The radical therapy is a British idea, initially developed by a Cambridge scientist, but funding for it has been repeatedly rejected by the UK's Medical Research Council.
Results of two clinical trials, to be presented tomorrow at a conference in London, show that the onset of Aids in HIV- positive people can be significantly delayed if they receive blood plasma taken from other, healthy HIV-positive patients. Death rates in those with full- blown Aids can also be reduced, one of the trials indicates.
Researchers involved in the work are cautious, saying the transfusion therapy is far from a proven cure. Nevertheless, they say, it is the closest scientists have yet come to an effective, non-toxic treatment for Aids.
The treatment, passive-immune therapy, was conceived by Abraham Karpas, assistant director of research at the department of haematology at Cambridge University. Three times since 1986, Dr Karpas, the first scientist to isolate HIV in the UK, has applied for funding from the MRC to conduct clinical trials in Britain; each time he was turned down.
However, clinical trials of the treatment have now been carried out in France and the United States. The American team, led by Joshua Levy of the HemaCare Corporation in California, found it produced a fivefold reduction in death rates of Aids patients. The research is to be published in Blood, journal of the American Society of Haematology.
The French research, led by Jean-Jacques Lefrere at the National Blood Transfusion Institute in Paris, found the incidence of disease was threefold higher in a control group receiving placebo transfusions than in those receiving passive- immune therapy.
Both donors and recipients benefit from the treatment, according to Dr Karpas. The theory behind it is that healthy HIV-positive people possess effective antibodies against the virus, whereas people in the early stages of Aids do not. Plasma transfusions, which are chemically treated to kill HIV, contain these 'neutralising' antibodies and benefit Aids patients by helping to rid the blood of HIV.
There is significant evidence, Dr Karpas believes, to suggest that people who donate plasma also benefit because their immune systems are stimulated to make more CD4 white blood cells, the sort attacked by HIV.
Dr Karpas was the first person to attempt the treatment, in 1985. The next year he applied for MRC funds to extend his limited experiments to a proper clinical trial but was told that the work 'lacked originality' and 'in general provided inadequate rationale, background and information'.
Undaunted, he continued the research with a further 10 patients, helped by doctors at a London hospital. The trial was 'uncontrolled', meaning none of the patients took a placebo, and so only limited information could be inferred from the data.
Nevertheless, he found that levels of HIV circulating in the blood of the patients went down dramatically. In fact their blood remained free of HIV for as long as the plasma transfusions were continued. Dr Karpas said: 'Although passive immunisation does not eliminate the virus from the body, it probably reduces the rate of infection of new cells by the virus.'
The HemaCare Corporation and the French National Blood Transfusion Institute became interested in the research. They decided to conduct full 'phase two' clinical trials. These involve doctors treating some patients with placebo transfusions to see if there is a genuine difference between those who receive plasma from HIV-positive donors and those who do not. Neither patient nor doctor is aware of who has real therapy and who has placebo until the experimental 'code' is broken.
HemaCare used 220 volunteers but many proved unsuitable, mostly because they were too ill with Aids. The rest were split into three groups: one received the full dose of plasma, the second a half dose and the third took the placebo.
After 12 months one person had died in the group of 21 subjects on the full dose. Three had died in the 21 who took the half dose, and six had died in the group of 30 taking the placebo.
Unfortunately for the researchers, the results, indicating a fivefold reduction in death rates, reached only 'near statistical significance' because the numbers involved fell short of being able to confirm a scientifically significant result.
Nevertheless, the US Food and Drug Administration has given the company approval to extend the research to a 'phase three' clinical trial, involving potentially hundreds of volunteers. HemaCare has also abandoned the use of placebos because it was deemed unethical not to treat volunteers.
The French study, which also did not follow enough people for a long enough period to provide statistical significance in terms of death rates, did however find a significant difference in terms of onset of disease. Aids illnesses were three times higher in those taking a placebo, the researchers will report tomorrow at a conference at the Royal College of Physicians in London.
At the conference, Gary Blick, a New York doctor who has been treating about 60 of his patients with passive-immune therapy for roughly four years, will present further research supporting its role.
Some Aids scientists believe that even if it can be shown that passive-immune therapy works, it will prove far too expensive and cumbersome. 'It's a very elaborate process and terribly expensive,' Alan Stone, head of the Aids secretariat at the Medical Research Council, said.
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