GMPA Versus PPI for Gastric Protection and aGVHD Risk

The goal of this clinical trial is to observe whether different gastric protection strategies affect the incidence of acute graft-versus-host disease (aGVHD) in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Proton pump inhibitors (PPIs) are routinely used for gastric protection during transplantation, but their prolonged use may suppress gastric acid, alter gut microbiota, and potentially increase the risk of aGVHD. Teprenone, a gastric mucosal protective agent (GMPA), enhances mucosal defense mechanisms including promoting mucus secretion, increasing gastric mucosal blood flow, and facilitating epithelial cell repair, without affecting gastric acid secretion, and may therefore preserve microbial diversity and modify aGVHD risk. This study compares two strategies: continuous PPI use versus switching from PPIs to teprenone after transplantation. The main questions this study aims to answer are: * Does switching from PPIs to teprenone after transplantation reduce the cumulative incidence of aGVHD within +100 days post-transplantation compared with continuous PPI use? * What adverse events do participants experience with teprenone versus continuous PPI therapy? * Does teprenone therapy provide better preservation of gut microbial diversity and lower rates of gastrointestinal and infectious complications compared with continuous PPI use? In this prospective, randomized, parallel-controlled, single-center trial, approximately 198 patients undergoing allo-HSCT will be enrolled and assigned in a 1:1 ratio using a central randomization system. The experimental group (teprenone group) will receive standard-dose PPIs (esomeprazole, 40 mg/d, intravenous/oral) during conditioning and switch to teprenone (50 mg tid, orally) after transplantation through day +100. The control group (PPI group) will receive continuous standard-dose PPIs from conditioning through day +100. Probiotic use is prohibited from conditioning through day +100 in both groups. All other anti-infective, GVHD prophylaxis, and supportive care regimens are identical between the two groups. The primary endpoint of this study is the cumulative incidence of aGVHD within +100 days post-transplantation. Secondary endpoints include grade II-IV and grade III-IV aGVHD, lower gastrointestinal aGVHD, steroid-refractory aGVHD, gut and salivary microbiome dynamics (α-diversity, β-diversity, and specific taxa at pre-conditioning, day 0, day +14, and day +28), plasma biomarkers related to intestinal barrier integrity, systemic inflammation, and immune regulation , infectious and gastrointestinal complications (febrile neutropenia, diarrhea, C. difficile infection, bacteremia, EBV/CMV reactivation, upper GI bleeding, reflux), and 1-year survival outcomes (non-relapse mortality, overall survival, GVHD-free/relapse-free survival). During the study, participants will: * Receive the assigned gastric protection regimen (teprenone or PPI) according to randomization * Undergo regular assessments for safety and efficacy monitoring, including aGVHD surveillance and infection screening * Provide fecal and saliva samples at pre-conditioning, day 0, day +14, and day +28 post-transplantation for microbiome analysis * Provide peripheral blood samples at pre-conditioning, day 0, day +14, and day +28 post-transplantation for exploratory analysis * Be followed for up to 1 year post-transplantation