Gene therapy, concepts, current trials and future directions.

Since the initial human clinical trials of retroviral-mediated gene transfer in the USA in 1989, numerous additional protocols are in process or have been proposed. In the first therapeutic protocol, to treat the genetic disease ADA deficiency, encouraging signs of clinical benefit have been observed in the first two patients. Gene-marking properties are being extensively used in many protocols, particularly in the area of autologous bone marrow transplantation for various cancers. The drug delivery potential of gene therapy is initially being evaluated through delivery of various lymphokines and cytokines in cancer therapy protocols. Testing has also begun for other genetic diseases, Familial Hypercholesterolemia and Hemophilia B. Vector systems and retroviral vectors are developing rapidly, and a clinical trial using a liposome-based delivery has started. The pace of technical development and clinical application has intensified. Although significant clinical therapies are expected from these initial studies, the full potential of gene therapy for wide applications still requires innovative research programs, directed towards true in vivo vectors.