Autoantigen‐specific regulatory T cells, a potential tool for immune‐tolerance reconstitution in type‐2 autoimmune hepatitis

Effector CD4 and CD8 T cell immune responses to cytochrome P450IID6 (CYP2D6), the autoantigen of autoimmune hepatitis type 2 (AIH‐2), are permitted by a numerical and functional impairment of CD4posCD25high regulatory T cells (T‐regs). We aimed to investigate whether T‐regs specific for CYP2D6 immunodominant regions and restricted by the appropriate human leukocyte antigen (HLA)‐DR molecule can be generated in patients with AIH‐2 and can control CD4 and CD8 T cell effectors targeting identical or overlapping CYP2D6 regions. CYP2D6‐specific regulatory T cells (CYP2D6 T‐regs) were obtained from peptide‐pulsed monocyte‐depleted peripheral blood mononuclear cells of 17 patients with AIH‐2, who were positive for the predisposing HLA‐DR7 and/or HLA‐DR3 alleles. Their antigen specificity was assessed by cytofluorimetry using HLA class II tetramers and their cytokine profile by intracellular staining. T‐reg ability to suppress was ascertained by measuring reduction of CD4posCD25neg cell proliferation/effector cytokine secretion and of CD8 T cell cytotoxicity. The most efficient suppression of effector T cell proliferation, inflammatory cytokine release, and cytotoxicity was obtained by coculturing T‐regs with CYP2D6‐peptide‐loaded semimature dendritic cells (smDCs), and smDC‐CYP2D6 T‐regs also expressed high levels of FOXP3 (forkhead box P3). Possession of the appropriate HLA‐DR molecule and recognition of the CYP2D6 autoantigenic sequence were critical to the synergistic smDC‐CYP2D6 T‐reg immunoregulatory functions, and lack of either element led to poor control of responder cell proliferation and cytokine secretion. Moreover, interferon‐γ neutralization significantly boosted the suppressive ability of CYP2D6 T‐regs. Conclusion: T‐regs generated under CYP2D6‐specific conditions and cocultured with smDCs are highly effective at controlling autoreactive T cells, thus providing the basis for a powerful and tailored form of immunotherapy for AIH‐2. (HEPATOLOGY 2011;53:536‐547)