Human B-cell Maturation Antigen Research Articles

Lymphodepletion Enables Successful BCMA CAR-T Cell Engraftment and Tumour Control in the Syngeneic Vk*MYC Model of Aggressive Myeloma

DISCUSSION AND CONCLUSION Chimeric antigen receptor (CAR)-T cells directed against B-cell maturation antigen (BCMA), have yielded impressive results in clinical trials for multiply relapsed/refractory multiple myeloma (MM). However, progression-free survival is short, demonstrating a need for improvements. While numerous advances have been made to improve this treatment modality, these have not always translated to superior clinical outcomes. A major limitation is that novel therapeutics are often not tested in a relevant in vivo model. These novel strategies have been largely tested only in immunodeficient models of MM. To better recapitulate the host-tumour-effector cell interactions, particularly in the TME, we sought to develop a system to study CAR-T cell activity in the Vk*MYC model of MM. Here, we report on the first known successful model of CAR-T cell activity in an immunocompetent model of MM. We sought to identify a BCMA CAR construct that is capable of binding to both human and mouse BCMA. A novel nanobody recognizing BCMA was developed by immunizing llamas with human BCMA and the resulting single-domain antibodies (sdAbs) were subsequently isolated and cloned. These sdAbs were then screened for binding to mouse BCMA. A binder capable of recognizing both human and mouse BCMA was identified and cloned into our murine CAR construct, with CD28 and CD3z signaling domains, herein referred to as sdBCMA2.CD28.CD3z. Murine CAR-T cells were then generated by transducing activated healthy murine splenocytes with a retroviral vector carrying the sdBCMA2.CD28.CD3z construct. These CAR-T cells were then characterized in vitro using standard cytotoxicity, proliferation, and cytokine release assays. To assess activity in an immunocompetent model, female C57BL/6J mice were injected intravenously with Vk12598 Vk*MYC cells. CAR-T cells were later administered intravenously. Mice were bled weekly to quantify M-protein disease burden by serum protein electrophoresis and for phenotypic characterization of circulating cells. When co-cultured with BCMA+ human MM cell lines and with Vk*MYC cell lines, murine sdBCMA2.CD28.CD3z CAR-T cells effectively lysed target cells, proliferated, and released inflammatory cytokines. To assess the in vivo activity of these CAR-T cells, we injected intravenously female C57BL/6J mice with Vk12598 cells, and then administered sdBCMA2.CD28.CD3z CAR-T cells intravenously. While there was some evidence of survival improvement, the median overall survival (mOS) of 35 days compared to 28 days, for CAR-T vs. Mock T-cells, respectively, the difference was non-significant, and the survival benefit was not durable. To address this, we incorporated lymphodepletion by total body irradiation (TBI) followed by CAR-T cell administration the next day. By incorporating lymphodepletion prior to CAR-T cell administration we were able to significantly reduce M-protein surrogates of disease burden, as well as achieve durable remissions in the TBI + CAR-T arm with an mOS not yet reached after experimental day 91, compared to an mOS of 42 days in the TBI + Mock T-cell arm. The addition of TBI also significantly improved the engraftment of CAR-T cells, as assessed by flow cytometry. The TBI + CAR-T arm also had significantly increased IL-6, IL-1b, IL-2, and TNF-a in the serum, compared to the TBI + Mock arm, at 7 days post administration of CAR-T cells. The durable remission achieved using the combination of our novel sdBCMA2.CD28.CD3z CAR-T cells with lymphodepletion is a pivotal advancement in modelling MM CAR-T cell activity in this clinically relevant model system. Our approach represents the first time that CAR-T cells were successfully used to treat the Vk12598 model of MM that faithfully recapitulates relapsed MM. The incorporation of lymphodepletion significantly improves CAR-T cell engraftment, in line with clinical CAR-T cell therapy paradigms. The cytokine profile observed is consistent with the cytokine elevations typically observed after CAR-T cell administration in patients. As our construct is capable of binding to both human and mouse BCMA, we are therefore able to fully characterize our lead assets in a relevant model system. Our strategy will enable further research to dissect host-tumour-effector cell interactions, to better inform the design and characterization of novel CAR-T cell therapies in MM.

Abstract LB188: Discovery and development of fully human TACI/BCMA bispecific armored CAR for the treatment of relapsed/refractory multiple myeloma

Abstract Background: The introduction of novel targeted therapies and immunotherapies has dramatically improved responses and overall survival in multiple myeloma (MM) patients. However, greater than 50% MM achieve refractory or relapse (r/r) within five-year due to MM target heterogeneity and bone marrow tumor microenvironment (TME). The approved B-cell maturation antigen (BCMA) -directed CAR T therapies have shown unprecedented efficacy in advanced r/r MM, yet relapse remains to occur. The shedded soluble BCMA, target escape and bone marrow TME may contribute to the r/r MM mechanism through compromising clinical efficacy and durability. TACI and BCMA are co-expressed on the tumors of ~78% MM patients, and therefore, dual targeted TACI/BCMA CAR therapy could be an attractive strategy in addressing challenges of BCMA mono-CAR therapy. We have developed EPC-004, a fully human anti-TACI and BCMA bispecific armored tandem CAR, aiming to overcome BCMA target escape mechanism, reduce immunosuppression within the bone marrow tumor microenvironment, and be more persistent with engineered armor and the improved cell manufacturing process. Methods: Fully human anti-TACI, anti-BCMA and anti-PDL1 scFv antibodies with a broad affinity range and epitope coverage have been discovered by proprietary mRNADisTM mRNA display and live cell selection platform. The T cell modulatory activity fine-tuned IL2 was discovered by the mSCAFoldTM technology through the structure guided mutagenic library design and high throughput systemic screening. The anti-PDL1 scFv was then fused to the engineered IL2 to generate an armor molecule to enhance CAR activities and persistence. Finally, EPC-004, an optimal bispecific tandem TACI/BCMA armored CAR candidate, was developed by precision engineering of multiple pairs of anti-TACI and BCMA scFvs with monospecific and bispecific target binding properties, spacers and scFv orientation. Results: EPC-004 demonstrated both mono-specific and bispecific TACI and BCMA target cell engagement and effective cytotoxic cancer cell killing activities. EPC-004 showed potent anti-tumor activity in MM1R, BCMA knock out or TACI knock out MM1R -luciferase orthotopic animal models, which validated the mechanism of EPC-004 in overcoming BCMA or TACI target escape resistance. Furthermore, EPC-004 showed strong persistent CAR-T activity against tumor cells in re-challenging models in mice. Importantly, the secreted armor molecule selectively activates central memory T cells and contributed to the enhanced anti-tumor activity and persistence in vivo. Conclusion: EPC-004, engineered with multi-modules and multi-mechanisms is a promising candidate which enhances anti-tumor activity, prevents target escape, reduces immunosuppression within the bone marrow tumor microenvironment. These novel mechanisms could potentially translate EPC-004 into durable clinical efficacy in treating R/R multiple myeloma. Citation Format: Garima Agrahari, Wenle Liang, Katie O'Callaghan, Keming Zhang, Ning Jiang, Xiaoyi Jin, Ryan Feng, Jenna Nguyen, Sam Hassan, Annie Luu, Tony Ruan, Kehao Zhao, Yan Chen. Discovery and development of fully human TACI/BCMA bispecific armored CAR for the treatment of relapsed/refractory multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB188.

