Cell and Gene Therapy Basics: CAR-T, AAV and Beyond

Cell therapy treats disease by giving a patient living cells, and gene therapy treats disease by adding, inactivating or editing genetic material. The two often overlap: CAR-T cell therapy takes a patient's T cells, adds a gene so they recognise cancer, and infuses them back.

In the EU these are advanced therapy medicinal products (ATMPs). As they move into routine care, hospital labs, pharmacy, QA and regulatory teams in India and the GCC need to understand how they are made, handled and controlled.

Key definitions: in vivo vs ex vivo

• Gene therapy: delivers genetic material to treat or prevent disease, for example a working copy of a faulty gene.
• Cell therapy: transfers living cells, either the patient's own (autologous) or a donor's (allogeneic).
• Gene-modified cell therapy: cells are genetically changed before infusion, as with CAR-T.
• Gene editing therapy: changes the patient's existing DNA sequence, for example with CRISPR.

In vivo therapy delivers the gene directly into the patient, usually by infusion or local injection of a viral vector. Gene therapies for spinal muscular atrophy and an inherited retinal dystrophy work this way.

Ex vivo therapy removes cells, modifies them in a manufacturing facility and returns them, as with CAR-T. Cells can be tested before infusion, but logistics are far more complex.

Viral vectors and modalities at a glance

Most gene therapies use modified viruses with their replication genes removed. Adeno-associated virus (AAV) vectors are small and not known to cause disease. They mostly remain in the nucleus as episomes rather than integrating, and different serotypes favour tissues such as liver, muscle, retina or the nervous system. Limits include a small packaging capacity (about 4.7 kilobases), pre-existing antibodies that can exclude some patients, and immune or liver toxicity at high doses.

Lentiviral vectors, derived from HIV-1 and made replication-incompetent, integrate into the host genome, so the gene passes to every daughter cell. That suits ex vivo work with T cells and blood stem cells. Integration carries a risk of insertional mutagenesis, so manufacturers measure vector copy number and regulators require long-term follow-up. Some CAR-T products use gammaretroviral vectors instead.

The CAR-T process step by step

A chimeric antigen receptor (CAR) joins an antibody-derived binding domain, which recognises a protein on cancer cells such as CD19 or BCMA, to T-cell signalling domains. The first CAR-T therapy was approved in the US in 2017. A typical autologous process:

1. Leukapheresis: the patient's white cells are collected at a qualified apheresis unit.
2. Shipment: cells are labelled under strict chain-of-identity rules and shipped, often cryopreserved, to the manufacturer.
3. Engineering: T cells are activated and transduced with a vector carrying the CAR gene.
4. Expansion: CAR-T cells are grown to the target dose.
5. Testing and release: QC confirms identity, purity, potency and safety.
6. Lymphodepletion: the patient usually receives chemotherapy shortly before infusion.
7. Infusion and monitoring: cells are thawed, infused and the patient is closely observed.

In India, the first indigenously developed CAR-T therapy was approved by CDSCO in 2023.

Manufacturing and QC challenges

• Sterility: cells cannot be terminally sterilised, so the process relies on aseptic technique, closed systems and environmental monitoring. Short shelf life means rapid microbial methods are common, and some products are released before final sterility results under defined controls.
• Other safety tests: mycoplasma, endotoxin, replication-competent virus and vector copy number.
• Potency: assays such as CAR expression, cytotoxicity or cytokine release must reflect the mechanism of action, which is technically demanding.
• Vein-to-vein time: the interval from collection to infusion. Patients with aggressive disease may deteriorate while waiting, so every step is planned to keep it short.
• Chain of identity and custody: a patient mix-up would be catastrophic, so every step is traceable.

Safety: CRS and neurotoxicity

Cytokine release syndrome (CRS) is the most common serious acute toxicity of CAR-T. Activated T cells release large amounts of cytokines, causing fever, low blood pressure and low oxygen levels. It is graded with consensus criteria and treated with supportive care, the IL-6 receptor antibody tocilizumab and, if needed, corticosteroids.

Immune effector cell-associated neurotoxicity syndrome (ICANS) can cause confusion, speech difficulty and, rarely, seizures or cerebral oedema. Other risks include prolonged low blood counts, infections and low antibody levels.

