Neutrophil-associated plasma proteomics identifies HDAC1 as a baseline biomarker of immune tolerance during immunosuppressant withdrawal after pediatric liver transplantation: a single-center cohort study

Background In pediatric liver transplantation (pLT), long-term immunosuppression (IS) contributes to infection risk and chronic toxicity, yet IS minimization or withdrawal requires balancing rejection risk. Practical biomarkers for baseline risk stratification at the start of planned withdrawal remain scarce. This study investigated whether baseline neutrophil-associated proteomic signatures and histone deacetylase 1 (HDAC1) levels are associated with IS withdrawal outcomes. Methods Within an institutional IS withdrawal program (n = 77), 59 recipients had evaluable outcomes by the follow-up cut-off (June 30, 2025). Among these, 31 pLT recipients underwent planned IS withdrawal (primary analytic cohort), and baseline plasma from 10 patients was analyzed via liquid chromatography-mass spectrometry (LC-MS) proteomics to identify tolerance-associated proteins and pathways. HDAC1 was subsequently quantified by ELISA in 39 recipients with baseline plasma available. The diagnostic performance of HDAC1 in distinguishing immune-tolerant (IT) from non-immune-tolerant (NIT) outcomes was evaluated using receiver operating characteristic (ROC) analysis. To corroborate tissue-level consistency, HDAC1 expression was assessed by immunohistochemistry (IHC) in baseline liver biopsy sections from 10 recipients (5 IT and 5 NIT) selected from the planned withdrawal cohort. Results Proteomic profiling revealed distinct baseline differences enriched in neutrophil-related functions, including pathways linked to degranulation and neutrophil extracellular trap (NET) formation. HDAC1 was identified as a key candidate marker, with significantly lower baseline levels observed in the IT group. In the validation cohort, plasma HDAC1 demonstrated moderate discriminative performance for baseline risk stratification (AUC = 0.81). Furthermore, IHC analysis of baseline liver biopsies showed lower intrahepatic HDAC1 staining in IT recipients compared to the NIT group, consistent with the systemic plasma findings. Conclusions Baseline neutrophil-linked proteomic signals and diminished HDAC1 expression are associated with successful IS withdrawal in pLT recipients. These findings support HDAC1 as a hypothesis-generating candidate biomarker for baseline risk stratification and provide a clinically oriented framework to refine patient selection and enhance early monitoring during IS minimization and withdrawal protocols.