. [0112] In some embodiments, the recombinase comprises Cre, and the recombinase target sites comprise lox sites. In some embodiments, the recombinase comprises FLPase, and the recombinase target sites comprise FRT sites. In some embodiments, for each recombinase target site in the AAV vector, there is at least one other identical recombinase target site in the same orientation also in the vector, preferably at least two other identical sites in the same orientation, more preferably at least four other identical sites in the same orientation, more preferably at least five other identical sites in the same orientation.

[0113] In some embodiments, the WPRE is a full-length WPRE as described herein, or a variant thereof. In some embodiments, the WPRE is a full-length WPRE as described herein, or a variant thereof, for example SEQ ID NO: 27. In some embodiments, the WPRE is a "short" WPRE or a variant thereof, for example SEQ ID NO: 28. In some embodiments, the WPRE is a "no X" WPRE or a variant thereof, for example SEQ ID NO: 29.

[0114] In some embodiments, the AAV virus vector comprises a polyadenylation site. The polyadenylation site can be positioned downstream (3 ') of the WPRE and upstream (5') of the second ITR. In some embodiments, the polyadenylation site comprises a SV40 polyadenylation site as described herein. In some embodiments, the polyadenylation site comprises a synthetic polyadenylation site as described herein.

[0115] In some embodiments, the insertion site is configured for the insertion of polynucleotide encoding a gene product of interest. In some embodiments, the insertion site is configured for the insertion of two or more polynucleotides each encoding gene products of interest, and separated by a cleavage polynucleotide. In some embodiments, the insertion site is configured for insertion of a single polynucleotide comprising the two or more polynucleotides encoding gene products of interest (optionally with a cleavage polynucleotide or IRES positioned therebetween). In some embodiments, the insertion site configured for insertion of a first polynucleotide encoding a first gene product of interest and a second polynucleotide encoding a second gene product of interest. Such an insertion site can optionally comprise a cleavage polynucleotide or IRES positioned therebetween. The cleavage site can be configured to encode a cleavage site in-frame with the sequences encoding the gene products of interest. As such, the AAV vector can be configured to simultaneously express two or more gene products of interest. In some embodiments, the gene products of interest comprise the light chain and the heavy chain of an immunoglobulin, for example an antibody. In some embodiments, the gene products of interest comprise multimeric subunits of a gene product to be expressed in gene therapy, for example a multimeric extracellular receptor.

[0116] In some embodiments, the AAV vectors comprises vector 1806 (SEQ ID NO: 1) or a variant thereof. It is noted that vector 1806 comprises a "no X" WPRE, and an SV40 polyadenylation sequence. It is noted that vector 1806 comprises polypeptides encoding a heavy chain and light chain of antibody AC50, separated, in-frame by a 2A polypeptide. It is contemplated that in some embodiments, other polynucleotides encoding gene products of interest can readily be inserted into the backbone of vector 1806 or a variant thereof. As used herein, the "backbone" of vector 1806 refers to the sequence of vector 1806, excluding the polynucleotides encoding the light and heavy chains. In some embodiments, the backbone of vector 1806, or a variant having at least about 90% identity to the backbone vector 1806, for example about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% identity to the backbone of vector 1806 is provided. In some embodiments, at least one polypeptide encoding a gene product of interest is inserted therein. In some embodiments, at least two polypeptides, each encoding a gene product are inserted therein, and separated, in-frame by a cleavage polypeptide, for example a polypeptide encoding 2A. In some embodiments, the two polypeptides encode different gene products. In some embodiments, the two polypeptides each encode the same gene product.

[0117] In some embodiments, the AAV vector comprises a promoter, for example a CASI promoter or modified CASI promoter as described herein. The AAV vector can further comprise a first recombinase target site positioned 5 ' to a 3 ' end of the promoter, for example positioned inside the promoter, or downstream of the promoter. The AAV vector can further comprise a second recombinase target site positioned 3 ' to a 5' end of the promoter. The second recombinase target site can be positioned 3 ' to the first recombinase target site, and, for example, can be positioned inside the promoter or downstream of the promoter. In some embodiments, the first and second recombinase sites flank a synthetic intron of the promoter. In some embodiments, one or both of the first and second recombinase sites are positioned within a synthetic intron of the promoter. The AAV vector can further comprise an insertion site positioned 3 ' to the promoter and 3' to the second recombinase target site, such that the promoter would be operably linked to at least an inserted polynucleotide. The AAV vector can further comprise a third recombinase target site positioned 3' to the insertion site. In some embodiments, the AAV vector includes flanking ITRs, with a first ITR positioned 5' to the first recombinase target site and promoter, and a second ITR positioned 3' to the third recombinase site. In some embodiments, the first, second, and third recombinase sites are in the same orientation. In some embodiments, the first, second, and third recombinase target sites comprise lox sites, for example loxP sites, loxN sites, or lox2272 sites as described herein. In some embodiments, the first, second, and third recombinase target sites comprise FRT sites. In some embodiments, the AAV further comprises a WPRE positioned 3' to the insertion site, and 5' to the second ITR. The third recombinase target site can be positioned between the WPRE and the second ITR (e.g. 3' of the WPRE and 5' of the ITR). In some embodiments, the WPRE is a full-length WPRE as described herein. In some embodiments, the WPRE is a short WPRE as described herein. In some embodiments, the WPRE is a "no X" WPRE as described herein. The AAV vector can further comprise a fourth recombinase target site positioned 3' to the insertion site and 5' to a 3' end of the WPRE, for example within the WPRE or downstream of the WPRE. The AAV vector can further comprise a polyadenylation site, for example an SV40 polyadenylation site or synthetic polyadenylation site as described herein. The AAV can further comprise a fifth recombinase target site positioned 3' to the fourth recombinase target site and downstream of the WPRE (i.e. 3' to the WPRE). The AAV can further comprise a sixth recombinase target site positioned 3 ' to the first recombinase target site and 5' to the second recombinase target site. The fourth, fifth, and sixth recombinase target sites can be oriented in the same direction. In some embodiments, the first, second, third, fourth, fifth, and sixth recombinase target sites are oriented in the same direction. In some embodiments, the first, second, and third recombinase target sites are oriented in one direction, and the fourth, fifth, and sixth recombinase target sites are oriented in the other direction, for example if the first, second, and third recombinase target sites are identical (e.g. loxP sites) and the fourth, fifth, and sixth recombinase target sites are identical but different from the first, second, and third recombinase target sited (e.g. the fourth, fifth, and sixth sites are loxP sites). In some embodiments, at least two of the first, second, and third recombinase target sites are positioned flanking and/or within a synthetic intron of the promoter as described herein. In some embodiments, the promoter of the vector comprises a synthetic intron comprising a transcriptional enhancer as described herein. In some embodiments, each of the first and second recombinase target sites flank the synthetic intron. In some embodiments, one of the first and second recombinase target sites is positioned adjacent to the synthetic intron (e.g. upstream of the splice donor or downstream of the splice acceptor), and the other is positioned within the synthetic intron (e.g. between the splice donor and splice acceptor). In some embodiments, both of the first and second recombinase target sites are positioned within the synthetic intron.

