Ifngr1–/– or Stat1–/– donor T cells are severely impaired in their ability to induce GVHD across major and minor histocompatibility disparities, with a concomitant reduction in Th1 differentiation and increased Treg generation, suggesting that the IFN-γ signal pathway in donor lymphocytes is critical in CD4- and CD8-mediated GVHD (14, 15, 51, 52). This evidence concerns the gene CD8A and graft versus host disease.