Rapamycin-modified novel tolerogenic dendritic cells induce liver graft tolerance through MHC-II+CD8+ regulatory T cells

BACKGROUND: Inducing transplant tolerance to achieve long-term graft survival without immunosuppression remains a central objective in liver transplantation. METHODS: Using a rat liver transplantation model, we evaluated the effects of infusing rapamycin-modified tolerogenic dendritic cells (Rapa-tolDCs) on graft survival and tolerance induction. Underlying molecular and cellular mechanisms were investigated through activation and inhibition experiments to assess the generation, signaling pathways, and suppressive functions of regulatory T and B cell populations. RESULTS: Infusion of Rapa-tolDCs induced donor-specific tolerance and markedly prolonged graft survival (median survival time of 65 days, maximum of 102 days). Mechanistically, Rapa-tolDCs, characterized by low expression of Siglec1 and Spp1, functioned independently of the PI3K-mTOR pathway and promoted the differentiation and proliferation of CD8+CD45RClow/- regulatory T cells (CD8+CD45RClow/- Tregs). We identified that these Tregs acquired MHC-II molecules from donor cells via trogocytosis, becoming immune chimeric cells that predominantly secreted interleukin-10 (IL-10) to mediate immune suppression. The generation of these MHC-II+CD8+ Tregs was regulated by the Wnt5a/Fzd4/RhoD signaling axis. Furthermore, elevated levels of Foxp3+ Tregs and IL-10+ Bregs were found to contribute to prolonged graft survival following Rapa-tolDC infusion. CONCLUSIONS: These findings delineate a complete mechanistic pathway from cell therapy to donor-specific tolerance and provide a foundational strategy for clinical tolerance induction and post-transplant immunomodulation.