Abstract 6251: Evaluation of a dual-targeting BCMA-CS1 HLE BiTE® molecule for multiple myeloma

Abstract Multiple myeloma (MM) is a cancer of the antibody-producing plasma cells (PC). MM is invariably fatal due to frequent disease relapse and/or treatment refractoriness, and therapies that provide deeper and more durable responses are needed. BiTE® (Bispecific T Cell Engager) molecules are immunotherapy agents that redirect a patient’s T cells to lyse tumor cells by simultaneously engaging a tumor associated antigen (TAA) on cancer cells and CD3ε on T cells. Clinical activity has been observed in MM using BiTE® molecules and other T cell engagers that target B-cell maturation antigen (BCMA). BCMA is an attractive MM TAA due to its broad prevalence and restricted normal tissue profile, mainly PCs and plasmablasts. However, heterogenous expression in MM cancer cells, potential antigen loss, and the presence of high levels of soluble BCMA in MM patient sera present challenges that may prevent BCMA-only-targeted therapies from achieving their full potential. To address these issues, we generated a BiTE® molecule capable of engaging BCMA and a second MM TAA, CS1 (also known as SLAMF7). This BiTE® molecule also contains an Fc-based domain to provide half-life extension (HLE). Here, we evaluated the in vitro and in vivo properties of this BCMA-CS1 HLE BiTE® molecule. The BCMA-CS1 HLE BiTE® molecule had nanomolar binding affinity for human BCMA, CS1, and CD3ε and the non-human primate (NHP) orthologues. In vitro, we observed picomolar activity against human MM cell lines with a range of BCMA and CS1 expression in a T cell dependent cellular cytotoxicity (TDCC) assay using human T cells or NHP peripheral blood mononuclear cells. The BCMA-CS1 HLE BiTE® molecule retained TDCC activity in the presence of soluble BCMA up to 2500 ng/mL as well as against human MM cells engineered to express only BCMA or CS1. In vivo, this BiTE® molecule inhibited tumor growth in a MM xenograft model. We also evaluated the BCMA-CS1 HLE BiTE® molecule in NHP over 15 days (IV dosing; intra-animal dose escalation from 60→240 μg/kg or 180→540 μg/kg on days 1 and 8). We observed hallmarks of BiTE® molecule activity in all groups, including transient decreases in circulating lymphocytes and moderate increases in cytokines like MCP-1. We measured the PC-specific transcripts BCMA and J-chain in NHP bone marrow and blood as surrogates for PC levels using ddPCR. These transcripts were reduced in both treatment groups (≥90%) with the strongest effects occurring in the 180→540 μg/kg group. Lastly, we showed that CS1 is highly and broadly expressed in MM patient samples and is restricted to a few normal hematopoietic cell types including PCs, NK cells, T cells, and some monocytes. These data suggest that the BCMA-CS1 HLE BiTE® molecule has potent in vitro and in vivo activity and may provide therapeutic benefit for MM patients by expanding the population of MM cancer cells that can be eliminated by a BiTE® molecule while overcoming common mechanisms that can impair BCMA-only-targeted MM therapies. Citation Format: Elizabeth T. Andrews, Stephanie C. Casey, Mohammad Farhad Amani, Grit Lorenczewski, Mozhgan Farshbaf, Lisa Winkel, Matthias Klinger, John M. Harrold, Famke Aeffner, Ana Goyos, Matthias Friedrich, Tara Arvedson, Matthew G. Chun. Evaluation of a dual-targeting BCMA-CS1 HLE BiTE® molecule for multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6251.

Comparison of FACS and PCR for Detection of BCMA-CAR-T Cells.

Chimeric-antigen-receptor (CAR)-T-cell therapy is already widely used to treat patients who are relapsed or refractory to chemotherapy, antibodies, or stem-cell transplantation. Multiple myeloma still constitutes an incurable disease. CAR-T-cell therapy that targets BCMA (B-cell maturation antigen) is currently revolutionizing the treatment of those patients. To monitor and improve treatment outcomes, methods to detect CAR-T cells in human peripheral blood are highly desirable. In this study, three different detection reagents for staining BCMA-CAR-T cells by flow cytometry were compared. Moreover, a quantitative polymerase chain reaction (qPCR) to detect BCMA-CAR-T cells was established. By applying a cell-titration experiment of BCMA-CAR-T cells, both methods were compared head-to-head. In flow-cytometric analysis, the detection reagents used in this study could all detect BCMA-CAR-T cells at a similar level. The results of false-positive background staining differed as follows (standard deviation): the BCMA-detection reagent used on the control revealed a background staining of 0.04% (±0.02%), for the PE-labeled human BCMA peptide it was 0.25% (±0.06%) and for the polyclonal anti-human IgG antibody it was 7.2% (±9.2%). The ability to detect BCMA-CAR-T cells down to a concentration of 0.4% was similar for qPCR and flow cytometry. The qPCR could detect even lower concentrations (0.02–0.01%). In summary, BCMA-CAR-T-cell monitoring can be reliably performed by both flow cytometry and qPCR. In flow cytometry, reagents with low background staining should be preferred.

