The presence of
tumor-infiltrating lymphocytes (TILs) either within the tumor stroma or tumor
epithelium reflects the immune response of the host against the tumor, defined
as cancer “immunoediting”. Large tumors are in the “escape” phase during which
immune cells are not able to stop tumor growth but their presence at least
denotes standby immunocompetency which can be reactivated by treatment.
Many TILs have been recognized.
Of those, fork head box P3- positive (Foxp3+) regulatory T cells (Tregs), CD8+
T cells, and CD4+ T cells are known to be the main keys for immune surveillance
and tolerance, respectively [4]. CD8+ T cells are mediators of antitumor
immunity and can lyse tumor cells directly. The clinical
importance of CD8+ T cells has been suggested by many recent studies that
reported a survival benefit in correlation with an increase in CD8+ T cells in large
cohorts of various human cancer patients.
CD4+ T cells have an important
role in antitumor immunity that was implicated by their helper or memory cell
functions. CD4+ T cells may have several effector functions, such as priming
tumor-specific cytotoxic T cells or macrophages that are involved in clearance
of tumor cells. In contrast, Tregs are known to have a very important role in
escape of antitumor T-cell response in cancer cells [13], due to their ability
to potently suppress immune reaction against tumors in vivo.
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