Endotoxin neutralization by an O-antigen specific monoclonal antibody: A potential novel therapeutic approach againstKlebsiella pneumoniaeST258

Abstract

Klebsiella pneumoniae ST258 is a globally distributed multi-drug resistant pathogen responsible for severe invasive infections. In this study, the different virulence potential of K. pneumoniae ST258 isolates in endotoxin susceptible versus resistant animal models was shown. Furthermore, ST258 clinical isolates were found highly sensitive to the bactericidal effect of naive animal and human serum. These observations imply that LPS, released from the rapidly lysed bacteria, may contribute to the high mortality associated with ST258 bacteremia cases.A humanized version (mAb A1102) of a previously described murine mAb specific for the conserved LPS O-antigen, was tested for endotoxin neutralization. A1102 was able to neutralize TLR-4 activation by ST258-derived LPS in vitro with an efficacy exceeding that of polymyxin B by 3 orders of magnitude. Passive immunization with A1102 afforded a significant level of protection in a galactosamine-sensitized mouse model of endotoxemia, induced by ST258-derived LPS, or upon challenge with live bacteria. Efficacy was retained using an aglycosylated IgG, as well as upon complement depletion, suggesting that Fc-independent endotoxin neutralization may be the main protective mechanism in this model, in spite of the complement-dependent bactericidal and opsonic activities additionally observed for A1102 in vitro. Furthermore, rabbits that are naturally highly susceptible to endotoxin, were also significantly protected by low doses of A1102 when challenged with an ST258 strain.Given this unique mode of action and the high protective efficacy of this mAb, passive immunization, as prophylactic or adjunct therapeutic approach for the treatment of infections caused by ST258 isolates should be considered.

Multiple Modes of Action of a Monoclonal Antibody against Multidrug-Resistant Escherichia coli Sequence Type 131-H30

“…Another mechanism of action of O-antigen-specific MAbs is the neutralization of the endotoxin activity of LPS. Although recognizing the carbohydrate part of LPS, O-antigen binding was reported to neutralize endotoxin activity associated with the lipid A portion in the case of several MAbs ( 28 – 30 ) and O-type-specific immune serum ( 31 , 32 ). Finally, antivirulence activities, such as motility arrest ( 33 , 34 ), were reported upon binding of MAbs to O antigens of different enterobacterial pathogens.…”

“…Importantly, this activity was confirmed in the presence of human serum, where naturally occurring LPS binding proteins and preexisting antibodies might compete with A1124 for the binding of LPS molecules. Recently, we reported a MAb specific to the K. pneumoniae ST258 O antigen that outcompetes endotoxin neutralization potency of polymyxin B (an antibiotic that binds endotoxin stoichiometrically), by 3 orders of magnitude ( 28 ). This observation also supports a model in which O-antigen-specific MAbs act on the supramolecular structure of LPS.…”

Evaluation of Recombinant Multi-Epitope Outer Membrane Protein-Based Klebsiella pneumoniae Subunit Vaccine in Mouse Model

“…Apart from these, a humanized MAb (A1102) specific for the conserved LPS O-antigen was found effective for endotoxin neutralization. Passive administration of A1102 showed efficacy more than that of polymyxin B by three orders of magnitude and afforded significant protection in a galactosamine-sensitized mouse model of endotoxemia or upon challenge with live bacteria ( Szijártó et al, 2017 ). Other passive immunotherapy approach to reduce bacterial counts and delayed onset of infection was tried mainly using the antibodies directed against CPSs ( Cryz et al, 1985 ), inactivated whole cells ( Cooper and Rowley, 1982 ), ribosomal preparations ( Riottot et al, 1979 ), cell surface preparations ( Fournier et al, 1981 ), cytotoxins ( Singh and Sharma, 2001 ) and conjugate vaccine preparations ( Chhibber and Bajaj, 1995 ).…”

Using Omics Technologies and Systems Biology to Identify Epitope Targets for the Development of Monoclonal Antibodies Against Antibiotic-Resistant Bacteria

“…A plausible strategy may be to focus on the development of mAbs tailored to circulating hypervirulent and/or hyperresistant clones for which the recognized epitope is conserved. This is, for instance, the case for mAbs directed against K. pneumoniae O-antigen from the ST258 clone, since it is a recurrent infective lineage and a strong producer of this endotoxin (26). In addition, such clonal specificity preserves the microbiota, highlighting one of the advantages of immunological interventions with respect to antibiotics (27).…”