Figure 1.

Mechanisms of tumor immune escape. (A) Tumor-associated antigens show low immunogenicity and/or develop several antigen presentation problems. (B) Upregulation of immune checkpoints like PD-1 on T-cell surface or its ligand PD-L1 on tumor surface can cause T-cell anergy and inhibit the antitumor immune response. (C) Low secretion of immune stimulatory molecules in the TME, like IL-2, which inhibits the activation of APCs and other effector cells such as CD8⁺/CD4⁺ T cells. (D,E) Production of immunosuppressive cytokines by tumor cells, such as TGF-β and IL-10 and recruitment of several immunosuppressive cells like regulatory T cells (Tregs), Tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs), are able to attenuate antitumor immune response. (F,G) Chronic inflammation and nutrient competition promote immune dysfunction. Abbreviations: MHC (major histocompatibility complex); CD (cluster of differentiation).