Novel lentiviral vectors displaying "early acting cytokines" selectively promote survival and transduction of NOD/SCID repopulating human hematopoietic stem cells

A major limitation of current lentiviral vectors (LVs) is their inability to govern efficient gene transfer into quiescent cells, such as human CD34+ cells that reside into G0 phase of the cell cycle and that are highly enriched in hematopoietic stem cells. This hampers their application for gene therapy of hematopoietic cells. Here, we designed novel lentiviral vectors that overcome this restriction by displaying early-acting cytokines on their surface. Display of thrombopoietin, stem cell factor or both cytokines on LV surface allowed efficient gene delivery into quiescent cord blood CD34+ cells. Moreover, these surface-engineered LVs preferentially transduced and promoted survival of resting CD34+ cells rather than cycling cells. Finally, and most importantly, these novel LVs allowed superior gene transfer in the most immature CD34+ cells as compared to conventional LVs, even when the latter vectors were used to transduce cells in the presence of recombinant cytokines. This was demonstrated by their capacity to promote selective transduction of CD34+ cell in in vitro derived long-term culture initiating cell colonies (LTC-ICs) and of long-term NOD/ SCID repopulating cells (SRCs) in vivo.