Oral tributyrin supplementation induces regulatory T cell–mediated immune regulation and prolongs allograft survival in preclinical transplant models

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, Treg-dependent prolongation of graft median survival time (33 [IQR 24.0–40.5] vs. 15.5 [IQR 12.0–18.0] days; p=0.0007 ). In a semi-allogeneic heart model, tributyrin similarly extended graft survival (52 [IQR 27.0–67.5] vs. 14.5 [IQR 12.25–22.0] days; p=0.0038 ). Oral tributyrin increased the frequency and activation of graft-infiltrating Tregs, marked by elevated IL-10, CTLA-4, LAG-3, and CD25, while reducing CD8 + T-cell infiltration and their 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.