Abstract
Swine are a critical amplifying host involved in human Japanese encephalitis (JE) outbreaks. Cross-genotypic immunogenicity and sterile protection are important for the current genotype III (GIII) virus-derived vaccines in swine, especially now that emerging genotype I (GI) JE virus (JEV) has replaced GIII virus as the dominant strain. Herein, we aimed to develop a system to generate GI JEV virus-like particles (VLPs) and evaluate the immunogenicity and protection of the GI vaccine candidate in mice and specific pathogen-free swine. A CHO-heparan sulfate-deficient (CHO-HS(-)) cell clone, named 51-10 clone, stably expressing GI-JEV VLP was selected and continually secreted GI VLPs without signs of cell fusion. 51-10 VLPs formed a homogeneously empty-particle morphology and exhibited similar antigenic activity as GI virus. GI VLP-immunized mice showed balanced cross-neutralizing antibody titers against GI to GIV viruses (50% focus-reduction micro-neutralization assay titers 71 to 240) as well as potent protection against GI or GIII virus infection. GI VLP-immunized swine challenged with GI or GIII viruses showed no fever, viremia, or viral RNA in tonsils, lymph nodes, and brains as compared with phosphate buffered saline-immunized swine. We thus conclude GI VLPs can provide sterile protection against GI and GIII viruses in swine.
Highlights
The current Japanese encephalitis (JE) vaccines for humans or domestic animals are derived from genotype III (GIII) viruses, with amino acid sequences on the E protein significantly different from those in the GI virus[17]
The viral E, NS1, prM, and M proteins were detectable in the JE virus (JEV) cultured sample, and the same size of E and prM proteins appeared in the 51-10 clone produced virus-like particles (VLPs) (Fig. 1B)
We analyzed the antigenicity of the viral E protein organized on VLPs with a panel of monoclonal antibodies including the flavivirus group (4G2, 6B3B-3, and 23–2) and complex cross-reactive (T16 and 7A6C-5), and JEV type-specific (2F2 and 2H4) mAbs by the antigen-capture enzyme-linked immunosorbent assay (Ag-ELISA)
Summary
The current JE vaccines for humans or domestic animals are derived from GIII viruses, with amino acid sequences on the E protein significantly different from those in the GI virus[17]. Overall results suggested that the GIII JEV vaccine might temporarily protect against GI virus infection, especially for travelers, but vaccine efficacy for long-term protection might be reduced in GI JEV epidemic or endemic countries or regions[18,19,20,21,22,23,24,25]. Considerations of a next-generation JEV vaccine for sows might include an ability to block virus transmission and induce cross-protective activity against the currently dominant GI virus and other genotypic viruses, especially the co-circulating GIII virus in some JEV endemic regions[18,26,27]. GI JEV VLPs elicited antibodies cross-neutralizing GI through GIV JEV and cross-protected mice and special pathogen-free (SPF) pigs against GI and GIII JEV infection. The sterile protection observed in pigs implied a potential for GI VLPs protection against abortion and blocking JEV transmission in the pig farm
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