BACKGROUNDMultiple myeloma cells uniformly overexpress CD38. We studied daratumumab, a CD38-targeting, human IgG1κ monoclonal antibody, in a phase 1-2 trial involving patients with relapsed myeloma or relapsed myeloma that was refractory to two or more prior lines of therapy. METHODSIn part 1, the dose-escalation phase, we administered daratumumab at doses of 0.005 to 24 mg per kilogram of body weight. In part 2, the dose-expansion phase, 30 patients received 8 mg per kilogram of daratumumab and 42 received 16 mg per kilogram, administered once weekly (8 doses), twice monthly (8 doses), and monthly for up to 24 months. End points included safety, efficacy, and pharmacokinetics. RESULTSNo maximum tolerated dose was identified in part 1. In part 2, the median time since diagnosis was 5.7 years. Patients had received a median of four prior treatments; 79% of the patients had disease that was refractory to the last therapy received (64% had disease refractory to proteasome inhibitors and immunomodulatory drugs and 64% had disease refractory to bortezomib and lenalidomide), and 76% had received autologous stem-cell transplants. Infusion-related reactions in part 2 were mild (71% of patients had an event of any grade, and 1% had an event of grade 3), with no dose-dependent adverse events. The most common adverse events of grade 3 or 4 (in ≥5% of patients) were pneumonia and thrombocytopenia. The overall response rate was 36% in the cohort that received 16 mg per kilogram (15 patients had a partial response or better, including 2 with a complete response and 2 with a very good partial response) and 10% in the cohort that received 8 mg per kilogram (3 had a partial response). In the cohort that received 16 mg per kilogram, the median progression-free survival was 5.6 months (95% confidence interval [CI], 4.2 to 8.1), and 65% (95% CI, 28 to 86) of the patients who had a response did not have progression at 12 months.

• CD38-expressing immunosuppressive regulatory T and B cells and myeloid-derived suppressor cells were sensitive to daratumumab treatment.• Cytotoxic T-cell number, activation, and clonality increased after daratumumab treatment in heavily pretreated relapsed and refractory MM.Daratumumab targets CD38-expressing myeloma cells through a variety of immunemediated mechanisms (complement-dependent cytotoxicity, antibody-dependent cellmediated cytotoxicity, and antibody-dependent cellular phagocytosis) and direct apoptosis with crosslinking. These mechanisms may also target nonplasma cells that express CD38, which prompted evaluation of daratumumab's effects on CD38-positive immune subpopulations. Peripheral blood (PB) and bone marrow (BM) from patients with relapsed/refractory myeloma from 2 daratumumab monotherapy studies were analyzed before and during therapy and at relapse. Regulatory B cells and myeloid-derived suppressor cells, previously shown to express CD38, were evaluated for immunosuppressive activity and daratumumab sensitivity in the myeloma setting. A novel subpopulation of regulatory T cells (Tregs) expressing CD38 was identified. These Tregs were more immunosuppressive in vitro than CD38-negative Tregs and were reduced in daratumumab-treated patients. In parallel, daratumumab induced robust increases in helper and cytotoxic T-cell absolute counts. In PB and BM, daratumumab induced significant increases in CD8 1 :CD4 1 and CD8 1:Treg ratios, and increased memory T cells while decreasing naïve T cells. The majority of patients demonstrated these broad T-cell changes, although patients with a partial response or better showed greater maximum effector and helper T-cell increases, elevated antiviral and alloreactive functional responses, and significantly greater increases in T-cell clonality as measured by T-cell receptor (TCR) sequencing. Increased TCR clonality positively correlated with increased CD81 PB T-cell counts. Depletion of CD38 1 immunosuppressive cells, which is associated with an increase in T-helper cells, cytotoxic T cells, T-cell functional response, and TCR clonality, represents possible additional mechanisms of action for daratumumab and deserves further exploration. (Blood. 2016;128(3):384-394)

Purpose Daratumumab treatment results in a marked reduction of CD38 expression on multiple myeloma (MM) cells. The aim of this study was to investigate the clinical implications and the underlying mechanisms of daratumumab-mediated CD38 reduction. Experimental design We evaluated the effect of daratumumab alone or in combination with lenalidomide-dexamethasone, on CD38 levels of MM cells and non-tumor immune cells in the GEN501 study (daratumumab monotherapy) and the GEN503 study (daratumumab combined with lenalidomide-dexamethasone). In vitro assays were also performed. Results In both trials daratumumab reduced CD38 expression on MM cells within hours after starting the first infusion, regardless of depth and duration of the response. In addition, CD38 expression on non-tumor immune cells, including NK-, T- B-cells and monocytes, was also reduced irrespective of alterations in their absolute numbers during therapy. In-depth analyses revealed that CD38 levels of MM cells were only reduced in the presence of complement or effector cells, suggesting that the rapid elimination of CD38high MM cells can contribute to CD38 reduction. In addition, we discovered that daratumumab-CD38 complexes and accompanying cell membrane were actively transferred from MM cells to monocytes and granulocytes. This process of trogocytosis was also associated with reduced surface levels of some other membrane proteins including CD49d, CD56, and CD138. Conclusion Daratumumab rapidly reduced CD38 expression levels, at least in part, through trogocytosis. Importantly, all these effects also occurred in patients with deep and durable responses, thus excluding CD38 reduction alone as a mechanism of daratumumab resistance.

