Immune system cells called CD8 lymphocytes stop HIVreplication by blocking production of viral RNA, according to areport delivered Thursday at the Seventh InternationalConference on AIDS in Florence, Italy. Discovery that themechanism works through RNA offers promise for maintainingthe blocking process in the body, where it eventually breaksdown.

A University of California, San Francisco, team found that CD8lymphocytes added to HIV-infected CD4 cells in laboratorycultures eliminated more than 90 percent of detectable virus.Although CD8 inhibits HIV in cultures, the defense fails in thebody and gives way to full-blown AIDS.

The breakdown of the CD8 defense system may have somethingto do with the disruption of the normal chain of command inthe immune system, according to Carl Mackewicz, a visitingpostdoctoral fellow at UCSF, who presented the team'sfindings. CD4 lymphocytes, the immune system cells attackedby HIV, normally direct the immune system. But when they'reattacked by HIV, other parts of the immune system may not getthe orders they need to function.

"Now that we know the cells act at the RNA level, we can lookat exactly how that works," Mackewicz said. "We mightunderstand how to keep the CD8 cells active against HIV."

The UCSF team, led by Dr. Jay Levy, first reported an anti-HIVfactor produced by CD8 cells in 1989. Earlier this week, Levypresented data showing that the CD8 cell product responsiblefor the suppression of HIV is a novel factor.

Levy said a number of drug companies have expressed interestin his lab's work on CD8. What's necessary, he said, is anapproach that will identify and clone only those CD8 cells thatare producing CD8 factor. Previous approaches to growing CD8cells and returning them to AIDS patients have used the entirepopulation of CD8 cells, which can shut off antibodyproduction.

Levy was not optimistic on the prospects for an AIDS vaccine."All the ways being tried would hit the free virus entering thebody," he said. "Last year's conference was very optimistic, butwe're far from a vaccine. We have to deal with virus-infectedcells passing this infection (from one person to another), notfree virus. This means you need local (mucosal) immunity inthe vaginal and anal canals."062191CD8

-- Karen Bernstein BioWorld Staff

(c) 1997 American Health Consultants. All rights reserved.