Monoclonal Antibodies in Multiple Myeloma Come of Age

Identification and elucidation of cross talk between SLAM Family Member 7 (SLAMF7) and Toll-like receptor (TLR) pathways in monocytes and macrophages

To further elucidate the expression, regulation and function of Signaling Lymphocytic Activation Molecule Family (SLAMF) protein members in human monocytes and macrophages. Un-differentiated monocytic THP-1 cell (u-THP-1) and differentiated THP-1 macrophage (d-THP-1) were used as culture models in the study. Responses of cells to the differentiation agents phorbol ester (25 ng/ml) and TLR (Toll-like receptor) ligands were assessed. RT-PCR and Western blot analysis were used to determine mRNA and protein level. Pro-inflammatory cytokine mRNA expression levels and phagocytosis were used as functional markers. Data analyzed using t-test, one-way or two-way ANOVA followed by post hoc test. SLAMFs were differentially expressed in THP-1 cells. Differentiation of u-THP-1 to d-THP-1 led to significantly higher SLAMF7 mRNA and protein levels than other SLAMF. In addition, TLR stimuli increased SLAMF7 mRNA expression but not protein expression. Importantly, SLAMF7 agonist antibody and TLR ligands synergistically increased the mRNA expression levels of IL-1β, IL-6 and TNF-α, but had no effect on phagocytosis. SLAMF7 knocked-down in d-THP-1 significantly lowered TLR-induced mRNA expressions of pro-inflammatory markers. SLAM family proteins are differentially regulated by differentiation and TLRs. SLAMF7 enhanced TLR-mediated induction of pro-inflammatory cytokines in monocytes and macrophages but not phagocytosis.

High affinity human Fc specific monoclonal antibodies for capture kinetic analyses of antibody-antigen interactions

We recently demonstrated that capturing human monoclonal antibodies (hmAbs) using high affinity anti-human Fc (AHC) antibodies allows reliable characterization of antibody-antigen interactions. Here, we characterized six human Fc specific mouse monoclonal antibodies (mAbs) and compared their binding profiles with three previously characterized goat AHC polyclonal antibodies (pAbs), exhibiting properties of a good capture reagent. All six mouse AHC mAbs specifically bound with high affinity to the Fc region of hIgG1, hIgG2, hIgG4 and to 43 different hIgG variants, containing substitutions and/or mutations in the hinge and/or Fc region, that have been reported to exhibit modified antibody effector function and/or pharmacokinetics. Biacore sensor surfaces individually derivatized with mouse AHC mAbs exhibited >2.5-fold higher hIgG binding capacity compared to the three goat AHC pAb surfaces and reproducibly captured hIgG over 300 capture-regeneration cycles. The results of the capture kinetic analyses performed on 31 antibody-antigen interactions using surfaces derivatized with either of the two highest affinity AHC mAbs (REGN7942 or REGN7943) were in concordance with those performed using goat AHC pAb surfaces. Our data demonstrate that AHC mAbs such as REGN7942 and REGN7943 that have properties superior than the three goat AHC pAbs are highly valuable research reagents, especially to perform capture kinetic analyses of antibody-antigen interactions on optical biosensors.

Individualized genetic makeup that controls natural killer cell function influences the efficacy of isatuximab immunotherapy in patients with multiple myeloma

BACKGROUND

Phase IIb clinical trial with isatuximab (Isa)-lenalidomide (Len)-dexamethasone (Dex) showed an improved progression-free survival (PFS) in patients with relapsed or refractory multiple myeloma (RRMM), but the efficacy varied by patient. Antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) cells plays a crucial role in arbitrating antitumor activities of therapeutic-antibodies. We tested if patient-specific genetic makeup known to set NK cell functional threshold influence response to Isa-Len-Dex therapy.

METHODS

We characterized 57 patients with RRMM receiving Isa-Len-Dex for polymorphisms of killer-cell immunoglobulin-like receptors (KIR), human leukocyte antigen (HLA) class I, and FCGR3A loci. In vitro ADCC assay, coincubating primary NK cells expressing specific KIR repertoire with multiple myeloma cell lines (MM cells) expressing selected HLA class I ligands, was used to confirm the identified genetic correlatives of clinical response.

