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Merck's HIV-1 Gag Vaccine Elicits Immune Response: Presented at AIDS-VACCINE

By Charlene Laino

NEW YORK, NY -- October 6, 2003 -- Final analyses of three phase I studies suggest that Merck's HIV-1 gag DNA vaccine for the prevention of HIV-1 infection elicits specific antiviral cellular immune responses, with the 5 mg dose showing better immunogenicity than the 1 mg dose.

The vaccine was also well tolerated, said Emilio A. Emini, PhD, senior vice president of vaccine research at Merck Research Labs in West Point, Pennsylvania, United States. However, contrary to what was demonstrated in rhesus monkeys, the addition of adjuvants – aluminium phosphate or Merck's proprietary CRL1005 -- did not appear to enhance the immune response to gag DNA, he said. The studies were presented here on September 21^st at AIDS Vaccine 2003.

At a press conference during the meeting, Gary Nabel, MD, PhD, director of the Vaccine Research Center at the National Institutes of Health in Bethesda, Maryland, United States, noted that the Merck vaccine is currently a frontrunner among the nearly 70 candidates being tested in phase I-III studies. Earlier this year, another leading candidate, made by VaxGen Inc., lowered the rate of HIV infection by only 3.8% in 5,400 high-risk men and women.

Across the three trials, the researchers randomised 356 healthy men and women, ages 18 to 55 years, at low risk for HIV infection to receive either an intramuscular injection of 1 mg of the HIV-1 gag DNA in saline, a 5 mg dose of the vaccine in saline, a 5 mg dose of the vaccine plus one of the two adjuvants or placebo. The vaccine was given at weeks 0, 4 and 8, with a booster at week 26.

As assessed by ELIspot assay at week 30, 35% of volunteers who received a 5 mg dose of the vaccine responded, compared with 17% of those given the 1 mg dose and none of those given placebo. A positive response for the assay was defined as 55 or more spot forming cells per 106 peripheral mononuclear blood cells and fourfold or more over the media control, according to Merck.

The response rates in the groups that received either adjuvant were not significantly different than those in the group that received a 5 mg dose of the vaccine in saline, Dr. Emini said.

The most common side effects were pain at the injection site and erythema, with no serious adverse events reported, Dr. Emini said. "These patients are now being boosted with [Merck's investigational HIV-1 gag replication-defective adenovirus vaccine], with results expected sometime next year, he told Doctor's Guide.


[Study title: The Safety and Immunogenicity of Merck's HIV-1 gag DNA Vaccines (with or without Adjuvants) in Healthy Adults. Abstract 144]

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