Live attenuated viruses used as vaccines are known for their efficacy to elicit protective immunity against viral diseases. More recently, with an increasing number of tumor-associated antigens (TAA) being identified and molecularly cloned (1 ) the development of vaccines for cancer immunotherapy has gained considerable interest. In particular, live recombinant viral vectors seem to be appropriate delivery systems for efficient presentation of TAA to the immune system. The promise of viral vectors is likely to be founded on their capacity for high-level expression of target genes combined with their intrinsic property to activate immunological control systems mimicking an infection with a disease causing agent.