Background: A skewed maturation of memory HIV-specific CD8 T-lymphocytes has been observed in HIV-infected patients (pts). In the present study, we have characterized HCV-specific memory CD8 T-cell responses in pts with chronic HCV infection.

Methods: We selected 51 chronically HCV infected patients for their HLA haplotype (A2 or B8) to study HCV-specific CD8 T-cell responses. Ex vivo tetramer staining was performed using 7 HLA-A2 tetramers (NS3-1₁₀₇₃, NS3-2₁₄₀₆, NS5B₂₅₉₄, Core₇₂₉, E2₁₅₉₁, E2₁₉₂₁, E2₂₇₄₃) and 2 HLA-B8 tetramers (NS3-4₁₃₉₅, NS3-5₁₆₁₁). Phenotypic and functional (IFN-γ production) analyses of HCV-specific CD8 T-cells were performed by flow cytometry. The presence of HCV-specific CD8 T-cells was also investigated in the liver tissue.

Results: HCV-specific, e.g., tetramer positive, CD8 T-cells were detected in 23% (n = 12) of the pts studied. The mean frequency of HCV-specific CD8 T-cells was 0.1 ± 0.1% n = 12. The frequency of CD8+ T-cells secreting IFN-γ after HCV-specific stimulation was 0.08 ± 0.2%. The different populations of HCV-specific CD8 T-cells were characterized using CD45RA and CCR7 antigens. HCV-specific CD8⁺ cells displayed mostly a CD45RA-CCR7- phenotype (81 ± 10%, n = 8) which was previously characterized as typical of pre-terminally differentiated cells. Furthermore, the percentage of CD45RA+CCR7+ CD8 T-cells was 4 ± 5%, CD45RA-CCR7+ were 13 ± 9%, and CD45RA+CCR7- cells 2 ± 2%. Preliminary studies of CD8 T-cells in liver tissue indicated a 10-fold higher density of CD8 T-cells compared to normal liver tissue. More importantly, higher frequencies (up to 5-fold) of HCV-specific CD8 T-cells were found in the liver tissue of pts with chronic HCV infection compared to the blood compartment (n = 7).

Conclusions: Similar to HIV-specific memory CD8 T-cells, the majority of HCV-specific CD8+ T-cells are pre-terminally differentiated. Therefore, the relative expansion of the pre-terminally differentiated memory CD8 T-cell populations is associated with poor control of virus replication and progressive disease.