Merck Begins Human Trials of New AIDS Vaccine CandidateMerck & Co. last week began "small human trials" for a new AIDS vaccine candidate that has shown to hold the virus in check in monkeys, the Wall Street Journal reports. Merck, one of the world's "largest and most experienced vaccine manufacturers," has not released specific details on the vaccine to the public to avoid raising "false hopes" but presented findings last month in two "closed-door sessions" with the NIH AIDS Vaccine Advisory Committee and "leading" AIDS activists. The new vaccine employs two strategies to augment a killer T cell attack against the virus. Killer T cells work by destroying cells HIV has already infected. The first strategy involves "priming" the immune system by injecting humans with bits of HIV DNA, called "naked DNA." Then the immune response is "boost[ed]" with a vaccine that "hooks HIV genes" onto an adenovirus, which normally causes colds in humans but is inactivated in the Merck vaccine.
AIDS Prevention in Monkeys
According to individuals who saw Merck's research data and spoke to the Journal "on condition of anonymity," the vaccinated monkeys did not get sick "after they were injected with a hybrid AIDS virus containing strains that can make humans and monkeys sick," while unvaccinated monkeys who were exposed to the virus died or developed AIDS. The vaccine did not prevent HIV infection in monkeys, but it helped the monkeys "control and contain" the virus. Thus far the vaccinated monkeys have shown "no signs of disease." Experts suspect this "partial protection" strategy may "merely delay, rather than fully prevent, the onset of AIDS." But NIH Chair Dr. David Baltimore noted that vaccines "rarely, if ever sterilize the body against an invading microbe;" they usually work by priming the immune system to "beat back an infection once it develops." The Journal reports that the AIDS research community -- including researchers from Harvard University in collaboration with Merck; a research team from Emory University and the National Institute of Allergy and Infectious Diseases; and a collaboration between Yale University and the Aaron Diamond AIDS Research Center in New York -- has been "moving toward" the "partial protection" strategy. Merck's vaccine is the first among these "partial protection" vaccine candidates to enter human trials.
Benefits of 'Partial Protection'
A vaccine that could delay the onset of AIDS could "still reap huge benefits," researchers say. For example, the vaccine could reduce the number of AIDS orphans in Africa by buying parents more time to raise their children. In addition, the Journal notes that the vaccine could keep viral levels low in HIV-positive individuals, thereby lowering the risk of viral transmission and "slowing the epidemic." Merck also hopes that the vaccine might prove effective in people who have already contracted HIV, and plans to test the vaccine in HIV-positive patients in about four months. The initial human trials seek to determine whether the vaccine is safe and stimulates a killer T cell response in healthy, uninfected volunteers who will not be exposed to HIV. Merck still hopes that the vaccine may fully prevent infection in humans, as the monkeys in animal trials were exposed to viral doses that were "much greater and more virulent than what humans are usually exposed to." The company plans to make a "formal presentation" of its findings in April at a scientific forum in Colorado (Schoofs, Wall Street Journal, 2/22).