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B-cell maturation antigen (BCMA) is selectively expressed as a surface protein on plasma cells and is a validated target for multiple myeloma (MM). A soluble form of BCMA (sBCMA) is elevated in the sera of patients with MM. The bispecific antibodies teclistamab (BCMA×CD3) and talquetamab (G protein-coupled receptor family C group 5 member D [GPRC5D]×CD3) are in clinical development as therapies for MM. Using data from patients with relapsed/refractory MM (N=300) who participated in phase 1 studies of teclistamab (NCT03145181) or talquetamab (NCT03399799), baseline serum sBCMA levels were quantitatively analyzed relative to response to treatment, percentage of bone marrow plasma cells (BMPCs), and cytogenetic risk. By cycle 3 day 1 of treatment, sBCMA levels declined from baseline in 50 (88%) of 57 responders and 49 (98%) of 50 responders to teclistamab and talquetamab, respectively. Depth of response correlated with the magnitude of sBCMA reduction. In contrast, sBCMA increased in 33 (80%) of 41 patients and 24 (49%) of 49 patients who did not respond to teclistamab or talquetamab, respectively. Baseline sBCMA levels correlated with the percentage of BMPC; patients with extramedullary plasmacytomas who had low levels of BMPC (≤10%) tended to have high baseline sBCMA levels (≥400 ng/mL), based on limited data. Baseline sBCMA levels and changes in sBCMA levels at cycle 3 day 1 were similar in patients with high- and standard-risk cytogenetics treated with teclistamab or talquetamab. These results support the use of sBCMA as a potential surrogate marker of tumor burden and treatment response in MM.

PURPOSE Smoldering multiple myeloma (SMM) is a precursor condition of multiple myeloma (MM) with a 10% annual risk of progression. Various prognostic models exist for risk stratification; however, those are based on solely clinical metrics. The discovery of genomic alterations that underlie disease progression to MM could improve current risk models. METHODS We used next-generation sequencing to study 214 patients with SMM. We performed whole-exome sequencing on 166 tumors, including 5 with serial samples, and deep targeted sequencing on 48 tumors. RESULTS We observed that most of the genetic alterations necessary for progression have already been acquired by the diagnosis of SMM. Particularly, we found that alterations of the mitogen-activated protein kinase pathway ( KRAS and NRAS single nucleotide variants [SNVs]), the DNA repair pathway (deletion 17p, TP53, and ATM SNVs), and MYC (translocations or copy number variations) were all independent risk factors of progression after accounting for clinical risk staging. We validated these findings in an external SMM cohort by showing that patients who have any of these three features have a higher risk of progressing to MM. Moreover, APOBEC associated mutations were enriched in patients who progressed and were associated with a shorter time to progression in our cohort. CONCLUSION SMM is a genetically mature entity whereby most driver genetic alterations have already occurred, which suggests the existence of a right-skewed model of genetic evolution from monoclonal gammopathy of undetermined significance to MM. We identified and externally validated genomic predictors of progression that could distinguish patients at high risk of progression to MM and, thus, improve on the precision of current clinical models.

Smoldering multiple myeloma (SMM) is a precursor condition of multiple myeloma (MM) with significant heterogeneity in disease progression. Existing clinical models of progression risk do not fully capture this heterogeneity. Here we integrate 42 genetic alterations from 214 SMM patients using unsupervised binary matrix factorization (BMF) clustering and identify six distinct genetic subtypes. These subtypes are differentially associated with established MM-related RNA signatures, oncogenic and immune transcriptional profiles, and evolving clinical biomarkers. Three genetic subtypes are associated with increased risk of progression to active MM in both the primary and validation cohorts, indicating they can be used to better predict high and low-risk patients within the currently used clinical risk stratification models.

PURPOSE In relapsed and/or refractory multiple myeloma, daratumumab reduced the risk of progression or death by > 60% in POLLUX (daratumumab/lenalidomide/dexamethasone [D-Rd]) and CASTOR (daratumumab/bortezomib/dexamethasone [D-Vd]). Minimal residual disease (MRD) is a sensitive measure of disease control. Sustained MRD negativity and outcomes were evaluated in these studies. METHODS MRD was assessed via next-generation sequencing (10−5) at suspected complete response (CR), 3 and 6 months following confirmed CR (POLLUX), 6 and 12 months following the first dose (CASTOR), and every 12 months post-CR in both studies. Sustained MRD negativity (≥ 6 or ≥ 12 months) was evaluated in the intention-to-treat (ITT) and ≥ CR populations. RESULTS The median follow-up was 54.8 months in POLLUX and 50.2 months in CASTOR. In the ITT population, MRD-negativity rates were 32.5% versus 6.7% for D-Rd versus lenalidomide and dexamethasone (Rd) and 15.1% versus 1.6% for D-Vd versus bortezomib and dexamethasone (Vd; both P < .0001). Higher MRD negativity rates were achieved in ≥ CR patients in POLLUX (D-Rd, 57.4%; Rd, 29.2%; P = .0001) and CASTOR (D-Vd, 52.8%; Vd, 17.4%; P = .0035). More patients in the ITT population achieved sustained MRD negativity ≥ 6 months with D-Rd versus Rd (20.3% v 2.1%; P < .0001) and D-Vd versus Vd (10.4% v 1.2%; P < .0001), and ≥ 12 months with D-Rd versus Rd (16.1% v 1.4%; P < .0001) and D-Vd versus Vd (6.8% v 0%). Similar results for sustained MRD negativity were observed among ≥ CR patients. More patients in the daratumumab-containing arms achieved MRD negativity and sustained MRD negativity, which were associated with prolonged progression-free survival. CONCLUSION Daratumumab-based combinations induce higher rates of sustained MRD negativity versus standard of care, which are associated with durable remissions and prolonged clinical outcomes.

Background B-cell maturation antigen (BCMA, CD269), a single transmembrane protein, can be shed as a soluble 6 kilodalton protein fragment (sBCMA) upon cleavage at the transmembrane domain by γ-secretase. Given its selective expression in the B-cell lineage, BCMA is a validated target for multiple myeloma. Teclistamab and talquetamab are CD3 bispecific antibodies developed to recruit CD3+ T cells to BCMA+ or G protein-coupled receptor family C group 5 member D (GPRC5D)+ multiple myeloma (MM) cells, respectively. Levels of sBCMA after teclistamab or talquetamab treatment were evaluated in patients with relapsed and/or refractory MM (RRMM). Methods Serum samples from patients with RRMM in teclistamab and talquetamab phase 1 studies (64007957MMY1001 and 64407564MMY1001, respectively) were collected at various timepoints between baseline and cycle 4 or end of treatment and analyzed for sBCMA by an electrochemiluminescence ligand binding assay. Quantitative analyses of sBCMA data were conducted with reference to a patient’s tumor burden and response, and to pharmacokinetic data. Results Teclistamab and talquetamab modulated levels of sBCMA in patients with high (≥50%) and low ( Conclusions Changes in the levels of sBCMA upon treatment with teclistamab and talquetamab correlated with clinical activity, supporting further clinical development. The findings support BCMA as a potential surrogate marker of myeloma tumor burden and as a valuable marker for response in patients with MM.

CD38-targeted antibody, daratumumab, is approved for the treatment of multiple myeloma (MM). Phase 1/2 studies GEN501/SIRIUS revealed a novel immunomodulatory mechanism of action (MOA) of daratumumab that enhanced the immune response, reducing natural killer (NK) cells without affecting efficacy or safety. We further evaluated daratumumab’s effects on immune cells in whole blood samples of relapsed/refractory MM patients from both treatment arms of the phase 3 POLLUX study (lenalidomide/dexamethasone [Rd] or daratumumab plus Rd [D-Rd]) at baseline (D-Rd, 40; Rd, 45) and after 2 months on treatment (D-Rd, 31; Rd, 33) using cytometry by time-of-flight. We confirmed previous reports of NK cell reduction with D-Rd. Persisting NK cells were phenotypically distinct, with increased expression of HLA-DR, CD69, CD127, and CD27. The proportion of T cells increased preferentially in deep responders to D-Rd, with a higher proportion of CD8+ versus CD4+ T cells. The expansion of CD8+ T cells correlated with clonality, indicating generation of adaptive immune response with D-Rd. D-Rd resulted in a higher proportion of effector memory T cells versus Rd. D-Rd reduced immunosuppressive CD38+ regulatory T cells. This study confirms daratumumab’s immunomodulatory MOA in combination with immunomodulatory drugs and provides further insight into immune cell changes and activation status following daratumumab-based therapy.

© The Author(s)., Background: Multiple myeloma (MM) patients with high cytogenetic risk have poor outcomes. In CASTOR, daratumumab plus bortezomib/dexamethasone (D-Vd) prolonged progression-free survival (PFS) versus bortezomib/dexamethasone (Vd) alone and exhibited tolerability in patients with relapsed or refractory MM (RRMM). [Methods]: This subgroup analysis evaluated D-Vd versus Vd in CASTOR based on cytogenetic risk, determined using fluorescence in situ hybridization and/or karyotype testing performed locally. High-risk patients had t(4;14), t(14;16), and/or del17p abnormalities. Minimal residual disease (MRD; 10-5 sensitivity threshold) was assessed via the clonoSEQ® assay V2.0. Of the 498 patients randomized, 40 (16%) in the D-Vd group and 35 (14%) in the Vd group were categorized as high risk. [Results]: After a median follow-up of 40.0 months, D-Vd prolonged median PFS versus Vd in patients with standard (16.6 vs 6.6 months; HR, 0.26; 95% CI, 0.19-0.37; P < 0.0001) and high (12.6 vs 6.2 months; HR, 0.41; 95% CI, 0.21-0.83; P = 0.0106) cytogenetic risk. D-Vd achieved deep responses, including higher rates of MRD negativity and sustained MRD negativity versus Vd, regardless of cytogenetic risk. The safety profile was consistent with the overall population of CASTOR. [Conclusion]: These updated data reinforce the effectiveness and tolerability of daratumumab-based regimens for RRMM, regardless of cytogenetic risk status. Trial registration: ClinicalTrials.gov, NCT02136134. Registered 12 May 2014, This CASTOR study was sponsored by Janssen Research & Development, LLC. Open access funding provided by Projekt DEAL.

