Safety and Immunogenicity of a 4-Component Toxoid-Based Staphylococcus aureus Vaccine in Rhesus Macaques

Abstract

Staphylococcus aureus is a leading cause of significant morbidity and mortality and an enormous economic burden to public health worldwide. Infections caused by methicillin-resistant S. aureus (MRSA) pose a major threat as MRSA strains are becoming increasingly prevalent and multi-drug resistant. To this date, vaccines targeting surface-bound antigens demonstrated promising results in preclinical testing but have failed in clinical trials. S. aureus pathogenesis is in large part driven by immune destructive and immune modulating toxins and thus represent promising vaccine targets. Hence, the objective of this study was to evaluate the safety and immunogenicity of a staphylococcal 4-component vaccine targeting secreted bi-component pore-forming toxins (BCPFTs) and superantigens (SAgs) in non-human primates (NHPs). The 4-component vaccine proved to be safe, even when repeated vaccinations were given at a dose that is 5 to 10- fold higher than the proposed human dose. Vaccinated rhesus macaques did not exhibit clinical signs, weight loss, or changes in hematology or serum chemistry parameters related to the administration of the vaccine. No acute, vaccine-related elevation of serum cytokine levels was observed after vaccine administration, confirming the toxoid components lacked superantigenicity. Immunized animals demonstrated high level of toxin-specific total and neutralizing antibodies toward target antigens of the 4-component vaccine as well as cross-neutralizing activity toward staphylococcal BCPFTs and SAgs that are not direct targets of the vaccine. Cross-neutralization was also observed toward the heterologous streptococcal pyogenic exotoxin B. Ex vivo stimulation of PBMCs with individual vaccine components demonstrated an overall increase in several T cell cytokines measured in supernatants. Immunophenotyping of CD4 T cells ex vivo showed an increase in Ag-specific polyfunctional CD4 T cells in response to antigen stimulation. Taken together, we demonstrate that the 4-component vaccine is well-tolerated and immunogenic in NHPs generating both humoral and cellular immune responses. Targeting secreted toxin antigens could be the next-generation vaccine approach for staphylococcal vaccines if also proven to provide efficacy in humans.

Hyperimmune Targeting Staphylococcal Toxins Effectively Protect Against USA 300 MRSA Infection in Mouse Bacteremia and Pneumonia Models

“…Hla toxoid harbors two mutations (H35L and H48L), PVL toxoid consists of mutated S and F subunit proteins (LukS mut9 and LukF mut1 ), a dimeric toxoid LukAB mut50 , and a fusion protein TBA 225 , which represents three superantigen toxoids fused together via a flexible linker (TSST-1, SEB and SEA). Each of these toxoids is fully attenuated, and the safety and immunogenicity had been extensively studied previously ( 40 ). Using five toxoid proteins blended at equal weight ratios as immunogen to immunize rabbits, strong antibody responses were elicited.…”

Staphylococcus aureus—A Known Opponent against Host Defense Mechanisms and Vaccine Development—Do We Still Have a Chance to Win?

“…The current paradigm for vaccine development is targeting multiple staphylococcal virulence factors, considering both the surface antigens and secreted biologically active substances. Thus S. aureus adhesins and other surface proteins will generate opsonic antibodies, while non-toxic forms of toxins and superantigens will stimulate the production of neutralizing antibodies and activate effector immune cells [93,94]. An example of such a complex preparation is the S. aureus toxoid vaccine, containing modified bi-component pore-forming toxins: mutants of the S and F subunits of PVL (LukS mut9 and LukF mut1 ) and a double mutant of alpha hemolysin (Hla H35L/H48L ), as well as the fusion toxoid TBA 225 of superantigens (SEA, SEB and TSST-1).…”

“…Moreover, the population of antigenspecific T cells of the Th1 and Th17 phenotype, as well as the production of some T cell cytokines (e.g., TNF, IFN-γ, IL-2, IL-17A), increased in response to ex vivo re-stimulation of peripheral blood mononuclear cells with the vaccine. It is suggested that such a T cell response may, via feedback, activate the innate immune cells that enhance phagocytosis and bacteria elimination [94].…”

Staphylococcus aureus Vaccine Research and Development: The Past, Present and Future, Including Novel Therapeutic Strategies

“…Notably, rabbits, while still much less than that of humans, are more susceptible to the effect of many S. aureus toxins, therefore suggesting rabbits as a more relevant in vivo model ( 106 ). S. aureus vaccines and monoclonal antibodies have also occasionally been tested in non-human primates, generating highly relevant data ( 107 , 108 ).…”