Basically, gene therapy is a technique that modifies a person’s genetic material (DNA or RNA) to treat or cure disease. More formally as defined by the U.S. Food and Drug Administration (FDA), gene therapy is the administration of genetic material (RNA or DNA) to modify or manipulate the expression of a gene product or to alter the biological properties of living cells for therapeutic use. Gene therapies offer the potential to treat diseases or conditions for which no or few treatments exist. They are being studied to treat cancer as well as genetic, infectious, and other diseases. FDA considers any use of CRISPR-Cas9 gene editing in humans to be gene therapy.
U.S. Food and Drug Administration (FDA): What is Gene Therapy?
U.S. Food and Drug Administration (FDA): Human Gene Therapy for Rare Diseases
NCATS Toolkit for Patient-Focused Therapy Development: Genetic Therapeutics
American Society of Gene and Cell Therapy: Gene Therapy Basics