Introduction: Multiple Myeloma (MM) is an incurable plasma cell malignancy commonly preceded by the asymptomatic stage smoldering multiple myeloma (SMM). MM is characterized with significant genomic heterogeneity of chromosomal gains and losses (CNVs), translocations, and point mutations (SNVs); alterations that are also observed in SMM patients. However, current SMM risk models rely solely on clinical markers and do not accurately capture progression risk. While incorporating some genomic biomarkers improves prediction, using all MM genomic features to comprehensively stratify patients may increase risk stratification precision in SMM. Methods: We obtained a total of 214 patient samples at SMM diagnosis. We performed whole-exome sequencing on 166 tumors; of these, RNA sequencing was performed on 100. Targeted capture was done on 48 additional tumors. Upon binarization of DNA features, we performed consensus non-negative matrix factorization to identify distinct molecular clusters. We then trained a random forest classifier on translocations, SNVs, and CNVs. The predicted clinical outcomes for the molecular subtypes were further validated in an independent SMM cohort of 74 patients. Results: We identified six genomic subtypes, four with hyperdiploidy (>48 chromosomes, HMC, HKR, HNT, HNF) and two with IgH translocations (FMD, CND) (Table 1). In multivariate analysis accounting for IMWG (20-2-20) clinical risk stages, high-risk (HMC, FMD, HKR) and intermediate-risk (HNT, HNF) genetic subtypes were independent predictors of progression (Hazards ratio [HR]: 3.8 and 5.5, P = 0.016 and 0.001, respectively). The low-risk, CND subtype harboring translocation (11;14) was enriched for the previously defined CD-2 MM signature defined by the B cell markers CD20 and CD79A (FDR = 0.003 ), showed upregulation of CCND1, E2F1, and E2F7 (FDR = 0.01, 0.0004, 0.08), and was enriched for G2M checkpoint, heme metabolism, and monocyte cell signature (FDR = 0.003, 0.003, 0.003, respectively). The FMD subtype with IgH translocations (4;14) and (14;16) was enriched for P53, mTORC1, unfolded protein signaling pathways and plasmacytoid dendritic cell signatures (FDR = 0.01, 0.005, 0.008, respectively). The HKR tumors were enriched for inflammatory cytokine signaling, MYC target genes, T regulatory cell signature, and the MM proliferative (PR) signatures (FDR = 0.02, 0.03, 0.007, 0.02, respectively). The APOBEC mutational signature was enriched in HMC and FMD tumors (P = 0.005), while there was no statistical difference across subtypes in the AID signature. The median follow-up for the primary cohort is 7.1 years. Median TTP for patients in HMC, FMD, and HKR was 3.8, 2.6, and 2.2 years, respectively; TTP for HNT and HNF was 4.3 and 5.2, respectively, while it was 11 years in CND patients (P = 0.007). Moreover, by analyzing the changes in MM clinical biomarkers over time, we found that patients from high-risk subgroups had higher odds of developing evolving hemoglobin and monoclonal protein levels over time (P = 0.01 and 0.002, respectively); Moreover, the absolute increase in M-protein was significantly higher in patients from the high-risk genetic subtypes at one, two, and five years from diagnosis (P = 0.001, 0.03, and 0,01, respectively). Applying the classifier to the external cohort replicated our findings where intermediate and high-risk genetic subgroups conferred increased risk of progression to MM in multivariate analysis after accounting for IMWG staging (HR: 5.5 and 9.8, P = 0.04 and 0.005, respectively). Interestingly, within the intermediate-risk clinical group in the primary cohort, patients in the high-risk genetic subgroups had increased risk of progression (HR: 5.2, 95% CI 1.5 - 17.3, P = 0.007). In the validation cohort, these patients also had an increased risk of progression to MM (HR: 6.7, 95% CI 1.2 - 38.3, P = 0.03), indicating that molecular classification improves the clinical risk-stratification models. Conclusion: We identified and validated in an independent dataset six SMM molecular subgroups with distinct DNA alterations, transcriptional profiles, dysregulated pathways, and risks of progression to active MM. Our results underscore the importance of molecular classification in addition to clinical evaluation in better identifying high-risk SMM patients. Moreover, these subgroups may be used to identify tumor vulnerabilities and target them with precision medicine efforts. Figure 1 Figure 1. Disclosures Bustoros: Janssen, Bristol Myers Squibb: Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria. Casneuf: Janssen: Current Employment. Kastritis: Amgen: Consultancy, Honoraria, Research Funding; Takeda: Honoraria; Pfizer: Consultancy, Honoraria, Research Funding; Genesis Pharma: Honoraria; Janssen: Consultancy, Honoraria, Research Funding. Walker: Bristol Myers Squibb: Research Funding; Sanofi: Speakers Bureau. Davies: Takeda: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Dimopoulos: Amgen: Honoraria; BMS: Honoraria; Takeda: Honoraria; Beigene: Honoraria; Janssen: Honoraria. Bergsagel: Genetech: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Patents & Royalties: human CRBN mouse; GSK: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Yong: BMS: Research Funding; Autolus: Research Funding; Takeda: Honoraria; Janssen: Honoraria, Research Funding; Sanofi: Honoraria, Research Funding; GSK: Honoraria; Amgen: Honoraria. Morgan: BMS: Membership on an entity's Board of Directors or advisory committees; Jansen: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees. Getz: IBM, Pharmacyclics: Research Funding; Scorpion Therapeutics: Consultancy, Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees. Ghobrial: AbbVie, Adaptive, Aptitude Health, BMS, Cellectar, Curio Science, Genetch, Janssen, Janssen Central American and Caribbean, Karyopharm, Medscape, Oncopeptides, Sanofi, Takeda, The Binding Site, GNS, GSK: Consultancy.

Introduction: Daratumumab (DARA)-based regimens are effective and well tolerated in both newly diagnosed and relapsed/refractory multiple myeloma (RRMM) patients. However, the prognosis for patients who have become refractory to proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs) and DARA is poor. A better understanding of determinants of response and mechanisms of resistance to DARA may lead to new rationally designed treatment strategies. We therefore characterized the effect of DARA on the immune system in MM patients treated with DARA monotherapy in part A of the DARA-ATRA study (ClinicalTrials.gov NCT02751255). Methods: In part A of this prospective multicenter phase 2 trial, 63 DARA-naïve patients were treated with DARA monotherapy (16 mg/kg; approved schedule). Median number of prior lines of treatment was 4 (range 2-11), all patients were previously exposed to lenalidomide and a PI; 89% was refractory to an IMiD, 71% to a PI and 67% to both IMiD and PI. Bone marrow (BM) aspirates obtained at baseline (BL) and at progression (PD; primary refractory, or acquired resistance after prior response) were subjected to deep immune profiling using 28 surface- and intracellular proteins measured by flow cytometry (BL n=51, PD n=47). In a subset of these patients (BL n=39, PD n=33) mass cytometry (CyTOF) was also performed profiling 39 proteins. In addition, peripheral blood (PB) samples obtained at BL (n=44) and PD (n=37) were analyzed using CyTOF. Computational analyses of flow data were performed using UMAP and FlowSOM; CyTOF data were analyzed using SPADE and Freeviz. Statistical analyses included Wilcoxon rank-sum and signed-rank tests, Generalized Linear Mixed Models and ANOVA. Results: A partial response or better was achieved in 41% of patients treated with DARA monotherapy. We compared immune profiles of responding and non-responding (primary-refractory) patients. At BL, the percentages of MM-, T-, B- and NK cells in BM were similar between both groups. However, NK cells of non-responding patients had a lower proportion of CD16 + (P=0.029), and a higher proportion of TIM-3 + (P=0.010) and HLA-DR + (P=0.043) NK cells, suggesting an exhausted phenotype. Non-responders also had a higher proportion of TIM-3 + CD4 + (P=0.022) and TIM-3 + CD8 + T-cells (P=0.004), and a higher proportion of TIM-3 + regulatory T-cells (Tregs) (P=0.042). A higher proportion of TIM-3 + -NK cells, -T-cells, or -Tregs in BM was also associated with poor progression-free and overall survival (PFS; OS). In addition, clinical characteristics associated with poor PFS such as LDH (P=0.016), extramedullary disease (P=0.001) and (R-)ISS stage III (P=0.015) were associated with an increased number of phenotypically exhausted NK- and T-cells. Similar to prior studies, DARA treatment resulted in reduced levels of CD38 on all immune cell subsets and a marked decrease in Tregs, regulatory B cells (Bregs) and NK cells in both BM and PB. Upon acquired resistance, remaining NK cells displayed higher proportions of TIM-3 + (P=0.022), HLA-DR + (P=0.0007) and LAG-3 + (P=0.011), and lower proportions of CD16 + (P=0.002) (Figure 1), compatible with an exhausted phenotype. Furthermore, disease progression was associated with an increase in CD4 + and CD8 + terminally differentiated effector memory T-cells and a decrease in CD4 + and CD8 + central memory T-cells in BM. There was no significant change in the proportion of T-cells expressing immune checkpoint molecules. CyTOF analysis of BM and PB samples confirmed flow cytometric findings. Furthermore, data-driven analysis identified immune profiles specific to progression, including a significant decrease in the fraction of Granzyme B + NK cells, and increase in the fraction of Granzyme B + Bregs at the time of progression. Based on NK cell depletion and -exhaustion observed at PD, we hypothesized that NK cell repletion may restore DARA sensitivity. Indeed, in ex vivo experiments we show that DARA-resistance can be overcome by addition of healthy donor derived NK cells to MM cells obtained from DARA-refractory patients. Conclusion: Here we show that an increased proportion of NK cells with an exhausted phenotype is associated with primary and acquired DARA-resistance, which is in line with the important role of NK cells in DARA-mediated tumor cell elimination ex vivo. Future DARA-based treatment strategies may benefit from reinvigorating NK cells and restoring their cytotoxic capacities. Figure 1 Figure 1. Disclosures Zweegman: Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees. Minnema: Celgene: Other: Travel expenses; Alnylam: Consultancy; Cilag: Consultancy; Janssen: Consultancy; Kite/Gilead: Consultancy; BMS: Consultancy. Broyl: Celgene/BMS: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Levin: Roche, Janssen, Abbvie: Other: Travel Expenses, Ad-Board. Kersten: Kite/Gilead: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; Roche: Honoraria; Takeda: Consultancy; BMS/Celgene: Consultancy; Miltenyi Biotech: Consultancy. Krevvata: Janssen: Current Employment. Casneuf: Janssen: Current Employment. Abraham: Janssen: Current Employment. Verona: Janssen: Current Employment. Smets: Janssen: Current Employment. Vanhoof: Janssen: Current Employment. Cortes-Selva: Janssen: Current Employment. van Steenbergen: Biolizard working for Janssen: Current Employment. Vieyra: Janssen: Current Employment. Sonneveld: Karyopharm: Consultancy, Honoraria, Research Funding; SkylineDx: Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Mutis: Janssen: Honoraria; Genmab: Research Funding; Takeda: Research Funding; Novartis: Research Funding; ONK Therapeutics: Research Funding. van de Donk: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cellectis: Research Funding; Servier: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Background: Multiple Myeloma (MM) is an incurable plasma cell malignancy with significant genomic heterogeneity. It is usually preceded by the asymptomatic stage known as smoldering multiple myeloma (SMM). SMM patients have a 10% annual risk of progression to MM. Genomic alterations that are observed in SMM patients include chromosomal gains and losses, translocations, and point mutations. However, current SMM risk models rely solely on clinical markers that do not accurately capture the progression risk. While incorporating some genomic biomarkers improves prediction, using all MM genomic features to comprehensively stratify patients may increase the precision of risk models. Methods: We obtained a total of 214 patients' samples at SMM diagnosis in the US and Europe. We performed whole exome sequencing on 166 tumors; of these, RNA sequencing was performed on 100. Targeted capture with a MM gene panel was done on an additional 48 tumors. We identified subgroups using binarized DNA features and performing consensus binary non-negative matrix factorization. Results: We identified six clusters (C1-C6) with the following features: four with a hyperdiploidy (HD) (>48 chromosomes) and two with IgH translocations. These subgroups have unique transcriptomic profiles overlapping with known MM signatures and biological pathways. One of the clusters harboring translocation (11;14), which we call C4-CCND1, was enriched with the previously defined CD-2 MM signature that uniquely expresses B cell markers CD20 and CD79A; shows upregulation of CCND1 and E2F7; and is enriched with pathways like DNA replication, heme metabolism, and NFkB signaling. The C3-MS_MF cluster with the IgH translocations (4;14) and (14;16) shows downregulation of ribosomal genes, TRAF2, and DUSP2. The MYC oncogene was highly expressed in the four HD clusters: C1-HD_NRAS, C2-HD_MAFB, C5-HD_KRAS, and C6-HD_1q (BH-P = 0.037). The clusters also showed different outcomes in terms of time to progression (TTP) to active MM (P = 0.005). Median TTP for patients in C2-HD_MAFB, C3-MS_MF, and C5-HD_KRAS was 3.7, 2.6, and 2.2 years, respectively; TTP for C1-HD_NRAS, C4-CCND1, and C6-HD_1q was 4.3, 11, and not reached, respectively. In multivariate analysis, C2-HD_MAFB, C3-MS_MF, and C5-HD_KRAS were independent predictors of progression after accounting for the clinical risk stage. Moreover, the odds of having evolving hemoglobin and monoclonal protein levels in these three clusters were 3.5 and 12.3 times higher than the other clusters, respectively (P = 0.01 and 0.002). Conclusion: We identified six distinct SMM molecular groups with corresponding transcription profiles and dysregulated pathways. These groups have different progression risks to active MM, with three groups being independent predictors of progression. Our results underscore the importance of molecular classification in MM to better understand and target various tumor vulnerabilities. Citation Format: Shankara Anand, Mark Bustoros, François Aguet, Romanos Sklavenitis-Pistofidis, Robert Redd, Benny Zhitomirsky, Andrew J. Dunford, Yu-Tzu Tai, Selina J. Chavda, Cody Boehner, Carl J. Neuse, Tineke Casneuf, Lorenzo Trippa, Chip Stewart, Kwee Yong, Irene Ghobrial, Gad Getz. Genomic profiling of smoldering multiple myeloma classifies distinct molecular groups [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2240.