Safety and Efficacy of Fully Human BCMA CAR T Cells in Combination with a Gamma Secretase Inhibitor to Increase BCMA Surface Expression in Patients with Relapsed or Refractory Multiple Myeloma

Safety and Efficacy of Fully Human BCMA CAR T Cells in Combination with a Gamma Secretase Inhibitor to Increase BCMA Surface Expression in Patients with Relapsed or Refractory Multiple Myeloma

Identification and Development of PHE885: A Novel and Highly Potent Fully Human Anti-BCMA CAR-T Manufactured with a Novel T-Charge TM Platform for the Treatment of Multiple Myeloma

Identification and Development of PHE885: A Novel and Highly Potent Fully Human Anti-BCMA CAR-T Manufactured with a Novel T-Charge TM Platform for the Treatment of Multiple Myeloma

A Preliminary Study on the Safety and Efficacy of a Novel Human BCMA-Targeting CAR-T Therapy in Patients with Relapsed/Refractory Multiple Myeloma

IntroductionMultiple myeloma is a hematological malignancy that is prone to be companied by bone marrow destruction, renal impairment and extramedullary infiltration. Current treatments include proteasome inhibitor, immunomodulatory drug, hematopoietic stem cell transplantation, and monoclonal antibody targeted therapies. However, it is still clinically incurable. Chimeric antigen receptor (CAR) T-cell therapy is a new immune targeted therapeutic strategy. It is reported better clinical efficacy for relapsed/refractory multiple myeloma (r/r MM) treatment has been achieved by immunotherapies targeted B-cell maturation antigen (BCMA). Therefore, it is important to investigate the treatment of a novel human BCMA-specific CAR-T therapy for r/r MM.ObjectiveThe objective of this clinical study is to evaluate the safety and efficacy of the novel human BCMA-targeting CAR-T therapy in patients with r/r MM, especially patients who relapsed from prior CAR-T therapy.MethodThis work is a clinical study registered and investigated by our center. CD3+ T cells were negatively selected from patients' peripheral blood mononuclear cells, activated and modified by lentivirus to produce anti-BCMA CAR-T cells. The cells were administrated intravenously to patients after expanding for 7-13 days in vitro. 24 patients had enrolled in this study, with 13 males and 11 females. The median age was 53 years old (range,41-75), and patients with cytogenetically high risk factors accounting for 41.66% (10/24). 50% (12/24) was infiltrated with extramedullary lesions. 16.6% (4/24) of them had relapsed from other CAR-T therapies before this enrollment. 50% (12/24) had been previously conducted autologous hematopoietic stem cell transplantation (HSCT), whereas 4.16% (1/24) with allogeneic HSCT. Patients with the expression of BCMA in the plasma cells higher than 30%, accounted for 25% (6/24). 2-3 days after being administered the lymphodepleting chemotherapy regimen, CAR-T cells were infused intravenously. The indicators of patients' condition were detected, including inflammatory cytokine concentration, serum protein levels, CAR-T cell number copies, and the proportion of plasma cells by bone marrow biopsy. The improvement of patients, the occurrence of adverse reactions, the incidence and grade of cytokine release syndrome (CRS), was analyzed and evaluated.ResultAll patients received infusions of CAR-T positive cells at the average dose of 9.45×10 6/kg (5-17.5) and the median injection day is the 10th day (8th-13th day) after cell isolation. After infusion, 100% (24/24) of the patients had fever lasting for 48 hours, with 37.5% (9/24) of them showing low blood pressure and being treated with drug. Heart rate increase was found in 45.8% (11/24). Nausea, diarrhea and transient consciousness disorder occurred in 50% (12/24), 33.3% (8/24), and 12.5% (3/24) of them, respectively. 16.6% (4/24) was administrated with dexamethasone to relieve symptoms, with the total dose less than 20 mg, while nobody was treated with IL-6 receptor antagonist. CAR-T cells had expanded in all patients, reaching the peak at the 4th day after infusion (Figure). The levels of IL-6, IL-8 and IFN-γ in peripheral blood also increased significantly. The incidence of CRS is 100%, of which grade I, II and III is 62.5%, 33.3% and 4.2%, respectively. 2 patients showed grade I CRES, constituting 8.3% (2/24). All patients were assessed for the efficacy of CAR-T cells 2 weeks after infusion. ORR was 100%, with 4.2% (1/24) MR, 8.3% (2/24) PR, 62.5% (15/24) VGPR and 25% (6/24) CR. 18 patients were treated for more than 1 month, with 11.1% (2/18) PR, 44.4% (8/18) VGPR, 11.1% (2/18) CR, and 33.3% (6/18) sCR. 16 patients were infused before more than 2 months, with 25% (4/16) VGPR, 12.5% (2/16) CR, 50% (8/16) sCR, and 12.5% (2/16) PD. 6 patents were administrated more than 3 months ago, with 1 developing deep remission to sCR from VGPR. The others remain the same condition.ConclusionThe novel human BCMA targeted CAR-T cell therapy of this study showed safety and efficacy in the treatment of r/r MM patients with extramedullary infiltration, high-risk cytogenetical factors as well as relapse with prior BCMA CAR exposures. Deep remission can be achieved. However, more observation need to be conducted. The CAR-T treatment of BCMA target still cannot prevent the disease progress of a small numbers of patients. The control after CAR-T therapy needs more investigation. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Serum Bcma May Interfere with Anti-Bcma-CAR-Transduced T Cells or Other Anti-Bcma Antibody-Based Immunotherapy in Multiple Myeloma

