Joseph R. Putnak

Safety and immunogenicity of attenuated dengue virus vaccines (Aventis Pasteur) in human volunteers

A randomized, controlled, double-blinded study was conducted to determine safety and immunogenicity of five live attenuated dengue vaccines produced by Aventis Pasteur (AvP). The study was completed with 40 flavivirus non-immune volunteers: five recipients of each monovalent (dengue-1, dengue-2, dengue-3, or dengue-4) vaccine, ten recipients of tetravalent (dengue-1, dengue-2, dengue-3, and dengue-4) vaccine, and ten recipients of vaccine vehicle alone. All vaccines were administered in a single subcutaneous dose (range, 3.6-4.4 log(10) plaque forming units). No serious adverse reactions occurred in volunteers followed for 6 months after vaccination. Five vaccine recipients developed fever (T > or = 38.0 degrees C), including four tetravalent vaccinees between days 8 and 10 after vaccination. Dengue-1, dengue-2, dengue-3, or dengue-4 vaccine recipients reported similar frequency of mild symptoms of headache, malaise, and eye pain. Tetravalent vaccinees noted more moderate symptoms with onset from study days 8-11 and developed maculopapular rashes distributed over trunk and extremities. Transient neutropenia (white blood cells < 4000/mm3) was noted after vaccination but not thrombocytopenia (platelets < 100,000/mm3). All dengue-3, dengue-4, and tetravalent vaccine recipients were viremic between days 7 and 12 but viremia was rarely detected in dengue-1 or dengue-2 vaccinees. All dengue-2, dengue-3, and dengue-4, and 60% of dengue-1 vaccine recipients developed neutralizing and/or immunoglobulin M antibodies. All tetravalent vaccine recipients were viremic with dengue-3 virus and developed neutralizing antibodies to dengue-3 virus. Seven volunteers also had multivalent antibody responses, yet the highest antibody titers were against dengue-3 virus. The AvP live attenuated dengue virus vaccines are safe and tolerable in humans. The live attenuated tetravalent dengue vaccine was most reactogenic, and preferential replication of dengue-3 virus may have affected its infectivity and immunogenicity.

Mice immunized with a dengue type 2 virus E and NS1 fusion protein made in Escherichia coli are protected against lethal dengue virus infection

A gene fragment encoding the C-terminal 204 amino acids (AA) from the structural envelope glycoprotein (E) and the N-terminal 65 AA from non-structural protein one (NS1) of dengue type 2 virus (DEN-2) was expressed in Escherichia coli (E. coli) as a fusion protein with staphylococcal protein A. The recombinant fusion protein was purified and analysed for its antigenicity, its immunogenicity and its ability to protect mice against lethal challenge with live DEN-2 virus. The recombinant protein was found to be reactive with anti-DEN-2 polyclonal and monoclonal antibodies. Mice immunized with the purified fusion protein made anti-DEN-2 antibodies measured by the hemagglutination-inhibition (HI) and neutralization (N) tests, and were protected against lethal challenge with DEN-2 virus administered by intracranial inoculation.

Morphogenesis of flaviviruses.

The flaviviruses consist of about 70 viruses that include some important pathogens that are responsible for a number of serious diseases, such as yellow fever, dengue fever, and various encephalitides (Porterfield, 1980; Shope, 1980). They are transmitted to humans by arthropod vectors, i.e., mosquitoes and ticks (Chamberlain, 1980) and are also called arboviruses. The number of known flaviviruses will undoubtedly increase in the future as more viruses are isolated from various hosts and their vectors. Until recently, the flavivirus genus was included with three others, alphavirus, pestivirus, and rubivirus, as part of the Togaviridae family (Porterfield et al., 1978). With the accumulation of experimental data, it has become increasingly clear that flaviviruses have substantially different genomic organization and mechanisms of replication and gene expression from those of alphaviruses, the other major genus of the Togaviridae family. Therefore, the possibility that the two genera have diverged from the same ancestor is remote. Consequently, flaviviruses are now classified in their own family, Flaviviridae (Westaway et al., 1985).