Global race to curb Aids

Scientists are working on a vaccine for Aids

Aids is among six infectious diseases which kill 50% of the world's children and young adults, according to the World Health Organisation.

Even in the developed world, where it has become almost a treatable condition due to expensive drug combinations, the cost of the disease has been immense.

The race to find a vaccine against HIV and a cure for Aids has mobilised scientists across the world.

So far the most promising efforts have concentrated on treatments which block the virus' ability to break down the immune system and on a vaccine which would protect against Aids.

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BBC News Online has been following the struggle of science to get to grips with HIV.

November 1998: Two major international initiatives are launched with $9m funding from the International Aids Vaccine Initiative.

The aim is to develop vaccines which can be used in the worst affected areas.

One is a joint venture between UK and Kenyan scientists.

They are looking at an immune-boosting vaccine which combines a small part of the gene for HIV and a modified form of a vaccine used to combat smallpox.

The vaccine may not be widely available for seven years.

The other is a US/South African joint venture which will attempt to develop a virus which can boost the body's immune system.

December 1998: Trials looking at the efficacy of an American Aids vaccine are launched in the US.

This uses proteins from the surface of two different strains of HIV rather than live virus so scientists claim there is no danger of it causing people to become HIV positive.

By July 2000, more than 5,000 US men, and thousands in Thailand have been recruited to take part in the trial.

January 1999:Scientists at Washington University School of Medicine say a new gene treatment for HIV, called TAT-Casp3, has successfully entered infected cells and killed them.

The treatment induces cell suicide and specifically targets infected cells.

Because it uses up to 10 molecular features of HIV, scientists say it is unlikely to produce resistance.

However, the treatment has yet to be tested on humans, and it could be some time before this happens.

Another research project at the university found that injecting killer T cells into HIV positive patients could destroy HIV-infected cells and boost the immune system.

But experts said it had little chance of working clinically because killer T cells are difficult to make and the process requires daily injections.

January 1999: US researchers reveal details of the first experimental Aids vaccine to produce antibodies that attack and kill the kinds of HIV found in humans.

Researchers at the Howard Hughes Medical Institute in New York and the University of Montana managed to freeze HIV in the act of breaking into a mouse cell.

By doing so, they could collect antibodies produced by the mouse to fight the virus.

These were effective against 24 out of 25 HIV strains taken from human patients around the world.

The scientists now plan to extend their work from mice to monkeys and humans - safety trials must precede full clinical efficacy tests, so even if it works, it could be at least a few years before it is available.

February 1999: A setback: scientists at Harvard Medical School in the USA announce that vaccines based on weakened forms of HIV have been shown to cause Aids in monkeys.

The vaccines, which had been seen as the best hope by many, use "crippled" HIV which has had a few key genes removed.

In theory these viruses should not be able to replicate, spread or cause illness.

But a delicate balance needs to be found: if they delete too many genes, it will not "look" enough like the real HIV virus to trigger the immune system if a genuine infection occurs.

If they delete too few, they could cause disease. Because HIV mutates so quickly, the scientists say it eventually manages to compensate for the deleted genes.

February 1999: The first trial of an Aids vaccine in Africa begins in Uganda.

The phase I trial on 40 non-HIV positive adults aims to show whether the vaccine is safe.

It uses a genetically engineered vaccine made by the Rhone-Poulenc Group.

The vaccine is based on the canarypox virus and contains three HIV genes.

The idea is that the immune system will recognise and attack the virus' relevant markers.

March 1999: Scientists publish their findings on a protein found in tears, saliva and the urine of pregnant women which, they say, could be used to create a new class of anti-Aids drugs.

Researchers from New York University School of Medicine and the US National Institutes of Health say the enzyme lysozyme, working in combination with other proteins, appears to break down HIV in pregnant women's urine.

The next step is to develop treatments using the enzyme.

April 1999: Scientists at the Yerkes Regional Primate Research Center in Georgia, USA, announce that a "safe" HIV vaccine has been successfully tested on monkeys.

The vaccine uses harmless parts of HIV and protected monkeys from extremely virulent strains of the virus for at least 62 weeks.

It uses a DNA vaccine which promotes the creation of HIV proteins and provokes an immune response.

The latter uses the same DNA, but packs it inside a smallpox virus which has been shown to be safe.

The virus is very successful at invading cells, producing very high levels of HIV proteins inside the cell.

2000

The joint UK/Kenyan vaccine begins safety testing in the UK - one of the volunteers to be given the jab is MP Dr Evan Harris.

The vaccine was originally developed after scientists in Kenya noticed that some prostitutes appeared to be immune to HIV infection, despite frequently coming into contact with the virus.

While this theory took a blow when some of the prostitutes later contracted the infection, trials continue in the UK and Kenya.

Elsewhere, some trials are well underway, while other prospective vaccines are being tested on animals.

One, developed by the Thomas Jefferson University in Philadelphia, uses a weakened version of the feared rabies virus to carry HIV proteins into the body and trigger an immune system response.

It is hoped that this response will then mean actual HIV is also attacked.