The cyclophilin-inhibitor alisporivir stimulates antigen presentation thereby promoting antigen-specific CD8(+) T cell activation

BACKGROUND & AIMS: Cyclophilin-inhibitors have potent antiviral activity against Hepatitis C virus (HCV) and are promising candidates for broad-spectrum antiviral therapy. Cyclosporine A (CsA) acts immunosuppressive by blocking T cell activation and antigen presentation. Alisporivir, a non-immunosuppressive CsA analog in clinical development, does not inhibit T cell activation. In this study we explored the impact of alisporivir on antigen presentation. METHODS: Hepatoma cells endogenously expressing the epitope-restricting major histocompatibility complex-class I (MHC-I) allele HLA-A2 and constitutively expressing a viral antigen were established to study the impact of cyclophilin-inhibitors on antigen presentation. Antigen-specific CD8(+) T cell activation and MHC-I surface expression were measured to quantify antigen presentation. RESULTS: Our work establishes a novel cell culture model to study antigen presentation in liver-derived cells. Authentic regulation of antigen presentation was ensured by the action of pro- and anti-inflammatory cytokines. Alisporivir pretreatment stimulated antigen presentation by hepatoma target cells, leading to enhancement of antigen-specific CD8(+) T cell activation by 40%. Alisporivir, as well as a panel of other cyclophilin-inhibitors, induced an increase of MHC-I and beta-2 microglobulin on the surface of several cell lines. The drug neither enhanced MHC-I transcript or protein levels nor affected surface expression of other proteins or protein trafficking in general. Proteasome-inhibitors completely blocked the alisporivir-directed enhancement of surface MHC-I, suggesting an influence of the drug on peptide-availability. CONCLUSIONS: Alisporivir stimulates antigen presentation by inducing enhanced MHC-I surface expression, thereby promoting antigen-specific CD8(+) T cell activation. This immunostimulatory function might further contribute to the antiviral activity of non-immunosuppressive cyclophilin-inhibitors.