Restoration of HCV-specific T cell functions by PD-1/PD-L1 blockade in HCV infection: Effect of viremia levels and antiviral treatment

Background/Aims HCV-specific T cells in acute hepatitis C with subsequent chronic evolution are dysfunctional and most of them express PD-1. The aim of the study was to investigate to what extent the antiviral T cell function can be restored by reversing T cell exhaustion by PD-1/PD-L1 blockade and to assess whether this restoration is favored by IFN-α treatment. Methods PD-1 and PD-L1 expression was studied on T cells and dendritic cells, respectively, of 14 patients with acute hepatitis C and different evolutions of infection. The effect of anti-PD-L1 was analyzed on proliferation, cytokine production and cytolytic activity of CD4 and CD8 T cells. Results While PD-1 expression dropped concurrently with spontaneous or IFN-α induced HCV–RNA decline, PD-L1 levels on dendritic cells increased during IFN-α treatment. Anti-PD-L1 antibodies improved expansion and cytokine production but not the cytolytic activity of HCV-specific T cells. This restoration tended to be greater at lower levels of viremia and PD-1 expression and during PEG-IFNα treatment. Conclusions PD-1/PD-L1 blockade has an immunoregulatory activity which may synergize with the antiviral effect of IFN-α therapy and should be thus explored further in long-lasting chronic HCV infections in the perspective of improving the efficacy of available antiviral treatments.