Virus-specific CD8⁺ T cells are required for the control of hepatitis C virus (HCV) infection. We investigated the extent to which different effector functions of CD8⁺ T cells contribute to the inhibition of viral replication.

We developed a novel immunologic model by stably transducing the HLA-A2 gene into the replicon system, matching the epitope sequence of the replicon to the sequence targeted by an HCV-specific CD8⁺ T-cell clone. Luciferase activity was then measured to quantitate HCV RNA replication.

HCV-specific CD8⁺ T cells strongly inhibited viral replication, through cytolytic and noncytolytic mechanisms, in a dose-dependent manner. HCV replication was almost completely inhibited at an effector-to-target ratio of 1:1 with significant cytotoxicity; however, >95% viral inhibition occurred at ratios as low as 1:100. Importantly, no cytotoxicity was observed at low effector-to-target ratios, indicating a dominant effect of noncytolytic effector functions that was confirmed by Transwell experiments. Neutralization experiments revealed that interferon gamma mediates the noncytolytic inhibition.

Only a very few HCV-specific CD8⁺ T cells are required to inhibit HCV replication; inhibition occurs primarily by noncytolytic effector functions.