The role of thymic versus peripheral epithelium in the regulation of the antigen-specific CD8 T-cell repertoire is still largely unresolved. We generated TCR-b chain transgenic mice in which an increased frequency of peripheral CD8 T cells recognizes an epitope from a viral oncoprotein (HPV16E7) in the context of H-2D b MHC class I. When T cells from these mice developed through the thymus of mice expressing functional E7 protein from a keratin 14 promoter, no major perturbation to transgenic T-cell development in the thymus was observed in these double-transgenic mice. In contrast, peripheral CD8 T-cell responses in the single-transgenic, K14E7 mice, including those unrelated to E7 antigen, are reduced whereas CD4 T-cell responses and antibody production are unchanged in these mice. Peripheral non-responsiveness among CD8 T cells was mediated largely by CD4 1 CD25 1 T cells. This suggested that epithelium expressing HPV16E7 protein inducesTreg that specifically down-regulate CD8 T-cell responses in the periphery. This may have important consequences for the treatment of cervical pre-cancers and provides a model for understanding differential suppression of T and B lymphocyte subsets by Treg.Key words: Skin . Suppression . T cells . Thymus . Transgenic mice
IntroductionT-cell development starts in the thymus, where lymphocytes expressing TCR recognize self-peptides bound to MHC class I. Immature T cells are either deleted if the affinity of interaction is high (negative selection) or retained for export to the periphery if the affinity is low (positive selection). Medullary epithelial cells and DC are thought to induce negative selection whereas cortical epithelial cells positively select the T-cell repertoire [1][2][3][4]. Evidence for the role of cortical epithelial cells in positive selection comes from studies of MHC expression driven from a keratin 14 (K14) promoter in otherwise MHC-deficient mice [5,6]. In contrast, expression of protein and peptide antigens in K14 1 thymic epithelium results in the deletion of antigen-specific CD8 T cells and the editing of the transgenic TCR [7][8][9]. Consequently, depending on the model, T cells are either positively selected or negatively selected after contact with thymic epithelium. HPV16E7 is one of the key oncogenes expressed during progression to cervical cancer: the protein is expressed in the epithelial cells of the cervix during human papillomavirus (HPV) infection and subsequent cancer development [10]. Given that mice cannot be naturally infected with HPV, human cervical cancer has been modeled in mice by transgenic expression of HPV16E7 leading to E7 expression in the thymus and peripheral epithelial sites, e.g. skin keratinocytes [11,12]. The first such K14E7 transgenic mice were generated on an FVB mouse
481background that failed to present the dominant CD8 T-cell peptide identified in the C57BL/6 background [12]. Subsequently, K14E7FVB Â C57 F1 mice were generated and shown to have poor CD8 T-cell responses that were attributable to the induction of per...