TNB‐383B is a fully human BCMA‐targeting T‐cell engaging bispecific monoclonal antibody (T‐BsAb). We assessed ex vivo efficacy of this drug to mediate killing of bone marrow mononuclear cells (BMMCs) freshly isolated from 10 patients with relapsed multiple myeloma (MM). BMMC were treated ex vivo with TNB‐383B at doses ranging from 0.001‐1 μg. Plasma cell (PC) lysis, viability, BCMA expression, CTL distribution, and degranulation were assessed by flow cytometry. Cytokine response to TNB‐383B was quantified by multiplex protein assay. Dose‐dependent PC lysis was triggered in all cases by TNB‐383B at doses as low as 0.001 μg (P = .0102). Primary MM cells varied in BCMA expression. High BCMA+ PC count correlated with increased PC lysis (P = .005) and significant CTL degranulation specific to TNB‐383B treatment (P = .0153 at 1 μg). High E:T ratio in bone marrow specimens led to lower viable and higher apoptotic PC compared with low E:T ratio (P < .001). Three cytokines were significantly modulated by TNB‐383B: IL‐2/TNFα increased by ∼4 ± 3.5‐fold average (P < .005 at 1 μg) and IP10 increased by ∼50 ± 15‐fold (P < .001 at 1 μg). We conclude that TNB‐383B triggers primary PC lysis and CTL degranulation in a dose‐dependent fashion ex vivo with no T cell expansion and mild increase of CRS‐associated cytokines.
INTRODUCTION: The human B-Cell maturation antigen (BCMA) is a surface marker that is highly expressed on plasma cells and has been recognized as a novel target in multiple myeloma (MM). TNB-383B is a fully human bispecific monoclonal IgG4 antibody. TNB-383B consists of 2 heavy and 1 light chain(s) paired through knob-in-hole technology. The first heavy chain and a kappa light chain form the paratope to recognize and bind human CD3. The second heavy chain is comprised of two identical VH domains in sequence and targets human BCMA with high affinity and avidity. Herein, we describe the ability of TNB-383B to mediate killing of patient-derived tumor cell lysis by endogenous T-cells was assessed ex vivo. METHODS: Bone marrow mononuclear cells (BMMCs) were isolated by density gradient centrifugation from 7 relapsed MM patients enrolled in an IRB-approved biospecimen collection protocol. Freshly isolated BMMC subsets were characterized by flow cytometry, specifically plasma cell (PC) / cytotoxic T cell (CTL) distribution, PC BCMA expression and PC viability were determined. BMMCs were then incubated for 24h (± 2h) with TNB-383B, or negative control, at concentrations ranging from 0.001-1μg. Following incubation, PC lysis, viability, BCMA expression, as well as CTL distribution and degranulation were assessed by flow cytometry. Tukey's sequential trend test was performed for each measured variable, utilizing ANOVA models and contrast statements, to detect linear dose response trends to TNB-383B or negative control treatments. Additionally, a parametric model (EMax) was used for each measured variable to estimate dose response curves, interpolating between tested doses. Two-way factorial ANOVA was utilized to compare the main effects of E:T ratio (or PC phenotype) and dose level and the interaction effect between E:T ratio and dose level on measured variables. RESULTS: Dose-dependent PC lysis was triggered by TNB-383B at concentrations as low as 0.001μg (p=0.0102) while no significant loss of PC was observed with negative control (Figure). This effect was coupled with significant CTL degranulation as expressed by increased CD107a mean fluorescence intensity (MFI) specific to TNB-383B treatment (p=0.0153 at 1μg). Although apoptotic rates (7-AAD+, Annexin V+) of the remaining PC tend to increase among TNB-383B treated compared with isotype control-treated cells, this trend was not significant. As opposed to CTL degranulation, CTL proliferation was not significantly triggered by TNB-383B but was significantly increased when BMMCs were exposed to negative control antibody (p=0.0057 at 0.001 μg). BMMC containing effector to target (E:T) ratio >10 contained lower viable (7-AAD-) PC and higher apoptotic PC counts compared with BMMC specimen with E:T ratio <10 (p<0.001). Using CD45 expression as a surrogate marker of PC maturation and BCMA expression, CD45+ PC displayed higher BCMA expression than CD45- PC (p=0.0189) and were more sensitive TNB-383B-induced killing (p<0.001). Noticeably, overall BCMA expression pre/post TNB-383B exposure remained unaltered. CONCLUSION: Taken together, our findings demonstrate TNB-383B triggers primary PC lysis and CTL degranulation