Researchers Halt Trial of Promising Sickle Cell Treatment February 22, 2021 Auto Bot Bluebird Bio Inc, Bone Marrow, Busulfan, Clinical Trials, DNA (Deoxyribonucleic Acid), Genetic Engineering, leukemia, National Heart, Lung and Blood Institute, Sickle Cell Anemia 0 Two patients in a gene therapy study developed cancer years after treatment. It is not clear whether the therapy was responsible.