Background: Group A Streptococcus (Strep A) infections are associated with diverse clinical manifestations from mild infections like impetigo and pharyngitis through to serious invasive disease and postinfectious sequalae such as acute rheumatic fever (ARF). There is currently no licenced vaccine for Strep A and investigations of antibody responses tend to focus on selected, putative vaccine candidates. Here, a novel Phage-Immunoprecipitation Sequencing (PhIP-Seq) library based on the entire Strep A genome (StrepScan) is utilised to comprehensively profile Strep A serum antibodies at extraordinary depth and breadth.
Methods: The StrepScan library was generated using a global atlas of Strep A genomes and represents 9847 open reading frames covered by >48,000 overlapping peptides. The library was incubated with sera from children (n=92) with different Strep A disease manifestations recruited in Aotearoa New Zealand (ARF, pharyngitis, impetigo, healthy) followed by immunoprecipitation and next-generation sequencing of enriched phage.
Results: StrepScan results for major virulence factors (normalised enrichment score per antigen) were highly correlated with immunoassays for the same antigen validating the methodology. Multiple overlapping peptides mapping to vaccine antigens, as well as novel targets, were shown to be significantly enriched in sera from participants with Strep A disease. Enrichment scores were leveraged to identify immunodominant regions of leading vaccine antigens and comparison of these epitopes in participants with different disease manifestations including ARF.
Conclusion: StrepScan enables unprecedented exploration of the circulating StrepA antibodiome and can be used to both identify novel antigenic targets following infection and epitope map reactivity across the entire StrepA proteome.