Presence of primary human hepatocytes inhibits expansion of virus-specific CD8+ T cells in vitro

Background: A hallmark of chronic infections with hepatotropic viruses such as HBV and HCV is the notoriously weak antiviral immune response by CD8 T cells. It is believed that the liver-specific environment can induce tolerance either by induction of dysfunctional CD8 T cells or by premature death of activated CD8 T cells. Recent reports from mouse models indicate that hepatocytes can act as antigen-presenting cells. Direct antigen presentation by virally infected hepatocytes thus might inhibit the CD8 T cell response. Methods: Primary hepatocytes were isolated from resected liver fragments of patients undergoing surgery and cultured in the presence of PBMCs with a memory CD8 T cell response to HLA-A2 restricted Flu- or CMV-epitopes. After 10 days the frequency of specific CD8 T cells and production of cytokines was determined. Results: The frequency of virus-specific CD8+ T cells after 10 days expansion is dramatically reduced in the presence of hepatocytes. 16h of co-culture of PBMCs with hepatocytes were sufficient for this suppressive effect. Expansion of CD8 T cells in the presence of hepatocytes was almost completely restored in transwell experiments indicating that the suppressive effect is cell-contact dependent. However, the effect was not dependent of antigen-specific contact between the virus-specific TCR on CD8+ T cells and the HLA/peptide complex on hepatocytes as the suppressive effect was observed in the presence of hepatocytes from both HLA-A2-positive and –negative donors. Analysis of the cytokine-profile from culture supernatants revealed 3-fold increased concentrations of TGFbeta in the presence of hepatocytes compared to their absence. Conclusions: Presence of primary human hepatocytes has a strong suppressive effect on expansion of virus-specific memory CD8 T cells from PBMC in vitro. The role of different cellular subsets and cytokines is currently investigated.