CD8A and graft versus host disease: It should be noted, however, that this mechanism is effective in preventing GVHD only in the absence of donor CD4+ T cells or lack of IL-2, because IL-2 from CD4+ T cells can help CD8+ T cells or help CD4+ T cells through autocrine signaling to become resistant against PD-L1-mediated anergy, exhaustion, and apoptosis, perhaps through the promotion of glycolysis (26).