Clinical efficacy and management of monoclonal antibodies targeting CD38 and SLAMF7 in multiple myeloma

Immunotherapeutic strategies are emerging as promising therapeutic approaches in multiple myeloma (MM), with several monoclonal antibodies in advanced stages of clinical development. Of these agents, CD38-targeting antibodies have marked single agent activity in extensively pretreated MM, and preliminary results from studies with relapsed/refractory patients have shown enhanced therapeutic efficacy when daratumumab and isatuximab are combined with other agents. Furthermore, although elotuzumab (anti-SLAMF7) has no single agent activity in advanced MM, randomized trials in relapsed/refractory MM have demonstrated significantly improved progression-free survival when elotuzumab is added to lenalidomide-dexamethasone or bortezomib-dexamethasone. Importantly, there has been no significant additive toxicity when these monoclonal antibodies are combined with other anti-MM agents, other than infusion-related reactions specific to the therapeutic antibody. Prevention and management of infusion reactions is important to avoid drug discontinuation, which may in turn lead to reduced efficacy of anti-MM therapy. Therapeutic antibodies interfere with several laboratory tests. First, interference of therapeutic antibodies with immunofixation and serum protein electrophoresis assays may lead to underestimation of complete response. Strategies to mitigate interference, based on shifting the therapeutic antibody band, are in development. Furthermore, daratumumab, and probably also other CD38-targeting antibodies, interfere with blood compatibility testing and thereby complicate the safe release of blood products. Neutralization of the therapeutic CD38 antibody or CD38 denaturation on reagent red blood cells mitigates daratumumab interference with transfusion laboratory serologic tests. Finally, therapeutic antibodies may complicate flow cytometric evaluation of normal and neoplastic plasma cells, since the therapeutic antibody can affect the availability of the epitope for binding of commercially available diagnostic antibodies.