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.
But a remnant of virus will still get through, infecting human cells. That's where a second arm of vaccination, called the "cell-mediated" response, comes in. This involves the mobilization of immune T-cells that seek out and destroy infected cells.
Any viable vaccine must wipe out the virus quickly and completely, Koff explained, "So, we need each of these two arms primed and ready for when you get exposed to HIV."
But there's yet one more hurdle unique to HIV. Unlike standard flu or cold viruses, HIV -- a more primitive retrovirus -- actually inserts a piece of its DNA into the genome of the human host cell.
This "integration" begins within hours
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