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

The bone marrow is continuously occupied by high numbers of neutrophils, and a tumor-supportive bias of these cells could significantly impact bone marrow-confined malignancies. In multiple myeloma, the bone marrow is characterized by inflammatory stromal cells with the potential to influence neutrophils. Here, we investigated myeloma-associated alterations in marrow neutrophils and the impact of stromal inflammation on neutrophil function. Mature neutrophils in myeloma marrow are activated and tumor-supportive, transcribing increased levels of pro-inflammatory cytokines, including IL-1β, and myeloma cell survival factors, such as the BCMA-ligand BAFF. Neutrophils were re-activated after first-line treatment, while this regimen reduced, but did not normalize, stromal inflammation. Interactions with inflammatory stroma induced neutrophil activation, including BAFF secretion, in a STAT3-dependent manner and once activated, neutrophils gained the ability to reciprocally induce stromal activation. Combined, our data define the presence of a neutrophil-stromal cell feed-forward loop driving tumor-supportive inflammation that could impact disease recurrence.EGA study EGAS00001007038