Evaluating Neutralizing Antibody Titers by Recombinant Feline Calicivirus with Heterologous Capsid Protein VP1

Feline calicivirus (FCV) is a major pathogen that threatens feline health worldwide. Its global prevalence, extensive genetic variability, and limited cross-protection among strains present significant challenges for vaccine development. In this study, an infectious clone of the FCV-GDJM202201 strain was constructed using the eukaryotic expression plasmid pcDNA3.1 under the control of the cytomegalovirus (CMV) promoter. The rescued virus, rGDJM-A4822T, exhibited growth kinetics comparable to those of the parental strain in vitro. Subsequently, two recombinant viruses, rGDJM-VP1_JL and rGDJM-VP1_SH, were generated by replacing the VP1 gene in the GDJM202201 backbone with those from heterologous FCV strains. Notably, these recombinant viruses exhibited reduced viral titers compared to rGDJM-A4822T. Finally, neutralization assays revealed differential neutralizing antibody titers among the recombinant FCVs, with rGDJM-A4822T inducing higher neutralizing antibody titers and cross-neutralizing activity. Collectively, this study establishes an FCV infectious clone that can be used to rescue recombinant viruses carrying heterologous VP1 proteins and to evaluate neutralizing antibody responses.