Autoimmune hepatitis type 2 (AIH-2) is a severe organ-specific disorder characterized by liver kidney microsomal antibody type 1 targeting cytochrome P4502D6 (CYP2D6). Growing evidence implicates the involvement of CD8 T cell immune responses in its pathogenesis. We investigated CYP2D6-specific CD8 T cell human leukocyte antigen (HLA)-A2 restricted responses in AIH-2 (20 patients, 11 HLA-A2؉). Binding affinity of CYP2D6 peptides to HLA-A2 was predicted by the algorithm SYFPEITHI and assessed in vivo by T2 cell assays. CD8 T cell interferon (IFN)-␥ production was assessed via intracellular cytokine staining, cytotoxicity via chromium release assay, and frequency of circulating and intrahepatic CYP2D6-specific CD8 T cells via tetramer staining. CYP2D6-specific CD8 T cell reactivity was tested at diagnosis and during treatment and correlated with indices of disease activity. Seven CYP2D6 peptides with high HLA-A2 binding affinity colocalizing with known B cell or CD4 T cell epitopes were selected. Five sequences inducing high levels of IFN-␥ were used for HLA-A2 tetramer construction. Frequency, IFN-␥ production, and cytotoxicity of CYP2D6-specific CD8 T cells were higher at diagnosis than during treatment. Intensity of CYP2D6-specific CD8 T cell responses correlated with disease activity. Immune responses to CYP2D6 245-254 were the strongest both at diagnosis and during treatment. Conclusion: HLA-A2-restricted, CYP2D6-specific CD8 T cell immune responses vary according to disease stage and correlate with hepatocyte damage. CD8 T cell targets on CYP2D6 -in particular CYP2D6 245-254 -may be the focus of novel immune intervention in AIH-2. (HEPATOLOGY 2007;46:472-484.