A large clinical trial of a novel HIV vaccine has begun enrolling volunteers at sites in North America, South America, the Caribbean and Australia. Organizers are seeking 1,500 participants.

The trial is co-funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), and the pharmaceutical company Merck & Co. Inc. Merck developed the experimental vaccine to stimulate HIV-specific cellular immunity, which prompts the body to produce T cells that kill HIV-infected cells. In previous smaller trials, this vaccine was found to be safe and to induce cellular immune responses against HIV in more than half of volunteers.

“This new study is the first time we have used such a large sample of people to test whether a vaccine that stimulates cellular immunity alone either blocks HIV infection, decreases the level of HIV early in infection or both,” says Anthony S. Fauci, M.D., director of NIAID.

This proof-of-concept trial is designed to yield vital information on the potential efficacy of cellular immunity against HIV, although it is not expected to provide enough data to support immediate licensing of the vaccine for public use, says Margaret (Peggy) Johnston, Ph.D., who oversees HIV vaccine research at NIAID’s Division of AIDS.

The Merck vaccine contains a weakened adenovirus that serves as a carrier for three subtype B HIV genes. Subtype B is the most prevalent HIV subtype in the regions of the study sites. Adenoviruses are among the main causes of upper respiratory tract ailments such as the common cold. Because the vaccine contains only three HIV genes housed in a weakened adenovirus, study participants cannot become infected with HIV or get a respiratory infection from the vaccine.

“If this study finds that the vaccine can prevent or control infection, we will work with Merck to evaluate the vaccine in a larger number of volunteers,” adds Dr. Johnston. “We will also work with the company to determine the best vaccine design to test in parts of the world where other subtypes of HIV are circulating.”

The study will be conducted jointly by NIAID’s multicenter HIV Vaccine Trials Network (HVTN) and by Merck. The lead researchers are Michael Robertson, M.D., of Merck and two HVTN investigators: Susan P. Buchbinder, M.D., of the San Francisco Department of Public Health and Daniel Fitzgerald, M.D., of Cornell University.

The organizers are seeking healthy, HIV-negative men and women volunteers between the ages of 18 and 45 who are at an increased risk of acquiring HIV. The researchers plan to enroll a significant number of volunteers from populations particularly hard-hit by AIDS, including African Americans and other ethnic minorities.

The trials will take place in the following locations:

• North America: Atlanta, Boston, Chicago, Denver, Houston, Los Angeles, Miami, New York, Philadelphia, St. Louis, San Francisco, Seattle, Toronto
• South America: Iquitos and Lima, Peru
• Caribbean: Santo Domingo, Dominican Republic; Port-au-Prince, Haiti; San Juan, Puerto Rico
• Australia: Sydney

Organizers expect that it will take approximately one year to fully enroll volunteers into the study. NIAID and Merck expect the trial be completed in four-and-a-half years, with results anticipated in 2010. For more information on enrolling, visit HVTN’s Web site at www.hvtn.org.

NIAID is a component of the National Institutes of Health, an agency of the U.S. Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose and treat infectious diseases such as HIV/AIDS and other sexually transmitted infections, influenza, tuberculosis, malaria and illness from potential agents of bioterrorism. NIAID also supports research on transplantation and immune-related illnesses, including autoimmune disorders, asthma and allergies. News releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at http://www.niaid.nih.gov.