RESULTS

Patients with KIR3DL2+ and its cognate-ligand HLA-A3/11+ had superior PFS than patients missing this combination (HR=0.43; p=0.02), while patients carrying KIR2DL1+ and HLA-C2C2+ compared with to patients missing this pair showed short PFS (HR=3.54; p=0.05). Patients with KIR3DL2+ and HLA-A3/11+ plus high-affinity FCGR3A-158V allele showed the most prolonged PFS (HR=0.35; p=0.007). Consistent with these clinical data, mechanistic experiments demonstrated that NK cells expressing KIR3DL2 trigger greater ADCC when MM cells express HLA-A3/11. Inversely, NK cells expressing KIR2DL1 do not kill if MM cells express the HLA-C2C2 ligand. NK cells expressing high-affinity FCGR3A-158VV-induced greater ADCC compared with those with low-affinity FCGR3A-158FF.

CONCLUSIONS

Our results suggest that KIR3DL2+ and HLA-A3/11+ with FCGR3A-158V markers lead to enhanced Isa-dependent NK-mediated cytolysis against MM cells and results in improved PFS in patients with RRMM treated by Isa-Len-Dex. Moreover, the presence of KIR2DL1+ and HLA-C2C2+ identifies patients who may have a lower response to Isa-Len-Dex therapy linked to a reduced NK-mediated ADCC. These biomarkers could potentially identify, via precision medicine, patients more likely to respond to Isa-Len-Dex immunotherapy.

TRIAL REGISTRATION NUMBER

NCT01749969.

Incidence and Management of Therapeutic Monoclonal Antibody Interference in Monoclonal Gammopathy Monitoring

BACKGROUND

The treatment of multiple myeloma (MM) has been revolutionized by the introduction of therapeutic monoclonal antibodies (tmAbs). Daratumumab, a human IgG1/κ tmAb against CD38 on plasma cells, has improved overall survival in refractory MM and was recently approved as a frontline therapy for MM. Work on tmAb interference with serum protein electrophoresis (SPE) during MM monitoring has failed to provide information for laboratories on incidence of interference and effective methods of managing the interference at a practicable level. We aimed to evaluate daratumumab and elotuzumab interference in a large academic hospital setting and implement immediate solutions.

METHODS

We identified and chart reviewed all cases of possible daratumumab interference by electrophoretic pattern (120 of 1317 total cases over 3 months). We retrospectively reviewed SPE cases in our laboratory to assess clinical implications of tmAb interference before the laboratory was aware of tmAb treatment. We supplemented samples with daratumumab and elotuzumab to determine the limits of detection and run free light chain analysis.

RESULTS

Approximately 9% (120 of 1317) of tested cases have an SPE and/or immunofixation electrophoresis (IFE) pattern consistent with daratumumab, but only approximately 47% (56) of these cases were associated with daratumumab therapy. Presence of daratumumab led to physician misinterpretation of SPE/IFE results. Limits of daratumumab detection varied with total serum gammaglobulin concentrations, but serum free light chain analysis was unaffected.

CONCLUSIONS

Clinical laboratories currently rely on interference identification by electrophoretic pattern, which may be insufficient and is inefficient. Critical tools in preventing misinterpretation efficiently include physician education, pharmacy notifications, separate order codes, and interpretive comments.

Approaches and Challenges in the Management of Multiple Myeloma in the Very Old: Future Treatment Prospects

The increasing incidence of geriatric patients with multiple myeloma has elevated concerns in clinical practice. While the introduction of novel therapeutic agents has substantially improved outcomes in younger patients with myeloma, poorer outcomes remain in older patients. Managing older patients requires a multidisciplinary team approach to consider factors that may influence both treatment selection and outcomes. Aging is associated with remodeling of vital organs, physiological downregulations of basal metabolism, susceptibility to multiple comorbidities with ultimate frailty, thereby contributing to the underrepresentation and exclusion of very old patients from clinical trials. Therefore, timely confirmation of a precise diagnosis is crucial for prompt initiation of treatment if the desired outcome is to be achieved. Adequate and judicious assessment using comprehensive geriatric assessment tools minimizes toxicities and treatment discontinuation. Initiating treatment with combinational therapy requires knowledge of indications and anticipated outcomes, as well as individualized therapy with appropriate dose-adjustment. Individualized therapy based on good clinical acumen and best practices obverts unwanted polypharmacy, preventing iatrogenic harm. This review will therefore address the approaches and challenges faced in managing myeloma in geriatric patients aged 80 years and older, highlighting recommended therapeutic strategies and future prospective regimens.

