Inducible T-cell costimulator (ICOS) is also known as Activation-inducible lymphocyte immunomediatory molecule (AILIM), CD278, which belongs to the CD28 family of immune costimulatory receptors consisting of CD28, CTLA-4 and PD-1. ICOS enhances all basic T-cell responses to a foreign antigen, namely proliferation, secretion of lymphokines, up-regulation of molecules that mediate cell-cell interaction, and effective help for antibody secretion by B-cells. CD278 / ICOS prevents the apoptosis of pre-activated T-cells and also plays a critical role in CD40-mediated class switching of immunoglobin isotypes.