Rational Design of a Live Attenuated Dengue Vaccine: 2′-O-Methyltransferase Mutants Are Highly Attenuated and Immunogenic in Mice and Macaques

Roland Züst, et al. PLoS Pathog (2013) 9(8): e1003521.

 

Speaker: Chung-Lin Li (利宗霖)                  Time: 15:10~16:00, Oct. 29, 2014

Commentator: Dr. Oscar Perng (彭貴春 老師)      Place: Room 601

 

Abstract

Based on WHO report, over 2.5 billion people are now at risk from dengue virus (DENV) and there may be 50–100 million DENV infections worldwide every year. However, there is still no approved antiviral treatment or vaccine available. Live-attenuated vaccine have been used for many viruses, such as vaccinia virus, poliovirus (Sabin) and others (1). Live-attenuated virus can induce host immune responses and immune memory but do not cause disease. DENV NS5 has multifunctions, including RNA-dependent RNA polymerase and methyltransferase (MTase) activities responsible for 5’ RNA cap formation (2). In this study, the authors generated a live attenuated dengue vaccine by using 2’-O-MTase mutant DENV. First, the authors found that single E217A mutation and double K61A+E217A mutation had no 2’-O-methylation activity. Both wild-type (WT) and mutant viruses produced similar plaque morphology while replication of 2’-O-MTase mutant viruses was attenuated in mammalian Vero and mosquito C3/36 cells. Furthermore, mutant viruses are highly sensitive to type I IFN inhibition. Next, immunization of AG129 mice with 2’-O-MTase mutant viruses can induce T cell responses and protect against homologous challenge even though the IgG titers were lower than WT-immunized mice. Moreover, mutant virus-immunized mice can also survive against challenge of virulent DENV-2 strain (D2Y98P). To assess the safety and efficacy of the 2’-O-MTase mutant DENV vaccine approach in an immunologically competent host, Rhesus monkeys were immunized with mutant virus. All monkeys can produce neutralizing antibody but viremia was detected in one monkey. After challenge with WT DENV-2, no viremia was detected in all mutant virus-immunized monkeys but was detected in control monkeys. Finally, 2’-O-MTase mutant virus was unable to infect Ae. aegypti and no dissemination was observed. These results demonstrate a potatential development of safety DENV vaccine strategy.

 

References:

1.     Pulendran B, Ahmed R (2011) Immunological mechanisms of vaccination. Nat Immunol 12: 509–517.

2.     Ray D, Shah A, Tilgner M, Guo Y, Zhao Y, et al. (2006) West Nile virus 5’-cap structure is formed by sequential guanine N-7 and ribose 2’-O methylations by nonstructural protein 5. J Virol 80: 8362–8370.