PADUA, Italy (Reuters Health) - Human tests to evaluate a new vaccine that could both prevent and treat HIV will begin shortly, Italian researchers told an international meeting on Wednesday.

"We have completed all the necessary procedures and are waiting for the final approval to proceed on phase I," Dr. Valeria Fiorelli, a colleague of Dr. Barbara Ensoli at the National Health Institute laboratory of virology, told Reuters Health.

Phase I tests are the earliest stage of human trials, and are designed to evaluate safety in a small number of people.

Fiorelli presented the most recent developments with the vaccine here at the Bionova biotechnology meeting.

Along with many other research groups, Ensoli is trying to halt HIV by inducing antibodies to a key building block of the virus, its transcriptional activation (Tat) protein.

"This protein, released by cells soon after the infection, has a key role in the virus life cycle. Basically, the virus replicates and spreads through the Tat protein," Dr. Fiorelli said.

The protein plays a dual role in HIV infection. As well as being critical for replication it also acts as a viral toxin.

The crucial role of the protein has been shown by previous studies by Ensoli's team. The presence of anti-Tat antibodies is associated with slower disease progression, which makes it an ideal candidate for both preventive and therapeutic vaccines.

In preliminary tests on monkeys, the vaccine had a 71 percent success rate. Vaccination with either the Tat protein or Tat DNA did not prove toxic for infected monkeys.

The first stage of human testing will examine the vaccine as both a preventive and as a treatment for infected people, Dr. Fiorelli said.

"The preventive vaccine trial will involve healthy, HIV uninfected adult volunteers of both genders between 18 and 50, without identifiable risk of HIV-1 infection," Fiorelli said. The therapeutic vaccine trial will enroll HIV-1 infected adult volunteers of either gender with mild immunodeficiency.

The vaccine could be effective against the subtypes of the virus that dominate different parts of the world, she said.

In a study to be published shortly in the Journal of Infectious Diseases, Ensoli and colleagues studied a group of patients from South Africa, Uganda and Italy, infected with different virus subtypes.

"Our tests and data confirmed immune cross-recognition and conservation of the HIV-1 Tat protein in circulating viruses in these three countries. It is important to say that the viral subtypes we have studied--subtype B in Italy, subtype A, D and others in Uganda, and subtype C in South Africa--represent more than 90% of the world HIV epidemic," Fiorelli said.