A clinical trial conducted by Prof. Philippe Leboulch from the François-Jacob Biology Institute, in collaboration with Prof. Marina Cavazzana from Hôpital Necker-Enfants malades, has led to the complete remission of sickle cell disease in an adolescent. Now 15 years old, this young boy had no compatible donor and presented particularly severe symptoms of the disease. He took part in the trial in September 2014. He now no longer requires any monthly transfusion or any other treatment to prevent sickle cell attacks. This complete remission of symptoms constitutes only a first step; the physicians will still have to wait a few more years before they can say it has been cured. The results of this clinical trial are yet another illustration of French expertise in the field of gene therapy.
The first phase of the clinical trial consisted of removing samples of hematopoietic stem cells, responsible for the production of all lineages of blood cells, from the bone marrow of the patient. A viral vector[1] carrying a therapeutic gene already developed to treat β-thalassemia was introduced into these cells in order to correct them. Developed within the Innovative Therapies Department of the François-Jacob Institute, and produced on a mass scale by American company Bluebird Bio[2], this lentiviral vector[3] is capable of transporting long segments of complex DNA. "We then reinjected the treated cells intravenously," said Prof. Leboulch. "Today, two years after administering the treatment, the patient produces more than 50% normal hemoglobin (instead of 20%, which would have been sufficient to treat the disease), with a complete inhibition of pathological sickle cell phenomena."
This result was the subject of a press release.
More on sickle cell disease
With 275,000 new cases detected each year in infants worldwide, sickle cell disease is the most widespread genetic disease in the world, and the most common in France. A gene mutation causes the production of abnormal hemoglobin. This protein, essential to the respiratory function, then affects the red blood cells by transforming them into a crescent, or sickle shape, instead of a disk shape. The consequences are a quicker destruction of the deformed globules and an increase in blood viscosity, which can lead to the obstruction of small arteries. The symptoms are extremely severe and debilitating, including chronic anemia, painful vaso-occlusive crises, increased sensitivity to infections, etc. The only curative treatment known today is the transplantation of stem cells from the bone marrow to restore normal cell production. This heavy surgical intervention is reserved for the most severe cases, as it requires identifying a compatible donor within the family (sibling), which is unfortunately only possible for a minority of patients.
Hemoglobinopathies are estimated to affect 7% of the world's population. Sickle cell disease is the most common hemoglobinopathy, with 50 million people at risk of transmitting the disease or affected by the disease. Genetic abnormalities of β-globin, sickle cell anemia and β-thalassemia are the most common inherited diseases in the world, more common than all other genetic diseases combined.[1] A vector is a DNA or RNA molecule capable of self-replication (plasmid, cosmid, viral DNA) and in which foreign DNA is introduced. The vector is then used to insert this DNA into a target cell.
[2] A company founded by Prof. Philippe Leboulch that promoted the clinical trial.
[3] A type of RNA virus.