Isolation of feline-derived scFvs against VP1-CDE region of feline calicivirus from phage display library and characterization of their antigen-binding and antiviral potential in vitro

Feline calicivirus (FCV) causes infectious upper respiratory and virulent systemic diseases in feline population, with a lack of specific antiviral agents available. To address this, we constructed a feline-derived scFv phage display library targeting the VP1-CDE neutralizing region of FCV, using lymphocytes from VP1-CDE-immunized cats. The library had a titer of 2.1×10 ⁸ CFU/mL and good sequence diversity. After three rounds of panning and phage ELISA screening (OD ₄₅₀ S/N > 10), 5 unique scFv clones (3A5, 3B8, 3H5, 2H5, 2I5) were identified. Eukaryotic expression of scFv-Fc fusion proteins and validation via Western blot, ELISA and immunofluorescence assay confirmed their specific binding to VP1-CDE and FCV-infected F81 cells. Viral neutralization tests showed that scFv-3A5 had the strongest FCV-neutralizing activity (titer 1:64, MNC 1.172 µg/mL), scFv-2H5 showed weak activity (titer 1:16, MNC 4.688 µg/mL), and the other three clones had no significant neutralizing activity. This study provides promising candidate molecules for FCV diagnostic reagents and antiviral therapies.