Gene therapy can be defined as the insertion of functional genes into cells to treat a disease. Cellular augmentation, whereby gene transfer confers a novel function to the cell, has proved to be useful in designing strategies for the treatment of cancer. In particular, a variety of cell types may be transduced with immune response genes that are intended to elicit a more effective immune attack against tumor cells. This process has been termed transgenic immunotherapy. Preclinical studies involving the transduction of tumor cells, stromal cells, and lymphocytes with a number of immune response genes have demonstrated potent cytotoxic lymphocyte responses against tumor cells, and in some cases the induction of long-lasting immunity against tumor rechallenge. It is hoped that this form of cancer immunotherapy will permit the development of vaccines effective in eradicating minimal residual disease and immunizing individuals at risk for cancer.