AIDS, an immunodeficiency disease caused by infection with the human immunodeficiency virus (HIV), is one of the ten leading causes of death worldwide. Thanks to antiviral therapies, the disease can be treated, but there is still no cure. A large-scale comparative study by scientists at the German Center for Infection Research (DZIF) and University Medical Center Hamburg-Eppendorf indicates a critical role of a group of specialised immune cells in suppressing the antiviral immune response of HIV-infected patients.