Failure of immunological cells to eradicate tumor and cancer cells: an overview

Abstract

Inflammation can be broadly understood as a successive immune response of an organism's immune system towards nonnative or foreign antigens. This is a protective mechanism of the immune system, mediated by diverse immunological cells, to ensure homeostasis of an individual. Once activated, these immunological cells release a number of cytokines, chemokines, reactive oxygen species, reactive nitrogen species, histamines, prostaglandins, and other materials leading to inflammation. Tumor cells express altered proteins due to mutations of their genes, DNA modifications such as histone modification, DNA methylation, or other mechanisms of altered protein expression. The body's immunological cells actively recognize these altered proteins, now acting as tumor antigens, and eliminate the tumor cell; this is popularly known as tumor immunosurveillance. However, in unmanaged or inexorable circumstances, tumor cells escape from immunosurveillance mechanisms. This ultimately leads to the cascading events of cancer development and progression. T regulatory cells, tumor-associated macrophages, and myeloid-derived suppressor cells are pronounced cells involved in immunosuppression. These cells not only dodge the immune system's surveillance but also significantly increase the survival, proliferation, and metastasis rates of tumor cells. They hinder T cytotoxic activation by secreting inhibitory cytokines (which inhibit the antitumor activity of natural killer cells) along with dendritic cells and disrupt presentation of antigens, ultimately leading to cancer development. On their own, these cells have emerged as promising therapeutic targets in cancer immunotherapy. This review highlights some of the mechanisms by which these cells escape immunosurveillance and mediate immune suppression.