 Bluebird Bio Inc. BLUE, 13.34 said Monday the Food and Drug Administration has placed a partial clinical hold on patients below the age of 18 in its lovo-cel sickle cell gene therapy program. The temporary halt is due to an investigation by the company into an adolescent patient who has suffered persistent, non-transfusion-dependent anemia following treatment with lovo-cel, now 18 months after the treatment. 