Persistence of neutralizing antibody and its protective efficacy induced by a live attenuated tetravalent dengue vaccine, KD-382, in cynomolgus monkeys.

An effective dengue vaccine should induce a long-lasting immune response against all four serotypes simultaneously with a minimum number of immunizations. Our live attenuated tetravalent dengue vaccine candidate, KD-382, was developed using a classical host range mutation strategy (no addition of artificial genetic modification). In our previous study, cynomolgus monkeys immunized with a single dose of KD-382 seroconverted to all four serotypes. However, it is important to determine if neutralizing antibodies (NAbs) induced by KD-382 can work as a long-lasting immune response to prevent dengue. In this study, a single dose of KD-382 induced a strong NAb response against all four serotypes in cynomolgus monkeys. We also confirmed that NAb titers against all four serotypes persist for at least five years, indicating its high potential as a dengue vaccine candidate. Next, we evaluated the effect of pre-existing dengue immunity on NAb responses induced by KD-382. We administered KD-382 to cynomolgus monkeys pre-administered one of the monovalent parental wild-type strains 60 days before vaccination. Regardless of the pre-immunized serotype, all the monkeys showed sufficient tetravalent NAb responses, which lasted for over two years. All the KD-382 vaccinated monkeys were then challenged with different parental wild-type viruses than that used for pre-administration; viral RNA in the serum was less than the lower limit of quantification, indicating complete protection against secondary heterologous dengue infection without any harmful disease enhancement. Consequently, KD-382 successfully induced a long-lasting and protective tetravalent NAb response in monkeys, suggesting that KD-382 is a promising vaccine candidate usable for both dengue seronegative and seropositive individuals.