Construction, safety, and immunogenicity in nonhuman primates of a chimeric yellow fever-dengue virus tetravalent vaccine

We previously reported construction of a chimeric yellow fever-dengue type 2 virus (YF/DEN2) and determined its safety and protective efficacy in rhes us monkeys (F. Guirakhoo et al., J. Virol. 74:5477-5485, 2000). In this pap er, we describe construction of three additional YF/DEN chimeras using prem embrane (prM) and envelope (E) genes of wild-type (WT) clinical isolates: D EN1 (strain PUO359, isolated in 1980 in Thailand), DEN3 (strain PaH881/88, isolated in 1988 in Thailand), and DEN4 (strain 1228, isolated in 1978 in I ndonesia). These chimeric viruses (YF/DEN1, YF/DEN3, and YF/DEN4) replicate d to similar to7.5 log(10) PFU/ml in Vero cells, were not neurovirulent in 3- to 4-week-old ICR mice inoculated by the intracerebral route, and were i mmunogenic in monkeys. All rhesus monkeys inoculated subcutaneously with on e dose of these chimeric viruses (as monovalent or tetravalent formulation) developed viremia with magnitudes similar to that of the YF 17D vaccine st rain (YF-VAX) but significantly lower than those of their parent WT viruses . Eight of nine monkeys inoculated with monovalent YF/DEN1 -3, or -4 vaccin e and six of six monkeys inoculated with tetravalent YF/DEN1-4 vaccine sero converted after a single dose. When monkeys were boosted with a tetravalent YF/DENI-4 dose 6 months later, four of nine monkeys in the monovalent YF/D EN groups developed low levels of viremia, whereas no viremia was detected in any animals previously inoculated with either YF/DEN1-4 vaccine or WT DE N virus. An anamnestic response was observed in all monkeys after the secon d dose. No statistically significant difference in levels of neutralizing a ntibodies was observed between YF virus-immune and nonimmune monkeys which received the tetravalent YF/DENI-4 vaccine or between tetravalent YF/DEN1-4 -immune and nonimmune monkeys which received the YF-VAX. However, preimmune monkeys developed either no detectable viremia or a level of viremia lower than that in nonimmune controls. This is the first recombinant tetravalent dengue vaccine successfully evaluated in nonhuman primates.