Abstract P3-08-07: Self-renewal signatures of peripheral blood T cells are associated with successful engraftment to establish a humanized mouse model of breast cancer

Background: Stable humanized immune mice transplanted with peripheral blood mononuclear cells (PBMCs) derived from breast cancer patients are important models for assessing the tumor immune responses and the tumor immune microenvironment in breast cancer, helping to advance both pre-clinical and clinical research. The PBMCs of breast cancer patients exhibit various differences from those of healthy individuals depending on the stage of cancer progression, subtype, and type of treatment. Recent studies indicate an association of the self-renewal signatures of T cells with successful generation of a humanized mouse model; however, the optimal T cell signature for the successful generation of a humanized mouse model derived from cancer patient cells is poorly understood. Therefore, we examined the relationship between the signature of T cell subsets, focusing on the self-renewal signatures, in PBMCs derived from patients with breast cancer and the successful generation of a humanized immune mouse model. Materials and Methods: We collected PBMCs from 12 patients with breast cancer. All samples were stimulated with interleukin-2 and beads coated with CD3 and CD28 agonist antibodies to expand T cells. After washing, 1 × 10^7 cells/mouse were intraperitoneally injected into NOD/Shi-scid IL2rgamma (null) (NOG) mice. Transplants were performed on three mice per case. Successful engraftment of immune cells into NOG mice was defined by the presence of human CD45+ cells in one or more mice. Self-renewal signatures of in vitro expanded T cells before injection into NOG mice, including the markers T cell factor-1 (TCF-1), CD45RA, CCR7, CD95, and CXCR3, were determined using flow cytometry, mass cytometry and quantitative RT-PCR. Comparisons between groups of data were evaluated by t-test. Results: The success rate of engraftment of immune cells derived from breast cancer patients into NOG mice was 66.7% (8 out of 12 patients). After expansion, the magnitude of the CD8+ stem cell memory subset and the TCF-1 expression level on the CD4+ and CD8+ T cells in the engrafted group were significantly higher than those in non-engrafted group. TCF-1 and CCR7 mRNA levels in the engrafted group were upregulated compared with those in non-engrafted group. The success of engraftment was not associated with clinical characteristics such as breast cancer progression, subtype, or prior chemotherapy treatment. Conclusion: The self-renewal signatures of T cells from breast cancer patients were associated with successful engraftment of a humanized mouse model. These results suggest that prior identification of the self-renewal signatures of the T-cell population is of direct relevance to the appropriate design of a pre-clinical model for testing immunotherapies and for elucidating the characteristics of the tumor immune microenvironment. Citation Format: Yukiko Fukui, Kosuke Kawaguchi, Ryuji Murakami, Wei Li, Yuki Nakamura, Yurina Maeshima, Sunao Tanaka, Shinpei Kawaoka, Eiji Suzuki, Masakazu Toi. Self-renewal signatures of peripheral blood T cells are associated with successful engraftment to establish a humanized mouse model of breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-08-07.