Abstract 112: The NSG-Flt3KO; Tg(hFLT3LG); hIL15 mouse strain improves engraftment of innate immune cells post-CD34+ humanization

Abstract Human immune system mouse models play critical roles in numerous preclinical drug development pipelines, including immunology, infectious diseases, and immuno-oncology. These models are constantly evolving, with addition of human cytokines to sustain engraftment of human immune cells. To date, most humanized models have primarily focused on T lymphocyte cell biology, leaving room for improvement in developing models that effectively represent NK cells and the myeloid lineage. Previously, we demonstrated that the introduction of human IL-15 (NSG-IL-15) or FLT3L (NSG-FLT3L) to NOD-scid IL2rγnull (NSG) mice enhanced engraftment of innate immune cells, including human CD56+ NK cells, CD141+ and CD1c+ DC subsets, CD123+ pDCs, and CD14+ monocytes. In this study, we describe a new NSG mouse variant (NSG-Flt3KO; Tg (hFLT3LG) ; hIL15) that expresses physiological levels of both human IL-15 and FLT3L and detail the immune cell diversity following HSC engraftment. NSG-Flt3KO; Tg (hFLT3LG) ; hIL15 mice, along with control strains NSG, NSG-IL15, and NSG-FLT3L, were engrafted with human umbilical cord blood derived CD34+ hematopoietic stem cells from three different donors, and blood samples were collected until Week 20 post-transplantation. Blood samples were analyzed via flow cytometry to assess the engraftment of innate and adaptive immune cells. Spleen and bone marrow samples were collected at Week 12 post-transplantation and analyzed for lymphoid and myeloid immune cell populations via flow cytometry. To compare the differences among the strains in terms of immune cell sub-populations across weeks, a Two-Way ANOVA (mixed-model) was conducted, with p0. 05 considered statistically significant. Overall, the results demonstrate that NSG-Flt3KO; Tg (hFLT3LG) ; hIL15 mice have enhanced CD56+/dim CD16+ NK cells compared to NSG-FTL3L strain (20. 5±12. 8% vs 7. 0±3. 5% at Week 12), but comparable to NSG-IL15. Furthermore, myeloid sub-lineage cells in NSG-IL15-FLT3L mice, such as monocytes, macrophages (M1), granulocytes, dendritic cells, and neutrophils, were greater than in NSG or NSG-IL15 strains, but comparable to NSG-FLT3L mice. Overall levels of hCD45+ and T cell sub-populations (CD3+ or CD4+ or CD8+) were comparable across all strains tested. In sum, our NSG-Flt3KO; Tg (hFLT3LG) ; hIL15 engraftment data suggest an improved model that supports drug development targeting human myeloid and NK cell populations. Citation Format: Srinivas Reddy Boreddy, Shuang Hu, Brian Soper. The NSG-Flt3KO; Tg (hFLT3LG) ; hIL15 mouse strain improves engraftment of innate immune cells post-CD34+ humanization 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 112.