PDCD1 and graft versus host disease: Although PD-1 signaling increased Mito-ROS production and Mito dysfunction in WT T cells (49), PD-L1/PD-1 signaling in GVHD target tissue infiltrating WT T cells did not sufficiently inhibit the GSH/Myc pathway to cause dysfunctional metabolic reprogramming and T cell dysfunction to a degree that prevents GVHD.