Single chain variable fragment antibodies selected by phage display against the sporozoite surface antigen S16 of Cryptosporidium parvum

Two human single chain variable fragment (scFv) libraries were used to select clones that bound to the surface glycoprotein S16 of Cryptosporidium parvum. Panning of the Tomlinson libraries I and J resulted in the isolation of nine distinct clones. Of the four clones which had full-length scFv, three contained stop codons. The remaining five clones were truncated, with four missing the heavy chain, and one missing most of the light chain. The full-length clones exhibited better binding to native C. parvum proteins and recombinant S16 than the truncated clones, with the exception of one truncated clone. None of the selected clones cross-reacted with Giardia lamblia, Escherichia coli, Streptococcus pyogenes, Listeria monocytogenes, Bacillus cereus or another immunogenic target of C. parvum, P23. Clones expressed as the soluble scFv-gIIIp construct were able to detect C. parvum native proteins and sporozoites. Panning from naïve libraries was an useful method for isolation and identification of recombinant antibodies that have the potential for use in pathogen detection and immunotherapy.