Here is the quote from the site itself:
For those who aren't familiar with HIV and how it works, "clearing the virus from the blood" is not a cure. Host cells which the virus has infected will stay infected and the virus will continue to try to replicate itself from within those cells. But with this new drug, the virus will be unable to infect more cells. Essentially, that's what most HIV drugs do now, but they disrupt the production of the virus in earlier stages of development. This one catches the virus at the last possible moment, and seems to be effective in people who are immune to most of the other drugs.
The latest research, in which the virus was examined under a microscope, shows that the drug binds to the capsid protein at a crucial stage in its manufacture (Journal of Virology, vol 80, p 5716). Normally, the capsid protein is clipped apart from a major structural protein called the gag protein, and is then assembled into a cone. PA-457 stops it being clipped off, causing it to form a leaky sphere that leaves the core RNA exposed
(see Diagram). This cripples the virus, preventing it from infecting any other cells once it buds out from the host.
Previous lab experiments on infected human cells have shown that the drug defeats strains of HIV which are resistant to other anti-HIV drugs. A small human trial of the drug, reported last August, showed that when given on its own it rapidly clears most HIV from the blood, driving down the levels tenfold in a matter of hours.