Fig. 1.

Tumor microenvironment. There is reciprocal interaction between several types of immune cells and tumor cells. Pro-tumor immune cells induce tumor cells growth through expression of many factors; in contrast, anti-tumor immune cells inhibit tumor cells growth and development.

Treg: regulatory T; TLRs: Toll like receptors; DC: Dendritic cell; Th-1: T helper cells; CTL: Cytotoxic T lymphocytes; PD-L1: Programmed death-ligand-1; GM-CSF: granulocyte-macrophage colony-stimulating factor; IFN: Interferon-α; TNF-α: Tumor necrosis factor; NKC: NK cytotoxicity; FGF: fibroblast growth factor.