While further research did not confirm a direct participation of PD-1 in programmed cell death of T cells, knockout mice revealed that loss of PD-1 increases the risk of severe T cell mediated autoimmune pathologies and lupus-like syndromes, showing that PD-1 negatively regulates T cell immune responses as an “immune-checkpoint” molecule [28,29,30]. The gene discussed is PDCD1; the disease is drug-induced lupus erythematosus.