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AIDS and antibodies: a too-specific fit?

AIDS and antibodies: A too-specific fit?

New findings depict "one of the worst possible scenarios" for developing an AIDS vaccine, according to a coauthor of the study. The researchers report that the AIDS-causing virus (HIV) can, by changing only one amino acid on its surface, thwart certain antibodies that prevent it from infecting cells. These "neutralizing antibodies" are often the basis of effective vaccination.

A disturbing fact about HIV is that it frequently mutates, and neutralizing antibodies against one genetic strain of HIV will not necessarily work against a second strain. Since each AIDS patient may harbor a slightly different variety of HIV, one vaccine may not suffice in halting AIDS. Also, studies show that HIV cultures isolated periodically from a single AIDS patient may reveal changes, becoming more virulent with time (SN: 4/9/88, p.232).

Now, a study reported in the July 15 SCIENCE suggests that AIDS viruses that differ by only one or two amino acids elicit drastically different responses from neutralizing antibodies. David Looney of the Walter Reed Army Institute of Research in Washington, D.C., and his colleagues tested viruses that varied in the amino acids of their protein envelope, the HIV shell. To the viruses they added a variety of blood-serum samples that previous tests had indicated contained HIV antibodies. They then recorded each samplehs geometric mean titer (GMT), a measure of its ability to neutralize a virus. They discovered that the various viruses, though almost identical, varied considerably in the degree to which the sera could neutralize them. A single amino acid change in the protein coat of a virus with a GMT of 2,000 for a particular serum sample could make the GMT drop to almost zero with the same serum.

Despite the findings' dismal implications for this approach to vaccine research, says one of the scientists, "they provide some hope by explaining why trials of neutralizing antibodies have not succeeded." According to the investigator, the study should warn AIDS researchers that their carefully cloned stock of virus may contain a mixture of HIV variants and that it only takes one amino acid change to abolish a virus' ability to be neutralized by a particular set of antibodies.
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Author:Hendricks, Melissa
Publication:Science News
Date:Jul 16, 1988
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