Stem Cell Researchers Develop New Method to Treat Sickle Cell Disease


Stem cells researchers from the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at the University of California, Los Angeles (UCLA) have shown that a new stem cell gene therapy protocol can potentially lead to a one-time, lasting treatment for sickle-cell disease, which remains the nation’s most common inherited blood disorder.

This study was led by Dr. Donald Kohn and was published March 2 in the journal Blood. This paper details a method that repairs a mistake in the beta-globin that causes sickle-cell disease and, for the first time, shows that such a gene therapy technique can lead to the production of normal red blood cells.

People with sickle-cell disease are born with a mutation in their beta-globin gene.

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Beta-globin is one of the protein chains that compose the protein hemoglobin. Hemoglobin is the protein in red blood cells that ferries oxygen from the lungs to the tissues and then returns to the lungs to load up with oxygen again and then goes back to the tissues. Red blood cells, which are made in the bone marrow, are packed from stem to stern with hemoglobin molecules, and normally are round, and slightly dished and flexible enough to squeeze through small capillary beds in tissues. The mutation in the beta-globin gene that causes sickle-cell disease, however, causes hemoglobin to form long, stiff rods of protein rather than tight, compactly packed clusters of hemoglobin. These protein rods deform the red blood cells and make them stiff, sickle-shaped, and unable to pass through tissue capillary beds.

sickle-cell-hemoglobin

These abnormally shaped red blood cells not only move poorly through blood vessels, but they also do not sufficiently carry oxygen to vital organs.

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The stem cell gene therapy method described by Kohn and his colleagues corrects the mutation in the beta-globin gene in the bone marrow-based stem cells so that they produce normal, circular-shaped blood cells. The technique uses specially engineered enzymes, called zinc-finger nucleases, to eliminate the mutation and replace it with a corrected version that repairs the beta-globin mutation. Kohn’s research showed that this method has the potential to treat sickle-cell the disease if the gene therapy achieves higher levels of correction.

“This is a very exciting result,” said Dr. Kohn, professor of pediatrics and microbiology, immunology and molecular genetics. “It suggests the future direction for treating genetic diseases will be by correcting the specific mutation in a patient’s genetic code. Since sickle-cell disease was the first human genetic disease where we understood the fundamental gene defect, and since everyone with sickle-cell has the exact same mutation in the beta-globin gene, it is a great target for this gene correction method.”

Stem-Cell Gene Therapy for Sickle Cell Disease


Donald Kohn, a professor of pediatrics and microbiology, immunology and molecular genetics in the UCLA College of Letters and Science, and his colleagues, have successfully established the means to cure sickle-cell disease. This strategy uses hematopoietic (blood-producing) stem cells from the bone marrow of patients with sickle-cell disease in order to treat the disease itself.

This approach provides a revolutionary alternative to current treatments, since it creates self-renewing, normal blood cells by inserting a gene that abrogates the sickling properties into hematopoietic stem cells. With this technique, there is no need to identify a matched donor, and therefore, patients avoid the risk of their bodies rejecting donor cells.

During the clinical trial, the anti-sickling hematopoietic stem cells will be transplanted back into patients’ bone marrow to increase the population of “corrected” cells that make red blood cells that don’t sickle. Kohn will hopefully begin enrolling patients in the trial within three months. The first subject will be enrolled and observed for safety for six months. The second subject will then be enrolled and observed for safety for three months. If evaluations show that no problems have arisen, the study will continue with two more subjects and another evaluation, until a total of six subjects have been enrolled.

Sickle cell disease, which affects more than 90,000 individuals in the U.S., is seen primarily in people of sub-Saharan African descent. It is caused by an inherited mutation in the beta-globin gene that transforms normal-shaped red blood cells, which are round and pliable, into rigid, sickle-shaped cells. Normal red blood cells are able to pass easily through the tiniest blood vessels (capillaries) and carry oxygen to organs like the lungs, liver and kidneys. However, sickled cells get stuck in the capillaries, depriving the organs of oxygen, which can lead to organ dysfunction and failure.

Current treatments include transplanting patients with hematopoietic stem cells from a donor. This is a potential cure for the disease, but due to the serious risks of rejection, only a small number of patients have undergone this procedure, and it is usually restricted to children with severe symptoms.

“Patients with sickle-cell disease have had few therapeutic options,” Kohn said. “With this award, we will initiate a clinical trial that we hope will become a treatment for patients with this devastating disease.”

Finding for this work comes from new grants to researchers at UCLA’s Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, which total nearly $21 million.  These grants were announced Dec. 12 at a meeting of the California Institute of Regenerative Medicine (CIRM) Citizen’s Oversight Committee.  They are apart of the state agency’s Disease Team Therapy Development III initiative.