Development of a Hydrashift 2/4 Isatuximab Assay to Mitigate Interference with Monoclonal Protein Detection on Immunofixation Electrophoresis in Vitro Diagnostic Tests in Multiple Myeloma

Introduction Evaluation of multiple myeloma (MM) response through quantification of M-protein, by serum protein electrophoresis (SPEP) and immuno-fixation electrophoresis (IFE) is challenging for clinical laboratories because therapeutic monoclonal antibodies (mAbs) can confound IFE when they converge with serum M-protein. This can be misleading when interpreting patients' response to therapy. Isatuximab (Isa), an IgG-kappa anti-CD38 mAb is approved based on the pivotal ICARIA-MM study in combination with pomalidomide (P) and dexamethasone (d), in the United States, the European Union, Canada, Australia, Switzerland and Japan for the treatment of adult patients with relapsed/refractory MM who have received at least two prior therapies including lenalidomide and a proteasome inhibitor. Recently, the Phase 3 IKEMA study evaluating Isa plus carfilzomib (K) and d met its primary endpoint at the first planned interim analysis, demonstrating significantly prolonged progression free survival (PFS) compared with Kd alone in patients with relapsed MM. Methods To overcome the interference mediated by Isa on the IFE test, we have developed an Isa-specific assay "HYDRASHIFT 2/4 Isa" using a highly specific rabbit, anti-Isa mAb. The HYDRASHIFT 2/4 Isa test is used in conjunction with the regular Hydragel IF procedure and the semi-automated Hydrasys 2 electrophoresis apparatus. The HYDRASHIFT 2/4 Isa test displaces Isa (IgG kappa) interference during the electrophoresis process by forming Isa/anti-Isa complex which is moved out of the gamma zone toward the alpha globulin fractions. Results: Sensitivity of the HYDRASHIFT 2/4 Isa assay was demonstrated on serum samples, including normal serum samples. Isa control and serum samples with different monoclonal components spiked with Isa (final concentrations in the range of 0.1 and 3.0 g/L) were analyzed with the HYDRASHIFT 2/4 Isa procedure used in conjunction with Hydragel 4 IF Acid Violet. The detection limit of Isa and/or the Isa / anti-Isa antibody complex visualized was 0.2 g/L. Importantly, efficient removal of Isa from the gamma globulin zone, with no trace signal evident, was demonstrated for all Isa concentrations tested, even for 3 g/L. Reproducibility of the HYDRASHIFT 2/4 Isa assay was also demonstrated between gels, between product lots, between instruments and on different test days. Ten different serum samples, including 1 normal serum sample and 9 serum samples with monoclonal components spiked with Isa at 1 g/L, were run using the HYDRASHIFT 2/4 Isa procedure in conjunction with Hydragel 4 IF Acid Violet. All samples gave 100% concordant results between gels on the different instruments and with different HYDRASHIFT 2/4 Isa lots. To evaluate specificity, 50 serum samples from MM patients were spiked with 1 g/L Isa and the anti-Isa mAb shifted Isa specifically with no impact on the patients' M-spike, demonstrating 100% specificity. Finally, the HYDRASHIFT 2/4 Isa test was evaluated on 15 samples from treated patients enrolled in Isa clinical trials at different therapy cycles. The evaluated samples demonstrated efficient removal of Isa from G and Kappa tracks on the gamma globulins zone and visualization of the Isa/anti-Isa complex on alpha zone and/or Isa on ELP track. For the pre-treatment samples, there was as expected no Isa detection, and no impact on M-protein was observed, further confirming the specificity of the assay toward Isa. Conclusions Therapeutic mAb inclusion in MM treatment regimens offer patients significant improvements in clinical outcomes. With rapid evolution of therapeutic options in MM, there is a clear need for a standardized and reliable method to ensure authentic IFE-based clinical assessment. Development of the Isa-specific HYDRASHIFT 2/4 Isa assay offers the advantage of high clinical utility due to the simplicity of the method as an add-on to the conventional IFE In vitro diagnostic test. Consequently, this assay will facilitate the correct assessment of clinical outcomes for patients receiving Isa as part of their MM treatment. Submission for global regulatory clearance for Isa-specific HYDRASHIFT 2/4 assay is planned in 2020. Disclosures Finn: Sanofi: Current Employment. Macé:Sanofi: Current Employment. Chu:Sanofi: Current Employment. van de Velde:Sanofi: Current Employment, Current equity holder in publicly-traded company. Melki:Sebia: Current Employment.

