Factors associated with operational tolerance after liver transplantation: a single center retrospective study.

Background: Liver transplantation has adverse effects from life-long immunosuppression that limit the improvement of long-term outcomes. Achieving clinical operational tolerance is a major goal in organ transplantation. Methods: This study analyzed liver transplantation patients at a single institution from 1998 to 2020, excluding those who died within 1-year posttransplant. Operational tolerance was defined as normal liver function even after immunosuppressive drugs were discontinued. Propensity score matching was implemented at a 1:2 ratio for the tolerant group (TG) and the nontolerant group (NTG). Results: Out of 2,300 recipients, 99 achieved operational tolerance without rejection. No significant differences in sex or body mass index (BMI) were found between the TG and NTG. There was a significantly higher percentage of children in the TG (24.0%) than in the NTG (10.1%). The NTG had more living donor liver transplants. Among 2,054 adult recipients, no significant differences in age, sex, or BMI were found between the TG and the NTG. However, the rate of living donor liver transplantation was 40.3% (29/75) in the TG and 84.8% in the NTG (P<0.001). The propensity score-matched analysis showed higher chronic renal failure rates and a higher graft recipient weight ratio in the TG, along with shorter warm ischemic times during surgery. After immunosuppressant withdrawal, a significant increase in the ratio of CD4+CD25+ T cells to total CD4+ T cells was observed in the TG. Conclusions: These findings suggest that larger, healthier grafts are more conducive to inducing tolerance, and regulatory T cells are crucial in achieving tolerance.