Biochemistry · Topic
Gene therapy !
Gene therapy treats a disease by adding, silencing or correcting a gene inside the patient's cells.
Updated 2026-11-01
Key facts
- Strategies: add a healthy copy, silence a harmful gene (RNAi, antisense), correct or edit the gene (CRISPR).
- In vivo: the vector is given to the patient (e.g. AAV to liver, muscle or retina). Ex vivo: stem cells or lymphocytes are modified outside the body and reinfused.
- Vectors: adeno-associated viruses (AAV, do not integrate), lentiviruses (integrate, for dividing cells), lipid nanoparticles.
- Only somatic cells are treated; germline editing is not allowed in clinical practice.
- Approved examples: ADA-SCID, spinal muscular atrophy, RPE65 retinal dystrophy, haemophilia, β-thalassemia and sickle cell disease, CAR-T cells.
In detail
- CAR-T cells are the patient's T cells given, by a lentivirus, a chimeric receptor against a tumour antigen (e.g. CD19 in B-cell leukaemias and lymphomas).
- Risks: immune response to the vector, insertion at a site that activates an oncogene (insertional mutagenesis, seen in early SCID-X1 trials), off-target effects.
- AAVs stay as episomes: the effect lasts in non-dividing tissues (neurons, muscle, retina) but fades in dividing ones.
- Antisense oligonucleotides and small interfering RNAs (siRNA) are 'RNA' gene therapies: they do not change DNA, they alter splicing or degrade an mRNA.
- For sickle cell disease and β-thalassemia there is a CRISPR therapy that reactivates fetal haemoglobin by editing the BCL11A enhancer.
Clinical notes
- These treatments are very expensive and offered in few centres; access in Latin America is still limited.
- ADA-SCID was the first disease treated with gene therapy (1990).
Related conditions
- Adenosine deaminase deficiency (ADA-SCID)
- Sickle cell disease
- Thalassemias (α and β)
- Duchenne muscular dystrophy
Related
- CRISPR-Cas9 and genome editing
- Recombinant DNA and cloning
- RNA processing (cap, poly-A tail and splicing)
Test yourself
Think of the answer, then tap the question to see it.
How does in vivo gene therapy differ from ex vivo?
In vivo the vector is given to the patient; ex vivo the patient's cells are modified outside the body and reinfused.
What special risk do integrating vectors carry?
Insertional mutagenesis: they can insert next to an oncogene and switch it on.
How does a CAR-T cell work?
It is a patient's T cell modified with a chimeric receptor that recognises a tumour antigen and kills the tumour cell.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: What is gene therapy?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); What are genome editing and CRISPR-Cas9?: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.