In a finding that could have profound implications for AIDS vaccine design, researchers led by a team at the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, have generated an atomic-level picture of a key portion of an HIV surface protein as it looks when bound to an infection-fighting antibody. Unlike much of the constantly mutating virus, this protein component is stable and—more importantly, say the researchers—appears vulnerable to attack from this specific antibody, known as b12, that can broadly neutralize HIV.