Cyclosporin A and Rapamycin Relieve Distinct Lentiviral Restriction Blocks in Hematopoietic Stem and Progenitor Cells

Improving hematopoietic stem and progenitor cell (HSPC) permissiveness to HIV-derived lentiviral vectors (LVs) remains a challenge for the field of gene therapy as high vector doses and prolonged ex vivo culture are still required to achieve clinically relevant transduction levels. We report here that Cyclosporin A (CsA) and Rapamycin (Rapa) significantly improve LV gene transfer in human and murine HSPC. Both compounds increased LV but not gammaretroviral transduction and acted independently of calcineurin and autophagy. Improved gene transfer was achieved across all CD34(+) subpopulations, including in long-term SCID repopulating cells. Effects of CsA were specific of HSPC and opposite to its known impact on HIV replication. Mutating the Cyclophilin A binding pocket of the viral capsid (CA) further improved transduction in combination with CsA. Tracking of the LV genome fate revealed that CsA relieves a CA-dependent early block and increases integration, while Rapa acts early in LV infection independently of the viral CA. In agreement, only Rapa was able to improve transduction by an integrase-defective LV harboring Wild-type CA. Overall, our findings pave the way for more efficient and sustainable LV gene therapy in human HSPCs and shed light on the multiple innate barriers specifically hampering LV transduction in these cells.