Comparison of Retroviral Transduction Efficiency in CD34 + Cells Derived from Bone Marrow versus G‐CSF–Mobilized or G‐CSF Plus Stem Cell Factor–Mobilized Peripheral Blood in Nonhuman Primates

Hematopoietic stem cells (HSCs) are ideal targets for genetic manipulation in the treatment of several congenital and acquired disorders affecting the hematopoietic compartment. Although G‐CSF–mobilized peripheral blood CD34 + cells are the favored source of hematopoietic stem cells in clinical transplantation, this source of stem cells does not provide meaningful engraftment levels of genetically modified cells compared with G‐CSF + stem cell factor (SCF)–mobilized cells in nonhuman primates. Furthermore, the use of G‐CSF mobilization can have disastrous consequences in patients with sickle cell disease, a long‐held target disorder for HSC‐based gene therapy approaches. We therefore conducted a study to compare the levels of genetically modified cells attainable after retroviral transduction of CD34 + cells collected from a bone marrow (BM) harvest with CD34 + cells collected from a leukapheresis product after mobilization with G‐CSF ( n = 3) or G‐CSF in combination with SCF ( n = 3) in the rhesus macaque autologous transplantation model. Transductions were performed using retroviral vector supernatant on fibronectin‐coated plates for 96 hours in the presence of stimulatory cytokines. BM was equal to or better than G‐CSF–mobilized peripheral blood as a source of HSCs for retroviral transduction. Although the highest marking observed was derived from G‐SCF + SCF–mobilized peripheral blood in two animals, marking in the third originated only from the BM fraction. These results demonstrate that steady‐state BM is at least equivalent to G‐CSF–mobilized peripheral blood as a source of HSCs for retroviral gene transfer and the only currently available source for patients with sickle cell disease.