Abstract 7230: New mouse strains NSG-SGM3xIL15xDKO and NSG- FLT3LxDKO are superior to NSG-MHC I/II DKO mice for humanization of peripheral blood mononuclear cells

Abstract Background: Peripheral blood mononuclear cells (PBMC)-humanized mice serve as important platforms to evaluate efficacy and toxicity. NSG-MHC I/II double-knock out (DKO) mice have been widely used due to being a humanized T cell model with delayed graft-versus-host disease. However, achieving at least 5% engraftment within a week requires 10-15e6 PBMCs per mouse with irradiation, which accelerates PBMCs to engraft compared to non-irradiated mice. Additionally, engraftment of certain cell populations, such as natural killer (NK) cells and monocytes from PBMC has been challenging in the DKO strain. Therefore, we aimed to develop new mouse strains that can be better humanized with lower PBMC cell counts while gaining a variety of cell subtypes. Next generation DKO strains including NSG-SGM3xIL15xDKO (SDKO) and NSG-FLT3LxDKO (FDKO) engrafted with multiple PBMC donors were compared. Methods: Nonirradiated SDKO, FDKO, and DKO mice were intravenously (IV) injected with 10e6 (5 donors) or 15e6 (2 donors) PBMCs and retro-orbital breeds were collected for engraftment comparisons for up to 70 days. Additionally, we compared PBMC engraftment of SDKO, FDKO, and DKO with and without irradiation (2 donors) for 70 days. Results: When mice were engrafted with 10e6 PBMCs without irradiation, SDKO and FDKO achieved higher human CD45+ cells engraftment level in the periphery blood compared to DKO. Depending on the PBMC donors, SDKO or FDKO can achieve the highest engraftment rate sooner and reach the highest human CD45+ cell count among all the three strains. The peak engraftment levels of hCD45+ cells in SDKO or FDKO were 1.5-2.6 times higher than that in DKO. When mice were engrafted with15e6 PBMCs without irradiation, SDKO was engrafted rapidly and reached the highest engraftment level compared to the other two strains. FDKO was engrafted faster and showed a higher level than DKO mice before 28 days post-humanization. hCD3+T cells and hCD19+ B cells were the major cell populations post PBMC engraftment with significantly higher levels in SDKO and FDKO, compared to DKO. In addition, hCD8+ T cells and hCD56+ NK cells were engrafted at significantly higher numbers in SDKO compared to FDKO and DKO. Irradiation helped B cells to engraft at higher levels in SDKO and DKO for short term studies. Conclusions: The two new mouse strains, SDKO and FDKO, are engrafted with human PBMCs at a faster rate, and higher levels compared to DKO mice. In addition, SDKO provides better engraftments of CD8+ T cells and NK cells. Irradiated SDKO mice reach a higher hCD45+ peak engraftment level compared to the DKO. Thus, SDKO and FDKO may serve as new and improved platforms to assess preclinical immuno-oncology efficacy and toxicity. Citation Format: Nancy (Xiaoqing) Zheng, Kevin Tsai, Guoxiang Yang, Beau Parry, Destanie Rose, James Keck, Li-Chin Yao. New mouse strains NSG-SGM3xIL15xDKO and NSG- FLT3LxDKO are superior to NSG-MHC I/II DKO mice for humanization of peripheral blood mononuclear cells [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 7230.