People with beta thalassemia know that gene therapy can be effective in reducing, if not eliminating, the need for transfusions, so much so that a therapy of this kind has recently been authorized in the USA. The company that produces it, however, decided that it was not worth marketing in Europe. Of different opinion are two other companies – Vertex Pharmaceuticals and CRISPR Therapeutics – which together have developed exagamglogene autotemcel (exa-cel) for the treatment of patients with sickle cell disease (SCD) or transfusion-dependent beta-thalassemia (transfusion -dependent beta thalassemia, TDT). Their application for marketing authorization presented to the European Medicines Agency was accepted and therefore, this is the hope, in a few months it will also be possible in Europe to intervene on these two blood diseases through genetic editing .
Beta-thalassemia, 9 out of 10 people can recover thanks to gene therapy
by Dario Rubino
A pioneering technique
Exa-cel is the first therapy based on the CRISPR/Cas9 technique for a genetic disease for which a marketing application is submitted in Europe; has already obtained the designation of Orphan Drug from the European Commission and Priority Medicine from EMA. How does it work? Patients’ haematopoietic stem and progenitor cells are harvested from their peripheral blood and modified using the CRISPR/Cas9 technique so that they are capable of producing elevated levels of fetal hemoglobin (HbF) in red blood cells. HbF is an oxygen-carrying form of hemoglobin naturally present during fetal development, which is replaced by the adult form of hemoglobin after birth. The increase in HbF levels caused by exa-cel treatment reduces the need for transfusions for patients with TDT and decreases painful and debilitating sickle cell crises for patients with SCD, as demonstrated by the clinical studies which underlie the application for marketing authorisation. Once modified, the cells are re-infused into the patient as part of a stem cell transplant.
Sickle cell anemia and transfusion-dependent beta-thalassemia are inherited blood disorders that affect red blood cells, which are essential for carrying oxygen to all organs and tissues in the body. Sickle cell anemia causes severe pain, organ damage, and is associated with a shorter than average life expectancy due to the effects of deformed blood cells. However, a lack of red blood cells, known as anemia, is the main manifestation of beta thalassemia and causes fatigue and shortness of breath, while children can have stunted growth, jaundice and feeding problems. Patients therefore need regular blood transfusions, which require numerous hospital visits, and which can lead to excessive accumulation of iron. In both cases, to date, the only cure for these diseases is stem cell transplantation from a compatible donor, but this option is only available to a small percentage of patients.