Efficient neutralization of anthrax toxin by chimpanzee monoclonal antibodies against protective antigen.
Four single-chain variable fragments (scFvs) against protective antigen (PA) and 2 scFvs against lethal factor (LF) of anthrax were isolated from a phage display library generated from immunized chimpanzees. Only 2 scFvs recognizing PA (W1 and W2) neutralized the cytotoxicity of lethal toxin in a macrophage lysis assay. Full-length immunoglobulin G (IgG) of W1 and W2 efficiently protected rats from anthrax toxin challenge. The epitope recognized by W1 and W2 was conformational and was formed by C-terminal amino acids 614-735 of PA. W1 and W2 each bound to PA with an equilibrium dissociation constant of 4x10-11 mol/L to 5x10(-11) mol/L, which is an affinity that is 20-100-fold higher than that for the interaction of the receptor and PA. W1 and W2 inhibited the binding of PA to the receptor, suggesting that this was the mechanism of protection. These data suggest that W1 and W2 chimpanzee monoclonal antibodies may serve as PA entry inhibitors for use in the emergency prophylaxis against and treatment of anthrax.
Chen
Zhaochun
Z
Hepatitis Viruses Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA. zchen@niaid.nih.gov
Moayeri
Mahtab
M
Zhou
Yi-Hua
YH
Leppla
Stephen
S
Emerson
Suzanne
S
Sebrell
Andrew
A
Yu
Fujuan
F
Svitel
Juraj
J
Schuck
Peter
P
St Claire
Marisa
M
Purcell
Robert
R
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000915:Antibody Affinity; D000942:Antigens, Bacterial / Q000737:chemistry / Q000276:immunology* / Q000633:toxicity; D001427:Bacterial Toxins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000276:immunology* / Q000633:toxicity; D018604:Epitope Mapping; D000939:Epitopes / Q000276:immunology; D005260:Female; D007128:Immunoglobulin Fragments / Q000276:immunology / Q000302:isolation & purification; D007074:Immunoglobulin G / Q000276:immunology; D007135:Immunoglobulin Variable Region / Q000276:immunology / Q000302:isolation & purification; D008264:Macrophages / Q000276:immunology; D051379:Mice; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D002679:Pan troglodytes; D019151:Peptide Library; D051381:Rats; D011916:Rats, Inbred F344; D018000:Receptors, Peptide / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D000939:Epitopes; D007128:Immunoglobulin Fragments; D007074:Immunoglobulin G; D007135:Immunoglobulin Variable Region; D019151:Peptide Library; D018000:Receptors, Peptide; C030325:anthrax toxin; C070309:anthrax toxin receptors