Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Investigating correlates of protection in the non-human primate model of pharyngitis by comparison of Combo#5 vaccines adjuvanted with Alum and SMQ (#297)

Steven J Hancock 1 , Tania Rivera-Hernandez 1 2 , Diane G Carnathan 3 , Johanna Richter 1 , Jacelyn M S Loh 4 , Charles Armitage 5 , Nichaela Harbison-Price 1 , Jack Na 1 , Maria Lawrenz 6 , Celine Lemoine 6 , Amanda J Cork 1 , Anca Grivei 5 , Nia Bickham 1 , Katelyn E Richards 1 , Khanh Nguyen 1 , Laura Davis 1 , Brody Pullinger 1 , Ruby Pelingon 1 , Reuben McGregor 4 , Gayathiri Elangovan 1 , Miguel Aguirre 1 , Stephan Brouwer 1 , Thomas Proft 4 , Nikki J Moreland 4 , Patrice Dubois 6 , Nicolas Collin 6 , Gabrielle T Belz 5 , Guido Silvestri 3 , Mark J Walker 1
  1. Centre for Superbug Solutions and Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
  2. Unidad de Investigación Médica en Inmunoquímica, Hospital de Especialidades del Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Mexico City, Mexico
  3. Emory Vaccine Center and Emory National Primate Research Center, Emory University, Atlanta, Georgia, USA
  4. School of Medical Science, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
  5. Frazer Institute, The University of Queensland, Brisbane, Queensland, Australia
  6. Vaccine Formulation Institute (VFI), Plan-les-Ouates, Switzerland

The preferred product characteristics for a Group A Streptococcus (GAS) vaccine, as outlined by the World Health Organization, recommend effective protection against pharyngitis as a relevant and feasible goal for early phase clinical development. The non-human primate (NHP) model of GAS pharyngitis has been used to investigate vaccine immunogenicity and efficacy. Whilst opsonophagocytic killing (OPK) has been suggested as a potential correlate of protection for M protein-based vaccines, factors that provide protective efficacy for non-M protein vaccines are not defined. Here, we explore efficacy, OPK and antigen neutralization using the NHP pharyngitis model to compare preclinical GAS vaccine Combo#5 antigens formulated with either aluminium hydroxide (Alum) the SMQ adjuvent. SMQ is a squalene-in-water emulsion containing the saponin QS21 and the synthetic toll-like receptor 4 ligand 3D(6-acyl)-PHAD®, which elicits a more balanced Th1/Th2-type immune response compared with aluminium hydroxide. Vaccination of NHPs with Combo#5-SMQ resulted in reduced GAS colonization whereas vaccination with Combo#5-Alum did not. Both Alum-adjuvanted and SMQ-adjuvanted vaccines generated high antibody titers against all five Combo#5 antigens. Neither vaccine generated detectable OPK titers. Both vaccines generated comparable functional inhibition of streptolysin O and Streptococcus pyogenes cell envelope IL8 protease (SpyCEP). These findings suggest that correlates of protection afforded by the Combo#5-SMQ vaccine formulation may be represented by differences in functional inhibition of other Combo#5 antigens or other immunological parameters.