Regulatory T cell therapy in solid organ transplantation: clinical applications and laboratory monitoring strategies.

Regulatory T cells (Tregs) play a fundamental role in maintaining immunological homeostasis and sustaining immune tolerance. In solid organ transplantation, Tregs have emerged as a promising strategy of cellular immunotherapy capable of reducing allograft rejection and mitigating long-term complications. Early-phase clinical studies have established the safety and feasibility of adoptive Treg therapy. Building on these pivotal findings, Treg therapy has created a solid foundation for translational application. However, successful clinical implementation requires a deeper understanding of Treg biology, clarification of their mechanisms of action, and the development of reliable strategies for in vivo monitoring. This review provides a detailed overview of Treg mechanisms, ongoing clinical trials, and methodological approaches for evaluating their phenotype and function through cell-based, protein-based, and gene-based assays. In addition, it highlights key considerations for optimizing therapeutic efficacy and ensuring safety, with the ultimate aim of advancing Treg therapy toward routine clinical use in solid organ transplantation.