(859) Conserved Human CD4 T Cell Targets Inform Group A Streptococcus Vaccine Design

Introduction/Rationale: Group A Streptococcus (GAS) is a globally prevalent bacterial pathogen responsible for over 500,000 deaths annually and a leading cause of post-infectious autoimmune diseases, yet no vaccine is available. Current vaccine development focuses primarily on antibody responses to a limited set of antigens, while targets of T cell immunity remain largely undefined.

Methods: In this study, we performed comprehensive mapping of human CD4 T cell responses to GAS through high-throughput screening of 2,661 peptides spanning 196 literature-curated antigens in donors with prior GAS exposure.

Results: We identified 392 epitopes mapping to 85 antigens, revealing an unexpectedly broad T cell repertoire. Notably, 20 immunodominant antigens, recognized by ≥20% of donors, accounted for 75% of total GAS-specific CD4 T cell responses. These included known vaccine candidates (SCPA, streptolysin O, SpyCEP) as well as multiple novel targets with comparable or superior immunogenicity (SibA, Isp and NADase). Functional enrichment analysis revealed that dominant antigens exhibited hydrolase activity (70%) and were predominantly extracellular or cell wall-associated (60%). Conservation analysis across 2,083 globally sampled GAS genomes revealed strong sequence conservation among dominant antigens, supporting universal vaccine potential. T cell response magnitude decreased with donor age, mirroring serological patterns and suggesting reduced recent infection frequency in older individuals. Lastly, we leveraged epitope mapping to develop optimized peptide pools enabling efficient detection of GAS-specific T cells for future mechanistic and clinical studies.

Conclusion: Together, this study defines the most comprehensive mapping of human GAS-specific CD4⁺ T cell targets to date. These findings provide a roadmap for next-generation GAS vaccines incorporating robust T cell targets and establish tools to investigate immunopathology in GAS-associated autoimmune sequelae.