Key Points• Daratumumab plus lenalidomide/dexamethasone elicited an overall response rate of 81% (63% very good partial response or better).• Adverse events were manageable and in accord with the individual toxicity profiles of daratumumab and lenalidomide/ dexamethasone.Daratumumab, a human CD38 immunoglobulin G1 kappa (IgG1k) monoclonal antibody, has activity as monotherapy in multiple myeloma (MM). This phase 1/2 study investigated daratumumab plus lenalidomide/dexamethasone in refractory and relapsed/refractory MM. Part 1 (dose escalation) evaluated 4 daratumumab doses plus lenalidomide (25 mg/day orally on days 1-21 of each cycle) and dexamethasone (40 mg/week). Part 2 (dose expansion) evaluated daratumumab at the recommended phase 2 dose (RP2D) plus lenalidomide/dexamethasone. Safety, efficacy, pharmacokinetics, immunogenicity, and accelerated daratumumab infusions were studied. In part 1 (13 patients), no dose-limiting toxicities were observed, and 16 mg/kg was selected as the R2PD. In part 2 (32 patients), median time since diagnosis was 3.2 years, with a median of 2 prior therapies (range, 1-3 prior therapies), including proteasome inhibitors (91%), alkylating agents (91%), autologous stem cell transplantation (78%), thalidomide (44%), and lenalidomide (34%); 22% of patients were refractory to the last line of therapy. Grade 3 to 4 adverse events ( ‡5%) included neutropenia, thrombocytopenia, and anemia. In part 2, infusion-related reactions (IRRs) occurred in 18 patients (56%); most were grade £2 (grade 3, 6.3%). IRRs predominantly occurred during first infusions and were more common during accelerated infusions. In part 2 (median follow-up of 15.6 months), overall response rate was 81%, with 8 stringent complete responses (25%), 3 complete responses (9%), and 9 very good partial responses (28%). Eighteen-month progression-free and overall survival rates were 72% (95% confidence interval, 51.7-85.0) and 90% (95% confidence interval, 73.1-96.8), respectively. Daratumumab plus lenalidomide/dexamethasone resulted in rapid, deep, durable responses. The combination was well tolerated and consistent with the safety profiles observed with lenalidomide/ dexamethasone or daratumumab monotherapy. This trial was registered at www.clinicaltrials.gov as

Daratumumab is a CD38‐targeted human monoclonal antibody with direct anti‐myeloma cell mechanisms of action. Flow cytometry in relapsed and/or refractory multiple myeloma (RRMM) patients treated with daratumumab revealed cytotoxic T‐cell expansion and reduction of immune‐suppressive populations, suggesting immune modulation as an additional mechanism of action. Here, we performed an in‐depth analysis of the effects of daratumumab on immune‐cell subpopulations using high‐dimensional mass cytometry. Whole‐blood and bone‐marrow baseline and on‐treatment samples from RRMM patients who participated in daratumumab monotherapy studies (SIRIUS and GEN501) were evaluated with high‐throughput immunophenotyping. In daratumumab‐treated patients, the intensity of CD38 marker expression decreased on many immune cells in SIRIUS whole‐blood samples. Natural killer (NK) cells were depleted with daratumumab, with remaining NK cells showing increased CD69 and CD127, decreased CD45RA, and trends for increased CD25, CD27, and CD137 and decreased granzyme B. Immune‐suppressive population depletion paralleled previous findings, and a newly observed reduction in CD38 + basophils was seen in patients who received monotherapy. After 2 months of daratumumab, the T‐cell population in whole‐blood samples from responders shifted to a CD8 prevalence with higher granzyme B positivity ( P = 0.017), suggesting increased killing capacity and supporting monotherapy‐induced CD8 + T‐cell activation. High‐throughput cytometry immune profiling confirms and builds upon previous flow cytometry data, including comparable CD38 marker intensity on plasma cells, NK cells, monocytes, and B/T cells. Interestingly, a shift toward cytolytic granzyme B + T cells was also observed and supports adaptive responses in patients that may contribute to depth of response. © 2018 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

This mini-review will summarize the present state of development of the CD38 antibody daratumumab for the treatment of multiple myeloma.