Introduction: CAR T cell-based immunotherapy has shown clinical activity in a variety of B-cell malignancies. Specifically, the engineered CAR-transduced T cells targeting B-cell maturation antigen (BCMA) on multiple myeloma (MM) have shown promising activity for the treatment of relapsed/refractory (RR) MM patients. However, MM patients have high levels of solubilized BCMA (sBCMA) in the blood especially those with RR disease. Due to these findings, we hypothesized that circulating levels of sBCMA may interfere with the efficacy of CAR T cell immunotherapy or other anti-BCMA antibody (Ab)-based therapeutic approaches for treating MM patients.Study design: Sera were collected from MM patients and healthy subjects after obtaining institutional review board approval (IRB). Serum levels of human BCMA were determined using an ELISA kit (R&D Systems, Minneapolis, MN). For the BCMA antibody binding assay, 50 µL of human BCMA fluorescein-conjugated polyclonal Ab or monoclonal Ab was incubated with 100 µL of diluent buffer and 100 µL of serum from human subjects with varying sBCMA concentrations. To demonstrate the effects of sBCMA interference with anti-BCMA CAR T function, we utilized a wide range of concentrations (0ng/ml, 3ng/ml, 18 ng/mL, 32ng/ml, 37ng/ml, 110ng/ml, 156ng/ml, 390ng/ml, 530ng/ml and 2167 ng/mL); recombinant BCMA (0ng/ml, 65ng/ml, 130ng/ml, 400ng/ml, 1200ng/ml). After one hour of incubation at room temperature (RT), each sample was added to primary tumor cells from MM patients with progressive disease. These cells were incubated for two hours at RT away from light. Following incubation, cells were washed three times using PBS. Flow cytometric analysis was performed using a Beckman Coulter Cytomics FC 500 with Cytomics CXP software. The same procedure was followed to observe the effects of recombinant human BCMA. To assess immunofluorescent (IFC) analysis of anti-BCMA binding to MM tumor cells, IFC staining was completed following a standard IFC assay protocol and the BCMA binding markers were identified under the microscope (Olympus BX51).Results and discussion: The experimental results demonstrate a concentration dependent response of anti-BCMA antibody binding to primary MM tumor cells. At sBCMA levels lower than 150ng/mL, there was no significant difference in anti-BCMA antibody binding to tumor cells. However, at concentrations greater than 150 ng/mL, a significant decrease in binding was observed. At 390ng/ml, serum sBCMA blocked 50% of anti-BCMA antibody binding to the tumor cells. At 2000ng/ml, serum sBCMA interfered with anti-BCMA antibody binding to tumor cells by more than 80%. When using recombinant BCMA, we observed the same concentration dependent effects on anti-BCMA binding to MM cells. As the levels of recombinant BCMA increased, the antibody binding to MM cells decreased. These results suggest that higher BCMA levels that are present in patients with MM interfere with binding to MM tumor cells; and, thus, could reduce the efficacy of CAR T cell and other immunotherapy approaches targeting BCMA. The fluorescent image further demonstrated serum sBCMA blocked anti-BCMA antibody binding to primary MM tumor cells in a concentration dependent fashion. In 2013 Carpenter et al . showed that sBCMA levels do not interfere with CAR-T-cells. However, the sBCMA concentrations used in those experiments are based on low sBCMA levels (10ng/ml). We have consistently detected concentrations much higher than 150ng/ml of sBCMA in MM patients. Our experimental data showed 30-35% serum BCMA level was above 150ng/ml in 500 MM serum samples and 50% serum BCMA level was above 150ng/ml in relapsed/refractory patients.Conclusion: The results demonstrated that higher serum sBCMA concentrations do interfere with anti-BCMA antibody directed CAR T cells immunotherapy therapies or any anti-BCMA antibody therapeutic agents in MM. We suggest determining serum sBCMA level before anti-BCMA antibody directed CAR T cells immunotherapy therapy or use of any anti-BCMA antibody therapeutic agents. DisclosuresBerenson:OncoTracker, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Research Funding.

Anti-Myeloma Effects of the Selective JAK1 Inhibitor INCB052793 Using a Platform Study Utilizing the Lagκ-1A Multiple Myeloma Xenograft Model

Introduction: We have previously shown that severe combined immune deficiency (SCID)mice bearing the human multiple myeloma (MM) LAGk-1A xenograft develop significantly smaller tumors when treated with the JAK1 inhibitor INCB052793 (INCB; Incyte, Wilmington, DE) alone. Additionally, mice receiving the doublets of this agent and dexamethasone (DEX), lenalidomide (LEN) or pomalidomide (POM) demonstrated enhanced anti-MM effects on LAGk-1A growth in vivo that was superior to the doublets of DEX with LEN or POM. Mice receiving the triple combination of INCB + DEX with LEN or POM demonstrated the most pronounced anti-MM effect on tumor growth in vivo compared to all other combinations tested. Herein, we evaluated the response and toxicity of animals treated in combination or sequentially with INCB as well as with LEN plus DEX. For example, is there enhanced anti-MM activity when INCB + LEN are administered first, and DEX is added after disease progression? Or is there enhanced anti-MM activity when INCB + LEN is administered first and then substituted with DEX? This same treatment strategy was evaluated with INCB + DEX administered first, followed by the various permutations of LEN. Additionally, given that in the clinical setting DEX plus LEN is commonly administered to patients with MM, we evaluated these combinations with the addition of INCB or substitution of one of these drugs with INCB. Similarly, we evaluated the anti-MM effects of mice progressing from DEX therapy and added in INCB, substituted DEX with INCB, continued DEX and added in INCB + LEN.Materials and Methods: For the in vivo studies, each SCID mouse was implanted into the hind limb with a piece of the human MM tumor LAGk-1A. All animal studies were approved by the Institutional Animal Care and Use Committee. Fourteen days post-implantation mice were randomized into various treatment groups, and tumor size was measured on a weekly basis following treatment with various drugs following progression from their initial treatment regimen. Progression is defined as an increase in human B-cell maturation antigen (BCMA) equal to or above 25% when compared to the prior assessment (plasma BCMA levels were assessed on a weekly basis). After the mouse meets the criteria for disease progression, the mouse was placed into their respective treatment group.Results: When each individual mouse progressed, their dosing regimen was changed according to the treatment group to which they were randomized. We observed pronounced anti-MM effects when DEX was administered, followed by additions, or substitutions, of INCB and/or LEN. No significant anti-MM effects were observed when comparing the vehicle control group to mice treated in the LEN, INCB or DEX + LEN cohorts. However, mice treated with the doublets INCB + DEX or INCB + LEN, or triplet of INCB + LEN + DEX showed smaller tumors compared to the vehicle control group, (P= 0.0420; P= 0.0388; P= 0.0079, respectively). Furthermore, mice treated with the triplet, INCB + LEN + DEX, had markedly smaller tumors when compared to those treated with LEN (P= 0.0005), DEX + LEN(P= 0.0244), or INCB + DEX(P= 0.0357).Conclusions: These in vivo studies should provide important data in support of the optimal clinical sequencing of INCB, as they clearly show that the sequencing of drug combinations involving the novel JAK1 inhibitor INCB052793 + anti-MM agents have a profound impact on the anti-MM effects of this new treatment regimen, and provide further support for the clinical evaluation of these drug combinations to treat relapsed/refractory MM patients. DisclosuresBerenson:Incyte: Consultancy, Research Funding; OncoTracker, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Phase 1, First-in-Human Study of MEDI2228, a BCMA-Targeted ADC in Patients with Relapsed/Refractory Multiple Myeloma

