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Bluebird Bio said Tuesday that it has suspended clinical trials involving its gene therapy for sickle cell disease after receiving reports that two patients treated with the one-time therapy were diagnosed with cancer.

The trials were placed on “temporary suspension” so that Bluebird can investigate the cancer cases to determine if they were caused by the re-engineered HIV virus used to deliver its gene therapy. No such link has been established yet, the company said.


In December 2018, Bluebird disclosed the diagnosis of myelodysplastic syndrome (MDS), a cancer-like disease of the bone marrow, in a sickle cell disease patient who had undergone treatment with its Lentiglobin gene therapy three years beforehand. At that time, Bluebird concluded that the chemotherapy administered to the patient to prepare for the gene therapy was likely the cause of the cancer, based on tests it conducted. The patient subsequently died last July.

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