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.

8047 Background: B-cell maturation antigen (BCMA, CD269) is a single transmembrane protein that is selectively expressed in the B-cell lineage and is a validated target for multiple myeloma. BCMA exists as both surface protein and as a free soluble form (sBCMA). γ-secretase activity at the transmembrane domain leads to a shed BCMA protein fragment of approximately 6 kilodalton that can exist as free circulating sBCMA in blood. Teclistamab and talquetamab are CD3 bispecific antibodies that have been developed to recruit CD3+ T-cells to BCMA+ or GPRC5D+ multiple myeloma (MM) cells, respectively. The objective of this work was to evaluate sBCMA in relapsed and/or refractory MM patients in response to treatment with teclistamab or talquetamab. Methods: Serum samples from relapsed and/or refractory MM patients in teclistamab and talquetamab phase 1 studies (64007957MMY1001 and 64407564MMY1001) were collected (at various timepoints between baseline and cycle 4 or end of treatment) and analyzed for sBCMA by an electrochemiluminescence ligand binding assay. Soluble BCMA data were quantitatively analyzed in reference to patient’s tumor burden and response, as well as pharmacokinetic data. Results: Teclistamab and talquetamab modulated levels of sBCMA in patients with high ( ≥ 50%) and low ( < 50%) frequency of tumor plasma cells (TPCs), as well as in high and low risk cytogenetic groups. In cycle 3, majority of the responders had reduction in sBCMA [88% (50 out of 57) for teclistamab and 98% (49 out of 50) for talquetamab] compared to baseline. On the contrary, non-responders (progressive disease, stable disease, or minimal response) seemed to show an increase in sBCMA [80% (33 out of 41) for teclistamab and 49% (24 out of 49) for talquetamab] from baseline. Patients with deep responses tend to have higher magnitude of sBCMA reduction compared to others. Based on few patients who responded to teclistamab or talquetamab and then relapsed, sBCMA seemed to have an initial reduction followed by an increase in the levels. Soluble BCMA corelated with % bone marrow TPCs. Majority of patients with plasmacytoma (limited data) seemed to have high sBCMA; suggesting sBCMA could be a comprehensive marker for tumor burden. Teclistamab preliminary population pharmacokinetic analysis showed that sBCMA did not appear to impact teclistamab exposure, suggesting that sBCMA was not acting as a sink for teclistamab. Conclusions: Teclistamab and talquetamab induced changes in levels of sBCMA that correlated with clinical activity, further supporting clinical development of these bispecific antibodies. Lastly, the results support that sBCMA is a potential surrogate marker of myeloma tumor burden, and as a valuable marker for response in MM patients. Clinical trial information: NCT03145181 and NCT03399799.

Introduction: Daratumumab (DARA) is a human IgGκ mAb targeting CD38 with both direct on-tumor and immunomodulatory mechanisms of action, and has been approved as monotherapy for RRMM and in combination with standard of care (SOC) regimens for RRMM and newly diagnosed MM (NDMM). Across three phase 3 DARA studies in RRMM and NDMM, DARA plus SOC reduced the risk of progression or death by ≥50%, enabled a doubling of CR rates, and elicited a ≥3-fold increase in MRD-negative rates. Among MRD-negative RRMM pts, pts treated with D-Rd or D-Vd rapidly achieved MRD negativity and demonstrated prolonged progression-free survival (PFS) vs MRD-positive pts (Avet-Loiseau H, et al. ASH 2016. Abstract 246). MRD assessment is being investigated as a potential surrogate for established endpoints such as overall survival (OS). When measured sequentially, sustained MRD-negativity provides an index of deep clinical responses that may provide a more robust assessment of disease control (Kumar S, et al. Lancet Oncol 2016. 17[8]:e328-e346). Here, we evaluate sustained MRD negativity with DARA plus SOC regimens and its association with PFS/OS outcomes in RRMM. Methods: Eligible pts in POLLUX and CASTOR received ≥1 prior line of therapy and were randomized (1:1) to receive SOC treatment regimens ± DARA. Pts in the POLLUX study were given lenalidomide (25 mg PO) on Days 1-21 and dexamethasone (40 mg) once per week in each 28-day cycle ± DARA (16 mg/kg IV) given weekly for Cycles 1-2, Q2W for Cycles 3-6, and Q4W thereafter. CASTOR pts received 8 cycles (21 d/cycle) of bortezomib (1.3 mg/m2 SC) on Days 1, 4, 8, and 11 and dexamethasone (20 mg) on Days 1, 2, 4, 5, 8, 9, 11, and 12 ± DARA (16 mg/kg IV) given weekly for Cycles 1-3, Q3W for Cycles 4-8, and Q4W thereafter. MRD was assessed at the time of suspected CR and at 3 and 6 months following confirmed CR in POLLUX, and at time of suspected CR and 6 and 12 months following the first treatment dose in CASTOR. Additional MRD evaluation was required in both studies every 12 months post-CR. MRD was assessed via next generation sequencing using the clonoSEQ® assay V2.0 (Adaptive Biotechnologies, Seattle, WA). Sustained MRD negativity was defined as the maintenance of MRD negativity in the bone marrow confirmed ≥6 or ≥12 months apart and was evaluated in the intent-to-treat (ITT) population. Sustained MRD negativity was also evaluated among ≥CR pts to account for different sustained MRD negativity rates between treatment arms. Results: A total of 569 (D-Rd, n = 286; Rd, n = 283) pts in POLLUX and 498 pts (D-Vd, n = 251; Vd, n = 247) in CASTOR were randomized; median (range) number of prior lines received was 1 (1-11) and 2 (1-10), respectively. Median duration of follow up was 39.5 months in POLLUX and 31.3 months in CASTOR for this analysis. Using the ≥6-month sustained MRD cutoff, a significantly higher proportion of pts achieved sustained MRD negativity for ≥6 months when treated with D-Rd vs Rd (16% vs 0.7%; P For the ≥12-month sustained MRD cutoff, more pts achieved sustained MRD negativity when receiving D-Rd vs Rd (13% vs 0.4%; P Additional analyses, including an analysis of baseline pt characteristics for pts with sustained MRD negativity, will be presented at the meeting. Conclusions: DARA combinations with SOC regimens enable a significantly higher proportion of pts to achieve deep and durable responses of ≥CR and MRD negativity at 10-5. Importantly, the ability to reach durable MRD negativity is associated with prolonged survival, suggesting that achieving durable MRD negativity should be a treatment goal for RRMM pts. Disclosures San-Miguel: Sanofi: Honoraria; Novartis: Honoraria; BMS: Honoraria; Amgen: Honoraria; Celgene: Honoraria; Janssen: Honoraria; Roche: Honoraria. Casneuf:Janssen Research & Development: Employment. Iida:Chugai: Research Funding; Astellas: Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Kyowa-Hakko Kirin: Research Funding; MSD: Research Funding; Gilead: Research Funding; Toyama Chemical: Research Funding; Teijin Pharma: Research Funding; Sanofi: Consultancy; Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Ono: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Lonial:Amgen: Research Funding. Usmani:Amgen, BMS, Celgene, Janssen, Merck, Pharmacyclics,Sanofi, Seattle Genetics, Takeda: Research Funding; Abbvie, Amgen, Celgene, Genmab, Merck, MundiPharma, Janssen, Seattle Genetics: Consultancy. Spencer:Celgene: Honoraria, Research Funding, Speakers Bureau; Janssen-Cilag: Honoraria, Research Funding, Speakers Bureau; Amgen: Honoraria, Research Funding; BMS: Research Funding; Takeda: Honoraria, Research Funding, Speakers Bureau; STA: Honoraria. Moreau:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Plesner:Celgene: Other: Independent Response Assessment Comittee; Janssen: Consultancy. Weisel:Amgen, BMS, Celgene, Janssen, Juno, Sanofi, and Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen, BMS, Celgene, Janssen, and Takeda: Honoraria; Amgen, Celgene, Janssen, and Sanofi: Research Funding. Ukropec:Janssen Scientific Affairs, LLC: Employment. Okonkwo:Janssen Research & Development, LLC: Employment. Trivedi:Janssen Research & Development, LLC: Employment. Velas:Janssen Research & Development, LLC: Employment. Qin:Janssen Research & Development, LLC: Employment. Qi:Janssen Research & Development, LLC: Employment. Chiu:Janssen Research & Development, LLC: Employment. Bahlis:Amgen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding.

Background Daratumumab, a human CD38 monoclonal antibody that has direct on-tumor and immunomodulatory mechanisms of action, demonstrated clinical benefit as monotherapy or in combination with established regimens in patients with multiple myeloma with one or more prior lines of therapy. Case presentation A male patient, who was 70 years of age at the time of diagnosis of multiple myeloma in 2011, relapsed after five lines of therapy, including autologous stem cell transplantation. The patient’s disease, which was considered high risk with a deletion of chromosome 17p, advanced quickly and was triple refractory 2 years after diagnosis leaving few treatment options. He was treated with daratumumab monotherapy in the SIRIUS clinical trial resulting in a stringent complete response and clearance of minimal residual disease. The duration of the patient’s clinical response is now over 3.5 years without relapse, compared with a median of 7.6 months for similarly treated patients. The patient’s immunophenotype revealed CD8+ T-cell expansion, clonal expansion of the T-cell receptor repertoire, and decreases in regulatory T cells during daratumumab therapy, suggesting a robust adaptive immune response. This immune response was still present 32 months into daratumumab therapy. Conclusions The results from this case report showed that a patient with advanced multiple myeloma, who had exhausted all treatment options with existing regimens, mounted an ongoing, deep, and durable response to daratumumab monotherapy. Further investigation of the immunologic profile provided additional patient-level evidence of an immunomodulatory mechanism of action of daratumumab. Trial registration ClinicalTrials.gov Identifier number NCT01985126. Submitted 22 July 2013

In the POLLUX study, daratumumab plus lenalidomide/dexamethasone significantly reduced risk of progression/death versus lenalidomide/dexamethasone alone in relapsed/refractory multiple myeloma. We provide one additional year of follow-up and include the effect on minimal residual disease and in clinically relevant subgroups. After 25.4 months of follow-up, daratumumab plus lenalidomide/dexamethasone prolonged progression-free survival versus lenalidomide/dexamethasone alone (median not reached vs 17.5 months; hazard ratio, 0.41; 95% confidence interval, 0.31-0.53; P 12 and =12 months, >6 and =6 months. No new safety signals were observed. In relapsed/refractory multiple myeloma patients, daratumumab plus lenalidomide/dexamethasone continued to improve progression-free survival and deepen responses versus lenalidomide/dexamethasone. TRIAL REGISTRATION: clinicaltrials.gov identifier: NCT02076009.

