HIV-specific CD8(+) T cells produce antiviral cytokines but are impaired in cytolytic function

Thc use of peptide-human histocompatibility leukocyte antigen (HLA) class I tetrameric complexes to identify antigen-specific CD8(+) T cells has provi ded a major development in our understanding of their role in controlling v iral infections. However, questions remain about the exact function of thes e cells, particularly in HIV infection. Virus-specific cytotoxic T lymphocy tes exert much of their activity by secreting soluble factors such as cytok ines and chemokines. We describe here a method that combines the use of tet ramers and intracellular staining to examine the functional heterogeneity o f antigen-specific CD8(+) T cells es vivo. After stimulation by specific pe ptide antigen, secretion of interferon (IFN)-gamma, tunlor necrosis factor (TNF)-alpha, macrophage inflammatory protein (MIP)-1 beta, and perforin is analyzed by FACS(R) within the tetramer-positive population in peripheral b lood. Using this method, we have assessed the functional phenotype of HIV-s pecific 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 w ith regards to the secretion of antiviral cytokines ill response to antigen , although a subset of tetramer-staining cells was identified that secretes IFN-gamma and MIP-1 beta but not TNF-alpha. However, a striking filming is that HIV-specific CD8(+) T cells express significantly lower levels of per forin than CMV-specific CD8(+) T cells. This lack of perforin is linked wit h persistent CD27 expression on HIV-specific cells, suggesting impaired mat uration, and specific lysis ex vivo is lower for HIV-specific compared with CMV-specific cells from the same donor. Thus, HIV-specific CD8(+) T cells are impaired in cytolytic activity.