CD4 and neoplasm: Specifically, while CD8+ T cells, Th1-type CD4+ T cells, and natural killer (NK) cells bear antitumor activity, regulatory T (Treg) cells, Th2-type CD4+ T cells, myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) have been shown to create a highly immunosuppressive microenvironment that decreases PDAC immunogenicity (7–16).