Above- Three essential tools for human gene therapy. AAV and lentiviral vectors are the basis of several recently approved gene therapies. Gene editing technologies are in their translational and clinical infancy but are expected to play an increasing role in the field.

BACKGROUND
Nearly five decades ago, visionary scientists hypothesized that genetic modification by exogenous DNA might be an effective treatment for inherited human diseases. This "gene therapy" strategy offered the theoretical advantage that a durable and possibly curative clinical benefit would be achieved by a single treatment. Although the journey from concept to clinical application has been long and tortuous, gene therapy is now bringing new treatment options to multiple fields of medicine. We review critical discoveries leading to the development of successful gene therapies, focusing on direct in vivo administration of viral vectors, adoptive transfer of genetically engineered T cells or hematopoietic stem cells, and emerging genome editing technologies.