Beta thalassemia is an inherited blood disorder caused by one of over 200 mutations in the HBB gene (or ß-globin gene). Patients with beta-thalassemia have low levels of haemoglobin, a protein in red blood cells that carries oxygen to cells throughout the body. Orchard’s gene therapy programme addresses the most severe form of thalassemia, referred to as “transfusion-dependent thalassemia” (TDBT) or beta-thalassemia major. Symptoms of TDBT appear within the first 2 years of life and include failure to gain weight and to grow, infections and life-threatening anaemia. In the absence of regular blood transfusions, TDBT is usually fatal in infancy. Beta-thalassemia is one of the most common genetic diseases, with a global incidence estimated at approximately 25,000 patients each year and a global prevalence of more than 200,000 patients (sources: Modell 2008; Williams 2012).
Most patients with TDBT major have such severe symptoms that they need frequent blood transfusions to replenish their level of haemoglobin in red blood cells. Because of these transfusions, iron accumulates in various organs, leading to risk of heart or liver failure. Therefore, patients who receive ongoing blood transfusions must also take medicines to remove the excess iron. These medicines, called iron chelation therapy, also have side effects and can negatively impact a patient’s quality of life. Allogenic haematopoietic stem cell transplantation is currently the only curative therapy for beta-thalassemia; however, this intervention carries a risk of mortality and morbidity, especially where there is not a good match between the donor and the patient.
Orchard is developing OTL-300, ex vivo autologous lentiviral gene therapy for transfusion-dependent beta-thalassemia. Data from an ongoing clinical study in seven patients with the β0/β0, β+/β+, and β0/β+ genotypes were presented at the American Society of Hematology (ASH) Annual Meeting in 2017. Treatment with OTL-300 resulted in a significant reduction in the need for transfusions in 5 out of 7 patients, and in transfusion-independence in 3 out of 4 pediatric patients from 1 month after gene therapy (source: Marktel 2017). The gene therapy procedure was well tolerated in all patients.
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