From these individuals, Dr Paxton and his colleagues have taken the white blood cells, known as CD4 cells, which are the particular target of HIV, cultured the cells in the laboratory, and tried unsuccessfully to infect them with HIV. In the case ofMr C rohn's cells, the researchers could only get the infection to "take" by flooding the cultured cells with huge amounts of virus, far more than would be present in the course of a naturally occurring form of infection. There have been indications that some people might be resistant to HIV infection, because of the chance shuffling of the genes they inherited from their parents. But this evidence is only statistical. The new research has identified specific individuals and their biochemistry to work out the precise mechanism of resistance. Dr Paxton said yesterday, "If we can determine what is protecting these people then you ca n envisage therapy or vaccine design." Dr Paxton and his colleagues have already identified one set of biochemical compounds, known as chemokines, which appear to be acting in these people to defeat HIV. These substances were first recognised only five years ago and appear to play a role in the immune system. They report their findings in the April issue of the scientific journal Nature Medicine. Conventional vaccines consist of antibodies to the infecting agent produced by the immune system. But, partly because HIV subverts the cells of the immune system itself and partly because it is highly variable, no one has succeeded in producing a vaccine against it. The chemokines Dr Paxton and his colleagues have found are not antibodies. They are involved in the "inflammatory" response, when a wound or site of infection becomes inflamed. "I do not believe that next week everybody will be injecting chemokines and curing Aids, but definitely we're on a line," Dr Paxton said. He stressed that any vaccine or treatment was still a long way off: "I'm really worried about how people will take this news - people should not give up a safe sex policy." For Mr Crohn, the thought that his blood might hold a vital secret in the battle against Aids "would be very touching to me." His partner, Jerry Greenwood, died in 1982, before the disease even had a name.
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Scientists have found a man who cannot catch the virus that causes Aids - and his blood may hold the key to developing the first vaccine. In his blood, the New Yorker, Steve Crohn, has the first known substance in the world that will defeat the HIV virus. Scientists already knew of many individuals who remain healthy for a very long time between infection with HIV and developing full blown Aids. The difference in the case of Mr Crohn and the others now identified is that they appear to be resistant to inf ection with HIV in the first place. Mr Crohn, 49, a freelance editor for Fodor's Travel Guides, and another New Yorker who also appears to be immune, were discovered by a young Glaswegian scientist, Dr Bill Paxton, of the Aaron Diamond Aids Research Center in New York. Dr Paxton and his co lleagues have found a further 23 people who, although not completely immune, show some degree of resistance to HIV infection. Many have remained free of HIV despite a history of unsafe sex with multiple sexual partners who subsequently died of Aids.