Proteomic Signatures and Early Biomarkers Predicting Veno-Occlusive Disease in Pediatric Patients Undergoing Haploidentical Hematopoietic Cell Transplantation with Busulfan-Based Conditioning and Post-Transplant Cyclophosphamide.

Hepatic veno-occlusive disease (VOD), or sinusoidal obstruction syndrome, is a life-threatening complication following hematopoietic cell transplantation (HSCT). In pediatric patients, busulfan-based myeloablative conditioning is a major risk factor. This study aimed to identify plasma proteomic biomarkers predictive of VOD development in children undergoing haploidentical HSCT with busulfan-based conditioning and post-transplant cyclophosphamide (PTCy). Plasma samples were collected from 51 children (VOD, n = 26; control, n = 25) at baseline and 1 to 4 h postbusulfan infusion on days -8 to -5. Proteomic profiles using liquid chromatography-tandem mass spectrometry identified 720 proteins. Differential abundance, longitudinal clustering, pathway enrichment, and machine learning-based biomarker selection were performed. The VOD group exhibited predominantly down-regulated proteins, with minimal changes from baseline during early treatment. Pathway enrichment analysis revealed distinct temporal patterns between the groups. At baseline, the VOD group showed enrichment in homeostasis-related pathways, while detoxification pathways were persistently activated postconditioning. In contrast, the control group demonstrated early activation of detoxification pathways, which gradually declined, suggesting effective oxidative stress management. A machine learning model, trained on a discovery cohort (70%) and 30% validated on a separate cohort (30%), identified 15 biomarkers. Notably, glutamate-cysteine ligase catalytic subunit (GCLC), crucial for glutathione biosynthesis, and fructose-bisphosphatase 1 (FBP1), a gluconeogenic enzyme, were down-regulated at baseline in the VOD group. Baseline down-regulation of proteins such as GCLC and FBP1 may serve as early biomarkers for predicting VOD, facilitating timely prophylactic interventions in high-risk pediatric patients undergoing haploidentical HSCT with busulfan-based conditioning and PTCy.