Experimental vaccine protects monkeys against Ebola virus

Scientists have created a two-part vaccine that has protected monkeys from the deadly Ebola virus, they reported in the 30 November 2000 issue of Nature.

One part of the vaccine consists of DNA, ‘‘naked DNA’’, coding for several Ebola virus proteins from the three strains of the virus — Zaire, Sudan, and Ivory Coast — known to cause disease in humans. This part is given in three monthly injections to ‘‘prime’’ the immune system of the vaccine recipient. The second part consists of an adenovirus, divested of its disease-causing potential, that carries a Zaire Ebola gene — one of the same genes contained in the prime part of the vaccine — into the cells of the vaccinated host. This second part of the vaccine, given 12 weeks after the initial priming series of injections, is designed to boost the immune response.

In the study, which was conducted by a group headed by Gary J. Nabel, director of the Vaccine Research Center at the National Institutes of Health (NIH) in Bethesda, Maryland, the ‘‘prime-boost’’ DNA vaccine protected all four vaccinated monkeys against lethal doses of the Zaire strain of Ebola virus. The monkeys were without symptoms or detectable virus 6 months after infection. The researchers plan to test the vaccine against the other two strains.

This is believed to be the first report of successful immunization of primates against Ebola. In earlier experiments performed at the University of Michigan and also by the NIH group, a similar DNA vaccine protected mice and guinea pigs.

‘‘There is still some way to go before a human vaccine is available, but this is a step in the right direction,’’ noted Dennis Burton and Paul Parren, of the California-based Scripps Research Institute in La Jolla, California, in a commentary in the same issue of Nature.

Dr Nabel told reporters that the prime-boost vaccination approach is ‘‘a highly effective way to boost immunity to otherwise deadly viruses’’. It is being tested in an experimental AIDS vaccine and could, he believes, be applied to infections such as malaria or tuberculosis.

Scott Gottlieb,
New York