Objective To construct the eukaryotic vector that expressing hepatitis B virus (HBV) S and the single fragment of variety chain (ScFv) of monoclonal antiboy against cytotoxic Tlymphocyte-associated antigen-4 (CTLA-4) and to analyze the immunological activity of recombinant S-ScFv protein.Methods The oringially constructed pSect2/ScFv4F10 and pSect2/S were double enzyme digested by Sfi I and Hind Ⅲ,respectively.Then the HBV S gene was cloned into the pSect2/ScFv4F10 vector.The pSect2/ScFv4F10 and pSect2/S-ScFv4F10 were expressed in Chinese hamster ovary (CHO) cells,and the expressed proteins were verified through sodium dodecyl sulfatepolyacrylamide gelelectrophoresis(SDS-PAGE)andWesternblotting.Afterultrafiltration concentration and affinity chromatography,the biological affinity of the expressed ScFv4F10 and S-ScFv4F10 proteins were examined by competitive enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) technology.The comparison between groups was done by One-way ANOVA.ResultsThe eukaryotic expression vector of pSect2/S-ScFv4F10was successfully constructed,and relative molecular mass of the expressed protein of S-ScFv4 F10 was about 52 000 that analyzed by SDS-PAGE and Western blotting.With the fixed concentration of 4F10-mAb against CTLA-4,the A570 value of the mixed reaction with purified CTLA-4 antigen gradually increased with the decrease of ScFc fusion protein proportion; when the molar ratio of ScFv,S-ScFv4F10∶4F10=2∶1,the competitiveinhibitionratesagainst 4F10conjugatedantigenwere72.6％and64.5％,respectively.The affinity constants of association kinetics for CTLA-4 mAb,ScFv4F10 and S-ScFv4F10 with CTLA-4 antigen were 7.29 × 108 mol/L,9.52 × 106 mol/L and 2.04 × 106 mol/L,respectively,and the dissociation constants of KD were 1.40 × 10-9 mol/L,1.05 × 10-7 mol/L and 4.91 × 10-7 mol/L,respectively.ConclusionsThe eukaryotic expression vector of pSect2/S-ScFv4F10is successfully constructed,and the recombinant protein of S-ScFv4 F10 has a fairly high affinity with CTLA-4 antigen.