Restoration of Hepatitis C virus-specific CD8+ T-cell responses in patients undergoing IFN-free antiviral therapy

Virus-specific CD8+ T cells play an important role in the outcome (elimination versus persistence) and pathogenesis of hepatitis C virus (HCV) infection. The mechanisms contributing to HCV-specific CD8+ T-cell failure in chronic infection are not completely understood. Importantly, the direct influence of ongoing viral replication on virus-specific CD8+ T-cell failure could not be studied previously since standard therapy regimens contained IFN with its known toxic effects on T cells. Therefore, it was the objective of this study to answer the important question whether inhibition of ongoing viral replication by IFN-free treatments will alter the phenotype and function of HCV-specific CD8+ T cells and may even restore exhausted HCV-specific CD8+ T cells.

To address this question, previously untreated patients with genotype 1 infection were treated with faldaprevir (a protease inhibitor), deleobuvir (a nonnucleoside polymerase inhibitor) and +/- ribavirin for 16 – 40 weeks. Comprehensive phenotypical and functional T-cell analyses were performed in 50 HLA-A*02 positive patients at baseline, week 4, week 12, and follow-up. Virus-specific CD8+ T cells were analyzed by MHC-I tetramers ex vivo and after in vitro expansion with virus-derived peptides and phenotypically characterized for the expression of differentiation and activation markers as well as inhibitory receptors. Functionality was measured by intracellular cytokine staining and proliferation assays.

Importantly, we found a significant increase in the frequency of HCV-specific CD8+ T cells during and after treatment compared to baseline that only occurred in patients with SVR. This effect could be observed directly ex vivo and after in vitro expansion. This increase in detectable HCV-specific CD8+ T-cell responses correlated with a decline of HCV viral load and successful viral clearance. In contrast, we did not observe any significant changes in the frequency of CMV- and Flu-specific CD8+ T cells, indicating a specific restoration of HCV-specific CD8+ T cells under successful IFN-free therapy. In sum, to our knowledge, this is the first study indicating a restoration of HCV-specific CD8+ T cells under IFN-free therapy. These results clearly suggest that ongoing viral replication directly contributes to HCV-specific CD8+ T-cell exhaustion. They also suggest that in contrast to patients with IFN-based therapy, patients with SVR after IFN-free therapy may have functional HCV-specific CD8+ T cells that may even contribute to protective immunity.