Scientists at the University of Pennsylvania have made strides in treating leukemia patients with a new technique that engineers blood cells to attack the cancer, according to studies published in The New England Journal of Medicine and Science Translational Medicine.

It is still very early in the study, but the results so far are striking. Scientists treated three patients with chronic lymphocytic leukemia, and two of them -- including one who had not responded to chemotherapy -- were cancer-free after a year. The third patient improved but still had cancer.

"We knew [the therapy] could be very potent," Dr. David Porter, director of the blood and marrow transplantation program at the Hospital of the University of Pennsylvania in Philadelphia and a coauthor of both papers, told The Los Angeles Times. "But I don't think we expected it to be this dramatic on this go-around."

The procedure entailed removing patients' white blood cells, also called T cells, and then infected the cells with a specially modified virus that would instruct the cells to attack cancer cells. Once the T cells were injected back into the patients' bloodstreams they multiplied rapidly and were highly successful in eradicating cancer cells, each destroying at least 1,000 cancer cells.

Scientists are tempering their enthusiasm by warning that it is early in the trial and that there were only three patients involved. But the study could extend beyond offering an alternative to treating leukemia with costly and dangerous bone marrow transplants. Researchers hope that the technique of recruiting a patient's immune system to fight cancer could be used against other forms of cancer.

"It is kind of a holy grail," said Dr. Gary Schiller, a researcher with UCLA's Jonsson Comprehensive Cancer Center who was not involved in the trial.