Natural regulatory T (Treg) cells, described as CD4+CD25+Foxp3+ cells have long been established as a subset of T lymphocytes critical for maintaining tolerance to self-constituents . Their suppressive activities however extend beyond self tolerance as they have been demonstrated to regulate various facets of immune responses against allergens, microbial and infectious agents, as well as tissue-derived alloantigens . Mounting evidence also shows their increased presence in cancer settings, often coinciding with attenuated antitumor T-cell responses . Although there is limited direct evidence to the antigen specificity of tumor-associated Treg cells, given that they develop in the thymus and seed the periphery primarily to curtail the activities of T cells that may have escaped thymic negative selection, it stands to reason that they are specific for tumor antigens which invariably are often self protein, albeit in altered or aberrantly expressed forms. What prompts Treg-cell accumulation within tumor microenvironment?
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