In breast carcinoma, tumor-associated pDC expression of ICOSL drives the expansion and suppressive function of ICOS+ Tregs, leading to preferential accumulation of this Treg subset in the close vicinity of pDCs in the tumor microenvironment and a secretion of the immunosuppressive mediator IL-10 by stimulation with tumor-associated antigen (TAA). Here, IL10 is linked to breast carcinoma.