Distinct Qualitative Differences between Normal and Abnormal Hemopoietic Stem Cells In Vivo and In Vitro

The transplantation of partially purified hemopoietic stem cells (HSCs) plus the engraftment of bone from autoimmune‐prone mice ((NZW × BXSB)F1 (W/BF1) mice) induces autoimmune diseases in major histocompatibility complex (MHC)‐incompatible normal C3H/HeN mice. In contrast, W/BF1 mice die of infection or anemia within three weeks due to a failure in hemopoietic reconstitution when the mice receive partially purified HSCs plus bones from normal C3H/HeN mice, although they survive more than a year without showing any symptoms of autoimmune diseases when they receive T cell‐depleted bone marrow cells (without bone grafts) from normal mice. This finding suggests that abnormal HSCs can proliferate even in MHC‐incompatible microenvironments, while normal HSCs cannot. This is confirmed by spleen colony‐forming assays (CFU‐S) on day 12, using pluripotent HSCs (P‐HSCs). The P‐HSCs of old (> 4 mo) W/BF1 mice (after the development of autoimmune diseases) form high CFU‐S counts on day 12 even in the allogeneic C3H environment, although the P‐HSCs of normal mice form high CFU‐S counts only in the MHC‐compatible environments. In addition, abnormal P‐HSCs of autoimmune‐prone mice can proliferate in vitro in collaboration with MHC‐incompatible stromal cells, although normal HSCs do so in collaboration with MHC‐compatible stromal cells, but not MHC‐incompatible stromal cells. These findings indicate that abnormal P‐HSCs are more “resilient” than normal P‐HSCs.