IN a potential breakthrough in cancer research, scientists at the University of Pennsylvania have genetically engineered patients T cells - a type of white blood cell - to attack cancer cells in advanced cases of a common type of leukemia. Two of the three patients who received doses of the designer T cells in a clinical trial have remained cancer-free for more than a year, the researchers said. Experts not connected with the trial said the feat was important because it suggested that T cells could be tweaked to kill a range of cancers, including ones of the blood, breast and colon. This is a huge accomplishment - huge, said Dr. Lee M. Nadler, dean for clinical and translational research at Harvard Medical School, who discovered the molecule on cancer cells that the Pennsylvania teams engineered T cells target. Findings of the trial were reported Wednesday in two journals. To build the cancer-attacking cells, the researchers modified a virus to carry instructions for making a molecule that binds with leukemia cells and directs T cells to kill them. Then they drew blood from three patients who suffered from chronic lymphocytic leukemia and infected their T cells with the virus. When they infused the blood back into the patients, the engineered T cells successfully eradicated cancer cells, multiplied to more than 1,000 times in number and survived for months. They even produced dormant memory T cells that might spring back to life if the cancer was to return. On average, the team calculated, each engineered T cell eradicated at least 1,000 cancer cells. Side effects included loss of normal B cells, another type of white blood cell, which are also attacked by the modified T cells, and tumor lysis syndrome, a complication caused by the breakdown of cancer cells. LA Times