Development of a GMMA-based candidate vaccine against invasive nontyphoidal Salmonella disease

Introduction Invasive nontyphoidal Salmonella (iNTS) disease is one of the most common causes of bacteremia in sub-Saharan Africa (sSA), mostly affecting children less than 5 years of age and with an associated 14.7% case fatality ratio. This disease is responsible for 62,018 deaths worldwide annually with more than 80% of those occurring in sSA. Methods This work describes the pre-clinical development of a Generalized Modules for Membrane Antigens (GMMA)-based bivalent vaccine candidate against iNTS disease, known as iNTS-GMMA. Salmonella enterica serovars Typhimurium ( S . Typhimurium) and Enteritidis ( S . Enteritidis) were genetically modified to induce hyperblebbing of outer membrane vesicles, referred to as GMMA, with a penta-acylated lipid A of the lipopolysaccharide (LPS), characterized by a reduced induction of proinflammatory cytokine release from monocytes compared to GMMA carrying wild-type species of lipid A. GMMA derived from the genetically modified Salmonella strains were produced at scale with high yields and purity under both non-good manufacturing practice (GMP) conditions and under GMP conditions. A simple two-step filtration process was used to purify the GMMA drug substances. Subsequently, the S . Typhimurium GMMA and S . Enteritidis GMMA were individually formulated on Alhydrogel to produce the drug products. Mixing of the two components prior to injection results in the iNTS-GMMA vaccine candidate. Results The iNTS-GMMA vaccine candidate induced in mice and rabbits high levels of IgG anti- S . Typhimurium and S . Enteritidis LPS O-antigens, the target antigens of the vaccine. Moreover, animal sera elicited strong in vitro bactericidal activity against S . Typhimurium and S . Enteritidis strains. Additionally, the highest envisioned human dose of iNTS-GMMA was well tolerated in a GLP repeated-dose toxicology study in rabbits. Conclusions These data supported clinical evaluation of this urgently needed vaccine against iNTS disease in sSA.