Host F4/80+ macrophages are increased after transplantation of embryonic stem cell derived hematopoietic progenitors (126.10)

Abstract

Abstract Mice transplanted with embryonic stem cell (ESC)-derived hematopoietic progenitors (ES-HPs) historically have displayed low levels of engraftment. We hypothesized that the innate immune system was an obstacle to ES-HP engraftment. To investigate this, we derived ES-HPs in vitro by growing D3-ESCs (strain 129, CD45.2, H-2b) on the bone marrow (BM) stromal cell line, OP9. We transplanted purified CD41+ ES-HPs into sublethally irradiated NOD.SCID.γc knockout (NSG) mice hosts (CD45.1, H-2g7) which lack B, T, and NK cells, but have functional macrophages. Host and donor-derived hematopoiesis was observed. However, at Day 18 post-transplant, ES-HP recipients displayed enlarged spleens that were primarily composed of host macrophages. The absolute numbers of host-derived splenic F4/80+ macrophages were increased 1.81 fold compared to untransplanted controls and 1.7 fold compared to BM transplanted controls. In vitro phagocytosis assays confirmed that NSG macrophages specifically engulfed allogeneic ES-HPs, but not allogeneic adult BM cells, supporting our in vivo results. Taken together, these results suggest that host F4/80+ macrophages may pose a barrier to allogeneic ES-HP engraftment. Importantly, these data suggest that adult macrophages preferentially phagocytose ES-HPs, which could reveal a novel mechanism of rejection unique to ESC-derived cells. Experiments to evaluate the effects of host macrophage depletion on ES-HP engraftment in vivo are ongoing.