BACKGROUND & AIMS: Dysfunctional CD8(+) T cells are believed to contribute to the ability of hepatitis C virus (HCV) to evade the immune response. Most studies have focused on the effector functions of HCV-specific CD8(+) T cells or their surface expression of inhibitory receptors. There is currently no information available about the ex vivo ability of HCV-specific CD8(+) T cells to inhibit viral replication (antiviral efficacy). METHODS: To analyze the antiviral efficacy of virus-specific CD8(+) T cells ex vivo, we used an immunologic model based on a cell line that expresses HLA-A*02 and contains a stably replicating HCV reporter replicon. We isolated HCV-specific CD8(+) T cells from 18 HLA-A*02-positive patients with chronic HCV infection and 15 subjects with resolved HCV infection (7 spontaneous, 8 after therapy). Replicon cells were labeled with virus-specific peptides; inhibition of HCV replication was determined by measuring luciferase activity after 72 hours of coculture with virus-specific CD8(+) T cells. RESULTS: HCV-specific CD8(+) T cells from patients with chronic HCV infection had a significantly lower antiviral efficacy than influenza-, Epstein-Barr virus-, and cytomegalovirus-specific CD8(+) T cells. Antiviral efficacy was associated with the ability of virus-specific CD8(+) T cells to secrete interferon gamma. The antiviral efficacy of HCV-specific CD8(+) T cells was linked to surface expression of CD127 and PD-1. The cytokines interleukin-2, interleukin-7, and interleukin-15 increased the antiviral efficacy of CD127-positive but not of CD127-negative, HCV-specific CD8(+) T cells. Spontaneous, but not antiviral therapy-induced, viral clearance was associated with increased antiviral efficacy. CONCLUSIONS: The ability of CD8(+) T cells to inhibit HCV replication ex vivo is associated with their ability to secrete interferon gamma and their surface expression of CD127 and PD-1