The AIDS virus: equine similarities?

The AIDS virus: Equine similarities?

The virus associated with AIDS is in the same family as a virus that causes an infectious, sometimes fatal disease in horses, according to research from the federally supported Frederick (Md.) Cancer Research Facility. Determining the family to which the AIDS virus belongs is a question of more than academic interest: An understanding of the virus's closest relatives could suggest a way to deal with the virus itself.

Robert Gallo of the National Cancer Institute (NCI) in Bethesda, Md., has categorized the AIDS virus -- which his group calls HTLV-III--within a family of leukemia-causing viruses. Other scientists, however, have maintained that the virus's structure and behavior in the body put it in a group of slow-acting, untreatable viruses called lentiviruses, a family that includes the equine infectious anemia virus (EIAV).

The Frederick group used a computer program to compare HTLV-III proteins with proteins from EIAV; from visna virus, a lentivirus that attacks sheep; and from two leukemia viruses, bovine leukemia virus (BLV) and HTLV-I. The computer analysis showed that EIAV had the most amino acid sequences in common with the AIDS virus. Visna virus ran second, with HTLV-I and BLV a distant third. The details of the analysis, made by Robert M. Stephens, James W. Casey and Nancy R. Rice, appear in the Feb. 7 SCIENCE.

This finding follows a discovery by Luc Montagnier and his colleagues at the Institut Pasteur in Paris that blood from people with the AIDS virus contains antibodies that react with one of the proteins manufactured by EIAV. Matthew A. Gonda, also of the Frederick laboratory, then showed that the AIDS virus was more similar to visna than to HTLV-I and -II (SN: 1/12/85, p. 22).

The similarity means the sheep and horse infections can be studied for their relevance to human AIDS, but it may be bad news for development of a vaccine, says Opendra Narayan of Johns Hopkins University in Baltimore. Narayan worked with Gonda, Gallo and others to show the visna virus similarity. "These viruses [lentiviruses] undergo a lot of mutation," he says. The constant changes may prove too much of a moving target for a vaccine.

More hopeful in terms of a vaccine, NCI researchers reported last week on a protein capable of stimulating AIDS-antibody production. According to a paper given by Flossie Wong-Staal at the Annual Congress for Recombinant DNA Research in Baltimore, regions of the gene that codes for the foreign were identical in four different AIDS virus isolates, suggesting the protein might provide a basis for a vaccine.

While the Frederick work firms up the virus's position in the lentivirus family, it won't help in naming the virus, which is variously called HTLV-III, LAV (for lymphadenopathy-AIDS virus) or ARV (for AIDS-related virus). According to Harold Varmus of the University of California at San Francisco, who is heading a nomenclature group sponsored by the International Committee on the Taxonomy of Viruses, the name will not depend on the virus's exact classification. The problem of what to call it "should be coming to a resolution in a few weeks," says Varmus.