title: A bispecific nanobody to provide full protection against lethal scorpion envenoming.
abstract: Envenoming following scorpion sting is a common emergency in many parts of the world. Our aim was to ameliorate the current 100-kDa horse plasma antivenom serum (PAS)-derived Fab'(2) to more quickly reach the highly diffusible scorpion toxins (7 kDa). We immunized dromedaries with toxins from Androctonus australis hector (Aah) scorpions and cloned the single-domain antibody fragments or nanobodies (15 kDa) from their B cells. Nanobodies against AahI' toxin (with AahII the most toxic compound of the venom) were retrieved from the libraries, and their AahI'-toxin neutralization was monitored in mice. Remarkably, the NbAahI'F12 fully protected mice against 100 LD(50) of AahI' administered intracerebroventricularly. Moreover, where PAS failed completely to neutralize 2 LD(50) of crude venom injected subcutaneously, the designed bispecific NbF12-10 against AahI'/AahII toxins succeeded in neutralizing 5 LD(50). Finally, in a challenge assay in which mice were subcutaneously injected with a lethal dose of scorpion venom, the subsequent intravenous injection of 85 microg of NbF12-10 protected all mice, even if the whole procedure was repeated 3 times. Furthermore, the NbF12-10 remained fully protective when mice with severe signs of envenoming were treated a few minutes before the untreated mice died.
authors.affiliation: Laboratoire des Venins et Toxines, Institut Pasteur de Tunis, 13 Pl. Pasteur, BP-74, 1002 Tunis, Tunisia.
authors.forename: Issam
authors.initials: I
authors.lastname: Hmila
authors.forename: Dirk
authors.initials: D
authors.lastname: Saerens
authors.forename: Rahma
authors.initials: R
authors.lastname: Ben Abderrazek
authors.forename: Cécile
authors.initials: C
authors.lastname: Vincke
authors.forename: Naima
authors.initials: N
authors.lastname: Abidi
authors.forename: Zakaria
authors.initials: Z
authors.lastname: Benlasfar
authors.forename: Jochen
authors.initials: J
authors.lastname: Govaert
authors.forename: Mohamed
authors.initials: M
authors.lastname: El Ayeb
authors.forename: Balkiss
authors.initials: B
authors.lastname: Bouhaouala-Zahar
authors.forename: Serge
authors.initials: S
authors.lastname: Muyldermans
mesh_terms: D000818:Animals; D002162:Camelus; D018604:Epitope Mapping; D007128:Immunoglobulin Fragments / Q000276:immunology* / Q000302:isolation & purification; D008297:Male; D051379:Mice; D012604:Scorpion Venoms / Q000276:immunology*
chemical_list: D007128:Immunoglobulin Fragments; D012604:Scorpion Venoms; C065314:scorpion toxin I, Androctonus; C053969:scorpion toxin II, Androctonus