EBV-reactive KIR+ CX3CR1+ CD8+ T cells mediate liver transplantation tolerance.

BACKGROUND & AIMS: Immune tolerance after transplantation reduces immunosuppression-related complications and improves the overall survival rates. The unique tolerogenic microenvironment of the liver enables a proportion of liver transplantation (LT) recipients to develop tolerance with intact liver function. However, the underlying immunological mechanisms remain unclear. METHOD: s: We integrated single-cell transcriptome/TCR profiling, flow cytometry, in vitro killing assays, HLA-E peptidome from a retrospective cohort including 347 LT recipients, murine LT models, and a 20-participant prospective immunosuppressant withdrawal trial in pediatric LT recipients with median 26 months follow-up. RESULTS: We demonstrated that Epstein-Barr virus (EBV)-derived peptides can be presented by HLA-E on alloreactive CD4+ T cells to prime KIR+ CX3CR1+ CD8+ T cells, thereby promoting immune tolerance after LT. As a subset of CD8+ TEMRA cells, KIR+ CX3CR1+ CD8+ T cells utilize perforin and granzyme B to suppress alloreactive CD4+ T cells after LT. In vitro analysis unveiled that the EBV-derived peptide SQAPLPCVL could stabilize HLA-E expression on alloreactive CD4+ T cells and mediate recognition and elimination by KIR+ CX3CR1+ CD8+ T cells through a TCR-dependent mechanism. Furthermore, BATF was indispensable for induction of KIR+ CX3CR1+ CD8+ T cells. In the prospective immunosuppressant withdrawal clinical trial, the peripheral ratio of CD8+ TEMRA and KIR+ CX3CR1+ CD8+ T cells were suggested to be potentially useful in identifying tolerant recipients. CONCLUSIONS: Our study demonstrated a new immune tolerance mechanism mediated by KIR+ CX3CR1+ CD8+ T cells and established the connection between viral infection and tolerance formation, providing new insights into tolerance-inductive strategies after transplantation.