Abstract 5208: Development of immunodeficient mice expressing human IL3, GM-CSF, CSF1 and THPO for improved human myeloid and lymphoid cell reconstitution
Authors: Lv Ruili , Nie Yanhui , Zhang Jing , Frame Jenna , Liu Qiang , Jin James 
Published: June 2023

Abstract
Mice reconstituted with human immune cells are essential tools to study human immune reactions in vivo, including those involving cancer immunotherapies. A major limitation of these models is the poor development of human myeloid cells to mediate effective human immune cell-tumor interactions. This is because hematopoietic cells are highly dependent on several human cytokines for efficient differentiation, maturation, and survival. THPO (thrombopoietin) can enhance the maintenance of functional human hematopoietic stem cells, and stimulates the production and differentiation of megakaryocytes, which produce large numbers of platelets in the bone marrow. IL3 (interleukin 3), GM-CSF (granulocyte-macrophage colony-stimulating factor, CSF2) and CSF1 (macrophage colony-stimulating factor, M-CSF) are cytokines that promote the proliferation and differentiation of a variety of myeloid cells, including monocytes, macrophages, granulocytes, dendritic cells, and platelets. Because these cytokines lack sufficient cross-reactivity between human and mice, it is difficult to reconstitute human immune cells of these lineages in immunodeficient mice. Therefore, we predict that genetic humanization of these four cytokines will improve the reconstitution of human myeloid cells in immunodeficient mice. We engineered an M-CSF, GM-CSF, THPO, and IL3 humanized strain in the background of B-NDG mice (NOD.CB17-PrkdcscidIl2rgtm1/Bcgen), termed B-NDG MGMT3 mice. The full sequences of mouse Il3, Csf2, Csf1 and Thpo genes (except the UTRs) were respectively replaced with the coding sequences (CDS) of human IL3, CSF2, CSF1 and THPO genes. Human GM-CSF, CSF1 and THPO proteins were confirmed to be expressed by ELISA in B-NDG MGMT3 mice. Human CD34+ HSCs (3E4) were intravenously engrafted into wild-type B-NDG mice and homozygous B-NDG MGMT3 male and female newborn mice via the temporal vein. B-NDG mice were treated with 1.0 Gy irradiation, while B-NDG MGMT3 mice were not irradiated. The survival rate of B-NDG MGMT3 mice was similar to B-NDG mice until 16 weeks post-CD34+ engraftment. However, the body weight of B-NDG MGMT3 mice was significantly higher than that of B-NDG mice. Analysis of peripheral blood lymphocytes showed that the proportion of hCD45+ cells in B-NDG MGMT3 mice reached 25% starting from 12 weeks after engraftment and continued to rise; levels were significantly higher than that observed in B-NDG mice. The proportions and cell number of T cells, NK cells, monocytes, MDSCs, DCs and Tregs engrafted in B-NDG MGMT3 mice were higher than B-NDG mice. The results indicate that B-NDG MGMT3 mice are a novel humanized model for human myeloid and lymphocytic cell reconstitution that does not require preconditioning.
Citation Format: Ruili Lv, Yanhui Nie, Jing Zhang, Jenna Frame, Qiang Liu, James Jin. Development of immunodeficient mice expressing human IL3, GM-CSF, CSF1 and THPO for improved human myeloid and lymphoid cell 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 5208.