Phase 1, First-in-Human Study of MEDI2228, a BCMA-Targeted ADC in Patients with Relapsed/Refractory Multiple Myeloma

Efficacy and Safety of Fully Human Bcma CAR T Cells in Combination with a Gamma Secretase Inhibitor to Increase Bcma Surface Expression in Patients with Relapsed or Refractory Multiple Myeloma

Efficacy and Safety of Fully Human Bcma CAR T Cells in Combination with a Gamma Secretase Inhibitor to Increase Bcma Surface Expression in Patients with Relapsed or Refractory Multiple Myeloma

Response to Bcma CAR-T Cells Correlates with Pretreatment Target Antigen Density and Is Improved By Small Molecule Inhibition of Gamma Secretase

Response to Bcma CAR-T Cells Correlates with Pretreatment Target Antigen Density and Is Improved By Small Molecule Inhibition of Gamma Secretase

Targeting BCMA in multiple myeloma using chimeric antigen receptor-engineered T cells

目的构建以B细胞成熟抗原（BCMA）的特异性配体APRIL为抗原结合区的BCMA-CAR，并验证该BCMA-CAR修饰的T细胞（BCMA-CAR-T）对多发性骨髓瘤的作用。方法以BCMA的特异性配体APRIL为抗原结合区、4-1BB为共刺激分子而构建BCMA-CAR，体外实验验证BCMA-CAR-T细胞对BCMA+骨髓瘤细胞系和原代骨髓瘤细胞的特异性细胞毒作用。此外，构建BCMA+骨髓瘤小鼠模型并评价BCMA-CAR-T细胞的体内抗肿瘤效应。结果BCMA-CAR-T细胞能特异性杀伤BCMA+骨髓瘤细胞系（当效靶比为1∶4时，BCMA-CAR-T细胞组中BCMA+细胞几乎检测不到）和骨髓瘤患者的骨髓单个核细胞（BCMA-CAR-T和空载组T细胞的残余细胞比例分别为16.00%和66.85%，P=0.003），并伴随显著的脱颗粒效应（CAR-T和空载组T细胞与MM1.S、H929、U266共培养的脱颗粒水平分别为33.30%对5.62%、16.97%对2.95%、25.87%对2.97%，P值均<0.001）和细胞因子释放（P值均<0.01）。在治疗人BCMA+骨髓瘤小鼠移植模型中，BCMA-CAR-T细胞可显著延长小鼠的生存期（BCMA-CAR-T和空载组T细胞治疗小鼠的中位生存期分别为87.5 d、67.5 d，P<0.001）。结论以APRIL为抗原识别区的BCMA-CAR-T细胞有望成为治疗BCMA+多发性骨髓瘤的理想策略。

Preclinical and Nonclinical Characterization of HPN217: A Tri-Specific T Cell Activating Construct (TriTAC) Targeting B Cell Maturation Antigen (BCMA) for the Treatment of Multiple Myeloma

