How HIV-1 lost control

Aminor change during evolution converted the relatively benign monkey SIV viruses into deadly HIV-1, according to Michael Schindler, Frank Kirchhoff (University of Ulm, Germany), and colleagues. They report that HIV-1, unlike most SIV strains, has lost the ability to protect its T cell hosts, and thus its human host, from death.

The critical difference is in a virus protein called Nef, which increases virus infectivity and replication. But even more important than what HIV-1 Nef does may be what it does not do.

The German group tested 30 different nef alleles in an HIV-1 vector. Most SIV Nef proteins down-regulated expression of the T cell receptor protein CD3 and thus blocked activation of infected T cells. Nef from HIV-1 and some closely related SIV relatives had neither of these effects.

The...