The findings of a new study on sickle cell disease may lead to a new era in the approach to treatment.
Sickle cell disease (often referred to as sickle cell anemia) is a group of blood disorders in which the blood cells have an abnormal sickle shape instead of the biconcave disk shape. The sickle-shaped cells have a shorter life span (leading to anemia), but they also block normal blood flow leading to pain and organ dysfunction. There is no cure, and treatments that exist are aimed to control symptoms and related complications.
The sickled blood cell shape of SCD is due to the presence of abnormal hemoglobin, hemoglobin S. The production of hemoglobin S is a result of a point mutation in the HBB gene of CD34 cells (hematopoietic stem cells) that codes for the beta-globin subunit of hemoglobin. The objective of a collaboration between scientists from Rice University, Baylor College of Medicine, Texas Children’s Hospital, and Stanford University was to use gene editing to correct the genetic defect responsible for SCD and determine its effect on the production of normal blood cells.
The study involved the collection of CD34 cells from patients with SCD. Then, CRISPR/Cas9 (from a genome editing system naturally occurring in bacteria) was used for gene editing. The gene-edited CD34 cells were injected into the bone marrow of laboratory mice. About five months later, the researchers observed that up to 40% of the CD34 cells were repaired. One drawback, however, was the occurrence of unintended gene alterations that could cause undesirable effects. This and the uncertainty regarding whether the observed level of repair is clinically sufficient in the human patient remain to be resolved.
The findings thus far are quite promising and may lead to a new era in the approach to the treatment of SCD. Further research is needed to prevent off-target gene alterations, determine the level of repair that is needed in clinical trials, and to determine how to raise the level of corrected CD34 cells. The gene-editing approach has the potential to eliminate the need for dependence on symptomatic treatment, reduce severe cases requiring bone marrow transplants and transfusions, and ultimately improve quality of life for those born with SCD.
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Progress in pursuit of sickle cell cure. (2018). ScienceDaily. Retrieved 19 March 2018, from https://www.sciencedaily.com/releases/2018/02/180216150341.htm