HIV-Specific Cd8+ T Cells Produce Antiviral Cytokines but Are Impaired in Cytolytic Function

The use of peptide–human histocompatibility leukocyte antigen (HLA) class I tetrameric complexes to identify antigen-specific CD8+ T cells has provided a major development in our understanding of their role in controlling viral infections. However, questions remain about the exact function of these cells, particularly in HIV infection. Virus-specific cytotoxic T lymphocytes exert much of their activity by secreting soluble factors such as cytokines and chemokines. We describe here a method that combines the use of tetramers and intracellular staining to examine the functional heterogeneity of antigen-specific CD8+ T cells ex vivo. After stimulation by specific peptide antigen, secretion of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, macrophage inflammatory protein (MIP)-1β, and perforin is analyzed by FACS® within the tetramer-positive population in peripheral blood. Using this method, we have assessed the functional phenotype of HIV-specific CD8+ T cells compared with cytomegalovirus (CMV)-specific CD8+ T cells in HIV chronic infection. We show that the majority of circulating CD8+ T cells specific for CMV and HIV antigens are functionally active with regards to the secreti