Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.
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Newsday - July 2, 1998
Laurie Garrett - Staff Correspondent
The protections do not appear to be genetic, and may offer some critical clues to those hoping to make a vaccine against HIV.
At Mount Sinai Hospital in Toronto, Dr. Kelly MacDonald and a team of pediatricians noticed something odd earlier this year: HIV-positive mothers did not pass the virus to babies who were born with immunologically incompatible blood. In cases of incompatibility, the mother has one genetic type of immune system markers, and the baby a different set. This can put the baby at risk of being attacked by the mother's immune system.
But, in the case of HIV-infected mothers, this immunological incompatibility saved the babies from HIV, MacDonald reported yesterday. The finding was based on a study of 111 mother / child pairs.
MacDonald believes that a key factor in the babies' genetic makeup - called A2/A6802 supertype - by fortunate coincidence prevents HIV from infecting the child. When the mother and child share the same genetic makeup in their immune system, MacDonald discovered, the child is 2.63 times more likely to get infected with HIV.
"Since approximately 40 percent of the population worldwide has the A2/A6802 supertype, it makes it an attractive target for vaccine design," MacDonald said.
The U. S. Centers for Disease Control and Prevention studied 280 prostitutes in Thailand who had worked in brothels for three years or more, and a group of non-prostitute Thai women. Not surprisingly, the prostitutes were far more likely to be infected with the virus, and 47 percent were HIV-positive, the CDC reported yesterday.
Remarkably, however, nine of the prostitutes were negative for HIV, even though they had genital herpes and syphilis - clear indications of unsafe sexual behavior. The women did not have any of the genetic mutations that have been shown to protect some Caucasians from HIV. But they did apparently have complete immunity. Cells of their immune systems were killing every HIV to which they were exposed, the CDC team discovered. And laboratory studies revealed that their CD8 T-cells, a type of white blood cell, were secreting a factor which, when mixed in a petri dish with human cells and HIV, stimulated immune cells to destroy the virus.
Dr. Jay Levy of the University of California in San Francisco has presented evidence of a CD8-produced factor that stops HIV, as well. For years he has tried to isolate the mysterious substance, to no avail. But it could result, he said in a speech, "in a way to maintain control of the virus without the need for antiviral" drugs.
Sharon Stranford, a researcher in Levy's laboratory, examined the immune system cells of gay San Francisco men who have been exposed repeatedly to HIV and never become infected. She said that the CD8 cells in these men make a mysterious factor that protects against HIV. But it is not the same as the one discovered in Thai prostitutes, Stranford said, because it blocks HIV without prompting immune system cells to kill the virus. It works by blocking the ability of HIV to make copies of itself, Levy said.
Finally, a CDC team working in Abijan, Ivory Coast, has also found a group of uninfected prostitutes. They, too, lack any genetic protection. And their ability to fight off HIV is also immunological. The team hasn't yet worked out the details, researchers said, but it is clear that immune system cells in the African prostitutes are highly activated, as if constantly ready to go to war.
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