Humanized mouse models are an invaluable tool to analyze human immune responses, particularly responses to immunotherapies for cancer. To accomplish humanization, immunodeficient mice are engrafted with human hematopoietic stem cells (hHSC) leading to the expression of diverse human immune cell lineages. There has been a recent surge in literature describing various humanized models that differ based on the source of hHSCs, mouse strain, mouse age at time of engraftment, and method of myeloablation. Furthermore, commercial strains of humanized mice are becoming available for investigators to purchase for their studies, albeit at a high cost. Most commonly, the highly immunodeficient NSG mouse is utilized in humanization studies, however, other NSG-based humanized models are emerging. The NSG-SGM3 strain combines the scid and IL2Rg mutations in NSG mice with transgenic expression of human cytokines SCF, GM-CSF, and IL3, to support the engraftment of myeloid cell lineages. For better engraftment of NK cells, the NSG-IL15 strain may be preferred as it expresses the NSG mutations combined with human IL15. NSG-b2M and NSG-(KbDb)null(IA)null strains are powerful models of resistance to graft vs. host disease (GvHD) due to the loss of either MHC class I or both MHC class I and II molecules, respectively, in addition to the NSG mutations.

Aims of this project are to (1) optimize and characterizing the CD34+ hHSC humanized models, (2) establishing humanized models of tumor growth, and (3) demonstrate altered response to immunotherapy in humanized mice bearing tumors. NSG, NSG-SGM3, and NSG-IL15 mice will each be engrafted with CD34+ hHSCs for a period of 12 weeks prior FACS analysis of peripheral blood to assess humanization. A subset of humanized animals will be injected with MDA-MB-231T cells in the mammary fat pad. Non-tumor bearing animals will be monitored for disease-free survival. Final analysis of blood, bone marrow, spleen, tumor, and thymus will be conducted by FACS and histology to determine the level of humanization, profile of human immune cell engraftment, presence of human immune cells in the tumors, and any secondary deleterious pathology. In the second phase of the project, an efficacy study will be conducted on humanized and non-humanized tumor-bearing animals treated with PD-1 inhibitor, a clinically approved immunotherapeutic agent for breast cancer, to examine the response to therapy in the humanized model compared to non-humanized mice.