Data presented at the European Hematology Association meeting this month suggest both bluebird bio Inc. and Acceleron Pharma Inc. could have the first two disease-modifying treatments for beta thalassemia. While bluebird's gene therapy approach could provide a more durable or even permanent benefit, its requirement for stem cell transplantation could mean it finds its niche in the sickest patients, while Acceleron already is testing its drug approach in patients with less severe disease.

In any case, both companies already are taking their programs into other indications.