Shares of Bluebird Bio (BLUE - Get Report) are flying Monday morning, initially up a whopping 27% to $217 at the open. Now, Bluebird stock is up about 17%, to $200.

In the words of JPMorgan analyst Cory Kasimov, Bluebird was the "star of the weekend" at the American Society of Hematology conference. The surge comes after the company provided an update on its Phase 1 clinical trial of its CAR-T treatment.

Kasimov called the bb2121 CAR-T data "remarkable," which achieved an objective response rate of 94% on the 18 patients in the test. While Kasimov maintained his overweight rating on Bluebird Bio stock, other analysts took notice, too.

Goldman Sachs ratcheted its price target up to $309 from $186 to go along with their conviction buy rating. Even after Monday's big pop, that still implies almost 50% more upside.

BMO analyst bumped its price target to $215 from $162, about where Bluebird Bio stock is now trading.

Jefferies analysts increased their price target to $211 from $130, with analyst Biren Amin also calling it the "star" of the weekend. The bb2121 data is promising and Bluebird is making positive strides with sickle cell disease treatments.

Finally, Cantor Fitzgerald analyst Elemer Piros raised his price target, too, but only to $113 from $58, reflecting almost 50% downside from current levels. He also maintains an underweight rating, saying the stock appears overvalued despite the positive steps shown at the ASH conference.

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This article is commentary by an independent contributor. At the time of publication, the author had no positions in the stocks mentioned.