Abstract
Immunosuppressive drugs remain essential for preventing rejection but carry significant toxicities, underscoring the need for safer, physiology-based immunomodulators. Tributyrin, a prodrug of butyrate with improved systemic bioavailability, has emerged as a metabolically driven immune regulator. Here, we evaluated whether oral tributyrin promotes immune tolerance and improves graft outcomes in preclinical transplantation models. In minor mismatch skin transplantation, tributyrin-treated recipients exhibited a significant, regulatory T cell-dependent prolongation of graft median survival time (33 [interquartile range {IQR} 24.0-40.5] vs 15.5 [IQR 12.0-18.0] days; P = .0007). In a semiallogeneic heart model, tributyrin similarly extended graft survival (52 [IQR 27.0-67.5] vs 14.5 [IQR 12.25-22.0] days; P = .0038). Oral tributyrin increased the frequency and activation of graft-infiltrating regulatory T cells, marked by elevated interleukin (IL)-10, cytotoxic T lymphocyte-associated protein 4 (CTLA-4), lymphocyte-activation gene 3 (LAG-3), and CD25, while reducing CD8+ T cell infiltration and their interferon gamma (IFN-γ) and granzyme B production. Tributyrin treatment also modulated the intragraft innate compartment, reducing proinflammatory M1 macrophage signatures while promoting M2 macrophages with increased IL-10 expression. Systemically, splenocytes from treated recipients produced more IL-10 and displayed selective hyporesponsiveness to donor, but not to third-party antigens, consistent with antigen-specific regulation. Collectively, these findings demonstrate that oral tributyrin enhances regulatory pathways, suppresses alloreactive effector responses, and prolongs allograft survival, supporting its potential as a safe metabolic adjunct in transplantation.