Abstract 31: Characterization and cross comparison of cancer xenografts in humanized mice

Abstract Immunotherapy has emerged as a promising cancer treatment strategy, including approaches such as immune checkpoint inhibitors (ICIs), cytokine-based therapies, chimeric antigen receptor (CAR) T-cell therapies, oncolytic viruses, cancer vaccines, and combination treatments. ICIs and CAR-T-cells have revolutionized cancer therapy, significantly enhancing the treatment landscape for a variety of cancers. However, despite encouraging results in preclinical models, translating novel therapies into clinical success remains challenging. Traditional rodent models, which have long been fundamental in cancer research, have limitations in mimicking human immune responses. To address these challenges, humanized mouse models have recently emerged as a critical tool. These models incorporate human immune components, providing a more accurate representation of how human immune systems interact with tumors. In this study, we explored the differences in the longitudinal dynamics of human immune cell populations across two distinct humanization mouse models. One model was generated using CD34+ hematopoietic stem cells (HSC) derived from cord blood donors, while the other was created by injecting human PBMCs. The PBMC-based model included characterization of several different PBMC donors, whereas the CD34+ HSC-based model involved evaluation of distinct stem cell donors across various CDX models.Our findings reveal dynamic changes in immune cell composition and behavior in humanized mouse models. In CD34+ HSC-humanized mice, the overall amount of human CD45+ cells in peripheral mouse blood declines over time including a shift of immune cell populations. B cells are initially predominant but decrease as the T cell compartment increases. In PBMC-humanized mice, the proportion of human immune cells in the circulation starts low (1-3% of total CD45+ cells) but increases significantly over time, reaching up to 70%, depending on the donor. These human immune cells are mainly comprised of T cells, whereas other hematopoietic compartments, like B cells or Monocytes are quickly lost. In both humanized mouse models, PBMC and CD34+ HSC, expression of the activation marker PD-1 on T cells increases over time. Notably, the CD4:CD8 T cell ratio, as well as overall numbers, are different for each model.Based on our studies tumor characteristics, rather than the type of PBMC or stem cell donor, are the primary drivers of immune cell infiltration. We found that tumor-specific factorsare key in shaping immune responses. This highlights the critical role of intrinsic tumor properties in modulating the immune microenvironment and influencing therapeutic outcomes. These results provide valuable insights into the selection of appropriate humanized models and can inform experimental timing for testing novel immuno-oncology therapies. This may ultimately lead to more personalized and effective cancer treatment strategies. Citation Format: Ulrike Litzenburger, Stephanie Stahnke, Oliver von Ahsen, Simon Heller, Philipp Renke, Natalie Altenburg, Ellen Hauke, Rene Zernicke, Carlo Stresemann. Characterization and cross comparison of cancer xenografts in humanized mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 31.