Role of Various Immune Cells in the Tumor Microenvironment

The tumor microenvironment (TME) has numerous promotive and suppressive effects on tumor growth. The TME harbors adaptive and innate immune cells such as T cells, B cells, natural killer (NK) cells, macrophages, neutrophils, and dendritic cells. The development, survival, and invasion of tumor cells at the tumor site are accompanied by various interactions with several biomolecules and cells. Identification of cells and molecules, differences between their roles in classical immune system and those that operate in the TME enhances the understanding of biological principles governing cancer cell mobility and plasticity to survive in adverse conditions against various defensive immune cells. Understanding the role of cellular and non-cellular components of TME in tumor growth and metastasis (pro and anti-tumor) is essential in designing appropriate molecular targeted therapies. Possibly, the accumulated knowledge would allow us to develop strategies to overcome major therapeutic barriers that operate in the TME such as cancer immune escape, stromal challenges, antigen escape, and invasion regulated by genetic and epigenetic modifications in the tumor cells and immunosuppressive TME. There are still many unknowns about the diversity, plasticity, modulators of adaptive and innate immune cells, and the mechanisms of cancer escape from immune cell surveillance. This review accounts for current understanding of immune cells’ function and their cross interaction in the TME.