STAT3 Silencing and TLR7/8 Pathway Activation Repolarize and Suppress Myeloid-Derived Suppressor Cells From Breast Cancer Patients.

Elham Safarzadeh,Nicola Silvestris,Behzad Mansoori,Vahid Khaze,Pascal H G Duijf,Afshin Derakhshani,Shahryar Hashemzadeh,Ali Mohammadi,Behzad Baradaran,Tohid Kazemi

doi:10.3389/fimmu.2020.613215

Abstract

Cancer cells escape immune destruction. From this perspective, myeloid-derived suppressor cells (MDSCs), which are immunosuppressive in various cancers including breast cancer (BC), are significant. However, the precise mechanisms are unknown. We isolated HLA-DR-CD33+ MDSCs and CD3+ T cells from BC patients’ peripheral blood and healthy donors through MACS and immunophenotyped by flow cytometry. Transfection of short-interfering RNAs and treatment with a TLR7/8 agonist altered pathway activities in vitro. Gene expression was analyzed using qRT-PCR, western blotting, and immunohistochemistry. Our findings showed an association between the progression of BC and increased levels of circulating HLA-DR-CD33+ MDSCs. These cells strongly suppress both autologous and analogous CD3+ T cell proliferation and enter the tumor microenvironment. We also identified increased STAT3 signaling and increased IDO and IL-10 expression in BC-derived MDSCs as immunosuppression mechanisms. Further, STAT3 inhibition and TLR7/8 pathway stimulation reduce the immunosuppressive activity of patient-derived MDSCs on T cells by inducing MDSC repolarization and differentiation into mature myeloid cells. This also alters the expression of critical cytokines and transcription factors in CD3+ T cells and, importantly, reduces breast cancer cells’ proliferation. Finally, while chemotherapy is able to significantly reduce circulating MDSCs’ level in patients with breast cancer, these MDSCs remained highly T cell-suppressive. We identified a novel molecular mechanism of MDSC-mediated immunosuppression. STAT3 inhibition and TLR7/8 pathway stimulation in MDSCs repolarize and suppress MDSCs from breast cancer patients. This offers new opportunities for BC immunotherapy.

Highlights

Following extensive immunological studies and significant preclinical and clinical findings over the years, researchers have found that the immune system has the crucial role of identifying and eliminating tumor cells [1, 2]
These results suggested that circulating M-Myeloid-derived suppressor cells (MDSCs) may have an essential role in the development and progression of breast cancer (BC)
We observed that the proliferation of CD3+ T cells in the treated group compared to control was suppressed, but the proliferation of T cells was increased in co-culture with treated MDSCs. These results indicate that treatment with si-STAT3 or TLR7/8 agonist alone or si-STAT3 plus TLR7/8 agonist abolishes the suppressive function of MDSCs

Summary

Introduction

Following extensive immunological studies and significant preclinical and clinical findings over the years, researchers have found that the immune system has the crucial role of identifying and eliminating tumor cells [1, 2]. Immunotherapy has been shown as a promising therapeutic approach, and numerous immunotherapeutic protocols are being tested or implemented in the clinic to treat breast cancer (BC). Targeted immunotherapies, such as monoclonal antibodies, that aim at inducing an antitumor immune response are becoming primary treatment functions for BC. Accumulating evidence represents a promising result in cancer vaccinology. This immunotherapeutic protocol activates both the adaptive immune response and immunological memory. Several studies on mice and humans have shown the importance of the tumor immune microenvironment in the development and progression of cancer [9, 10]

Methods

Results

Conclusion