[0118] In some embodiments, the AAV vector comprises a first ITR, a first recombinase target site positioned 3 ' to the first ITR and 5 ' of the 3 ' end of a promoter, a second recombinase target site within the promoter and 3 ' of the first recombinase target site, an insertion site 3 ' to the promoter, a third recombinase target site positioned 3 ' to the insertion site, a WPRE positioned 3 ' to the third recombinase target site, a fourth recombinase target site positioned 3 ' to the WPRE, a polyadenylation sequence positioned 3 ' to the fourth recombinase target site, a fifth recombinase target site positioned 3 ' to the polyadenylation sequence, and a second ITR positioned 3 ' to the fifth recombinase target site. In some embodiments, the promoter comprises a CASI promoter as described herein. In some embodiments, the promoter comprises a modified CASI promoter as described herein, in which the first recombinase target site and second recombinase target site are positioned either flanking a synthetic intron, within the synthetic intron, or such that one recombinase target site is positioned 5 ' to the splice donor or 3 ' to the splice acceptor of the synthetic intron and the other recombinase target site is positioned between the splice donor and splice acceptor. In some embodiments, the first, second, third, fourth, and fifth recombinase target sites are all in the same orientation. In some embodiments, the WPRE comprises one of a full-length WPRE, "short" WPRE, or "no X" WPRE as described herein. In some embodiments, the polyadenylation sequence comprises one of an SV40 polyadenylation sequence or synthetic polyadenylation sequence. Exemplary AAV vectors according to some of these embodiments are illustrated schematically in Figure 8B. In some embodiments, the recombinase target sites comprise lox sites as described herein. In some embodiments, the recombinase target sites comprise FRT sites as described herein.

[0119] In some embodiments, the AAV vector comprises a first ITR, a first recombinase target site positioned 3 ' to the first ITR and 5 ' of the 3 ' end of a promoter, a second recombinase target site within the promoter and 3 ' of the first recombinase target site, a third recombinase target site positioned within the promoter and 3 ' of the second recombinase target site. The AAV vector can comprise an insertion site 3 ' to the promoter, a fourth recombinase target site positioned 3 ' to the insertion site, a WPRE positioned 3 ' to the fourth recombinase target site, a fifth recombinase target site positioned 3 ' to the WPRE, a polyadenylation sequence positioned 3 ' to the fifth recombinase target site, a sixth recombinase target site positioned 3 ' to the polyadenylation sequence, and a second ITR positioned 3 ' to the sixth recombinase target site. In some embodiments, the promoter comprises a CASI promoter as described herein. In some embodiments, the promoter comprises a modified CASI promoter as described herein, in which the second recombinase target site and third recombinase target site are positioned either flanking a synthetic intron, within the synthetic intron, or such that one recombinase target site is 5 ' to the splice donor or 3 ' to the splice acceptor of the synthetic intron and the other recombinase target site is between the splice donor and splice acceptor. In some embodiments, the first, second, third, fourth, fifth, and sixth recombinase target sites are all in the same orientation. In some embodiments, the WPRE comprises one of a full-length WPRE, "short" WPRE, or "no X" WPRE as described herein. In some embodiments, the polyadenylation sequence comprises one of an SV40 polyadenylation sequence or synthetic polyadenylation sequence. Exemplary AAV vectors according to some of these embodiments are illustrated schematically in Figure 9B. In some embodiments, the recombinase target sites comprise lox sites as described herein. In some embodiments, the recombinase target sites comprise FRT sites as described herein.

[0120] In some embodiments, the AAV vector comprises a first ITR, a first recombinase target site positioned 3 ' to the first ITR and 5 ' of the 3 ' end of a promoter, a second recombinase target site within the promoter and 3 ' of the first recombinase target site, a first polynucleotide encoding a gene product of interest 3 ' to the promoter, and a third recombinase target site positioned 3 ' to the first polynucleotide. Optionally, the AAV vector can further comprise a second polynucleotide encoding a second gene product of interest positioned 3 ' to the first polynucleotide and 5 ' to the third recombinase target site. In some embodiments, the coding sequences of the first polynucleotide and second polynucleotide are in- frame with each other, and a cleavage polynucleotide is positioned 3 ' of (and in- frame with) the first polynucleotide and 5' to (and in- frame with) the second polynucleotide. Exemplary cleavage polynucleotides can include polynucleotides encoding 2A or 2A variant as described herein, or a furin site as described herein. In some embodiments, an IRES is positioned between the first and second polynucleotide. In some embodiments, the first polynucleotide encodes one of the heavy chain or light chain of an antibody, and the second polynucleotide encode the other of the heavy chain or light chain of an antibody. The AAV vector can further include a WPRE positioned 3 ' to the third recombinase target site, a fourth recombinase target site positioned 3 ' to the WPRE, a polyadenylation sequence positioned 3 ' to the fourth recombinase target site, a fifth recombinase target site positioned 3 ' to the polyadenylation sequence, and a second ITR positioned 3 ' to the fifth recombinase target site. In some embodiments, the promoter comprises a CASI promoter as described herein. In some embodiments, the promoter comprises a modified CASI promoter as described herein, in which the first recombinase target site and second recombinase target site are positioned either flanking a synthetic intron, within the synthetic intron, or with one recombinase target site 5 ' to the splice donor or 3 ' to the splice acceptor of the synthetic intron and the other recombinase target site between the splice donor and splice acceptor. In some embodiments, the first, second, third, fourth, and fifth recombinase target sites are all in the same orientation. In some embodiments, the WPRE comprises one of a full-length WPRE, "short" WPRE, or "no X" WPRE as described herein. In some embodiments, the polyadenylation sequence comprises one of an SV40 polyadenylation sequence or synthetic polyadenylation sequence. In some embodiments, the recombinase target sites comprise lox sites as described herein. In some embodiments, the recombinase target sites comprise FRT sites as described herein.

