In a paper published in the online version of Science on 8 March, Amara et al report a two-step AIDS vaccine strategy that can stimulate the immune system to target and eliminate already infected cells (Science 8 March 2001, 10.1126/science.1058915).

The authors used a laboratory-made hybrid of human immunodeficiency virus and simian immunodeficiency virus called SHIV. Amara et al vaccinated rhesus macaques at 0 and 8 weeks, using a DNA prime (DNA/89.6) that expressed SIV Gag, Pol, Vif and Vpx from a single transcript. This was followed by a boost at 24 weeks with a recombinant modified vaccinia Ankara (rMVA) booster that expressed SIV Gag, Pol and HIV1 Env under the control of vaccinia virus early/late promoters. This effectively controlled a challenge with SHIV administered intrarectally seven months after the booster.

This prime–boost strategy did not protect the animals from infection with SHIV but it did protect them from...