Monoclonal antibodies in multiple myeloma

Treatment of multiple myeloma (MM) patients has radically changed over the last years following the introduction of next generation proteasome inhibitors (PI) and immunomodulatory derivative (IMiDs). In the last years, one further therapeutic option for MM patients is represented by monoclonal antibodies (MoAbs), that seem to change the paradigm of MM treatment, particularly for heavily pretreated or double refractory to a PI and IMiDs patients. Antibodies have an immune-based mechanism, induce durable responses with limited toxicity and combine well with existing therapies. The therapeutic effects are prevalently obtained by means of antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cell-mediated phagocytosis (ADCP), complement-dependent cytotoxicity (CDC) and concurrently by the induction of signals on cell effectors. Immunotherapeutic strategies offer a new and exciting approach to target key molecular pathways that continue to be implicated in the survival of malignant plasma cells. These targets include cell surface proteins (CD38, CD138 [SDC1], B cell maturation antigen [BCMA, TNFRSF17]), cytokines that play a role in plasma cell survival and proliferation (interleukin 6 [IL6] and B cell activating factor), signal regulators of bone metabolism (RANKL [TNFSF11], DKK1) and regulators of the immune system (PD-1[PDCD1], PD-L1[CD274]). This article focuses on new MoAbs and related innovative immunotherapeutic modalities currently under investigation in the treatment landscape of MM.

CD38 as an immunomodulator in cancer

CD38 is a transmembrane glycoprotein that is widely expressed in a variety of human tissues and cells, especially those in the immune system. CD38 protein was previously considered as a cell activation marker, and today monoclonal antibodies targeting CD38 have witnessed great achievements in multiple myeloma and promoted researchers to conduct research on other tumors. In this review, we provide a wide-ranging review of the biology and function of the human molecule outside the field of myeloma. We focus mainly on current research findings to summarize and update the findings gathered from diverse areas of study. Based on these findings, we attempt to extend the role of CD38 in the context of therapy of solid tumors and expand the role of the molecule from a simple marker to an immunomodulator.

A novel approach to remove interference of therapeutic monoclonal antibody with serum protein electrophoresis

OBJECTIVES

Multiple myeloma (MM) is characterized by malignant growth of plasma cells, usually producing a monoclonal antibody (mAb). New treatments for MM include therapeutic monoclonal antibodies (tmAbs), but patients treated with tmAb demonstrate interference on serum electrophoresis (SPE) and immunoprecipitation electrophoresis (IEP). Evaluation of treatment efficacy and determination of MM remission include SPE and IEP which identifies mAb, but cannot differentiate between disease associated mAb and tmAb. We hypothesized that tmAb could be removed from patient sera before testing by SPE and IEP to provide accurate diagnoses for clinicians.

DESIGN AND METHODS

We developed the Antigen Specific therapeutic monoclonal Antibody Depletion Assay (ASADA), that utilizes magnetic beads coated with the cognate antigen of the tmAbs, to deplete two different tmAb (daratumumab, elotuzumab) from saline and patient sera and assessed for complete removal of tmAb by SPE and IEP.

RESULTS

We found that tmAb could be efficiently removed from saline and patient sera. ASADA demonstrated acceptable analytical specificity and sensitivity in IEP. Recovery of appropriate quantitative values by SPE was demonstrated with clinically acceptable precision. A single bead cocktail could be used to treat both daratumumab and elotuzumab.

CONCLUSIONS

This demonstrates proof of principle that ASADA can be used to remove current and future tmAb from patient sera, regardless of platform. This research provides for accurate diagnosis, disease monitoring, and remission status in MM patients being treated with tmAb.

