How modular protein nanoparticles may expand the ability of subunit anti-viral vaccines: The spring viremia carp virus (SVCV) case

Spring viremia of carp (SVC) remains as a vaccine orphan disease mostly affecting juvenile specimens. Young fish are especially difficult to vaccinate and oral administration of vaccine combined with food would be the election system to minimise stress and the vaccination costs associated to injection. However, administration of prophylactics with food pellets faces off several drawbacks mainly related with vaccine degradation and weak protection correlates of oral vaccines. Here we present a platform based on recombinant proteins (subunit vaccines) manufactured as highly resistant nanostructured materials, and providing excellent levels of protection against SVC virus in a preliminary i.p injection challenge. The G3 domain of SVCV glycoprotein G was overexpressed in E. coli together with IFNγ and the modular protein was purified from bacterial aggregates (inclusion bodies) as highly organised nanostructured biomaterial (nanopellets, NP). These SVCV-IFN NP were taken up by zebrafish cells leading to the enhanced expression of different antiviral and IFN markers (e.g vig1, mx, lmp2 or ifngr1 among others) in zebrafish liver cells (ZFL). To monitor if SVCV NP and SVCV-IFN NP can be taken up by intestinal epithelia and can induce antiviral response we performed experiments with SVCV NP and SVCV-IFN NP in 3 days post fertilization (dpf) zebrafish larvae. Both, SVCV NP and SVCV-IFN NP were taken up and accumulated in the intestine without signs of toxicity. The antiviral response in larvae showed a different induction pattern: SVCV-IFN NP did not induce an antiviral response while SVCV NP showed a good antiviral induction. Interestingly ZF4, an embryonic derived cell line, showed an antiviral response like ZFL cells, although the lmp2 and ifngr1 (markers of the IFNγ response) were not overexpressed. Experiments with adult zebrafish indicated an excellent level of protection against a SVCV model infection where SVCV-IFN NP vaccinated fish reached 20% cumulative mortality while control fish reached over 80% cumulative mortality.