Breast cancer is considered as the major cause of mortality by cancer for women. Even if chemotherapy, radiotherapy and surgery have improved the life expectancy of patients bearing tumours, breast cancer is responsible for the death of 42,000 women per year in USA and 25,000 women in France. In this context, cancer vaccines may add an attractive alternative therapeutic strategy to the current existing treatments. We describe here the construction of recombinant vaccinia viruses co-expressing a tumour associated antigen (MUC 1) and an "adjuvant" cytokine, which have potential applications in the active immunotherapy of breast cancer. Indeed, recombinant vaccinia viruses have been extensively used during the past decade to induce a protective response against a whole variety of pathogens, and has proven to be of great value in the elicitation of a cellular immune response leading to the rejection of tumour grafts in mouse models.