Summary While B cells are traditionally regarded as promoters of the immune response via antibody secretion and pro-inflammatory cytokine production, recent studies have also confirmed an important role for B-cell-mediated negative regulation of immunity. Tremendous advances in the characterization of the mechanisms by which regulatory B cells function has led to the identification of a novel subset of regulatory B cells known as B10 cells, which regulate immune responses through the production of the anti-inflammatory cytokine interleukin-10 (IL-10). B10 cells are best defined by their functional ability to produce IL-10, as they are not confined to any particular phenotypic subset. B10 cells function in an antigen-specific manner that requires cognate interactions with T cells in vivo to regulate immune responses and have been demonstrated to be potent regulators of allergic and autoimmune disease, cancer, infection, and transplant rejection. Importantly, the recent discovery of human B10 cells has accelerated this field to the forefront of clinical research where the possibility of harnessing the regulatory potential of B10 cells for treatment of aberrant immune responses and diseases may become feasible.

B cells are known to instigate and promulgate immune responses by producing antibodies and presenting antigens to T cells. However, a rare but potent B-cell subset in both humans and mice is capable of inhibiting immune responses through the production of the anti-inflammatory cytokine IL-10. Regulatory B cells do not express any unique combination of surface markers but instead represent a small population of B cells that have acquired the unique ability to produce IL-10. This numerically rare B-cell subset is therefore functionally referred to as 'B10 cells' to reflect both their molecular program and the fact that their anti-inflammatory effects in models of autoimmunity, infection and cancer are solely attributable to IL-10 production. As with most B cells, B10 cell development and function appear to be predominantly, if not exclusively, driven by antigen-receptor signals. Once generated, B10 cells respond to both innate and adaptive immune signals, with a requirement for antigen-specific local interactions with T cells to induce IL-10 production and to provide optimal immune suppression in mouse models of autoimmune disease. B10 cells therefore provide an antigen-specific mechanism for delivering IL-10 locally to sites of immune activation and inflammation. The ability of B10 cells to regulate innate and adaptive immune responses makes them an ideal therapeutic target for the treatment of many immune-related disorders.

Key Points A preclinical model system was developed to define the molecular landscape dictating lymphoma resistance to immunotherapy. This system revealed that Gal-1 significantly inhibits CD20 immunotherapy within the lymphoma microenvironment in vivo.