Balancing Tumor Response and Rejection Risk After Pre-Transplant Immunotherapy: A Scoping Review

Importance: Immune checkpoint inhibitors (ICIs) have expanded downstaging options for hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), enabling bridging to liver transplantation (LT). However, the immunologic consequences of pre-transplant checkpoint blockade, particularly the risk of allograft rejection mediated by persistent T-cell activation, remain insufficiently characterized, creating a critical knowledge gap at the intersection of immuno-oncology and transplant medicine. Objective: To synthesize current evidence on oncologic outcomes, rejection risk, washout intervals, donor-type considerations, and immunosuppression strategies in LT recipients with pre-transplant ICI exposure. Evidence Review: A PRISMA-ScR-guided review was conducted using MEDLINE, Embase, Cochrane Library, and Web of Science from January 2015 through December 2025. Studies reporting outcomes in adult LT recipients with documented pre-transplant ICI exposure for HCC or CCA were included. Methodological quality was descriptively assessed using the Newcastle-Ottawa Scale and JBI tools. Given study heterogeneity, findings were narratively synthesized. Findings: Thirty studies were included. In HCC, neoadjuvant ICI therapy achieved downstaging to Milan criteria in 75.6% of candidates in the largest multicenter cohort (n = 117), with complete pathologic response rates ranging from 23.8% to 40%. Rejection rates ranged from 16.3% to 20.2% in large series but increased to 56.3% with short washout intervals. Washout intervals exceeding 50 days were associated with rejection rates approaching non-ICI controls, while an individual patient meta-analysis of 91 patients estimated each additional week of washout was associated with approximately 8% reduction in rejection risk, suggesting that approximately 94 days may be required to achieve a rejection probability of 20% or less. Rejection occurred at a median of 7-10 days post-transplantation, earlier than typical acute cellular rejection. Three-year overall survival exceeded 85.3% in major cohorts. Donor type was not consistently associated with rejection after adjustment for washout duration. CCA data remain limited. Immune-related adverse events during ICI therapy were associated with increased post-transplant rejection risk. Conclusions: Pre-transplant ICI therapy may expand transplant eligibility in advanced hepatobiliary malignancies but carries time-dependent rejection risk. Current evidence supports a minimum washout interval of at least 50 days, with emerging data favoring 90-94 days when feasible. Prospective multicenter studies, biomarker-guided risk stratification, and standardized immunosuppression protocols are needed to refine patient selection and optimize timing.