Gene therapy is a medical strategy that aims to treat or prevent disease by modifying the genetic material of a patient’s cells. Approaches include supplying a functional copy of a defective gene, repairing a mutation, altering gene expression, or introducing a new gene to help fight disease. The objective can be to correct a single-gene disorder, to improve immune responses against cancer, or to provide a long-term source of a missing protein. Techniques range from adding DNA or RNA to making precise edits in the genome.

Basic concepts and classifications

Clinical interventions are usually somatic: they alter non‑reproductive cells and affect only the treated person. Germline modification, which would change eggs, sperm or embryos and pass changes to future generations, is widely restricted or prohibited in many countries. Operationally, therapies are also classified by delivery method: in vivo delivery introduces the genetic material directly into the body, whereas ex vivo approaches remove cells, modify them in the laboratory, and return them to the patient.

Delivery systems and methods

Because naked DNA and RNA are fragile and may be quickly degraded or fail to enter target cells, most clinical strategies use delivery systems called vectors. Viral vectors—engineered viruses that carry therapeutic genetic material—are common. Examples of vector families used in human studies include adenovirus, lentivirus, and adeno‑associated virus (AAV). Nonviral delivery methods include lipid nanoparticles, plasmid DNA with electroporation, and other physical or chemical carriers. The process of introducing genetic material is often described as transfection (usually nonviral) or transduction (viral).

Clinical applications and notable examples

Gene therapies have been developed for inherited metabolic disorders, some forms of inherited blindness, blood disorders, and certain cancers. Early successes include treatments for some forms of severe combined immunodeficiency (SCID) and approved products that deliver genes to the eye or to other target tissues. One regulatory milestone in Europe was approval of a product that delivered a functioning lipase gene to muscle to treat a rare disorder that causes fat‑processing failure and recurrent pancreatitis; that treatment used a viral vector and received marketing authorisation in the EU. Other notable clinical developments include gene‑based treatments for spinal muscular atrophy and engineered immune‑cell therapies (CAR‑T) that have transformed management of some hematologic cancers.

Benefits and limitations

Advantages of gene therapy include the potential for long‑lasting, and in some cases one‑time, treatments; the ability to address diseases with no effective conventional therapies; and the capacity to target molecular causes directly. Limitations include challenges achieving efficient delivery to every affected cell, variability in how long an effect lasts, manufacturing complexity, and high cost in many current products.

Risks, safety and monitoring

Important safety concerns are immune responses to the vector or the introduced protein, unintended insertion of genetic material that can disrupt other genes (insertional mutagenesis), and off‑target changes when genome‑editing tools are used. Because risks may appear months or years after treatment, clinical programmes typically include long‑term follow‑up and regulatory oversight. Ongoing research aims to improve targeting, reduce immune reactions, and increase precision of gene editing.

Regulation, ethics and access

Regulatory frameworks vary by jurisdiction but generally require phased clinical trials, evidence of safety and efficacy, and post‑marketing surveillance. Ethical issues include fair access to costly therapies, informed consent, and debates about heritable genome modification. Most countries maintain strict limits on germline editing while supporting regulated clinical development of somatic gene therapies.

Research directions

Active areas of research include improving vector design, developing nonviral delivery platforms, enhancing gene‑editing precision (for example with CRISPR‑based techniques), and applying gene therapy to common diseases. Researchers are also working on manufacturing scale‑up and strategies to make treatments more affordable and widely available.

Further reading