Gene therapy is moving from experimental science to clinical reality, offering cures for diseases once thought incurable by directly correcting the genetic errors at their source.
The FDA has approved over 30 gene and cell therapies as of 2026, marking a dramatic acceleration from just a handful of approvals five years ago. These therapies treat conditions ranging from inherited blindness and spinal muscular atrophy to certain blood cancers. The first in vivo gene therapy, Luxturna, was approved in 2017 to treat a rare form of inherited retinal dystrophy.
Gene therapy works by delivering a functional copy of a gene into a patient's cells to compensate for a defective or missing gene. The most common delivery vehicle is an adeno-associated virus (AAV) vector, a harmless virus modified to carry the therapeutic gene. AAV vectors are preferred because they do not cause disease in humans and can target specific cell types.
The most expensive drug in history is a gene therapy. Hemgenix, approved in 2022 for hemophilia B, costs $3.5 million per treatment. However, a single infusion can eliminate the need for lifelong, incredibly expensive clotting factor replacement therapy that can cost $500,000-$800,000 per year, making it cost-effective over a patient's lifetime.
Spinal muscular atrophy (SMA), once the leading genetic cause of infant death, is now treatable with gene therapy. Zolgensma delivers a functional SMN1 gene to motor neurons, halting disease progression. Children treated before showing symptoms have achieved normal motor milestones — sitting, standing, and even walking — outcomes that would have been impossible a decade ago.
Researchers at University College London successfully treated a young girl's aggressive leukemia in 2015 using "off-the-shelf" gene-edited T-cells from a healthy donor. This approach, called universal CAR-T therapy, could dramatically reduce the cost and waiting time for cell-based cancer treatments compared to the current method of engineering each patient's own cells.
In vivo gene editing, where CRISPR components are delivered directly into the body rather than editing cells in a lab, achieved a major milestone in 2023. Intellia Therapeutics reported that a single intravenous infusion of CRISPR therapy successfully inactivated the disease-causing gene in patients with transthyretin amyloidosis, with reductions in the toxic protein exceeding 90%.
The first gene therapy for Duchenne muscular dystrophy, Elevidys, received accelerated FDA approval in 2023. DMD is caused by mutations in the dystrophin gene, the largest known human gene. Because the full gene is too large to fit in an AAV vector, the therapy delivers a shortened but functional version called micro-dystrophin.
Gene therapy is being explored for HIV treatment. Several patients have been functionally cured of HIV after receiving stem cell transplants from donors with a natural CCR5-delta32 mutation that prevents the virus from entering cells. Researchers are now working on gene therapies that could edit a patient's own cells to carry this protective mutation without requiring a donor transplant.
Sickle cell disease became the first condition treated with an approved CRISPR-based therapy when Casgevy received FDA approval in December 2023. The therapy edits a patient's blood stem cells to produce fetal hemoglobin, which prevents red blood cells from sickling. In clinical trials, over 90% of treated patients remained free from severe pain crises for at least a year.
Delivery remains the single greatest challenge in gene therapy. AAV vectors cannot carry large genes, sometimes trigger immune responses that neutralize the therapy, and do not efficiently target all cell types. Researchers are developing larger-capacity vectors, including lentiviruses and non-viral delivery systems like lipid nanoparticles, to overcome these limitations.
In 2024, a landmark clinical trial at the University of Pennsylvania used gene therapy to restore hearing in children born with profound deafness caused by mutations in the OTOF gene. After a single injection into the cochlea, children who had never heard sound began responding to voices and music within weeks — a result that stunned even the research team.
Gene therapy manufacturing is extraordinarily complex and expensive. Producing a single batch of AAV vector can cost over $500,000 and take months. The industry is racing to develop scalable manufacturing processes, including insect cell and stable producer cell line technologies, to bring costs down and make these therapies accessible to more patients.
Insurance coverage for gene therapy is evolving rapidly. The high upfront cost has led to innovative payment models, including outcomes-based agreements where insurers pay only if the therapy works, and installment plans that spread payments over multiple years. Some countries are exploring subscription-style models where a government pays a flat annual fee for unlimited access to a manufacturer's gene therapy.