Why Global Blood Therapeutics Inc. Skyrocketed and bluebird bio Inc. Sank Today

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What: Global Blood Therapeutics is up 16% at 1:00 p.m. EDT while bluebird bio is down 8% after Global Blood Therapeutics released positive data for its sickle-cell disease drug GBT440. Because bluebird bio is developing a treatment for the same disease, this explains why investors are hitting the sell button -- at least on the surface.

So what: At the European Hematology Association's 21st Congress, Global Blood Therapeutics presented updated data from a phase 1/2 trial, showing that GBT440 is helping sickle-cell disease patients for as long as 90 days; previously presented data only went out as far as 28 days.

After patients took the drug at 700 mg for 90 days, their irreversibly sickled cells -- the ones that clump -- decreased by a median of approximately 70%, compared to an increase of approximately 15% for patients that took placebo. Other measurements also suggest the drug is working with an increase in hemoglobin, the red blood cells that carry oxygen, and there is evidence that fewer blood cells are dying. It's a small data set with just six patients on the drug and two placebo patients, so no statistics were given, but at least the numbers are going in the right direction.

Global Blood Therapeutics is also testing GBT440 at 900 mg for 90 days, but that part of the trial is still enrolling patients.

We don't know how much of a competition GBT440 may be for bluebird bio's gene therapy, LentiGlobin BB305. The treatment is likely to be more risky than GBT440, but that means with or without a successful approval of GBT440, bluebird bio would likely only be treating the sickest patients. And since it's designed to cure sickle-cell patients,LentiGlobin BB305might still be a viable option, even if GBT440 can treat patients with the severe form of the disease.

But we don't even know that yet. To enter the Global Blood Therapeutics trial, patients needed to have not received a red blood cell transfusion in the last 30 days, but the one patient on whom bluebird bio's LentiGlobin BB305 worked "required chronic blood transfusions" before the treatment, and it was clear the treatment worked because "he was successfully weaned off of transfusions."

Now what: Global Blood Therapeutics plans to talk to the FDA and start a pivotal trial later this year that could be used to get the drug approved. We'll have to wait and see what types of patients the company enrolls in the study, but it seems possible that bluebird bio has nothing to worry about -- at least for now -- with the companies splitting the market, and Global Blood Therapeutics taking the easier-to-treat patients while bluebird bio takes the most severe.

The article Why Global Blood Therapeutics Inc. Skyrocketed and bluebird bio Inc. Sank Today originally appeared on Fool.com.

Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends bluebird bio. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.