An adhesion molecule (glycoprotein) on the envelope (surface membrane) of HIV (i.e., AIDS-causing) viruses that directly interacts with the CD4 protein on helper T cells; enabling the HIV viruses to bind to and infect helper T cells. In 1994, a group at America’s Scripps Research Institute led by Dennis Burton and Carlos Barbas III announced that they had generated a recombinant human antibody to the GP120 protein; which neutralized more than 75% of HIV isolates that it was tested against. This advance holds the potential to someday lead to a vaccine against AIDS.