Single-cell RNA sequencing reveals the reconstitution of the hepatic immune microenvironment in pediatric liver transplantation

Liver transplantation is a highly effective treatment for end-stage liver disease; however, long-term immunosuppression leads to various adverse effects. Thus, operational tolerance has gained attention. Pediatric liver transplant recipients show a greater likelihood of attaining operational tolerance compared to adults in a previous study, serving as an ideal model for exploring immune reconstitution and tolerance. Here, we used single-cell transcriptomics to monitor immune reconstitution in pediatric recipients initially treated with tacrolimus and later withdrawn to identify tolerance. Our data revealed that comprehensive immune reconstitution occurs after pediatric liver transplantation, including the activation of CD4 + T cells, NK cells and B cells, and a marked inflammatory signature in myeloid cells, demonstrating that liver-infiltrating immune cells maintain long-term activation phenotypes. Intriguingly, recipients with failed tacrolimus withdrawal exhibited higher proinflammatory status in myeloid cells and increased cytotoxicity in FGFBP2 high CD8 T cells, compared to those with successful withdrawals. More importantly, we revealed that FGFBP2 high CD8 T cells enriched in the transplanted liver after tacrolimus withdrawal potentially interacted with HSCs via TGFB1-TGFBR2 pathways. Concurrently, HSCs underwent an activation, indicating a risk of liver fibrotic progression, even among patients who had attained operational tolerance. Hence, our findings illuminate a dynamic immune reconstitution landscape occurring within transplanted livers, offering valuable insights into operational tolerance associated with pediatric liver transplantation.