ICOS and breast cancer: Expression of ICOS and PD-1 as markers of activated Tfh cells in breast cancer has been reported while RNA analysis showed enhanced expression of IL-21, IFN-γ, and CXCL13 on sorted Tfh TIL, and only ICOS+PD-1+Tfh TIL from HER2+ and triple negative breast cancer were capable of inducing in vitro IgG secretion by B cells (46).