A controlled human infection model of Streptococcus pyogenes pharyngitis (CHIVAS-M75): an observational, dose-finding study
Authors: Joshua Osowicki, Kristy I Azzopardi, Loraine Fabri, Hannah R Frost, Tania Rivera-Hernandez, Melanie R Neeland, Alana L Whitcombe, Anneke Grobler, Sarah J Gutman, Ciara Baker, Janet M F Wong, Jason D Lickliter, Claire S Waddington, Manisha Pandey, Tibor Schuster, Allen C Cheng, Andrew J Pollard, James S McCarthy, Michael F Good, James B Dale, Michael Batzloff, Nicole J Moreland, Mark J Walker, Jonathan R Carapetis, Pierre R Smeesters, Andrew C Steer
Journal: The Lancet Microbe (2021)

BackgroundStreptococcus pyogenes is a leading cause of infection-related morbidity and mortality. A reinvigorated vaccine development effort calls for new clinically relevant human S pyogenes experimental infection models to support proof of concept evaluation of candidate vaccines. We describe the initial Controlled Human Infection for Vaccination Against S pyogenes (CHIVAS-M75) study, in which we aimed to identify a dose of emm75 S pyogenes that causes acute pharyngitis in at least 60% of volunteers when applied to the pharynx by swab.MethodsThis observational, dose-finding study was done in a clinical trials facility in Melbourne (VIC, Australia). Groups of healthy volunteers aged 18–40 years, at low risk of complicated S pyogenes disease, and without high type-specific anti-emm75 IgG antibodies against the challenge strain were challenged and closely monitored as inpatients for up to 6 days, and then as outpatients for 6 months. Antibiotics were started upon diagnosis (clinical signs and symptoms of pharyngitis and a positive rapid molecular test) or after 5 days in those without pharyngitis. Rapid test results were confirmed by standard bacterial culture. After a sentinel participant, cohorts of five and then ten participants were challenged, with protocol-directed dose-escalation or de-escalation for subsequent cohorts. The primary outcome was the proportion of participants at each dose level with pharyngitis by day 5 after challenge. The study is registered with ClinicalTrials.gov, NCT03361163.FindingsBetween July 10, 2018, and Sept 23, 2019, 25 healthy adults were challenged with emm75 S pyogenes and included in analyses. Pharyngitis was diagnosed in 17 (85%; 95% CI 62–97) of 20 participants at the starting dose level (1–3 × 105 colony-forming units [CFU]/mL). This high proportion prompted dose de-escalation. At the lower dose level (1–3 × 104 CFU/mL), pharyngitis was diagnosed in one of five participants. Immunological, biochemical, and microbiological results supported the clinical picture, with acute symptomatic pharyngitis characterised by pharyngeal colonisation by S pyogenes accompanied by significantly elevated C-reactive protein and inflammatory cytokines (eg, interferon-γ and interleukin-6), and modest serological responses to streptolysin O and deoxyribonuclease B. There were no severe (grade 3) or serious adverse events related to challenge.InterpretationWe have established a reliable pharyngitis human infection model with reassuring early safety findings to accelerate development of vaccines and other interventions to control disease due to S pyogenes.FundingAustralian National Health and Medical Research Council.