PDCD1 and graft versus host disease: Cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4; CD152) (23), programmed death−1 (PD-1; CD279) and its ligand (PD-L1; CD274) (24, 25), B and T lymphocyte attenuator (CD272) (26), and B7-H3 (CD276) (27) have been shown to attenuate GVHD lethality.