Tissue-resident memory CD8<sup>+</sup> T cells and their role in the immune response to infection and vaccination

A variety of body tissues contain tissue-resident memory CD8+ T cells — long-lived multifunctional effector cells formed during the immune response to infection, which populate previously infected tissue long term. The localization of these cells is determined due to expression of a set of adhesive molecules that hold the cell in a specific tissue microenvironment, as well as the lack of molecules involved in exiting into the blood and lymphatic vessels. The program for establishing such cell phenotype can apparently be launched at various stages of T cell maturation during the immune response. Resident memory CD8+ T cells protect tissues from viruses and other intracellular parasites, kill transformed cells, and in some cases participate in the pathogenesis of immune-mediated inflammatory diseases. The accumulation of resident memory T cells can be induced by vaccination, and targeting these cells by vaccines, along with triggering a protective humoral response, appears desirable for the prevention of many intracellular infections. At the site of pathogen entry, resident memory CD8+ T cells can provide tissue protection quicker than circulating T cells, which is essential for preventing rapidly evolving viral infections. Localization of memory CD8+ T cells in tissues allows the pool of these cells to be increased without obvious restrictions. Accordingly, it is possible to carry out a large number of different vaccinations to stimulate these cells without losing the vaccines effectiveness. Finally, not all pathogens antigenic epitopes recognized by CD8+ T cells undergo rapid and systematic changes such as the surface B-cell epitopes of the same pathogens. Additional recruitment of resident memory CD8+ T cells in response to a vaccine may ensure greater coverage of pathogen variants and contribute to developing heterosubtypic immunity. The review presents data on resident memory CD8+ T cells in various tissues, their participation in the immune response to infections and vaccinations, as well as molecules that control their localization.