A NOVEL vaccine might help stem the continuing spread of genital herpes, which now infects 1 in 5 people in the US alone.
While most people infected with the sexually transmitted herpes simplex 2 virus (HSV-2) remain blissfully unaware of the fact, others suffer from periodic outbreaks of painful sores. More seriously, having genital herpes also makes you five times as likely to contract HIV.
In Kenya and Zimbabwe, for example, over half the adult population is infected with HSV-2. In Africa as a whole, genital herpes is responsible for as much as 40 per cent of HIV transmission, according to some estimates. A vaccine could have a dramatic impact on the rate of HIV spread, says Julian Hickling at vaccine research company Xenova in Cambridge, England.
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But creating a vaccine has proved tricky. As viruses go, herpes is large and complex, which makes it difficult to isolate components that will prompt an effective immune response. A vaccine consisting of part of the outer coat of HSV-2, created by GlaxoSmithKline, has had some success in clinical trials (New Scientist, 23 September 2000, p 8). But for an unknown reason it only protects women 鈥� and then only those who have not been infected with HSV-1, the virus that causes cold sores.
Another approach is to create a live but weakened virus, as has been done for the related chickenpox virus. But there are safety worries about such vaccines. Herpes virus can lie dormant in cells for decades and then re-emerge when the immune system is compromised by age or stress.
Instead, Hickling and his team have adopted a unique approach, creating a virus that can only replicate once. They did this by knocking out the gene for the coat protein gH, which the virus needs to invade cells.
The engineered viruses are produced in human cells altered to provide the missing protein (see Diagram). The viruses pick up gH in the human cells as they form and so are capable of infecting host cells when injected into people. But the next generation of viruses lacks the protein and so cannot spread further. The team say tests show that the vaccine virus does not pick the gH gene from the cells in culture.
In an initial safety study, nearly 200 volunteers were injected with the vaccine. There were no significant side effects, and it boosted HSV-2 immunity, Hickling told the Society for General Microbiology conference in Edinburgh this week. However, a larger trial will be needed to establish what level of protection it provides.
It also remains to be seen if the vaccine will provide any protection against the cold-sore virus, HSV-1, which is now responsible for most new genital herpes cases in Britain.