CD8A and neoplasm: The mechanism by which the cytotoxicity of tumor-resident CD8+ T cells becomes blunted in the tumor microenvironment is incompletely understood, though it has been associated with the presence of significant populations of immune regulators including CD4+ regulatory T cells (Treg), and suppressive myeloid cells such as tumor-associated macrophages and myeloid-derived suppressor cells (MDSC) [9, 10].