IL-22 Administration Protects Intestinal Stem Cells from Gvhd

Factors regulating damage and regeneration of the intestinal epithelium after allogeneic BMT are poorly understood. We have previously shown that IL-22 produced by recipient-derived innate lymphoid cells (ILCs) provides a critical signal for epithelial recovery following experimental BMT. However, intestinal IL-22 levels are reduced in GVHD due to the elimination of radioresistant host ILCs. We therefore sought to determine if IL-22 administration post-BMT could negate the effect of ILC elimination and reduce GVHD pathology. We utilized a clinically modeled LP into C57BL/6 (B6) minor antigen mismatched model with T cell-depleted marrow and purified T cells transplanted into lethally irradiated mice.

We found that daily administration of rIL-22 (4ug IP starting day +7) led to decreased GVHD pathology in recipient small and large intestine three weeks post-BMT (p<0.001). Further assessment of the intestinal pathology indicated that recipients of rIL-22 had decreased intestinal crypt apoptosis in both small and large intestine (p<0.01) with no difference in intestinal and splenic  lymphocytes or inflammatory cytokine levels.

To assess the effects of IL-22 administration on the intestinal stem cell (ISC) compartment, we performed LP into B6 allo-HCT using Lgr5-LacZ ISC reporter mice. Recipients treated with rIL-22 demonstrated increased numbers of Lgr5+ ISC three weeks post-HCT during active GVHD with no immunosuppression (p<0.05). Furthermore, we found increased ISC Ki-67 expression in Lgr5-GFP reporter mice with GVHD after IL-22 treatment, indicating increased ISC proliferation in response to IL-22.

In addition to Lgr5+ cells, it has been reported that BMI-1+ crypt cells may possess ISC activity after crypt damage. Crypt cells from BMI-1-GFP reporter mice were indeed found to be IL-22R+ at baseline (7-10% IL-22R surface expression). However, BMI-1 mRNA expression in small intestine of mice with GVHD was not affected by IL-22 administration, suggesting that the effect of IL-22 administration in vivo was not due to stimulation of BMI-1+ cells. Additionally, there was no difference in Wnt3 or EGF expression, arguing that improved ISC survival after IL-22 administration was not due to improvement in ISC niche function. In contrast, IL-22 treatment demonstrated increased Reg3γ (p<0.001) and Reg3β (p<0.01) expression, suggesting a potential antimicrobial benefit of IL-22 administration.

In summary, we found that IL-22 administration could reduce intestinal pathology and improve ISC recovery in GVHD. This appeared to be due to direct stimulation of Lgr5+ ISCs, and not due to improved support of the ISC niche. These results suggest that post-transplant IL-22 administration represents a novel strategy to reduce gut GVHD by direct protection of intestinal epithelium without limiting immune function post-transplant.