Feature: The challenge of a herpes simplex vaccine
Thursday, 17 February, 2011
HSV-2 is a well-known ailment that is transmissible through contact, including sexual contact. Where HSV-1 commonly causes oral herpes, or cold sores, HSV-2 is primarily responsible for genital herpes.
After the initial outbreak, the virus has a tendency to go latent, squireling itself away in nerve cells at the base of the spine, only to re-emerge unbidden again at a later date.
At least one in 10 Australians carry the herpes virus, possibly a great many more, making it an ideal target for a new vaccine. “The reason we chose herpes simplex type 2 is that it’s a common enough disease,” says Professor Ian Frazer. “It’s also one which, up until now, vaccine strategies have not been successful for.”
That’s not to say people haven’t tried to tackle the obstinate virus. In fact, GlaxoSmithKline recently launched a series of trials with a new protein-based vaccine, although to disappointing effect.
“The recent vaccine trial run by GSK got as far as phase III clinical trials twice, and failed twice. We believe the problem with that vaccine has simply been getting the right sort of immune response to last for long enough to be useful.”
The trouble with HSV-2, says Frazer, is that it has a couple of devious tricks for evading the immune system. “There are two fundamental problems with developing an effective HSV-2 vaccine. One: the virus has a latent phase, where it can creep inside nerve cells and remain dormant for a long period of time. That has made getting an immunotherapy to work hard, because there’s nothing to fight most of the time. “Secondly, the virus doesn’t have a systemic phase, where it spreads through the body, and that’s when antibodies are best able to neutralise a virus. The simple approach to vaccine development, which is to make lots of antibody and keep your fingers crossed, worked for a lot of viruses, but it won’t work for the herpes virus.”
This resistance to traditional vaccine strategies – such as the approach Frazer and Dr Jian Zhou used against human papillomavirus – made it an attractive target for the experimental new DNA viruses which, if they work, could find a way around HSV-2’s defences.
This feature appeared in the January/February 2011 issue of Australian Life Scientist. To subscribe to the magazine, go here.
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