A DEVICE that filters HIV from blood has been developed by a company in California.

It says the device could be used in conjunction with antiretroviral drugs, which slow the progress of AIDS by lowering levels of the virus. Unlike drugs, though, it should have no side effects, nor should the virus be able to develop resistance.

The device, called the HIV-Hemopurifier, comes in a cartridge that fits into kidney dialysis machines. It contains hollow fibres with pores just large enough for the virus to pass through. Inside the fibres there are beads coated with antibodies that bind to Gp120, a protein found on the surface of HIV, as well as antisense DNA that binds to viral RNA.

As with normal dialysis, the idea is to pass blood through the cartridge and back into the patient. Viruses that enter the fibres should stick to the beads. The manufacturer, Aethlon Medical of La Jolla, says that in preclinical trials the device removed 90 per cent of HIV from contaminated blood plasma.

The idea for the device came from Julian Ambrus of the State University of New York at Buffalo. Different versions of the device could be used to filter out other viruses, such as the hepatitis C virus, or even heavy metals, he says.

It's a clever approach, says Stuart Shapiro of the AIDS division at the US National Institutes of Health. But he points out that the company has yet to prove that it will work on a real person.

Patricia D'Souza, also of the NIH, is more doubtful. "There is a major issue with this device in that the Gp120 proteins, which are like stalks, are very fragile and easily broken off." The resulting "bald" virus particles could easily pass through the filter without being captured, she says. While the role of Gp120 protein is to help HIV enter cells, the bald virus might still be able to do this, she says. "This is a worry."

Another problem is that dialysis is time-consuming and the equipment expensive. Blood dialysis treatments for kidney patients take around four hours, for example.

Marina Murphy