Vaccine candidates for dengue virus type 1 (DEN1) generated by replacement of the structural genes of rDEN4 and rDEN4Δ30 with those of DEN1

Background: Antigenic chimeric viruses have previously been generated in which the structural genes of recombinant dengue virus type 4 (rDEN4) have been replaced with those derived from DEN2 or DEN3. Two vaccine candidates were identified, rDEN2/4 Delta 30(ME) and rDEN3/4 Delta 30(ME), which contain the membrane (M) precursor and envelope (E) genes of DEN2 and DEN3, respectively, and a 30 nucleotide deletion (Delta 30) in the 3' untranslated region of the DEN4 backbone. Based on the promising preclinical phenotypes of these viruses and the safety and immunogenicity of rDEN2/4 Delta 30(ME) in humans, we now describe the generation of a panel of four antigenic chimeric DEN4 viruses using either the capsid (C), M, and E (CME) or ME structural genes of DENI Puerto Rico/94 strain. Results: Four antigenic chimeric viruses were generated and found to replicate efficiently in Vero cells: rDENI/4(CME), rDENI/4 Delta 30(CME), rDENI/4(ME), and rDENI/4 Delta 30(ME). With the exception of rDENI/4(ME), each chimeric virus was significantly attenuated in a SCID- HuH-7 mouse xenograft model with a 25-fold or greater reduction in replication compared to wild type DENI. In rhesus monkeys, only chimeric viruses with the Delta 30 mutation appeared to be attenuated as measured by duration and magnitude of viremia. rDENI/4 Delta 30(CME) appeared over- attenuated since it failed to induce detectable neutralizing antibody and did not confer protection from wild type DENI challenge. In contrast, rDENI/4 Delta 30(ME) induced 66% seroconversion and protection from DENI challenge. Presence of the Delta 30 mutation conferred a significant restriction in mosquito infectivity upon rDENI/4 Delta 30(ME) which was shown to be non- infectious for Aedes aegypti fed an infectious bloodmeal. Conclusion: The attenuation phenotype in SCID-HuH-7 mice, rhesus monkeys, and mosquitoes and the protective immunity observed in rhesus monkeys suggest that rDENI/4 Delta 30(ME) should be considered for evaluation in a clinical trial.