Control of vertical transmission of HIV-1 has progressed remarkably despite a lack of understanding of precise mechanisms by which infection may occur (1 ). The latter situation partially resulted from inadequate tools for in vitro analysis. However,in uterodata suggest that placental infection coincides with vertical transmission. In many cases of fetal infection, placental infection is also present; detection of fetal infection without placental infection is relatively rare. An interesting observation is that not all placentae of HIV-1-infected women are infected (2 –5 ). This raises the possibility that understanding how the placenta becomes infected will give insight into mechanisms of vertical transmission and may lead to therapies to prevent infection.
