Lentiviral vectors (LVs) can transduce both mitotic cells and post-mitotic neurons, and are, therefore, promising as gene therapy vectors for the treatment of neurodegenerative diseases. However, LVs have a potential risk of insertional mutagenesis, because the proviruses are inserted into the host chromosome. In this study, we produced integrase-defective LVs (IDLVs) with a mutant (D64V) integrase and examined the levels and duration of transgene expression in the mouse brain. Moreover, using spinocerebellar ataxia type 3 (SCA3) model mice, their therapeutic potential was explored in comparison with LVs having a wild-type integrase (WTLVs).
The proviral integration of IDLVs were significantly reduced to approximately 1/3,850 in vitro and to approximately 1/111 in vivo as compared with WTLVs. During long-term observation, transgene expression by IDLVs expressing GFP, which was assessed by the mRNA levels and GFP fluorescence, was not significantly differ from that by WTLVs at 2 months after LV injection, but the mRNA levels by IDLVs were reduced at 6 months (26%) and 12 months (5%) compared with WTLVs. To investigate the therapeutic potential of IDLVs, we injected the IDLV or WTLVs, both of which expressed CRMP5-associated GTPase (CRAG) gene, a therapeutic gene that facilitates an ubiquitin-proteasome pathway, to SCA3 mouse cerebellum. Injection of WTLVs or IDLVs to the SCA3 mouse cerebella significantly improved their motor function at 6 months after the injection. At 1 year after injection, SCA3 mice that received IDLVs showed significantly better rota-rod performance than non-injected SCA3 mice.
Our results suggest that because of the substantially reduced risk of lentiviral mutagenesis, IDLVs are safer and potentially effective as gene therapy vectors.