Merck HIV vaccine enters Phase II testing

A potential HIV vaccine developed by Merck that uses synthetic genes to prepare cells to fight the deadly virus is moving into the second stage of testing. An approved vaccine would be about a decade away if the trial and a third study are successful, say officials with the international coalition that is collaborating on the work. "It is the most promising candidate that we've seen so far," said Sarah B. Alexander, associate director of the HIV Vaccine Trials Network, or HVTN. She cautions, however, that "something better could come along tomorrow." Volunteers began enrolling last month for the Phase II study, which will eventually give the potential vaccine's three doses to 1,500 people in North and South America, the Caribbean, and Australia, the network and Merck announced Monday. The study is using male and female volunteers, ages 18 to 45, of diverse racial groups who are at high risk for contracting HIV. Participants will receive counseling about how to reduce their risk of HIV infection, Alexander said. The Merck vaccine candidate--called the MRKAd5 HIV-1 gag/pol/nef, or trivalent, vaccine--is designed to prompt killer T cells to attack HIV when the virus enters the cell. Other vaccines generate an antibody response to the virus. The potential vaccine uses the virus of a common cold, modified so it cannot reproduce or cause people to catch a cold, to transport three synthetically produced HIV genes to the cells. "We give the body enough of the virus so it can recognize it and create an immune response," but not enough to infect a person, Alexander said. The Phase I study of the possible vaccine, involving about 1,000 people, "generated strong and durable cellular immune responses against HIV," said Merck spokeswoman Janet Skidmore. (AP)