Earlier studies demonstrated that immunization of monkeys with baculovirus-expressed dengue virus E alone induced only partial protection against dengue virus infection. Analysis of sera from immunized monkeys showed that antibodies to E were low or not detectable. Thus, the poor immunogenicity of E was idendfied as an obstacle to further development of a subunit protein strategy using the recombinant DNA approach. Fortunately, recent studies of vaccinia virus expressed E showed that a C-terminally truncated E, approximately 80% in length, is more immunogenic and protective than the full-length E in mice. Unlike the full-length E, 80% E is expressed on the cell surface and is secreted extracellularly. These new properties of truncated E probably play a major role in its increased immunogenicity and efficacy. In any case, the increase in immunogenicity and efficacy associated with the specific truncation of E has implications for the development of effective subunit vaccines for dengue as well as other flavivirus diseases. For these reasons, we constructed a total of 8 recombinant baculoviruses that expressed full-length E or 80% E of 3 different dengue virus serotypes (type 4, 2, and 3) and Japanese B encephalitis (JE) virus. The baculovirus-expressed 80% E of dengue type 4 or type 2 virus was secreted into the medium fluid of infected cells and we are currently purifying secreted E and will evaluate its immnunogenicity in mice,and in primates.
