Gene therapy of cancer includes strategies for augmentation of immunotherapeutic and chemoterapeutic approaches. These strategies mainly involve ex vivo and in vivo cytokine gene transfer, drug sensitization with genes for prodrug delivery, and the use of drug-resistance genes for protecting bone marrow from high-dose chemotherapy (1 ). Vector development remains the primary focus for any future research in the field. Retroviral vectors, especially those derived from Moloney murine leukemia virus (MoMLV), remain among the most widely utilized vectors in gene therapy trials.