Two pieces of research, both published in this week's issue of The Lancet, suggest different ways in which humans might be protected against the virus that causes severe acute respiratory syndrome (SARS). And investigators say they could be combined to control an epidemic more effectively.
According to researchers from the US National Institute of Allergy and Infectious Diseases (NIAID), monkeys can be protected against the SARS virus using a single dose of a test vaccine sprayed into the nose. Meanwhile, a team of scientists in Holland has successfully protected ferrets from the virus by treating them with human antibodies.
The NIAID research team, led by Alexander Bukreyev, treated four monkeys with a test vaccine produced by inserting the gene responsible for producing a key SARS protein (known as SARS-S) into a weakened version of a human influenza virus. A further four monkeys received an inactive placebo vaccine; in all eight monkeys, the treatments were sprayed directly into the monkeys' nostrils.
One month after immunisations, both groups were deliberately infected with the SARS virus. The researchers found replicated virus in samples taken from the respiratory tracts of the animals that had received the placebo vaccine, a sign that immunisation had failed. In contrast, animals that had received the full vaccine showed no such signs.
"This study shows that delivering the vaccine directly to the respiratory tract can effectively protect primates from SARS," said Brian Murphy, one of the study's authors and co-chief of the host laboratory.
"With more research, we hope to develop a vaccine based on this approach that could be used to rapidly immunise medical personnel, helping them control a potential outbreak."
Murphy says that the potential SARS vaccine would be most effective in young children. The team is planning to conduct studies to effectively immunise adults as well. "In the long run, we want to establish a weakened respiratory vector — or 'shell' — that all people are susceptible to," he says. "That way, we can quickly develop vaccines for numerous diseases by simply inserting the protective genes of those viruses into our generalised vector."
In a separate study, a team headed by Jan ter Meulen of Dutch company Crucell Holland, found that treatment with human antibodies — one of our bodies' defences against disease — significantly reduced viral replication in infected ferrets.
The results "show that administration of a human monoclonal antibody might offer a feasible and effective prophylaxis for the control of human SARS coronavirus infection," say the investigators.
Ter Meulen told SciDev.Net he thought an antibody treatment could be tested in humans as early as next year, and estimated that a vaccine might take a few more.
In the long run, the investigators speculate that a vaccine and antibodies taken prophylactically might work together to control the extent of a SARS epidemic. "You could give patients antibodies and vaccines simultaneously," says ter Meulen. While the patients build up their immunity thanks to the vaccine, the administration of antibodies would protect them from infection.
Another study also conducted in Murphy's lab and published this week in the Proceedings of the National Academy of Sciences, shows that SARS-S is the only known SARS protein that can elicit a protective immune response.
Ursula Buchholz and her colleagues immunised hamsters with potential vaccines containing the three SARS structural proteins, either individually or in combinations. They found that only vaccines containing the gene for SARS-S could trigger the production of protective antibodies. Combining SARS-S with genes for other structural proteins did not boost the immune response.
The investigators hope this finding will simplify the development of a vaccine. "What this means," says Peter Collins, a member of the NIAID lab, "is that if you want to follow a recombinant approach [where a SARS gene is combined with another virus such as influenza], you really only need to focus on SARS-S."
References: The Lancet 363, 2139, The Lancet 363, 2122
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