Tumor-released autophagosomes induce IL-10-producing B cells with suppressive activity on T lymphocytes via TLR2-MyD88-NF-κB signal pathway

ABSTRACT

Recent studies have shown that tumor cells can release autophagosomes, which transport a broad array of biologically active molecules with potential modulatory effects on immune cell functions. In this study, we aimed to investigate the role of tumor cells-released autophagosomes (i.e. TRAP) in regulating B cell differentiation and function. TRAPs from murine tumor cell lines were found to induce splenic B cells to differentiate into IL-10-producing regulatory B cells (Bregs) with a distinct phenotype of CD1d⁺ CD5⁺, which could potently inhibit CD8⁺ and CD4⁺ T cell responses in IL-10-depedent manner both in vitro and in vivo. Notably, adoptive transfer of TRAP-induced Bregs abrogated the immune response and antitumor effect induced by OVA-loaded DC vaccinations in E.G7-OVA-bearing mouse model. Mechanistic studies revealed that membrane-bound high-mobility group B1 (HMGB1) on the intact TRAPs was crucial for inducing Breg differentiation via the activation of TLR2-MyD88-NF-κB signal pathway in B cells. Moreover, TRAPs enriched from malignant effusions of cancer patients could induce human B cells to differentiate into IL-10-producing B cells with immunoregulatory functions, the frequency of which were positively correlated with the HMGB1 levels on TRAPs. Together, our findings have demonstrated that TRAPs promote the generation of IL-10⁺ Bregs, which may contribute to the suppression of antitumor immunity.

KEYWORDS:

• HMGB1
• IL-10
• regulatory B cells
• tumor-released autophagosomes (TRAP)
• TLR2

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Acknowledgments

The authors thank Dr Bernard A. Fox (Earle A. Chiles Research Institute, Portland, OR) for his advice; Dr Suyu Shu (Cleveland Clinic, USA, Ret.) and Dr Pengju George Luo (Sherman College of Chiropractic, USA) for their critical review of this manuscript. The authors also thank Dr Yunlang Cai (Zhongda Hospital, Medical School of Southeast University) for providing human samples and Dr Guangming Gan (Electron microscope laboratory, Medical School of Southeast University) for electron microscopy sample preparation and imaging.

Author contributions

M.Z. and L.X.W. designed the study. M.Z., F.C., Z.W., W.L., H.R., Y.S., and L.X.W. performed the experiments and collected the data. M.Z. and L.X.W. prepared the figures. All authors analyzed and discussed the data. M.Z. and L.X.W. wrote the manuscript. L.L. and H.M.H. contributed in writing the manuscript.

Funding

This work received grant support from the National Natural Science Foundation of China (Grant # 31370895, 31170857, 30972783 to L.X.W.).