Development of a Recombinant Goose Parvovirus VP2 Neutralizing Epitope-Containing Region Vaccine Adjuvanted with IL-2 and FliC for Enhanced Immune Responses and Protection Against Challenge

Gosling plague (GP), caused by goose parvovirus (GPV), is a highly contagious and fatal viral disease. Vaccination is essential for disease prevention; however, conventional attenuated and inactivated vaccines have several limitations. Genetically engineered vaccines based on defined antigenic regions represent a promising alternative strategy. This study aimed to identify neutralizing epitope-containing regions within the GPV VP2 protein and develop effective recombinant vaccines. The GPV VP2 protein was divided into 11 overlapping fragments, and the anchored periplasmic expression (APEx) bacterial display system combined with flow cytometry (FCM) was used for antigenic region screening. GPV VP2-specific single-domain antibodies (VHHs) were further applied to identify neutralizing epitope-containing regions. Six neutralizing epitope-containing regions were identified and linked together to construct the VP2M recombinant antigen. The VP, VP2M, interleukin-2 (IL-2), and flagellin (FliC) genes were inserted into prokaryotic and eukaryotic expression vectors to generate protein and DNA vaccines. Three-day-old goslings were randomly assigned into 15 experimental groups for immunization. Immune responses were evaluated by measuring anti-GPV antibody levels, IgG, IgM, and IgA production, IFN-γ levels, immune-related gene expression, splenocyte proliferation, neutralizing activity, and protective efficacy against GPV challenge. The results showed that vaccines containing neutralizing epitope-containing regions induced stronger immune responses than control vaccines. Vaccinated groups exhibited increased anti-GPV antibody levels, IgG, IgM, IgA production, IFN-γ levels, immune-related gene expression, and splenocyte proliferation. Following GPV challenge, VP2M-based vaccines significantly reduced viral genome copies in the bursa of Fabricius, spleen, thymus, and intestinal tissues, accompanied by decreased histopathological lesions based on semi-quantitative scoring. Furthermore, the protective efficacy exceeded 50% in vaccines without adjuvants and reached 90% in groups containing combined IL-2 and FliC adjuvants. In conclusion, this study identifies novel neutralizing epitope-containing regions within GPV VP2 and provides a potential strategy for developing safe and effective recombinant vaccines against GP infection.