Comparison Of Hevylite™ Assay and Plasma Cell Immunophenotyping For Response Evaluation and Residual Disease Characterisation In IgA Myeloma

The evaluation of multiple myeloma response to treatment as defined by international guidelines is currently based on morphologic examination of bone marrow plasma cells, serum protein electrophoresis (SPEP), immunofixation electrophoresis (IFE) and serum free light chain assay. For several years new tools are available as bone marrow plasma cell immunophenotyping and the Hevylite^TM assay. Hevylite^TM IgA assay provides an automated evaluation of serum heavy/light chain ratio (HLC) of the involved and uninvolved immunoglobulin (Ig) (i.e. IgAΚ/IgAλ). This is particularly interesting in IgA myeloma where the use of SPEP is limited due to a frequent comigration of monoclonal IgA with other proteins. We therefore compared the IgA quantification by Hevylite™ assay and the bone marrow plasma cell immunophenotyping for response evaluation and residual disease characterisation in IgA myeloma.

Hevylite™ assay, SPEP, IFE were performed in eleven IgA myeloma patients at different times: after induction chemotherapy, after the consolidation phase and after autologous stem-cell transplantation (ASCT). In the same time, minimal residual disease (MRD) assessment was performed on bone marrrow by multiparameter flow cytometry (MFC). Hevylite™ assay was performed on a Binding Site SPAplus analyser (Hevylite, Binding Site, Birmingham, UK) following the manufacturer recommendations. SPE and IFE were realized on Sebia Hydrasys analyser (Sebia, Evry, France) and results were read by two experienced biologists.

1. We found a perfect agreement between the IFE and immunophenotyping results at each time of evaluation, for positive results as for negative results.

2. The SPEP was contributive only in two patients and in these cases it was less sensitive than IFE. In the other patients, the monoclonal IgA migrated in beta region and/or as multiple bands, making the quantitative estimation difficult.

3. In all patients, when MRD by MFC was undetectable and IFE was negative, the HLC ratio was normal.

4. In 3 patients, HLC ratio was consistent with the IFE and MRD by MFC at each time of evaluation. Nevertheless, in 8 patients out of 11, while HLC ratio became normal, MRD by MFC and IFE were still positive. In all cases, the normalization of HLC ratio was followed, at the next step of evaluation, by the normalization of MFC and IFE.

5. In 5 patients, the normalization of HLC ratio occurred before ASCT, while IFE and MRD by MFC were still positive. Nevertheless, after ASCT, IFE and MRD by MFC became also negative, in accordance with the HLC ratio (Table 1).

During the evaluation of response to treatment of IgA myeloma, we observed a normalization of HLC ratio (Hevylite™ IgA assay) preceding the normalization of MRD by MFC and IFE. This could be explained by the fact that IFE and immunophenotyping provide very sensitive information but only on the monoclonal component. HLC ratio reflects the balance between the monoclonal and polyclonal Igs of involved and uninvolved isotype. A normalization of HLC ratio can be interpreted as an increasing polyclonal Ig proportion parallel with a decreasing monoclonal Ig proportion and may reflect the reconstitution of polyclonal plasma cells. If confirmed by other studies and long term follow-up, HLC ratio could be a non-invasive predictive marker of a good response in IgA myeloma.

No relevant conflicts of interest to declare.