Introduction: Identifying risk factors for allograft injury is fundamental to preserve its long-term function in pediatrics. Preliminar evidence at our center showed that tacrolimus variability and HLA-DQ eplet mismatch (eMM) load are independent risk factors for developing biopsy-proven acute rejection (BPAR). Still, the role of donor-specific antibodies (DSA) has been elusive in liver transplantation. In this study we aim to evaluate the correlation between BPAR and demographic, immunological, pharmacological, and transplant-related factors, and to characterize the development of de-novo DSA (dnDSA) in pediatric liver transplantation.
Methods: Pediatric patients transplanted between 2018-2021 were included and prospectively followed. Donor/recipient pairs were HLA-typed by Next Generation Sequencing and the HLA eplet mismatch (eMM) was quantified using the HLA-Matchmaker algorithm. Tacrolimus variability was quantified as tortuosity and dnDSA was evaluated from available serum using LIFECODES Single Antigen Assays. Demographic, clinical, and pharmacological covariates were included in univariate and multivariate Cox regression models to identify predictors for BPAR development. Chi-square test was used to assess the association between the two categorical variables dnDSA and BPAR.
Results: Sixty-six of the 112 enrolled patients had data available on HLA typing and were on tacrolimus as primary immunosuppression. BPAR-free survival at 1 year post-transplant was 69.9% (95%CI, 67.0-87.8), but only 39.1% (95%CI, 24.4-62.7) of the patients were free of rejection at 4 years post-transplant. Tacrolimus tortuosity (HR 11.50, 95%CI, 4.55-28.96; p<0.001) and HLA-DQ antibody-verified (ab) eMM (HR 1.20, 95%CI, 1.02-1.40; p=0.026) were identified as independent risk factors for BPAR. Single-antigen assay results were available in 56 patients, and 15 of them (26.8%) were DSA positive of whom 12 had DSA anti-HLA class II, 2 had anti-HLA class I, and 1 had anti-HLA class I and II antibodies. The most frequent DSA was anti-HLA-DQ (n=9) and all of these patients developed BPAR. The proportion of patients who were positive for total DSA (p=0.027), anti-class II DSA (p=0.001), or anti-DQ DSA (p=0.002) was greater in those with BPAR than in patients free of rejection.
Conclusion: In this large cohort of patients, we emphasize the role of tacrolimus variability and HLA molecular mismatch as factors associated with BPAR. Our data supports the role of DSA in pediatric liver allograft health and further studies are being performed to assess the time-dependence between the development of BPAR and DSA, and their association with other histopathologic findings, including chronic rejection and fibrosis.