CAR-T cell therapy works by genetically reprogramming a patient’s own immune cells to recognize and destroy cancer. The process involves extracting white blood cells from the patient, engineering them in a lab to target a specific protein on cancer cells, then infusing them back into the body as a living treatment. The entire process takes roughly three to five weeks from cell collection to infusion, and it has produced complete remission rates above 70% in certain blood cancers.
What CAR-T Cells Actually Do
Your immune system’s T cells are natural cancer fighters, but they have a limitation: they rely on a recognition system called MHC to identify threats. Cancer cells exploit this by downregulating the molecules T cells need to spot them, essentially going invisible. CAR-T therapy sidesteps this problem entirely.
Scientists insert a synthetic gene into the patient’s T cells that codes for a chimeric antigen receptor, or CAR. This artificial receptor sits on the surface of the T cell and binds directly to a protein on the cancer cell, no MHC system required. Once the CAR locks onto its target, the T cell activates and kills the cancer cell the same way it would kill any infected cell. Because the recognition is direct, tumors can’t hide using the tricks that normally let them evade the immune system.
The Targets: CD19, BCMA, and Why They’re Chosen
The most widely used target is a protein called CD19, which appears on the surface of B cells throughout nearly every stage of their development. Since B cell cancers like leukemia and lymphoma express CD19 at very high rates, a CAR designed to grab CD19 can find and kill the vast majority of tumor cells. CD19-targeted CAR-T cells have achieved complete remission rates above 90% in B cell acute lymphoblastic leukemia.
CD19 isn’t a perfect target, though. It also sits on healthy B cells, so the treatment wipes out normal B cells along with cancerous ones. This side effect, called B cell aplasia, is manageable because patients can receive antibody infusions to compensate. The same tradeoff applies to other common targets like CD20 (also found on B cells) and BCMA, a protein used to target multiple myeloma. None of these targets are exclusive to cancer cells, but the collateral damage is tolerable enough to justify the treatment.
Step by Step: From Blood Draw to Infusion
The process begins with leukapheresis, a procedure similar to blood donation. Blood is drawn from the patient, run through a machine that separates out white blood cells (including T cells), and the remaining blood is returned. The collected T cells are then shipped to a manufacturing facility.
In the lab, the T cells are genetically modified using a viral vector, a deactivated virus that delivers the CAR gene into the cell’s DNA. Two types of vectors are commonly used. Lentiviral vectors can modify T cells whether they’re actively dividing or not, making them versatile. Retroviral vectors only work when cells are dividing, since they need the cell’s nuclear membrane to break down during division to access the DNA. Both approaches permanently integrate the CAR gene, so the modified cells will continue producing the receptor as they multiply.
After modification, the cells are grown in large numbers over a manufacturing period that typically runs 21 to 35 days. Once enough CAR-T cells are produced, they’re frozen and shipped back to the treatment center.
Preparing the Body for Infusion
Before the CAR-T cells go in, patients undergo a few days of lymphodepletion chemotherapy. This step clears out existing immune cells to make room for the engineered ones. Without it, the patient’s native immune system would compete with the CAR-T cells for space and resources, limiting how well they expand after infusion. The most common regimen combines two chemotherapy agents given over three consecutive days. Studies have shown that adding the second drug significantly improves how well CAR-T cells proliferate and persist in the body. After lymphodepletion, the CAR-T cells are infused through a standard IV, similar to a blood transfusion.
How Well It Works
Effectiveness depends heavily on the type of cancer. In patients with relapsed or treatment-resistant B cell acute lymphoblastic leukemia, complete response rates in large clinical trials have ranged from 71% to 81%. For aggressive B cell lymphomas, the numbers are lower but still significant: 40% to 54% of patients achieve a complete response. Mantle cell lymphoma falls in between at around 67%, while indolent (slow-growing) B cell lymphomas respond well, with complete response rates of 69% to 74%.
These numbers are remarkable considering that CAR-T therapy is typically used in patients who have already failed multiple rounds of conventional treatment. For many, it represents a last option after chemotherapy and other therapies have stopped working.
FDA-Approved CAR-T Products
Six CAR-T products are currently approved in the United States, each targeting specific blood cancers:
- Yescarta (axi-cel): large B cell lymphoma, follicular lymphoma
- Kymriah (tisa-cel): B cell acute lymphoblastic leukemia, large B cell lymphoma, follicular lymphoma
- Tecartus (brexu-cel): mantle cell lymphoma, relapsed B cell acute lymphoblastic leukemia
- Breyanzi (liso-cel): large B cell lymphoma
- Abecma (ide-cel): multiple myeloma
- Carvykti (cilta-cel): multiple myeloma
The first four all target CD19 on B cells. The last two target BCMA on plasma cells, making them the go-to options for multiple myeloma.
Side Effects to Expect
The most common serious side effect is cytokine release syndrome, or CRS. When CAR-T cells activate in large numbers, they release a flood of signaling molecules called cytokines. This can cause high fevers, dangerously low blood pressure, and difficulty breathing. Most cases are mild to moderate and resolve within days, but severe CRS requires intensive care. Treatment teams monitor patients closely in the hospital for at least a week after infusion.
The second major concern is neurotoxicity, which can cause confusion, difficulty speaking, tremors, and in rare cases seizures. This typically appears within the first two weeks and is usually temporary, though the exact mechanism isn’t fully understood. Both CRS and neurotoxicity are graded on severity scales, and treatment centers have established protocols for managing each level.
Why It Doesn’t Work for Solid Tumors Yet
Nearly all approved CAR-T therapies treat blood cancers. Solid tumors like breast, lung, or colon cancer present a fundamentally different challenge. Blood cancers circulate freely, making them accessible to CAR-T cells traveling through the bloodstream. Solid tumors form dense masses surrounded by a microenvironment that actively suppresses immune activity. CAR-T cells struggle to physically penetrate the tumor, and even when they do, the local environment can shut them down.
Solid tumors also lack the clean targets that blood cancers offer. A protein like CD19 is reliably present on nearly all B cell cancers, but solid tumors are more heterogeneous. Cancer cells within the same tumor may express different surface proteins, allowing some cells to escape even a well-designed CAR. This phenomenon, called antigenic escape, is one of the core barriers researchers are working to overcome.