An IL-1ß driven neutrophil-stromal cell axis fosters a BAFF-rich microenvironment in multiple myeloma

Neutrophils are the most abundant nucleated cell type in the bone marrow. A pro-tumor bias in this cell type may have implications for bone-marrow residing malignancies, such as multiple myeloma. Here, we generated single cell transcriptomic overviews of the entire myeloid compartment, including the entire neutrophilic lineage, of the bone marrow of 6 newly diagnosed myeloma patients, 5 treated myeloma patients and 4 non-cancer controls. We find dat mature neutrophils in myeloma patients, both newly diagnosed and treated, have an activated and pro-inflammatory phenotype, accompanied by increased transcription of pro-inflammatory cytokines, such as IL-1ß, and myeloma cell survival factors, such as BCMA-ligand BAFF/TNFSF13B. Moreover, inflammatory stromal cells can activate naive neutrophils to acquire an inflammatory phenotype as is seen in patients. Previously, we have shown that inflammatory stromal cells characterized the bone marrow of newly diagnosed myeloma patients. Here, we generate single cell RNA sequencing dataset of non-hematopoietic bone marrow cells of patients after induction treatment, high-dose melphalan, stem cell transplantation and consolidation treatment. We show that this intensive treatment reduced, but did not normalize, stromal inflammation.