United Press International; Thursday June 18 9:56 PM EDT
Mara Bovsun in New York City

A mouse antibody that has been used for several years to prevent rejection in kidney transplant patients and cellular messengers known as cytokines may provide an answer, says Dr. David Ho, one of the pioneers of the combination therapies that can bring HIV levels down below detectable levels.

In an article in Friday's issue of the journal Science, Ho says that there are "latent reservoirs" of HIV, even after treatment with AIDS drug cocktails. He says HIV can hide in resting immune cells, called CD4 lymphocytes, that lie dormant in people for years. These are known as memory cells, functioning as kind of cellular recordkeeper of earlier infections.

If cells are resting, the HIV will rest also, eluding attack by drugs that are effective only against active virus.

"This latent reservoir of HIV...represents the major documented hurdle to virus eradication," says Ho of the Aaron Diamond AIDS Research Center at New York City's Rockefeller University.

Ho says scientists have proposed several strategies for eradicating these hidden viruses. One approach would be to continue to bombard the patient for more than five years with high doses of antiviral drugs.

But, Ho says, such long-term treatment is "unacceptable because of the complexity, toxicity and cost of the current drug regimens."

Another approach is blow the virus' cover by waking the sleeping immune cells. He says cytokines, chemical messengers for the immune system like interleukin and tumor necrosis factor, have been shown to activate resting cells in a test-tube, and may work the same way in the body.

OKT3, an antibody that is used in high doses to prevent organ rejection in kidney transplant patients, appears to stimulate immune cells at low doses, he says.

Ho suggests that OKT3 "should be judiciously tested not only to define its safety profile in this context, but also to determine the magnitude of T cell activation achievable without prohibitive toxicity."

Other HIV hiding places may be in organs, such as the brain, say Winston Cavert and Ashley T. Haase in the same issue of Science.

The scientists, from the Unversity of Minnesota, Minn., say it is currently impossible to accurately track down these concealed viruses, because there is no safe way to probe organs of a living patient.

The scientists suggest setting up banks of tissues from HIV-positive patients who die in car wrecks or from other trauma, to give researchers a range of tissues to investigate.

Tissues would be collected from AIDS patients who, like organ donors, will carry a card that says they are willing to donate their bodies to science.

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