Nine leukemia patients are cancer-free after being treated with genetically altered versions of their own immune cells, giving strength to a promising new approach for treating the blood cancer.

The trial of 12 patients, two of them children, bolsters findings from 2011. Then, scientists from the University of Pennsylvania in Philadelphia reported that two of the first three patients treated showed no traces of the malignancy after receiving the therapy. Today's results were presented at the American Society of Hematology's annual meeting in Atlanta.

For Walter Keller, 59, who had failed every other treatment for his chronic lymphocytic leukemia (CLL) diagnosed in 1996, the regimen meant he's been in remission since his treatment in April. Before the therapy, "I thought I had a year to live," he said.

"I feel better than I have in a long, long time," said Keller, of Upland, Calif., in a telephone interview. "I'm excited because I think this will help a lot of people."

The scientists, led by Carl June, a professor of pathology and laboratory medicine at the Abramson Cancer Center at the University of Pennsylvania and a study author, used genetic engineering to manipulate white blood cells extracted from the patients. The researchers reprogrammed the cells to specifically target the leukemia cells, and then reinjected them into the patients.

CLL is a slow-growing cancer that starts from white blood cells in the bone marrow and interferes with the production of healthy blood cells. The condition leads to complications such as immune deficiencies and swollen lymph nodes. The disease strikes about 16,000 adults each year and 4,600 die from it, according to the American Cancer Society.

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Emma Whitehead, 7, from Philipsburg, Pa., is in full remission from leukemia.

Two of the original three patients treated have maintained their remissions over 2 years later. The scientists found signs of the designer blood cells still circulating in their bodies.

Two girls, ages 7 and 10, were also treated for a fast-growing blood cancer that affects children called acute lymphoblastic leukemia. Both had been treated and had then relapsed, said Stephan Grupp, director of Translational Research in the Center for Childhood Cancer Research at the Children's Hospital of Philadelphia. He presented research on their care at the hematology meeting.

One of the girls, Emma Whitehead, 7, has been in complete remission in the 8 months since her treatment. The other had a remission of "a few months" before relapsing again, Grupp said. Emma had severe side-effects due to her overactive immune system.