Promising Gene Therapy For Sickle Cell Ready for Clinical Trial

By Alexandra Anderson PhD

A new engineered gene therapy virus, inserted into blood stem cells and then transplanted into mice with sickle cell disease, markedly reduced red blood cell damage according to the study “Lineage-specific BCL11A knockdown circumvents toxicities and reverses sickle phenotype,” published in theJournal of Clinical Investigation.

A clinical gene therapy trial is expected in the coming year in which researchers will use a gene manipulated harmless virus to prevent the “sickling” of red blood cells. The new gene therapy is based on research going back to the 1980s which revealed that people with a milder form of sickle cell disease carried a fetal form of hemoglobin.

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This form is present in the human fetus and normally tapers off after birth. It differs most from “adult” (beta) hemoglobin because it is able to bind oxygen to a larger extent and is not seen to “sickle”.

In later studies, Dana-Farber/Boston Children’s Cancer and Blood Disorders Center researchers showed that suppressing a gene (BCL11A) that acts as an “off-switch” on the fetus hemoglobin, could restart the production again. With this approach the team was able to replace much of adult hemoglobin with the fetus form, in mice with sickle cell disease.

Dr. David A. Williams and colleagues from the center later adopted the approach.

“BCL11A represses fetal hemoglobin and also activates ‘adult’ hemoglobin, which is affected by the sickle-cell mutation,” Williams, the study’s senior author, said in a news release. “So when you knock BCL11A down, you simultaneously increase fetal hemoglobin and repress sickling hemoglobin, which is why we think this is the best approach to gene therapy in sickle cell disease.”

The new team tried to turn this insight into a therapy approach but they faced a problem. They discovered that the BCL11A gene also plays an important role in blood stem cells — which caused serious problems with the general blood development.

After some engineering in which the team used different gene techniques to silence the “switch-off” gene, without influencing the general blood development, they inserted the whole package into a lentivirus made for safe use in humans. Blood stem cells treated with this gene therapy were then successfully transplanted into mice and reduced the signs of sickle cell disease.

Additionally, in red blood cells from mice and four patients with the disease, the fetal hemoglobin surpassed the sickling “adult” hemoglobin, making up at least 80 percent of the total hemoglobin in the cell. According to the researchers, these results are more than enough to avoid the disease.

Williams believes this gene therapy approach will substantially increase the ratio of non-sickling versus sickling hemoglobin in patients, and his team is now taking the final steps toward FDA clearance for a clinical gene-therapy trial in sickle cell disease, that is expected to begin in early 2017.

New Biophysical Markers Could Help Develop Treatments for Sickle Cell Disease

by Dr. Trupti Shirole

Sickle cell disease is an inherited blood disorder that affects an estimated 80,000 to 100,000 Americans each year. People with sickle cell disease have an abnormal form of hemoglobin, a protein found in red blood cells that carry oxygen throughout the body.

Normal red blood cells are flexible discs that easily bend and stretch to flow through the body's narrow blood vessels. In sickle cell disease, the abnormal hemoglobin forms fibers that cause the blood cells to take on a flattened, sickled shape and stiffen when they lose oxygen. This change in shape and rigidity causes the red blood cells to be stuck in the blood vessels and prevents the transport of oxygen to the surrounding tissue. This can cause anemia and extreme pain and impact the health of the body's tissue and organs. 

Currently, hydroxyurea is the only FDA-approved drug for sickle cell disease. The drug reduces sickling in red blood cells and is used to treat pain and reduce the need for blood transfusions in some patients, but it does not work in all patients. Researchers have been divided over what mechanisms cause the drug to work. Some believe it works by reactivating fetal hemoglobin, which is better at transporting oxygen than the abnormal hemoglobin that causes sickling. Others believe it works by increasing the volume of red blood cells, reducing the concentration of sickle hemoglobin. 
An interdisciplinary, international group of researchers has found new biophysical markers that could help improve the understanding of treatments for sickle cell disease, a step toward developing better methods for treating the inherited blood disorder.

"There is a critical need for patient-specific biomarkers that can be used to assess the effectiveness of treatments for sickle cell disease," said Subra Suresh, president of Carnegie Mellon University and co-author of the study. "This study shows how techniques commonly used in engineering and physics can help us to better understand how the red blood cells in people with sickle cell disease react to treatment, which could lead to improved diagnostics and therapies."

The findings from engineers, physicists and clinicians from Carnegie Mellon, the University of Pittsburgh, the Massachusetts Institute of Technology, Florida Atlantic University, Korea University, the Korea Advanced Institute of Science and Technology, and Harvard University will be published this week in the online early edition of the Proceedings of the National Academy of Sciences (PNAS).

In the current study, the international research team evaluated the biophysical properties - shape, surface area and volume - and biomechanical properties - flexibility and stickiness - of red blood cells under normal oxygenated conditions using electromagnetic waves to measure small differences in physical properties. The technique, known as common-path interferometric microscopy, allowed researchers to get a three-dimensional view of the cells.

Using blood samples from patients with sickle cell disease, the researchers separated red blood cells into four groups based on their density. Normal, disc-shaped red blood cells were the least dense, while severely sickled cells were the most dense. They then took samples from people receiving hydroxyurea treatment and those not receiving treatment. The red blood cells of those receiving treatment showed an improvement in all of the biophysical and biomechanical properties tested across all density levels. Furthermore, improvement in the physical properties of red blood cells of people treated with hydroxyurea correlated more with an increase in the red blood cell volume than with levels of fetal hemoglobin.

"Our findings shine a light on the mechanism behind hydroxyurea action, which has long been debated in the scientific community," said Ming Dao, principal research scientist in MIT's Department of Materials Science and Engineering and co-author of the study. "It's exciting to see that using the latest optical imaging tools, we can now confirm which one is the dominating mechanism. Understanding the key mechanism of action will allow us to explore novel and improved therapeutic approaches for sickle cell disease."

The researchers hope that these biophysical markers can be combined with biochemical and molecular-level markers to assess things like the severity of a patient's sickle cell disease, determine whether or not a patient will respond to hydroxyurea treatment and monitor the effectiveness of that treatment.

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 Source: Eurekalert