Introduction : Daratumumab (DARA) is a human anti-CD38 IgG1κ monoclonal antibody that showed synergistic anti-tumor activity in combination with lenalidomide (LEN) in in vitro preclinical studies (van der Veer M. Haematologica 2011;96(2):284-90). DARA has shown favorable safety and robust efficacy as a single agent in patients with relapsed and refractory (RR) multiple myeloma (MM) (Lokhorst HM. J Clin Oncol 2014;32 Suppl:abstr 8513. Lonial S. J Clin Oncol 2015;33 Suppl:abstr LBA8512) and in combination with LEN/Dexamethasone (DEX) in patients with relapsed or RR MM (Plesner T. Blood 2014;124(21):84). This study assessed the updated safety and efficacy of DARA in combination with LEN/DEX following more than 12 months of exposure in patients with relapsed or RR MM. Methods : The study design of this ongoing, open-label phase 1/2 study of DARA in combination with LEN/DEX has been presented previously (Plesner T. Blood 2014;124(21):84). Briefly, the study comprised a 3 + 3 design dose escalation study (DARA 2-16 mg/kg + LEN/DEX; Part 1) and a cohort expansion study using the recommended phase 2 dose (DARA 16 mg/kg + LEN/DEX; Part 2). In Part 2, patients refractory to LEN were excluded and patients with ≥1 prior line of therapy were included. In Part 2, DARA 16 mg/kg was administered weekly during the first two 28-day cycles, every other week during Cycles 3 through 6, and monthly in Cycle 7 and beyond until disease progression or unacceptable toxicity. LEN 25 mg was administered orally on Days 1 through 21 of each cycle, and DEX 40 mg was given weekly. The primary objective was safety. Efficacy was evaluated per the International Myeloma Working Group criteria. The last patient was enrolled in August 2014. Results: Updated safety and efficacy results (data cut January 9, 2015) of DARA 16 mg/kg plus LEN/DEX in the expansion cohort (n = 32) are presented. The median (range) number of prior lines of therapy was 2 (1-3) and the median (range) duration of follow up was 7.8 (3.0-10.4) months. Eleven (34%) patients received prior LEN treatment. Six (19%) patients discontinued treatment due to either disease progression (n = 3), treatment-emergent adverse events (TEAE; 1 patient with gastric adenocarcinoma and 1 patient with laryngeal edema that was a grade 3 infusion-related reaction [IRR]), or physician decision (n = 1). The most common (>25%) TEAEs included neutropenia (81%), muscle spasms (44%), cough (38%), diarrhea (34%), fatigue and hypertension (28% each). Only 1 (3%) patient experienced febrile neutropenia (grade 1). Neutropenia was the most frequently (>25%) reported grade 3 or 4 TEAE (75%). Eighteen (56%) patients had IRRs and these were generally mild to moderate and occurred mostly during the first cycle. IRRs included cough (25%), allergic rhinitis, nausea, and vomiting (9% each), as well as dyspnea, nasal congestion, and hypertension (6% each). Two (6%) patients had grade 3 IRRs (laryngeal edema and hypertension). All patients with IRRs recovered and continued to receive treatment, with the exception of the patient with grade 3 laryngeal edema, who recovered but was discontinued from treatment per protocol. The overall response rate (Rajkumar SV. Blood. 2011;117:4691-5) was 88%, with 11 (34%) partial responses and 17 (53%) ≥very good partial responses (VGPRs) that included 7 (22%) stringent complete responses, 1 (3%) complete response, and 9 (28%) VGPRs. The median time to first and best response was 1 (95% confidence interval [CI], 0.9-1.9) month and 4.5 (95% CI, 1.9-5.6) months, respectively. The median duration of response was not reached, as 26 (93%) of 28 responders had not progressed or relapsed at the time of this analysis and remained on treatment at data cutoff. Importantly, responses deepened over time in 17 (61%) of 28 responders. The 12-month duration of response will be updated at the time of ASH. Conclusions : In the expansion cohort, the combination of DARA and LEN/DEX continues to be associated with a remarkably favorable benefit/risk profile for treatment of relapsed or RR MM. Deep and durable responses were maintained throughout the study. Additional updates on the safety and efficacy results of the expansion cohort with over 12 months of exposure will be presented at the time of the meeting. Disclosures Plesner: Roche and Novartis: Research Funding; Janssen and Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genmab: Membership on an entity's Board of Directors or advisory committees. Gimsing:Amgen: Honoraria. Laubach:Novartis: Research Funding; Onyx: Research Funding; Celgene: Research Funding; Millennium: Research Funding. Palumbo:Novartis, Sanofi Aventis: Honoraria; Celgene, Millennium Pharmaceuticals, Amgen, Bristol-Myers Squibb, Genmab, Janssen-Cilag, Onyx Pharmaceuticals: Consultancy, Honoraria. Lisby:Genmab: Employment. Basse:Genmab A/S: Employment. Wang:Janssen: Employment. Sasser:Janssen Pharmaceuticals: Employment. Guckert:Janssen: Employment. Yeh:Janssen: Employment. Ahmadi:Janssen: Employment. Lokhorst:Genmab: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Amgen: Honoraria. Richardson:Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Millennium Takeda: Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees.

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