Daratumumab, a CD38 human monoclonal antibody, demonstrated significant clinical activity in combination with bortezomib and dexamethasone versus bortezomib and dexamethasone alone in the primary analysis of CASTOR, a phase 3 study in relapsed and/or refractory multiple myeloma. A post hoc analysis based on treatment history and longer follow-up is presented. After 19.4 (range: 0 to 27.7) months of median follow-up, daratumumab plus bortezomib and dexamethasone prolonged progression-free survival (median: 16.7 versus 7.1 months; hazard ratio, 0.31; 95% confidence interval, 0.24-0.39; P 12, ≤6, or >6 months), or cytogenetic risk. Minimal residual disease-negative rates were >2.5-fold higher with daratumumab across subgroups. The safety profile of daratumumab plus bortezomib and dexamethasone remained consistent with longer follow-up. Daratumumab plus bortezomib and dexamethasone demonstrated significant clinical activity across clinically relevant subgroups and provided the greatest benefit to patients treated at first relapse.

Daratumumab, a human CD38 imunoglobulin G 1κ monoclonal antibody, has demonstrated clinical activity and a manageable safety profile in monotherapy and combination therapy clinical trials in relapsed and/or refractory multiple myeloma. CD38 is expressed at high levels on myeloma cells and, to a lesser extent, on immune effector cells, including natural killer (NK) cells, which are important for daratumumab-mediated antibody-dependent cellular cytotoxicity (ADCC). Here, the pharmacodynamic effects of daratumumab monotherapy on NK cells, and the effect of NK cell dynamics on daratumumab efficacy and safety, were assessed. Daratumumab, like other CD38 antibodies, reduced NK-cell counts in peripheral blood mononuclear cells (PBMCs) of healthy donors in vitro. Data on NK-cell counts, clinical efficacy, and adverse events were pooled from two single-agent daratumumab studies, GEN501 and SIRIUS. In daratumumab-treated myeloma patients, total and activated NK-cell counts reduced rapidly in peripheral blood after the first dose, remained low over the course of treatment, and recovered after treatment ended. There was a clear maximum effect relationship between daratumumab dose and maximum reduction in NK cells. Similar reductions were observed in bone marrow. PBMCs from daratumumab-treated patients induced lysis by ADCC of CD38+ tumor cells in vitro, suggesting that the remaining NK cells retained cytotoxic functionality. There was no relationship between NK-cell count reduction and the efficacy or safety profile of daratumumab. Furthermore, although NK cell numbers are reduced after daratumumab treatment, they are not completely depleted and may still contribute to ADCC, clinical efficacy, and infection control.

Multiple myeloma (MM) is a malignancy of plasma cells that arises from premalignant Monoclonal Gammopathy of Undetermined Significance (MGUS) and often progresses through an asymptomatic Smoldering (SMM) phase lasting months or years before manifesting clinical symptoms warranting therapy. Current research indicates that the tumor microenvironment (TME) in the bone marrow may play a significant role in governing progression to symptomatic disease. Therefore, understanding of the interactions between malignant plasma cells and the TME in early disease states is critical in the pursuit of therapies that will prevent progression to symptomatic disease. We performed high dimensional genomic and immunologic analysis of bone marrow specimens from 73 subjects with SMM. We performed RNA-seq on the malignant plasma cells isolated by anti-CD138 magnetic bead positive selection, mass cytometry (CyTOF) and T cell receptor sequencing (TCR Seq) of CD138-depleted bone marrow mononuclear cells, and proteomics, seromic, and grand serology analysis of bone marrow plasma. These samples and assays provided a broad view of the tumor cells and the cellular and soluble components of the TME. Each of these assays identified self-organizing clusters of subjects, indicating that subgroups of SMM patients shared common characteristics in the tumor or TME populations. We then applied novel bioinformatic methods to compare data from pairs, trios, quartets, and quintets of assays to identify communities of subjects with similar immunologic and genomic characteristics. Integrated analysis of CyTOF, proteomic, and TCR Seq resolved three distinct communities with a high degree of significance. These communities shared distinct cellular and proteomic features that suggested early adaptive, activated adaptive, or innate immune characteristics. These results suggest that the continuum from MGUS to MM does not consist of a single pathway in either the tumor cells or the TME, and that complex interactions ultimately determine progression. This suite of assays (CyTOF, proteomics, and TCR Seq) may be applicable in translational and clinical studies to understand key tumor and immune determinants of SMM and lead to rationally designed therapy to replicate these conditions to prevent progression to symptomatic disease. Disclosures Cho: Genentech: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; The Multiple Myeloma Research Foundation: Employment; Takeda: Research Funding; BMS: Consultancy; Agenus: Research Funding; GSK: Consultancy. Adams:Janssen Pharmaceuticals R&D: Employment, Other: Own Stock. Parekh:Foundation Medicine Inc.: Consultancy; Celgene Corporation: Research Funding; Karyopharm Inc.: Research Funding.

Interleukin-6 (IL6) plays a central role in multiple myeloma pathogenesis and confers resistance to corticosteroid-induced apoptosis. We therefore evaluated the efficacy and safety of siltuximab, an anti-IL6 monoclonal antibody, alone and in combination with dexamethasone, for patients with relapsed or refractory multiple myeloma who had ≥ 2 prior lines of therapy, one of which had to be bortezomib-based. Fourteen initial patients received siltuximab alone, 10 of whom had dexamethasone added for suboptimal response; 39 subsequent patients were treated with concurrent siltuximab and dexamethasone. Patients received a median of four prior lines of therapy, 83% were relapsed and refractory, and 70% refractory to their last dexamethasone-containing regimen. Suppression of serum C-reactive protein levels, a surrogate marker of IL6 inhibition, was demonstrated. There were no responses to siltuximab but combination therapy yielded a partial (17%) + minimal (6%) response rate of 23%, with responses seen in dexamethasone-refractory disease. The median time to progression, progression-free survival and overall survival for combination therapy was 4.4, 3.7 and 20.4 months respectively. Haematological toxicity was common but manageable. Infections occurred in 57% of combination-treated patients, including ≥ grade 3 infections in 18%. Further study of siltuximab in modern corticosteroid-containing myeloma regimens is warranted, with special attention to infection-related toxicity.

The anti-CD38 monoclonal antibody daratumumab is well tolerated and has high single agent activity in heavily pretreated relapsed and refractory multiple myeloma (MM). However, not all patients respond, and many patients eventually develop progressive disease to daratumumab monotherapy. We therefore examined whether pretreatment expression levels of CD38 and complement-inhibitory proteins (CIPs) are associated with response and whether changes in expression of these proteins contribute to development of resistance. In a cohort of 102 patients treated with daratumumab monotherapy (16 mg/kg), we found that pretreatment levels of CD38 expression on MM cells were significantly higher in patients who achieved at least partial response (PR) compared with patients who achieved less than PR. However, cell surface expression of the CIPs, CD46, CD55, and CD59, was not associated with clinical response. In addition, CD38 expression was reduced in both bone marrow-localized and circulating MM cells, following the first daratumumab infusion. CD38 expression levels on MM cells increased again following daratumumab discontinuation. In contrast, CD55 and CD59 levels were significantly increased on MM cells only at the time of progression. All-trans retinoic acid increased CD38 levels and decreased CD55 and CD59 expression on MM cells from patients who developed daratumumab resistance, to approximately pretreatment values. This resulted in significant enhancement of daratumumab-mediated complement-dependent cytotoxicity. Together, these data demonstrate an important role for CD38 and CIP expression levels in daratumumab sensitivity and suggest that therapeutic combinations that alter CD38 and CIP expression levels should be investigated in the treatment of MM. These trials were registered at www.clinicaltrials.gov as #NCT00574288 (GEN501) and #NCT01985126 (SIRIUS).

8036 Background: Daratumumab (D), a human, CD38-targeting mAb, is well tolerated and induces deep and durable responses in patients (pts) with RRMM. We provide an update of CASTOR (NCT02136134), a multicenter, phase 3, randomized study of DVd vs Vd in RRMM. Methods: All pts received ≥1 prior line of therapy (LOT) and were administered 8 cycles (Q3W) of Vd (1.3 mg/m2 SC bortezomib on days 1, 4, 8, and 11; 20 mg PO/IV dexamethasone on days 1-2, 4-5, 8-9, and 11-12) ± D (16 mg/kg IV once weekly in Cycles 1-3, every 3 weeks for Cycles 4-8, then every 4 weeks until progression). Bortezomib-refractory pts were ineligible. Minimal residual disease (MRD) was assessed upon suspected CR and at 6 and 12 months following the first dose at sensitivities of 10–4, 10–5, and 10–6using the ClonoSEQ assay (Adaptive Biotechnologies, Seattle, WA). Results: Pts received a median (range) of 2 (1-10) prior LOTs. 66% were previously treated with bortezomib and 21% were refractory to lenalidomide in their last prior LOT. After a median follow-up of 13.0 months, PFS was significantly prolonged with DVd vs Vd (median: not reached vs 7.1 months; HR, 0.33; 95% CI, 0.26-0.43; P< 0.0001). This PFS benefit was seen regardless of number of prior LOTs received, with greatest benefit observed in 1 prior line pts (median: not reached vs 7.9 months; HR, 0.22; 95% CI, 0.14-0.34; P< 0.0001). ORR was also significantly higher for DVd vs Vd (84% vs 63%), along with ≥VGPR (62% vs 29%) and ≥CR (26% vs 10%; P< 0.0001 for all). MRD-negative rates were ≥4-fold higher at all three sensitivity thresholds with DVd vs Vd (10% vs 2% at 10–5 threshold). Pts who achieved MRD negativity demonstrated prolonged PFS compared with MRD-positive pts. 37 (15%) and 58 (24%) deaths were observed in DVd vs Vd, respectively, and follow up is ongoing. The most common grade 3/4 TEAE was thrombocytopenia (45% vs 33%). Updated efficacy and safety data will be presented. Conclusions: DVd provided significant benefits with respect to PFS, ORR, depth of response, and MRD-negative rate vs Vd. No new safety signals were reported. These data continue to support the use of DVd in RRMM pts and indicate that pts with 1 prior LOT will derive the most benefit. Clinical trial information: NCT02136134.

Recent analysis of complete eukaryotic genome sequences has revealed that gene duplication has been rampant. Moreover, next to a continuous mode of gene duplication, in many eukaryotic organisms the complete genome has been duplicated in their evolutionary past. Such large-scale gene duplication events have been associated with important evolutionary transitions or major leaps in development and adaptive radiations of species. Here, we present an evolutionary model that simulates the duplication dynamics of genes, considering genome-wide duplication events and a continuous mode of gene duplication. Modeling the evolution of the different functional categories of genes assesses the importance of different duplication events for gene families involved in specific functions or processes. By applying our model to the Arabidopsis genome, for which there is compelling evidence for three whole-genome duplications, we show that gene loss is strikingly different for large-scale and small-scale duplication events and highly biased toward certain functional classes. We provide evidence that some categories of genes were almost exclusively expanded through large-scale gene duplication events. In particular, we show that the three whole-genome duplications in Arabidopsis have been directly responsible for >90% of the increase in transcription factors, signal transducers, and developmental genes in the last 350 million years. Our evolutionary model is widely applicable and can be used to evaluate different assumptions regarding small- or large-scale gene duplication events in eukaryotic genomes.

