PDCD1 and immune system disorder: In summary, we have identified the PD-1+CD8+ TSCM-like regulatory cells possessing unique immunological properties of both alleviating aGVHD and preserving GVL, which have the potential to help optimize current allo-HSCT donor selection and to facilitate development of a new T cell therapy for GVHD in allo-HSCT in addition to recently FDA-approved MSC clinical products and preclinical MDSC immunotherapy,90,91 as well as auto-immune diseases.