Capecitabine mitigates cardiac allograft rejection via inhibition of TYMS-Mediated Th1 differentiation in mice.

Objectives: Previous studies elucidated that capecitabine (CAP) works as an anti-tumor agent with putative immunosuppressive effects. However, the intricate mechanisms underpinning these effects remain to be elucidated. In this study, we aimed to unravel the molecular pathways by which CAP exerts its immunosuppressive effects to reduce allograft rejection.

Methods: Hearts were transplanted from male BALB/c donors to male C57BL/6 recipients and treated with CAP for seven days. The rejection of these heart transplants was assessed using a range of techniques, including H&E staining, immunohistochemistry, RNA sequencing, LS-MS/MS, and flow cytometry. In vitro, naïve CD4 T cells were isolated and cultured under Th1 condition medium with varying treatments, flow cytometry, LS-MS/MS were employed to delineate the role of thymidine synthase (TYMS) during Th1 differentiation.

Results: CAP treatment significantly mitigated acute allograft rejection and enhanced graft survival by reducing graft damage, T cell infiltration, and levels of circulating pro-inflammatory cytokines. Additionally, it curtailed CD4 T cell proliferation and the presence of Th1 cells in the spleen. RNA-seq showed that TYMS, the target of CAP, was robustly increased post-transplantation in splenocytes. In vitro, TYMS and its metabolic product dTMP were differentially expressed in Th0 and Th1, and were required after activation of CD4 T cell and Th1 differentiation. TYMS-specific inhibitor, raltitrexed, and the metabolite of capecitabine, 5-fluorouracil, could inhibit the proliferation and differentiation of Th1. Finally, the combined use of CAP and the commonly used immunosuppressant rapamycin can induce long-term survival of allograft.

Conclusion: CAP undergoes metabolism conversion to interfere pyrimidine metabolism, which targets TYMS-mediated differentiation of Th1, thereby playing a significant role in mitigating acute cardiac allograft rejection in murine models.