Introduction: Daratumumab is a human IgGκ monoclonal antibody targeting CD38 with a direct on-tumor and immunomodulatory mechanism of action. Daratumumab induces rapid, deep, and durable responses in combination with a proteasome inhibitor (bortezomib) or an immunomodulatory drug (lenalidomide or pomalidomide) in patients with RRMM (Palumbo A, et al. N Engl J Med 2016. 375(8):754-766; Dimopoulos MA, et al. N Engl J Med 2016.375(14):1319-1331; Chari A, et al. Blood 2017. Epub ahead of print). At the time of the pre-specified interim analysis of the phase 3 study POLLUX (median follow-up of 13.5 months), DRd reduced the risk of disease progression or death by 63% and significantly improved the overall response rate (ORR) compared with Rd alone (92.9% vs 76.4%; P Methods: Patients (pts) who received ≥1 prior line of therapy were randomized (1:1) to Rd (lenalidomide: 25 mg PO on Days 1-21 of each 28-day cycle; dexamethasone: 40 mg PO per week) with or without daratumumab (16 mg/kg IV weekly for Cycles 1 and 2, q2w for Cycles 3-6, then q4w until disease progression). The primary endpoint was progression free survival (PFS). Minimal residual disease (MRD) was assessed on bone marrow aspirate samples at the time of suspected complete response (CR) and at 3 and 6 months after suspected CR at sensitivity thresholds of 10-4, 10-5, and 10-6 via the clonoSEQTM next-generation sequencing assay (V.1.3; Adaptive Biotechnologies, Seattle, WA). For PFS on subsequent line of therapy (PFS2; defined as time from randomization to progression after next line of subsequent therapy or death) was examined as an exploratory endpoint. Results: Pts in both treatment groups (DRd, n=286; Rd, n=283) received a median of 1 prior line of therapy and 18% of patients received prior treatment with lenalidomide. After a median follow-up of 25.4 months, PFS was significantly prolonged with DRd vs Rd (median, not reached [NR] vs 17.5 months; HR, 0.41; 95% CI, 0.31-0.53; P MRD-negative rates were >3-fold higher with DRd vs Rd at all sensitivity thresholds evaluated. At a sensitivity threshold of 10-5, MRD-negative rates were 26% with DRd vs 6% for Rd (P PFS2 was significantly improved with DRd vs Rd in the intent to treat (ITT) population (HR, 0.55; 95% CI, 0.40-0.76; P=0.0002; Figure 2A). Among MRD-negative (10-5) pts who received DRd (n=75) or Rd (n=18), no significant differences in PFS2 were observed between treatment groups (Figure 2B). Time to next therapy was also significantly prolonged with DRd vs Rd in the ITT population (median, NR vs 22.7 months; HR, 0.34; 95% CI, 0.25-0.46; P The most common (≥10%) grade 3/4 TEAEs included neutropenia (54% vs 40%), anemia (16% vs 21%), thrombocytopenia (14% vs 16%), and pneumonia (12% vs 9%), in pts treated with DRd vs Rd, respectively. The incidence of TEAE-related treatment discontinuations was similar between groups, occurring in 12% of pts in both treatment groups. No differences in the incidence of secondary primary malignancies were observed between treatment groups (16 [6%] patients in each group). Updated data will be presented at the meeting. Conclusion: This updated analysis reveals that DRd continues to demonstrate a significant PFS benefit compared with Rd alone, and pt responses continue to deepen with DRd with longer follow up. Pts who receive DRd demonstrated longer time to next therapy and responded more favorably to subsequent therapy as evidenced by prolonged PFS2, suggesting that patients continue to observe clinical benefit from prior daratumumab treatment. Importantly, the favorable safety profile was maintained with longer follow-up. These data support the addition of daratumumab to standard of care regimens in RRMM. Disclosures Dimopoulos: Genesis Pharma: Research Funding; Amgen Inc, Celgene Corporation, Janssen Biotech Inc, Onyx Pharmaceuticals, an Amgen subsidiary, Takeda Oncology: Consultancy, Honoraria, Other: Advisory Committee: Amgen Inc, Celgene Corporation, Janssen Biotech Inc, Onyx Pharmaceuticals, an Amgen subsidiary, Takeda Oncology; Novartis: Consultancy, Honoraria. White: Bristol-Myers Squibb: Consultancy, Honoraria; Amgen, Celgene, Janssen, Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Benboubker: Takeda, Celgene, Janssen, Amgen: Consultancy. Cook: Glycomimetcs: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau. Ho: Amgen, Bristol-Myers Squibb, Celgene, Novartis, Janssen, Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Trivedi: Janssen: Employment. Wu: Janssen: Employment. Casneuf: Janssen: Employment. Chiu: Janssen: Employment. Schecter: Janssen: Employment. Moreau: Amgen: Honoraria; Millennium: Consultancy, Honoraria; Celgene, Janssen, Takeda, Novartis, Amgen, Roche: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria; Onyx Pharmaceutical: Consultancy, Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Consultancy, Honoraria; Takeda: Honoraria; Novartis: Consultancy, Honoraria.

8025 Background: Daratumumab (D) is a human CD38-targeting mAb that significantly prolongs progression-free survival (PFS) when added to standard-of-care regimens in patients (pts) with RRMM. We examined updated efficacy and safety data from POLLUX (NCT02076009), a randomized phase 3 study of DRd vs Rd in RRMM. Methods: Pts with ≥1 prior line of therapy (LOT) received Rd (25 mg PO lenalidomide on days 1-21 of each q4w cycle; 40 mg dexamethasone weekly) ± D (16 mg/kg IV qw for cycles 1 and 2, q2w for cycles 3-6, then q4w until disease progression). Pts refractory to lenalidomide were ineligible. Minimal residual disease (MRD) was assessed on bone marrow samples at time of suspected complete response (CR) and at 3 and 6 months post-suspected CR at sensitivities of 10–4, 10–5, and 10–6 via next-generation sequencing (Adaptive Biotechnologies, Seattle, WA). Results: Pts received a median (range) of 1 (1-11) prior LOT. 55% received prior IMiDs (18% lenalidomide). Based on previous median follow-up of 17.3 months, DRd significantly prolonged PFS (median: not reached vs 17.5 months; HR, 0.37; 95% CI, 0.28-0.50; P< 0.0001) and significantly improved overall response rate (ORR; 93% vs 76%, P< 0.0001) vs Rd. DRd induced higher rates of deep responses vs Rd (≥very good partial response [VGPR]: 78% vs 45%; ≥CR: 46% vs 20%; all P< 0.0001) and included MRD negativity, which was > 3-fold higher across all 3 sensitivity thresholds for DRd vs Rd (25% vs 6% at the 10–5 threshold). MRD-negative pts demonstrated longer PFS vs MRD-positive pts. Follow up for overall survival (OS) is ongoing (OS events: 40 [14%] in DRd and 56 [20%] in Rd). No new safety signals were identified with longer follow up. Updated efficacy and safety data based on approximately 25-months follow up will be presented at the meeting. Conclusions: DRd provided significant benefits vs Rd in terms of PFS, ORR, and MRD negativity, and the favorable safety profile of DRd was maintained with longer follow up. These data further validate the use of DRd in RRMM pts who received ≥1 prior therapy. Clinical trial information: NCT02076009.

Introduction: Daratumumab is a first-in-class monoclonal antibody targeting the plasma cell antigen, CD38, that demonstrated significant activity in combination with bortezomib and dexamethasone (DVd) compared with bortezomib and dexamethasone alone (Vd) in a pre-specified interim analysis of CASTOR, a randomized phase 3 study of relapsed or refractory multiple myeloma (RRMM; Palumbo A. N Engl J Med 2016; in press). In this abstract, we report on subgroup analyses according to the number of prior lines of therapy received, and include outcomes based on cytogenetic status, in order to identify the patient population who derived the most benefit from the DVd combination. Methods: Eligible patients (pts) received at least 1 prior line of therapy and were randomized (1:1) to 8 cycles (q3w) of Vd with or without daratumumab (16 mg/kg IV qw in Cycles 1-3, Day 1 of Cycles 4-8, then q4w until progression). For each cycle, bortezomib 1.3 mg/m2 SC was administered on Days 1, 4, 8, and 11, and dexamethasone 20 mg PO was given on Days 1, 2, 4, 5, 8, 9, 11, 12. Progression-free survival (PFS) was the primary endpoint. Numbers of prior lines of therapy were determined by the site investigator according to the IMWG consensus guidelines. High-risk cytogenetic status based on local laboratory assessments was defined as having at least one of the following abnormalities via karyotyping or fluorescence in-situ hybridization: del17p, t(4;14), or t(14;16). Minimal residual disease (MRD) was evaluated on bone marrow aspirate samples that had been prepared with Ficoll using three different thresholds (10-4, 10-5, and 10-6) based on the ClonoSEQ assay (Adaptive Biotechnologies, Seattle, WA, USA). Results: Median follow-up was 7.4 months. In the 1 to 3 prior lines (1-3 PL) subgroup (DVd, n=229; Vd, n=219), PFS was significantly longer with DVd vs Vd (median: not reached [NR] vs 7.3 mo; HR, 0.39; 95% CI, 0.28-0.55; P In the 1 prior line (1 PL) subgroup (DVd, n=122; Vd, n=113), PFS was also significantly improved for DVd vs Vd (median: NR vs 7.5 mo; HR, 0.31; 95% CI, 0.18-0.52; P Updated efficacy and safety data, including analyses of MRD status across different sensitivity thresholds (10-4, 10-5, and 10-6), will be presented at the meeting. Conclusions: The treatment benefit of DVd vs Vd was maintained across 1-3 PL and 1 PL pts. Responses for DVd were deep and durable and correlated with significantly improved outcomes vs Vd. Despite small group sizes, treatment benefit of DVd vs Vd was also observed in high-risk cytogenetic pts receiving 1-3 PL. These data continue to support the addition of daratumumab to a standard-of-care regimen in RRMM. Figure Progression-free Survival in High-risk Patients (Defined by Cytogenetic Abnormalities) who Received 1 to 3 Prior Lines of Therapy Figure. Progression-free Survival in High-risk Patients (Defined by Cytogenetic Abnormalities) who Received 1 to 3 Prior Lines of Therapy Disclosures Mateos: Janssen, Celgene, Amgen, Takeda, BMS: Honoraria. Estell:Janssen: Membership on an entity's Board of Directors or advisory committees. Corradini:Celgene, Janssen, Novartis, Roche, Takeda, Sanofi, Servier, Gilead: Honoraria; Takeda: Consultancy. Medvedova:Oregon Health and Science University: Employment. Qi:Janssen: Employment. Schecter:Janssen: Employment, Equity Ownership. Amin:Janssen: Employment. Qin:Janssen: Employment. Deraedt:Janssen: Employment; Johnson & Johnson: Equity Ownership. Casneuf:Johnson & Johnson: Equity Ownership; Janssen R&D, Beerse, Belgium: Employment. Chiu:Janssen: Employment. Sasser:Janssen: Employment; Johnson & Johnson: Equity Ownership. Nooka:Amgen, Novartis, Spectrum: Consultancy.

