Novel Structurally Designed Vaccine for S. aureus α-Hemolysin: Protection against Bacteremia and Pneumonia

Abstract

Staphylococcus aureus (S. aureus) is a human pathogen associated with skin and soft tissue infections (SSTI) and life threatening sepsis and pneumonia. Efforts to develop effective vaccines against S. aureus have been largely unsuccessful, in part due to the variety of virulence factors produced by this organism. S. aureus alpha-hemolysin (Hla) is a pore-forming toxin expressed by most S. aureus strains and reported to play a key role in the pathogenesis of SSTI and pneumonia. Here we report a novel recombinant subunit vaccine candidate for Hla, rationally designed based on the heptameric crystal structure. This vaccine candidate, denoted AT-62aa, was tested in pneumonia and bacteremia infection models using S. aureus strain Newman and the pandemic strain USA300 (LAC). Significant protection from lethal bacteremia/sepsis and pneumonia was observed upon vaccination with AT-62aa along with a Glucopyranosyl Lipid Adjuvant-Stable Emulsion (GLA-SE) that is currently in clinical trials. Passive transfer of rabbit immunoglobulin against AT-62aa (AT62-IgG) protected mice against intraperitoneal and intranasal challenge with USA300 and produced significant reduction in bacterial burden in blood, spleen, kidney, and lungs. Our Hla-based vaccine is the first to be reported to reduce bacterial dissemination and to provide protection in a sepsis model of S. aureus infection. AT62-IgG and sera from vaccinated mice effectively neutralized the toxin in vitro and AT62-IgG inhibited the formation of Hla heptamers, suggesting antibody-mediated neutralization as the primary mechanism of action. This remarkable efficacy makes this Hla-based vaccine a prime candidate for inclusion in future multivalent S. aureus vaccine. Furthermore, identification of protective epitopes within AT-62aa could lead to novel immunotherapy for S. aureus infection.

Characterization and Immunological Properties of Pseudomonas aeruginosa Hemolytic Phospholipase C

“…Results for antigenic properties of tested PLC especially for induction of IgG antibodies after 2 weeks was consistent with those reported for P. aeruginosa PLC in mice model of Preston et al (1991). Also Adhikari et al (2012) reported that vaccinated mice showed higher ELISA and neutralizining antibody titer, this finding was consistent with the ability of antibodies to neutralize Staphylococcus aureus hemolysin (HLa) via inhibition of Hla oligomerization . On the other hand the lowering in titer of anti-PLC antibodies during the circulating time after 2 weeks assumed that these antibodies became incapable of neutralizing fresh or detoxified PLC activity in situ and don't affect the enzymatic function.…”

Role of Antibodies in Protection Elicited by Active Vaccination with Genetically Inactivated Alpha Hemolysin in a Mouse Model of Staphylococcus aureus Skin and Soft Tissue Infections

“…The assay was designed based on one described by Adhikari et al (22). Briefly, serial dilutions of mouse serum were preincubated with 20 ng Hla (List Biological Laboratories, Campbell, CA) for 30 min at 37°C in 100 l total volume of PBS supplemented with 2.5% fetal bovine serum (Gibco, Life Technologies, Grand Island, NY) in a 96-well plate (MaxiSorp; Thermo Fisher, Waltham, MA).…”

Children with Invasive Staphylococcus aureus Disease Exhibit a Potently Neutralizing Antibody Response to the Cytotoxin LukAB

“…These toxins are lytic to host immune effector cells, are important for disease pathogenesis, and have been identified as putative vaccine targets (9)(10)(11). LukAB (12), also known as LukGH (13), is a recently described bicomponent leukotoxin that promotes S. aureus pathogenesis in both ex vivo and in vivo models of disease (7,8,12).…”