Tumor immunology and tumor escape mechanisms from immune response

Over the past decade, tumor immunology as a main topic of cellular and molecular immunology has achieved a great progress. Malignant tumor is defined by proliferation of the cells which loss proliferation control and invade host tissue causing metastasis. The most important characteristics of tumor cells are high proliferation capacity and invasion. Based on "Immune surveillance" theory, physiologic recognition and distraction of transformed cells is the main function of the immune system. Nowadays according to "Cancer immunoediting" framework theory, the immune system can play a dual role in protection against cancer as well as promoting cancer growth. In the immunoediting process, the immune system checks the normal cells by all surface antigen changes constantly. Immune response can recognize and remove the cancerous cells before they can develop into tumor ("elimination" of cancer). Surviving cancer cells continue to divide rapidly, providing a balance between the immune system and tumor growth (equilibrium phase). Over the time, tumor cells can eventually enter into the third and final phase which is called "tumor escape". The switch from equilibrium to escape phase can be due to either changes in tumor cells in response to immune editing function or because of immune system changes in response to tumor induced immunosuppression. In escape phase tumor microenvironment consists of immune suppressor cells such as Treg and Myeloid Derived Suppressor Cells and immune suppress biomolecules such as IL-10, Indoleamine-pyrrole 2, 3-dioxygenase (IDO) and TGF-β. Deep knowledge on the complexity and mechanisms of immunomodulation in tumor microenvironment is a prerequisite for development of an effective cancer immunotherapy regiment. In an effective cancer treatment strategy immune effector cells and molecules in tumor microenvironment need to be activated whiel tumor induced immunosuppression has to be inhibited.