CD8A and breast cancer: MDSCs are a population of immature myeloid cells that suppress adaptive immune function, utilizing a variety of pathways, such as arginase, IL-10, IL-4, iNOS, reactive oxygen species, induction of other regulatory cell populations such as regulatory T cells, and their potent suppressive activities against effector lymphocytes (47, 58, 59) Additionally, previous evidence has shown that a high infiltration of M2 macrophages and a low presence of CD8 T cells in the high-risk group of BC are associated with a poor response to immunotherapy (60).