Single-Chain Variable Fragment Antibodies Selected by Phage Display Against the Sporozoite Surface Antigen P23 of Cryptosporidium parvum

Abstract

Cryptosporidium parvum, an apicomplexan parasite transmitted via animal fecal wastes, is the causative agent of cryptosporidiosis. Clones were selected from 2 synthetic naïve human single-chain variable fragment (scFv) phagemid libraries that bound to the recombinant P23 protein of C. parvum. Panning the Tomlinson I and J phagemid libraries resulted in 6 distinct clones. Two clones had full-length scFv sequences, while the remaining clones were either truncated or missing a section of the heavy chain. Despite these differences, all clones were able to detect both native C. parvum proteins and recombinant P23. None of the selected clones cross-reacted with Escherichia coli, Streptococcus pyogenes, Listeria monocytogenes, Bacillus cereus, Giardia lamblia (cysts or trophozoites), or with S16, another dominant surface antigen on C. parvum sporozoites. Clones expressed as the scFv-gIIIp fusion construct in soluble form detected C. parvum. Panning from naïve libraries is a useful method for isolation and identification of recombinant antibodies that have the potential for use in pathogen detection and immunotherapy.