Glycosylated GM-CSF expands B-1b cells and B-1b plasma cells and programs them for immunosuppression

Abstract The myeloid growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF) exhibits paradoxical pro- and anti-inflammatory functions, but the factors determining these divergent outcomes remain unclear. Here, we report that this functional divergence is controlled by its glycosylation. Murine recombinant fully glycosylated GM-CSF (rgGM-CSF) specifically induces immunosuppressive cell types, whereas its recombinant non-glycosylated counterpart (rngGM-CSF) promotes effector immune cells. Using single-cell ATAC-sequencing and flow cytometry, we show that rgGM-CSF has a previously unrecognized ability to effectively expand IL-10 + LAG-3 + PD-L1 + B-1b plasma cells (PCs) with immunosuppressive properties and self reactive natural IgM secretion. Although rgGM-CSF also promotes the expansion of hematopoietic stem and progenitor cells (HSPCs) and monocytic myeloid-derived suppressor cells (M-MDSCs), adoptive transfer experiments demonstrate that the rgGM-CSF-induced B-1b PCs are responsible for an IL-10-dependent long-term protection in mice from experimental autoimmune-encephalomyelitis (EAE). Our data suggest that glycosylation enhances the systemic bioavailability and activity of GM-CSF and promotes the expansion of immunoregulatory cells rather than pro-inflammatory myeloid effector cells. Together, these results demonstrate that the ‘dual activity’ of GM-CSF is controlled by its glycosylation, resulting in opposing immune functions. These findings support a re-evaluation of human rgGM-CSF (regramostim) as a potential therapeutic strategy for immunosuppression in transplantation and autoimmune diseases. Key points Glycosylated GM-CSF promotes B-1b cells and B-1b plasma cells expansion and establishes their long-term imprinting as IL-10 + LAG3 + PD-L1 + natural IgM secreting regulatory cells. Albumin binding enhances the systemic activity of glycosylated GM-CSF in generating regulatory B-1b plasma cells. Glycosylated GM-CSF injections into mice expand M-MDSCs, but their suppressive iNOS production is only maintained short-term. Non-glycosylated GM-CSF injections preferentially promote expansion of pro-inflammatory effector monocytes and neutrophils. Graphical Abstract