Myeloid‐derived suppressor cells from tumour‐bearing mice induce the population expansion of CD19hiFcγRIIbhi regulatory B cells via PD‐L1

Abstract Myeloid‐derived suppressor cells (MDSCs) increase in number and gain immunosuppressive functions in tumours and many other pathological conditions. MDSCs are characterized by their strong T‐cell immunosuppressive capacity. The effects that MDSCs may have on B cells, especially within the tumour microenvironment, are less well understood. Here, we report that either monocytic MDSCs or polymorphonuclear MDSCs can promote increases in interleukin (IL)‐10‐expressing CD19 hi FcγRIIb hi regulatory B cells in vitro and in vivo. Splenic transitional‐1, ‐2, and ‐3 cells and marginal zone B cells, but not follicular B cells, differentiate into IL‐10‐expressing CD19 hi FcγRIIb hi regulatory B cells. The adoptive transfer of CD19 hi FcγRIIb hi regulatory B cells via tail vein injection can promote subcutaneous 3LL tumour growth in mice. The expression of programmed death‐ligand 1 on MDSCs was found to be strongly associated with CD19 hi FcγRIIb hi regulatory B cell population expansion. Furthermore, the frequency of circulating CD19 + FcγRII hi regulatory B cells was significantly increased in advanced‐stage lung cancer patients. Our results unveil a critical role of MDSCs in regulatory B‐cell differentiation and population expansion in lung cancer patients.