[0121] In some embodiments, the AAV vector comprises a first ITR, a first recombinase target site positioned 3 ' to the first ITR and 5 ' of the 3 ' end of a promoter, a second recombinase target site within the promoter and 3 ' of the first recombinase target site, a third recombinase target site positioned within the promoter and 3 ' of the second recombinase target site. The AAV vector can comprise a first polynucleotide encoding a gene product of interest 3 ' to the promoter, and a fourth recombinase target site positioned 3 ' to the first polynucleotide. Optionally, the AAV vector can further comprise a second polynucleotide encoding a second gene product of interest positioned 3' to the first polynucleotide and 5' to the fourth recombinase target site. In some embodiments, the coding sequences of the first polynucleotide and second polynucleotide are in-frame with each other, and a cleavage polynucleotide is positioned 3' of (and in- frame with) the first polynucleotide and 5' to (and in-frame with) the second polynucleotide. Exemplary cleavage polynucleotides can include polynucleotides encoding 2A or 2A variant as described herein, or a furin site as described herein. In some embodiments, an IRES is positioned between the first and second polynucleotide. In some embodiments, the first polynucleotide encodes one of the heavy chain or light chain of an antibody, and the second polynucleotide encode the other of the heavy chain or light chain of an antibody. The AAV vector can include a WPRE positioned 3 ' to the fourth recombinase target site, a fifth recombinase target site positioned 3' to the WPRE, a polyadenylation sequence positioned 3' to the fifth recombinase target site, a sixth recombinase target site positioned 3 ' to the polyadenylation sequence, and a second ITR positioned 3 ' to the sixth recombinase target site. In some embodiments, the promoter comprises a CASI promoter as described herein. In some embodiments, the promoter comprises a modified CASI promoter as described herein, in which the second recombinase target site and third recombinase target site are positioned either flanking a synthetic intron, within the synthetic intron, or such that one recombinase target site is 5 ' to the splice donor or 3 ' to the splice acceptor of the synthetic intron and the other recombinase target site is between the splice donor and splice acceptor. In some embodiments, the first, second, third, fourth, fifth, and sixth recombinase target sites are all in the same orientation. In some embodiments, the WPRE comprises one of a full-length WPRE, "short" WPRE, or "no X" WPRE as described herein. In some embodiments, the polyadenylation sequence comprises one of an SV40 polyadenylation sequence or synthetic polyadenylation sequence. Exemplary AAV vectors according to some of these embodiments are illustrated schematically in Figure 1A. In some embodiments, the recombinase target sites comprise lox sites as described herein. In some embodiments, the recombinase target sites comprise FRT sites as described herein. Reversible Expression Systems

[0122] According to some embodiments, reversible expression systems are provided. The expression systems can include a first AAV vector as described herein. In some embodiments, the first AAV vector comprises a polynucleotide encoding a desired gene product. In some embodiments, the first AAV vector comprises at least one insertion site for a polynucleotide encoding a desired gene product. The expression systems can include a source of recombinase as described herein. In some embodiments, the recombinase is encoded on a second AAV vector. In some embodiments, the recombinase is encoded on a second vector that is not an AAV vector, for example an adenoviral vector. The AAV or non-AAV vector encoding the recombinase can comprise promoter operably linked to a recombinase polypeptide. In some embodiments, the recombinase polypeptide is fused to a cell-penetration peptide, for example Tat or a variant thereof, to facilitate entry of the cell by the recombinase polypeptide.

[0123] [0105] In some embodiments, the source of the recombinase comprises a second vector encoding the recombinase. In some embodiments, an AAV vector encodes the recombinase. In some embodiments, an adenoviral vector encodes the recombinase. In some embodiments, a fusion polypeptide of a cell-penetration peptide and recombinase (for example Tat-Cre or Tat-FLPase) is provided. In some embodiments, a polynucleotide encoding a fusion polypeptide of a cell-penetration peptide and recombinase is provided.

Kits

[0124] In some embodiments kits are provided. The kit can comprise a reversible expression system as described herein, including a AAV vector for expressing a gene product of interest as described herein and a source of recombinase as described herein. In some embodiments, the kit comprises at least one type of cell for expressing the reversible expression system as described herein some embodiments, the cell comprises a mammalian cell suitable for production of gene products, for example a Chinese hamster ovary (CHO) cell, baby hamster kidney (BHK) cell, HeLa cell, monkey kidney cell (COS), human hepatocellular carcinoma cell (e.g. Hep G2), or the like. In some embodiments, the cell comprises a cell suitable for replacement therapy, for example, least one of a hematopoetic stem cell, embryonic stem cell, induced pluripotent stem cell, or the like.

[0125] In some embodiments, the kit comprises packaging, instructions, and the like.

Methods of expressing a gene product of interest

[0126] According to some embodiments, reversible gene expression as described herein can be performed in vivo. In some embodiments, a gene product of interest in expressed in a subject for a period of time, and then expression is reduced or eliminated. In some embodiments, the subject is a mammal. The subject can be, in some embodiments, a non-human mammal, for example, a non-human primate such as a monkey, a dog, a cat, a mouse, or a cow. The subject can be in some embodiments, a human. In some embodiments, the human is a participant in a clinical trial. The method can include administering to the subject a first AAV vector configured for reversible gene expression encoding a desired gene product as described herein. The method can include expression of the desired gene product in the subject after administration of the first AAV vector. The method can include administering a recombinase to the subject. The recombinase can induce recombination between at least two of the recombinase target sites of the AAV vector after the first gene product is expressed, thus reducing expression of the first gene product. In some embodiments, the recombinase is administered in a second AAV vector. In some embodiments, the recombinase is administered in an adenovirus vector. In some embodiments, a fusion polypeptide comprising the recombinase and a cell-penetration peptide is administered to the host.

