Recombinant vaccinia viruses expressing dengue type 4 virus (D4) and dengue type 2 virus (D2) proteins from cloned DNA were constructed for evaluation in experimental immunoprophylaxis. Previously we showed that mice immunized with recombinant vaccinia viruses which expressed the D4 pre-M and E glycoproteins, or E alone, were protected against homotypic dengue virus encephalitis. However, an attempt to prevent dengue viremia in rhesus monkeys by immunization with a vaccinia virus recombinant expressing pre-M, E and nonstructural protein NS1 was unsuccessful. Mice immunized with an E recombinant developed a low level of neutralizing antibodies, but antibodies were not detectable by radio-immunoprecipitation. Recently, recombinants expressing pre-M and E of the S-1 candidate live vaccine strain of D2 virus induced solid protection in mice against challenge with 100 LD50 of D2 strain New Guinea C. A recombinant expressing D2 E alone induced only partial protection against D2 challenge, in contrast to complete homotypic protection provided by a D4 E recombinant. A recombinant which expressed the N-terminal 79% of D2 E, that is secreted into the medium, induced a strong antibody response to E in immunized and provided solid protection against homotypic virus challenge equivalent to that provided by vD2 pM-E. Prior infection with a vaccinia recombinant expressing apparently authentic E did not prime the antibody response to subsequent immunization with dengue virus or baculovirus expressed E. An analysis of vaccinia recombinants that expressed E fusion proteins, in which the N-terminal half consisted of D4 E and the C-terminal half of D2 E, or vice-versa failed to identify the region of the E molecule responsible for eliciting a type specific protective immune response.
