Patients with chronic lymphocytic leukemia who were treated with a gene therapy protocol began making antibodies that reacted against their own leukemia cells. Researchers inserted a gene with the potential to activate an immune response into six patients with CLL, the most common form of adult leukemia. Several of the patients started making antibodies that reacted against their own leukemia cells. When tested in the lab, the antibodies also reacted with the leukemia cells of other patients with the disease.