Induction Therapy for Newly Diagnosed Multiple Myeloma

The frontline therapy for newly diagnosed multiple myeloma (MM) has continued to evolve over the last 10 years. There has been a growing emphasis on achieving the best depth of response in the context of minimal residual disease negativity, given its prognostic correlation with superior overall survival. Another important area of emphasis has been to improve prognostication and staging by including information on disease biology. There also a growing appreciation of global differences in drug access and patterns of care. The current review explores each of these areas and how best to incorporate the emerging induction regimens in to schema of MM therapy.

A CS1-NKG2D Bispecific Antibody Collectively Activates Cytolytic Immune Cells against Multiple Myeloma

Multiple myeloma (MM) is an incurable hematologic malignancy of plasma cells, with an estimated 30,000 new cases diagnosed each year in the United States, signifying the need for new therapeutic approaches. We hypothesized that targeting MM using a bispecific antibody (biAb) to simultaneously engage both innate and adaptive cytolytic immune cells could present potent antitumor activity. We engineered a biAb by fusing an anti-CS1 single-chain variable fragment (scFv) and an anti-NKG2D scFv (CS1-NKG2D biAb). Although NKG2D is a potent activation receptor ubiquitously expressed on mostly cytolytic immune cells including NK cells, CD8⁺ T cells, γδ T cells, and NKT cells, the CS1 tumor-associated antigen on MM represents a promising target. CS1-NKG2D biAb engaged human MM cell lines and NKG2D⁺ immune cells, forming immune synapses. In effector cells, CS1-NKG2D biAb triggered the phosphorylation of AKT, a downstream protein kinase of the activated NKG2D-DAP10 complex. The EC₅₀ values of CS1-NKG2D biAb for CS1^high and for CS1^low MM cell lines with effector PBMCs were 10^-12 and 10^-9 mol/L, respectively. CS1-NKG2D biAb acted through multiple types of immune cells, and this induced cytotoxicity was both CS1- and NKG2D-specific. In vivo, survival was significantly prolonged using CS1-NKG2D biAb in a xenograft NOD-SCID^IL2γc-/- (NSG) mouse model engrafted with both human PBMCs and MM cell lines. Collectively, we demonstrated that the CS1-NKG2D biAb facilitated an enhanced immune synapse between CS1⁺ MM cells and NKG2D⁺ cytolytic innate and antigen-specific effector cells, which, in turn, activated these immune cells for improved clearance of MM. Cancer Immunol Res; 6(7); 776-87. ©2018 AACR.

Systematic review and meta-analysis of the efficacy and safety of novel monoclonal antibodies for treatment of relapsed/refractory multiple myeloma

Although two newly launched monoclonal antibodies (mAbs), elotuzumab and daratumumab, performed well in patients with relapsed or relapsed/refractory multiple myeloma (RRMM), their efficacy and safety remain uncertain. We therefore performed a systematic review and meta-analysis of the most recent clinical trials that evaluated elotuzumab and/or daratumumab for the treatment of patients with RRMM. Our meta-analysis included 13 clinical trials with 2,402 patients participating. The overall response rate (ORR) was 57% (95% confidence interval [CI]: 38-76%), and the at least very good partial response rate (VGPR) was 32% (95% CI: 19-46%). mAb-based regimens prolonged progression-free survival (PFS, hazard ratio: 0.52, 95% CI: 0.36-0.75) compared to non-mAb-based regimens. Additionally, the efficacy of triplet regimens was superior to that of single or doublet regimens. The same trend was observed in a subgroup analysis of daratumumab and elotuzumab. The most common grade 3/4 adverse events included neutropenia, lymphopenia, thrombocytopenia, anemia, leukopenia, pneumonia, and fatigue. Elotuzumab and daratumumab improved the ORR, at least VGPR, and PFS compared to non-mAb-based regimens. In a pooled analysis, both mAbs had promising efficacy and safety profiles, particularly in triplet regimens. The same trend was observed in daratumumab- and elotuzumab-based regimens. Daratumumab triplet therapy (daratumumab, lenalidomide, and dexamethasone) was superior to other triplet regimens for the treatment of RRMM, and daratumumab monotherapy was more effective than either single agent in heavily pretreated MM patients, suggesting CD38 is an effective target for treatment of RRMM. Additional clinical studies of elotuzumab and daratumumab will be required to validate these results.

