Donor-specific immune senescence as a candidate biomarker of operational tolerance following liver transplantation in adults: Results of a prospective, multicenter cohort study.

Immunosuppression can be withdrawn from selected liver transplant recipients, although robust clinical predictors of tolerance remain elusive. The Immune Tolerance Network ITN056ST study (OPTIMAL; NCT02533180) assessed clinical outcomes and mechanistic correlates of phased immunosuppression withdrawal (ISW) in nonautoimmune, nonviral adult liver transplant recipients. Enrolled subjects were ≥3 years posttransplant with minimal/absent inflammation or fibrosis on a screening liver biopsy. The primary end point was operational tolerance at 52 weeks following complete ISW. Of 61 subjects who initiated ISW, 34 failed during ISW and 10 restarted immunosuppression after completing ISW due to clinically manifest acute rejection. Only 10 of 17 clinically stable subjects remaining off immunosuppression at 1 year were ultimately deemed tolerant by biopsy. There were no cases of chronic rejection or graft loss; 28.3% developed de novo donor-specific antibody during ISW, which persisted in 11.3%. The majority of subjects (78.6%), including those who experienced rejection, ended the study on same or less calcineurin inhibitor than at baseline. A minority (16.4%) of histologically and clinically stable long-term adult liver transplant recipients can successfully discontinue and remain off immunosuppression. Increased frequency of donor-specific T cell senescence, C4d deposition, and higher density of immune synapses on the screening liver biopsy emerged as potential candidate biomarkers for operational tolerance.