About 31,000 new cases of multiple myeloma (MM) will be diagnosed in the US in 2018. In addition to chemotherapeutic agents, several targeted therapies utilizing distinct mechanisms of action, e.g., proteasome inhibitors (bortezomib, carfilzomib, ixazomib), HDAC inhibitors (panobinostat), Cullin-RING E3 ubiquitin ligase activators (thalidomide, lenalidomide, pomalidomide), and antibodies (daratumumab, elotuzumab) have become available for treating MM. However, MM remains an incurable disease. Patients who relapse after or are refractory to standard of care treatments generally have poor prognosis. In 2018, close to 13,000 patients will die of the disease in the US. Targeting the B cell maturation antigen (BCMA), a BAFF/BLyS and APRIL receptor, for treating MM patients can provide a new treatment approach complementary to existing therapies. CAR-T therapies and an antibody-drug conjugate targeting BCMA have demonstrated early clinical success in the treatment of relapsed refractory MM (RRMM).HPN217 is a tri-specific T cell activating construct (TriTAC) consisting of three binding domains: an N-terminal single domain antibody (sdAb) that binds to human BCMA, a middle sdAb that binds to human serum albumin (HSA), and a C-terminal single chain Fv (scFv) that binds to CD3ε of the T cell receptor (TCR) complex. HPN217 is a highly stable single polypeptide of ~ 53 kDa expressed by CHO cells. Simultaneous engagement of BCMA on a target MM cell and CD3 on a T cell results in T cell activation, functional differentiation and the eventual lysis of the target MM cell. Engineering of an HSA binding domain into HPN217 represents a unique strategy in extending serum half-life, giving the TriTAC molecule a small molecular size and flexibility. This approach is different from Fc-engineering applied in other CD3-based bispecific T cell engaging molecules.The KD of HPN217 binding to recombinant human BCMA, HSA, and recombinant human CD3ε was determined to be 5.5 nM, 6 nM, and 17 nM, respectively, as measured by biolayer interferometry. Flow cytometric analysis on a panel of T cells from normal donors and BCMA positive and BCMA negative tumor cell lines confirmed binding of HPN217 to its native targets expressed on cell surface. The in vitro pharmacological activity of HPN217 was evaluated by T cell-dependent cellular cytotoxicity (TDCC) assays. In co-cultures of T cells from normal human or cynomolgus monkey donors, target tumor cells, and HSA, HPN217 mediated dose-dependent and BCMA-dependent cytotoxicity with EC50 values ranging from 0.05 to 0.7 nM. Killing was dependent on expression of BCMA on target tumor cells. Concomitant with target tumor cell killing, HPN217 also mediated dose-dependent upregulation of CD25 and CD69 on T cells in the TDCC co-cultures when BCMA positive tumor cells were presence. Consistent with the mechanism of action of CD3-based T cell engaging molecules, T cell derived cytokines, e.g., TNFα and IFNγ, were detected. Similar T cell activation could be observed using human or cynomolgus monkey whole blood as a source of T cells.Nonclinical in vivo properties of HPN217 were evaluated in xenograft models and a single dose pharmacokinetic (PK) study in cynomolgus monkeys. HPN217 mediated dose-dependent growth suppression against the RPMI-8226 MM model and Jeko-1 mantle cell lymphoma model expressing relatively low levels of 5,600 and 2,200 copies of BCMA per cell, respectively. In the PK study, a single dose of HPN217 at 0.01, 0.1, or 1 mg/kg was given to cynomolgus monkeys. HPN217 exhibited linear PK behavior over this dose range. Serum half-life was in the range of 64 to 85 hours. Serum half-life, volume of distribution, and clearance appeared to be independent of dose. HPN217 was demonstrated to be stable and remained intact up to 3 weeks in vivo as demonstrated by a functional ligand binding assay using recombinant CD3ε and BCMA, respectively, to capture and detect HPN217. Importantly, serum samples collected one week after dosing were as potent as stock HPN217 in MM tumor cell killing in TDCC assays.Collectively, preclinical and nonclinical characterization suggests that HPN217 is an efficacious novel therapeutic candidate that can provide a convenient dosing schedule for patients. A first-in-human phase 1 clinical trial is planned to evaluate HPN217 in RRMM. DisclosuresLaw:Harpoon Therapeutics: Employment. Aaron:Harpoon Therapeutics: Employment. Austin:Harpoon Therapeutics: Employment. Barath:Harpoon Therapeutics: Employment. Callihan:Harpoon Therapeutics: Employment. Evans:Harpoon Therapeutics: Employment. Gamez Guerrero:Harpoon Therapeutics: Employment. Hemmati:Harpoon Therapeutics: Employment. Jones:Harpoon Therapeutics: Employment. Kwant:Harpoon Therapeutics: Employment. Lao:Harpoon Therapeutics: Employment. Lemon:Harpoon Therapeutics: Employment. Patnaik:Harpoon Therapeutics: Employment. Sexton:Harpoon Therapeutics: Employment. Wesche:Harpoon Therapeutics: Employment. Xiao:Harpoon Therapeutics: Employment. Yu:Harpoon Therapeutics: Employment. Yu:Harpoon Therapeutics: Employment.

Ex Vivo Assessment of Tnb-383B, a Bcma-Bispecific Antibody, Against Primary Tumor and Endogenous T Cells from Relapsing Multiple Myeloma Patients

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. [Display omitted] DisclosuresFoureau: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.

REGN5458, a Bispecific BCMAxCD3 T Cell Engaging Antibody, Demonstrates Robust In Vitro and In Vivo Anti-Tumor Efficacy in Multiple Myeloma Models, Comparable to That of BCMA CAR T Cells

