BACKGROUND: We have developed a manufacturing strategy that can improve the safety and genetic stability of recombinant live-attenuated chimeric dengue vaccine (DENVax) viruses. These viruses, containing the pre-membrane (prM) and envelope (E) genes of dengue serotypes 1-4 in the replicative background of the attenuated dengue-2 PDK-53 vaccine virus candidate, were manufactured under cGMP. METHODOLOGY/PRINCIPAL FINDINGS: After deriving vaccine viruses from RNA-transfected Vero cells, six plaque-purified viruses for each serotype were produced. The plaque-purified strains were then analyzed to select one stock for generation of the master seed. Full genetic and phenotypic characterizations of the master virus seeds were conducted to ensure these viruses retained the previously identified attenuating determinants and phenotypes of the vaccine viruses. We also assessed vector competence of the vaccine viruses in sympatric (Thai) Aedes aegypti mosquito vectors. CONCLUSION/SIGNIFICANCE: All four serotypes of master vaccine seeds retained the previously defined safety features, including all three major genetic loci of attenuation, small plaques, temperature sensitivity in mammalian cells, reduced replication in mosquito cell cultures, and reduced neurovirulence in new-born mice. In addition, the candidate vaccine viruses demonstrated greatly reduced infection and dissemination in Aedes aegypti mosquitoes, and are not likely to be transmissible by these mosquitoes. This manufacturing strategy has successfully been used to produce the candidate tetravalent vaccine, which is currently being tested in human clinical trials in the United States, Central and South America, and Asia.

Formulations of chimeric dengue vaccine (DENVax) viruses containing the pre-membrane (prM) and envelope (E) genes of serotypes 1-4 expressed in the context of the attenuated DENV-2 PDK-53 genome were tested for safety, immunogenicity and efficacy in interferon receptor knock-out mice (AG129). Monovalent formulations were safe and elicited robust neutralizing antibody responses to the homologous virus and only limited cross-reactivity to other serotypes. A single dose of monovalent DENVax-1, -2, or -3 vaccine provided eighty or greater percent protection against both wild-type (wt) DENV-1 (Mochizuki strain) and DENV-2 (New Guinea C strain) challenge viruses. A single dose of monovalent DENVax-4 also provided complete protection against wt DENV-1 challenge and significantly increased the survival times after challenge with wt DENV-2. In studies using tetravalent mixtures, DENVax ratios were identified that: (i) caused limited viremia, (ii) induced serotype-specific neutralizing antibodies to all four DENV serotypes with different hierarchies, and (iii) conferred full protection against clinical signs of disease following challenge with either wt DENV-1 or DENV-2 viruses. Overall, these data highlight the immunogenic profile of DENVax, a novel candidate tetravalent dengue vaccine and the advantage of sharing a common attenuated genomic backbone among the DENVax monovalent vaccines that confer protection against homologous or heterologous virus challenge.