Novel Lentiviral Vectors Displaying ‘Early-Acting-Cytokines’ Preferentially Promote the Survival and Transduction of NOD/SCID Repopulating Human Hematopoietic Stem Cells.

A major limitation of current generation lentiviral vectors (LVs) is their inability to govern efficient gene transfer into quiescent target cells which hampers their application for hematopoietic stem cell gene therapy. Human CD34+ cells that reside into G0 phase of the cell cycle and thus are quiescent, are indeed higly enriched in hematopoietic stem cells. Here, we designed novel lentiviral vectors that overcome this type of restriction by displaying early-acting-cytokines on their surface. Presentation of a single cytokine, thrombopoietin (TPO), or co-presentation of TPO and stem cell factor (SCF) on the lentiviral vector surface improved gene transfer into quiescent CD34+ cord blood cells by 45-fold and 77-fold, respectively, as compared to conventional lentiviral vectors. Moreover, these new LVs preferentially transduced and promoted the survival of immature resting cells rather than cycling CD34+ cells. Most importantly, the new early-cytokine-displaying lentiviral vectors allowed highly efficient gene transfer in CD34+ immature cells with long-term in vivo NOD/SCID mice repopulating capacity, a hallmark of bona fide HSCs. In conclusion, the novel ‘early-acting cytokines’ displaying LVs described here provide simplified, reproducible gene transfer protocols that ensure efficient gene transfer in hematopoietic stem cells. As such, these novel reagents bring us one step closer to selective in vivo gene therapy.