Decreased homing of retrovirally transduced human bone marrow CD34+ cells in the NOD/SCID mouse model.

Many clinical gene therapy trials have described poor engraftment of retrovirally transduced CD34(+) cells. Because engraftment is dependent upon successful homing of graft cells to the bone marrow (BM), we examined whether retroviral-mediated gene transfer (RMGT) induces a homing defect in CD34(+) cells. Homing of fluorescently labeled human BM CD34(+) cells transduced with three separate retroviral vectors (MFG-eGFP, LNC-eGFP, and LXSN) was assessed in nonobese diabetic/severe combined immunodeficient mice. Homing of transduced CD34(+) cells was significantly decreased 20 hours after transplantation compared with freshly isolated control and cultured untransduced control cells. Specifically, homing of GFP(+) cells in the graft was preferentially decreased thus skewing the contribution of transduced cells to engraftment. Transduced cells were not selectively trapped in other organs and BM-homed transduced cells did not undergo apoptosis at a higher rate than untransduced cells. Adhesion molecule expression and binding activity was not altered by RMGT. This homing defect was reversed when transduced cells were cultured over CH-296 for 2 additional days with SCF only. These data suggest that RMGT of hematopoietic cells may compromise their homing potential and implicate transduction-induced reduced homing in the observed low engraftment of retrovirally transduced CD34(+) cells. These results may have a direct clinical application in gene therapy protocols.