This study has the aim to analyze intestinal expression of endogenous antimicrobial peptides in patients with acute GVHD. The expression will be compared to intestinal expression of defensins in patients with colitis and patients without intestinal inflammation.

Acute graft-versus-host disease (GVHD) is a major cause of morbidity and mortality in patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT). Acute GVHD is characterized by complex deficiencies of the mucosal antimicrobial barrier and intestinal dysbiosis, which contribute to disease pathogenesis. Defensins are endogenous epithelial cell-derived antimicrobial peptides, which can protect epithelial barrier integrity, shape the intestinal microbiota composition and contribute to host immunoregulation. Deregulated expression of defensins has been reported in patients with colitis, including Chron's Disease and ulcerative colitis.

In this study, the investigators aim to analyze the expression of defensins in the intestine of patients with acute GVHD to study whether it is deregulated. The results will be valuable to study the role of defensins during acute GVHD pathogenesis or as potential biomarkers for disease activity.

Inclusion Criteria:

• age ≥ 18 years
• diagnostic endoscopy was performed
• diagnosis results available
• written informed consent
• ability to understand the nature of the study and the study related procedures and to comply with them

Exclusion Criteria:

• age < 18 years
• gastrointestinal cancer
• lack of informed consent

Adult patients who underwent diagnostic endoscopy