363 Human Hematopoietic Stem Cells With a Defined Immunodeficiency and Enteropathy Transfer Clinical Phenotype to a Novel Humanized Mouse Strain

Abstract

Investigation into the pathogenesis of IBD has been limited by the absence of humanized murine IBD models. The development of immunodeficient mouse strains has facilitated the study of human immune reconstitution in murine hosts. However, adaptive immune responses and antibody class switching are generally weak in models that lack autologous fetal thymic grafts, possibly due to human CD4+ T cell selection in the mouse thymus occurring on murine major histocompatibility complex II (MHCII). To address this, we modified the widely utilized NOD.Prkdc.Il2rγ (NSG) immunocompromised strain to be deficient for murine MHCII (NSGAbo) and instead expressed human leukocyte antigen-DR1 under the control of the murine MHCII promoter (NSGAboDR1). We tested whether CD4+ T cell development and adaptive immune responses are improved following reconstitution using human HLA-matched CD34+ hematopoietic stem cells (HSCs) and whether immune reconstitution using HSCs from a patient with IPEX (immunodeficiency, polyendocrinopathy, enteropathy, X-linked), a well-defined immunodeficiency, that is caused by a mutation in the transcription factor FOXP3, would transfer the clinical phenotype to NSGAboDR1 mice. Results: At 20 weeks following HSC injection into radiation-conditioned neonates, we found that the development of human T cells and dendritic cells were increased in NSGAboDR1 mice and that these mice displayed delayed-type hypersensitivity response to a secondary recall antigen challenge. There was an increase in T cell clonotype diversity as determined by CDR3 sequencing of the TCRβ gene in CD4+ T cells in NSGAboDR1 mice compared to NSG mice. In addition, NSGAboDR1 mice had an increase in mature B cells and antibody class switching compared to NSG and NSGAbo mice. We then reconstituted NSGAboDR1 mice using HSCs from a patient with IPEX that is associated with functional defects in Treg and assessed if the clinical phenotype would be transferred to NSGAboDR1 mice. All mice reconstituted with IPEX CD34+ HSCs were deceased by 18 weeks while all control mice receiving healthy bone marrow CD34+ cells remained viable. IPEX mice developed lymphocytic infiltrate in lung, portal tract and bile ducts of the liver, and slight accumulation of lymphocytes in the small intestine similar to scurfy mice, which also harbor a mutation in Foxp3. CD4+ T cell in IPEX mice had an expanded effector memory T cell population and concomitant decrease in Naive CD4+ T cells. Conclusions: We demonstrate that human HSCs from a patient with a defined genetic immunodeficiency and enteropathy can transfer the disease phenoytpe in a novel humanized mouse strain. This strain does not require grafts of human fetal tissue nor is it restricted to autologous fetal HSCs allowing for reconstitution using human HSCs with defined genetics to study human immune cells and IBD pathogenesis in vivo.