A London baby with end-stage leukemia has received a remarkable new cancer treatment: off-the shelf T cells with several gene modifications. Doctors say it’s too early to know whether she’s cured, but the announcement advances a frontier in cancer immunotherapy, in which the body’s immune system tackles the disease. For the past several years, researchers have been modifying T cells so they can attack leukemia, but the cells must be painstakingly isolated from the patients themselves and grown in a lab. Drug companies and many doctors dream of using off-the-shelf cells to make the therapy more like a regular drug. Now, by harnessing advances in genome editing to slice and dice genes in donor T cells, researchers have created a new type of cancer immunotherapy.