Humanized Mouse Models to Study Mechanisms of Intestinal Inflammation

Abstract

IBD can result from hyperactivation of T effector cells, and/or regulatory T cells (Tregs) dysfunction. Studies in mice show that Treg function is critical to maintain mucosal immune homeostasis, yet, a critical barrier to understanding human Treg function in the intestinal mucosa is the lack of a robust in vivo model and limitations on experimenting with human subjects. Development of immunodeficient mouse strains such has NOD.SCID.IL-2Rγ-/- (NSG) has enabled engraftment of human leukocytes into a murine host, permitting the study of human immune cells in vivo in a xenobiotic setting. Using this approach, we have developed two novel mouse models of intestinal inflammation that are dependent on human T cells. For anti-CD3 enteritis, 8-10 week old NSG mice were injected with 2x106human CD4+ (hCD4+) T cells, and12 days later, mice received either a single i.p. injection of OKT3 or control IgG. Serum was collected at 0,1,6, and 24 hours and analyzed for human cytokines by luminex. Intestinal inflammation was assessed after 24 hours based on clinical and histological scores. T cell activation was quantified by flow cytometry for spleen and small intestine lamina propria. qPCR was performed on RNA isolated from splenic T cells and small intestine RNA. For TNBS-induced colitis, two days following transfer of 2 ×106hCD4+ T cells, mice were sensitized with 1% TNBS solution applied to 1 cm2 patch of skin at the base of the neck. One week post-sensitization, mice were administered a single intrarectal dose of 0.125 mg TNBS in 50% ethanol. Weight loss was monitored daily and mice were sacrificed three days following the TNBS enema. Colonic inflammation was assessed by H&E stained colon sections. OKT administration resulted in diarrhea and severe small intestine villous atrophy within 24 hours, only in hCD4+ reconstituted NSG mice. In addition, OKT3 promoted T cell recruitment into the SI lamina propria, reduced cell surface CD3 expression and concomitant increase in CD25, a marker of activation. NSG mice receiving OKT3 in the absence of hCD4+ T cells were free of clinical or histological signs of inflammation, indicating that hCD4+ T cells are necessary for OKT3-induced enteritis. hCD4+ reconstituted NSG mice, following sensitization and exposure to TNBS, exhibited clinical and histological features of colitis in contrast to control NSG mice lacking hCD4+ T cells. Human CD4+ T cells adoptively transferred into NSG mice can induce small bowel and colonic inflammation in mice following exposure to OKT3 and TNBS respectively. These models will facilitate preclinical assessment of therapeutic applications targeting T cells and aid in mechanistic studies evaluating pathways controlling mucosal homeostasis.