Influence of interleukin-3, interleukin-6, and stem cell factor on retroviral transduction of Rhesus monkey CD34⁺ hematopoietic progenitor cells measured in vitro and in vivo

As a preclinical test for bone marrow gene therapy, we transduced Rhesus monkey CD34⁺ CD11b-hematopoietic progenitor cells with recombinant retroviruses. We investigated the effects of the recombinant hematopoietic growth factors interleukin-3 (IL-3), interleukin-6 (IL-6) and stem cell factor (SCF) on the susceptibility of in vitro clonogenic progenitor cells and in vivo repopulating stem cells to retroviral transduction. IL-6 did not contribute to transduction of progenitor cells, whereas IL-3 and SCF supported expansion and transduction of progenitors. The combination of IL-3 and IL-6 was most efficient at promoting transduction of more mature progenitor cell types. Cultures containing IL-6+SCF yielded optimal maintenance of CD34⁺CD11b- cells without evidence for lineage-restricted maturation. Autologous transplantation of transduced grafts cultured in the presence of SCF, with or without IL-3 or IL-6, into lethally irradiated Rhesus monkeys resulted in a severely delayed hematopoietic reconstitution as compared with grafts transduced in the presence of IL-3 alone. After in vivo repopulation, transduced cells were found among peripheral blood mononuclear cells, granulocytes and CD34⁺CD11b- progenitor cells in the bone marrow of engrafted animals. However, no significant difference in transduction efficiency on in vivo repopulating stem cells could be demonstrated among the tested growth factor conditions.