Two-Vaccine Combination Stimulates Immune Response

DENVER—A combination of two investigational HIV vaccines has produced anti-HIV immune responses in more than 90% of volunteers at least 1 year after vaccination, Robert Belshe, MD, of St. Louis University, said at the International Society for Sexually Transmitted Diseases Research meeting. “These preliminary data indicate both vaccines are safe, and side effects associated with the injections are generally mild,” Dr. Belshe said.

The phase II trial, known as AVEG 202/HIVNET 014, is being carried out at 14 sites nationwide by two networks sponsored by the National Institute of Allergy and Infectious Diseases (NIAID)—the AIDS Vaccine Evaluation Group (AVEG) and the HIV Prevention Trials Network (HIVNET).

The two vaccines being used in the trial are vCP205 (Pasteur Merieux Connaught, Lyon, France) and SF-2 rgp120 (Chiron, Emeryville, California) (see box below)

About the Vaccines

The two vaccines used in the AVEG trial show promise for activating both components of the immune system.

The vCP205 vaccine consists of an attenuated canarypox virus genetically altered to contain a few selected HIV genes; it stimulates cellular immunity, resulting in cytotoxic T cells that can kill HIV-infected cells.

SF-2 rgp120 is a genetically engineered copy of the HIV surface protein gp120. (SF-2 is a laboratory-adapted HIV strain.) It stimulates the production of HIV neutralizing antibodies, which can stop HIV from infecting cells.

Since the vaccines contain only selected HIV genes or proteins, and not the whole virus, an individual cannot become infected from receiving the vaccine.

435 Volunteers Enrolled

The trial enrolled 435 healthy men and women not infected with HIV. More than 80% of the participants had a recent history of intravenous drug use or high-risk sexual behavior. All participants received extensive and repeated counseling on reducing high-risk behaviors.

Enrollment began in May 1997, and the volunteers were randomly assigned to one of three arms. One group received both vaccines; a second group got vCP205 and a placebo; the third group received two placebos. Volunteers received four doses, by injection, spread out over 6 months.

All immunizations were completed by July 1998. One year later, more than 90% of the volunteers in the two-vaccine arm and more than 50% of those receiving vCP205 had developed antibodies that can inhibit HIV in a laboratory assay, Dr. Belshe said.

So far, 11 volunteers have become infected with HIV, all as the result of high-risk behavior—six in the placebo group, three in the single-vaccine arm, and two in the group receiving the combination of vaccines. However, the trial is not designed to test whether the vaccine combination can protect against HIV infection or AIDS, Dr. Belshe said. Participants in the trial will continue to be followed for a further 3 years.

Additional NIAID-sponsored studies are gathering more data on this vaccination strategy before a large-scale efficacy trial is considered. For example, two newer canarypox HIV vaccines are undergoing a head-to-head evaluation. At this time, the data needed to consider moving into the next phase of testing are expected to be available by late 2000.