To address this, we performed mixed GVHD/GVL experiments where irradiated BALB/c mice received syngeneic or allogeneic HCT with T cells from WT, Gzma–/–, or Gzma–/– CD4+ T cells and WT CD8+ T cells along with GFP+ MLL-AF9 leukemia cells. This evidence concerns the gene CD4 and graft versus host disease.