Figure 1. Breg cells are suppressors of anti-tumor immunity.

The tumor immune microenvironment is highly immunosuppressive. Recent reports indicate that apart from MDSC and regulatory T cells, subsets of immunosuppressive B cells (Breg) are important for controlling anti-tumor immune responses. Bregs expand intratumorally, in tertiary lymphoid structures, draining lymph nodes, and major secondary lymphoid organs, and can produce immune suppressive cytokines such as IL-35 and IL-10 in response to tumor-associated inflammation. B cell-derived IL-35 can dampen the effector T cell response by inhibiting effector CD4⁺ and CD8⁺ T cell responses and enhance the proliferation of Treg cells to simultaneously affect multiple arms of the anti-tumor immune response.