An inactivated Vero cell-grown Japanese encephalitis vaccine formulated with Advax, a novel inulin-based adjuvant, induces protective neutralizing antibody against homologous and heterologous flaviviruses

Abstract

Advax is a polysaccharide-based adjuvant that potently stimulates vaccine immunogenicity without the increased reactogenicity seen with other adjuvants. This study investigated the immunogenicity of a novel Advax-adjuvanted Vero cell culture candidate vaccine against Japanese encephalitis virus (JEV) in mice and horses. The results showed that, in mice, a two-immunization, low-dose (50 ng JEV antigen) regimen with adjuvanted vaccine produced solid neutralizing immunity comparable to that elicited with live ChimeriVax-JE immunization and superior to that elicited with tenfold higher doses of a traditional non-adjuvanted JEV vaccine (JE-VAX; Biken Institute) or a newly approved alum-adjuvanted vaccine (Jespect; Novartis). Mice vaccinated with the Advax-adjuvanted, but not the unadjuvanted vaccine, were protected against live JEV challenge. Equine immunizations against JEV with Advax-formulated vaccine similarly showed enhanced vaccine immunogenicity, confirming that the adjuvant effects of Advax are not restricted to rodent models. Advax-adjuvanted JEV vaccine elicited a balanced T-helper 1 (Th1)/Th2 immune response against JEV with protective levels of cross-neutralizing antibody against other viruses belonging to the JEV serocomplex, including Murray Valley encephalitis virus (MVEV). The adjuvanted JEV vaccine was well tolerated with minimal reactogenicity and no systemic toxicity in immunized animals. The cessation of manufacture of traditional mouse brain-derived unadjuvanted JEV vaccine in Japan has resulted in a JEV vaccine shortage internationally. There is also an ongoing lack of human vaccines against other JEV serocomplex flaviviruses, such as MVEV, making this adjuvanted, cell culture-grown JEV vaccine a promising candidate to address both needs with one vaccine.

Fig. 1.

Protection against JEV challenge with adjuvanted ccJE vaccine. Groups of 8-week-old C57Bl/6 mice were immunized with 0.5 μg JE-VAX or ccJE without or formulated with Advax adjuvant and boosted 3 weeks later. For pre-challenge serology, see Table 1, experiment 1. At 6 weeks after completion of the vaccination schedule, mice were challenged intranasally with 2×10⁵ p.f.u. JEV (Nakayama strain). Mice were monitored twice daily for morbidity and mortality for 28 days.

Fig. 2.

Stimulation of JEV serocomplex cross-neutralizing antibodies with Advax-adjuvanted JE-VAX vaccine. Groups of 8-week-old C57Bl/6 mice (n=6) were immunized with 0.5 μg JE-VAX without or formulated with Advax adjuvant and boosted 3 weeks later. A third group was vaccinated with 10⁵ p.f.u. ChimeriVax-JE, but did not receive a booster immunization. At 6 weeks after completion of the vaccination schedules, sera were collected and anti-JEV ELISA end-point and PRNT₅₀ titres against MVEV were determined for individual sera. Dotted lines indicate the detection limits of the assays. Solid lines indicate the mean value.