[0127] In some embodiments, the method comprises administering to a subject an AAV vector as described herein. In some embodiments, the AAV vector comprises three recombinase target sites as described herein. In some embodiments, the AAV vector comprises five recombinase target sites as described herein. In some embodiments, the AAV vector comprises six recombinase target sites as described herein. Exemplary subjects include, but are not limited to humans, mice, non-human primates, non-human mammals, cow, sheep, pigs, and the like as described herein. In some embodiments, the AAV vector is administered to a cell that is transplanted into the subject. In some embodiments, the AAV vector comprises one polynucleotide encoding a gene product of interest. In some embodiments, the AAV vector comprises a first polynucleotide encoding a first gene product of interest, and a first polynucleotide encoding a first gene product of interest. In some embodiments, the first and second polynucleotides are separated, in-frame, by a cleavage polynucleotide as described herein. In some embodiments, the first and second polynucleotides are separated by an IRES. In some embodiments, the method comprises expressing both the first and second gene products of interest simultaneously in a subject, for example if the first and second gene products of interest comprise the heavy chain and light chain of an antibody. After the first and second gene products are expressed for a period of time as described herein, the method can comprise reducing or eliminating expression of the first and second gene products of interest. The method can comprise administering a recombinase as described herein to the subject. In some embodiments, the recombinase is administered in a vector. In some embodiments, the recombinase is administered in an AAV vector. In some embodiments, the recombinase is administered in a non-AAV vector, for example an adenovirus vector. In some embodiments, a recombinase polypeptide fused to a cell-penetration peptide is administered to the subject. In some embodiments, the recombinase target sites comprise lox sites as described herein (as such, the recombinase can comprise Cre). In some embodiments, the recombinase target sites comprise FRT sites as described herein (as such, the recombinase can comprise FLPase). Without being limited by any particular theory, administration of the recombinase can induce recombination events between recombinase target sites in the AAV, excising at least portions of the AAV, so as to reduce or eliminate expression of the gene product or products of interest. In some embodiments, administration of the recombinase reduces gene expression at least 10-fold, for example about 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, or 10000-fold, including ranges between any of the listed values.

[0128] Reversible gene expression systems, including AAV vectors, other vectors, and polypeptides can be administered to a subject in a variety of ways in accordance with some embodiments herein. In some embodiments, the reversible gene expression system is administered to a subject (e.g., a human or a non-human mammal) in need thereof. The route of the administration is not particularly limited. For example, a therapeutically effective amount of the recombinant viruses can be administered to the subject by via routes standard in the art. Non-limiting examples of the route include intramuscular, intravaginal, intravenous, intraperitoneal, subcutaneous, epicutaneous, intradermal, rectal, intraocular, pulmonary, intracranial, intraosseous, oral, buccal, or nasal. In some embodiments, the expression system or component thereof is administered to the subject by intramuscular injection. In some embodiments, the expression system or component thereof is administered to the subject by intravaginal injection. In some embodiments, the expression system or component thereof is administered to the subject by the parenteral route (e.g., by intravenous, intramuscular or subcutaneous injection), by surface scarification or by inoculation into a body cavity of the subject. Route(s) of administration and serotype(s) of the expression system or component thereof can be readily determined by one skilled in the art taking into account the infection and/or disease state being treated and the target cells/tissue(s) that are to express the protein of interest. In some embodiments, the expression system or component thereof is administered to muscle cells.

[0129] Although the exact dosage will be determined on a drug-by-drug basis, in most cases, some generalizations regarding the dosage can be made. In some embodiments, the recombinant AAV expressing a gene product of interest can be administered via injection to a subject at a dose of about lxl 0 ⁹ genome copies (GC) of the recombinant virus per kg of the subject to about lxlO ¹³ GC per kg, for example about lxlO ⁹ GC/kg to lxlO ¹⁰ GC/kg, about lxlO ⁹ GC/kg to 5xl0 ¹⁰ GC/kg, about lxlO ⁹ GC/kg to lxlO ¹¹ GC/kg, about lxlO ⁹ GC/kg to 5xlO ⁿ GC/kg, about lxlO ⁹ GC/kg to lxlO ¹² GC/kg, about lxlO ⁹ GC/kg to 5xl0 ¹² GC/kg, about lxlO ⁹ GC/kg to lxlO ¹³ GC/kg, about 5xl0 ⁹ GC/kg to lxlO ¹⁰ GC/kg, about 5xl0 ⁹ GC/kg to 5xl0 ¹⁰ GC/kg, about 5xl0 ⁹ GC/kg to lxlO ¹¹ GC/kg, about 5xl0 ⁹ GC/kg to 5xlO ⁿ GC/kg, about 5xl0 ⁹ GC/kg to lxlO ¹² GC/kg, about 5xl0 ⁹ GC/kg to 5xl0 ¹² GC/kg, about 5xl0 ⁹ GC/kg to lxlO ¹³ GC/kg, about lxlO ¹⁰ GC/kg to 5xl0 ¹⁰ GC/kg, about lxlO ¹⁰ GC/kg to lxlO ¹¹ GC/kg, about lxlO ¹⁰ GC/kg to 5xlO ⁿ GC/kg, about 5xl0 ¹⁰ GC/kg to lxlO ¹² GC/kg, about lxlO ¹⁰ GC/kg to 5xl0 ¹² GC/kg, about lxlO ¹⁰ GC/kg to lxlO ¹³ GC/kg, about 5xl0 ¹⁰ GC/kg to lxlO ¹¹ GC/kg, about 5xl0 ¹⁰ GC/kg to 5xlO ⁿ GC/kg, about 5xl0 ¹⁰ GC/kg to lxlO ¹² GC/kg, about 5xl0 ¹⁰ GC/kg to 5xl0 ¹² GC/kg, about 5xl0 ¹⁰ GC/kg to lxlO ¹³ GC/kg, about lxlO ¹¹ GC/kg to 5xlO ⁿ GC/kg, about lxlO ¹¹ GC/kg to lxlO ¹² GC/kg, about lxlO ¹¹ GC/kg to 5xl0 ¹² GC/kg, about lxlO ¹¹ GC/kg to lxlO ¹³ GC/kg, about 5xlO ⁿ GC/kg to lxlO ¹²

11 13

GC/kg, or about 5x10" GC/kg to lxl0 ^1J GC/kg. In some embodiments, for example if the administered source of recombinase comprises a vector encoding the recombinase, the recombinase vector is delivered at least the dose, or more preferably, an excess of the dose of the AAV vector encoding the gene product of interest.

