ICOS Gene

The ICOS gene (ICOS stands for Inducible T Cell Costimulator) is a protein coding gene located on chromosome 2q33.2. The protein encoded by this gene belongs to the CD28 and CTLA-4 cell surface receptor family. It forms homodimers and plays an important role in cell-cell signaling, immune responses, and regulation of cell proliferation.

The "Inducible T Cell Costimulator" promotes all basic T cell responses to a foreign antigen. In contrast to the constitutively expressed CD28, the inducible costimulatory molecule (ICOS) is expressed on the surface of T cells after activation. ICOS enhances all basic T cell responses to a foreign antigen, namely proliferation, secretion of lymphokines, upregulation of molecules mediating cell-cell interactions, and effective support of antibody secretion by B cells (Karabon L et al. 2011). ICOS is essential for both efficient interaction between T and B cells and normal antibody responses to T cell-dependent antigens. It does not stimulate the production of interleukin-2 but promotes the synthesis of interleukin-10. ICOS prevents apoptosis of activated T cells and plays a critical role in CD40-mediated class switching of immunoglobulin isotypes.

Diseases associated with ICOS include:

• Immunodeficiency, Common Variable, 1 (CVID1/OMIM: 607594) as "Primary Congenital Immunodeficiency (PID)" (Bossaller L et al. 2006).

Oncology (ICOS/ICOSL pathway): Due to its multifaceted link to anti-tumor immunity, both antagonistic/agonistic antibodies in the ICOS/ICOSL pathway may be useful for tumor treatment in the future (Amatore F et al 2020).

1. Amatore F et al (2020) Role of inducible co-stimulator (ICOS) in cancer immunotherapy. Expert Opin Biol Ther 20:141-150.

2. Bossaller L et al (2006) ICOS deficiency is associated with a severe reduction of CXCR5+CD4 germinal center Th cells. J Immun 177: 4927-4932.

3. Karabon L et al. (2011) ICOS gene polymorphisms in B-cell chronic lymphocytic leukemia in the Polish population. Folia Histochem Cytobiol 49: 49-54.