Background: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment for hematological malignancies and non-malignant disorders. However, graft-versus-host disease (GvHD) remains a major complication, and achieving durable immune tolerance without compromising graft-versus-leukemia (GvL) effects is a significant clinical challenge.
Aim: The aim of this master’s thesis is to systematically review randomized controlled trials (RCTs) evaluating immunological or pharmacological strategies aimed at promoting immune tolerance in allo-HSCT.
Materials and Methods: A systematic review was conducted in accordance with PRISMA 2020 guidelines. PubMed, Web of Science, and Scopus databases were searched for RCTs published between 2015 and 2025 investigating tolerance-inducing strategies in allo-HSCT recipients. Data were extracted on study design, interventions, outcomes, and immune biomarkers, and a narrative synthesis was performed.
Results: Seven RCTs met inclusion criteria. Included RCTs evaluated interventions such as conditioning regimens (total lymphoid irradiation anti-thymocyte globulin (TLI-ATG)), graft source modification, synbiotics, mesenchymal stromal cells (MSC), daclizumab, sirolimus-based regimens, and anti-T lymphocyte globulin (ATLG). Several strategies increased Treg frequencies or improved immune reconstitution. Synbiotics and MSC infusions significantly reduced severe acute or chronic GvHD. However, heterogeneity in study designs and small sample size limited the certainty of evidence.
Conclusion: Multiple immunomodulatory strategies demonstrate potential for enhancing immune tolerance in allo-HSCT by modulating Treg reconstitution and immune pathways, with promising effects on GvHD outcomes. Integration of cellular, microbial, and pharmacological approaches could optimize transplant success, but further large-scale RCTs are required to strengthen this evidence
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