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The patient was dying of leukemia. One hundred seventy out of every 200 cells in his bone marrow had a cancer-causing mutation, and his lymph nodes were swelling, a sign the cancer was getting worse. He'd already been on multiple courses of chemotherapy, but his disease showed few signs of improvement. Then, in July 2010, he enrolled in a clinical trial for an experimental treatment, designed to turn his own immune cells against his cancer. Months later, all signs of leukemia had vanished, his physicians report today.