Sickle cell disease (SCD) is a genetic disorder that affects red blood cells. This disease affects people of color more commonly and is due to the effect of abnormally shaped red blood cells (crescent or sickle-shaped instead of disc shaped). The misshapen red blood cells contain a form of hemoglobin, hemoglobin S, resulting from mutation of the beta-globin gene. Hemoglobin S does not hold oxygen efficiently, and the abnormal shape of the red blood cells prevents normal flow through the blood vessels, leading to vessel blockage. This leads to the pain and tissue damage seen in patients with SCD.
There have been some advances in past years regarding treatments for SCD, but there is still no cure and the current treatments are aimed to reduce symptoms, manage SCD crises, and improve patient quality of life. Only two drugs are FDA approved for treating SCD, hydroxyurea (used to increase the amount of fetal hemoglobin) and Endari (recently approved and reduces oxidative stress). However, gene therapy approaches are showing promise in significantly controlling the effects of SCD by addressing the fundamental cause of the disease.
A therapy developed by Bluebird Bio Inc., LentiGlobin, is a modified human beta-globin gene encoding an anti-sickling variant and transferred to CD34+ stem cells using a lentivirus. Recent results in a patient treated with this gene therapy showed significant clinical improvement and provide exciting hope for the future of SCD treatment. LentiGlobin was transferred to the patient’s own CD34+ stem cells and the cells reinfused. At fifteen months post-treatment, the patient had no SCD crises or hospitalizations, medications were stopped, and the level of sickled red blood cells were lower than in untreated patients with SCD.
Approaches to permanently change the DNA of red blood cell precursors via CRISPR (genome editing) are also being studied. Gene therapy may well be medical science’s tool to realize a cure for SCD in the not-too-distant future. While the new approaches are being improved and tested, medical treatments such as Voxelotor (increases oxygen affinity) and Endari are available to help increase quality of life in patients with SCD.
Badat M, Davies J. Gene Therapy in a Patient with Sickle Cell Disease. N Engl J Med. 2017 May 25;376(21):2093-4.