BOCA RATON · Dr. Robert C. Gallo, credited as a co-discoverer of HIV, the retrovirus that causes AIDS, said on Tuesday that the key to a successful vaccine to prevent AIDS is to block the retrovirus from getting into healthy cells.

Gallo said his lab is developing such a vaccine to prevent HIV from inserting its genetic code into healthy cells and reproducing each time the cells divide, a characteristic of retroviruses. Gallo predicted the new vaccine would have its first safety trials in humans within 18 months, and if all goes well, could be in widespread use within five years.

The founder and director of the Institute of Human Virology in Baltimore, Gallo described his vaccine approach during a science lecture that preceded a program where Gov. Jeb Bush dedicated Florida Atlantic University's $20 million Charles E. Schmidt Biomedical Science Center.

"To us, the goal of a preventive vaccine is sterilizing immunity -- complete block of infection," Gallo said. He predicted the approach will work on all strains of HIV anywhere in the world and any mutations that develop.

Current vaccines in testing allow HIV infection but attempt to keep it under control, he said.

"That worries me. How do you know it will keep the virus down forever?" he said. "They're going forward with [vaccine] trials in Thailand, but they won't work."

Animals exposed to the virus after getting the vaccine are showing signs of infection, he said.

"Everyone has their heads hanging down, but we're not," he said. "We're quite excited."

He said research at his lab involves a combination of ways to block the virus from getting into cells, including the use of neutralizing antibodies that block the virus at the last stage before it infects a healthy cell. The vaccine research is being done in collaboration with Dr. Luc Montagnier, president of the World Foundation for AIDS Research and Prevention and the other discoverer of HIV.

Before his discovery, Gallo searched for retroviruses because he theorized that they were responsible for certain cancers, including some types of leukemia and lymphoma. He said his work was not popular because many scientists thought retroviruses were present only in animals.

That work led him to theorize that AIDS was being caused by a retrovirus, he said.

In 1983, Montagnier's laboratory discovered HIV. The same year, Gallo's laboratory isolated the virus, and controversy developed over whether the virus in Gallo's lab had actually come from Montagnier's lab. Both labs used the discovery to develop an HIV test, which helped to protect the blood supply against contamination.

Gallo said he would like to see the first human trials of the vaccine in a country such as Botswana, where, in some towns, 60 percent of the population has HIV.

Gallo's lecture was attended by FAU students, faculty and high school science students.

Nancy McVicar can be reached at nmcvicar@sun-sentinel.com or 954-356-4593.