CD4 and graft versus host disease: We examined thymic reconstitution — a key marker of GVHD progression and severity — in these BM transplant recipients and found that recipients given Fli1fl/WTCre+ grafts had superior CD4+CD8+ thymic reconstitution compared with those given either Fli1fl/flCre+ or Fli1WT/WT grafts (Figure 1, C–E).