What Does CAR T-Cell Therapy Mean?

This page is for patients and caregivers who have heard the term CAR T-cell therapy and want to know what it involves. It covers how the treatment works, the main side effects, the FDA's 2025 changes, and when to call for help.

CAR stands for chimeric antigen receptor. Chimeric means built from parts of different sources. The receptor is a built protein. One end grips a target on the cancer cell. The other end is the switch a T cell uses to turn itself on.

T cells are the immune system's attack cells. CAR T-cell therapy gives them a receptor that helps them find and attach to cancer cells.

The target matters. FDA labels name CD19 as the target for products such as Kymriah, used in some lymphomas and leukemias. That is a protein on the surface of B cells, a type of white blood cell. For multiple myeloma, the target is BCMA, short for B-cell maturation antigen. The CARVYKTI label calls it a BCMA-directed autologous T cell therapy. Autologous means the cells came from you.

The National Cancer Institute lays out the steps. Blood is drawn and the T cells are pulled out. Those T cells are engineered to carry the CAR. They are then grown, or expanded, until there are hundreds of millions. Then they go back in by vein.

NCI puts the whole process at about 3 to 5 weeks.

That gap is a real planning problem, not a footnote. Ask whether you will need bridging treatment (treatment to hold the cancer back while you wait) during those weeks. Ask what happens if the batch fails and has to be made again. The CARVYKTI label says a second batch may be tried.

Lymphodepletion means lowering the number of immune cells in your blood. Before the infusion, you get chemotherapy for this.

The CARVYKTI label names the drugs: cyclophosphamide and fludarabine, both by vein, both daily for 3 days, at amounts based on body size.

Cytokine release syndrome, or CRS. When the new cells switch on, they release cytokines. Cytokines are immune signals. Too many at once cause fever, low blood pressure, and low oxygen. NCI says CRS can be managed in many patients with tocilizumab, sold as Actemra, and with steroids if needed.

Nerve and brain effects, often called ICANS. Signs include confusion, trouble finding words, tremor, changed handwriting, sleepiness, or seizures. NCI names steroids as the first treatment. If steroids fail, anakinra, sold as Kineret, may be used.

The label calls these reactions fatal or life-threatening in some cases. The monitoring rules below exist so that they are found quickly.

For years, CAR T therapy ran under a Risk Evaluation and Mitigation Strategy, or REMS. It required that hospitals and clinics giving these products be specially certified. They also had to keep tocilizumab on site, ready at once.

On June 26, 2025, the FDA dropped the REMS for six of these products. They are Abecma (idecabtagene vicleucel), Breyanzi (lisocabtagene maraleucel), Carvykti (ciltacabtagene autoleucel), Kymriah (tisagenlecleucel), Tecartus (brexucabtagene autoleucel), and Yescarta (axicabtagene ciloleucel).

Labeling changed at the same time:

• Stay near a health care facility for at least 2 weeks after the infusion.
• Do not drive for 2 weeks after the infusion.
• Be watched for at least 2 weeks. That includes daily checks for at least 1 week.

The boxed warning for CRS and nerve effects stayed. Dropping the REMS cut paperwork for hospitals. It did not cut the risk.

In plain terms, you need three things for those 2 weeks:

• a caregiver who can stay with you
• a place to sleep near the center
• someone else to drive

A boxed warning is the FDA's strongest safety warning on a drug label. The CARVYKTI label carries several:

• CRS
• nerve and brain effects
• a severe immune overreaction called HLH, or macrophage activation syndrome
• long-lasting low blood counts, known as cytopenia
• new blood cancers caused by the treatment

In October 2025 the FDA added one more: immune effector cell-associated enterocolitis, a severe swelling of the gut.

Two of those need unpacking. Cytopenia here means blood counts that stay low for weeks or months. That raises the risk of infection and bleeding long after you go home. New blood cancers have also been reported after treatment. That is why blood counts are checked again and again.

Boxed warnings differ by product. Ask for the label of the exact product you will get, not a general handout.

NCI lists approvals across six diseases:

• B-cell acute lymphoblastic leukemia, in children and adults
• diffuse large B-cell lymphoma
• follicular lymphoma
• mantle cell lymphoma
• chronic lymphocytic leukemia
• multiple myeloma

Approvals are written by line of therapy, meaning how many treatments someone has already had. Those rules have changed over time. Take CARVYKTI. It is now approved for adults with relapsed or refractory multiple myeloma. Relapsed means the cancer came back. Refractory means it stopped responding to treatment. They must have had at least 1 prior line of therapy. That line must include a proteasome inhibitor and an immune-modulating drug. The cancer must also have stopped responding to lenalidomide. Ask which prior treatments your own approval requires.

The CARVYKTI label says to get medical attention right away for the signs below. Do not wait to see if they pass. The label says some nerve effects can start days, weeks or months after the infusion, so keep watching after the first 2 weeks too.

• Call 911 or go to the nearest emergency department for a seizure, fainting, breathing that is fast or hard, or chest tightness.
• Call 911 or go to the nearest emergency department for sudden confusion, or if someone is hard to wake.
• Call your care team's 24-hour number right away for a fever of 100.4°F (38°C) or higher. Go to an emergency department if nobody answers. Fever is the first sign the label lists for CRS, and it can also be a sign of a serious infection. Do not take a fever reducer before you call.
• Call right away, day or night, for chills, a sore throat, a cough, mouth sores, burning when you urinate, or redness at a catheter site. The label lists infections among the risks, and a normal temperature is not a reason to wait.
• Dizziness, lightheadedness or a racing heart. Call right away.
• Slurred speech, trouble naming objects, or odd sleepiness. Call right away.
• Tremor, or handwriting that suddenly looks different. Call right away.
• Severe diarrhea or belly pain. Call right away.

The handwriting item comes from the label, which lists trouble writing (dysgraphia) and tiny handwriting (micrographia) among the signs of nerve effects.

https://www.cancer.gov/about-cancer/treatment/research/car-t-cells

https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/fda-eliminates-risk-evaluation-and-mitigation-strategies-rems-autologous-chimeric-antigen-receptor

https://www.fda.gov/media/156560/download

https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/carvykti