Inducible T-cell co-stimulator (ICOS)

Inducible T-cell co-stimulator (ICOS), also known as CD278, is a transmembrane receptor belonging to the CD28/CTLA‑4 family expressed on activated T cells. It is rapidly upregulated following antigen stimulation and delivers an essential secondary co-stimulatory signal upon binding its ligand (ICOS-L/CD275), which is primarily expressed on antigen-presenting cells such as B cells. The ICOS–ICOS-L interaction promotes proliferation and differentiation of both CD4+ and CD8+ T cells, supports follicular helper T cell development critical for germinal center formation and antibody class switching, regulates cytokine production including IL‑10 superinduction but not IL-2 upregulation, and plays a central role in adaptive immunity. Dysregulation of this pathway has been linked to cancer progression as well as autoimmune diseases; thus it represents an important target for therapeutic intervention with several monoclonal antibodies currently under clinical evaluation as part of cancer immunotherapy strategies.[3][5][7][9]

Other names

CD278Activation-inducible lymphocyte immunomediatory molecule (AILIM)

Drugs targeting ICOS typically act by modulating the co-stimulatory signal delivered to activated T cells—either enhancing anti-tumor responses or dampening autoimmunity by blocking or stimulating the ICOS/ICOS-L interaction.[4]