Immune Engineering Genetically engineered immune cells are saving the lives of cancer patients. That may be just the start.

The doctors looking at Layla Richards saw a little girl with leukemia bubbling in her veins. She’d had bags and bags of chemotherapy and a bone marrow transplant. But the cancer still thrived. By last June, the 12-month-old was desperately ill. Her parents begged—wasn’t there anything?

There was. In a freezer at her hospital—Great Ormond Street, in London—sat a vial of white blood cells. The cells had been genetically altered to hunt and destroy leukemia, but the hospital hadn’t yet sought permission to test them. They were the most extensively engineered cells ever proposed as a therapy, with a total of four genetic changes, two of them introduced by the new technique of genome editing.

Soon a doctor from Great Ormond was on the phone to Cellectis, a biotechnology company with French roots that is now located on the East Side of Manhattan. The company owned the cancer treatment, which it had devised using a gene-editing method called TALENs, a way of making cuts and fixes to DNA in living cells. “We got a call. The doctors said, ‘We’ve got a girl who is out of T cells and out of options,’” André Choulika, the CEO of Cellectis, remembers. “They wanted one of the vials made during quality-control testing.”

The doctors hoped to make Layla a “special,” a patient who got the drug outside a clinical trial. It was a gamble, since the treatment had been tried only in mice. If it failed, the company’s stock and reputation could tank, and even if it succeeded, the company might get in trouble with regulators. “It was saving a life versus the chance of bad news,” Choulika says.

Cellectis began developing the treatment in 2011 after doctors in New York and Philadelphia reported that they’d found a way to gain control over T cells, the so-called killer cells of the immune system. They had shown that they could take T cells from a person’s bloodstream and, using a virus, add new DNA instructions to aim them at the type of blood cell that goes awry in leukemia. The technique has now been tested in more than 300 patients, with spectacular results, often resulting in complete remission. A dozen drug firms and biotechnology companies are now working to bring such a treatment to market.