Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Development of a whole blood assay to detect Group A Streptococcus (GAS) specific T cell responses and application to school-based studies in The Gambia (#293)

Ya Jankey Jagne 1 , Dawda Jobe 1 , Mustapha Jarju 1 , Chilel Sanyang 1 , Edward Monk 1 , Fatoumata Sillah 1 , Jainaba Njie Jobe 1 , Edwin Armitage 1 2 , Alex Remmington 3 , Helen Alexandra Shaw 3 , Fatme Mawas 3 , Michael Marks 4 , James Hindley 5 , Martin Scurr 5 , Thushan De Silva 1 6
  1. Medical Research Council Unit, The Gambia at LSHTM, Bakau, United Kingdom
  2. Bristol Medical School,Population Health Sciences,, University of Bristol, Bristol, United Kingdom
  3. Vaccines Division, Science, Research & Innovation, Medicines and Healthcare Products Regulatory Agency, Potters Bar EN6 3QG, UK, United Kingdom
  4. London School of Hygiene and Tropical Medicine, London, United Kingdom
  5. ImmunoServ Ltd., , Cardiff, United Kingdom
  6. Division of Clinical Medicine, School of Medicine and Population Health, The University of Sheffield, Sheffield, United Kingdom

Background:
Protective cellular immunity to Group A Streptococcus (GAS) is poorly characterised in human studies, partly due to the lack of standardised and reproducible assays. We aimed to design and evaluate a whole blood T-cell assay suitable for use in field studies to assess GAS-specific T-cell immunity.

Methods:

Fresh heparinised whole venous blood samples were stimulated overnight with lyophilised GAS antigens (SCPA, SpyCEP, and SpyAD) to measure cytokine secretion from harvested plasma using ELISA and multiplex bead assays. Testing for antigen immunogenicity, concentration optimisation and antigen stability was performed in five UK adult donors using reconstituted and lyophilised antigens. Cytokine responses to GAS antigen stimulation were analysed in a cohort of 40 schoolchildren (ages 6-14) in The Gambia.

Results :
Immune responses generated by UK-based adult donors were lower to lyophilised than reconstituted GAS antigens; however, they remained strong and consistent to all antigens tested. Amongst schoolchildren in The Gambia, younger children (6-9 years) showed higher IFN-g, IL-4, and IL-6 responses to SpyCEP, while older children (10-14 years) had higher TNF-a responses to SCPA. IFN-g responses showed strong correlations with IL-17a. Isolated low-IFN-g responders demonstrated high responses to other cytokines.

Conclusion:
This standardised whole blood T-cell assay using lyophilised antigens is a promising tool for identifying cellular immune correlates of protection against GAS, supporting vaccine development and facilitating use in field trials, especially in resource-limited settings. Ongoing work in this cohort will characterise responses before and after pharyngitis and pyoderma.