Scientists at Genentech Inc. and collaborators have preventedtwo chimpanzees from developing HIV infection by immunizingthem with CD4 linked to a human antibody fragment.

The two treated chimps, challenged with the IIIB strain of theHIV-1 virus, stayed uninfected for at least 47 weeks afterchallenge. A control chimp that was not pretreated with theCD4-linked molecule, called an immunoadhesin, developed HIVinfection by three weeks after being challenged with the virus,the researchers reported today in Nature.

Chimpanzees do not develop immune deficiency or depletion ofT cells, but do show viral infection in their blood afterchallenge with HIV IIIB.

Analogs of CD4 compete with the AIDS virus at the site forbinding and entry of the virus into T immune cells. The CD4analog linked to a portion of human immunoglobulin has alonger life in the body than does CD4 alone, which results in a25-fold increase of the molecule in the blood.

The Genentech researchers and their colleagues at CellGenesys Inc. in Foster City, Calif.; Southwest Foundation forBiomedical Research in San Antonio, Texas; and the New YorkBlood Center said that CD4 immunoadhesin was given for nineweeks. But the optimal dose and length of treatment with CD4is yet to be determined, they wrote.

The scientists point out that the challenge to the chimps wasgiven as cell-free virus and that cell-associated virus may bemore difficult to stop. The clinical effectiveness of the CD4immunoadhesin is yet to be determined, and some HIV strainsare less sensitive to the preventive action of CD4 analogs thanis IIIB. But the researchers said they hope that their approachcan prevent the transfer of virus from mother to fetus, as CD4immunoadhesin is transferred across the placenta in rhesusmonkeys.

Other data reported this week in Nature suggests that passiveimmunity therapy could also work against AIDS.

A single high dose of purified hyperimmune gamma globulinobtained from AIDS patients can protect chimps from theinfection, according to unpublished results from the lab of oneof the Genentech collaborators, Alfred Prince of The New YorkBlood Center.

In another report, researchers at the Swedish NationalBacteriological Laboratory and the Karolinska Institute inStockholm showed that sera from infected monkeys protectedfive out of seven other monkeys from developing simian AIDS.080191CD4

-- Roberta Friedman, Ph.D. Special to BioWorld

(c) 1997 American Health Consultants. All rights reserved.