Hevylite™ Assays Detect a Hidden Immunoparesis Associated with Adverse Biology in Myeloma Precursor Disease: A Prospective Clinical Study

Abstract 5065

Recent studies have found immunoparesis (suppression of an uninvolved heavy-chain immunoglobulin (Ig) isotype; e.g. low quantitative IgA and/or IgM levels in a patient with an IgG M-spike) to be an independent risk factor for transformation from smoldering multiple myeloma (SMM) to multiple myeloma (MM). About 70–80% of SMM patients have evidence of immunoparesis. Among remaining 20–30% of SMM patients without immunoparesis, it is currently unknown whether there could be a hidden immunoparesis, reflected in suppression of the uninvolved light chain counter part of the same heavy-chain Ig isotype (e.g. IgG kappa in a patient with an IgG lambda M-spike), which in turn may be associated with adverse biology.

A total of 50 SMM patients were enrolled in the first analysis of this prospective study (target: 124 SMM patients). At baseline, a bone marrow core biopsy/aspirate was conducted, and comprehensive immunohistochemistry and flow cytometry analyses were done to confirm the diagnosis and to generate risk profile data for individual patients. For each patient we obtained peripheral blood at baseline. Using serum, we performed the following clinical analyses: serum protein electrophoresis (SPEP); immunofixation electrophoresis (IFE); serum free light chains (sFLC); and quantitative Ig levels for IgG, IgA, and IgM. Using the Hevylite™ assay on a SPAplus (Specialty Protein Analyzer) platform, for each patient, we measured the heavy-light chain (HLC) protein pairs for the complete pair of the patient's heavy-chain Ig isotype (e.g. IgG kappa and IgG lambda for a patient with an IgG M-spike).

Consistent with the literature; overall, we found 32/50 (64%) SMM patients to have immunoparesis of an uninvolved heavy-chain Ig isotype; 31 (97%) of these patients also had suppression of the uninvolved HLC counterpart. Among remaining SMM patients without immunoparesis of an uninvolved heavy-chain Ig isotype, using the Hevylite™ assay we found 8/18 (44%) to have a hidden immunoparesis of the uninvolved HLC counterpart. Compared to SMM patients without any type of Ig suppression, adverse biological features were profound in patients with a hidden immunoparesis of the uninvolved HLC counterpart. For example, the FLC-ratios were more skewed (mean: 14.2 vs. 2.5), the distribution of abnormal/normal plasma cells was more pronounced (90.1% vs. 80.3%), the concentration of the M-spike was higher (1.4 g/dL vs. 1.0 g/dL), and the plasma cell percentage in the bone marrow was higher (15.1% vs. 11.9%).

In conclusion, using the Hevylite™ assay we identified, for the first time, among SMM patients without immunoparesis, a hidden immunoparesis of the uninvolved HLC counterpart, associated with adverse biological features. Our ongoing prospective study will evaluate whether immunoparesis of the uninvolved HLC counterpart is associated with an increased risk of progression to MM.