BAFF is involved in macrophage-induced bortezomib resistance in myeloma

We aimed to characterize the role of B-cell activating factor (BAFF) in macrophage-mediated resistance of multiple myeloma (MM) cells to bortezomib (bort), and to further understand the molecular mechanisms involved in the process. First, we detected BAFF and its three receptors on myeloma cells and macrophages using the quantitative reverse transcriptase-polymerase chain reaction and flow cytometry. The secretion of BAFF was tested in patients with MM, MM cell lines, and macrophages. The ability of macrophages to protect MM cells from bort-induced apoptosis was significantly attenuated using BAFF-neutralizing antibody in the co-culture system or knocking down the expression of BAFF in macrophages with small interfering RNA. We also showed that the MM–macrophage interaction through BAFF and its receptors was primarily mediated by the activation of Src, Erk1/2, Akt, and nuclear factor kappa B signaling and the suppression of caspase activation induced by bort. Our data demonstrated that BAFF played a functional role in the macrophage-mediated resistance of MM cells to bort, suggesting that targeting BAFF may provide a basis for the molecular- and immune-targeted therapeutic approach.

Nanobodies effectively modulate the enzymatic activity of CD38 and allow specific imaging of CD38+ tumors in mouse models in vivo

The cell surface ecto-enzyme CD38 is a promising target antigen for the treatment of hematological malignancies, as illustrated by the recent approval of daratumumab for the treatment of multiple myeloma. Our aim was to evaluate the potential of CD38-specific nanobodies as novel diagnostics for hematological malignancies. We successfully identified 22 CD38-specific nanobody families using phage display technology from immunized llamas. Crossblockade analyses and in-tandem epitope binning revealed that the nanobodies recognize three different non-overlapping epitopes, with four nanobody families binding complementary to daratumumab. Three nanobody families inhibit the enzymatic activity of CD38 in vitro, while two others were found to act as enhancers. In vivo, fluorochrome-conjugated CD38 nanobodies efficiently reach CD38 expressing tumors in a rodent model within 2 hours after intravenous injection, thereby allowing for convenient same day in vivo tumor imaging. These nanobodies represent highly specific tools for modulating the enzymatic activity of CD38 and for diagnostic monitoring CD38-expressing tumors.

New mAb therapies in multiple myeloma: interference with blood transfusion compatibility testing

PURPOSE OF REVIEW

Immunotherapeutic strategies are emerging as novel therapeutic approaches in multiple myeloma, with several mAbs being in advanced stages of clinical development. Of these, CD38 targeting antibodies appear very promising. In trials with anti-CD38 mAb daratumumab, all patients demonstrated panreactivity in red blood cell (RBC) panel testing, complicating the selection of compatible RBCs for transfusion. This review provides an overview of the interferences and solutions to safely transfuse these patients.

RECENT FINDINGS

CD38 is weakly expressed on human erythrocytes. Since the first reports on the interference, different solutions have been reported, including the neutralization of anti-CD38 mAbs in plasma by sCD38 or antiidiotype antibodies, CD38 depletion of RBCs using dithiothreitol or cord blood test cells, and transfusion of extensively typed RBCs.

SUMMARY

All methods have (dis)advantages, and it depends on the facilities of the immunohematology laboratory what strategy to choose. As the selection of suitable RBC units can be seriously delayed, hospitals should have protocols to communicate this interference with patients, laboratories, and physicians in a timely manner. As CD38 antibodies may also have a role in the treatment of diseases beyond hematological malignancies, chances are high that health professionals will encounter this issue in the nearby future.