Introduction: Daratumumab is a human monoclonal antibody targeting CD38 that demonstrated superior efficacy in combination with lenalidomide and dexamethasone (DRd) versus lenalidomide and dexamethasone alone (Rd) in a pre-specified interim analysis of a randomized phase 3 study of relapsed or refractory multiple myeloma (RRMM; Dimopoulos MA, et al. N Engl J Med 2016; in press). We report subgroup analyses from this study in patients (pts) who received 1 to 3 prior lines of therapy (1-3 PL), including outcomes based on high-risk cytogenetics within these subgroups. Methods: Patients (pts) who received ≥1 prior line of therapy were randomized (1:1) to Rd (lenalidomide: 25 mg PO on Days 1-21 of each 28-day cycle; dexamethasone: 40 mg PO weekly) with or without daratumumab (16 mg/kg IV qw for 8 weeks, q2w for 16 weeks, then q4w until progression). The primary endpoint was progression-free survival (PFS). The site investigator determined the number of prior lines of therapy according to IMWG consensus guidelines. Treatment-free interval (TFI) was defined as the duration between the end/start date of last line of prior therapy and the date of randomization. Pts with high-risk cytogenetic status had at least one of the following abnormalities as assessed via fluorescence in-situ hybridization or karyotyping by local laboratory assessment: t(4;14), t(14;16), or del17p. Results: In the 1-3 PL subgroup (DRd, n=272; Rd, n=264), PFS was significantly improved with DRd vs Rd (median: not reached [NR] vs 18.4 months; HR, 0.36; 95% CI, 0.25-0.50; P For 1-3 PL pts who had a TFI of >12 months (DRd, n=138; Rd, n=145), median PFS was NR in DRd vs 18.4 months in Rd (HR, 0.42; 95% CI, 0.24-0.74; P=0.0019; Figure A); the estimated 12-month PFS rate was 88.0% vs 74.5%, respectively. ORR was significantly higher with DRd vs Rd (96% vs 86%, P=0.0084), along with rate of VGPR or better (77% vs 56%; P=0.0008) and rate of CR or better (43% vs 27%; P=0.0083). Among pts with a TFI of ≤12 months (DRd, n=134; Rd, n=119), median PFS was NR in DRd vs 10.3 months in Rd (HR, 0.32; 95% CI, 0.21-0.51; P Among pts with 1-3 PL who were refractory to their last line of therapy (DRd, n=73; Rd, n=67), PFS was significantly prolonged with DRd vs Rd (median: NR vs 10.3 mo; HR, 0.42; 95% CI, 0.25-0.72; P=0.0010). ORR (92% vs 66%; P=0.0002), rate of VGPR or better (72% vs 34%; P Data for all subgroup analyses will be updated for the meeting. Conclusions: Responses with DRd were deep and durable which translated into significantly improved clinical outcomes vs Rd in 1-3 PL pts with RRMM. The results of these subgroup analyses suggest that the treatment benefit of DRd vs Rd was maintained across these subgroups, including pts with TFI of ≤12 months and those who were refractory to their last line of therapy. Figure Progression-free survival in patients with 1 to 3 prior lines of therapy and treatment-free interval of (A) >12 months (B) ≤12 months prior to randomization Figure. Progression-free survival in patients with 1 to 3 prior lines of therapy and treatment-free interval of (A) >12 months (B) ≤12 months prior to randomization Disclosures Usmani: Britsol-Myers Squibb: Consultancy, Research Funding; Skyline: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Array: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pharmacyclics: Research Funding; BioPharma: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Millenium: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Speakers Bureau; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Onyx: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Consultancy, Research Funding, Speakers Bureau; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Dimopoulos:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Genesis: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Belch:Celgene: Honoraria; Takeda: Honoraria; Amgen: Honoraria; Janssen: Honoraria. White:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria. Benboubker:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cook:Takeda Oncology: Consultancy, Research Funding, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding, Speakers Bureau; Sanofi: Consultancy, Speakers Bureau; Glycomimetics: Consultancy. Ho:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Khokhar:Janssen: Employment. Guckert:Janssen: Employment; Johnson & Johnson: Equity Ownership. Wu:Janssen: Employment. Qin:Janssen: Employment. Casneuf:Johnson & Johnson: Equity Ownership; Janssen R&D, Beerse, Belgium: Employment. Chiu:Janssen: Employment. Sasser:Janssen: Employment; Johnson & Johnson: Equity Ownership. San-Miguel:Amgen: Membership on an entity's Board of Directors or advisory committees; MSD: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Onyx: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees.

Introduction: Daratumumab (DARA) is a human monoclonal IgG1κ CD38-targeting antibody that functions through several mechanisms of action (MOA), including CDC, ADCC, ADCP and induction of apoptosis. An additional, novel role of immune modulation and increased adaptive immune response was revealed from translational studies of DARA (16 mg/kg) in single-agent, phase 1/2 studies (SIRIUS [MMY2002] and GEN501; Krejcik J et al, Blood 2016;128:384-94). To further explore the ability of DARA to promote adaptive T-cell responses, we profiled T-cell repertoires (TCR) to evaluate T-cell clonality, expansion, and diversity from samples collected in POLLUX (MMY3003), a phase 3, randomized, open-label, multicenter study for patients with relapsed/refractory MM, in which DARA was tested in combination with lenalidomide plus dexamethasone versus lenalidomide plus dexamethasone alone (DRd vs. Rd; Dimopoulos MA et al, N Engl J Med 2016; in press). Methods: T-cell receptor beta (TCRβ) sequencing for repertoire profiling was conducted on whole blood samples collected at baseline and eight weeks after DARA treatment (cycle 3 [C3]) from subjects on both arms using the ImmunoSEQ assay (Adaptive Biotechnologies. Seattle, WA, USA). 133 subjects in DRd and 124 subjects in Rd treatment groups were included in this analysis and represented a balanced subgroup of the POLLUX clinical trial subjects. T-cell metric changes were compared between arms with ANOVA, including the treatment arm and visit interaction term. Within treatment-arm changes were evaluated with a Wilcoxon signed-rank test comparing baseline to on-treatment values per patient. Results: Consistent with the randomized treatment groups, no baseline differences were observed in T-cell repertoire metrics between the treatment arms, including T-cell clonality, diversity (or richness), and T-cell fraction. Similar to prior findings from DARA monotherapy studies, significantly larger increase of TCRβ clonality was observed in the DRd arm (median of 0.166 at baseline to 0.263 at C3). Interestingly, there was no increase in TCRβ clonality in the Rd arm (median of 0.175 at baseline to 0.175 at C3). The change in TCRβ clonality between C1 and C3 was significantly different between DRd and Rd (p=3.26E-10), demonstrating that the addition of DARA to Rd induces a specific clonal expansion of T cells. Estimated richness (diversity), on the other hand, slightly decreased with DRd treatment but not with Rd treatment (median of 503,951 at baseline to 427,096 at C3 [p= 1.01E-04] vs 572,182 to 532,806 [p= 3.58-01]). Among patients in both treatment groups, a bigger increase in T-cell fraction was observed in DRd vs Rd (median of 0.231 at baseline to 0.278 at C3 [p= 2.62E-3] vs 0.228 to 0.249 [p= 1.91E-01]). Although there were no significant differences in baseline characteristics in T-cell clonality, richness, and T-cell fraction, quartile analysis demonstrated that high baseline TCR richness predicted for better PFS with DRd but not for Rd. Conclusion: DARA in combination with lenalidomide plus dexamethasone specifically induced robust increases in T-cell clonality, which was not observed within the control lenalidomide plus dexamethasone arm. Interestingly, baseline TCR richness was associated with improved PFS in DRd subjects. This observation is similar to results with immune checkpoint inhibitors (Postow MA et al, J Immunother Cancer 2015;3:23), and together with the significant increase in T-cell clonality, provides further evidence for the immunomodulatory activity of DARA, even in combination therapy. These data support DARA's immune-modulatory MOA and provide additional insights into DARA's effect on the TCR in combination with standard of care treatment. Figure Figure. Disclosures Chiu: Janssen: Employment. Casneuf:Janssen R&D, Beerse, Belgium: Employment; Johnson & Johnson: Equity Ownership. Axel:Janssen Pharmaceuticals Research and Development: Employment. Lysaght:Immuneering Corp: Employment; Janssen: Research Funding. Bald:Janssen: Employment. Khokhar:Janssen: Employment. Plesner:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Usmani:Amgen: Consultancy, Research Funding, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Onyx: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Millenium: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Skyline: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Speakers Bureau; BioPharma: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pharmacyclics: Research Funding; Array: Research Funding; Britsol-Myers Squibb: Consultancy, Research Funding. Goldschmidt:Onyx: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Chugai: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees. Ahmadi:Janssen: Employment. Chan:Adaptive Biotechnologies: Employment; University of Washington: Other: Visiting scholar. Sasser:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals R&D: Employment.

Introduction: Daratumumab (DARA) is a human CD38-targeting monoclonal antibody that induces deep clinical responses in MM pts through multifaceted mechanisms of action (MOA) including complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis and induction of apoptosis. Flow cytometry analysis revealed a previously unknown immunomodulatory role of DARA, via T-cell induction expansion, T-cell activity enhancement, and reduction of immune suppressive cell populations including CD38+ myeloid-derived suppressor cells, CD38+ regulatory T cells (TRegs), and CD38+ regulatory B cells (BRegs). Next-generation mass cytometry (CyTOF), which allows high parameter evaluation of the immune system, was used to assess the effects of DARA alone or in combination on a more comprehensive profile of immune cell subpopulations. Methods: Relapsed/refractory MM pt samples from a subset of single agent studies; SIRIUS (32 pts; whole blood [WB] only; Lonial S et al. The Lancet, 2016) and GEN501 (5 pts; WB and bone marrow [BM], Lokhorst HM et al. NEJM, 2015) along with GEN503, a study of DARA plus lenalidomide and dexamethasone (9 pts; WB and BM; Plesner T et al. ASH 2015) were analyzed. Fluorochrome or metal-conjugated antibody panel stained samples were evaluated by flow cytometry or cytometry by time-of-flight (CyTOF®) platforms, respectively. FACS analyses were performed and analyzed by FACS Canto II flow cytometers and FACSDiva software. For CyTOF analysis, events were clustered by phenotype by a spanning tree progression of density normalized events (SPADE) algorithm, and each cluster was associated with an immune population via Cytobank® software. Differential analysis of population fractions and marker intensity, over time and between response groups, derived raw P values from t-tests and single cell level bootstrap adjusted P values corrected for multiple dependent hypothesis testing. Results were visualized using SPADE trees (Figure) and Radviz projections, a new method that allows for the comparison of populations and conditions while preserving the relation to original dimensions. Results: Flow cytometry and high-dimensional CyTOF analyses confirmed previous findings including higher CD38 expression on plasma cells compared with other immune populations of natural killer (NK), monocytes, B and T cells, and depletion of both plasma cells and NK cells upon DARA treatment. Interestingly, while NK cells were significantly reduced with DARA treatment, remaining active NK cells (CD16+CD56dim) demonstrated increased expression of activation markers CD69, CD25 and CD137 while also decreasing granzyme B and increasing naive marker CD27. Though functionality tests weren't performed, the ability to evaluate several markers simultaneously suggests these cells possess limited cytotoxicity. Additionally, these studies indicated depletion of CD38 positive immune suppressive subsets of Tregs and Bregs. CD38+ basophil reductions occurred independent of response and may provide insight to short-lived infusion related reactions. Several observations within the T-cell compartment were indicative of a DARA-mediated adaptive response in both WB and BM samples. T cells displayed increases in total numbers and shifted towards higher CD8:CD4 and effector:naïve ratios after 2 months of DARA treatment. Responders had higher expression levels of several activation markers including CD69 and HLA-DR along with increased production of cytolytic enzyme granzyme B in CD8+ T cells following DARA treatment. Interestingly, in the GEN503 sample set, pts who achieved a complete response presented with a distinct BM CD4 T-cell phenotype of high granzyme B positivity versus those that achieved a partial response or very good partial response. This observation suggests pts with an active immune phenotype may achieve deeper responses to DARA in combination with standard of care agents lenalidomide and dexamethasone. Conclusion: CyTOF analysis of pt samples from both single agent and combination DARA studies agree with flow cytometry and support the pharmacodynamics and immune modulatory MOA of DARA while providing additional insight into changes in T-cell subtypes and activation status. Future CyTOF analyses of clinical samples from phase 3 combination studies aim to confirm these observations and expand the understanding of the MOA of DARA. Disclosures Adams: Janssen Research & Development, LLC: Employment. Stevenaert:Janssen: Employment. Van der Borght:Janssen: Employment. Casneuf:Janssen R&D, Beerse, Belgium: Employment; Johnson & Johnson: Equity Ownership. Smets:Janssen: Employment. Bald:Janssen: Employment. Abraham:Janssen: Employment. Ceulemans:Janssen: Employment. Vanhoof:Janssen: Employment; Johnson & Johnson: Equity Ownership. Ahmadi:Janssen: Employment. Usmani:Onyx: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Array: Research Funding; BioPharma: Research Funding; Pharmacyclics: Research Funding; Takeda: Consultancy, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Research Funding; Millenium: Membership on an entity's Board of Directors or advisory committees; Skyline: Membership on an entity's Board of Directors or advisory committees. Plesner:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Lonial:Janssen: Consultancy; BMS: Consultancy; Merck: Consultancy; Novartis: Consultancy; Janssen: Consultancy; Onyx: Consultancy; Onyx: Consultancy; Millenium: Consultancy; Celgene: Consultancy; Novartis: Consultancy; BMS: Consultancy; Celgene: Consultancy. Lokhorst:Genmab: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Mutis:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genmab: Research Funding; Celgene: Research Funding. van de Donk:Janssen: Research Funding; BMS: Research Funding; Amgen: Research Funding; Celgene: Research Funding. Sasser:Janssen Pharmaceuticals R&D: Employment; Johnson & Johnson: Equity Ownership.

