Major advances have been achieved in targeted immunotherapy with significant clinical benefits for patients. However, on-target/off-tumor toxicity is a major concern. This issue highlights the clinical need for better targets to improve the safety profile of immunotherapies. On-target/off-tumor toxicity is mainly based on the expression of tumor-associated antigens (TAA) in healthy tissues under physiological conditions. Thus, new approaches have to be developed to restrict specificity of targeted immunotherapy selectively towards cancerous cells. One way to improve target specificity is multi-targeting of cancer cells, i.e. targeting more than one TAA per cancer cell. We developed a workflow to identify new tumor markers employing an unbiased high throughput flow cytometry-based screen on primary ovarian cancer samples. Co-expression of THY1, a marker of fibroblasts and hematopoietic stem cells, was revealed on cancer cells characterized by EPCAM expression, a marker of epithelial cells. We confirmed our findings by high content imaging analyzing several ovarian carcinoma samples. Next we assessed the safety profile of the target combination THY1-EPCAM by analyzing the expression across a multitude of healthy human tissue samples using again high content imaging. Cluster analysis showed correlation patterns within the datasets confirming our previous findings. In order to investigate the functionality of THY1-EPCAM as therapeutic t we combined this target pair with the adaptor CAR technology, a modular system composed of a CAR recognizing biotin and biotinylated antibodies which are specific for a certain antigen. This technology combines the flexibility and controllability of antibodies with the efficacy of CAR T cell-dependent killing of target cells. The functional in vitro characterization of adaptor CAR T cells targeting the THY1-EPCAM pair shows high specificity and efficacy. Moreover, we are going to conduct in vivo studies with adaptor CAR T cells to investigate the efficacy and safety of targeting THY1-EPCAM in a solid tumor model. In conclusion, we successfully identified a novel target combination in ovarian cancer utilizing flow cytometry-based screening complemented by high content imaging. The new target pair combination shows promising results in vitro in combination with adaptor CAR T cells indicating its potential use as future immunotherapy.

Citation Format: Christoph Herbel, Vera Dittmer, Manuel Martinez-Osuna, Sandy Reiß, Peter Mallmann, Dominik Ratiu, Michael Mallmann, Paurush Praveen, Werner Müller, Dominik Eckardt, Andreas Bosio. Identification of a novel tumor marker combination THY1-EPCAM for adaptor CAR T cell therapy in ovarian cancer [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 2813.