Background: Since the association between hepatitis C virus (HCV)-specific T-cell responses both pretreatment and during interferon-a based therapy and viral clearance is unresolved, a combined analysis of distinctive T-cell characteristics (proliferation and interferon-gamma production) is important to clarify this issue. Methods: Peripheral blood mononuclear cells (PBMC) collected in 22 chronic HCV infected patients at pretreatment and at week 4 during pegIFN-alpha/ribavirin therapy, were stimulated with overlapping peptide pools in a [H-3]-thymidine assay, an interferon-gamma-ELISA, and a sensitive 12-day T-cell expansion assay. Results: Compared to the [H-3]-thymidine proliferation and interferon-gamma secretion assays, the 12-day T-cell expansion assay was more sensitive in detecting T-cell responses. No significant association was demonstrated between pre-treatment HCV-specific CD4(+) or CD8(+) T-cell responses and either a sustained virological response (SVR) or a rapid virological response (RVR). However, a skewing of individual responses towards the non-structural antigens was observed. During pegIFN-a/ribavirin therapy, HCV-specific CD4(+) and CD8(+) T-cells declined similarly in both SVR/RVR and non-SVR/non-RVR patients. Conclusion: No correlation was found between the magnitude of pre-treatment HCV-specific T-cell responses and the outcome of pegIFN-a/ribavirin therapy in terms of SVR and RVR. Moreover, the magnitude of HCV-specific T-cell responses declined in all patients early during treatment. (C) 2010 Elsevier B.V. All rights reserved.