CAR T-cell therapy is a cancer treatment in which a person’s own T cells are changed in the laboratory to make a protein called a chimeric antigen receptor, or CAR, which helps them attach to specific proteins on cancer cells.
It is one of the best-studied examples of cell-based medicine, and it sits alongside work described in stem cell research, although the cells involved are immune cells rather than stem cells.
How CAR T cells work
The National Cancer Institute places CAR T-cell therapy within T-cell transfer therapy, which it describes as a type of immunotherapy that makes a person’s own immune cells better able to attack cancer. There are two main types: tumor-infiltrating lymphocyte (TIL) therapy and CAR T-cell therapy. Both involve collecting a person’s own immune cells, growing large numbers of them in the lab and giving them back through a needle in a vein.
The NCI explains that CAR T-cell therapy is similar to TIL therapy, but the T cells are changed in the lab so that they make the CAR protein before they are grown and given back. CARs are designed to allow the T cells to attach to specific proteins on the surface of cancer cells, improving their ability to attack them.
Because the cells come from the person receiving them, the therapy is described as autologous. That differs from products made from donor cells, a category the FDA also regulates and that is covered in the guide to FDA regulation of cell therapy.
The treatment process
According to the NCI, the process of growing T cells in the lab can take 2 to 8 weeks. During this time a person may have treatment with chemotherapy and sometimes radiation therapy to get rid of other immune cells, because reducing the immune cells helps the transferred T cells to be more effective.
After those treatments, the lab-grown T cells are given back through a needle in a vein. The steps, from collection to infusion, make this a complex and specialised procedure rather than a routine drug.
How it differs from TIL therapy
The two forms of T-cell transfer start from different cells. According to the NCI, TIL therapy uses T cells called tumor-infiltrating lymphocytes that are found in the tumor itself. Doctors test these lymphocytes in the lab to find out which ones best recognize tumor cells, and the selected lymphocytes are treated with substances that make them grow to large numbers quickly.
The reasoning behind TIL therapy is that lymphocytes in or near a tumor have already shown the ability to recognize tumor cells, but there may not be enough of them to kill the tumor or overcome the signals the tumor releases to suppress the immune system. Giving large numbers of the best-reacting lymphocytes can help to overcome those barriers.
CAR T-cell therapy takes a different route. Instead of selecting cells that already recognize the tumor, it changes the T cells in the lab so that they carry the CAR protein. The NCI notes that a TIL therapy has been approved by the FDA to treat melanoma and has been described as the first cell therapy approved for a solid tumor, while its use in other cancers is still experimental. TIL therapy can cause capillary leak syndrome, in which fluid and proteins leak out of tiny blood vessels into surrounding tissues, resulting in dangerously low blood pressure.
What has been approved and what is experimental
The NCI reports that several CAR T-cell therapies have been approved by the FDA for blood cancers; the FDA’s licensed-products list gives the current set. It also says CAR T-cell therapy has been studied for the treatment of solid tumors, including breast and brain cancers, but use in such cancers is still experimental.
The FDA publishes its list of licensed cellular and gene therapy products, maintained by its Office of Therapeutic Products, on its approved products page, which is the place to confirm whether a specific product is licensed and for which use.
The distinction matters. An approval applies to a defined product and a defined use. Anything outside those uses, including solid tumors, belongs to research and clinical trials rather than established care.
Taken together, these points explain how to read news about the therapy. A report about success in a blood cancer does not carry over to a solid tumor, a report about one engineered cell product does not describe every other, and a regulator’s licensed-product list is a better guide to current approvals than a headline.
Side effects and safety
The NCI states that T-cell transfer therapy can cause side effects, and that how serious they are depends on how healthy a person is before treatment, the type of cancer, how advanced it is, the type of therapy and the dose. Doctors and nurses cannot know for sure when or if side effects will occur.
CAR T-cell therapy can cause a serious side effect known as cytokine release syndrome. It occurs when the transferred T cells, or other immune cells responding to them, release a large amount of cytokines into the blood. A sudden increase can cause fever, nausea, headache, rash, rapid heartbeat, low blood pressure and trouble breathing. Most people have a mild form, but in some people it may be severe or life-threatening.
The NCI adds that although CAR T cells are designed to recognize proteins found only on cancer cells, they can also sometimes recognize normal cells. Depending on which normal cells are recognized, this can cause a range of side effects, including organ damage.
These side effects are the reason the therapy is given under close medical supervision. The NCI tells readers that it is important to know which signs to look for and what to do if problems start, which is a task for the treating team and not for general reading.
Where research is heading
The NCI says researchers hope to expand use of these immunotherapies while making them safer and more effective. That includes the experimental work in solid tumors noted above.
Laboratory systems such as the tissue models described in what are organoids are among the tools researchers use to study disease outside the body, and cell-based cancer treatments are tested in clinical trials that follow the phase structure laid out by regulators.
Whether CAR T-cell therapy or any other cancer treatment is appropriate for a particular person is a decision for a licensed physician who knows that person’s situation, and not something that general information can settle.
Frequently asked questions
Is CAR T-cell therapy a stem cell therapy?
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No. CAR T-cell therapy uses a person’s own T cells, which are immune cells, and changes them in the laboratory. It is a cell therapy but not a stem cell therapy.
What does CAR stand for?
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CAR stands for chimeric antigen receptor, a protein that is designed to let the T cells attach to specific proteins on the surface of cancer cells.
Is CAR T-cell therapy approved for solid tumors?
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According to the National Cancer Institute, approvals are for blood cancers, and use in solid tumors such as breast and brain cancers is still experimental.
What is cytokine release syndrome?
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It is a serious side effect in which transferred T cells or other responding immune cells release a large amount of cytokines into the blood, causing symptoms such as fever and low blood pressure.
