Transduction of dendritic cells (DC) can result in presentation of tumor-associated antigens and induction of immunity against undefined epitopes. The present studies demonstrate adenovirus (Ad)-mediated transduction of the β-galactosidase gene in mouse DC. Similar transductions have been obtained with the gene encoding the DF3/MUC1 tumor-associated antigen. We show that the Ad-transduced DC are functional in primary allogeneic mixed lymphocyte reactions. Mice immunized with Ad-transduced DC develop cytotoxic T lymphocytes that are specific for the β-galactosidase or DF3/MUC1 antigens. The results also demonstrate that Ad. MUC1-transduced DC induce a specific response which inhibits the growth of DF3/MUC1-positive tumors. These findings support the usefulness of Ad-transduced DC for in vivo immunization against tumor-associated antigens.