Suzie Vardanyan

=0.0044) were found to have shorter progression-free survival. Importantly, serum B-cell maturation antigen levels did not show any dependence on renal function and maintained independent significance when tested against other known prognostic markers for multiple myeloma such as age, serum β2 microglobulin, hemoglobin, and bone disease. These data identify serum B-cell maturation antigen as a new biomarker to manage multiple myeloma patients.

PURPOSE: Reduced uninvolved immunoglobulin (Ig) levels are a hallmark of multiple myeloma. We previously showed that B-cell maturation antigen (BCMA) is solubilized and at high levels in multiple myeloma patient serum. We hypothesize that soluble BCMA binds B-cell-activating factor (BAFF) preventing its function to stimulate late B cells, and would result in lower polyclonal antibody levels in these patients. EXPERIMENTAL DESIGN: Mice were dosed with recombinant human BCMA (rhBCMA) and BCMA-BAFF complexes were analyzed in plasma, and its effects on antibody and Ig heavy chain mRNA levels determined. Using flow cytometry, BAFF binding to B cells was examined in the presence of rhBCMA and sera from multiple myeloma patients. In multiple myeloma sera, BCMA-BAFF complex formation and BCMA, IgA, IgG levels, and heavy-light chain isoform pair levels were determined. RESULTS: rhBCMA-BAFF complexes formed in immune-competent and deficient mice. Mice with human multiple myeloma xenografts, which contain plasma hBCMA and hBCMA-BAFF complexes, showed reduced plasma-free BAFF levels. rhBCMA administered to immune competent mice markedly reduced plasma IgA, IgG, and IgM levels and splenic Ig heavy chain mRNA levels. In serum from multiple myeloma patients, BCMA-BAFF complexes were detected and BAFF levels were reduced. Multiple myeloma patient sera containing BCMA prevented binding of BAFF to B cells. There is an inverse correlation between serum BCMA and uninvolved polyclonal Ig level in multiple myeloma patients. CONCLUSIONS: Our results show that soluble BCMA sequesters circulating BAFF, thereby preventing it from performing its signaling to stimulate normal B-cell and plasma cell development, resulting in reduced polyclonal antibody levels in multiple myeloma patients. Clin Cancer Res; 22(13); 3383-97. ©2016 AACR.

Multiple myeloma (MM) is characterized by the enhanced production of the same monoclonal immunoglobulin (M-Ig or M protein). Techniques such as serum protein electrophoresis and nephelometry are routinely used to quantify levels of this protein in the serum of MM patients. However, these methods are not without their shortcomings and problems accurately quantifying M proteins remain. Precise quantification of the types and levels of M-Ig present is critical to monitoring patient response to therapy. In this study, we investigated the ability of the HevyLite (HLC) immunoassay to correlate with clinical status based on levels of involved and uninvolved antibodies. In our cohort of MM patients, we observed that significantly higher ratios and greater differences of involved HLC levels compared to uninvolved HLC levels correlated with a worse clinical status. Similarly, higher absolute levels of involved HLC antibodies and lower levels of uninvolved HLC antibodies also correlated with a worse clinical status and a shorter progression-free survival. These findings suggest that the HLC assay is a useful and a promising tool for determining the clinical status and survival time for patients with multiple myeloma.