Magic year for multiple myeloma therapeutics: Key takeaways from the ASH 2015 annual meeting

Despite the availability of various anticancer agents, Multiple Myeloma (MM) remains incurable in most cases, along with high relapse rate in the patients treated with these agents. The year 2015 saw major advancements in our battle against multiple myeloma. In 2015, the U.S. Food and Drug Administration (FDA) approved three new therapies for multiple myeloma, namely Ixazomib (an oral proteasome inhibitor), Daratumumab and Elotuzumab (monoclonal antibodies against CD38 and SLAMF7 respectively). The purpose of this review is to provide a detailed analysis of these aforementioned breakthrough therapies and two other newer agents, Filanesib (kinesis spindle inhibitor) and selinexor (SINE inhibitor), presented at the 2015 annual meeting of American Society of Hematology (ASH). We also describe the role of agents targeting PD-1 axis and chimeric antigen receptor T (CAR-T) cells in the treatment of MM.

Role of Flow Cytometry in the Diagnosis and Prognosis of Plasma Cell Myeloma

This article provides an overview of the role of flow cytometry in the diagnosis and follow-up of plasma cell myeloma. A brief introduction to the general immunophenotypic features of normal and myeloma plasma cells is provided, followed by a discussion of technical issues as they relate to the application of flow cytometry in this entity. The prognostic and therapeutic utility of flow cytometric immunophenotyping in myeloma is also analyzed, with an emphasis on the growing role of minimal residual analysis as potential biomarker for evaluating treatment efficacy and for tailoring risk-adapted treatment, in prospective clinical trials.

An update on the role of daratumumab in the treatment of multiple myeloma

Monoclonal antibodies (mAbs) have emerged as a promising new drug class for the treatment of multiple myeloma (MM). Daratumumab (DARA), a CD38 mAb, has demonstrated safety, tolerability and activity in a range of clinical trials, both as monotherapy and in combination strategies for MM. The favorable efficacy results in heavily pretreated patients with advanced MM have provided the rationale for the investigation of DARA in a number of ongoing and future phase II and III trials. The general tolerability of mAbs has allowed for widespread investigation and use of DARA among a variety of MM patients, however their use requires special consideration. Infusion-related reactions (IRRs), interference with blood compatibility assays and response assessments are all unique factors related to the use of DARA. This review provides an update of the results from the DARA clinical trials conducted to date, its future plans for investigation, and practical management considerations for the use of DARA in daily practice.

Osteoclasts promote immune suppressive microenvironment in multiple myeloma: therapeutic implication

OCs play a crucial role in myeloma-induced immunosuppressive microenvironment. Therapeutic anti-CD38 mAb partially overcomes the immunosuppressive effect of OCs.

Phase 1 Study of Tabalumab, a Human Anti-B-Cell Activating Factor Antibody, and Bortezomib in Patients with Relapsed/Refractory Multiple Myeloma

PURPOSE

Tabalumab, a human mAb that neutralizes B-cell-activating factor (BAFF), demonstrated antitumor activity in xenograft models of multiple myeloma. Here we report on a phase I study of relapsed/refractory multiple myeloma patients in which the primary objective was to identify a tolerable and potentially efficacious dose of tabalumab when combined with bortezomib.

EXPERIMENTAL DESIGN

Forty-eight patients were enrolled; 20 to the dose-escalation cohort, and 28 to cohort expansion in which a dose of 100 mg of tabalumab was evaluated. All patients had received either prior bortezomib or an immunomodulatory drug; the median number of prior therapies was 3. Bortezomib was administered intravenously on days 1, 4, 8, and 11 of a 21-day schedule. Tabalumab was given every 21 days for 3 cycles, then every 42 days thereafter.

RESULTS

The most common grade 3/4 toxicities included thrombocytopenia, neutropenia, pneumonia, and peripheral sensory neuropathy. There were no dose-limiting toxicities, and the maximum tolerated dose was not reached. Pharmacokinetic data suggested serum exposure increased in a greater than dose-proportional manner up to a dose of 100 mg. Out of 46 evaluable patients, 20 had confirmed responses. The median time to progression (9 patients censored) was 4.8 months, and the median response duration (4 patients censored) was 7.2 months.

CONCLUSIONS

A dose of 100 mg tabalumab in combination with bortezomib was well tolerated and active and is currently under further investigation. Clin Cancer Res; 22(23); 5688-95. ©2016 AACR.

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.