Most tumor cell line vaccines are lethally irradiated, but not genetically modified. However, a newer generation of tumor vaccines that have been genetically modified to enhance tumor-associated antigen presentation to patient T cells have reached early clinical trials. Based on extensive preclinical studies and clinical allogeneic prostate cancer vaccine data, a strong impression exists that ex vivo GM-CSF gene transfer may make human prostate cancer cell lines more potent in inducing clinically relevant antitumor immune responses in men with micrometastatic prostate cancer.