TGFB1 and neoplasm: Additionally, certain negative regulators, including the PD-L1 on tumor cells, interleukin 10 (IL-10), transforming growth factor β (TGF-β), regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment (TME) can prevent the activation of immune cells and prevent the tumor infiltration of CTLs and antigen-presenting cells (APCs) 35, 36.