Baker's vaccine does use an HIV protein that is not as prone to evolution, and therefore takes a similar form in most HIV strains. This may allow the immune system to recognize even highly divergent versions of the virus.

Besides its promise as an HIV vaccine, the new technology also has the potential to radically change the face of smallpox vaccination by obviating the need to use a live virus. While smallpox was eradicated three decades ago, maintaining stockpiles of the vaccine has remained a priority due to concerns about bioterrorism. In 2002, President Bush announced a program to vaccinate certain military personnel and civilian health-care workers against the virus. But concerns remain about the safety of existing vaccines.

All smallpox vaccines employ a virus called vaccinia, which is less deadly than the smallpox virus but similar enough to induce immunity against it. In fending off smallpox infection, the most important component of the immune system is cellular immunity, in which infected cells are identified and destroyed. Since existing vaccines require a live vaccinia virus to produce adequate cellular immunity, adverse effects are common. As a result, many of those targeted by Bush's program declined the vaccine.

The nanoemulsion--which, thanks to the destructive surface tension of its oil droplets, is an effective antimicrobial solution--actually kills the vaccinia virus. But because it shuttles the dead virus directly to dendritic cells, says Baker, the establishment of cellular immunity is not compromised. In Baker's experiments, mice given the nanoemulsion smallpox vaccine survived doses of the vaccinia virus that were lethal in unvaccinated mice. The results appear in the February issue of Clinical and Vaccine Immunology.

"We prevent replication entirely, but we maintain the strong immune response that one would get with a live viral infection," says Baker. "So it's the best of all worlds."

These new smallpox and HIV studies further expand the repertoire of diseases amenable to nanoemulsion vaccines, although no such vaccines have yet been used on humans. In earlier work, Baker has shown the technology to be effective for vaccinating against both influenza and anthrax in animal models, and he is currently working with the Bill and Melinda Gates Foundation to develop a new hepatitis B vaccine. Nanoemulsions are uniquely suited to the demands of vaccination in developing countries because the constituent proteins are stabilized, require no needles or costly inhalers, and can survive high temperatures. Baker says that human trials for the nanoemulsion hepatitis B vaccine could begin by the end of this year.