Abstract LB360: Discovery and development of fully human IL13Ra2/B7H3 bispecific armored CAR-T for treatment of glioblastoma

Abstract Background: Glioblastoma (GBM) is a highly lethal cancer with limited effectiveness of current treatments, highlighting an urgent need for new therapeutic approaches. Tumor target heterogeneity, an immunosuppressive tumor microenvironment (TME) and challenges in penetrating blood-brain barrier contribute to the reduced efficacy of current therapies. Recent advancements in CAR-T cell therapies for GBM such as bispecific CAR-T have demonstrated improved overall response rates but are not sufficient to achieve sustained tumor regression. In contrast, monospecific armored CAR-T cells have shown tumor regression; however, rapid relapse remains a significant challenge. We have developed EPC-003, a fully human bispecific armored CAR targeting IL13Rα2 and B7H3, which are co-expressed in approximately 78% of GBM tumors. The bispecific CAR represents promising therapeutic opportunities to overcome tumor heterogeneity and escape mechanisms. The precision engineered multi-mechanism armor reduces immunosuppression within the TME, and exhibits greater persistence through enhanced T central memory (TCM) modulation. Methods: We have discovered a set of human anti-IL13Rα2, anti-B7H3, and anti-PD-L1 single-chain variable fragments (scFvs) with a broad affinity range and extensive epitope coverage. This was achieved using our proprietary mRNADis™ mRNA display technology combined with live-cell selection from proprietary human B cell libraries.To enhance therapeutic efficacy, we have engineered a multi-mechanism armor by fusing an anti-PD-L1 scFv with a fine-tuned IL-2 variant, optimized via our mSCAFold™ cytokine engineering platform. Using these innovations, we developed EPC-003, a bispecific armored CAR candidate targeting IL13Rα2 and B7H3. EPC-003 was precision-engineered by systematically optimizing multiple combinations of anti-IL13Rα2 and B7H3 scFvs, considering both monospecific and bispecific target-binding properties, tandem scFv orientation, spacer design, and the incorporation of a secreted armor. Results: EPC-003 demonstrated robust mono-specific and bispecific engagement of IL13Rα2 and B7H3 target cells, leading to effective cytotoxic killing of cancer cells. In an orthotopic U87 glioblastoma mouse model, EPC-003 induced tumor regression as early as day 6 following intracranial injection of 2 × 106 CAR-T cells. Moreover, intravenous injected CAR-T cells successfully penetrated the blood-brain barrier (BBB), achieving significant tumor regression by day 13 post-treatment. The secreted armor of EPC-003 significantly reduces regulatory T cell activation, selectively activates TCM cells, blocks immune checkpoint pathways, and enhances anti-tumor activity while significantly improving CAR-T cell persistence. Conclusion: The multi-modular and multi-mechanism EPC-003 is a promising candidate that potentially enhances anti-tumor activity, prevents/treat target escape, and reduces immunosuppression within the TME. These novel mechanisms of EPC-003 could potentially translate into durable and enhanced clinical efficacy for GBM therapy. Citation Format: Keming Zhang, Ning Jiang, Katie O'Callaghan, Ryan Feng, Tony Ruan, Jenna Nguyen, Sam Hassan, Kehao Zhao, Yan Chen. Discovery and development of fully human IL13Ra2/B7H3 bispecific armored CAR-T for treatment of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB360.