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Receptor decoy shows promise against AIDS.

Receptor decoy shows promise against AIDS

The first two clinical trials of a novel AIDS drug suggest the experimental treatment is safe, researchers report, and one study provides subtle evidence that the treatment may help slow progression of the disease.

Scientists emphasize that both studies -- the first to investigate the value of a genetically engineered compound called soluble CD4 -- are preliminary and that detailed efficacy trials remain far from complete. But they express enthusiasm that the drug caused no significant toxicity even at the highest doses given. If the still-experimental treatment helps slow viral replication in AIDS patients, as hinted by one of the studies, then it may prove especially useful in conjunction with AZT or other antiviral drugs currently under investigation, reseachers say.

"There are some real scientific hurdles before we can say this treatment works," warns Robert T. Schooley, an infectious-disease specialist at Massachusetts General Hospital in Boston, who led one of the studies. "This is a progress report along a long road that may go nowhere."

However, with promising results starting to emerge in the patients who received the largest doses, Schooley says his team plans to test even higher doses. "There's no particular reason to stop when you don't see toxicity," he told SCIENCE NEWS.

Schooley and 21 colleagues tracked the effects of soluble CD4 injected into 25 patients with AIDS or advanced AIDS-related complex (ARC). The drug mimics the lymphocyte receptor CD4, through which the AIDS virus (HIV) infects these white blood cells. On the basis of previous work in vitro, researchers had hypothesized that by flooding the body with excess quantities of free-floating CD4 receptors, they might "mop up" circulating HIV before the viruses had a chance to invade white blood cells.

In the Schooley study, patients gave themselves, intramuscular injections of the soluble CD4--much as diabetics self-administer insulin--three times a day for up to 28 days. The most serious side effect was a rash that disappeared when the patient who developed it stopped taking the drug. On average, patients receiving the highest dose of soluble CD4 experienced a 23 percent drop in blood levels of HIV p24 antigen -- an indication of modestly reduced HIV activity.

In the other study, James O. Kahn of San Francisco General Hospital and his colleagues provided soluble CD4 to 42 AIDS and ARC patients by intravenous, intramuscular or subcutaneous injection for 11 weeks. Using doses about one-third those of Schooley's group, the researchers noted no serious side effects, but they also saw no immediate benefits.

The two studies, described in the Feb. 15 ANNALS OF INTERNAL MEDICINE, allay some of the fears previously expressed by researchers, who until now could only guess about soluble CD4's safety. For instance, scientists had wondered whether the protein might trigger an immune response that could destroy useful white blood cells bearing CD4 receptors. So far, that does not appear to be a problem. The studies also provide valuable data on the schedules and dosages required to maintain significant quantities of the drug in the bloodstream.

But other questions remain, such as whether soluble CD4 blocks HIV infection of other white cells such as macrophages and monocytes, which can also serve as HIV reservoirs. Scientists also wonder whether CD4 may prove even more valuable as a "carrier molecule" to deliver toxins to HIV or infected cells.

Ultimately, cost may emerge as a serious problem. A British company, SmithKline Beecham PLC, announced this week it had abandoned its efforts to make a commercial CD4-based AIDS drug, citing high costs and production hurdles. Only two other companies make soluble CD4 -- Genentech Inc. of South San Francisco and Biogen Inc. of Cambridge, Mass.

"It's going to be expensive," Schooley warns. Although Biogen has developed a new process that cuts production costs to one-tenth, he says, the drug will probably remain more expensive than AZT, the only AIDS drug to gain FDA approval.

Despite such concerns, the new results suggest "cautious optimism is warranted," write virologists Edmund C. Tramont and Robert R. Redfield of the Walter Reed Army Medical Center in Washington, D.C., in an editorial accompanying the research report.
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Author:Weiss, R.
Publication:Science News
Date:Feb 17, 1990
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