[0130] Actual administration of the AAV vector encoding a gene product of interest, expression system, or component thereof can be accomplished by using any physical method that will transport the recombinant AAV vector into the target tissue of the subject. For example, the recombinant AAV vector can be injected into muscle, the bloodstream, and/or directly into the liver. Capsid proteins of the recombinant AAV vector may be modified so that the recombinant AAV vector is targeted to a particular target tissue of interest such as muscle or bone marrow. Pharmaceutical compositions can be prepared as injectable formulations or as topical formulations to be delivered to the muscles by transdermal transport.

[0131] For intramuscular injection, solutions in an adjuvant such as sesame or peanut oil or in aqueous propylene glycol can be employed, as well as sterile aqueous solutions. Such aqueous solutions can be buffered, if desired, and the liquid diluent first rendered isotonic with saline or glucose. Solutions of the AAV vector as a free acid (DNA contains acidic phosphate groups) or a pharmacologically acceptable salt can be prepared in water suitably mixed with a surfactant such as hydroxpropylcellulose. A dispersion of the AAV vector can also be prepared in glycerol, liquid polyethylene glycols and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

[0132] The AAV vector to be used can be utilized in liquid or freeze-dried form (in combination with one or more suitable preservatives and/or protective agents to protect the virus during the freeze-drying process). For gene therapy (e.g., of neurological disorders which may be ameliorated by a specific gene product) a therapeutically effective dose of the recombinant virus expressing the therapeutic protein is administered to a host in need of such treatment. The use of the recombinant virus disclosed herein in the manufacture of a medicament for inducing immunity in, or providing gene therapy to, a host is within the scope of the present application. In some embodiments, the AAV can be administered to a cell that is subsequently transplanted into the host, for example a hematopoietic stem cell, embryonic stem cell, induced pluripotent stem cell, or the like. [0133] In instances where human dosages for the AAV vectors have been established for at least some condition, those same dosages, or dosages that are between about 0.1% and 500%, more preferably between about 25% and 250% of the established human dosage can be used. Where no human dosage is established, as will be the case for newly-discovered pharmaceutical compositions, a suitable human dosage can be inferred from ED ₅ o or ID ₅₀ values, or other appropriate values derived from in vitro or in vivo studies, as qualified by toxicity studies and efficacy studies in animals.

[0134] A therapeutically effective amount of the AAV vector encoding a gene product of interest can be administered to a subject at various points of time. For example, the AAV vector can be administered to the subject prior to, during, or after the infection by a virus. The AAV vector can also be administered to the subject prior to, during, or after the occurrence of a disease {e.g., cancer). In some embodiments, the AAV vector is administered to the subject during cancer remission. In some embodiments, the AAV vector is administered prior to infection by the virus for immunoprophylaxis.

[0135] The dosing frequency of the AAV vector can vary. For example, the AAV vector can be administered to the subject about once every week, about once every two weeks, about once every month, about one every six months, about once every year, about once every two years, about once every three years, about once every four years, about once every five years, about once every six years, about once every seven years, about once every eight years, about once every nine years, about once every ten years, or about once every fifteen years. In some embodiments, the AAV vector is administered to the subject at most about once every week, at most about once every two weeks, at most about once every month, at most about one every six months, at most about once every year, at most about once every two years, at most about once every three years, at most about once every four years, at most about once every five years, at most about once every six years, at most about once every seven years, at most about once every eight years, at most about once every nine years, at most about once every ten years, or at most about once every fifteen years.

[0136] In some embodiments the source of the recombinase is administered at the same time as the AAV vector. In some embodiments, a mixture of AAV vector encoding the gene product of interest and the recombinase source is administered. In some embodiments, for example if the recombinase provided in a vector and is under the control of an inducible promoter, the recombinase is administered but is not active at or immediately after administration. Recombinase activity can subsequently be induced to reduce or eliminate expression of the gene product of interest. In some embodiments, for example if the recombinase target sites of the AAV vector comprise lox sites, the recombinase comprises Cre. In some embodiments, for example if the recombinase target sites of the AAV comprise FRT sites, the recombinase comprises FLPase. In some embodiments, the recombinase is administered along the same route of administration as the AAV encoding the gene product of interest. In some embodiments, the source of recombinase is administered via a different route administration than the AAV encoding the gene product of interest, for example intramuscular, intravaginal, intravenous, intraperitoneal, subcutaneous, epicutaneous, intradermal, rectal, intraocular, pulmonary, intracranial, intraosseous, oral, buccal, or nasal. In some embodiments, the source of recombinase is delivered at a greater dose that the AAV vector encoding the gene product of interest. For example, in some embodiments in which the recombinase is administered as a vector, at least a 2-fold ratio of recombinase vector to AAV vector encoding gene product of interest can be administered, for example at least about a 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100, 200, 500, 1000, 1500, 2000, 5000, 10,000, 20,000, 50,000, 100,000, 500,000, or 1 ,000,000,000-fold ratio of recombinase vector to AAV vector.

[0137] In some embodiments, the source of recombinase is provided after the AAV vector is administered to the subject. In some embodiments, the source of recombinase is provided after the gene product of interest has been expressed from the AAV vector. In some embodiments, expression of the gene product of interested is monitored in the subject (for example through direct monitoring of levels of gene product, or through monitoring of biomarkers indicative of levels of gene product or gene product activity), and the source of recombinase is subsequently administered to the subject. In some embodiments, the source of recombinase is administered to the subject upon or after the subject reaching a clinical endpoint. In some embodiments, the source of recombinase is administered to the subject if the subject experiences undesired side effects from the AAV vector encoding the gene product of interest. In some embodiments, the source of recombinase is administered at least about 1 week after the AAV vector encoding the gene product of interest is administered to the subject, for example about 1 week, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 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, 55, 56, 57, 58, 59, 60, 61 , 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 , 72, 73, 74, 75, 76, 77,78, 79, 80, 81 , 82, 83, 84, 85, 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98, 99, 100, 101 , 102, 103, 104, 105, 106, 107, 108, 109, 1 10, 1 1 1 , 1 12, 1 13, 1 14, 1 15, 1 16, 1 17, 1 18, 1 19, 120, 121 , 122, 123, 124, 125, 126, 127, 128, 129, 130, 131 , 132, 133, 134, 135, 136, 137, 138, 139, 140, 141 , 142, 143, 144, 145, 146, 147, 148, 149, 150, 151 , 152, 153, 154, 155, 156, 157, 158, 159, 160, 161 , 162, 163, 164, 165, 166, 167, 168, 169, 170, 171 , 172, 173, 174, 175, 176, 177,78, 179, 180, 181 , 182, 183, 184, 185, 186, 187, 188, 189, 190, 191 , 192, 193, 194, 195, 196, 197, 198, 199, or 200 weeks after, including ranges between any two of the listed values.

