Passive immunotherapy: New studies of its effects both on receipients and on donors

Passive immunotherapy: New studies of its effects both on receipients and on donors

AIDS TREATMENT UPDATE, Issue 27 - March 1995
Keith Alcorn

Passive immunotherapy is a treatment based on the theory that antibodies to HIV taken from infected but healthy individuals may prevent disease progression in other people with low CD4 counts. Blood plasma is taken from donors with high CD4 counts, heat-treated to kill HIV, and then infused into recipients with low CD4 counts. This is done on a monthly basis. Although there is controversy over the benefits of the treatment for plasma recipients (see AIDS Treatment Update issue 23), there have been suggestions that it may be good for plasma donors by filtering out harmful debris from their blood. New data to be presented at a conference in the USA in March provide further evidence that donating plasma may help to prevent CD4 cell loss in HIV-positive people with high CD4 counts.

After analysing the donors of plasma in a US trial conducted in 1993, researchers have found that donors with CD4 counts above 400 were much less likely to suffer a fall in CD4 count than would normally be expected. 6.7% of donors who were followed for at least 1 year experienced a CD4 fall below 400, while the remaining 93.3% had stable or increased CD4 counts. Comparing this group to what is known from other trials and studies about the progression of HIV infection, the researchers estimated that 21% would be expected to have a CD4 count fall below 400 in the 12 month minimum follow-up period.

However, the researchers noted that plasma donors were still at some risk of developing AIDS. Twelve out of 487 donors did develop AIDS during the study.

A similar phenomenon has been observed amongst plasma donors in London. At a symposium in October, Dr Douglas Bainbridge of the Royal London Hospital reported that donors' CD4 counts appeared to stabilise. These findings are expected to be published shortly.

PIT and viral load - don't panic!

Research findings on the effects of passive immunotherapy on plasma recipients remain confusing. At the Second National Conference on Human Retroviruses and Related Infections held in Washington at the end of January, French researchers reported that passive immunotherapy seemed to increase levels of HIV in the blood.

As reported in AIDS Treatment Update issues 15 and 23, in late 1993 the researchers reported that people who received infusions of plasma taken from people with high levels of HIV antibodies were less likely to develop opportunistic infections than those who received infusions of plasma from HIV-negative people. That report only looked at the development of symptoms. But the researchers have now found that recipients of HIV antibody-rich plasma suffered a significantly greater increase in viral load when compared with the control group, and at the end of the study period had higher levels of HIV in their blood. There was no difference between the CD4 count of treated people and the untreated control group.

Dr Abraham Karpas, the pioneer of passive immunotherapy in the UK, told AIDS Treatment Update that he believes the finding is due to the nature of the test being used, and does not represent a real surge in virus in response to the treatment. He points out that HIV will be present in the plasma donated by HIV-positive donors, and that although this is killed before it is given to recipients, the killed HIV will still show up on the PCR test. Dr Karpas told us that tests that only detect live, infectious HIV show that levels fall after a few months of passive immunotherapy treatment. "The study we conducted in 1988 showed that passive immunotherapy does reduce viral load".

Dr Clive Loveday, a virologist at University College London, confirmed that it is quite possible that the apparent rise in viral load is a consequence of the heat treatment of the virus, which disrupts the coat of the virus and releases genetic material which is picked up by the PCR test. This genetic material isn't capable of infecting other cells.

At present passive immunotherapy is available on a compassionate basis as part of an ongoing study at Ealing Hospital. Those interested in the therapy need to identify a donor who has a CD4 count above 500 and who is free of hepatitis B and C infection. Potential donors are encourgaed to contact Dr Stephen Ash on 0181-967 5551.

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