CAR-T cell therapy

Your immune system already has cells whose job is to hunt and kill — T cells, the soldiers of the body. The trouble is that cancer cells came from you, so they often look too much like self for T cells to attack. CAR-T therapy is a strikingly direct fix: take a patient's own T cells out, genetically re-engineer them to recognize the cancer, and put the upgraded soldiers back in.

Here is the engineering, step by step. Doctors collect a patient's T cells from their blood. In the lab, they use a virus to insert a gene for a designer protein called a chimeric antigen receptor (CAR) — "chimeric" because it is stitched together from parts that do not naturally go together. The CAR sticks out of the T cell's surface like a custom-built grappling hook, shaped to latch onto a specific protein found on the cancer cells (for blood cancers, often a marker called CD19). The reprogrammed cells are multiplied into the millions and infused back; once inside, each engineered T cell that grabs a cancer cell kills it and then divides, so the therapy is a "living drug" that grows in the patient.

CAR-T is one of the great recent triumphs of cell-and-gene engineering: in some blood cancers that had resisted every other treatment, it has driven patients into long-lasting remission. But the honesty is essential. It can trigger a violent, sometimes fatal immune storm (cytokine release syndrome) as the army activates all at once, and serious nerve toxicity. It has worked dramatically in blood cancers but, so far, much less well against solid tumours, which hide better and are harder to enter. And because every batch is custom-made from one patient's cells, it is extraordinarily expensive and complex to produce.