Multiple Myeloma (MM): Impact of Immunoglobulin Isotype on the Speed of Response

Background: Detection and/or measurement of monoclonal components by serum protein electrophoresis (SPE) is essential for evaluation of response in multiple myeloma according to the International Myeloma Working Group (IMWG) criteria. Patient peak on SPE has a single presentation due to the extreme heterogeneity of monoclonal components based on isotype of immunoglobulin (Ig), charge, polymerization, viscosity, precipitation … Regarding the Ig isotype, distribution of myelomas has been known for a long time with about 55 % of IgG myelomas, 25 % of IgA myelomas, and 15% of light chain multiple myelomas (LCMM). Therefore differences in terms of various physical and chemical characteristics are observed according to isotype such as half-lives (IgG : 7-21 days ; IgA : 6 days ; only a few hours for light chains of Ig). Considering both differences about frequency and clearance according to Ig isotype, we addressed the question of the impact of isotype on the speed of response in multiple myeloma. Objective: The aim of this study was to assess if the different isotypes of monoclonal components involved in multiple myeloma have an impact on the velocity and the depth of response. Design and methods: Data from two recent clinical trials conducted by IFM were analysed. The first analysis was based on patients enrolled in the IFM DFCI 2009 clinical trial who benefited of each of the three MRD points planned in this trial (after induction and autograft for one arm, pre-maintenance and post-maintenance). Patients were categorized on the isotype of the monoclonal component involved : IgG, IgA or IgD intact immunoglobulin multiple myelomas (IIMM) with serum measurable disease according to IMWG criteria (i.e. serum monoclonal peak ≥ 10 g/L), LCMM, and IIMM without any serum measurable disease (i.e. serum monoclonal peak < 10 g/L).The percentage of patients who achieved at least a very good partial response (VGPR) was evaluated globally as well as for each category defined. The same analysis was carried out for the IFM 2013-04 clinical trial with one response assessment, after four induction cycles. Results: Concerning IFM DFCI 2009 trial, 398 patients evaluated on the three MRD points could be included in this analysis, divided into 185 and 213 in each arm of treatment. Within the total enrolment, two types of response kinetics could be distinguished : for IgA, IgD IIMM, IIMM without serum measurable disease and LCMM, the gain of response between post-induction +/- autograft and post-maintenance is on average 11,1 points (6,7 - 15) when IgG myelomas presented a difference of VGPR percentage of 27,9 points. The same observation could be made for each arm of treatment : 16,6 and 5,8 points of VGPR percentage gained in each arm for the "faster response" group as defined previously, whereas 33,3 and 23,3 points were gained for IgG myelomas. Apart from this difference of kinetics, we notably observed that IgG myelomas never reached VGPR rates obtained with other isotype myelomas. About IFM 2013-04 trial, 264 patients could be evaluated in our analysis after four cycles of VTD (131) or VCD (133) for induction. 98,0% of IgA myelomas achieved at least VGPR after induction (96,3% for VTD arm and 100% for VCD arm) whereas only 50,6% for IgG myelomas (57,3% and 43,2%) and 68,3% for LCMM (46,7% for VTD arm and 80,8 for VCD arm). Conclusion: This study shows that time of evaluation is a key factor regarding the different speed of response for each isotype of Ig. IgA myelomas and LCMM have a faster response than IgG myelomas. IgG myelomas have a lower biochemical response than other isotype myelomas. Consequently, for an accurate interpretation of data in clinical trials, patients should be equally distributed in each arm of treatment according to their isotype. Ideally, to be compared, clinical trials should always have the same isotype distribution, especially when an early evaluation is performed such as after induction. Disclosures Attal: jansen: Honoraria; celgene: Membership on an entity's Board of Directors or advisory committees. Moreau:Celgene, Janssen, Takeda, Novartis, Amgen: Membership on an entity's Board of Directors or advisory committees.