Glycosylation-dependent opsonophagocytic activity of staphylococcal protein A antibodies

Abstract

Antibodies may bind to bacterial pathogens or their toxins to control infections, and their effector activity is mediated through the recruitment of complement component C1q or the engagement with Fcγ receptors (FcγRs). For bacterial pathogens that rely on a single toxin to cause disease, immunity correlates with toxin neutralization. Most other bacterial pathogens, including Staphylococcus aureus, secrete numerous toxins and evolved multiple mechanisms to escape opsonization and complement killing. Several vaccine candidates targeting defined surface antigens of S. aureus have failed to meet clinical endpoints. It is unclear that such failures can be solely attributed to the poor selection of antibody targets. Thus far, studies to delineate antibody-mediated uptake and killing of Gram-positive pathogens remain extremely limited. Here, we exploit 3F6-hIgG1, a human monoclonal antibody that binds and neutralizes the abundant surface-exposed Staphylococcal protein A (SpA). We find that galactosylation of 3F6-hIgG1 that favors C1q recruitment is indispensable for opsonophagocytic killing of staphylococci and for protection against bloodstream infection in animals. However, the simple removal of fucosyl residues, which results in reduced C1q binding and increased engagement with FcγR, maintains the opsonophagocytic killing and protective attributes of the antibody. We confirm these results by engineering 3F6-hIgG1 variants with biased binding toward C1q or FcγRs. While the therapeutic benefit of monoclonal antibodies against infectious disease agents may be debatable, the functional characterization of such antibodies represents a powerful tool for the development of correlates of protection that may guide future vaccine trials.

Antivirulence Strategies for the Treatment of Staphylococcus aureus Infections: A Mini Review

“…Additionally, passive neutralization of SpA encourages production of effective anti-staphylococcal antibodies that promote bacterial decolonization from nasal and gastrointestinal mucosa of mice ( Chen et al, 2019 ). Furthermore, humanized anti-SpA KKAA antibodies promote bacterial clearance upon binding SpA through the induction of the complement cascade, and effective complement activation is dependent upon the glycosylation of SpA-binding mAbs ( Chen et al, 2020 ). SpA KKAA has been proposed as part of a four-antigen S. aureus vaccine that demonstrates improved survival in systemic S. aureus infection in mice ( Kim et al, 2011 ; Rauch et al, 2014 ).…”

Improving Chicken Responses to Glycoconjugate Vaccination Against Campylobacter jejuni

“…It has been shown that human antibody N-glycosylation (IgG glycan at N297) and the structure of the N-glycan are important for antibody functionality ( Krapp et al, 2003 ; Jefferis, 2009 ). For example, changes in IgG glycosylation play a role in autoimmune disease and cancer in humans and impact viral and bacterial colonization ( Chen et al, 2020 ; Irvine and Alter, 2020 ). But little is known about IgY glycosylation and its contribution to antibody functionality in chickens.…”

Monoclonal Antibodies Targeting Surface-Exposed and Secreted Proteins from Staphylococci

“…The mouse mAb 3F6 binds to each of the five immunoglobulin-binding domains (IgBDs) of SpA, blocks IgG binding to SpA and protects against bloodstream infection when administered to mice [ 85 , 86 , 87 ]. A human version of this antibody (3F6-hIgG1) improves the outcome of MRSA bloodstream infections in animal models [ 87 , 88 ] and its Fc glycosylation enhances C1q binding and the recruitment and killing of staphylococci by phagocytosis and favors protection against infection [ 101 ]. Moreover, Varshney et al isolated and studied a human mAb, named 514G3, belonging to the subclass IgG3, a condition that does not allow binding via the Fc region to SpA.…”