ICOS is associated with poor prognosis in breast cancer as it promotes the amplification of immunosuppressive CD4⁺T cells by plasmacytoid dendritic cells

Regulatory T cells (Tregs) and plasmacytoid dendritic cells (pDCs) that infiltrate primary breast tumors impair patient survival. The ICOS-mediated interaction between tumor-infiltrating CD4+ T cells and pDCs leads to the amplification of Tregs and interleukin-10 secretion. Importantly, ICOS+ cell infiltration correlates with adverse patient prognosis, identifying ICOS as a new target for cancer immunotherapy.