Selection and characterization of MUC1-specific CD8(+) T cells from MUC1 transgenic mice immunized with dendritic-carcinoma fusion cells

Mice transgenic for the human MUC1 carcinoma-associated antigen (MUC1.Tg) a re tolerant to immunization with MUC1 antigen. Recent studies, however, hav e demonstrated that immunization of MUC1.Tg mice with fusions of MUC1-posit ive tumour and dendritic cells (FC/MUC1) reverses MUC1 unresponsiveness and results in rejection of established MUC1-positive pulmonary metastases. He re we demonstrate that lymph node cells from MUC1.Tg mice immunized with th e FC/MUC1 fusion cells proliferate in response to MUC1 antigen by a mechani sm dependent on the function of CD4, major histocompatibility complex (MHC) class II, B7-1, B7-2, CD28, CD40 and CD40 ligand. The findings demonstrate that stimulation of lymph node cells with MUC1 results in selection of MUC 1-specific CD8(+) T cells. We show that the CD8(+) T cells exhibit MUC1-spe cific cytotoxic T lymphocyte (CTL) activity by recognition of MUC1 peptides presented in the context of MHC class I molecules K-b and D-b. The MUC1-sp ecific CD8(+) T cells also exhibit antitumour activity against MUC1-positiv e metastases, but with no apparent reactivity against normal tissues. These results indicate that immunization of MUC1.Tg mice with FC/MUC1 reverses i mmunological unresponsiveness to MUC1 by presentation of MUC1 peptides in t he presence of costimulatory signals and generates MHC-restricted MUC1-spec ific CD8(+) T cells.