Enhanced diversity of human immune cells in a PBMC-engrafted NSG-SGM3-IL15-DKO (S15-DKO) immunodeficient mouse model

Background Peripheral blood mononuclear cell (PBMC)-humanized mouse models are critical tools for preclinical evaluation of cancer immunotherapies, yet current models offer limited recapitulation of human immune diversity, particularly myeloid and natural killer (NK) cells. To address this limitation, we generated a novel immunocompromised mouse strain NSG-SGM3-IL15-DKO (S15-DKO) combining the NSG-MHC I/II double-knockout (DKO), which delays xenogeneic graft-versus-host disease, with the NSG-SGM3-IL15 human cytokine-expressing strain. Here, we evaluated PBMC engraftment and established a humanized immune-oncology model to test bispecific T cell engager (BiTE) efficacy and cytokine release in S15-DKO mice compared to DKO mice. Methods S15-DKO and DKO mice were engrafted with 1x107 human PBMCs from various healthy donors, with or without prior exposure to Raji lymphoma cells or irradiation. Retro-orbital (RO) blood (and spleen) was collected to assess human immune cells engraftment by flow cytometry. Irradiated, Raji-bearing S15-DKO and DKO mice were treated with PBS or anti-CD3xCD19 BiTE. Bioluminescence imaging was performed to measure tumor burden, and plasma was collected to measure cytokine levels. Results S15-DKO mice engrafted with PBMCs from multiple donors supported significantly higher levels of human CD45 + cells, CD4 + and CD8 + T cells, and NK cells compared to DKO mice without the need for irradiation, with body weight changes and survival comparable to DKO controls. B cells, dendritic cells, and macrophages also showed significantly improved engraftment in S15-DKO mice compared to DKO mice with certain PBMC donors. Engraftment of PBMCs in S15-DKO mice bearing Raji lymphoma cells was also higher compared to DKO mice, with significantly elevated numbers of NK cells and dendritic cells in addition to T cells. Preconditioning the S15-DKO mice with irradiation prior to PBMC engraftment further enhanced immune cell reconstitution, accelerating engraftment kinetics and increasing absolute cell counts across multiple immune subsets. In a therapeutic model, irradiated S15-DKO mice bearing Raji-luc cells demonstrated superior tumor reduction and significantly higher levels of cytokine release compared to DKO mice following anti-CD3xCD19 BiTE treatment. Discussion These findings establish PBMC-humanized S15-DKO mice as a novel preclinical platform for evaluating efficacy and cytokine release of immunotherapies that require diverse populations of human immune cells.