Inflammatory Waldenström macroglobulinemia is associated with monocyte dysregulation and IL-1β production

Abstract Background Waldenström macroglobulinemia (WM) is a rare, indolent B-cell neoplasm characterized by bone marrow (BM) infiltration by lymphoplasmacytic cells producing monoclonal IgM. A distinct inflammatory subset (iWM) has recently been described, defined by persistent elevation of C-reactive protein (CRP ≥20 mg/L) in the absence of infection or autoimmune disease. This phenotype is observed in ~33% of symptomatic cases, is more frequent at relapse (42%), and remains rare in asymptomatic patients (<10%). iWM has been associated with 6q deletion, clonal hematopoiesis, and a lower frequency of CXCR4 mutations. Clinically, it correlates with shorter time to next treatment (TTNT) following immunochemotherapy, but improved TTNT in patients receiving BTK inhibitors. However, its underlying pathophysiology remains poorly understood. Methods We prospectively collected blood and BM samples from 36 individuals with symptomatic WM. Based on CRP levels, patients were classified as having iWM (n = 20, median age 76 years) or non-inflammatory WM (nWM, n = 16, median age 74 years). Patients with elevated IgM levels but concurrent malignancies or inflammatory disorders—including Schnitzler syndrome—were excluded. Ederly healthy donors (HD, n = 13, median age 58 years) served as controls. Serum concentrations of inflammatory cytokines, including IL-1β, IFN-α2, IFN-γ, TNF-α, MCP-1, IL-6, IL-8, IL-10, IL-12p70, IL-17A, IL-18, IL-23, and IL-33, were measured using multiplex ELISA. High-dimensional immune profiling by 40-marker spectral flow cytometry and single-cell RNA sequencing (scRNA-seq) were performed on peripheral blood to characterize immune cell populations. Results iWM was not associated with tumor burden at the symptomatic phase, as assessed by IgM levels and BM infiltration. However, plasma cytokine analysis at steady state revealed significantly higher levels of inflammasome-related cytokines in iWM compared to nWM and HD. IL-1β showed the strongest difference, with median concentrations threefold higher in iWM (2630 fg/mL) compared to nWM (976 fg/mL, p = 0.02). IL-18 levels were also significantly higher in iWM (1205 pg/mL) versus nWM (500 pg/mL, p = 0.006). IL-6 levels were elevated in iWM (median 37 pg/mL vs 11 pg/mL) but did not reach statistical significance (p = 0.11). No correlation with age was observed for IL-1β (r = 0.14, p = 0.31) or IL-18 (r = 0.05, p = 0.77), and cytokine levels were similar between nWM and healthy donors. In peripheral blood, spectral cytometry (n = 7 per group; 100,000 cells/patient) and scRNA-seq (n = 3 per group; 43,000 cells total) revealed a higher proportion of intermediate and non-classical monocytes in iWM compared to nWM (p < 0.001). Overall, IL-1β expression was significantly increased in iWM relative to both nWM and HD (p < 0.001), with monocytes identified as the principal source. Subclustering revealed a population of cytokine-producing classical monocytes in iWM as the main IL-1β producers, with upregulation of inflammasome-related genes compared to their counterparts in nWM. In the bone marrow (n = 4 per group; 100,000 cells/patient), spectral cytometry showed an increased abundance of monocytes/macrophages in iWM compared to nWM. Mast cell density did not differ between groups. Discussion iWM represents a biologically distinct inflammatory subset of WM, independent of tumor burden, and seems to be associated with alterations in the immune microenvironment. Cytokine-producing monocytes, more transcriptionally active in iWM and functionally suppressed in nWM, may be key contributors to the inflammatory profile. Given the role of BTK in inflammasome regulation—and the superior clinical responses observed in iWM under BTK inhibitor therapy—these findings highlight potential therapeutic strategies targeting IL-1β signaling and monocyte–B-cell interactions. Additional investigations are ongoing, including BM scRNA-seq and monocyte stimulation assays, to further characterize the inflammatory mechanisms underlying iWM.