1495: Multi-Omic Signatures of Overactive Autoantibody Activation After Pediatric Traumatic Brain Injury

Introduction: Evidence grows that autoantibody-mediated secondary injury in traumatic brain injury (TBI) can result in long-term outcomes. We implemented a multi-omic (transcriptomic, metabolomic, and immune-repertoire) workflow to identify early signals forecasting broad autoantibody expansion correlated to prolonged rehabilitation in pediatric TBI. Methods: Samples were collected on days 0, 2, and 9 from seventeen children (median age13. 1 y) with severe TBI (GCS < 8, mean ISS of 31), critically ill patients. Whole-blood RNA-seq, untargeted LC-MS metabolomics, and immunoglobulin heavy-/light-chain (IGH, IGK, IGL) repertoire modeling were assessed relative to clinical recovery. Results: IGH clonal expansion was significantly elevated at day 9 (2. 4 ± 1. 2 clones/clonotype, p = 0. 02) compared to controls (1. 4 ± 0. 2), day 0 (1. 3 ± 0. 2), and day 2 (1. 3 ± 0. 2). The patient with the longest rehab showed pronounced IGH activation at day 9 (6. 0 clones/clonotype, z-score = 5. 4), with 3, 505 IGH clonotypes linked to brain antigens including Amyloid-beta, S100B, Synapsin I, NMDAR, MOG, Aquaporin-4, GAD65, and GFAP. This individual had a day 0 response enriched for immune activation (HSA-168256, FDR = 2. 5E-7), membrane trafficking (HSA-199991, FDR = 4. 2E-6), and Epstein-Barr virus response (hsa05169, FDR = 1. 1E-5), alongside elevated lipids (PG 18: 0₁8: 3, LPI 17: 0, PE P-20: 0/17: 1, LPI 14: 1). All timepoints showed elevated UFA/PUFA-LPC to SFA-LPC ratios and unconjugated bile acids, with enrichment of nervous system-specific genes (BTO: 0001484), alternative splicing (KW-0025), and membrane-bound organelles (GOCC: 0043227). Splicing outlier analysis revealed consistent use of NPC2 isoform-201 rather than isoform-207 (average z-score –1. 5), resulting in a three–amino acid deletion in a protein linked to brain-lipid damage response. Conclusions: An isoform switch in the cholesterol-regulating NPC2 may promote lipid buildup and lysosomal stress that prime antigen-presenting cells and B Cell mediated downstream injury. These findings demonstrate the power of multi-omic integration to reveal early molecular drivers of autoantibody amplification in pediatric TBI, offering critical pathways for antibody-targeted diagnostics and immunotherapy.