Clonal Bone Marrow Plasma Cells Are Common in Patients with Vexas Syndrome
Authors: Dulau-Florea Alina , Braylan Raul C. , Ding Yanna , Patel Nisha , Calvo Katherine , Hill Elizabeth , Groarke Emma M. , Young Neal S. , Patel Bhavisha A. 
Published: December 2023

Introduction
Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant plasma cell disorder. Its prevalence increases with age, reaching 5.3% at 70 years and older. MGUS progression rate to multiple myeloma (MM) or lymphoplasmacytic malignancies is about 1% per year. Patients with autoimmune diseases are at increased risk for developing MGUS and MM. VEXAS ( vacuoles, E1 enzyme, X-linked, autoinflammatory and somatic syndrome), an autoinflammatory disorder caused by somatic mutations in ubiquitin-activating enzyme, UBA1 gene, has been associated with plasma cell disorders, specifically MGUS, but the rate of progression is unknown. Cyclin D1, important in cell cycle progression, is regulated by ubiquitin-proteasome mediated degradation, and deregulated cyclin D1 degradation appears to be responsible for the increased levels of cyclin D1 in several cancers. We aim to assess marrow characteristics of plasma cell disorders (MGUS and MM) in VEXAS, and the impact of a defective UBA1 gene product on protein expression of cyclin D1.
Methods
We assessed 28 patients with VEXAS for the presence of plasma cell disorders, and studied the clinical and laboratory characteristics of those with clonal plasma cells (PC) in the marrow. Bone marrow biopsies and aspirates were evaluated by morphology, immunohistochemistry (IHC) dual staining CD138/cyclin D1, dual staining MUM-1/CD20), in situ hybridization (Kappa and Lambda light chains) and flow cytometry (FC) using antibodies for CD45, CD19, CD20, CD38, CD138, CD56, CD27, CD81, and cytoplasmic Kappa and Lambda immunoglobulins. Serum free kappa and lambda light chains, IgG, IgM, and IgA, and level of M paraprotein by serum protein electrophoresis with immunofixation were obtained. Fluorescent in situ hybridization (FISH) analysis for MM was performed in most patients with clonal PCs.
Results
Patients' characteristics are shown in Table 1. Eight out of 28 (28.6%) patients with VEXAS syndrome, all males, had clonal plasma cells in their bone marrows: 3 MGUS, and 5 MM (3 smoldering, SMM; 2 active MM). Median age at diagnosis of plasma cell disorder was 69.5 years (range 60-75). All patients had pathogenic UBA1 somatic mutations (5 M41T, 1 each with M41V, M41L, and splice). Clinically, monoclonal protein size was small, with no specific selection of the type of M protein. Strikingly, most (7/8) clonal plasma cells showed cyclin D1 expression by IHC (dual immunohistochemical stain cyclinD1/CD138 shows double-positive plasma cells; figure not shown), displaying nuclear immunoreactivity in 6 cases, and cytoplasmic immunoreactivity in 1 case. FC showed positive CD20 expression of clonal plasma cells in 4 cases, dim to negative CD19 expression in 4 cases, variable CD56 (positive in 3 cases, partial positive in 1 case, negative in 2 cases), dim to negative CD27 in 3 cases, dim to negative CD81 in 3 cases. FISH for MM revealed: t(11;14) in 4 cases, gain of 11q (CCND1) in 2 cases (in one case, CCND1 gain was present in addition to t(11;14); in the second case, CCND1 gain was associated with gains of 1q and 17p(TP53). The cyclin D1-negative MM case was negative for t(11;14) but had t(4;14). All cases with t(11;14) were positive for cyclin D1 by IHC (nuclear staining). The one MM case with negative nuclear staining for cyclin D1 but positive cytoplasmic staining, was negative for t(11;14) but had gain of 11q (CCND1).One patient evolved from SMM to active MM after 4 years. No evolution to MM was seen in patients with MGUS with median follow-up of 30 months.
Conclusions
Patients with VEXAS have a high prevalence of clonal plasma cell disorders. Clonal plasma cells in VEXAS patients are associated with t(11;14), and with nuclear cyclin D1 expression by IHC. Cytoplasmic cyclin D1 staining in the absence or weak nuclear staining was observed with CCND1 gain and absence of t(11;14). Cytoplasmic cyclin D1 expression may be related to lack of cyclin D1 protein degradation by a defective UBA1 gene product. Our results suggest that defective UBA1 and autoinflammation pose an increased risk for developing MGUS or multiple myeloma.