S230: HUMAN ΒETA-DEFENSIN 2 TREATMENT MODULATES THE INTESTINAL MICROBIOME AND THE ALLOGENEIC T CELL RESPONSE TO LIMIT ACUTE GRAFT-VERSUS-HOST DISEASE

Abstract

Background: Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy option for patients with hematological malignancies. Acute graft-versus-host disease (GVHD) is primarily driven by allogeneic donor T cells and remains a serious cause of morbidity and mortality post allo-HCT. In particular, acute GVHD of the gastrointestinal tract (GI GVHD) is associated with a high mortality rate and treatment options are limited. Human β-defensin 2 (hBD-2) is an endogenous epithelial cell-derived host-defense peptide, which is induced by inflammatory stimuli and possesses both antimicrobial and immunomodulatory functions. Aims: In this study, we aimed to investigate the expression of beta defensins in human and murine GI GVHD and the therapeutic effect of recombinant hBD-2 on acute GVHD development in mouse models. Methods: To investigate the functional role of hBD-2 post allo-HCT, we employed established murine GVHD and graft-versus-leukemia (GVL) models and analyzed the allogeneic T cell response using transcriptome and kinome profiling. Shotgun metagenomic sequencing was used to examine the effect of hBD-2 on the intestinal microbiome. Furthermore, we studied beta-defensin expression in two independent acute GVHD patient cohorts and in mice with acute GVHD. Results: We found that expression of murine beta-defensin 4 (mBD-4), the murine orthologue for hBD-2, was reduced in the colon and ileum of mice developing acute GVHD. Oral treatment of mice with recombinant hBD-2 post allo-HCT reduced weight loss and acute GVHD severity and mortality. Furthermore, hBD-2 treatment affected the intestinal microbial composition, including a shift towards higher abundance of Bacteroides species in hBD-2 treated compared to vehicle treated mice. The changes in the microbiome resulted in reduced neutrophil infiltration of the ileum during acute GVHD induction in hBD-2 treated mice. Additionally, hBD-2 dampened pro-inflammatory Th1 cytokine production (TNF, IFN-gamma) by allogeneic T cells in vivo, while preserving the beneficial GVL effect in two different leukemia models. Mechanistically, oral hBD-2 treatment decreased alloreactive T cell infiltration and the expression of genes involved in T cell receptor (TCR) signaling in the ileum of mice with acute GVHD. Using transcriptome and kinome profiling, we found that hBD-2 directly dampened primary murine and human allogeneic T cell proliferation, activation and metabolism by reducing proximal TCR signaling. In patients with acute GI GVHD, intestinal hBD-2 expression was inadequately induced in response to inflammation at the mRNA and protein level when compared to healthy subjects and patients with ulcerative colitis. Summary/Conclusion: In conclusion, our study demonstrates that hBD-2 reduces acute GVHD severity, likely through its effects in shaping the intestinal microbiota, reducing neutrophil infiltration in the ileum and dampening allogeneic T cell responses. Both human and murine acute GVHD are characterized by a lack of intestinal beta-defensin induction and recombinant hBD-2 represents a potential novel therapeutic strategy to counterbalance endogenous hBD-2 deficiency.