Abstract B070: Logic-gated CAR T cell product AB-1015 response to ovarian cancer models with heterogeneous levels of ALPG/P antigen

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Abstract In solid tumors, CAR T cell efficacy is limited by on-target off-tumor toxicity, as well as functional suppression by the tumor microenvironment (TME). AB-1015 is an integrated circuit T cell (ICT cell) developed for use in ovarian cancer. The AB-1015 transgene cassette includes two functional modules: A) a sequential ”AND” logic gate designed to limit off-tumor toxicity through dual tumor antigen recognition, which consists of a priming receptor (PrimeR) against ALPG/P and an inducible Mesothelin(MSLN)-targeted chimeric antigen receptor (CAR) that is upregulated in response to PrimeR engagement; as well as B) a dual shRNA-miR targeting FAS and PTPN2 to resist TME suppression and improve ICT cell function. The AB-1015 is generated by CRISPR-based, targeted insertion of a single transgene into a safe harbor locus. AB-1015 is currently being studied in a phase I clinical trial (NCT05617755) for patients with platinum-resistant ovarian cancer. The heterogeneity in antigen expression among different tumor cells within solid tumors can hinder the efficacy of targeted CAR T cell therapy. To investigate this, we initially assessed the percentage of tumor cells expressing ALPG/P and MSLN in ovarian cancer samples using immunohistochemistry (IHC). Most tumor cores evaluated had detectable MSLN expression; however, the percentage of ALPG/P expressing tumor cells was heterogeneous. To model the heterogeneity of ALPG/P observed in the tumor samples, we developed a human ovarian carcinoma mixed-cell model system with an increasing proportion of ALPG/P expressing cells. The human ovarian carcinoma cell line, OVCAR3, expresses high levels of MSLN with ≤5% endogenous expression of ALPG/P. In the mixed-cell model system, these cells were then engineered to express ALPG/P (OVCAR3-ALPG) and mixed with the parental OVCAR3 cells at increasing ratios. In this system, we demonstrated that CAR induction is tightly linked to the percentage of ALPG/P-positive tumor cells in co-culture. We demonstrated that as few as 5-15% of ALPG-positive tumor cells were capable of inducing sufficient CAR expression to eliminate an otherwise MSLN-positive tumor culture. These preclinical data show that very few ALPG-positive tumor cells are needed to elicit anti-tumor activity from AB-1015, suggesting potential efficacy of AB-1015 in ovarian cancer with low percentage of ALPG/P expressing cells, similar to the antigen heterogeneity found in patients’ tumors. Citation Format: Dina Polyak, Erik Beckman, Preethi Bala Balakrishnan, Hongruo Yun, Xinyan Tang, Jun Feng, Nickolas Attansio, Ashley Cass, Stephen Santoro, Alba Gonzalez-Junca, W. Nicholas Haining, Christopher L. Murriel. Logic-gated CAR T cell product AB-1015 response to ovarian cancer models with heterogeneous levels of ALPG/P antigen [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B070.

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