[0138] In some embodiments, upon administration, the source of recombinase provides recombinase activity, which results in a fold-reduction of expression and/or activity of the gene product of interest. In some embodiments, expression, activity, or expression and activity of the gene product of interest are reduced at least about 10-fold, for example about lxlO ¹ , 5X10 ¹ , lxlO ² , 5xl0 ² , lxlO ³ , 5xl0 ³ , lxl O ⁴ , 5xl0 ⁴ , lxl O ⁵ , 5xl0 ⁵ , lxl O ⁶ , or 5xl0 ⁶ -fold. In some embodiments, prior to recombinase administration, the AAV vector encoding a gene product of interest produces at least a comparable yield of gene product and gene product activity as a comparable AAV vector lacking the recombinase sites. In some embodiments, the addition recombinase eliminates or substantially eliminates expression and/or activity of the gene product of interest.

[0139] In some embodiments, addition of the recombinase induces recombination between one pair of the recombinase target sites of the AAV vector encoding the gene product of interest. In some embodiments, addition of the recombinase induces recombination between at least two pairs of the recombinase target sites of the AAV vector encoding the gene product of interest, for example two, three, four, five, six, seven, eight, nine, or ten pairs of recombinase target sites as described herein.

[0140] In some embodiments, the AAV encodes a heavy chain and a light chain of an immunoglobulin as described herein. In some embodiments, the immunoglobulin is an antibody. In some embodiments, the antibody binds specifically to a pathogen, for example a virus such as HIV, and thus can be administered as an immunoprophylactic vaccine. In some embodiments, the polynucleotides encoding the heavy chain and light chain are orientated in the same orientation and operationally linked to a promoter of the AAV. A cleavage polynucleotide, for example a 2A polynucleotide can be positioned in-frame between the heavy chain and light chain polynucleotide. In some embodiments, the polynucleotide encoding the heavy chain is upstream (5') of the polynucleotide encoding the light chain. In some embodiments, the polynucleotide encoding the light chain is upstream (5') of the polynucleotide encoding the heavy chain. In some embodiments, the heavy chain and light chain are administered on separate AAV vectors configured for reversible gene expression as described herein, and each AAV vector comprises recombinase target sites configured to reduce or eliminate expression of the respective heavy or light chain upon the addition of recombinase. In some embodiments, the heavy chain and light chain are administered on separate vectors, and only one of the two vectors (heavy chain or light chain) comprises an AAV vector configured for reversible gene expression as described herein.

Example 1 : Transfection of 293T Cells with LoxP Constructs +/- Cre (1 LoxP site)

[0141] 293T cells were transfected with AAV vector comprising a CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPPvE, and an SV40 polyadenylation site (see Figure 2A). Vector 1490 had no LoxP sites. Each of vectors 1592, 1593, 1595, and 1602 had one LoxP site, positioned as shown in Figure 2C (solid arrows). For each vector, one population of cells was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 2B, each vector produced approximately the same Luciferase activity (RLU) in the presence or absence of Cre.

Example 2: Transfection of 293T Cells with LoxP Constructs +/- Cre (2 LoxP sites)

[0142] 293T cells were transfected with AAV vector comprising a CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPRE, and an SV40 polyadenylation site (see Figure 3 A). Vector 1490 had no LoxP sites. Each of vectors 1594, 1603, 1604, and 1608 had two LoxP sites, positioned as shown in Figure 3C (solid arrows). For each vector, one population of cells was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 3B, cotransfection with Cre yielded substantially reduced luciferase activity (about 10 ² -fold) for vectors 1603 and 1604 (each of which had LoxP sites in the same orientation, as shown), but not for vectors 1490, 1594, and 1680. Since 1490 lacks LoxP sites, and 1608 possesses LoxP sites in opposite orientations flanking the promoter, coding, and regulatory sequences (and thus would be expected to invert the flanked sequences), the insubstantial effect of Cre on luciferase activity was as expected. On the other hand, as 1594 possessed LoxP sites in the same orientation flanking the vector, it was unexpected that Cre did not reduce luciferase activity for this vector, as Cre would have been expected to mediate a recombination event that excised the promoter, coding, and regulatory sequences from the vector.

Example 3: Transfection of 293T Cells with LoxP Constructs +/- Cre (3 LoxP sites)

[0143] 293T cells were transfected with AAV vector comprising a CASI promoter or modified CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPRE, and an SV40 polyadenylation site. Vector 1490 had no LoxP sites. Each of vectors 1605, 1633, 1655, 1661, 1754, 1755, and 1756 had three LoxP sites, positioned as shown in Figure 4B (solid arrows). Vectors 1490, 1605, 1661, 1754, 1755, and 1756 had a CASI promoter. Vectors 1633 and 1655 had a modified CASI promoter, in which Lox P sites were inserted within the promoter sequence (see Figure IB, in which positions of solid arrows indicate placement of LoxP sites). In each modified CASI promoter, a first LoxP site was positioned either upstream or downstream of the splice donor, and a second LoxP site was positioned either upstream or downstream of the splice acceptor. For each vector, one population of cells was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 4A, cotransfection with Cre yielded substantially reduced luciferase activity (about 10 ³ to 10 -fold) for vectors 1605 and 1633 (each of which had LoxP sites in the same orientation, with one LoxP site upstream of the promoter, and one LoxP site immediately downstream of the promoter; see Figure 4B). It is noted that for the remaining vectors (1655, 1661, 1754, 1755, 1756), even though all of the LoxP sites were in the same orientation and positioned throughout the construct, they did not reduce expression nearly as much as for vectors 1605 and 1633. Example 4: Transfection of 293T Cells with LoxP Constructs +/- Cre (4 LoxP sites)

[0144] 293T cells were transfected with AAV vector comprising a CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPPvE, and an SV40 polyadenylation site. Vector 1490 had no LoxP sites. Each of vectors 1782, 1783, 1784, and 1785 had four LoxP sites, positioned as shown in Figure 5C (solid arrows). For each vector, one population of cells was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 5B, cotransfection with Cre yielded substantially reduced luciferase activity (about 10 -fold) for vectors 1782, 1783, 1784, and 1785 (each of which four had LoxP sites in the same orientation; see Figure 5B).

