Abstract 7235: New mouse strain NSG-SGM3xIL15xDKO is better for PBMC engraftment in Raji-bearing mice of minor immune subsets compared to NSG-MHC I/II DKO mouse

Abstract Introduction: PBMC-humanized MHC I/II double knock-out (#025216, DKO) strain has shown strong T cell engraftment with minimal acute GVHD. We recently have developed two new mouse strains, NSG-SGM3xIL15xDKO (SDKO) and NSG-FLT3LxDKO (FDKO), and their engraftment comparison data will be presented in the same meeting. Here we aimed to investigate the engraftment of various immune cell types in SDKO and FDKO mice in the presence of tumor stimulation. Methods: We assessed PBMC engraftment levels and immune subtypes in irradiated SDKO, FDKO, and DKO implanted with lymphoma (Raji-luc and Nalm6-luc) and breast cancer (MDA-MB-231-luc) xenografts. In addition, we investigated the differences between irradiated and non-irradiated mice of the above three strains implanted with Raji-Luc cells. Whole blood via retro-orbital bleeds and spleen were collected to analyze engraftment and immune cell populations by flow cytometry. Five different PBMC donors were used. Results: We found irradiated SDKO and FDKO achieved higher PBMC humanization levels compared to DKO. Interestingly, Raji-luc cells stimulated PBMCs to engraft at a significantly higher level compared to PBS, MDA-MB-231-luc and Nalm6-luc cells. hCD3+ T cells were activated (HLA-DR+) in Raji-luc groups. The stimulatory effect of Raji-luc cells was also validated in the three strains without irradiation. PBS treated irradiated mice without tumor stimulation, both SDKO and FDKO had approximately 9-15 folds engraftment of CD19+ B cells and CD56+ natural killer (NK) cells, and some donors showed 2-4 folds engraftment of CD11c+HLA-DR+ dendritic cells and CD64+ macrophages compared to what was seen in DKO mice in early engraftment. After Raji-luc cells stimulation, the engraftments of above cell types were enhanced 3-4 folds over the DKO. Non-irradiated SDKO and FDKO showed a 2-3 folds increase in B cells and NK cells compared to those in DKO mice in early engraftment in peripheral blood in the PBS group. With Raji-luc cells, the engraftments of B cell and NK cells were enhanced 2-4 folds in SDKO and FDKO over DKO mice. Other tumor data will also be presented. Conclusion: Both PBMC-humanized SDKO and FDKO show improved NK cells and myeloid cells engraftment compared to DKO after tumor antigen stimulation. The response may vary based on PBMC donors and cancer cell lines. Irradiation also helps certain cell types like myeloid cells to engraft compared to no irradiation in the cancer models. Citation Format: Nancy (Xiaoqing) Zheng, Guoxiang Yang, James Keck, Li-Chin Yao. New mouse strain NSG-SGM3xIL15xDKO is better for PBMC engraftment in Raji-bearing mice of minor immune subsets compared to NSG-MHC I/II DKO mouse [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 7235.