First Things First

Although considerable research is being conducted into developing techniques to shrink or eliminate viral reservoirs in the body, some researchers actually have had to take a step back and first devise effective ways to examine infected memory CD4 cells in their labs. Latency is very hard to study, says Eric Verdin, MD, an investigator at the University of California, San Francisco's Gladstone Institute of Virology and Immunology. 'In HIV-positive people it's really easy to detect latency, but you can't do it in vitro,' he explains. 'In the lab you never see latency. It appears as though all cells become productively infected.' But his team reported in May that a special process it developed shows that a very small number of HIV-infected cells produced in the lab do harbor latent virus and can be easily identified. They engineered a strain of HIV to contain a small piece of fluorescent protein that glows green when present in an active cell with actively replicating virus. The less than 1% of the cells that were infected with HIV but did not glow green were determined to be resting memory cells in which the virus lay dormant. 'It's the first time we've been able to demonstrate that latency occurs in vitro,' Verdin says, adding that being able to produce and isolate the cells in the lab will speed research into how memory T cells work and the processes that activate and deactivate them. Jerome Zack, MD, associate director of basic sciences at the University of California, Los Angeles, AIDS Institute, and his colleagues have focused on a way to generate significant quantities of latently infected cells in the lab, which he says was difficult to achieve using CD4 cells culled from the blood of HIV-positive people. 'You can't get them to activate then shut down,' he explains. Instead, his team used tissue from the thymus, which generates CD4 cells, to produce latently infected cells in genetically engineered mice. About 10% of the CD4 cells produced by the mice are latently infected'a 100,000-fold increase over the number of latently infected cells experts believe exist in the bodies of HIV-positive people.