A.I.D.S. virus variants may provide immunity

Press, 30 July 1986, Page 51

A.I.D.S. virus variants may provide immunity

By

WARREN LEARY,

Associated Press Washington, Infection with one strain of the A.LD.S. virus appears to protect against infection with other types, researchers say, adding that some unknown protective mechanism might help develop protective vaccines. New research into the virus causing acquired immune deficiency syndrome indicates that the viral variants in some patients are closely related mutations of the original strain, they say. Infected, promiscuous, homosexual men — who may have had hundreds of exposures to versions of the A.LD.S. virus from various sex partners — appear to carry only one strain of the virus or several closely related variants of that strain, scientists say. “The finding may imply that once infected with one A.LD.S. virus, individuals are protected from infection by other A.I.D.S. viruses,” says a report published in the journal, "Science.” Beatrice Hahn, George Shaw and Maria Taylor, of the University of Alabama Medical Centre in Birmingham, working with researchers from

three other institutions, said it was unlikely that this possible protection resulted from classical viral immunity mechanisms.

Usually a cell infected with one virus loses its receptor, or gateway, for that or related viruses to enter.

However, many people chronically infected with the A.LD.S. virus, known as HTLV-3 or LAV, still have normal numbers of the uninfected white blood cells that the virus targets. These seemingly would be candidates for invasion by another strain of the virus.

“We really can’t explain why a person seems to be infected by only one genotype of the virus,” Dr Shaw said in a telephone Interview.

“It may be some kind of immune repsonse that occuis after the inital infection, or perhaps even a nonimmunologic factor. “In any case, if we could find out what it is, activating such a factor before any infection could be a way of preventing A.1.D.5.,” he said. Dr Shaw said there may be relationship between this preventive factor and a variant of the A.I.D.S. virus recently discovered

in people in West Africa. Dr Myron Essex and others at the Harvard School of Public Health announced in March that they discovered a form of the virus, which they dubbed HTLV-4, that does not produce disease.

“There has been some speculation, and that’s all it is at this point, that perhaps HTLV-4 protects against infections by the disease virus,” Dr Shaw said.

In the newly reported research, the Alabama scientists and colleagues from Walter Reed Army Medical Centre, the National Cancer Institutes and the University of Miami Medical School found that the A.I.D.S. virus inside each patient mutates very rapidly. Samples of the virus taken from the blood of the same patients over periods of up to two years show that each variant goes through subtle genetic changes as it reproduces within infected cells, the scientists report.

The variants do not evolve directly, they found, with one version springing from the last and moving to another. Instead, they say, isolates of the virus appear to evolve in parallel and a

single patient can be simultaneously infected with several versions of the original strain. “By looking at the genetic change of the virus in a single person, we can for the first time measure the rate of change within infected people,” Dr Shaw said, “and that rate is very fast.”

The researchers said the genetic change of HTLV-3 may be tenfold greater than for other similar viruses, known as RNA viruses, and equally faster than influenza A virus.

Constant change in the unrelated influenza virus, for example, is the reason new flu vaccines must be developed so often to stem epidemics.

This rapid, continuous change makes it hard to find a part of the virus that is stable enough to serve as a target for vaccines or treatment drugs, scientists say.

However, Dr Shaw said, the research shows that there are some stable, conserved regions that appear to be shared by most variants of the virus which could be candidate targets for prevention and treatment.