Development of an Oral Subunit Vaccine to Protect Rainbow Trout Against Infectious Hematopoietic Necrosis Virus (IHNV)

Infectious hematopoietic necrosis virus (IHNV) is a highly virulent pathogen of salmonids that causes severe mortality in aquaculture, particularly during early developmental stages. Current vaccination strategies rely mainly on injectable DNA vaccines, which are labour-intensive and unsuitable for large-scale immunization of juvenile fish. In this study, we developed and evaluated two recombinant nanostructured subunit vaccines based on the IHNV glycoprotein: IHNV NP and IHNV-IFN NP , the latter incorporating interferon-gamma (IFNγ) as an immunomodulatory adjuvant. Both vaccines were produced in Escherichia coli as nanoparticles. In vitro assays using the rainbow trout macrophage-like cell line RTS11 showed efficient cellular uptake of both subunit vaccines and colocalization of IHNV-IFN NP within acidic lysosomes, where antigen processing takes place. Gene expression analysis in RTS11 revealed that the IFNγ-adjuvanted vaccine significantly upregulated antiviral and immune-related genes associated with innate and adaptive responses, including vig1 , ip10 , mx , ccl4 , il-1β , mhcI , and mhcII , compared with the non-adjuvanted formulation. Furthermore, an in vivo trial demonstrated that oral administration by intubation of IHNV-IFN NP induced partial protective responses against IHNV challenge in rainbow trout fingerlings. In addition, ELISA and hindgut gene expression analysis in juvenile rainbow trout following oral intubation with IHNV-IFN NP provided further evidence of the vaccine’s potential to induce mucosal immune responses. These findings indicate that an IFNγ-functionalized nanostructured subunit vaccine enhances immune activity against IHNV and represent a promising strategy for the development of practical, modular antiviral oral vaccines in aquaculture.