Few researchers become legends in their own time, but David Ho’s relentless quest to understand and conquer the AIDS virus has earned him worldwide renown. He elucidates the approach his lab has taken in the last decade to understanding how HIV replicates in cells, and how effective drugs have been developed to stymie the progress of the virus once a patient is infected. Within weeks of contracting HIV, there is exponential growth of the virus, which peaks swiftly, followed by a long period where the number of virus particles produced equal the number of particles cleaned out by a patient’s liver and spleen. There’s a “steady flow out and a steady flow in,” says Ho. During this period, which might last 10 years, the virus may not cause symptoms, but it steadily depletes the patient’s supply of a type of crucial immune cell.

Ho’s research in the 1990s took a quantitative approach to the dynamics of viral infection. By using a drug that helped block the reproduction of the virus, Ho discovered that virus replication and clearance happened very swiftly. “Half of what’s in circulation is removed in a half-hour, to be replaced by an equal amount of virus.” He also measured the total virus production per day, which for an average patient, meant somewhere between 1010 and 10 12 virus particles.

Ho says that one of the implications “of this relentless replication at very high levels” is a high mutation rate. HIV can shape shift and evade control by a single drug. Ho’s research helped generate the AIDS cocktail -- multiple antiretroviral drugs to block the progression of HIV at different points in its replication cycle.

While these therapies have diminished the AIDS mortality rate, mainly in western nations, Ho hopes to slow the spread of HIV worldwide, especially in parts of Africa where it continues to grow exponentially in the population. A vaccine that could “put more pressure on the virus,” at the earliest days of infection, could potentially “cause a shut off of infection and abolish it from taking hold.”

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