Monoclonal Antibodies Against the Staphylococcus aureus Bicomponent Leukotoxin AB Isolated Following Invasive Human Infection Reveal Diverse Binding and Modes of Action

Abstract

The 2-component leukotoxin LukAB is critical for Staphylococcus aureus targeting and killing of human neutrophils ex vivo and is produced in the setting of human infection. We report 3 LukAB-specific human monoclonal antibodies (mAbs) with distinct mechanisms of toxin neutralization and in vivo efficacy. Three hybridomas secreting mAbs with anti-LukAB activity (designated SA-13, -15, and -17) were generated from B cells obtained from a 12-year-old boy with S. aureus osteomyelitis. Each of the 3 mAbs neutralized LukAB-mediated neutrophil toxicity, exhibited differing levels of potency, recognized different antigenic sites on the toxin, and displayed at least 2 distinct mechanisms for cytotoxic inhibition. SA-15 bound exclusively to the dimeric form of the toxin, suggesting that human B cells recognize epitopes on the dimerized form of LukAB during natural infection. Both SA-13 and SA-17 bound the LukA monomer and the LukAB dimer. Although all 3 mAbs potently neutralized cytotoxicity, only SA-15 and SA-17 significantly inhibited toxin association with the cell surface. Treatment with a 1:1 mixture of mAbs SA-15 and SA-17 resulted in significantly lower bacterial colony counts in heart, liver, and kidneys in a murine model of S. aureus sepsis. These data describe the isolation of diverse and efficacious antitoxin mAbs.

Leukocidins: staphylococcal bi-component pore-forming toxins find their receptors

“…Owing to leukocidin structural dissimilarities, this mAb does not neutralize LukAB 103 . However, the identification of a series of mAbs that specifically neutralize LukAB was recently described 22 , this included naturally occurring mAbs isolated from infected chlidrens 105 . The role of LukAB in the intracellular compartment, where it promotes bacterial escape after phagocytosis 37,63 , is likely to pose challenges for neutralization of this toxin.…”

Commercial Intravenous Immunoglobulin Preparations Contain Functional Neutralizing Antibodies against the Staphylococcus aureus Leukocidin LukAB (LukGH)

“…To date, all antibody-based therapeutics against S. aureus have failed to show significant efficacy in clinical trials (9). Results of preclinical studies of leukocidin-specific monoclonal antibodies are promising, and important issues such as breadth of neutralization and potency in vivo warrant further investigation (20,21). Passive immunization with an "antibody cocktail" against multiple different S. aureus virulence factors will likely be needed for a successful antibodybased therapeutic (9,22).…”

“…Our study results provide insight into direct toxin neutralization by naturally occurring antibodies pooled in IVIg. Previous data from our group have shown that functional antitoxin antibody responses following invasive human infection are diverse and that toxin neutralization can be achieved by interfering with multiple steps in the cytolysis pathway (20).…”

A natural human monoclonal antibody targeting Staphylococcus Protein A protects against Staphylococcus aureus bacteremia

“…Therefore, targeting alternate antigens on the S . aureus cell surface as well as toxins, and the identification of novel immunotherapeutics are still being explored with priority [ 11 – 21 ]. One of the key virulence factors on the surface of S .…”