PDCD1 and graft versus host disease: Although antioxidant NAC was able to improve STAT3–/– T cell function in an in vitro MLR assay in a PD-L1/PD-1 signaling–dependent manner, in vivo administration of antioxidant NAC or MnTBAP did not augment GVHD induced by STAT3–/– T cells, although previous studies have shown that antioxidants augment acute GVHD induced by WT T cells (20).