March 1, 2002 -- It's not the only AIDS vaccine in development. It's not even the one that's furthest along. Yet it's the one on which most AIDS experts pin their hopes.
Now there's some human data. It's not earthshaking, but it means that development will continue. A report presented this week at a major U.S. AIDS conference shows that the vaccine is safe and that it just might work.
"Of course we need to collect more data ... but it's fair to say we are encouraged by the results to date," says John W. Shiver, PhD, senior director of viral vaccine research at Merck, in a news release. Merck is developing the vaccine.
Everything about the conference report by Merck researcher Emilio Emini, PhD, is unusual. Rarely does very early human trial data get much attention -- and these are the very first human studies of the Merck vaccine. It's even more uncommon practice for a report to be based on a study that isn't even finished yet. Yet interest in the vaccine is so great that Emini was asked to present the findings.
Why the excitement? Merck's HIV vaccine won't keep a person from getting the AIDS virus. It's just supposed to keep people from getting sick if they do get infected. This it does very well -- in monkeys. Other vaccines based on the same so-called "prime-boost" concept also work in animals. But Merck's vaccine is the only one backed by a huge company with the resources and the will to carry out advanced human trials.
The idea behind the prime-boost strategy is to start with a shot of DNA that produces important pieces of HIV. This primes the immune system to start making the weapons -- killer T cells -- thought to work best against HIV. The priming shot would be followed by several booster shots of a harmless virus genetically engineered to produce pieces of HIV. The boosts kick anti-HIV weapons production into high gear.
Merck conducted a series of studies. In the first trial using the shot of DNA, 109 healthy people volunteered to get four injections. Some got fake shots, some got low-dose shots, and others got higher-dose shots. Nobody had any ill effects. About one in five of the low-dose subjects and about two in five of the high-dose subjects developed anti-HIV killer T cells.
In the trial of the virus booster, 48 healthy volunteers got either fake shots or different doses of the vaccine. After three shots, nearly three in five of the high-dose subjects developed anti-HIV killer T cells.
This isn't as bad as it sounds. After all, the two parts of the vaccine are supposed to be used together. The main point of the study was to show that the vaccine is safe. These are about the same results seen in early monkey studies.
Human tests using both parts of the vaccine began in December 2001. Results should be ready in a year. These anxiously awaited findings will make or break the vaccine. If it looks good, Merck will go ahead with large-scale studies.
Emini warns that even if everything goes perfectly -- something that rarely happens in medical research -- it will be at least five years before the vaccine is ready for use.
One ominous warning came from a monkey study reported earlier this year in the journal Nature. One of the monkeys that at first seemed to be protected against AIDS later got sick and died. What happened? The sneaky AIDS virus found a way around the vaccine. It's not clear that this would happen in people -- but it's a reminder of how unrelenting and clever a killer HIV can be.
Meanwhile, two other AIDS vaccines are in much more advanced stages of testing. A protein-based vaccine from VaxGen is in advanced clinical trials in Thailand and the U.S.; results are expected soon. And the U.S. Department of Defense is about to begin large-scale trials of a poxvirus-based vaccine in Africa and Thailand.
Test-tube evidence makes many researchers doubtful about the VaxGen product, AIDSVax. But the truth is that nobody knows whether a vaccine will work until it's tested on a large scale.