Introduction: Daratumumab is a human CD38 IgGκ monoclonal antibody that demonstrated significant activity and a manageable safety profile in combination with bortezomib and dexamethasone. In a randomized phase 3 study, daratumumab in combination with bortezomib and dexamethasone (DVd) significantly prolonged progression-free survival (PFS) versus bortezomib and dexamethasone alone (Vd) in a pre-specified interim analysis of patients (pts) with relapsed or refractory multiple myeloma (RRMM; Palumbo A. N Engl J Med 2016; in press). Herein, we examine subgroups from this study to compare the efficacy of DVd vs Vd in bortezomib-naive and bortezomib-experienced pt populations. In addition, the efficacy of DVd vs Vd in pts who were refractory to lenalidomide at last prior line of therapy was also evaluated. Methods: Pts who received ≥1 prior line of therapy were randomized (1:1) to 8 cycles (q3w) of Vd (bortezomib: 1.3 mg/m2 SC on Days 1, 4, 8, 11; dexamethasone: 20 mg PO on Days 1, 2, 4, 5, 8, 9, 11, 12) with or without daratumumab (16 mg/kg IV qw in Cycles 1-3, Day 1 of Cycles 4-8, then q4w until progression). Pts who were refractory to bortezomib were not eligible. The primary endpoint was PFS. Bone marrow aspirate samples that had been prepared with Ficoll were evaluated for minimal residual disease (MRD) using three different thresholds (10-4, 10-5, and 10-6) based on the ClonoSEQ assay (Adaptive Biotechnologies, Seattle, WA, USA). Results: Median follow-up was 7.4 months. Among bortezomib-naive pts (DVd, n=89; Vd, n=83), PFS was significantly improved with DVd vs Vd (median: not reached [NR] vs 7.5 months; HR, 0.25; 95% CI, 0.13-0.47; P For pts who previously received a bortezomib-containing regimen (DVd, n=162; Vd, n=164), PFS was also significantly longer with DVd vs Vd (median: 12.3 vs 6.7 months; HR, 0.46; 95% CI, 0.32-0.66; P Among pts who were refractory to lenalidomide at the last prior line of therapy (DVd, n=45; Vd, n=60), PFS was significantly longer in DVd vs Vd (median: 10.3 vs 4.4 mo; HR, 0.37; 95% CI, 0.21-0.65; P=0.0004; Figure). Within this subgroup, ORR was significantly higher for DVd vs Vd (81% vs 50%; P=0.0021), and the same trends were observed for rates of ≥VGPR (54% vs 12%; P Updated efficacy and safety data, including MRD analyses across different sensitivity thresholds (10-4, 10-5, and 10-6), will be presented at the meeting. Conclusions: These analyses confirm that addition of daratumumab to Vd significantly improves outcomes for RRMM pts regardless of prior treatment with bortezomib. Importantly, this treatment benefit of DVd vs Vd was maintained in pts who were refractory to lenalidomide at the last prior line of therapy. These data lend further support to adding daratumumab to a standard-of-care regimen in RRMM. Figure Progression-free Survival in Patients Refractory to Lenalidomide at the Last Prior Line of Therapy Figure. Progression-free Survival in Patients Refractory to Lenalidomide at the Last Prior Line of Therapy Disclosures Lentzsch: BMS: Consultancy; Foundation One: Consultancy; Celgene: Consultancy, Honoraria. Quach:Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen Cilag: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Ovilla:Janssen: Consultancy. Qi:Janssen: Employment. Deraedt:Janssen: Employment, Equity Ownership. Schecter:Janssen: Employment, Equity Ownership. Amin:Janssen: Employment. Qin:Janssen: Employment. Casneuf:Johnson & Johnson: Equity Ownership; Janssen R&D, Beerse, Belgium: Employment. Chiu:Janssen: Employment. Sasser:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals R&D: Employment. Sonneveld:Karyopharm: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Research Funding.

Introduction: Daratumumab (DARA) is a human monoclonal IgG1κ CD38 antibody that functions through multifaceted mechanisms of action, including CDC, ADCC, ADCP, induction of apoptosis and immunomodulatory activity (Krejcik et al, Blood 2016;128:384-394). DARA was added to standard of care (SOC) regimens in two randomized, controlled, phase 3 trials in RRMM: POLLUX (DARA+lenalidomide/dexamethasone [DRd] vs lenalidomide/dexamethasone [Rd]) and CASTOR (DARA+bortezomib/dexamethasone [DVd] vs bortezomib/dexamethasone [Vd]). The addition of DARA to these regimens resulted in significant improvements in PFS (hazard ratio for PFS: 0.37 and 0.39 for POLLUX and CASTOR, respectively) and ORR (POLLUX: 93% DRd vs 76% Rd; CASTOR: 83% DVd vs 63% Vd) (Dimopoulos MA et al, N Engl J Med 2016; in press; Palumbo A et al, N Engl J Med 2016; in press). To determine the ability of DARA to drive deep clinical responses beyond complete response (CR), MRD was assessed in both POLLUX and CASTOR using next-generation sequencing (NGS) of B cell receptor (Ig). This is the first comprehensive and prospective study of MRD to date in randomized phase 3 clinical trials of RRMM patients and investigates the ability of DARA-containing regimens to drive deep responses in this challenging population. Methods: MRD was assessed in POLLUX (blinded to treatment group) at the time of suspected CR, and at 3 and 6 months post-suspected CR for patients who maintained this response. Similarly, in CASTOR, MRD was assessed for patients at the time of suspected CR (blinded to treatment group) and at 6 months and 12 months after first dose (at the end and 6 months after end of Vd background therapy, respectively). MRD was assessed on bone marrow aspirate samples prepared using Ficoll and evaluated by the ClonoSEQTM assay (Adaptive Biotechnologies, Seattle, WA, USA) at sensitivities of 0.01% (1 cancer cell per 10,000 nucleated cells or 10-4), 0.001% (10-5), and 0.0001% (10-6). The MRD negative rate per treatment arm was determined as the proportion of patients with negative MRD at any time point after the first dose and compared using the likelihood-ratio test. To allow for a stringent, unbiased evaluation of MRD in these studies, the entire intent-to-treat population was evaluated where patients were considered MRD positive if they had only MRD positive test result or had no MRD assessment. In POLLUX, 63% in DRd and 87% in Rd did not receive a MRD assessment, and for CASTOR, 76% in DVd and 87% in Vd were not assessed for MRD. Results: Median duration of follow-up was 13.5 months and 7.4 months in POLLUX and CASTOR, respectively. The addition of DARA to SOC regimens (Rd in POLLUX or Vd in CASTOR) resulted in significantly higher MRD negative rates at all three thresholds examined (10-4, 10-5, and 10-6; Table). Additionally, patients who achieved MRD negative status experienced fewer PFS events compared with MRD positive patients at a threshold of 10-5 (Figure). Among pts who achieved CR or better, the rate of MRD negativity was at least 3-fold higher across all sensitivity thresholds in the DARA + SOC treatment groups compared with SOC alone. In MRD positive patients, PFS was significantly longer in the DARA + SOC treatment groups compared with SOC alone treatment arms. Updated data from both studies will be presented at the annual meeting. Conclusion: These two studies represent the first randomized, controlled, prospective evaluation of MRD in the RRMM phase 3 clinical trial setting and demonstrate that DARA-containing therapies are able to drive patients to remarkably deep levels of clinical response. Regardless of the SOC component, DARA-containing regimens consistently demonstrated ≥3-fold increase in MRD negative rate compared with the control groups at all evaluated thresholds. Importantly, since patients who achieved MRD negative status demonstrated low PFS event rates, the deep clinical responses induced by DARA may lead to improved survival. Table MRD negative Rate Based on Threshold Used Table. MRD negative Rate Based on Threshold Used Figure Progression-free survival by MRD status in POLLUX and CASTOR Figure. Progression-free survival by MRD status in POLLUX and CASTOR Disclosures Avet-Loiseau: Celgene: Honoraria, Research Funding, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Sanofi: Honoraria, Speakers Bureau; Janssen: Honoraria, Research Funding, Speakers Bureau. Casneuf:Janssen R&D, Beerse, Belgium: Employment; Johnson & Johnson: Equity Ownership. Chiu:Janssen: Employment. Moreau:Janssen: Honoraria, Speakers Bureau; Amgen: Honoraria; Novartis: Honoraria; Takeda: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria. Plesner:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Khokhar:Janssen: Employment. Qi:Janssen: Employment. Schecter:Janssen: Employment, Equity Ownership. Carlton:Adaptive Biotechnologies: Employment, Equity Ownership. Qin:Janssen: Employment. Liu:Janssen: Employment; J&J: Equity Ownership; Merck: Equity Ownership. Wu:Janssen: Employment. Zhuang:Janssen: Employment. Ahmadi:Janssen: Employment. Sasser:J&J: Equity Ownership; Janssen: Employment. San-Miguel:Amgen: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Onyx: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; MSD: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees.

