A new vaccine against the SARS coronavirus has shown promise in early tests, researchers report in the 6 December issue of The Lancet. The vaccine revved up immune responses in six monkeys, but the researchers haven't yet tested its ability to fend off disease. No vaccine for humans exists yet.
To develop the vaccine, Andrea Gambotto and colleagues at the University of Pittsburgh turned to adenoviruses, the culprit behind the common cold. They engineered three adenoviruses so that each one expresses a different protein component of the SARS virus. The idea behind the vaccine is to stimulate a mild attack against the cold virus, and a fiercer attack against the SARS proteins. Making a vaccine with the SARS proteins alone would have been more expensive and have taken longer, says Gambotto. And it would not have triggered the production of both T cells and antibodies--two components of the immune system attack thought to be necessary for protection.
To see if the vaccine could trigger an immune response, the team injected six macaques with the adenoviruses and gave them a booster shot 28 days later. After 6 weeks, all the monkeys had mobilized killer T cells against SARS and had high levels of protective antibodies. Two control monkeys, injected with a plain cold virus, did not mount an attack. Because macaques don't develop SARS, the monkeys weren't infected with the virus.
It is an early, but important step, says Gary Nabel, director of the vaccine research center at the National Institute of Allergy and Infectious Diseases (NIAID), who earlier this year suggested using adenoviral vaccines against SARS. Getting the two-pronged immune response is important, says Nabel. "If you have one but not the other, the protection that you see tends to be more short-lived," he says.
Although Gambotto's team is the first to publish results from SARS vaccine tests, the list of vaccine candidates is burgeoning. Nabel says it's too early to say which is best. A Canadian team is working on another adenovirus vaccine, and Chinese researchers may start human studies using inactivated virus in a few months, says Nabel, who adds that his group hopes to begin human trials later next year with an adenovirus vaccine that protects mice against SARS infection.