Genetic Medicine and Gene Therapy

Gene therapy is the medical practice of correcting a faulty gene inside a patient’s cells by delivering a working copy of that gene, silencing the broken one, or editing the DNA letter that causes the disease. It is a targeted intervention, not a wholesale rewrite of a person’s genome. The treatment addresses one specific gene or a small set of genes linked to a disease, while the rest of the patient’s DNA remains untouched. This is the central idea behind genetic medicine, and it separates real gene therapy from the popular myth of “rewriting your DNA.”

The field grew out of decades of work on inherited disorders like haemophilia, sickle cell disease, spinal muscular atrophy, and certain inherited forms of blindness. As of the mid-2020s, several gene therapies are approved for clinical use globally, and India has begun manufacturing its own CAR-T cell therapy for blood cancers. The science is moving from rare genetic diseases into common conditions such as high cholesterol and chronic infections.

How Gene Therapy Works

A gene therapy product has two parts: the genetic payload (the corrective DNA or RNA sequence, or the editing machinery) and the delivery vehicle that gets that payload into the right cells. Getting the payload to the right tissue, at the right dose, without triggering immune rejection is the harder half of the problem.

Replacement, Silencing, and Editing

There are three broad strategies. Gene replacement adds a functional copy of a gene to cells that carry a non-working version, used in spinal muscular atrophy and inherited retinal dystrophy. Gene silencing uses short RNA molecules to switch off a harmful gene, used in conditions like transthyretin amyloidosis. Gene editing, the newest approach, uses CRISPR-Cas9 or similar tools to make a precise cut and corrects the DNA letter responsible for the disease.

Each strategy changes the cells it reaches. None of them rewrite the rest of the genome.

Delivery: Viral Vectors and Lipid Nanoparticles

The genetic payload cannot cross a cell membrane on its own. It needs a carrier.

Viral Vectors

The most established carriers are engineered viruses, mostly adeno-associated virus (AAV) and lentivirus, stripped of their disease-causing genes and loaded with the therapeutic sequence. AAV is favoured for in vivo delivery because it is small, relatively non-pathogenic, and can target specific tissues based on its capsid variant. Lentivirus is used in ex vivo therapies, where a patient’s own cells are removed, modified in a lab, and re-infused.

Viral vectors are precise but expensive to manufacture, and pre-existing immunity to the carrier can block treatment in some patients.

Lipid Nanoparticles

Lipid nanoparticles, or LNPs, are tiny fat bubbles that wrap the genetic payload and fuse with cell membranes to release it inside. LNPs became famous as the delivery system for mRNA Covid-19 vaccines, and the same chemistry now ships gene-editing tools to the liver and other organs. They are cheaper to make than viral vectors, less likely to trigger anti-vector immunity, but harder to aim at tissues outside the liver.

The choice of carrier shapes which diseases a given therapy can address.

What Gene Therapy Does Not Do

Gene therapy does not change every cell in the body. It does not rewrite a patient’s full DNA. It does not pass corrections to children unless the therapy is applied to germline cells, which is banned in clinical practice in India and most other countries.

A liver-directed therapy edits liver cells; bone marrow cells and skin cells remain unchanged. An eye injection acts on retinal cells; the rest of the body is untouched. This tissue-level specificity is a feature, not a limitation: it keeps the intervention focused and reduces off-target risk.

Gene Therapy in India

India approved its first indigenous CAR-T cell therapy, NexCAR19, in late 2023, developed by IIT Bombay and ImmunoACT for B-cell lymphomas and leukaemias. The price point of roughly thirty to forty lakh rupees is a fraction of imported CAR-T products, opening access to Indian patients. The Department of Biotechnology, ICMR, and the Central Drugs Standard Control Organisation have published a regulatory framework for cell and gene therapy products. Public-sector hospitals at AIIMS, Tata Memorial, and CMC Vellore are running clinical trials in sickle cell disease, thalassaemia, and inherited retinal disorders.

For wider context, see our explainer on gene therapy versus gene editing and the broader landscape of epigenetics.

Risks and Open Questions

Gene therapy carries real risks. Viral vectors can trigger immune responses, sometimes severe. CRISPR-based edits can produce off-target changes elsewhere in the genome, though newer base-editing and prime-editing tools reduce that risk substantially. Long-term safety data are still being collected, since the oldest in-vivo therapies are barely a decade old. Cost remains the largest barrier outside specialist centres.

Affordability is the policy question that will define the next decade. A one-time gene therapy that cures a lifelong illness is cheap in lifetime terms but unaffordable as an out-of-pocket payment. India’s mix of public hospitals, indigenous manufacturing, and price-controlled procurement is one of the more promising models being tested anywhere.

FAQs

Does gene therapy change a person’s entire DNA?

No. Gene therapy targets one gene or a small set of genes inside specific tissues. The vast majority of the genome remains unchanged.

What is the difference between gene therapy and gene editing?

Gene therapy is the broader practice of treating disease by adding, silencing, or correcting genes. Gene editing is one technique within gene therapy that uses tools like CRISPR-Cas9 to make precise changes to DNA.

Are viral vectors safe?

Engineered viral vectors have their disease-causing genes removed and are generally safe, but they can trigger immune responses and, rarely, more serious adverse events. Patient screening and dose control reduce these risks.

What are lipid nanoparticles used for?

Lipid nanoparticles are fatty carriers that deliver RNA or DNA payloads into cells. They were used in mRNA Covid vaccines and are now used to deliver gene-editing tools, particularly to liver cells.

Can gene therapy be inherited by children?

Standard gene therapy targets body cells (somatic cells) and is not inherited. Germline editing, which would be inheritable, is not permitted in clinical practice in India or most other countries.

Is gene therapy available in India?

Yes. India approved its indigenous CAR-T cell therapy NexCAR19 in 2023, and several gene therapy trials are running at AIIMS, Tata Memorial, and CMC Vellore for sickle cell disease, thalassaemia, and inherited blindness.

Why is gene therapy so expensive?

Manufacturing viral vectors and patient-specific cell products is technically demanding and low-volume. Indian indigenous products are bringing costs down sharply compared to imported therapies.

Does gene therapy cure disease in one dose?

For some conditions, a single dose produces lasting benefit because corrected cells continue to function. For others, repeated dosing or follow-up treatment is needed. The duration of effect depends on which tissue is treated and how stable the correction is.

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