Since the approval of the many protocols in human gene therapy, 1 a new chapter in medicine has begun in which genes are the key elements for therapy. 2 – 4 The ultimate goal is to replace a defective or missing gene with the normal copy in the patient’s own tissues where the genes are normally expressed. Although this goal has not been reached with current technologies, rapid progress in research within the next decade will likely achieve most, if not all, of the ideal tenets of human gene therapy as envisioned by Anderson. 5 A rather unexpected direction that somatic gene therapy has taken is its application to the treatment of “nongenetic” diseases. These are the multifactorial cardiovascular, 6 neoplastic, 7 and infectious disorders 8 in which genetics only accounts for some of the etiologic factors. In these applications, genes are integrated into the patient’s own cells to produce products that ameliorate the disease phenotype. In other words, genes are used as drugs. The therapeutic outcome is achieved by the gene products delivered in vivo. Hence, the basis for somatic gene therapy has expanded to include both genetic and multifactorial disorders that can be treated by the delivery of recombinant gene products from genetically-modified host cells.