Tumor associated macrophages: current research and perspectives of clinical use

Abstract

Macrophages are the key cells of the innate immune system. One of the main functions of macrophages is the regulation of inflammation. Being common in all tissues and organs of the human body, tissue macrophages control their condition and guarantee a timely and effective response to damage, pathogen penetration or cell transformation. After eliminating the cause of inflammation, macrophages initiate the processes of healing and restoration of tissue homeostasis. At the end of the 20thcentury, the concept of macrophage activation dichotomy was proposed, which divided them into classically (M1) and alternatively (M2) activated ones. The development of this concept has led to the description of a wide variety of macrophage phenotypes. At the same time, M2 continues to be considered a prototype of tumor associated macrophages (TAM).TAM represent one of the most important cell types in the tumor microenvironment. Like all macrophages, they have a certain level of heterogeneity and plasticity, which develop under the influence of cytokines and growth factors produced by tumor cells. TAM, in turn, produces growth factors, cytokines and extracellular matrix components that support the progression of the tumor and increase its malignant potential. Numerous clinical studies have shown that the amount of TAM is often correlated with a poor prognosis of the disease. TAM perform a large number of functions necessary to maintain tumor progression. They are capable of stimulating angiogenesis and reorganization of the vascular system. Since the role of TAM in tumor development has become apparent, various attempts have been made to use them in the clinic.  It can be confidently asserted that various TAM markers are very attractive as diagnostic and prognostic markers of various tumors, and also as promising targets for the development of new targeted therapeutic agents.