Background: Adoptive cell transfer therapy with genetically engineered chimeric antigen receptor (CAR)-T cells is rapidly revolutionizing treatment against cancers. However, limited success of CAR T cells against large metastatic solid tumors has been made to date. It is largely due to safety concerns regarding on-target off-tumor toxicity to vital healthy tissues, and poor efficacy after adoptive transfer. Epithelial cell adhesion molecule (EpCAM) was found to be frequently over-expressed in a wide variety of carcinomas, including colon, gastric, pancreas, and breast cancers, making EpCAM an attractive molecule for targeted therapeutics. However, clinical trials with anti-EpCAM antibodies (ING-1, 3622W94) and bispecific T cell engager antibodies (Solitomab) have shown significant dose-limiting toxicities, resulting in very limited clinical responses. To selectively target EpCAM high tumors, we are developing affinity tuned EpCAM CAR T cells with varying affinities to EpCAM.

Methods: The human glioblastoma cell line U251, breast cancer cell lines MDA-MB-231 and SK-BR-3, gastric cancer cell lines MKN28 and MKN45, pancreatic cancer cell lines SW1990 and Capan2, and colon cancer cell line HT29 were transduced with Luciferase-F2A-GFP (FLuc/GFP) lentivirus. EpCAM expression levels on tumor cell lines were measured by flow cytometry. Primary human T cells were transduced with EpCAM CAR lentivirus twice at 24 and 48 hours after activation with anti-CD3/CD28 Dynabeads. NSG mice bearing intraperitoneal or subcutaneous MKN28 xenografts, systemic metastatic MKN45 xenografts, and orthotopic Capan2 xenografts were treated with EpCAM CAR T cells to test the in vivo efficacy. PET/CT imaging was adopted to monitor T cell dynamics using 18F-NOTA-octreotide which binds specifically to somatostatin receptor 2 (SSTR2) introduced in CAR T cells.

Results: Jurkat cells transduced with C215 and UBS54 CARs displayed 3.5 nM and 264.3 nM binding affinities to soluble EpCAM, respectively. EpCAM CAR expression in primary human T cells was higher than 50%. CD8+ to CD4+ T cell ratios were 1:1. Compared to high-affinity C215 CAR T cells, low-affinity UBS54 CAR showed equivalent cytotoxicity against high-density EpCAM-expressing targets (MKN28, MKN45 and HT29), but slower killing of low-density EpCAM-expressing cell line MDA-MB-231. T cell activation as monitored by CD69 upregulation and cytokine secretion (IL2, IFN-γ, TNF-α, GM-CSF and MIP-1β) of C215 and UBS54 CAR T cells were similar, and correlate well with EpCAM density on tumor cell surfaces. In immunodeficient mouse models, low-affinity UBS54 CAR potently eliminated intraperitoneal and subcutaneous gastric tumors (MKN28), systemic metastatic gastric tumor (MKN45), and orthotopic pancreatic tumor (Capan2). Notably, the level of T cell expansion in the course of tumor killing, observed by PET/CT imaging, was significantly lower for UBS54 CAR than high-affinity C215 CAR.

Conclusions: Low-affinity EpCAM targeting CAR T cells demonstrated durable antitumor activity against various tumor models in vivo. To enhance safety and therapeutic efficacy, micromolar affinity anti-EpCAM CAR T cells are currently being evaluated to limit cell killing to EpCAM-positive tumor cells while sparing normal cells with basal levels of EpCAM expression.

Citation Format: Yanping Yang, Jaclyn E. McCloskey, Huan Yang, Janusz Puc, Angel A. Gomez Gallegos, Yogindra Vedvyas, Irene M. Min, Eric von Hofe, Moonsoo M. Jin. Eradication of EpCAM expressing solid tumors by low-affinity CAR T cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6598.