Protected by pregnancy
an enigmatic protein extracted from the urine of pregnant women can slow the progression of an aids -like disease in laboratory animals. It can also destroy cells from tumours that afflict some aids patients and boost the production of immune cells, according to Robert Gallo of the University of Maryland in Baltimore, us (New Scientist, Vol 153, No 2070).
"We're still in the early days. We don't even know what the active component is exactly," says Gallo. "But we may have the basis here for a whole new avenue of aids drugs." The search started with a chance observation by Gallo and his colleagues while they were studying Kaposi's sarcoma, a skin cancer that often claims the lives of patients with aids.Kaposi's sarcoma is particularly common in gay men with the disease, and is thought to be triggered by a herpes virus.
The researchers grew the tumour cells in mice with crippled immune systems. Soon nearly all the animals were afflicted by the disease and they died. Surprisingly, the survivors were female mice that had become pregnant soon after infection and were able to destroy the deadly cancer cells.
Gallo and his team were spurred by this observation and they examined the anti-sarcoma activity of different hormones that pregnant woman produce. Late last year, they announced that partially purified commercial preparations of one particular hormone could kill Kaposi's tumours when it was injected into the skin lesions of human patients. The hormone, called human chronic gonadotropin (hcg), allows implantation of the fertilised egg and subsequently helps to prevent miscarriage.
The researchers found that the hormone's effectiveness could not be improved by purifying it further. This was true of both hormones from commercial sources and directly from the urine of pregnant women. The partially purified hormone contains a smaller protein thought to be a breakdown product of hcg and this seemed to be attacking the tumours. Gallo says that the active molecule is a fragment of one protein chain that makes up hcg. But the exact sequence of amino acids in the protein is still unknown.
Why women produce such a potent anti-cancer agent early in pregnancy is not clear. "It must be something important to the early life of the embryo," says Gallo. One possibility is that the hormone might have a general protective effect, stimulating the immune system and attacking viruses and other microorganisms that might attack the foetus.
The protein fragment activates the production of bone marrow cells resulting in immune cells and blood cells. It can also eliminate siv, the monkey equivalent of hiv, from infected macaques if given early enough. So far Gallo's team has not identified any toxic side effects associated with the compound.
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