Piper Jaffray analyst Tyler Van Buren believe Bluebird Bio's update on LentiGlobin gene therapy in patients with severe sickle cell disease was "very positive," attributing the pullback in the stock to expectations that remain high. Investors have been more skeptical of the sickle cell opportunity than TDT, but Van Buren thinks that will change as the patients continue making progress and more have positive responses, he tells investors. The analyst, who sees a $2B global opportunity in TDT and a similar but underappreciated opportunity in SCD, keeps an Overweight rating on Bluebird Bio shares.