Retroviral Transfer of the Herpes Simplex Virus-Thymidine Kinase (HSV-tK) Gene for the Treatment of Cancer

Gene therapy is defined as the alteration of the genetic material of a cell with resultant benefit to a patient. Gene transfer has two broad categories: one in which a therapeutic gene is delivered to the cells with the aim of treating a disease; and another where a marker gene is delivered to label a cell type to determine the fate of a cell or the marker gene. Gene therapy is now becoming a rapidly developing therapeutic modality for experimental treatment of some cancers and diseases that have no alternative treatment (1 ,2 ).