Regulation: ATMPs and beyond

In the EU, ATMPs are regulated under Regulation (EC) No 1394/2007 in four groups: gene therapy, somatic cell therapy and tissue-engineered medicinal products, plus combined ATMPs. The European Medicines Agency's Committee for Advanced Therapies (CAT) assesses them. In the US, the FDA's Center for Biologics Evaluation and Research (CBER) is responsible.

In India, CDSCO regulates these products under the New Drugs and Clinical Trials Rules, 2019, supported by national gene therapy guidelines. GCC regulators such as the SFDA, MOHAP and emirate-level health authorities have their own requirements, so confirm current rules with the relevant authority before planning a trial or service.

Worked example: an Abu Dhabi hospital preparing to deliver CAR-T

A tertiary hospital in Abu Dhabi plans to offer an approved CAR-T product for adults with relapsed lymphoma. A haematologist leads a team from QA, pharmacy, the cell therapy lab, ICU and nursing. The readiness plan:

• Licensing: confirm with the Department of Health - Abu Dhabi which approvals the service needs.
• Site qualification: the manufacturer audits the apheresis unit and cell lab and trains staff.
• Storage: validated liquid nitrogen vapour-phase storage with continuous monitoring, alarms and a back-up plan.
• Chain of identity: two-person checks at collection, receipt, thaw and bedside.
• Toxicity management: written CRS and ICANS protocols, tocilizumab on site before every infusion, neurological assessments and ICU access.
• Quality system: deviation reporting, CAPA, competency records and a full mock run.

The mock run shows that thawing needs a second trained nurse on night shifts, a gap far better found before the first patient.

Careers in cell and gene therapy

Roles include GMP manufacturing technologists, QC microbiologists, flow cytometry analysts, QA and batch release staff, regulatory specialists, clinical research coordinators and hospital cell therapy lab scientists. Experience in aseptic processing, sterility testing and GMP documentation transfers well.

Common mistakes

• Handling an autologous product like a standard pharmacy item, without chain-of-identity checks.
• Underestimating vein-to-vein time when scheduling patients.
• Potency assays not linked to the mechanism of action.
• Discharging patients without clear CRS and ICANS warning signs and contacts.

Key takeaway: Gene therapy changes genetic material and cell therapy delivers living cells; CAR-T does both, ex vivo. Success depends as much on aseptic manufacturing, potency testing, chain of identity and toxicity management as on the science itself.

Frequently Asked Questions

What is the difference between cell therapy and gene therapy?

Cell therapy gives a patient living cells, their own or a donor's, to repair, replace or fight disease. Gene therapy changes genetic material, usually by delivering a gene with a viral vector. Some products combine both: CAR-T cells are a cell therapy whose cells are genetically modified before infusion, so they are called gene-modified cell therapies.

How long does CAR-T therapy take?

Timelines vary by product, manufacturer and patient. The process includes cell collection, shipment, manufacturing, quality testing and release, lymphodepleting chemotherapy, infusion and a period of close monitoring. Patients with aggressive cancers may need bridging treatment while their cells are made, so the treating team should give product-specific timelines.

What is cytokine release syndrome?

Cytokine release syndrome is an inflammatory reaction that occurs when activated immune cells, such as CAR-T cells, release large amounts of cytokines. Symptoms range from fever and fatigue to low blood pressure and breathing difficulty. It is graded with consensus criteria and managed with supportive care, tocilizumab and sometimes corticosteroids, which is why CAR-T centres need ICU access.

What does ATMP mean?

ATMP stands for advanced therapy medicinal product, the EU term for medicines based on genes, cells or tissues. ATMPs include gene therapy, somatic cell therapy and tissue-engineered medicines, plus combined products that include a medical device. They are regulated under Regulation (EC) No 1394/2007 and assessed by the EMA's Committee for Advanced Therapies.

Next steps

To understand genome editing and advanced therapies in depth, explore our Frontier Biotechnology: Genome Editing, Advanced Therapies and AI course. If you are heading towards QC or aseptic manufacturing, Pharmaceutical Microbiology and Contamination Control builds the core skills.

Related reading: CRISPR gene editing explained, media fill and aseptic process simulation and bacterial endotoxin testing methods. Questions about your path? Speak to a counsellor.