Isolation of a human-like antibody fragment (scFv) that neutralizes ricin biological activity.
BACKGROUND
Ricin is a lethal toxin that inhibits protein synthesis. It is easily extracted from a ubiquitously grown plant, Ricinus communis, and thus readily available for use as a bioweapon (BW). Anti-ricin antibodies provide the only known therapeutic against ricin intoxication.


RESULTS
In this study, after immunizing a non-human primate (Macaca fascicularis) with the ricin chain A (RTA), a phage-displayed immune library was built (2 x 108 clones), that included the lambda light chain fragment. The library was screened against ricin, and specific binders were sequenced and further analyzed. The best clone, 43RCA, was isolated using a new, stringent neutralization test. 43RCA had a high, picomolar affinity (41 pM) and neutralized ricin efficiently (IC50 = 23 +/- 3 ng/ml, corresponding to a [scFv]/[ricin] molar ratio of 4). The neutralization capacity of 43RCA compared favourably with that of polyclonal anti-deglycosylated A chain (anti-dgRCA) IgGs, obtained from hyperimmune mouse serum, which were more efficient than any monoclonal at our disposal. The 43RCA sequence is very similar to that for human IgG germline genes, with 162 of 180 identical amino acids for the VH and VL (90% sequence identity).


CONCLUSIONS
Results of the characterization studies, and the high degree of identity with human germline genes, altogether make this anti-ricin scFv, or an IgG derived from it, a likely candidate for use in humans to minimize effects caused by ricin intoxication.
Pelat
Thibaut
T
Groupe de biotechnologie des anticorps, Département de biologie des agents transmissibles, Centre de Recherche du Service de Santé des Armées, La Tronche, France. t.pelat@orange.fr
Hust
Michael
M
Hale
Martha
M
Lefranc
Marie-Paule
MP
Dübel
Stefan
S
Thullier
Philippe
P
D000595:Amino Acid Sequence; D000818:Animals; D000915:Antibody Affinity; D015723:Gene Library; D006801:Humans; D007128:Immunoglobulin Fragments / Q000302:isolation & purification* / Q000378:metabolism; D008252:Macaca fascicularis; D008297:Male; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D019151:Peptide Library; D012276:Ricin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012680:Sensitivity and Specificity
D007128:Immunoglobulin Fragments; D019151:Peptide Library; D012276:Ricin