Using cutting-edge molecular techniques, a team led by geneticist Stephen Elledge at Brigham and Women's Hospital in Boston found that the HIV virus relies on 273 human proteins to infect the host's immune cells. These so-called HIV dependency factors (HDFs) enable the virus to attach to immune cells, wiggle in, shed the protein coat that surrounds its RNA, convert that to DNA and help newly minted HIV viruses bud through the surface where they can go on and infect the other cells.