More positive results from CRISPR trial for sickle cell and thalassaemia

16 August 2021

A genome editing-based gene therapy for blood diseases sickle cell disease and beta-thalassaemia continues to be effective more than two years after treatment.

The clinical trial for the therapy, named CTX001, previously reported good preliminary results (see BioNews 1052) and new data was presented at the European Haematology Association 2021 Virtual Congress.

‘We are hearing that it is life-changing.’ said Professor Stephan Grupp from the Cell and Gene Therapy Laboratory at Children’s Hospital of Philadelphia, one of the researchers collaborating on the trial. 

Patients with sickle cell disease or beta-thalassaemia carry a mutation in a single gene that causes problems in an essential blood molecule called haemoglobin. Patients usually require lifelong blood transfusions, sometimes stem cell transplants, as well as ongoing pain management. Sickle cell disease can also impact reproductive health in women (see BioNews 1105).

This clinical trial involved taking a patient’s own blood stem cells, called hematopoietic stem cells, and editing them outside the body. CRISPR/Cas9 genome editing was used to reactivate a different haemoglobin gene that is usually only expressed in the fetus and is switched off at birth. The edited stem cells were transplanted back into the patients, who started producing fetal haemoglobin, replacing the nonfunctional haemoglobin that caused disease symptoms.

‘The data presented today in 22 patients are impressive in both the consistency and durability of effect. These results add to the growing body of evidence that CTX001 may hold the promise for a one-time functional cure for sickle cell disease and beta-thalassemia.’ said Dr Reshma Kewalramani, CEO of Vertex Pharmaceuticals in Boston, Massachusetts, who developed the treatment in partnership with CRISPR Therapeutics from Zug, Switzerland.

After two years post-gene therapy, the sickle cell disease patients were reported to be free of vaso-occlusive crises; a painful organ injury occurring when blood cells cause blockages, common to sickle cell disease patients. None of the beta-thalassaemia patients has required any further blood transfusions as all have started producing functional levels of fetal haemoglobin in their blood. 

‘The evidence so far indicates that it is durable in the time frame we’ve seen, and we just have to continue to follow the patients’ said Professor Grupp.