Abstract LB188: Discovery and development of fully human TACI/BCMA bispecific armored CAR for the treatment of relapsed/refractory multiple myeloma
Authors: Agrahari Garima , Liang Wenle , O'Callaghan Katie , Zhang Keming , Jiang Ning , Jin Xiaoyi , Feng Ryan , Nguyen Jenna , Hassan Sam , Luu Annie , Ruan Tony , Zhao Kehao , Chen Yan 
Published: April 2023

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.