http://news.bbc.co.uk/hi/english/health/newsid_1842000/1842855.stm

 

Tuesday, 26 February, 2002, 18:09 GMT

HIV vaccines show promise

No preventative vaccine currently exists for HIV

Human trials of two potential HIV vaccines have produced promising results.

Merck, the company which is developing the new vaccines, said the indications were that they can help control the virus that causes Aids by stimulating the body's immune system to attack it.

It is still too early to tell whether they will also prevent HIV infection.

However, the Merck team is hopeful that the vaccines will eventually be used to improve the effectiveness of existing treatments.

Keeping levels of the virus low might also reduce the risk of HIV positive people infecting others.

In the latest trials, volunteers who were not infected with HIV were given vaccines containing a gene that controls production of a protein called gag that is found inside HIV.

On its own the protein poses no threat to human health.

Two types

The volunteers were given one of two vaccines. The first comprised only the gag gene, while the second was made up of the gag gene crammed inside the outer coating of a common cold virus.

The second vaccine is the one which has produced the best results in tests on monkeys.

The same results were found in the human trials - the second vaccine stimulated an immune response in a far greater proportion of the volunteers who received it.

Even six out of nine of the volunteers who received the lowest dose of the vaccine recorded a positive immune response.

Dr John Shiver, Merck's senior director of vaccine research, said the apparent success of the second vaccine might be due to Americans having natural antibodies against the common cold virus shell used to house the gag gene.

Preventing infection

In tests on monkeys, neither type of vaccine was able to prevent infection with an HIV-like virus.

But combined use of the vaccines stimulated dramatic immune responses in monkeys who were later infected with the virus - enabling long-term suppression of the virus and Aids-like symptoms.

The human volunteers given the gene-only version of the vaccine will now also been given the second form to see to see if their immune responses can also be further stimulated.

Dr Shiver said controlling the virus in people already infected with HIV might not only moderate or prevent Aid symptoms, but could slash bloodstream HIV levels so greatly that patients will be unlikely to infect others.

It is estimated that 40m people world-wide have been infected with HIV.

The results were unveiled at a conference on retroviruses and opportunistic infections being held in Seattle.

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