Abstract 5207: Development of MHC I/II knock-out immunodeficient mouse strains for alleviating GvHD induced by human PBMC reconstitution
Authors: Liu Qiang , Shang Chengzhang , Zhou Xiaofei , Frame Jenna , Shen Zhiyuan , Yu Zhaoxue 
Published: April 2023

Abstract
Severely immunodeficient mouse strains, such as B-NDG mice, lack B, T, and NK cells, and have been widely used as an in vivo model to evaluate human immune responses, including applications in immuno-oncology in recent years. However, when human peripheral blood mononuclear cells (PBMCs) are engrafted in these mice, severe acute xenogeneic graft-versus-host disease (GvHD) arises due to engagement of human T cell receptors (TCRs) with major histocompatibility complex (MHC) proteins I and II on the surface of murine immune cells. GvHD shortens the animal life span such that there is only a brief window of evaluation of human immune cell functions in these mouse models. Consequently, efforts have been undertaken to reduce human PBMC-induced GvHD and to subsequently extend the window of human immunity assessment in immunodeficient mouse strains by eliminating mouse MHC I and MHC II. We previously engineered a novel B2m gene knock-out strain on the B-NDG background (NOD.CB17-PrkdcscidIl2rgtm1/Bcgen), which is deficient in MHC I expression, but expresses the B2m gene fused into the FcRn gene to retain FcRn-mediated antibody metabolism. In order to eliminate MHC II expression, we also engineered an H2-Ab1 gene knock-out strain on the same B-NDG background and cross-bred the two strains together to obtain an MHC I/II double KO mouse model, termed B-NDG MHC I/II DKO mice plus. Splenocytes collected from the engineered strains were analyzed by flow cytometry. As expected, mouse H-2Kb/H-2Db was not detectable in B-NDG B2m KO plus mice or B-NDG MHC I/II DKO mice plus. While mouse I-Ak was detected in B-NDG mice and B-NDG B2m KO plus mice, it was not detected in B-NDG MHC I/II DKO mice plus. Pharmacokinetic assessments demonstrate that B-NDG mice and B-NDG B2m KO mice plus groups were able to recycle human IgG, with no differences when compared with wild-type C57BL/6 mice, indicating normal FcRn function. Finally, the three strains of mice were irradiated and engrafted with human PBMC from three donors to evaluate GvHD incidence. As expected, the reconstitution levels of CD45+ leukocytes, T cells, CD4+ T cells, CD8+ T cells, Tregs and NK cells were similar among the three strains. However, lack of MHC I/II in B-NDG MHC I/II DKO mice plus can significantly extend the life span and reduce GvHD induced by human PBMC engraftment compared to B-NDG mice and B-NDG B2m KO mice plus. These results indicate that B-NDG MHC I/II DKO mice plus provides a useful mouse model for reducing GvHD after human PBMC reconstitution in immunodeficient mice. This model may be a powerful preclinical tool for future in vivo evaluation of cell therapies and antibodies.
Citation Format: Qiang Liu, Chengzhang Shang, Xiaofei Zhou, Jenna Frame, Zhiyuan Shen, Zhaoxue Yu. Development of MHC I/II knock-out immunodeficient mouse strains for alleviating GvHD induced by human PBMC reconstitution. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5207.