Efficacy of Active Immunization With Attenuated α-Hemolysin and Panton-Valentine Leukocidin in a Rabbit Model of Staphylococcus aureus Necrotizing Pneumonia

Abstract

Staphylococcus aureus is a common pathogen causing infections in humans with various degrees of severity, with pneumonia being one of the most severe infections. In as much as staphylococcal pneumonia is a disease driven in large part by α-hemolysin (Hla) and Panton-Valentine leukocidin (PVL), we evaluated whether active immunization with attenuated forms of Hla (HlaH35L/H48L) alone, PVL components (LukS-PVT28F/K97A/S209A and LukF-PVK102A) alone, or combination of all 3 toxoids could prevent lethal challenge in a rabbit model of necrotizing pneumonia caused by the USA300 community-associated methicillin-resistant S. aureus (MRSA). Rabbits vaccinated with Hla toxoid alone or PVL components alone were only partially protected against lethal pneumonia, whereas those vaccinated with all 3 toxoids had 100% protection against lethality. Vaccine-mediated protection correlated with induction of polyclonal antibody response that neutralized not only α-hemolysin and PVL, but also other related toxins, produced by USA300 and other epidemic MRSA clones.

Vaccination with VLPs Presenting a Linear Neutralizing Domain of S. aureus Hla Elicits Protective Immunity

“…Hla promotes invasive infection and is therefore a target for therapeutic and prophylactic interventions. Although Hla-targeting vaccines have shown promise in animal models of pneumonia [ 12 , 13 , 36 ], SSTI [ 10 , 17 , 37 , 38 ], and bacteremia [ 13 ], even vaccines inducing opsonophagocytic Abs show efficacy in animal models, but subsequently failed in human clinical trials [ 39 ]. The VLP-based vaccines reported here focus on a targeted, essential domain of Hla and thus direct the immune response towards a vulnerable epitope while avoiding non-neutralizing regions present in the native toxin.…”

Studying Staphylococcal Leukocidins: A Challenging Endeavor

“…To further complicate things, humans carry pre-existing or develop antibodies against S-and F-components of leukocidins upon infection (Adhikari et al, 2015;Spaan et al, 2017). Due to the high homology between these components, the antibodies crossreact and cross-neutralize toxicity (Diep et al, 2016;Tran et al, 2020). This, in in conjunction with the likely non-canonical combination, complicates the in vivo determination of the exact role of each independent toxin.…”

“…However, most rabbits are likely to have been previously exposed to S. aureus (Vancraeynest et al, 2006), resulting in the presence of antibodies against S. aureus that could influence the adequate assessment of leukocidins and other S. aureus virulence factors. Nevertheless, a recent study shows that active immunization with attenuated Hla and PVL prevents lethal development of necrotizing pneumonia in rabbits following challenge with a USA300 strain (Tran et al, 2020). The lack of an adequate in vivo model additionally hinders the assessment of the apparent redundant deployment of two leukocidins that target the same human C5aR1 (Spaan et al, 2013a(Spaan et al, , 2014(Spaan et al, , 2015b.…”

Exploring Virulence Factors and Alternative Therapies against Staphylococcus aureus Pneumonia

“…It can also stimulate a hyperinflammatory response, and disrupt epithelial and endothelial barriers, even at sublytic levels [ 110 , 114 ]. The importance of Hla as a virulence factor in SAP has been researched in mouse, rabbit and ferret pneumonia models [ 72 , 85 , 86 , 115 ], with studies reporting a disruptive effect on the air-blood barrier [ 116 ]. Moreover, isogenic hla mutants consistently demonstrated reduced infection severity compared to their wild type strains [ 85 , 114 , 117 ].…”