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)

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Summary

Introduction

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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