Government scientists have found natural HIV antibodies necessary for an AIDS vaccine, reports Scientific American, but stimulating their production in the body remains a hurdle. "Variations in individuals' innate and adaptive immune systems can dramatically affect responses to infection—HIV is no exception. The result generally can be shown as a bell curve, with a group of people whose disease progresses rapidly, a broad middle segment who progress typically, and a small group of 'elite controllers' whose immune systems are quite effective at containing HIV viral replication."