Tineke Casneuf,1 Amy E Axel,2 Peter King,2 John D Alvarez,2 Jillian L Werbeck,3 Tinne Verhulst,1 Karin Verstraeten,1 Brett M Hall,2 A Kate Sasser2 1Janssen Research and Development, Beerse, Belgium; 2Janssen Research and Development, Spring House, PA, 3LabConnect LLC, Seattle, WA, USAIntroduction: Interleukin-6 (IL-6) is an important growth factor for estrogen receptor-α (ERα)-positive breast cancer, and elevated serum IL-6 is associated with poor prognosis.Methods: The role of the phosphorylated signal transducer and activator of transcription 3 pathway was investigated in ERα-positive breast cancer. A panel of cell lines was treated with exogenous IL-6. An IL-6 specific gene signature was generated by profiling ten ERα-positive breast cancer cell lines alone or following treatment with 10 ng/mL recombinant IL-6 or human marrow stromal cell-conditioned media, with or without siltuximab (a neutralizing anti-IL-6 antibody) and grown in three-dimensional tumor microenvironment-aligned cultures for 4 days, 5 days, or 6 days. The established IL-6 signature was validated against 36 human ERα-positive breast tumor samples with matched serum. A comparative MCF-7 xenograft murine model was utilized to determine the role of IL-6 in estrogen-supplemented ERa-positive breast cancer to assess the efficacy of anti-IL-6 therapy in vivo.Results: In eight of nine ERα-positive breast cancer cell lines, recombinant IL-6 increased phosphorylation of tyrosine 705 of STAT3. Differential gene expression analysis identified 17 genes that could be used to determine IL-6 pathway activation by combining their expression intensity into a pathway activation score. The gene signature included a variety of genes involved in immune cell function and migration, cell growth and apoptosis, and the tumor microenvironment. Validation of the IL-6 gene signature in 36 matched human serum and ERα-positive breast tumor samples showed that patients with a high IL-6 pathway activation score were also enriched for elevated serum IL-6 (≥10 pg/mL). When human IL-6 was provided in vivo, MCF-7 cells engrafted without the need for estrogen supplementation, and addition of estrogen to IL-6 did not further enhance engraftment. Subsequently, we prophylactically treated mice at MCF-7 engraftment with siltuximab, fulvestrant, or combination therapy. Siltuximab alone was able to blunt MCF-7 engraftment. Similarly, siltuximab alone induced regressions in 90% (9/10) of tumors, which were established in the presence which were established in the presence of hMSC expressing human IL-6 and estrogen.Conclusion: Given the established role for IL-6 in ERα-positive breast cancer, these data demonstrate the potential for anti-IL-6 therapeutics in breast cancer.Keywords: breast cancer, estrogen receptor, gene signature, paracrine IL-6, siltuximab

The Affymetrix ATH1 array provides a robust standard tool for transcriptome analysis, but unfortunately does not represent all of the transcribed genes in Arabidopsis thaliana. Recently, Affymetrix has introduced its Arabidopsis Tiling 1.0R array, which offers whole-genome coverage of the sequenced Col-0 reference strain. Here, we present an approach to exploit this platform for quantitative mRNA expression analysis, and compare the results with those obtained using ATH1 arrays. We also propose a method for selecting unique tiling probes for each annotated gene or transcript in the most current genome annotation, TAIR7, generating Chip Definition Files for the Tiling 1.0R array. As a test case, we compared the transcriptome of wild-type plants with that of transgenic plants overproducing the heterodimeric E2Fa-DPa transcription factor. We show that with the appropriate data pre-processing, the estimated changes per gene for those with significantly different expression levels is very similar for the two array types. With the tiling arrays we could identify 368 new E2F-regulated genes, with a large fraction including an E2F motif in the promoter. The latter groups increase the number of excellent candidates for new, direct E2F targets by almost twofold, from 181 to 334.

Introduction: Daratumumab (DARA) is a human IgG1κ monoclonal antibody that binds with high affinity to a unique epitope on CD38. DARA monotherapy has shown promising activity in relapsed and/or refractory multiple myeloma (MM) patients with a median of 5 prior lines of therapy in two clinical studies (Study GEN501; Lokhorst HM. J Clin Oncol. 2014;32 Suppl:abstr 8513 and Study MMY2002; Lonial S. J Clin Oncol. 2015;33 Suppl:abstr LBA8512). The aim of this analysis was to identify proteins indicative of DARA's multiple mechanisms of action (MOA) and potential predictive pharmacodynamic response markers. A broad aptamer based proteomics platform (SomaSCANTM) evaluated clinical serum samples at study entry and during treatment to determine proteins and biological pathways associated with DARA MOA or clinical response. Methods: All patients were treated with 16 mg/kg DARA and whole blood samples were collected at baseline and after 8 weeks of treatment. Blood samples were processed for serum and stored frozen until batch analysis. Profiling of 1129 serum proteins was performed using the SOMAscan assay. Patients were classified based on overall best response: responders (stringent and complete responses, very good partial and partial responses), stable disease (stable disease or minimal response) and non-responders (progressive disease). Differential level testing included application of the Wilcoxon rank sum test and Limma for responder versus non-responder analysis, and ANOVA for repeated-measures with post-hoc test validation, Wilcoxon signed rank and Friedman tests for baseline versus on-treatment analysis. Results: In MMY2002 at baseline, 51 proteins were significantly different between responders and non-responders. Many have known associations with MM or CD38, and interestingly a subset is associated with T-cell biology. We recently observed that DARA induces a multi-factorial T-cell response in patients including CD8+ T-cell expansion and activation, and increased clonality. Proteins differentially expressed between responders/non-responders at baseline included tumor necrosis factor subfamily 8 (TNFSF8/CD30L), TNFSF9/CD137L, macrophage stimulating 1 (MST1), interleukin-1B (IL1B), cadherin 1 (CDH1) and cadherin 3 (CDH3). Protein profiles were evaluated at baseline and at 8 weeks (Cycle 3 Day 1) to study pharmacodynamic changes. Significant treatment-induced changes were identified in 142 proteins. Of particular interest were the 60 proteins that changed differentially over time in responders vs non-responders. Proteins associated with MM tumor load, such as beta-2-microglobulin [B2M], and immunoglobulins decreased in responders and increased in non-responders. Novel MM therapeutic targets such as signaling lymphocyte activation molecule F7 [SLAMF7] (i.e. CS1) and B-cell maturation antigen [BCMA] decreased in responders and increased in non-responders during DARA treatment. Many proteins associated with immune or T-cell response were also significantly changed by DARA treatment, including TNFRSF1B, CD163, TNFRSF25, TLR2, CCL5, IL5RA, FCGR2A, ICOS, Granzyme B, and programmed cell death ligand 1 [PD-L1] many of which were differential between responders and non-responders. Differential level testing of GEN501 samples identified a small set of proteins that were significantly altered by DARA treatment over time. Many of these proteins overlapped with those identified in the MMY2002 analysis, increasing confidence in the statistical results. Conclusions: This exploratory serum proteomic analysis identified proteins that were differentially expressed between responders and non-responders at baseline, including proteins associated with immune response and T-cell biology (TNFSF8/CD30L, TNFSF9/CD137L, IL1B). In addition, significant differential changes in protein expression between responders and non-responders after DARA treatment were seen. Many of these are associated with MM tumor load (BCMA, immunoglobulins, SLAMF7, and B2M) and decreased in responders and increased in non-responders. In addition, proteins related to T-cell activity, immune checkpoints and immune response (TNFRSF1B, CD163, TNFRSF25, TLR2, CCL5, IL5RA, FCGR2A, ICOS, Granzyme B, PD-L1) also showed changes associated with DARA treatment, supporting the recent findings that DARA induces a T-cell response in MM patients that may contribute to clinical response. Disclosures Casneuf: Janssen: Employment. Lysaght:Immuneering Corp: Employment, Other: Stockholder. LeFave:Immuneering Corp.: Employment. Bald:Janssen: Employment. Weiss:Janssen and Millennium: Consultancy; Janssen and Onclave: Research Funding. van de Donk:Janssen Pharmaceuticals: Research Funding; Amgen: Research Funding; Celgene: Research Funding. Lokhorst:Amgen: Honoraria; Janssen: Honoraria, Research Funding; Genmab: Honoraria, Research Funding. Ahmadi:Janssen: Employment.

Introduction: Daratumumab (DARA) is a novel human monoclonal antibody that targets CD38, a protein that is highly expressed on multiple myeloma (MM) cells. DARA acts through multiple immune effector-mediated mechanisms, including complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and antibody-dependent cellular phagocytosis. In two clinical studies (NCT00574288 [GEN501] and NCT01985126 [Sirius]) of DARA monotherapy in patients with relapsed and refractory MM, overall response rates were 36% and 29%, respectively. CD38 is highly expressed in myeloma cells but also expressed in lymphocytes and other immune cell populations. Therefore, the effects of DARA on immune cell populations and adaptive immune response pathways were investigated. Methods: The patient population investigated included treated subjects with MM that were relapsed after or were refractory to ≥2 prior therapies (GEN501) or had received ≥3 prior therapies, including a proteasome inhibitor (PI) and an immunomodulatory drug (IMiD), or were refractory to both a PI and an IMiD (Sirius). Patients assessed in this analysis were treated with 16 mg/kg DARA. When both studies were combined, median age (range) was 64 (31-84) years and median time from diagnosis was 5.12 (0.77-23.77) years. Seventy-six percent of patients had received >3 prior therapies and 91% were refractory to their last treatment. Clinical response was evaluated using IMWG consensus recommendations. Peripheral blood (PB) samples and bone marrow (BM) biopsies/aspirates were taken at prespecified time points and immunophenotyped by flow cytometry to enumerate various T-cell sub-types. T-cell clonality was measured by TCR sequencing. Antiviral T-cell response and regulatory T-cell (Treg) activity were analysed by functional in vitro assays. T-cell subpopulation counts were modelled over time with linear mixed modelling. Two group comparisons were performed using non-parametric Wilcoxon rank sum tests. Results: Data from 148 patients receiving 16 mg/kg DARA in GEN501 (n = 42) and Sirius (n = 106) were analyzed for changes in immune response. In PB, robust mean increases in CD3+ (44%), CD4+ (32%) and CD8+ (62%) T-cell counts per 100 days were seen with DARA treatment. However, responding evaluable patients (n = 45) showed significantly greater increases from baseline than nonresponders (n = 93) in CD3+ (P = 0.00012), CD4+ (P = 0.00031), and CD8+ (P = 0.00018) T cells. In BM aspirates the number of CD3+, CD4+, and CD8+ T-cells increased during treatment compared to baseline (the median percent increases were 19.95%, 5.66%, and 26.99% [n = 58]). Additionally, CD8+: CD4+ T-cell ratios significantly increased compared to baseline in both PB (P = 0.00017), and BM (P = 0.00016). T cell clonality, assessed by TCR sequencing, increased after DARA treatment compared with pretreatment (P = 0.049), with greater sums of absolute expansion in the repertoire (P = 0.037), as well as greater maximum expansion of a single clone (P = 0.048) in responders compared to nonresponders. Increased antiviral T-cell responses were observed post-DARA treatment, particularly in responders. Interestingly, a novel subpopulation of regulatory T cells was identified that expressed high levels of CD38. These cells comprised ~10% of all Tregs and were depleted by one DARA infusion. In ex vivo analyses, CD38+ Tregs appeared to be highly immune suppressive compared to CD38-Tregs. Conclusions: Robust T cell increases, increased CD8+: CD4+ ratios, increased antiviral responses, and increased T cell clonality were all observed after DARA treatment in a heavily pretreated, relapsed, and refractory patient population not expected to have strong immune responses. Improved clinical responses were associated with changes in these parameters. In addition, a sub-population of regulatory T cells expressing high CD38 levels was determined to be extremely immune suppressive and sensitive to DARA treatment. These data suggest a previously unknown immune modulatory role of DARA that may contribute to its efficacy, and a potential role for CD38 immune targeted therapies. We postulate that there are several distinct and complementary mechanisms that contribute to DARA's efficacy including increased antigen presentation through phagocytosis, targeting of immune suppressive Tregs, and increased adaptive immune responses. JK and TC contributed equally to this work. Disclosures Casneuf: Janssen: Employment. Verbist:Janssen: Employment. Bald:Janssen: Employment. Plesner:Genmab: Membership on an entity's Board of Directors or advisory committees; Roche and Novartis: Research Funding; Janssen and Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Liu:Janssen: Employment. van de Donk:Janssen Pharmaceuticals: Research Funding; Amgen: Research Funding; Celgene: Research Funding. Weiss:Janssen and Onclave: Research Funding; Janssen and Millennium: Consultancy. Ahmadi:Janssen: Employment. Lokhorst:Genmab: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Amgen: Honoraria. Mutis:Janssen: Research Funding; Genmab: Research Funding.