Methods and compositions for integration defective lentiviral vectors

An integration-defective lentiviral vector (IDLV) based on a parental lentivirus, the integration-defective lentiviral vector comprising one or more of the following:

• a) a mutation, deletion or other modification selected from the group consisting of
• i) deletion of an AP-4 binding site;
• ii) mutation of contiguous nucleotides CNRG to DNRG, CNYG or CNRH, wherein N=A or C or G or T, R=A or G, Y=C or T, H=A or C or T, and D=A or G or T;
• iii) deletion of a TATA box;
• iv) deletion of a negative regulatory element (NRE);
• v) insertion of an NEκB binding site;
• vi) insertion of an SP1 binding site;
• and
• vii) any combination thereof;
• (b) insertion of one or more binding sites for a transcription activator, which can be natural or synthetic, and incorporated into the 3′ U3 region in either a self-inactivating (SIN) or a non-SIN form of the lentiviral vector and wherein the transcription activator is selected from the group consisting of SP1;
• NFkB;
• a binding site for tetracycline regulated trans activators tTA, rtTA, tT65 and/or rtT65;
• and any combination thereof;
• (c) insertion of one or more nucleic acid sequences from a SV40 genome, wherein the one or more nucleic acid sequences are a 3f46 region, s2f2R region and/or a USE region of the SV40 genome upstream to the SV40 poly-adenylation signal, and inserted in the lentiviral vector either in the opposite or same orientation to the long terminal repeats (LTRs);
• (d) a short hairpin RNA (shRNA) expression cassette, which encodes a shRNA directed to a host gene involved in epigenetic silencing and/or ubiquitination or proteasome activity;
• and
• (e) any combination of (a), (b), (c) and (d), wherein as compared to the parental lentivirus, the integration-defective lentiviral vector resists gene silencing, and further wherein the integration-defective lentiviral vector comprises a site-directed recombination site.