A new test is being developed that could help narrow the field of promising AIDS vaccine candidates. If successful, time and money could be concentrated on vaccines with the greatest potential to block HIV.
The test is called a viral inhibition assay and is being developed by scientists at the International AIDS Vaccine Initiative, IAVI, and Imperial College London. Dr. Jill Gilmour, IAVI's senior director of clinical research, explains why the test is needed.
"So far, I think a number of the tests that have been used sort of take indirect measurements. And we felt that we wanted a test that measured something much more akin to what the human body would actually have to do and measure the total function of the immune response. So, ultimately, we want the immune response to be able to stop HIV from replicating. And that's exactly the test that we set up," she says.
The test would determine whether immune cells could fend off HIV after getting a boost from a potential vaccine.
She says, "You know, we take CD-4 T-Cells and infect them with HIV, which is exactly what would happen in your body, and then look to see whether the immune cells from a vaccinated individual could stop the virus replicating. And that's exactly what we would need a vaccine to be able to do, possibly more relevant than a lot of the other tests out there."
Gilmour, who's based at the Human Immunology Lab in London, says the new test would examine several aspects of a vaccine.
"This is measuring total function. A lot of the other tests to assess current vaccines look at whether the vaccine induces an immune response. It doesn't necessarily tell us about the quality of the response or whether the response could stop the virus from replicating or indeed how many viruses the response could inhibit. So, it's taking a broader sweep at the function," she says.
The test results will be compared to data collected during a vaccine clinical trial now underway in London.
"Ultimately, we will not be able to say whether this test can predict whether a vaccine works until we get a vaccine into a clinical trial that demonstrates efficacy, that actually shows the vaccine works. But what we do believe is that it will give us a much better handle on how to select those vaccine candidates to go forward," she says.
Dr. Gilmour says clinical trials cost millions of dollars and often involve thousands of volunteers. So, selecting only the most promising candidates could save a great deal of time and money.
IAVI is collaborating with the US National Institutes of Health and Merck to acquire a good sample of vaccine candidates. If eventually proven effective, the test could determine within three weeks whether a vaccine candidate is worthy of clinical trial.
Scientists are often asked how long it will take to find an effective AIDS vaccine. Gilmour says the answer remains elusive.
"I'm probably going to give you the answer you've heard on many occasions. We don't know. This endeavor is certainly not for the fainthearted. But I do believe that Mother Nature tells us that it's possible. For example, there are people who are multiply exposed and don't become infected. Or there are individuals who control their HIV for many, many years without treatment. The vaccine effort really only has had a concerted effort since the mid-90s. And the polio vaccine took, for example, 40 years to develop. So, I think we're still quite early in," she says.
The International AIDS Vaccine Initiative hopes to have definitive word on its vaccine test by early next year.