IPNV inactive vaccine supplemented with GEL 02 PR adjuvant: Protective efficacy, cross-protection, and stability

Recently, outbreaks of infectious pancreatic necrosis (IPN) in worldwide rainbow trout farms caused by IPN virus (IPNV) strains belonging to genogroup 1 and genogroup 5 are reported. In this study, formaldehyde-inactivated vaccines supplemented with or without GEL 02 PR adjuvant were developed by using both genogroups IPNV strains and were intraperitoneally injected into rainbow trout. At 30 days post-vaccination, the viral loads of IPNV challenged rainbow trout (Oncorhynchus mykiss) in the vaccine groups were significantly decreased compared with those in the PBS group (P < 0.05), about 2.4 log and 2.5 log in the genogroup 1 and 5 IPNV inactivated vaccine with or without GEL 02 PR adjuvant groups, and the protective effect was not weakened after storage of the adjuvant vaccines at 4 °C for 12 months. Each vaccine could stimulate the expression of CD4, CD8, and IgM, and the adjuvant vaccines induced higher neutralizing antibody titers. In the long-term protection test, both the adjuvant vaccines could still effectively reduce IPNV viral loads in fish at 120 days post-vaccination, and the genogroup 5 IPNV inactivated vaccine showed cross-protection against the genogroup 1 IPNV strain. In the study of cell lines and virus seeds, CHSE-214 was successively passaged to 30 generations, and its growth characteristics and sensitivity to IPNV remained stable. When IPNV was passaged to 10 generations, the viral titers were not affected, but mutations were found in the VP2 protein of both genogroup 1 and 5 IPNV strains. The study is conducive to the improvement of IPNV vaccine development for rainbow trout.