Many studies have been conducted with the aim to stimulate a therapeutic immune response against tumors. In most cases, efforts have been directed toward the induction of tumor-specific cytotoxic T lymphocytes (CTL), because this T lymphocyte subpopulation is considered to play a major role in the destruction of tumor cells (1). In particular, vaccination protocols have been designed to increase the immunogenicity of intact cancer cells by using adjuvants or engineering tumor cells with cytokine or costimulatory molecule genes. A second line of research has employed immunization with tumor-associated antigens (TAA). These antigens are expressed from derepressed or mutated genes in tumor cells, and are recognized by CTL in the form of peptides associated with MHC class I molecules. Genes encoding TAA have been inserted into recombinant viral vectors, which are then used to infect the host’s cells and induce expression of the transgene. Moreover, immunization with purified TAA peptides or with antigen-presenting cells, such as dendritic cells, pulsed with TAA peptides have been proposed.