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Novel structurally designed vaccine for S. aureus α-hemolysin: protection against bacteremia and pneumonia.

Adhikari RP, Karauzum H, Sarwar J, Abaandou L, Mahmoudieh M, Boroun AR, Vu H, Nguyen T, Devi VS, Shulenin S, Warfield KL, Aman MJ - PLoS ONE (2012)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Integrated Biotherapeutics Inc., Gaithersburg, Maryland, United States of America.

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.

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Related in: MedlinePlus

Comparative antibody response to vaccine candidates.(A) Individual serum antibody titers towards wild-type Hla determined after three immunizations (B) Neutralization titers of pooled sera towards wild-type Hla after three immunizations.
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pone-0038567-g003: Comparative antibody response to vaccine candidates.(A) Individual serum antibody titers towards wild-type Hla determined after three immunizations (B) Neutralization titers of pooled sera towards wild-type Hla after three immunizations.

Mentions: Previous reports using AT-50aa protein indicated the efficacy of this vaccine candidate against pneumonia by the S. aureus Newman strain [15], when used with Freund’s adjuvant. Since Freund’s adjuvant cannot be used in humans, we sought to perform a comparative efficacy study with the three vaccine candidates using GLA-SE, an adjuvant currently in clinical development [23], [24]. Groups of 20 mice were vaccinated intramuscularly three times at 2 week intervals with 5 μg of AT-50aa, AT-62aa or AT-79aa, formulated with 5 μg of GLA-SE in PBS (in an interim study we showed that similar titers can be achieved with 5 or 20 μg of GLA-SE; data not shown). On day 35, mice were bled for determination of antibody titers. As shown in Figure 3A, mice vaccinated with AT-62aa showed robust ELISA titers against wild type Hla with median EC50 of 2022 (range: 510–14,900). Mice vaccinated with AT-79aa showed much lower ELISA titer with median of 49 (range: 0–6,050) followed by mice vaccinated with AT-50aa with a median EC50 of 11 (range: 0–1,150). Similarly, when neutralization titers were determined in pools of serum samples mice vaccinated with AT-62aa showed highest NT50 of 1277 followed by AT-79aa with NT50 of 213 (`ure 3B). Neutralization was below the limit of detection of this assay in the pool of sera from AT-50aa vaccinated mice (NT50<40). For the challenge studies, each group was broken into two subgroups of ten mice each and challenged as described below to determine vaccine efficacy against S. aureus pneumonia and sepsis.


Novel structurally designed vaccine for S. aureus α-hemolysin: protection against bacteremia and pneumonia.

Adhikari RP, Karauzum H, Sarwar J, Abaandou L, Mahmoudieh M, Boroun AR, Vu H, Nguyen T, Devi VS, Shulenin S, Warfield KL, Aman MJ - PLoS ONE (2012)

Comparative antibody response to vaccine candidates.(A) Individual serum antibody titers towards wild-type Hla determined after three immunizations (B) Neutralization titers of pooled sera towards wild-type Hla after three immunizations.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3368876&req=5

pone-0038567-g003: Comparative antibody response to vaccine candidates.(A) Individual serum antibody titers towards wild-type Hla determined after three immunizations (B) Neutralization titers of pooled sera towards wild-type Hla after three immunizations.
Mentions: Previous reports using AT-50aa protein indicated the efficacy of this vaccine candidate against pneumonia by the S. aureus Newman strain [15], when used with Freund’s adjuvant. Since Freund’s adjuvant cannot be used in humans, we sought to perform a comparative efficacy study with the three vaccine candidates using GLA-SE, an adjuvant currently in clinical development [23], [24]. Groups of 20 mice were vaccinated intramuscularly three times at 2 week intervals with 5 μg of AT-50aa, AT-62aa or AT-79aa, formulated with 5 μg of GLA-SE in PBS (in an interim study we showed that similar titers can be achieved with 5 or 20 μg of GLA-SE; data not shown). On day 35, mice were bled for determination of antibody titers. As shown in Figure 3A, mice vaccinated with AT-62aa showed robust ELISA titers against wild type Hla with median EC50 of 2022 (range: 510–14,900). Mice vaccinated with AT-79aa showed much lower ELISA titer with median of 49 (range: 0–6,050) followed by mice vaccinated with AT-50aa with a median EC50 of 11 (range: 0–1,150). Similarly, when neutralization titers were determined in pools of serum samples mice vaccinated with AT-62aa showed highest NT50 of 1277 followed by AT-79aa with NT50 of 213 (`ure 3B). Neutralization was below the limit of detection of this assay in the pool of sera from AT-50aa vaccinated mice (NT50<40). For the challenge studies, each group was broken into two subgroups of ten mice each and challenged as described below to determine vaccine efficacy against S. aureus pneumonia and sepsis.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Integrated Biotherapeutics Inc., Gaithersburg, Maryland, United States of America.

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.

Show MeSH
Related in: MedlinePlus