Abstract 5189: Comparisons of Rituximab and CD19xCD3 BiTE antitumor response across multiple humanized NSG strains engrafted with human hematopoietic stem cells
Authors: Kang Won Yeong , Yang Guoxiang , Radichev Ilian , Yao Li-Chin , Cheng Mingshan , Keck James G. 
Published: April 2023

Abstract
Humanized NSG mice engrafted with hematopoietic stem cells (HSCs) is a well-known in vivo platform for reconstitution of human immune system in a mouse host. In this study we tried to dissect the role of various human cytokines in the generation of the human immune system, expansion of human B cell lymphoma cells, and drug response to two anti-cancer therapies - Rituximab and CD19XCD3 BiTE (Bispecific T-cell Engager). To exclude donor variabilities, we first humanized five NSG-based, human cytokine-transgenic mouse strains (NSG, NSG-IL15, NSG-SGM3, NSG-SGM3-IL15, and NSG-FLT3L) with HSCs from one donor (0084). We found that tumor growth was enhanced in NSG-SGM3 mice when compared to NSG mice. In contrast, IL15 expression suppressed tumor growth in NSG-IL15 and NSG-SGM3-IL15 mice. Furthermore, NK cell frequencies in blood are higher in NSG-IL15 and NSG-SGM3-IL15 than in other strains. suggesting that NK cell-mediated cytotoxicity is involved in suppression of tumor cell growth in the strains expressing human IL-15. Rituximab treatment resulted in tumor growth inhibition and significant B cell depletions across NSG-IL15, NSG-SGM3, and NSG-SGM3-IL15 mice engrafted with 0084 PBMC. We also observed a donor variability of tumor growth rates in NSG-SGM3-IL15 mice engrafted with donors 0084, 0662A, and 0733. The tumor growth in NSG-SGM3-IL15 mice engrafted with 0084 PBMC was significantly slower than the one in mice engrafted with the other two donors (0084 vs. 0662A, P=0.002; 0084 vs. 0733, P=0.004 on day 21); interestingly, this strain of mice exhibited higher frequencies of CD8+ T cells and lower frequencies of NK cells. Next, we tested CD19XCD3 BiTE treatment in multiple NSG strains engrafted with HSCs from different donors. The BiTE administration inhibited Raji tumor growth and significantly depleted B cells in all tested strains as NSG-SGM3-IL15 showed highest frequencies of NK cells and CD8+ T cells. The combination of Rituximab and BiTE showed even better tumor inhibition efficacy. In conclusion, regardless of the donor and strain variations in tumor growth and human immune cell subset development, the administrations of rituximab or BiTE significantly and consistently inhibited tumor growth and depleted peripheral B cells across all mouse strains. These results indicate that utilizing a comprehensive humanized mouse platform could drive more impactful conclusions in terms of evaluating the anti-tumor efficacy of immune therapies.
Citation Format: Won Yeong Kang, Guoxiang Yang, Ilian Radichev, Li-Chin Yao, Mingshan Cheng, James G. Keck. Comparisons of Rituximab and CD19xCD3 BiTE antitumor response across multiple humanized NSG strains engrafted with human hematopoietic stem cells. [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 5189.