Different strains of the AIDS virus coexist in people and spawn hybrids more often than scientists thought, says a report with possible implications for designing AIDS vaccines.
Scientists examined genes from 114 strains of HIV-1 and found that at least 10 strains appeared to be hybrids, blending genetic material from different major subtypes of the virus.HIV-1 is divided into eight or possibly nine subtypes, plus another much different group found in West Africa. Virtually all infections in the United States come from a single subtype. The hybrids in the study were isolated in Africa and South America.
The study raises the question of whether a vaccine that works against parental strains will also protect against their hybrid offspring, researchers said.
The work is reported in Thursday's issue of the journal Nature by Paul Sharp of the University of Nottingham in England, Dr. Beatrice Hahn of the University of Alabama at Birmingham, and others.
While scientists had known that hybrids of HIV formed within the body's cells occasionally, the study suggests "it may be happening at a much bigger frequency than we thought," said Dr. Dani Bolognesi, director of the AIDS Center at the Duke University Medical School.
The study does not explain how a person gets infected with two strains of HIV or why the immune system's response to the first infection would not protect against the second infection. Maybe there is not enough time between infections to build immune defenses, the researchers said.
Bolognesi said it is not clear how long it takes for the body's defenses to reach full strength after an HIV-1 infection but that it probably takes several months.
If a person did build defenses against one strain and they failed to protect against a different strain, then a similar immune defense created by an AIDS vaccine could fail too, Bolognesi said.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said it is too soon to say what the study means for AIDS vaccines, but "the potential certainly exists that there will be some implications."
Scientists have long suspected that a vaccine directed against one strain of HIV-1 might not work against a much different strain.
The possibility of designing a "cocktail" vaccine against many diverse strains becomes even more formidable if one vaccine can't even protect against closely related strains, Bolognesi said.