Increased cytolytic T lymphocyte activity and decreased B7 responsiveness are associated with CD28 down-regulation on CD8+ T cells from HIV-infected subjects. - Vingerhoets JH; Vanham GL; Kestens LL; Penne GG; Colebunders RL; Vandenbruaene MJ; Goeman J; Gigase PL; De Boer M; Ceuppens JL (Clinical and experimental immunology, 1995)