Newsday - August 27, 1993
Laurie Garrett - Staff Writer

AIDS-infected people are known to have a mix of human immunodeficiency viruses in their bodies. In a study of seven New Yorkers, the researchers found that only one class of the viruses could pass to another person by sexual contact. Once inside the recipient's body, however, most of these viruses mutated into a non-infectious, but more deadly form of HIV that actually caused illness.

All potential AIDS vaccines currently under development are designed to stop the later stage viruses - not the infectious types, according to Dr. David Ho, who discovered this pattern of viral mutation in research done at the Aaron Diamond AIDS Research Laboratory in Manhattan.

That might be good for therapeutic vaccines, intended for use by thosealready infected. But it's bad news if the goal of vaccination is to prevent infection in the first place, Ho said.

"It's a particularly sensitive issue," Ho said. "We better wake up to this and cover that gap fast. There is a glaring defect there that we better do something about right away."

Ho said the finding, reported in the journal Science, has strong implications for treatment as well. Nearly all test tube experiments with potential AIDS drugs have been performed on the later stage viruses because they are the only ones that grow rapidly and multiply in the laboratory. Drugs have been tested to see how well they slow that growth.

But treatment of people in the early stages of infection should be designed to target the slower-growing transmissible forms of the virus, Ho said.

"We went through this in the laboratory with CD4," Ho said, referring to a therapy that looked promising in test tube studies but failed when tried three years ago on people in early stages of HIV disease, when the virus might be easier to control. "It failed in patients because all of the laboratory work was done on [late stage] HIV variants."

Ho's finding is in line with a host of studies from the Netherlands, France and the United States. But the new research is the first to link only the milder class to transmission.

Ho and his colleagues studied human immunodeficiency viruses found in the bodies of three New York City gay men, two women and their two male sexual partners..

The researchers found only one class of HIV viruses - those that were weakest in terms of damaging the body - were passed sexually from one person to another. In some cases, the transmissible form represented less than 5 percent of all HIV types found in the swarm that infected the original individual who passed the virus on.

Ho suspects that the reason some forms of HIV are infectious is that they have the genetic ability to get inside the recipient's macrophages - large white blood cells that inhabit mucousal areas, such as the vaginal lining. Later forms of the virus can't infect macrophages, he said, but have widespread deadly effects on the rest of the immune system.
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