WASHINGTON — The Food and Drug Administration has approved the first treatment that genetically engineers patients’ own blood cells to seek and destroy childhood leukemia. The move opens a new era in cancer care.

FDA’s action Wednesday makes Novartis Pharmaceutical’s CAR-T cell treatment the first type of gene therapy to hit the U.S. market. It’s one in a wave of “living drugs” being developed for blood cancers and maybe other tumors, too.

The Novartis therapy is for children and young adults with acute lymphoblastic leukemia, or ALL, who have relapsed despite today’s best treatments. It’s made from scratch, an expensive process that takes about three weeks. Despite some serious side effects, a key test found a one-time infusion put about 80 percent of hard-to-treat patients into remission.