Comparative evaluation of three protein nanoscaffolds for IHNV G ectodomain display in rainbow trout (Oncorhynchusmykiss).

Infectious hematopoietic necrosis virus (IHNV) causes severe losses in rainbow trout (Oncorhynchus mykiss) aquaculture. Vaccination is a critical control strategy, and the surface glycoprotein (G) is the primary target for protective immunity. However, recombinant G protein alone is poorly immunogenic, prompting the use of self-assembling nanoparticle scaffolds to display its ectodomain and enhance immunogenicity. The optimal scaffold for anti-IHNV vaccination remains unclear. We constructed three nanovaccines by fusing the IHNV G ectodomain to ferritin (Fe), I3-01, and E2p scaffolds, and compared their efficacy in rainbow trout. Fish were intraperitoneally vaccinated with a prime-boost regimen (day 0 and 14) and challenged on day 42. Serum IgM titers and the expression of key immune-related genes were measured weekly during the four weeks after the booster immunization; viral loads and histopathology were assessed post-challenge. All nanovaccines elicited higher antibody responses than soluble G protein. The I3-01-G group showed the highest IgM levels at day 35, strong upregulation of IFN-γ, MHC-II, CD4, and Mx-1, the lowest viral loads, the least histopathological lesions, and achieved a relative percent survival (RPS) of 75.0%, compared to 58.3% for E2p-G and 50.0% for Fe-G. The I3-01-based nanovaccine confers strong protection against IHNV and represents a promising next-generation vaccine candidate for aquaculture.