Japanese encephalitis virus (JEV) is a major health problem in the world. Each year 50,000 cases of Japanese encephalitis are reported officially and more than 30% are fatal. Development of effective, safe and economical JEV vaccines for human use is necessary. A highly attenuated recombinant JEV, IC47, has been generated using a system for recovering viruses from infectious RNA transcribed from cDNA templete (infectious cDNA clones). This virus has potential for used as a human live vaccine since: I) it is highly attenuated in mice, 2) it is highly immunogenic, 3) immunization with the virus protects mice from lethal virulent JEV infection, 4) infected mice do not develop viremia, 5) it is molecularly defined, 6) seed virus can be generate from cDNAs, 7) the cost for the vaccine is reasonable, and 8) manufacturing methods are established. In this Phase I project, the infectious clone system will be used to introduce multiple mutations in the IC47 genome to stabilize the attenuation phenotype. Neurovirulence and immunogenicity of the modified virus are studied in mice.Awardee's statement of the potential commercial applications of the research:A significant market exists for JEV vaccines that includes several million travelers/year in the US and Europe and 40 million children/year in JEV-endemic regions. The killed mouse-brain JEV vaccine now available in the US and Europe is costly and requires 3 doses. It is too expensive for use in Asia, except in the most affluent countries. We will develop and commercialize an inexpensive, live attenuated, single-dose vaccine.National Institute of Allergy and Infectious Diseases (NIAID)