CD4 and leukemia: 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.