EVALUATION OF MOLECULAR STRATEGIES TO DEVELOP A LIVE DENGUE VACCINE

Background: Millions of individuals are estimated to become infected w ith dengue virus each year, particularly in tropical and subtropical r egions. Mortality is low but infection can lead to a severe form of de ngue, characterised by haemorrhage and shock. A safe and effective vac cine against dengue is still not available. Objective: To use the succ essful construction of dengue type 4 virus (DEN4) cDNA, which yields i nfectious RNA transcripts, to provide a new approach to the developmen t of safe and effective dengue vaccines. Study design: The 3' and 5' n oncoding (NC) regions of the genome were targeted to construct DEN4 de letion mutants, because the sequences in these regions are thought to play an important role in the regulation of viral replication DEN4 cDN A was also employed to construct a viable chimeric virus with dengue t ype 1, 2 or 3 antigenicity, by substitution of heterotypic structural protein genes. Results: Most viable mutants, recovered from the cDNA c onstructs, were partially restricted for growth in simian cells as ana lysed by plaque morphology assay and viral yield analysis. Several 3' NC deletion mutants which exhibited a range of growth restriction in c ell culture were further evaluated for infectivity and immunogenicity in rhesus monkeys. Occurrence and duration of viraemia were reduced fo r these deletion mutants, compared to the wild type DEN4. Analysis of antibody response to infection in rhesus monkeys also indicated that s ome of these mutants were attenuated. These DEN4 deletion mutants repr esent promising live dengue vaccine candidates that merit further clin ical evaluation. Chimera DEN1/DEN4 or DEN2/DEN4 which expresses DEN1 o r DEN2 antigenicity were also used to infect monkeys. Most monkeys imm unised with these chimeric viruses, singly or in combination, develope d high titres of neutralising antibodies and were protected against ho motypic wild type DEN1 or DEN2 challenge. Conclusions: DEN4 and its de rived chimeric viruses of other three dengue serotype specificity, tha t contain appropriate attenuating mutations, have a potential use in a tetravalent live vaccine against dengue. (C) 1998 Elsevier Science B. V. All rights reserved.