THURSDAY, Nov. 13 (HealthDay News) -- An HIV-1 vaccine designed to elicit cell-mediated immunity is no better than placebo in preventing HIV infection or reducing viral loads in individuals at high risk of contracting HIV, according to a study published online Nov. 13 in The Lancet.

Susan P. Buchbinder, M.D., from the San Francisco Department of Public Health, and colleagues randomly assigned 3,000 HIV-negative individuals to three injections of the MRKAd5 HIV-1 vaccine (made in adenovirus type 5, Ad5) designed to elicit cell-mediated immunity, or placebo. The researchers found that among patients with low Ad5 antibody titers at baseline, 24 (3 percent) of 741 vaccine recipients and 21 (3 percent) of 762 placebo recipients became infected with HIV-1 (hazard ratio 1.2). Mean plasma HIV-1 RNA levels were similar in the placebo and vaccine groups. The risk of HIV-1 infection was higher in Ad5-positive men (HR, 2.3) and uncircumcised men (HR, 3.8).

In a related article also published online Nov. 13 in the same journal, M. Juliana McElrath, M.D., from the Fred Hutchinson Cancer Research Center in Seattle, and colleagues analyzed the immune responses of patients in the trial. They found that 73 percent of vaccine recipients showed HIV-1-specific CD8+ T cell responses and 41 percent showed HIV-1-specific CD4+ T cell responses.

"Consistent with previous trials, the MRKAd5 HIV-1 gag/pol/nef vaccine was highly immunogenic for inducing HIV-specific CD8+ T cells," McElrath and colleagues conclude. "Our findings suggest that future candidate vaccines have to elicit responses that either exceed in magnitude or differ in breadth or function from those recorded in this trial."

The studies were funded by Merck Research Laboratories, the U.S. National Institutes of Health (NIH), and the NIH-sponsored HIV Vaccine Trials Network.

Abstract - Buchbinder
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Abstract - McElrath
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