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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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  • You stated this:
    “The investigation of the cancer cases will seek to determine if the Lentiglobin gene therapy could have caused the patients’ cancer, by possibly inserting the modified stem cells in the wrong place. This is a theoretical risk for any gene therapy that uses viruses as a delivery vehicle, but had not yet materialized in clinical trials until Bluebird’s reports.” There are several problems with this comment. One is that it is the modified GENE that is inserted in the wrong place in the blood stem cells. Additionally, the advent of leukemia in a gene transfer clinical trial in which hematopoietic (blood) stem cells are modified, is not a new phenomenon. There were several cases of leukemia in the early gene transfer clinical trials for X-linked Severe Combined Immunodeficiency Disease (X-SCID); the viral vector used for those trials was a retroviral vector. See: Hacein-Bey-Abina S, Garrigue A, Wang GP, et al. Insertional oncogenesis in 4 patients after retrovirus-mediated gene therapy of SCID-X1. J Clin Invest. 2008;118(9):3132-3142. doi:10.1172/JCI35700

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