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MILAN (TheStreet) -- Two patients with a serious, inherited blood disorder have been able to stop blood transfusions following a single treatment with an experimental gene therapy developed by Bluebird Bio (BLUE) - Get bluebird bio, Inc. Report, according to new but preliminary data presented Saturday. 

The two patients reported on today have beta-thalassemia (B-thal), a disease caused by a missing or defective gene which prevents oxygen-carrying hemoglobin from functioning properly. The BlueBird therapy, known as LentiGlobin, replaces the defective gene with one that is fully functional.

Beta-thalassemia patients suffer from chronic anemia and typically require regular and lifelong blood transfusions. Following a single infusion of Bluebird's LentiGlobin gene therapy, the two B-thal patients started producing functional hemoglobin and within 10 and 12 days, respectively, were able to halt blood transfusions. The patients have now been blood-transfusion independent for approximately 6 and 3 months, respectively, according to Bluebird Chief Medical Officer David Davidson. The data are being presented Saturday at the European Hematology Association annual meeting.

"Following the [gene] transplant, we're seeing near normal levels of hemoglobin," said Davidson. "These early results far exceeded our expectations."

Bluebird only has limited data on two patients and the study, conducted in France, continues with seven B-thal patients expected to enroll and be treated. Bluebird has begun another Lentiglobin B-Thal study in the U.S., which will enroll 15 patients. The company expects to report updated results from the Lentiglobin studies at the end of the year. 

Bluebird went public last year partly on the back of some encouraging proof of concept data showing a first-generation gene therapy approach was feasible for B-thal patients. LentiGlobin is a second-generation gene therapy designed to be more potent -- and hopefully more effective. The results presented today suggest Bluebird's improved gene therapy is leading to more clinical benefit for patients.

The two patients entered the study with the "major" or Beta E/Beta 0 genotype of B-thal, which required them to undergo monthly blood transfusions to deal with chronic anemia. Following the Lentiglobin infusion, patient 1 produced 6.6 g/dl of "marked" beta-globin at 4.5 months, a measure of functional hemoglobin produced by the working gene inserted by LentiGlobin. Patient 2 produced 4.2 g/dl of "marked" beta-globin at 2 months. In both cases, LentiGlobin is producing more functional hemoglobin and at a faster rate than Bluebird's first generation gene therapy. 

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With two weeks, both patients were transfusion independent, which is the most important measure of clinical benefit in B-thal.

Bluebird estimates there are about 15,000 patients with B-thal in the U.S. and Europe, a majority of which have the major genotype which requires regular blood transfusions and would be candidates for LentiGlobin. 

In addition to B-tha, Bluebird is developing LentiGlobin as a treatment for sickle cell anemia, a related but more prevalent disease.

Bluebird closed Friday at $26.09.

-- Reported by Adam Feuerstein in Boston.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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