TCR β CDR3 repertoire remodeling in pediatric myocarditis reveals clonal expansion and disease-associated public clonotypes

Background: Pediatric myocarditis is an inflammatory disease of the heart with heterogeneous clinical presentations and poorly understood immune mechanisms. T cell receptor (TCR) repertoire profiling provides insights into disease-associated adaptive immune responses. Methods: We performed high-throughput sequencing of TCR β chain CDR3 repertoires from 28 peripheral blood samples of pediatric myocarditis patients (Myo) and nine age-matched healthy controls (NC). Clonal diversity, V and J gene usage, CDR3 length distribution, clonotype sharing, and antigen-specific annotations were systematically analyzed. Results: The Myo group exhibited significantly reduced clonal diversity as measured by D50 and Chao1 indices, accompanied by expansion of large clones and reduced representation of small clones. Distinct biases in V and J gene usage were observed, with increased TRBV14, TRBV28, TRBJ1-1, TRBJ1-2, TRBJ1-5, TRBJ1-6, and TRBJ2-2, and decreased TRBV9, TRBJ2-4, TRBJ2-5, and TRBJ2-7. CDR3 length distribution showed an enrichment of longer sequences in myocarditis patients, alongside altered nucleotide insertions/deletions and amino acid usage. Clonotype sharing was markedly higher in the Myo group, and 16,460 public clonotypes were detected in ≥10 patients. Database annotation revealed an enrichment of matches to pathogen-associated TCR records, predominantly associated to Mycobacterium tuberculosis, influenza, cytomegalovirus, and Epstein-Barr virus. Seventeen high-frequency clonotypes were highlighted as candidate myocarditis-related TCR signatures based on database matches. Conclusions: Our study demonstrates distinct repertoire remodeling in pediatric myocarditis, characterized by reduced diversity, skewed V/J gene usage, biased CDR3 composition, and enriched public clonotypes. These findings provide novel insights into disease-related adaptive immune responses and may inform biomarker discovery for diagnosis and therapeutic strategies.