CD8+ T cells (T[CD8+]) can directly recognize malignant cells because processed fragments of tumor associated antigens (TAA), 8-10 amino acids in length and complexed with MHC class I molecules, are displayed on tumor cell surfaces. Tumor cells have been genetically modified in a variety of ways in efforts to enhance the immune recognition of TAA. An alternative strategy has been developed and involves the expression of TAA in recombinant or synthetic forms. This has been made possible by the recent cloning of TAA recognized by T[CD8+]. In addition to their use as synthetic peptides in vivo and in vitro, model TAA have expressed by """"""""naked"""""""" plasmid DNA injected intramuscularly or transdermally, and by recombinant viruses including vaccinia, fowlpox (rFV), and adenovirus (rAd). The expression of TAA in recombinant and synthetic forms allows increased control over the quantity, location, and kinetics of TAA presentation and can result in powerful, specific, anti-tumor immune responses. We have shown that these recombinant viruses are capable of eliciting powerful and specific anti-tumor T[CD8+] that can shown to directly kill tumor in vitro. More importantly, these recombinant and synthetic an?i-cancer vaccines have been shown to successfully immunized mice against subsequent development of a tumor challenge. Furthermore, these constructs have also been shown to be useful in adoptive immunotherapy strategies. Most surprisingly, these constructs are also useful in models of active immunotherapy. In work using synthetic peptides, insertion signal sequences fused to a minimal antigenic determinant synthetic peptides were found to elicit specific CD8+ T cell responses in murine model systems. Furthermore, these fusion peptides were found to prolong the survival of thymoma- bearing mice. The """"""""second generation"""""""" of recombinant viruses have been constructed and co-express model tumor antigens together with cytokines (TNF-alpha, IFN- gamma, GM-CSF, and IL-2), restriction elements (class I alpha-chains and beta2-m), and co-stimulatory and accessory molecules (B7-1 and ICAM-1). Preliminary results show that the co-expression of a model Ag together with IL-2 can be effective in an active immunotherapy model.