Example 5: Transfection of 293T Cells with LoxP Constructs +/- Cre (5 LoxP sites)

[0145] 293T cells were transfected with AAV vector comprising a CASI promoter or modified CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPRE, and an SV40 polyadenylation site. Vector 1490 had no LoxP sites. Each of vectors 1793, 1794, 1795, 1796, 1797, and 1798 had five LoxP sites, positioned as shown in Figure 6B (solid arrows). Vectors 1490, 1793, 1795, 1797, and 1798 had a CASI promoter. Vectors 1794 and 1796 had a modified CASI promoter, in which LoxP sited were inserted into the promoter sequence as described herein. For each vector, one population of cells was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 6A, cotransfection with Cre yielded substantially reduced luciferase activity for vectors 1793, 1794, 1795, 1796, 1797, and 1798 (about 10 ² -fold), with expression especially low (about 10 -fold) for vectors 1793 and 1794 (each of which had a LoxP site upstream of the promoter, and another LoxP site immediately downstream of the promoter, both in the same orientation; see Figure 6B).

Example 6: Transfection of 293T Cells with LoxP Constructs +/- Cre (6 LoxP sites)

[0146] 293T cells were transfected with AAV vector comprising a CASI promoter or modified CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPRE, and an SV40 polyadenylation site. Vector 1490 had no LoxP sites. Each of vectors 1799 and 1800 had six LoxP sites, positioned as shown in Figure 7C (solid arrows). For each vector, one population of cells was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 7B, cotransfection with Cre yielded substantially reduced luciferase activity (about 10 -fold) for vectors 1799 and 1800.

Example 7: Transfection of 293T Cells with Shortened LoxP Constructs +/- Cre (5 LoxP sites)

[0147] AAV vectors with CASI promoters operatively linked to a luciferase coding sequence (Luc2), shortened WPRE sites and/or SV40 sites were prepared as shown in Figure 8B. Control vector 1490 had a full-length WPRE (SEQ ID NO: 27) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and no LoxP sites as shown in Figure 8B. Vector 1798 had a full-length WPRE (SEQ ID NO: 27) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and five LoxP sites as shown in Figure 8B. Vector 1801 had a full-length WPRE (SEQ ID NO: 27) and a synthetic polyadenylation sequence (SEQ ID NO: 43) and five LoxP sites as shown in Figure 8B. Vector 1803 had a "No X" WPRE (SEQ ID NO: 28) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and five LoxP sites as shown in Figure 8B. Vector 1804 had a "short" WPRE (SEQ ID NO: 29) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and five LoxP sites as shown in Figure 8B. Vector 1807 had a "No X" WPRE (SEQ ID NO:28) and a synthetic polyadenylation sequence (SEQ ID NO: 43) and five LoxP sites as shown in Figure 8B. Vector 1808 had a "short" WPRE (SEQ ID NO: 29) and a synthetic polyadenylation sequence (SEQ ID NO: 43) and five LoxP sites as shown in Figure 8B.

[0148] 293T cells were transfected with the indicated vectors. For each vector, one population of cells 293T cells were transfected with AAV vector comprising a CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPRE, and an SV40 polyadenylation site was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 8A, cotransfection with Cre yielded substantially reduced luciferase activity for vectors 1798, 1801, 1803, 1804, 1807, and 1808. It is noted that in the absence of Cre, vectors 1803, 1804, 1807, and 1808 produced comparable luciferase expression to the other vectors, but had much shorter WPREs.

Example 8: Transfection of 293T Cells with Shortened LoxP Constructs +/- Cre (6 LoxP sites)

[0149] AAV vectors with CASI promoters operatively linked to a luciferase coding sequence (Luc2), shortened WPRE sites and/or SV40 sites were prepared as shown in Figure 9B. Control vector 1490 had a full-length WPRE (SEQ ID NO: 27) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and no LoxP sites as shown in Figure 9B. Vector 1800 had a full-length WPRE (SEQ ID NO: 27) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and six LoxP sites as shown in Figure 9B. Vector 1802 had a full-length WPRE (SEQ ID NO: 27) and a synthetic polyadenylation sequence (SEQ ID NO: 43) and six LoxP sites as shown in Figure 9B. Vector 1805 had a "short" WPRE (SEQ ID NO: 29) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and six LoxP sites as shown in Figure 9B. Vector 1806 (SEQ ID NO: 1) had a "no X" WPRE (SEQ ID NO: 28) and an SV40 polyadenylation sequence (SEQ ID NO: 26) and six LoxP sites as shown in Figure 9B. Vector 1809 had a "short" WPRE (SEQ ID NO: 29) and a synthetic polyadenylation sequence (SEQ ID NO: 43) and six LoxP sites as shown in Figure 9B. Vector 1810 had a "no X" WPRE (SEQ ID NO: 28) and a synthetic polyadenylation sequence (SEQ ID NO: 43) and six LoxP sites as shown in Figure 9B.

