Gene therapy of malignant tumors

New techniques in molecular biology and increasing insights in the genetic basis of tumorigenesis led to the development of therapeutic agents compose d of genetic information. The majority of gene therapy trials is targeted t owards cancer therapy. The most frequently used strategy is immunotherapy w hich comprises transfer of genes encoding cytokines, costimulatory molecule s or tumorspecific antigens to enable cells of the immune system to identif y and destroy tumor cells. The second important strategy makes use of suici de genes to selectively kill tumor cells. Compensation of genetic defects b y the downregulation of activated oncogenes or the restoration of tumor sup pressor gene functions is the third concept to revert the malignant phenoty pe of cancer cells.