Abstract 22: Development and characterization of human tumor specific cytotoxic lymphocytes for preclinical drug development

Abstract Heterogeneity within a tumor allows it to better adapt to changing conditions and can have therefore a negative impact on a patient’s prognosis, response to treatment and overall health. Breast cancer is a highly heterogeneous disease caused by distinct genetic mutations in mammary epithelial cells, resulting in significantly different forms of the disease and a need for highly personalized treatment schemes for patients. Hence, it is important to develop and improve (immuno) therapies for breast cancer patients. Adoptive T-cell therapy with autologous CD8+ cytotoxic T cell lymphocytes (CTL) is a promising method that has already shown promising effects in melanoma patients. Unfortunately, there is almost no information about the use in breast cancer patients. We developed an in vitro protocol to generate tumor-specific CTLs by priming on HER2+ breast cancer cell lines JIMT-1 and SKBR-3. Subsequently, these primed CTLs were tested in 2D and 3D immune cell killing assays in a life cell imaging device in combination with an endpoint viability assay. The activity was compared with unspecific CD8+T cells activated by phytohemagglutinin (PHA) or αCD2/αCD3/αCD28, HER2-peptide specific T cells and HER2-CAR T cells serving as a positive control. We investigated the feasibility to freeze CTLs for use in subsequent studies and validated the relevance of HER2 as the main druggable target in the tumor lines using an siRNA approach. The CTLs were most effective on JIMT-1 in a 3D setting, whereas the SKBR-3 CTLs displayed similar activity in 2D and in 3D. The respective CTLs were tumor line specific, as SKBR-3 CTLs did not kill efficiently the JIMT-1 cells and vice versa. The same CTLs displayed the same efficacy pattern after thawing but less pronounced. Thus, within one experimental set-up it is recommended to use either one. The Her2 knockdown in the target cells reduced the killing activity of the CTLs slightly. However, this effect was not statistically significant proving the importance of CTLs as treatment option as well as neoantigens as targets in drug development. In summary, the CTLs proved to capture the respective tumor heterogeneity showing high killing rates in both SK-BR3 and JIMT-1 being more active than HER2-peptide specific T cells. The availability of CTLs in a preclinical setting facilitates screening approaches for combinational studies. Beyond that they can serve as starting material to develop cancer vaccines and identify highly immunogenic neoantigens. Citation Format: Ina Rohleff, Lea Gröne, Kanstantsin Lashuk, Julia B. Schueler. Development and characterization of human tumor specific cytotoxic lymphocytes for preclinical drug development abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 22.