The B7 family ligands include B7-1 (1), B7-2 (2), PD-L1 (B7-H1) (3, 4), PD-L2 (B7-DC) (5, 6), inducible T cell co-stimulator ligand (ICOSL) (also known as, B7-H2, B7h, B7RP-1, GL50, LICOS) (7–10), B7-H3 (11), B7-H4 (B7x, B7S1) (12–14), B7-H5 (HHLA2) (15, 16), and B7-H6 (17), etc. The importance of these molecules has been highlighted by the FDA approval of several drugs for the treatment of cancer and autoimmune disease by targeting the ligands or their receptors. The gene discussed is ICOSLG; the disease is autoimmune disease.