(Reuters) - Patients who previously were not helped by repeated treatments for multiple myeloma showed strong benefits from a new type of therapy in a small study, and with no worrisome side effects, drugmaker Bluebird Bio Inc said on Wednesday.

The data sent Bluebird shares up 22.6 percent to $74 in after-hours trading.

The Phase 1 study enrolled patients who had basically run out of options for the blood cancer, after failing on average six previous rounds of treatment, including stem cell transplants. Data from nine patients evaluated for safety and efficacy will be presented on Thursday at a medical meeting in Munich.

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Among three patients given the lowest dose of the experimental treatment, one showed at least a 50 percent reduction in signs of the disease, including of a protein considered a hallmark of the cancer.

All three patients receiving a medium dose of the treatment, and all three who got the highest dose showed at least a 50 percent reduction in signs of cancer. Among those six, two had no minimum residual disease (MRD), meaning they had no remaining detectable trace of the cancer as evaluated by the most highly sensitive available diagnostic.

"The consistency of the response and the depth of the response is surprising, especially getting patients that are MRD negative, which is something you typically do not see in this population," Bluebird Chief Executive Nick Leschly said in an interview.

The treatment, called bb2121 and being developed in partnership with larger U.S. biotech Celgene Corp, targets a protein called BCMA found on cancerous blood plasma cells. Normal plasma cells are found in the bone marrow and are an important part of the immune system.

Bluebird's infused treatment is a member of an emerging potent new type of cancer therapy called CAR T cells. The treatments take T-cells that act as soldiers against foreign invaders and genetically alter them to make them better able to spot and attack cancer.

Leschly said other researchers, including ones sponsored by Novartis AG, are also attempting to develop CAR T cells that target the BCMA protein. But he said side effects of those treatments have included a potentially life-threatening inflammatory condition called cytokine release syndrome (CRS), although it typically can be controlled with steroids.

Bluebird said no CRS incidents, or side effects that could preempt higher doses of bb2121 in future studies, have been seen with its treatment.

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(Reporting by Ransdell Pierson; additional reporting by Bill Berkrot; Editing by Diane Craft and Andrew Hay)