Description: Fundamentally understanding the suppressive mechanisms used by different subsets of tumor-infiltrating regulatory T (Treg) cells is critical for the development of effective strategies for antitumor immunotherapy. Treg cells have recently been identified in human diseases including cancer. However, the suppressive mechanisms and functional regulations of this new subset of unconventional Treg cells are largely unknown. In the current studies, we explored the suppressive mechanism(s) used by breast tumor-derived Treg cells on innate and adaptive immunity. We found that Treg cells induced immunosenescence in the targeted naive and effector T cells, as well as dendritic cells (DCs). Furthermore, senescent T cells and DCs induced by Treg cells had altered phenotypes and impaired functions and developed potent suppressive activities, further amplifying the immunosuppression mediated by Treg cells. In addition, we demonstrated that manipulation of TLR8 signaling in Treg cells can block Treg–induced conversion of T cells and DCs into senescent cells in vitro and in vivo. Our studies identify the novel suppressive mechanism mediated by tumor-derived Treg cells on innate and adaptive immunity, which should be critical for the development of strong and innovative approaches to reverse the tumor-suppressive microenvironment and improve effects of immunotherapy.

Description: Understanding and dissecting the role of different subsets of regulatory tumor-infiltrating lymphocytes (TILs) in the immunopathogenesis of individual cancer is a challenge for anti-tumor immunotherapy. High levels of regulatory T cells have been discovered in breast TILs. However, the clinical relevance of these intratumoral T cells is unknown. In this study, T cell populations were analyzed by performing immunohistochemical staining in primary breast cancer tissues from patients with different stages of cancer progression. Retrospective multivariate analyses of the correlations between T cell levels and other prognostic factors and clinical outcomes were completed. We found that T cell infiltration and accumulation in breast tumor sites was a general feature in breast cancer patients. Intratumoral T cell numbers were positively correlated with advanced tumor stages, HER2 expression status, and high lymph node metastasis but inversely correlated with relapse-free survival and overall survival of breast cancer patients. Multivariate and univariate analyses of tumor-infiltrating T cells and other prognostic factors further suggested that intratumoral T cells represented the most significant independent prognostic factor for assessing severity of breast cancer compared with the other known factors. Intratumoral T cells were positively correlated with FOXP3 + cells and CD4 + T cells but negatively correlated with CD8 + T cells in breast cancer tissues. These findings suggest that intratumoral T cells may serve as a valuable and independent prognostic biomarker, as well as a potential therapeutic target for human breast cancer.