HIV-1 dynamics revisited: biphasic decay by cytotoxic T lymphocyte killing?

The biphasic decay of blood viraemia in patients being treated for human im munodeficiency virus type 1 (HIV-1) infection has been explained as the dec ay of two distinct populations of cells: the rapid death of productively in fected cells followed by the much slower elimination of a second population the identity of which remains unknown. Here we advance an alternative expl anation based on the immune response against a single population of infecte d cells. We show that the biphasic decay can be explained simply, without i nvoking multiple compartments: viral load falls quickly while cytotoxic T l ymphocytes (CTL) are still abundant, and more slowly as CTL disappear. We p ropose a method to test this idea, and develop a framework that is readily applicable to treatment of other infections.