Neutralizing human anti crotoxin scFv isolated from a nonimmunized phage library

Combinatorial phage display technology offers a new possibility for making human antibodies which could be used in immune therapy. We explored the use of this technology to make human scFvs specific for crotoxin, the main tox ic component of the venom of the South-American rattlesnake Crotalus duriss us terrificus. Crotoxin, a phospholipase A(2) neurotoxin constituted by the association of two subunits, exerts its lethal action by blocking neuromus cular transmission. This is the first report of human anticrotoxin scFvs (s cFv 1, scFv 6 and scFv 8) isolated from a naive library of more than 10(10) scFv clones with in vivo neutralizing activity. Nevertheless, differences are observed at the level of biological and immunological effects. Only scF v 8 is able to reduce the myotoxicity induced by crotoxin and scFv 1 is cap able of altering the in vitro enzymatic activity of this toxin. All three s cFvs recognize a region of one subunit located at the junction with the oth er one. Moreover these scFvs share strong amino acid homologies at the leve l of either the heavy or the light chain. Taken together, our results sugge st that the use of human anticrotoxin scFvs may lead to a new and less aggr essive passive immune therapy against poisoning by the venom of Crotalus du rissus terrificus.