A new study evaluating the safety and efficacy of exa-cel (CTX001) in adults and adolescents with severe sickle cell disease (SCD), βS/βC genotype (HbSC), will be started.

After myeloablative conditioning with busulfan, the interventional study will administer exa-cell to 12 participants aged 12 to 35 years in a single infusion through a central venous catheter. The primary outcome measure will be the proportion of participants with a mean fetal hemoglobin of at least 20% on or after 6 months.

Secondary outcomes include adverse events, neutrophil and platelet engraftment, transplant and all-cause mortality, vaso-occlusive crises, hospitalizations, transfusions, pain levels, and quality of life, among other measures.

To be included, patients must have the βS/βC (HbSC) genotype and be eligible for autologous stem cell transplantation.

Read more about SCD therapies

The study is expected to start in January 2024, and the estimated completion date is December 2029.

Exa-cel is a genetically modified (CRISPR) cell therapy that alters a specific point in the DNA sequence of a gene that codes for BCL11A, the protein that stops the production of fetal hemoglobin after birth.

The US Food and Drug Administration is conducting a priority review of a biologic license application for exa-cel for SCD and a standard review of the gene-editing therapy for transfusion-dependent beta thalassemia. A decision on the application for SCD is expected by December 8, 2023.

Similar applications are being reviewed in the United Kingdom and the European Union.

Sickle cell disease comprises a group of rare, inherited blood disorders characterized by alterations in the structure of hemoglobin leading to sickling and early death of red blood cells. It is caused by a point mutation on chromosome 11 in the gene that codes for the beta subunit of hemoglobin.


A phase 3 study to evaluate efficacy and safety of a single dose of exa-cel in subjects with severe sickle cell disease, βS/βC genotype. ClinicalTrials.gov. Updated July 18, 2023. Accessed July 25, 2023.