CD4 and cancer: The reasons for this failure are complex, and likely stem from the nature of the stroma-rich tumor microenvironment (TME) in PDA, with abundant immunosuppressive cells such as cancer associated fibroblasts (CAFs) (6), CD4+ T cells (7) and myeloid cells including tumor associated macrophages (TAMs) and myeloid derived suppressor cells (MDSCs) (8–11).