For the nearly 1,000 babies born each year in the United States with sickle cell disease, a painful and arduous road awaits them. The only cure is to find a bone marrow donor—an exceedingly rare proposition. Instead, the standard treatment for this inherited blood disorder is regular blood transfusions, with repeated hospitalizations to deal with complications of the disease. And even then, life expectancy is less than 40 years old.
But now, scientists at UCLA are offering up a potentially superior alternative: a new method of gene therapy that can correct the genetic mutation that causes sickle cell disease—and thus help the body on its way to generate normal, healthy blood cells for the rest of the patient’s life. The study, funded in part by CIRM and reported in the journal Blood, offers a great alternative to developing a functional cure for sickle cell disease. The UCLA team is about to begin a clinical trial with another gene therapy method, so they—and their patients—will now have two shots on goal in their effort to cure the disease.
Though sickle cell disease causes dangerous changes to a patient’s entire blood supply, it is caused by one single genetic mutation in the beta-globin gene—altering the shape of the red blood cells from round and soft to pointed and hard, thus resembling a ‘sickle’ shape for which the disease is named. But the UCLA team, led by Donald Kohn, has now developed two methods that can correct the harmful mutation. As he explained in a UCLA news release about the newest technique:
“[These results] suggest 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.”
The latest gene correction technique used by the team uses special enzymes, called zinc-finger nucleases, to literally cut out and remove the harmful mutation, replacing it with a corrected version. Here, Kohn and his team collected bone marrow stem cells from individuals with sickle cell disease. These bone marrow stem cells would normally give rise to sickle-shaped red blood cells. But in this study, the team zapped them with the zinc-finger nucleases in order to correct the mutation.
Then, the researchers implanted these corrected cells into laboratory mice. Much to their amazement, the implanted cells began to replicate—into normal, healthy red blood cells.
Kohn and his team worked with Sangamo BioSciences, Inc. to design the zinc-finger nucleases that specifically targeted and cut the sickle-cell mutation. The next steps will involve improving the efficiency and safest of this method in pre-clinical animal models, before moving into clinical trials.
“This is a promising first step in showing that gene correction has the potential to help patients with sickle cell disease,” said UCLA graduate student Megan Hoban, the study’s first author. “The study data provide the foundational evidence that the method is viable.”
This isn’t the first disease for which Kohn’s team has made significant strides in gene therapy to cure blood disorders. Just last year, the team announced a promising clinical trial to cure Severe Combined Immunodeficiency Syndrome, also known as SCID or “Bubble Baby Disease,” by correcting the genetic mutation that causes it.
While this current study still requires more research before moving into clinical trials, Kohn and his team announced last month that their other gene therapy method, also funded by CIRM, has been approved to start clinical trials. Kohn argues that it’s vital to explore all promising treatment options for this devastating condition:
“Finding varied ways to conduct stem cell gene therapies is important because not every treatment will work for every patient. Both methods could end up being viable approaches to providing one-time, lasting treatments for sickle cell disease and could also be applied to the treatment of a large number of other genetic diseases.”