In primate research Merck set out to find a vaccine that prevented HIV infection. It failed at that, but it may have produced the next best thing — a vaccine that suppresses HIV so thoroughly that those receiving it may not even be able to pass along the disease to other human beings.
Researchers were obviously disappointed when their vaccines failed to prevent HIV infection in monkeys. But after a bit of tinkering the vaccines did almost completely suppress the virus and the associated symptoms.
Very preliminary clinical testing of these vaccines have begun in human beings, and the results so far are promising. Two small groups of human volunteers were injected with different versions of the vaccines in Phase I tests designed largely to determine whether or not the vaccine is safe to move into larger trials in human beings.
The vaccine exposes the body to a protein that HIV relies upon to reproduce. In the two vaccines tested, one simply exposes the immune system to that protein, while the other exposes it to a cold virus that is wrapped around the protein. Even with the relatively low dose vaccines used to evaluate the safety of the approach, large percentages of both groups saw immune response systems much like those experienced by the monkeys who were exposed to the vaccine.
There was some concern about these sorts of vaccines earlier this year when one of eight monkeys injected with a similar virus finally succumbed to infections caused by SIV. In that a case a single mutation in the SIV virus carried by that particular monkey rendered the vaccine useless, although the seven other monkeys continue to have suppressed the disease and remain healthy.
In that case, though, the monkey that died received a relatively weak form of the vaccination, suggesting that vaccination should produce the strongest immune response possible to provide longer term suppression of the disease.
Given the clinical trial results of Merck’s vaccine, hopefully it will not be too long before the vaccine is tested on those already infected with HIV to see if it can provide the sort of disease suppression in humans that it does in monkeys. So far, the results are encouraging.
Source:
HIV vaccines show promise. The BBC, February 26, 2002.