Improving therapies for multiple myeloma (MM) remains a high medical need because of the significant morbidity and mortality of the disease. Targeted immunotherapies represent a promising opportunity to fill this clinical need. B cell maturation antigen (BCMA) is an attractive cell-surface target for MM due to its consistent expression on MM patient malignant plasma cells and expression limited in normal tissue primarily to plasma cells. Redirection of a patient's T cells to recognize tumors by CD3-binding bispecific molecules or through the generation of chimeric antigen receptor (CAR) T cells, has shown preliminary evidence of clinical activity. Bispecific antibodies concurrently engage a tumor antigen on cancer cells and the CD3 signaling machinery on T cells, bringing the tumor cell and T cell into proximity and facilitating T cell activation and tumor cell killing. By contrast, CAR T cell therapy involves re-infusion of the patient's own T cells after ex vivo engineering to express CARs targeting tumor antigens and triggering T cell signaling.Here we describe the generation of REGN5458, a human bispecific antibody that binds to BCMA and CD3. In vitro, REGN5458 efficiently activates T cells and induces polyclonal T cell killing of myeloma cell lines with a range of BCMA cell-surface densities, and also induces cytotoxicity of primary human plasma cells. Similar to gamma-sectretase inhibitors, incubation of myeloma cell lines with REGN5458 increased surface levels of BCMA. In xenogenic studies, after BCMAhigh NCI-H929 and BCMAlow MOLP-8 MM cells were co-implanted with PBMC and grown subcutaneously in immunodeficient NOD/SCID/L2Rgamma-deficient (NSG) mice, REGN5458 doses as low as 0.4 mg/kg significantly suppressed the growth of both tumors. Using aggressive, systemic xenogenic tumor models, in which NSG mice were engrafted with PBMC and intravenously injected with BCMAhigh OPM-2 cells or BCMAlow MOLP-8 cells expressing luciferase, REGN5458 reduced tumor burden and suppressed tumor growth at doses as low as 0.4 mg/kg. In immunocompetent mice genetically engineered to express human CD3, REGN5458 inhibited the growth of syngeneic murine tumors expressing human BCMA at doses as low as 0.04 mg/kg. Finally, as REGN5458 binds to cynomolgus CD3 and BCMA and mediates cytotoxicity of primary cynomolgus plasma cells, the pharmacology of REGN5458 was evaluated in cynomolgus monkeys. REGN5458 administration was well-tolerated, resulting in a mild inflammatory response characterized by transiently increased CRP and serum cytokines. Importantly, REGN5458 treatment led to the depletion of BCMA+ plasma cells in the bone marrow, demonstrating cytotoxic activity in non-human primates.The anti-tumor efficacy of REGN5458 was compared to BCMA-specific CAR T cells using 2nd generation CAR lentiviral constructs containing a single-chain variable fragment binding domain from REGN5458's BCMA binding arm and 4-1BB and CD3z signaling domains. Human PBMC-derived T cells were transduced to express this CAR and expanded. Both REGN5458 and the BCMA CAR T cells demonstrated similar targeted cytotoxicity of myeloma cell lines and primary patient blasts in vitro, and were capable of clearing established systemic OPM-2-luciferase myeloma tumors in NSG mice, but with different kinetics: treatment with REGN5458 resulted in rapid clearance of tumors within 4 days, whereas treatment with BCMA CAR T cells allowed tumors to continue to grow for 10-14 days following injection before rapidly inducing tumor clearance. Thus, REGN5458 exerts its therapeutic effect rapidly after injection, using effector T cells that are already in place. In contrast, BCMA CAR T cells require time to traffic to the tumor site and expand, before exerting anti-tumor effects.Collectively, these data demonstrate the potent pre-clinical anti-tumor activity of REGN5458 that is comparable to that of CAR T cells, and provide a strong rationale for clinical testing of REGN5458 in patients with MM. DisclosuresDilillo:Regeneron Pharmaceuticals: Employment. Olson:Regeneron Pharmaceuticals: Employment. Mohrs:Regeneron Pharmaceuticals: Employment. Meagher:Regeneron Pharmaceuticals: Employment. Bray:Regeneron Pharmaceuticals: Employment. Sineshchekova:Regeneron Pharmaceuticals: Employment. Startz:Regeneron Pharmaceuticals: Employment. Retter:Regeneron Pharmaceuticals: Employment. Godin:Regeneron Pharmaceuticals: Employment. Delfino:Regeneron Pharmaceuticals: Employment. Lin:Regeneron Pharmaceuticals: Employment. Smith:Regeneron Pharmaceuticals: Employment. Thurston:Regeneron Pharmaceuticals: Employment. Kirshner:Regeneron Pharmaceuticals: Employment.

ALLO-715, an Allogeneic BCMA CAR T Therapy Possessing an Off-Switch for the Treatment of Multiple Myeloma

Autologous chimeric antigen receptor (CAR) T cells targeting B-Cell Maturation Antigen (BCMA) have demonstrated promising clinical activity, inducing durable responses in patients with relapsed/refractory multiple myeloma (MM). Development of autologous CAR T therapies is however limited by logistical challenges and the time required for manufacturing, which has to be done for each patient. In addition, manufacturing may not be feasible in some patients. An allogeneic approach that utilizes engineered cells from a healthy donor could potentially expand patient access to these therapies by providing a readily available off-the-shelf product. We have previously described the screening of a library of single chain variable fragments (scFvs) with high affinity to human BCMA and the identification of candidate BCMA CARs with potent antitumor activity. Here we sought to further characterize ALLO-715, our lead allogeneic BCMA CAR T cell product, for its specificity to human BCMA, antitumor efficacy in vitro using a long-term killing assay and in xenograft mouse models with physiologic levels of human IL-7 and IL-15, and suitability for scale-up manufacturing.Allogeneic ALLO-715 CAR T cells were generated by lentiviral transduction with a second generation CAR construct incorporating a novel scFv derived from a fully-human antibody with high affinity to BCMA (KD value ~ 5 nM, determined at 37°C) and featuring a rituximab-driven off-switch. Transduced T cells were then transfected with mRNAs encoding Transcription Activator-Like Effector Nucleases (TALEN®) designed to specifically disrupt the T cell receptor alpha chain and CD52 loci. These modifications result in a cell product with a lower risk of TCR-mediated graft-versus-host disease and resistance to the CD52 antibody alemtuzumab, a lymphodepleting agent. BCMA CAR T cells exhibited robust cell expansion, with low levels of tonic signaling that resulted in minimal differentiation (> 50% Tscm/Tcm phenotype). In in vitro assays, ALLO-715 CAR T cells displayed potent cytotoxic activity when co-cultured with the target cell lines MM.1S, Molp-8, and BCMA-REH but negligible cytotoxicity against BCMA-negative REH cells.The high proliferative potential indicated by the high frequency of memory T cells was validated in long-term killing assays, where ALLO-715 CAR T cells showed substantial expansion in the presence of MM.1S cells with no evidence of exhaustion or diminished cytolytic activity after seven days of continuous exposure to target. The potency of ALLO-715 CAR T cells was unaffected by high concentrations of soluble BCMA (>10 ug/mL), which has been shown previously to interfere with the activity of some BCMA-specific CARs.In MM xenograft mouse models, ALLO-715 CAR T cells were highly efficacious at single dose. High serum IL-15 levels have been associated with CAR T cell expansion in clinical trials. To evaluate the impact of homeostatic cytokines on CAR T cell survival and antitumor activity in our xenograft models, mice were administered adeno-associated viruses (AAV) for the expression of human IL-7 and IL-15. In the presence of physiological concentrations of these cytokines, enhanced BCMA CAR T cell expansion and anti-tumor activity were observed.To assess potential off-target interactions of ALLO-715 CAR, tissue cross-reactivity studies were carried out on standard human tissue panels using a scFv-human IgG fusion protein. Consistent with the limited expression pattern of BCMA, reactivity was seen on scattered cells in lymphoid tissues such as tonsil and abundantly on BCMA-expressing cell lines, but no appreciable staining was detected in other tissues.We examined BCMA CAR T cells manufactured following a proprietary GMP-like clinical scale process and found that cell expansion and viability, T cell phenotype and in vivo antitumor efficacy were preserved.These results demonstrate the potential of ALLO-715 as a novel allogeneic BCMA CAR T therapy for the treatment of relapsed/refractory MM and other BCMA-positive malignancies. DisclosuresSommer:Allogene Therapeutics: Employment, Equity Ownership, Patents & Royalties. Boldajipour:Pfizer Inc.: Employment, Patents & Royalties. Valton:Cellectis.Inc: Employment, Equity Ownership, Patents & Royalties. Galetto:Cellectis SA: Employment, Equity Ownership, Patents & Royalties. Bentley:Allogene Therapeutics: Employment, Equity Ownership. Sutton:Allogene Therapeutics: Employment, Equity Ownership. Ni:Allogene Therapeutics: Employment, Equity Ownership. Leonard:Allogene Therapeutics: Employment, Equity Ownership. Van Blarcom:Allogene Therapeutics: Employment, Equity Ownership. Smith:Cellectis. Inc: Employment, Patents & Royalties. Chaparro-Riggers:Pfizer Inc.: Employment, Patents & Royalties. Sasu:Allogene Therapeutics: Employment, Equity Ownership, Patents & Royalties.

