Expression of interferon-γ by stromal cells inhibits murine long-term repopulating hematopoietic stem cell activity

Several lines of evidence suggest that overexpression of interferon γ (IFN-γ) in the marrow microenvironment may play a role in the pathogenesis of marrow suppression in aplastic anemia. We previously showed that overexpression of IFN-γ by marrow stromal cells inhibits human long-term culture initiating cell activity assayed in vitro to a much greater degree than the addition of soluble IFN-γ. The effect of IFN-γ on true repopulating stem cells assayed in vivo has not been studied previously. We compared the effect of co-culture of murine marrow cells in the presence of stromal cells transduced with a retroviral vector expressing murine IFN-γ vs stromal cells transduced with a control neo vector. Using a murine congenic competitive repopulation assay, there was significantly less long-term repopulating stem cell activity remaining after culture on mIFN-γ–expressing stroma as compared to control stroma. We also investigated the effect of directly transducing murine bone marrow cells with the mIFN-γ or control vector. Marrow cells transduced with either vector were transplanted into W/Wv recipient mice. The percentage of vector-containing cells in the mIFN-γ mice was significantly lower than in the control mice, suggesting that mIFN-γ–transduced primitive cells may not have survived culture, or that mIFN-γ directly decreases gene transfer into repopulating cells. Despite no significant differences in white or red blood cells in the mice transplanted with the mIFN-γ–transduced cells, the number of bone marrow colony-forming unit-C 16 weeks after transplantation was significantly lower in the IFN-γ group. These data indicate that ectopic or overexpression of mIFN-γ, especially by marrow microenvironmental elements, may have a marked effect on primitive hematopoiesis as assayed in vivo. Published by Elsevier Science Inc.