CAR-T cell therapy is a form of immunotherapy that uses a patient’s own T-cells to recognise and attack cancer cells. It has shown significant clinical benefit in several blood cancers and represents a fundamentally different approach to treatment compared with conventional drugs. CAR-T therapy combines cell biology, genetic engineering and advanced manufacturing. This article explains what CAR-T therapy is, how it works, and how these therapies are manufactured.
Starting with the immune system: T-cells
To understand CAR-T, it helps to start with the cell it is built from. A T-cell is a type of white blood cell (a lymphocyte) and one of the immune system’s key defenders. Like all blood cells, T-cells originate from stem cells in the bone marrow. Immature T-cells then travel to the thymus, where they mature before entering circulation.
What makes T-cells important is their surface receptors. A native T-cell recognises threats through its T-cell receptor (TCR), which detects fragments of protein (peptides) displayed on other cells by molecules called MHC. When a T-cell identifies an abnormal cell, cytotoxic T-cells bind to it and release proteins such as perforin and granzymes that trigger cell death.
How cancers evade the immune system
Many cancers survive because they can avoid immune detection and destruction. Blood cancers may do this by resembling normal cells, suppressing local immune responses, or disrupting the body’s ability to produce healthy immune cells. The result is an ineffective anti-tumour immune response, where the immune system detects abnormalities but cannot mount an effective and sustained attack.
CAR-T therapy is designed to overcome this limitation by enabling a patient’s T-cells to recognise cancer cells more effectively.
What a CAR actually is
The “CAR” in CAR-T stands for Chimeric Antigen Receptor. It is a synthetic receptor, engineered in the laboratory and not found in nature, that is introduced into a patient’s T-cells so they can recognise cancer directly.
A CAR is called chimeric because it combines components from different sources into a single construct:
- An extracellular targeting domain, usually a single-chain variable fragment (scFv) derived from an antibody, which is chosen to bind a specific protein (antigen) found on the surface of the cancer cell.
- A hinge and transmembrane domain that anchor the receptor in the cell membrane.
- Intracellular signalling domains, typically a CD3ζ activation domain paired with a co-stimulatory domain such as 4-1BB (CD137) or CD28, which activate the T-cell and promote tumour cell killing and proliferation after target recognition.
There is one crucial difference between a CAR and a native T-cell receptor. A natural TCR can only recognise a target when that target is presented via MHC. A CAR bypasses this requirement by recognising its antigen directly on the cell surface, independent of MHC. This allows CAR-T cells to identify cancer cells that might otherwise escape immune recognition.
The most clinically validated targets to date are CD19, expressed on B-cell malignancies such as acute lymphoblastic leukaemia and certain lymphomas, and BCMA, expressed in multiple myeloma. Because a target antigen can also be present on healthy cells, CAR-T therapy can produce predictable “on-target, off-tumour” effects. For example, CD19 is expressed on normal B-cells as well as malignant B-cells. This is one reason why CAR-T therapies are delivered and monitored in specialised treatment centres.
The manufacturing journey
- Collection (leukapheresis).
The process begins by collecting the patient’s white blood cells through leukapheresis, a procedure that separates mononuclear cells, including T-cells, from the rest of the blood and returns the remaining blood components to the patient. This apheresis product serves as the starting material for manufacturing. - Selection and activation.
In the manufacturing facility, T-cells are enriched from the apheresis product, often using magnetic cell selection techniques. The selected T-cells are then activated using reagents that mimic signals involved in a natural immune response, typically anti-CD3/anti-CD28 stimulation. This prepares the cells for genetic modification and proliferation. - Genetic modification (transduction).
The activated T-cells are engineered to express the CAR. Most approved therapies use viral vector-mediated transduction, typically with lentiviral or gammaretroviral vectors, to introduce the CAR gene. Because the inserted gene becomes part of the cell’s genetic material, it is passed to daughter cells as the population expands. Non-viral approaches, including transposon systems and mRNA-based methods, are also being investigated. - Expansion.
The engineered CAR-T cells are expanded under controlled conditions, often using automated bioreactor systems, until sufficient cell numbers are obtained for treatment. This process can increase the cell population many hundred-fold. - Formulation, cryopreservation and release.
The expanded cells are washed, concentrated and formulated into the final therapeutic product. Before release, the product must pass a comprehensive range of quality control tests, including sterility, mycoplasma and endotoxin testing, cell viability and identity testing, transduction efficiency and vector copy number (VCN) assessment, potency testing, and, for viral-vector products, replication-competent lentivirus or retrovirus (RCL/RCR) testing. The product is then typically cryopreserved and transported to the treating hospital under controlled conditions.
The total elapsed time from cell collection to infusion is often referred to as “vein-to-vein” time. This metric reflects both manufacturing performance and the logistics required to deliver treatment within a clinically meaningful timeframe.
Completing the journey: the patient’s treatment
Manufacturing produces the therapy, but two clinical steps complete the process. Before the cells are returned, most patients receive a short course of lymphodepleting chemotherapy. This reduces existing immune cells and creates an environment that supports CAR-T cell engraftment and expansion.
The CAR-T cells are then infused back into the patient, where they circulate, recognise their target antigen and eliminate cancer cells while continuing to proliferate in vivo.
Why manufacturing is the linchpin
The biological concept behind CAR-T therapy is relatively straightforward. Delivering a safe, effective and consistent product for an individual patient is considerably more complex. Every stage of the manufacturing process, from cell selection and activation to genetic modification, expansion, formulation and release testing, must be performed under tightly controlled conditions and documented to meet regulatory requirements.
Manufacturing capability and process control are therefore central to the successful delivery of CAR-T therapies. As the use of CAR-T therapies has expanded in Australia, manufacturing has remained a critical component in translating these treatments from development into clinical practice.
CAR-T therapies differ from conventional medicines because they are personalised cellular products manufactured for individual patients. Their effectiveness depends not only on the biological design of the therapy but also on the quality and consistency of the manufacturing process.
Understanding how CAR-T therapies are produced provides important context for both their clinical impact and the operational challenges involved in delivering them safely and reliably.
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This educational series was written by Josh Downing and designed by Ryan Harding as part of the Cell Therapies Marketing team.
