Figure 2.

An imbalance between pro-tumor and anti-tumor immune cells and factors in the tumor microenvironment (TME) can lead to tumor growth and progression or tumor suppression and elimination. Pro-tumor immune cells can promote tumor progression, including type II M2 or TAMs (tumor-associated macrophages), regulatory T cells (Tregs), and type II Th2 cells. Moreover, factors that influence tumor progression are low tumor infiltrating lymphocytes (TILs) in the TME, low antigenicity and immunogenicity of tumor cells, and inflammation. Anti-tumor immune cells can reduce tumor growth and suppress tumor progression in the TME. These include CD8+ T cells, type I Th1 cells, NK cells, and type I M1 cells and their type I cytokines such as IFNγ, TNFα, IL-2, and granzyme B. Furthermore, anti-tumor immune factors can also influence tumor suppression, including high infiltration of functional TILs, and greater antigenicity and immunogenicity of the tumor cells, such as high MHC-I expression and tumor-associated antigen expression.