Statement on NHLBI decision to pause the Pilot and Feasibility Study of Hematopoietic Stem Cell Gene Transfer for Sickle Cell Disease

February 22, 2021


On Feb. 16, 2021, bluebird bio, Inc. suspended its clinical trial exploring the curative potential of genetic therapy for sickle cell disease using its lentiviral vector (gene therapy delivery system), because two research participants in this trial developed myeloid neoplasms following gene therapy. Out of an abundance of caution, on Feb. 17, 2021, the National Heart, Lung, and Blood Institute (NHLBI), part of the NIH, paused participant enrollment and gene transfers in an NHLBI-funded trial at the Boston Children’s Hospital, Pilot and Feasibility Study of Hematopoietic Stem Cell Gene Transfer for Sickle Cell Disease. Since this trial began in February 2018, nine individuals with sickle cell disease have been treated. The Boston Children’s trial uses a different, yet related, vector, and targets a different gene than those used in the bluebird bio, Inc. trial. However, despite having no indications of such harm in the Boston Children’s trial, NHLBI is taking this action following the announcement that bluebird bio, Inc. temporarily suspended its study.

For more than a decade, gene therapy has been considered a promising approach to a cure for sickle cell disease. Lentiviral vectors have been a critical part of the process, as they are used to deliver a therapeutic gene into blood producing stem cells in the bone marrow. This therapy results in the production of healthy (or normal) hemoglobin in red blood cells. 

The Institute has requested that its Data and Safety Monitoring Board (DSMB) conduct an independent safety review of the NHLBI-funded Boston Children’s Hospital. Patient volunteers and their safety are the highest priority in any research endeavor, and their participation is the foundation for scientific progress. NHLBI recognizes and honors the important contributions of these and all clinical research volunteers in advancing science toward a cure for this disease. 

NHLBI remains committed in its pursuit of a cure for sickle cell disease. The Institute will reassess this pause following a thorough review of the Boston Children’s Hospital study by the DSMB and input from the U.S. Food and Drug Administration, which provides regulatory oversight of all gene therapy in the United States.