Research article

Isolation of a human-like antibody fragment (scFv) that neutralizes ricin biological activity

Thibaut Pelat^1* , Michael Hust^2* , Martha Hale³ , Marie-Paule Lefranc⁴ , Stefan Dübel² and Philippe Thullier¹

¹  Groupe de biotechnologie des anticorps, Département de biologie des agents transmissibles, Centre de Recherche du Service de Santé des Armées, La Tronche, France

²  Institut für Biochemie und Biotechnologie, Technische Universität Braunschweig, Braunschweig, Germany

³  Integrated Toxicology, United States Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Frederick MD, USA

⁴  IMGT, Laboratoire d'ImmunoGénétique Moléculaire, LIGM, Université Montpellier 2, UPR CNRS 1142, Institut de Génétique Humaine, IGH, Montpellier, France, and Institut Universitaire de France, Paris, France

author email corresponding author email* Contributed equally

BMC Biotechnology 2009, 9:60doi:10.1186/1472-6750-9-60

Published:	30 June 2009

Abstract

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 × 10⁸ clones), that included the λ 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).

Conclusion

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.