TGFB1 and cancer: Secondly, the tumor microenvironment, rich in immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), regulatory T-cells (Tregs), and cancer-associated fibroblasts (CAFs), as well as anti-inflammatory cytokines such as tumor growth factor (TGF-β) and interleukin-10 (IL-10), forms a second physical barrier and renders the tumor immunologically “cold” and resistant to immunotherapy.