Dendritic cells (DC) derived from peripheral blood monocytes are currently being investigated in clinical trials for their role in stimulating the immune system. We performed a phase I/II clinical trial using human autologous DC transfected with cDNA of the human tumor antigen mucin (MUC1) as a vaccine in 10 patients with advanced breast, pancreatic or papillary cancer. After liposomal transfection, flow cytometry testing showed that 2% to 53% of the DC expressed mucin epitopes. Patients were immunized two or three times with 1 million transfected DC injected subcutaneously (s.c.). A vaccine-specific delayed-type hypersensitivity (DTH) reaction was observed in 3 out of 10 patients. After vaccination, 4 patients showed a 2- to 10-fold increase in the frequency of mucin-specific interferon-gamma (IFN-gamma)-secreting CD8+ T cells. We demonstrated the feasibility and safety of a vaccine consisting of autologous gene-transfected DC, and that immunologic responses could be induced even in patients with pretreated and advanced disease.