in a dose-dependent fashion ex vivo. The ex vivo bispecific monoclonal antibody assay employed in this study allowed us to identify underlying biological drivers of PC killing efficacy by TNB-383B and may provide a valuable preclinical platform to screen bispecific antibodies and clinical platform to identify mechanism of primary or acquired resistance to the drug. Enrollment of patients with relapsed/refractory MM into a phase I clinical trial with TNB-383B is expected in early 2019. Figure. Figure. Disclosures Foureau: Teneobio Inc.: Research Funding. Pham:Teneobio Inc.: Employment. Force Aldred:Teneobio Inc.: Employment. Buelow:Teneobio Inc.: Employment. Voorhees:Oncopeptides: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: served on an IRC; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Other: served on an IRC; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: served on an IRC; Amgen Inc.: Speakers Bureau; TeneoBio: Consultancy, Membership on an entity's Board of Directors or advisory committees. Usmani:Abbvie, Amgen, Celgene, Genmab, Merck, MundiPharma, Janssen, Seattle Genetics: Consultancy; Amgen, BMS, Celgene, Janssen, Merck, Pharmacyclics,Sanofi, Seattle Genetics, Takeda: Research Funding.
Background: Multiple myeloma (MM) is the most common hematologic malignancy in the African American population, with an incidence more than 2 times higher than Caucasian population [Landgren O et al Blood 2006]. Historically, the African American MM patients have had better outcomes compared with other races [Ailawadhi S et al Br J Haematol 2012], but no biologic explanations exist for this observation. Greenberg et al [Blood Cancer J 2015] have recently reported on differences in commonly observed baseline cytogenetic abnormalities (CA) between African American and Caucasian MM patients seen at Mayo Clinic (Rochester, MN), Cook County Hospital (Chicago, IL) and University of Maryland (Baltimore, MD). We examined the MM cohort at our referral center to validate these observations. Patients and Methods: The Levine Cancer Institute MM database was interrogated for all patients presenting with MM between January 2012 and April 2015. Baseline clinical and pathology variables were compared between the African American and Caucasian cohorts. Continuous variables were compared using nonparametric rank tests, while incidences and proportions (e.g. CAs including t(11;14), t(4;14), monosomy13/del13q and del17p) were compared using Fisher's exact tests. Results: A total of 662 patients were identified; excluding those with MGUS classification, 368 patients were included in the analysis (African Americans n = 130, Caucasian n = 238). The median age of African American MM patients was significantly younger than Caucasian MM patients (median age 60 years vs. 65 years, p=0.010), with similar gender distribution. There was a numerically larger proportion of African American patients with anemia (40.8% vs 30.8%, p =0.166), however, there was no significant difference in degree of BM plasmacytosis amongst the two groups. The overall distribution of MM patients by IMWG risk stratification (Chng et al, Leukemia 2013) was also similar between the two groups. The African American MM patients had a numerically higher incidence of a metaphase abnormality on conventional cytogenetics (21.7% vs. 13.9%, p =0.154). They had a significantly lower incidence of t(11;14) [7.7% vs. 16%, p=0.024], a numerically higher incidence of t(4;14) [6.2% vs. 3.8%, p=0.309], and similar incidence of deletion 13/del13q [22.3% vs. 18.9%, p=NS] and del17p [7.7% vs. 7.6%, p=NS]. Conclusions: The present dataset is the largest single institution report on CA racial differences in MM patients. We observed that unlike previous reports of lower incidence of t(4;14) or del17 p in African American MM patients by Greenberg et al, we have observed a higher incidence of t(4;14) and similar incidence of del17p in our experience compared to Caucasian MM patients. The different pattern of CA distribution compared to published literature may represent geographic heterogeneity and potentially influence survival outcomes. Citation Format: Preeya Patel, Manisha Bhutani, Kyle Madden, Myra R. Robinson, Rupali Bose, James Symanowski, Saad Z. Usmani. Distribution of cytogenetic abnormalities in African American multiple myeloma patients may be unique for different geographic regions. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr B41.
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