Non-clinical and phase I clinical trials of a Vero cell-derived inactivated Japanese encephalitis vaccine.

The safety and effectiveness of a Vero cell-derived inactivated Japanese encephalitis (JE) vaccine were compared with those of a current JE vaccine in non-clinical studies and a phase I clinical trial. The single-dose toxicity study showed no toxicity of either the current JE vaccine or the investigational Vero cell-derived JE vaccine. In a local irritation study, the degree of irritation caused by both vaccines was determined to be the same as that induced by normal saline. To investigate genotoxicity, a chromosomal aberration test was conducted and the results were negative. Both JE vaccines were administered to a group of 30 subjects who were seronegative (neutralizing antibody titer <10(1)) for JEV virus (Beijing-1 Strain). Each subject was subcutaneously inoculated twice at an interval of 1-4 weeks, followed by an additional booster inoculation 4-8 weeks later, and clinical reactions and serological responses were subsequently investigated. Adverse drug reactions of local reaction, headache and malaise were mild, occurring at a rate of 6.7 and 20.0% after administration of the Vero cell-derived JE vaccine and the current JE vaccine, respectively. The seroconversion rate after three doses of both JE vaccines was 100%, while the geometric mean titer for the Vero cell-derived and current JE vaccines was 10(2.35) and 10(2.03), respectively. These results suggest that the safety and effectiveness of the Vero cell-derived inactivated JE vaccine are equal to those of the currently available conventional vaccine in humans, and that the Vero cell-derived vaccine could be a useful second-generation JE vaccine.

Development of Vero cell-derived inactivated Japanese encephalitis vaccine.

We have established a manufacturing system for a Vero cell-derived inactivated Japanese encephalitis vaccine at a 500l scale. The production system involves expansion of Vero cells using microcarrier, followed by virus infection. Except for an additional purification step, the downstream purification processes are similar to those used for the current mouse brain-derived vaccine; cell removal, concentration and removal of low-molecular weight impurities by membrane filtration, formalin-inactivation, sucrose density gradient ultracentrifugation, and Sulfate-Cellulofine column chromatography are conducted. The antigen obtained from the manufacturing system was highly purified and its physico-chemical and immunological properties were comparable with those of antigen derived from mouse brains. Our system is very simple and could be easily scaled-up to allow vaccine production at a several thousand litre scale.