Until a few years ago HIV seemed invincible. Once it infects a person’s cells it replicates wildly, quickly generating billions of genetically varied offspring. A single drug such as AZT may paralyze most of those variants, but a few inevitably prove resistant. As the survivors multiply, the drug loses its effect. This grim scenario changed dramatically a few years ago with the arrival of the protease inhibitors. Researchers found that when previously untreated patients combined the new drugs with older ones, the amount of virus circulating in their blood often fell to undetectable levels. Combination therapy is costly and inconvenient, requiring a dozen or more noxious pills every day. The hope was that patients who adhered carefully to the regimen would eventually be able to stop.
The new studies suggest they won’t. Writing in the journal Science last week, two research teams described experiments in which they extracted inactive immune cells from patients who were responding favorably to combination therapy. Though the drugs had pushed HIV to undetectable levels on standard blood tests, lab analysis showed that the virus was still present in the idle immune cells. And when those cells were prodded to multiply in culture dishes, they readily infected their HIV-negative neighbors. The good news is that the stowaway HIV had not become drug-resistant. Because it hadn’t been actively replicating, it was in effect meeting the drugs for the first time–and they still had the power to quash it.
For researchers the next challenge is to find ways of flushing inactive virus from patients’ bodies. That could take years–but with luck, patients who take their pills faithfully will still be around to celebrate the breakthrough.
