In both MMTV-PyVT and MCaP0008 breast cancer models, tiMDSC (Gr1+F4/80−) inhibited T cell proliferation induced by anti-CD3/CD28 monoclonal antibodies; however, TAM (Gr1−F4/80+) was much more potent than tiMDSC in suppressing T cell proliferation (Figure 2A). Here, CD28 is linked to breast carcinoma.