Five birds, one stone: Neutralization of α-hemolysin and 4 bi-component leukocidins of Staphylococcus aureus with a single human monoclonal antibody

Abstract

Staphylococcus aureus is a major human pathogen associated with high mortality. The emergence of antibiotic resistance and the inability of antibiotics to counteract bacterial cytotoxins involved in the pathogenesis of S. aureus call for novel therapeutic approaches, such as passive immunization with monoclonal antibodies (mAbs). The complexity of staphylococcal pathogenesis and past failures with single mAb products represent considerable barriers for antibody-based therapeutics. Over the past few years, efforts have focused on neutralizing α-hemolysin. Recent findings suggest that the concerted actions of several cytotoxins, including the bi-component leukocidins play important roles in staphylococcal pathogenesis. Therefore, we aimed to isolate mAbs that bind to multiple cytolysins by employing high diversity human IgG1 libraries presented on the surface of yeast cells. Here we describe cross-reactive antibodies with picomolar affinity for α-hemolysin and 4 different bi-component leukocidins that share only ∼26% overall amino acid sequence identity. The molecular basis of cross-reactivity is the recognition of a conformational epitope shared by α-hemolysin and F-components of gamma-hemolysin (HlgAB and HlgCB), LukED and LukSF (Panton-Valentine Leukocidin). The amino acids predicted to form the epitope are conserved and known to be important for cytotoxic activity. We found that a single cross-reactive antibody prevented lysis of human phagocytes, epithelial and red blood cells induced by α-hemolysin and leukocidins in vitro, and therefore had superior effectiveness compared to α-hemolysin specific antibodies to protect from the combined cytolytic effect of secreted S. aureus toxins. Such mAb afforded high levels of protection in murine models of pneumonia and sepsis.

Safety and immunogenicity of a recombinant Staphylococcus aureus α-toxoid and a recombinant Panton-Valentine leukocidin subunit, in healthy adults

“…In addition, while only 5-10% of S. aureus strains carry the LukSF gene, almost all strains express the HlgAB cytotoxin and approximately 50-75% also carry LukED, resulting in improved potency of antibodies due to cross-neutralization of multiple leukocidins that play an integral role in staphylococcal pathogenesis. 47 Rabbit models of S. aureus infection maybe helpful in evaluating the effectiveness of anti-PVL antibodies generated in such Phase I immunogenicity studies for passive immunization.…”

Targeting Alpha Toxin To Mitigate Its Lethal Toxicity in Ferret and Rabbit Models of Staphylococcus aureus Necrotizing Pneumonia

“…Consequently, it has been the focus of much research to better understand its role in pneumonia and its utility as a target for novel methods to treat or prevent S. aureus pneumonia (6)(7)(8)(9)(10). In fact, two anti-AT MAbs (MEDI4893 and AR-301) are currently in clinical development for the treatment or prevention of S. aureus pneumonia (11).…”

Improved Protection in a Rabbit Model of Community-Associated Methicillin-Resistant Staphylococcus aureus Necrotizing Pneumonia upon Neutralization of Leukocidins in Addition to Alpha-Hemolysin

“…Previously, we reported the discovery of unique human monoclonal antibodies (MAbs) with simultaneous, high-affinity binding to Hla and to three F components (HlgB, LukF-PV, and LukD) of the leukocidin family, resulting in potent inhibition of lysis of human cells by Hla, HlgAB, HlgCB, LukSF-PV, and LukED in in vitro assays (17). Such an antibody was shown to be highly protective in mouse pneumonia models with several S. aureus strains (17).…”