Rational Design of Toxoid Vaccine Candidates for Staphylococcus aureus Leukocidin AB (LukAB)

Abstract

Staphylococcus aureus (SA) infections cause high mortality and morbidity in humans. Being central to its pathogenesis, S. aureus thwarts the host defense by secreting a myriad of virulence factors, including bicomponent, pore-forming leukotoxins. While all vaccine development efforts that aimed at achieving opsonophagocytic killing have failed, targeting virulence by toxoid vaccines represents a novel approach to preventing mortality and morbidity that are caused by SA. The recently discovered leukotoxin LukAB kills human phagocytes and monocytes and it is present in all known S. aureus clinical isolates. While using a structure-guided approach, we generated a library of mutations that targeted functional domains within the LukAB heterodimer to identify attenuated toxoids as potential vaccine candidates. The mutants were evaluated based on expression, solubility, yield, biophysical properties, cytotoxicity, and immunogenicity, and several fully attenuated LukAB toxoids that were capable of eliciting high neutralizing antibody titers were identified. Rabbit polyclonal antibodies against the lead toxoid candidate provided potent neutralization of LukAB. While the neutralization of LukAB alone was not sufficient to fully suppress leukotoxicity in supernatants of S. aureus USA300 isolates, a combination of antibodies against LukAB, α-toxin, and Panton-Valentine leukocidin completely neutralized the cytotoxicity of these strains. These data strongly support the inclusion of LukAB toxoids in a multivalent toxoid vaccine for the prevention of S. aureus disease.

IBT-V02: A Multicomponent Toxoid Vaccine Protects Against Primary and Secondary Skin Infections Caused by Staphylococcus aureus

“…The 5-component vaccine IBT-V02 presented here includes toxoids of Hla, both PVL subunits, LukAB as well as a fusion of toxoids for TSST-1, SEB, SEA formulated in Alhydrogel (Al(OH) 3 ). All individual components of the vaccine were characterized and published previously and shown to be highly attenuated and to induce broad neutralizing antibody responses (24)(25)(26)(27). Here we show that the blended vaccine formulated with Al(OH) 3 is highly immunogenic in mice and rabbits, inducing a strong total IgG and neutralizing antibody response.…”

“…We had previously demonstrated the immunogenicity of the IBT-V02 components in combination with Alhydrogel R (24)(25)(26). To optimize the formulation for the multicomponent vaccine we incubated the blended vaccine components with Alhydrogel R at ratios of 1, 2, 3, and 4 (protein:Alhydrogel R ) for 60 min at room temperature (RT) followed by centrifugation.…”

“…We hypothesized that vaccination with key staphylococcal toxins can protect against SA infections by protecting tissues and the immune system, thus preventing the complications of disease via clinical protection even in the absence of sterile immunity. To this end, we have developed a multicomponent vaccine IBT-V02, comprised of toxoids for Hla (Hla H35LH48L ), subunits of PVL (LukS mut9 , LukF mut1 ), LukAB (LukAB mut50 ) and a fusion of three SAgs (TSST-1, SEB, and SEA; TBA 225 ) and reported the attenuation and efficacy of individual components or partial combinations in bacteremia, pneumonia, and toxic shock models in mice and rabbits (24)(25)(26)(27).…”

Staphylococcus aureus Toxins: Armaments for a Significant Pathogen

“…Papers by Kailasan et al [18] and Ouyang et al [19] explored treatment options for S. aureus infections. Kailasan et al generated a library of leukotoxin gene mutations that targeted functional domains of the leukocidin protein that were in turn used to make polyclonal antibodies to the lead toxoid candidate.…”

Exploring Virulence Factors and Alternative Therapies against Staphylococcus aureus Pneumonia

“…Three LukAB-specific human mAbs, which were generated from human B cells, neutralized LukAB cytotoxicity, and improved bacterial clearance in a murine S. aureus sepsis model [ 105 ]. Moreover, neutralizing Abs were recently generated from two S. aureus strains with mutated lukAB genes (LukA D39A and LukB R23E ), which were able to block the CD11b cellular target, and prevent LukAB-dependent cell lysis in a human monocytic cell line [ 106 ]. These components were also tested as part of a multivalent toxoid vaccine, described under “7.…”