Recently, new tumor vaccine approaches were developed in animal systems that modify tumor cells genetically to secrete certain cytokines. Engineering tumor cells to secrete cytokines in a paracrine fashion can induce powerful local cytokine effects without producing significant systemic toxicity. In addition to local inflammation, this approach can alter the presentation of tumor antigens or activation of tumor antigen-specific T lymphocytes, resulting in systemic antitumor immunity. The development of high efficiency gene transfer technologies such as defective retroviral vectors allows for the translation of these preclinical studies to clinical trials. However, before large investments are made in this area of gene therapy, it will be important to demonstrate that the actual gene transfer component of the strategy significantly enhances antitumor immune responses relative to alternative nongenetic approaches.