Hopes for AIDS Vaccine Still Alive Despite Setbacks

MONDAY, Dec. 1 (HealthDay News) -- Nobody said HIV would give up without a fight.

As World AIDS Day arrives Dec. 1, scientists are taking a sobering look back at what went wrong in recent, high-profile failures of two human trials of candidate AIDS vaccines.

The consensus: A viable vaccine is still very possible, and with it comes the potential to wipe out HIV/AIDS. But the science behind any new candidate vaccine must be much stronger than it has been in the past before testing begins in humans.

"We are going to be better served to try and find out the basics of what the immune response is to HIV, what the limitations are, and how we can tweak or change that, or come up with something entirely new," said Rowena Johnston, vice president of research at the Foundation for AIDS Research (amFAR) in New York City. "And only then can we start to think about a product that could be taken into humans."

Just two potential HIV vaccines have made it so far to human clinical trials: VaxGen's AIDSVAX, tested in Thailand, until the trial was stopped in 2003; and Merck & Co.'s HIV vaccine, which was tested in North and South America, the Caribbean and Australia, until it proved a failure in 2007.

In the Merck case, the trial results have also been shadowed by speculations that the vaccine somehow tweaked some recipients' immune systems to make them slightly more vulnerable to HIV infection.

Some experts in the field now believe that both vaccines were rushed too soon into human trials. One big flaw: Primate trials matched the vaccine to the strain of HIV the monkey was exposed to. That's unlike "real world" human infections, where people may be randomly confronted with any number of strains, experts said.

"What you want to do is have evidence in primates that you can block completely, or nearly completely, a challenge with at least one, if not two or three challenges with heterologous [varied] strains of virus," said U.S. AIDS pioneer Dr. Robert Gallo, who is credited (along with French researcher Luc Montagnier) of pinpointing HIV as the cause of AIDS back in the early 1980s.

A broadly protective vaccine would be tested against "very different strains than the strains used to make the vaccine," Gallo explained. "None of that had been done before the clinical trials that have been in the press."

Still, it's a daunting task considering that the variety of viral strains circulating in a single infected human body exceeds the variety of flu strains circulating globally each year, according to Wayne Koff, senior vice president of research and development at the International AIDS Vaccine Initiative (IAVI), based in New York City.

According to Koff, a good AIDS vaccine's reach "needs to be broad to be able to tackle whatever isolate of HIV the individual happens to be exposed to."

Vaccines work in two key ways. First, they prime the body's immune cells to recognize proteins on the virus' surface so they can be identified and destroyed. This "neutralizing antibody" effect typically eliminates all but a fraction of invading virus.