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 AIDS vaccine A hypothetical vaccine intended to either prevent HIV infection or ensure that those infected will not fall victim to AIDS; the most promising vaccine is that using a naked DNA plasmid, reported by Letwin et al in 20/10/00 Science; as of early 2001, , according to a coauthor of the study. The researchers report that the AIDS-causing virus (HIV HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States. ) can, by changing only one amino acid amino acid (əmē`nō), any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins. 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 Mutates Undergoes a spontaneous change in the make-up of genes or chromosomes. Mentioned in: Antiretroviral Drugs , 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 This article is about the U.S. Army medical research institute (not the hospital). Otherwise, see Walter Reed (disambiguation). The Walter Reed Army Institute of Research (WRAIR) is the largest biomedical research facility administered by the U.S. 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 (mathematics) geometric mean - The Nth root of the product of N numbers. If each number in a list of numbers was replaced with their geometric mean, then multiplying them all together would still give the same result. titer (GMT (Greenwich Mean Time) See UTC. GMT - Universal Time 1 ), 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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