Severe and rapid autoimmunity can also result from transfer of PD-1−/− thymocytes to Rag−/− recipients, but not established peripheral cells from adult PD-1−/− mice [note, on the B6 background, PD-1−/− mice develop only a mild lupus-like autoimmune disease upon aging (34)]. The gene discussed is PDCD1; the disease is Autoimmunity.