The national study, sponsored by Merck & Co., will assess the vaccine's safety and ability to produce immunity in healthy, uninfected adult volunteers. If successful, the small preliminary study would pave the way for a larger study of the vaccine's effectiveness in people at high risk for HIV infection.
"Of all the potential vaccines studied over the last 20 years, this is one of the most promising to move forward as a candidate for prevention of HIV disease," Jeffrey Nadler, MD, professor of medicine and principal investigator for the HIV vaccine trial in Tampa.
This is the first time that all three components of Merck's HIV vaccine using a prime boost regimen will be tested in humans.
USF/TGH is one of two research centers in Florida and 16 nationwide involved in the placebo-controlled clinical trial. Merck expects to enroll 126 people nationwide in the 18-month clinical trial, including 10 at TGH.
Traditionally, vaccines, such as the polio vaccine, work by encouraging antibodies to prevent infection. However, most vaccines designed to stimulate production of antibodies against HIV have not worked well because the cryptic virus changes itself slightly to evade attack.
Instead of building antibodies, this new HIV vaccine boosts the activity of killer cells in the immune system, called T-lymphocytes, to target and kill the cells containing HIV. "The challenge is to stimulate very specific responses that are directed at the HIV itself" without destroying healthy immune cells, Dr. Nadler said.
Earlier this year, Merck announced that the vaccine sharply slowed the reproduction of the AIDS virus in laboratory monkeys that became infected with HIV. In contrast, most unvaccinated monkeys died or developed AIDS. In addition, small numbers of healthy people have been administered components of the vaccine separately to test their safety.
The development of a safe, effective and inexpensive vaccine for HIV is the best chance for curbing the spread of AIDS worldwide, Dr. Nadler said. New, more potent antiviral drugs have helped patients with AIDS live longer, but the complicated treatment regimen is expensive (an average of $10,000 a year per patient) and its effectiveness depends on patients' ability to take the oral medications correctly.
"As many as 50 percent of HIV-infected patients we treat are unable to fully comply with their combination drug therapy," Dr. Nadler said.
"This is a pivotal study," he said. "We must make sure the vaccine is safe and stimulates the appropriate immune response in healthy people at low risk for acquiring HIV before testing it in people who are more likely to become infected with the AIDS virus."
Dr. Nadler is director of research in the Division of Infectious Diseases at USF, TGH and the Hillsborough County Health Department. He has been an investigator for numerous clinical HIV studies, including diagnostic testing and drug therapies.