The CD28 family member ICOS, which interacts with a ligand ICOSL, was first reported on activated human T cells. This pathway can promote T cell production of several cytokines including IL-10, IL-4, IL-5, IFNγ and IL-17, depending on which cell type the effect dominates. A recent study showed that the ICOS mediates interaction between tumor-infiltrating CD4+ T cells and plasmacytoid dendritic cells (pDCs), which leads to the amplification of regulatory T cells (Tregs) and interleukin-10 secretion, then Tregs and pDCs that infiltrate primary breast cancers impair patient survival.
Zhang Y, Luo Y, Qin S-L, et al. The clinical impact of ICOS signal in colorectal cancer patients. Oncoimmunology. 2016;5(5):e1141857. doi:10.1080/2162402X.2016.1141857.