CTX001, an investigational gene-editing cell therapy, has been granted priority medicines (PRIME) designation by the European Medicines Agency (EMA) for the treatment of severe sickle cell disease (SCD).

The announcement was made by CRISPR Therapeutics and Vertex Pharmaceuticals, which are jointly developing CTX001 for severe SCD and transfusion-dependent beta thalassemia (TDT).

PRIME designation is given to candidate therapies with promising clinical data showing a potential to treat diseases of high unmet medical need. It helps speed clinical development and review of the medicines, helping them reach patients earlier.

In addition to this designation, CTX001 has also been granted orphan drug designation from the European Commission, as well as regenerative medicine advanced therapy, fast track, and orphan drug designations from the U.S. Food and Drug Administration for SCD and TDT.

CTX001 uses the CRISPR-Cas9 gene-editing tool to modify a patient’s own blood cell precursors (hematopoietic stem cells) and induce the production of high levels of fetal hemoglobin in red blood cells. Once gene editing is complete, the cells are re-introduced back into the patient in the form of a stem cell transplant.

By increasing the levels of fetal hemoglobin — a form of hemoglobin that’s produced during fetal development and more efficient at transporting oxygen than the adult form — CTX001 is expected to lower the frequency of vaso-occlusive crises (VOCs) in SCD patients.

The EMA’s decision was based on promising clinical data from the ongoing the Phase 1/2 CLIMB-SCD-121 trial (NCT03745287), which is assessing the safety and effectiveness of a single dose of CTX001 in patients with severe SCD.

The trial is recruiting participants, ages 12–35, at several sites across North America and Europe. Up to 45 patients will be included and followed-up for nearly two years. All will have the opportunity to join a long-term follow-up study.

To date, two patients have been dosed in the trial. In both cases, the transplanted cells survived and expanded, meaning that the transplants were successful.

The first patient had been experiencing an average of seven VOCs and requiring five blood transfusions each year before joining the trial. CTX001 safely increased the levels of fetal hemoglobin in this woman, and helped her remain free of VOCs for at least nine months. Also, no blood transfusions were required after CTX001 treatment.

CTX001 also increased total hemoglobin levels, the percentage of fetal hemoglobin, and the number of red blood cells producing this fetal form of hemoglobin.

Following infusion of CTX001, the patient experienced three serious adverse events, but all were deemed unrelated to treatment and subsequently resolved.

In addition to CLIMB-SCD-121, CRISPR Therapeutics and Vertex are also examining CTX001 as a potential treatment for TDT in the Phase 1/2 CLIMB-Thal-111 trial (NCT03655678). Patient enrollment is ongoing, and more information is available here.


Patricia holds her Ph.D. in Cell Biology from University Nova de Lisboa, and has served as an author on several research projects and fellowships, as well as major grant applications for European Agencies. She also served as a PhD student research assistant in the Laboratory of Doctor David A. Fidock, Department of Microbiology & Immunology, Columbia University, New York.

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Inês holds a PhD in Biomedical Sciences from the University of Lisbon, Portugal, where she specialized in blood vessel biology, blood stem cells, and cancer. Before that, she studied Cell and Molecular Biology at Universidade Nova de Lisboa and worked as a research fellow at Faculdade de Ciências e Tecnologias and Instituto Gulbenkian de Ciência.



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