182 Original article The immunogenicity of tetravalent dengue DNA vaccine in mice pre-exposed to Japanese encephalitis or Dengue virus antigens Eakachai Prompetchara, 1 Chutitorn Ketloy, 1,2 Poonsook Keelapang, 3 Nopporn Sittisombut 3,4 and Kiat Ruxrungtham 1,5 Summary Background: Asian countries are an endemic area for both dengue (DENV) and Japanese encephalitis viruses (JEV). While JEV vaccines have been used extensively in this region, DENV vaccines remains under development. Whether preexisting naturally acquired or vaccination- induced immunity against JEV may affect the immune response to dengue vaccine candidate is unclear. In this study we used mice previously immunized with JEV vaccines to evaluate the impact on dengue-specific neutralizing antibody responses to a tetravalent dengue DNA vaccine candidate (TDNA). Methods: A tetravalent cocktail of plasmids encoding pre-membrane and envelope proteins from each dengue serotype was administered into mice which had been previously primed with inactivated or live-attenuated JEV vaccines, or dengue serotype2 virus (DENV-2). Neutralizing antibody response was measured employing a plaque reduction neutralization test at two weeks after the priming and at four weeks after the second dose of the dengue tetravalent plasmids. Results: Inactivated or live-attenuated JEV vaccines, or DENV-2 induced low levels of neutralizing antibodies against the homologous viruses (JE and dengue virus, respectively). DENV-2 injection induced also low levels of cross-reactive antibodies against DENV-1, -3 and -4. JEV vaccines have no effect on the dengue- specific neutralizing antibody responses to the subsequent TDNA immunization. Pre-exposure to DENV-2 infection increased DENV-2 specific response neutralizing antibody to two doses of TDNA plasmids by six folds, but did not affect antibody response to other serotypes. Conclusions: Priming with JEV vaccines did not impact on dengue virus-specific neutralizing antibody response to a dengue TDNA vaccine candidate in mice. (Asian Pac J Allergy Immunol 2015;33:182-8) Keywords: dengue virus, Japanese encephalitis virus, preexisting immunity, tetravalent dengue DNA vaccine, neutralizing antibody Introduction Several flaviviruses cause human diseases, including dengue virus (DENV), Japanese encephalitis virus (JEV), yellow fever virus and tick-borne encephalitis virus. Infection by DENV may result in undifferentiated fever, dengue fever or dengue hemorrhagic fever (DHF). Infection with any of the four serotypes of DENV induces long- term immunity against the homologous serotype. DHF, an immunopathological disease, occurs with an increased risk during secondary infections. 1,2 Although there have been several decades of investigation, vaccines targeting all four serotypes of DENV currently remain under development. In some DENV endemic areas, particularly the Indian subcontinent, East and South-East Asia, JEV From 1. Dengue Vaccine Research Unit, Chula Vaccine Research Center (ChulaVRC), Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand 2. Department of Laboratory Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand 3. Department of Microbiology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand 4. Medical Biotechnology Unit, National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Bangkok, Thailand, 5. Vaccine and Cellular Immunology Laboratory, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Corresponding author: Kiat Ruxrungtham E-mail: rkiatchula@gmail.com Submitted date: 21/4/2014 Accepted date: 5/11/2014