BU researchers have developed a way to test treatments for sickle cell disease—a genetic disorder of the red blood cells—by working with stem cells grown from a small vial of patients’ blood. “It’s a clinical trial in a test tube,” says molecular biologist George J. Murphy, a School of Medicine assistant professor of medicine and a codirector of BU’s Center for Regenerative Medicine (CReM).
The BU team recently received a five-year, $9 million grant from the National Heart, Lung, and Blood Institute of the National Institutes of Health to grow the versatile cells—called induced pluripotent stem, or iPS, cells—as well as generate a living library of genetic variations of sickle cell disease. Known as disease modeling, it is one of the ways the scientists at CReM are working in collaboration with clinicians to tackle hereditary and incurable conditions.
Growing iPS cells enables researchers to study a range of subtle genetic factors and mutations and test treatments on human tissue. Reflecting the cutting edge of the rapidly evolving field of regenerative medicine, the versatile iPS cells, which CReM researchers had previously derived from small samples of their own skin, resemble embryonic stem cells. Like embryonic cells, under optimal conditions they can be made to differentiate into any type of cell found in the body, and might replace embryonic cells completely once researchers eliminate risks associated with them. Murphy says that the iPS cells represent a crucial step toward the eventual use of regenerative medicine to customize cells with a donor’s own DNA, using the donor’s own cells, and replace diseased tissue or organs with healthy ones.
The recent grant supports the University’s multidisciplinary approach, involving a repertory of molecular biologists, hematologists, and genetics experts, to scale up drug studies in iPS lines, whose production is extremely labor-intensive. (In Murphy’s lab, researchers must tend the delicate cell cultures seven days a week.) “The grant brings together two of the most dynamic entities” on the Medical Campus, says Murphy, referring to BU’s Center of Excellence in Sickle Cell Disease in addition to CReM.
When all goes well, it takes a month in the lab for sickle cell donors’ blood cells to be redifferentiated, through a complex process involving a “vector”—in this case a virus—followed by cultivation and selection of cell colonies returned to an embryonic-like state. Like embryonic cells, the cultures can develop into any type of human cells. Their progress can be tracked visually under the microscope and in more refined and complex ways, explains Murphy, a former Fulbright scholar and an advisor for NASA’s SLS 2 Life Sciences Space Shuttle mission. The result—a renewable supply of stem cells with the donors’ genetics—makes the cells immortal. Murphy and Martin Steinberg, a MED professor of medicine, pediatrics, pathology, and laboratory medicine and director of the Center of Excellence in Sickle Cell Disease, say that the NHLBI grant will see the iPS research to the next level, making it possible to maintain and predict the health and purity of cell cultures. It will be many years before the results of this research translate into human trials, which would be preceded by studies on animals.
About 80,000 Americans live with sickle cell disease, which can result in a range of potential complications, including severe pain, fatigue, infections, and impaired development. The disease is most often diagnosed in the United States at birth, although doctors can test for it in utero with amniocentesis. The condition can lead to stroke, even in very young children. Abnormalities in hemoglobin, the oxygen-carrying protein responsible for blood’s red color, give the short-lived sickle cells their characteristic rod-like shape and make them stiffen and stick to each other, blocking blood vessels and arteries. The genetic trait for the disease, found in people of African, Mediterranean, Middle Eastern, East Indian, Caribbean, and South and Central American descent, affects one in 12 African Americans, according to the Centers for Disease Control. (The iPS study is being done in collaboration with scientists in Saudi Arabia, which has a population at high risk for sickle cell disease.) Healthy people can carry the trait; the disease results when a baby inherits the gene from both parents. In the United States, testing newborns for sickle cell disease is now mandated by law, according to the U.S. Department of Health and Human Services.
Sickle cell can be a cruel disease. Patients experience “sudden attacks of severe pain, pneumonia-like infections, stroke, liver disease, and problems walking,” says Steinberg. One of the world’s foremost experts on sickle cell genetics, he has worked with sickle cell patients in treatment, diagnosis, and research for most of his career.
Several treatments are available that prolong the lives of sickle cell patients. The fairly inexpensive anti-tumor drug hydroxyurea, which reduces mortality by as much as 40 percent, must be taken daily and indefinitely to be effective, Steinberg notes. It appears to stimulate production of fetal hemoglobin, a type usually found only in newborns, which helps prevent the sickling of red blood cells. Most recently, the disease has been reversed through bone marrow transplants, but the procedure is extremely risky and requires an identical sibling donor, he says. Still in the experimental phase is a procedure to transplant patients with their own marrow, after it has been genetically “corrected” through the recombinant techniques commonly known as gene therapy.
With the help of the new funding, the iPS procedure will replace human subjects in the testing of more effective treatments and potential cures for sickle cell disease. The elegance, and promise, of the procedure is that “you can make as many cells as you want,” says Murphy, explaining that the growth factors and cell cultures used in the CReM lab are the result of years of trial and error. Although the iPS cells offer the promise of a versatile, inexhaustible alternative, until the process of deriving them is perfected, the researchers use embryonic stem cells as controls.
With the researchers’ efforts focused on the disease modeling phase, iPS cells hold “enormous promise,” says Murphy, but also one that must be approached cautiously. “We have to be prepared for the fact that anything could turn out wrong,” he says.