It makes for some interesting moral decisions on the part of the PC's. Such as wether or not it's actually a good thing that vampires die from the cure. Maybe they could actually enter the story line as government agents dispatched to stop the research on the grounds that the nation's secret arsenal of biological HIV-carrying weapons would go obsolete if the existence of the cure was made public. Naturally, the true objectives and reasons for the mission won't be relayed to the PC's. Instead they may be told that the scientists are terrorists working on an aggresive biological agent designed to be released on the unsuspecting population killing thousands of innocents. Makes for another moral issue; will the PC's carry out their mission, even after they've been told that it's actually a cure for HIV? Will they "accidentally" fail to obtain some of the substance, allowing the scientists to get away with it? How will they respond to the fact that the cure kills vampires? Will they accept that as evidence suggesting that the cure was indeed as bio-weapon?
I just love a good, classic, twisted conspiracy with noone to trust, like 24 with Kiefer Sutherland. Good luck. Keep the plot-suggesting business up. I always have such a hard time coming up with good ones, thanks(Think I'll use this one)