Poster Presentation 16th Lorne Infection and Immunity 2026

Experimental Streptococcus pyogenes pharyngitis expands memory B and CD4+ T cells in humans (132052)

Sabrina M. Bush 1 , Holly A. Fryer 1 , Catherine Pitt 1 , Nitika Kandhari 1 2 , Hannah R. Frost 3 , Alana L. Whitcombe 4 5 , Pailene S. Lim 6 7 , Rainbow Chan 6 , Stephen W Scally 6 7 , Nicole J. Moreland 4 5 , David M. Tarlinton 8 , Joshua Osowicki 3 9 10 , Andrew C. Steer 3 9 10 , Danika L. Hill 1
  1. Precision Vaccinology Laboratory, Department of Immunology, School of Translational Medicine, Monash University, Melbourne, VIC, Australia
  2. Monash Genomics and Bioinformatics Platform, Monash University, Melbourne, VIC, Australia
  3. Tropical Diseases Research Group, Murdoch Children's Research Institute, Melbourne, VIC, Australia
  4. Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand
  5. School of Medical Sciences, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
  6. Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia
  7. Department of Medical Biology, University of Melbourne, Melbourne, VIC, Australia
  8. Immune Memory Laboratory, Department of Immunology, School of Translational Medicine, Monash University, Melbourne, VIC, Australia
  9. Department of Paediatrics, University of Melbourne, Melbourne, VIC, Australia
  10. Department of Infectious Diseases, Royal Children's Hospital Melbourne, Melbourne, VIC, Australia

Streptococcus pyogenes is a globally ubiquitous bacterium often associated with mild, self-limiting cases of “strep throat”, or pharyngitis, in young children. However, it is also responsible for lesser-known pathogeneses like invasive skin infections and acute rheumatic fever, both of which disproportionately afflict First Nations Australians and low- and middle-income countries. There is an urgent need to develop an effective vaccine against S. pyogenes, yet our limited understanding of how infection-induced cellular and antibody-mediated immune memory develop and contribute to protection against infection remains a hurdle for vaccine development. Here, we combine antigen tetramers and activation-induced marker (AIM) assays to phenotypically profile S. pyogenes antigen-specific B and T cell responses, respectively, in blood from healthy adults (n=25) before and after experimental pharyngeal challenge of emm75 S. pyogenes. Memory B and CD4+ T cells specific to all antigens (n=4-6) were detectable before challenge in most participants. In participants who developed symptomatic pharyngitis, antigen-specific memory T and B cells significantly expanded at one week post challenge and, in some cases, remained elevated for at least three months. Infection also induced a transient burst of antibody-secreting cells and elicited a CD4+ T cell response dominated by regulatory T cells, Th17, and Th17.1 subsets. Pre-existing B cell memory to some antigens was associated with milder clinical symptoms, and more severe infection correlated with some stronger T and B cell responses. Together, our findings demonstrate that human infection generates immune memory to key vaccine candidate antigens and reveal how a single exposure shapes S. pyogenes humoral and cellular immunity.