Fig. 3.

Physiological conditions and cellular interaction network of the protumor- and antitumor-microenvironment. Pro-tumor microenvironment is composed of immunosuppressive cells (MDSCs, Tregs, and M2-type macrophages), immunosuppressive cytokines (IL-10 and TGF-β), immunomodulatory enzymes (IDO-expressing cells). In addition, PD-L1, PD-1 and therapeutic barriers (high tumor hypoxia, acidic condition) can restrict the function of the effector T cells. In contrast, anti-tumor microenvironment is composed of a high number of innate immune cell (NK cells), effector T cells (CD8⁺ and CD4⁺ T cells), and M1-type macrophages for tumor-killing