[0150] 293T cells were transfected with the indicated vectors. For each vector, one population of cells 293T cells were transfected with AAV vector comprising a CASI promoter which was operatively linked to a luciferase coding sequence (Luc2), a full-length WPRE, and an SV40 polyadenylation site was cotransfected with pUC (control), while another population was cotransfected with a separate plasmid encoding Cre recombinase. As shown in Figure 9A, cotransfection with Cre yielded substantially reduced luciferase activity for vectors 1800, 1802, 1805, 1806, and 1809. It is noted that in the absence of Cre, vectors 1805, 1806, and 1810 produced comparable luciferase expression to the other vectors, but had much shorter WPREs. Example 9: In vivo testing of LoxP AAV vectors

[0151] LoxP AAV vectors in accordance with some embodiments herein encoding luciferase were injected into mice. Each luciferase vector was injected into four mice, of which two received a mixture of AAV vector encoding luciferase and control AAV vector 1788 - AAV-CASI-ZsGreen-W-SV40 ("ZsGreen;" no Cre), and two received a mixture AAV vector encoding luciferase and Cre-encoding AAV vector 1742 - AAV-CASI- nlsCre2-W-SV40 (+ Cre). The vectors were provided at a ratio of 2.5x10 ⁹ GC Luciferase to 1.25xlO ⁿ GC ZsGreen or Cre Vector, which represented a 50x Excess Cre-expression vector versus Luciferase-encoding vector. Luciferase expression was monitored via Xenogen imaging at 7, 14, 21, 28, 42, 70, and 126 days after injection. The design of this experiment is schematically illustrated in Figure 10. Xenogen imaging of luciferase activity at 7 days after injection is shown in Figures 11A-11M. Xenogen imaging of luciferase activity at 4 weeks after injection is shown in Figures 12A-12M. Representative Xenogen imaging 10 weeks after AAV administration is shown in Figures 14A (vector 1490; no LoxP sites) and 14B (vector 1806; six loxP sites). Representative Xenogen imaging 18 weeks after AAV administration is shown in Figures 14A (vector 1490; no LoxP sites) and 14B (vector 1806; six loxP sites). Notably, at both 10 and 18 weeks, the mice that received vector 1806 (six loxP sites) and Cre have substantially less luciferase activity than controls.

[0152] A comparison of luciferase activity (via Xenogen imaging) at 18 weeks after injection for zsGreen-injected mice and Cre-injected mice is shown in Figure 13. Notably, vectors 1800, 1806, and 1810 produced very high levels of luciferase activity in the absence of Cre (levels even higher than vectors that lacked LoxP sites), but these activity levels were reduced more than 10-fold in the presence of Cre.

Example 10: In vivo testing of LoxP AAV vectors

[0153] LoxP AAV vectors in accordance with some embodiments herein encoding luciferase were injected into mice. Each luciferase vector was injected into four mice, of which two received a mixture of AAV vector encoding luciferase and control AAV vector 1788 - AAV-CASI-ZsGreen-W-SV40 ("ZsGreen;" no Cre), and two received a mixture AAV vector encoding luciferase and Cre-encoding AAV vector 1742 - AAV-CASI- nlsCre2-W-SV40 (+ Cre). Mice were injected with 5uL, lOuL, 20uL, or 40uL solution containing 5x10 GC vector 1806 (Luc-LoxP). 20 weeks later, the mice were injected with 40uL of 5xlO ⁿ GC of a second AAV vector encoding either ZsGreen (-Cre) or Cre (+ Cre). The vectors were provided at a ratio of 2.5xl0 ⁹ GC Luciferase to 1.25xlO ⁿ GC ZsGreen or Cre Vector, which represented a lOx excess of Cre-expression vector versus Luciferase- encoding vector. The design of this experiment is schematically illustrated in Figure 17. Luciferase expression was monitored via Xenogen imaging prior to administration of the second AAV vector (see Figure 26), at the time that the second AAV vector was injected (i.e. 20 weeks after administration of the first, luciferase-encoding vector, see Figure 18), and at 3, 7, 14, 21 , 28, 56, and 84 days after injection (see Figures 19, 20, 21, 22, 23, 24, and 25, respectively). The luciferase activity along the timecourse is summarized in Figure 26 (total body), Figure 27 (liver), and Figure 28 (leg).

[0154] Luciferase activity prior to administration of Cre was highest for lOuL of vector 1806. As such, it is contemplated that total luciferase activity is not simply a function of the amount of luciferase vector administrated. After administration of Cre, whole-body luciferase activity was reduced substantially for all doses.

Example 1 1 : In vivo expression of antibody

[0155] AAV vectors in accordance with some embodiments herein were used to express AC50 in mice, and subsequently exposed to Cre. Mice received intramuscular injection of either 2xl0 ¹⁰ GC of vector 1677 encoding the heavy chain and light chain of antibody AC50, but lacking loxP sites, or 2xl0 ¹⁰ GC of vector 1834 (SEQ ID NO: 3) encoding the heavy chain and light chain of antibody AC50, and containing six loxP sites (see Figure 31C). 7 weeks later, the mice were injected intramuscularly with either 2.5xl0 ¹² GC of vector 1787 (encoding GFP) or 2.5xl0 ¹² GC of vector 1742 (encoding Cre). Levels of antibody expression were detected by a sandwich ELISA. Plates were coated with an Anti-Fc antibody, and a sample was added. Binding of antibody was detected using an anti-Kappa Light Chain-HRP. Although initial antibody expression levels were comparable, Antibody expression was substantially decreased for the combination of vector 1834 (LoxP sites) and vector 1742 (Cre) in comparison to the other vectors. [0156] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0157] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g. , "a" and/or "an" should be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., " a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g. , " a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0158] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0159] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non- limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like include the number recited and refer to ranges which can be subsequently broken down into sub-ranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1 -3 articles refers to groups having 1 , 2, or 3 articles. Similarly, a group having 1 -5 articles refers to groups having 1 , 2, 3, 4, or 5 articles, and so forth.

[0160] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

[0161] While the present invention has been described in some detail for purposes of clarity and understanding, one skilled in the art will appreciate that various changes in form and detail can be made without departing from the true scope of the invention. [0162] The term "comprising" as used herein is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps.

[0163] All numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of any claims in any application claiming priority to the present application, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[0164] The above description discloses several methods and materials of the present invention. This invention is susceptible to modifications in the methods and materials, as well as alterations in the fabrication methods and equipment. Such modifications will become apparent to those skilled in the art from a consideration of this disclosure or practice of the invention disclosed herein. Consequently, it is not intended that this invention be limited to the specific embodiments disclosed herein, but that it cover all modifications and alternatives coming within the true scope and spirit of the invention.

[0165] The foregoing description and Examples detail certain embodiments. It will be appreciated, however, that no matter how detailed the foregoing may appear in text, the invention may be practiced in many ways and the invention should be construed in accordance with the appended claims and any equivalents thereof.