Gene therapy provides modern medicine with new perspectives that were unthinkable two decades ago. Progress in molecular biology and, especially, molecular medicine is now changing the basics of clinical medicine. Reports of long-term side effects of the first successful human gene therapy study have slowed the penetration of DNA usage into clinical routine. However, the main safety problem lies in the secure and efficient delivery of genes into target cells and tissues. A number of older and more recently discovered techniques have been developed for therapeutic gene transfer. A variety of viral and non-viral possibilities are available for basic and clinical research. This review summarizes the delivery routes and methods for gene transfer used in gene therapy. The best known are viral vectors derived from adenoviruses and adeno-associated viruses. Specific properties of lentiviruses and retroviruses ensure their status in current gene therapy procedures. Recent advances in the preparation of lipoplexes and greater safety support the use of naked DNA transfer. The latest approach, using bacteria as vectors for gene therapy or as in situ producers of therapeutic proteins (alternative gene therapy), must undergo critical evaluation in further experiments.

Keywords: Viruses - classification, Viruses - genetics, Electroporation, Gene Expression Regulation, Gene Transfer Techniques, Genetic Therapy - methods, Genetic Vectors, Oligodeoxyribonucleotides, Viruses - genetics