Generation of rabbit single-chain variable fragments with different physicochemical and biological properties by complementary determining region-grafting technology.

In this study, we have demonstrated a complementary-determining region (CDR) grafting technology for the generation of rabbit scFvs with different antigen recognition and physicochemical properties. The antigen-binding affinity of the CDR-grafted anti-CRP scFv, C1R/B1R (V1), which was generated by the CDR/framework region (CDR/FR) definition based on the traditional numbering rule, was insufficient when compared to that of the original clone, C1R, suggesting that the amino acid residues outside the original CDRs might significantly contribute to antigen recognition in rabbit scFvs. We redefined new CDRs and FRs to maintain antigen-binding affinities through the extension of multiple amino acid residues for CDRH1 and CDRH2, based on the amino acid sequence alignments of rabbit scFvs isolated from phage libraries. The new version successfully maintained the antigen binding affinity. CDR-grafted scFvs possessing a common CDR sequence and different FR sequences were successfully generated based on this new CDR/FR definition, and their physicochemical properties were further investigated. The antigen-binding activities of rabbit scFvs on Maxisorp varied between the tested clones in sandwich ELISA, supporting the idea that the combination of CDR with different FRs might change the physicochemical properties of scFvs on a solid material. The CDR-grafted scFvs possessing a frame sequence of anti-CRP scFv C2R maintained the ability to bind to protein L and were successfully purified. Expression titers showed improved solubility by diminishing the amount of insoluble scFvs. Thus, the method developed in this study is promising for generating alternatives with strict antigen binding recognition and different physicochemical properties.