Fully Human Bcma Targeted Chimeric Antigen Receptor T Cells Administered in a Defined Composition Demonstrate Potency at Low Doses in Advanced Stage High Risk Multiple Myeloma

Fully Human Bcma Targeted Chimeric Antigen Receptor T Cells Administered in a Defined Composition Demonstrate Potency at Low Doses in Advanced Stage High Risk Multiple Myeloma

Development and Evaluation of an Optimal Human Single-Chain Variable Fragment-Derived BCMA-Targeted CAR T Cell Vector.

B cell maturation antigen (BCMA) has recently been identified as an important multiple myeloma (MM)-specific target for chimeric antigen receptor (CAR) Tcell therapy. In CAR Tcell therapy targeting CD19 for lymphoma, host immune anti-murine CAR responses limited the efficacy of repeat dosing and possibly long-term persistence. This clinically relevant concern can be addressed by generating a CAR incorporating a human single-chain variable fragment (scFv). We screened a human B cell-derived scFv phage display library and identified a panel of BCMA-specific clones from which human CARs were engineered. Despite a narrow range of affinity for BCMA, dramatic differences in CAR Tcell expansion were observed between unique scFvs in a repeat antigen stimulation assay. These results were confirmed by screening in a MM xenograft model, where only the top preforming CARs from the repeat antigen stimulation assay eradicated disease and prolonged survival. The results of this screening identified a highly effective CAR Tcell therapy with properties, including rapid invivo expansion (>10,000-fold, day 6), eradication of large tumor burden, and durable protection to tumor re-challenge. We generated a bicistronic construct including a second-generation CAR and a truncated-epithelial growth factor receptor marker. CAR Tcell vectors stemming from this work are under clinical investigation.

Abstract 4979: Development of KITE-585: A fully human BCMA CAR T-cell therapy for the treatment of multiple myeloma

Abstract Background: Multiple myeloma (MM) is a usually fatal malignancy of plasma cells, with no current therapy considered curative. About 15% of patients diagnosed with MM are stratified as high risk with poor treatment outcomes and short (2-3 years) survival from diagnosis. Standard risk patients tend to live longer but undergo chronic and/or high intensity therapy and likely experience a relapsing and remitting disease pattern. Therefore, there is still a considerable unmet need for innovative therapies that improve outcomes in MM. One such approach is to use adoptive transfer of engineered autologous T cells expressing a chimeric antigen receptor (CAR) directed against malignant cells. The efficacy of CAR T cells directed against hematological malignancies, particularly CD19-expressing B cell leukemia and lymphomas, has been demonstrated in multiple clinical studies. KITE-585 was developed as a CAR T cell immunotherapy product candidate directed against B cell maturation antigen (BCMA). BCMA is nearly ubiquitously expressed on MM cells, plasma cells and subsets of mature B cells, but with limited or absent expression on other tissues. Methods: We generated &amp;gt;50 fully human IgGs directed against BCMA using the BCMA protein as antigen and selection criteria including affinity, cross-reactivity and poly-specificity. Following assessment of the binding of the IgGs to a MM cell line known to express BCMA, &amp;gt;10 IgGs were identified that met the criteria for affinity and selectivity and had a &amp;gt;50-fold binding over background. The 8 IgGs that demonstrated the highest specific binding were then sequence-converted to single-chain variable fragments (scFvs) and incorporated into CARs. Results: In all but one case, human T cells engineered to express these CAR constructs exhibited specific cytolytic activity against MM cell lines (NCI-H929 and MM.1s). These CAR T cells demonstrated killing efficiencies of &amp;gt;95% at effector:target ratios of 1:1 over a 24-hour period. Similarly antigen-specific production of inflammatory cytokines was observed in response to target cell lines in vitro. Assessment of antigen-dependent proliferation over a 5 day period revealed &amp;gt;80% proliferation in the 7 constructs that showed cytolytic activity in vitro. Multiple different anti-BCMA CAR constructs representing distinct epitope binding bins of BCMA were then selected for in vivo evaluation. In two disseminated tumor models of luciferase labeled NCI-H929 or MM.1s cells injected intravenously (i.v.), a single i.v. injection of anti-BCMA CAR T-cells delayed the progression of disease and significantly increased survival when compared to control treatment. Conclusions: The results of these studies highlight the potential of targeting BCMA with adoptive transfer of engineered T cells for the treatment of MM. Given these positive findings, progress towards Phase 1 clinical studies in MM patients with KITE-585 is continuing. Citation Format: Gregor B. Adams, Jun Feng, Atefah Ghogha, Armen Mardiros, Jodi Murakami, Tammy Phung, Ruben Rodriguez, Stuart Sievers, Tassja J. Spindler, Jed Wiltzius, Clare Yarka, Sean C. Yoder, Tony Polverino. Development of KITE-585: A fully human BCMA CAR T-cell therapy for the treatment of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4979. doi:10.1158/1538-7445.AM2017-4979