Protective immunity against nervous necrosis virus in convict grouper Epinephelus septemfasciatus following vaccination with virus-like particles produced in yeast Saccharomyces cerevisiae

- RGNNV causes viral nervous necrosis which inflicts economic losses in fish farming.
- Virus-like particles (VLPs) of RGNNV were produced in yeast expression system.
- Protective immunity conferred by the VLPs was evaluated in seven-band grouper.
- Immunization with VLPs provoked efficiently neutralizing antibodies against RGNNV.
- Immunization with VLPs enhanced survival of fish post RGNNV challenge.

Infection with nervous necrosis virus (NNV) causes viral nervous necrosis, which inflicts serious economic losses in marine fish cultivation. Virus-like particles (VLPs) are protein complexes consisting of recombinant virus capsid proteins, whose shapes are similar to native virions. VLPs are considered a novel vaccine platform because they are not infectious and have the ability to induce neutralizing antibodies efficiently. However, there have been few studies of protective immune responses employing virus challenge following immunization with NNV VLPs, and this is important for evaluating the utility of the vaccine. In the present study, we produced red-spotted grouper (Epinephelus akaara) NNV (RGNNV) VLPs in Saccharomyces cerevisiae and investigated protective immune responses in convict grouper (Epinephelus septemfasciatus) following intraperitoneal injection and oral immunization with the RGNNV VLPs. The parenterally administered VLPs elicited neutralizing antibody with high efficacy, and provided the fish with full protection against RGNNV challenge: 100% of the immunized fish survived compared with only 37% of the control fish receiving phosphate-buffered saline. RGNNV VLPs administered orally provoked neutralizing antibody systemically and conferred protective immunity against virus challenge: however only 57% of the fish survived. Our results demonstrate that RGNNV VLP produced in yeast has great potential as vaccine in fish.