Induced pluripotent stem cell therapy
||The neutrality of this article is disputed. (May 2011)|
In 2006, Shinya Yamanaka of Kyoto University in Japan was the first to disprove the previous notion that reversible cell differentiation of mammals was impossible. He reprogrammed a fully differentiated mouse cell into a pluripotent stem cell by introducing four genes, Oct-4, SOX2, KLF4, and Myc, into the mouse fibroblast through gene-carrying viruses. With this method, he and his coworkers created induced pluripotent stem cells (iPS cells), the key component in this experiment. Scientists have been able to conduct experiments that show the ability of iPS cells to treat and even cure diseases. In this experiment, tests were run on mice with inherited sickle cell anemia.Skin cells were turned into cells containing genes that transformed the cells into iPS cells. These replaced the diseased sickled cells, curing the test mice. The reprogramming of the pluripotent stem cells in mice was successfully duplicated with human pluripotent stem cells within about a year of the experiment on the mice.
Basics of sickle cell anemia
Sickle cell anemia is a disease in which the body produces abnormally shaped red blood cells. Red blood cells are flexible and round, moving easily through the blood vessels. Infected cells are shaped like a crescent or sickle (the namesake of the disease). As a result of this disorder the hemoglobin protein in red blood cells is faulty. Normal hemoglobin bonds to oxygen, then releases it into cells that need it. The blood cell retains its original form and is cycled back to the lungs and re-oxygenated.
Sickle cell hemoglobin, however, after giving up oxygen, cling together and make the red blood cell stiff. The sickle shape also makes it difficult for the red blood cell to navigate arteries and causes blockages. This can cause intense pain and organ damage. The sickled red blood cells are fragile and prone to rupture. When the number of red blood cells decreases from rupture (hemolysis), anemia is the result. Sickle cells also die in 10–20 days as opposed to the traditional 120-day lifespan of a normal red blood cell.
Sickle cell anemia is inherited as an autosomal (meaning that the gene is not linked to a sex chromosome) recessive condition. This means that the gene can be passed on from a carrier to his or her children. In order for sickle cell anemia to affect a person, the gene must be inherited from both the mother and the father, so that the child has two recessive sickle cell genes (a homozygous inheritance). People who inherit one sickle cell gene from one parent and one normal gene from the other parent, i.e. heterozygous patients, have a condition called sickle cell trait. Their bodies make both sickle hemoglobin and normal hemoglobin. They may pass the trait on to their children.
The effects of sickle cell anemia vary from person to person. People who have the disease suffer from varying degrees of chronic pain and fatigue. With proper care and treatment, the quality of health of most patients will improve. Doctors have learned a great deal about sickle cell anemia since its discovery in 1979. They know its causes, its effects on the body, and possible treatments for complications. Sickle cell anemia has no widely available cure. A bone marrow transplant is the only treatment method currently recognized to be able to cure the disease, though it does not work for every patient. Finding a donor is difficult and the procedure could potentially do more harm than good. Treatments for sickle cell anemia are generally aimed at avoiding crises, relieving symptoms, and preventing complications. Such treatments may include medications, blood transfusions, and supplemental oxygen.
During the first step of the experiment, skin cells (also known as fibroblasts) were collected from infected test mice and put in a culture. The fibroblasts were reprogrammed by infecting them with retroviruses that contained genes common to embryonic stem cells. These genes were the same four used by Yamanaka (Oct-4, SOX2, KLF4, and Myc) in his earlier study. The investigators were trying to produce cells with the potential to differentiate into any type of cell needed (i.e. pluripotent stem cells). As the experiment continued, the fibroblasts multiplied into identical copies of iPS cells. The cells were then treated to form the mutation needed to reverse the anemia in the mice. This was accomplished by restructuring the DNA containing the defective globin gene into DNA with the normal gene through the process of homologous recombination. The iPS cells then differentiated into blood stem cells, or hematopoietic stem cells. The hematopoietic cells were injected back into the infected mice, where they proliferate and differentiate into normal blood cells, curing the mice of the disease.[verification needed]
To determine whether the mice were cured from the disease, the scientists checked for the usual symptoms of sickle cell disease. They examined the blood for mean corpuscular volume (MCV) and red cell distribution width (RDW) and urine concentration defects. They also checked for sickled red blood cells. They examined the DNA through gel electrophoresis, checking for bands that display an allele that causes sickling. Compared to the untreated mice with the disease, which they used as a control, “the treated animals had marked increases in RBC counts, healthy hemoglobin, and packed cell volume levels”.
Researchers examined “the urine concentration defect, which results from RBC sickling in renal tubules and consequent reduction in renal medullary blood flow, and the general deteriorated systemic condition reflected by lower body weight and increased breathing.” They were able to see that these parts of the body of the mice had healed or improved. This indicated that “all hematological and systemic parameters of sickle cell anemia improved substantially and were comparable to those in control mice.” They cannot say if this will work in humans because a safe way to inject the genes for the induced pluripotent cells is still needed.
The reprogramming of the induced pluripotent stem cells in mice was successfully duplicated in humans within a year of the successful experiment on the mice. This reprogramming was done in several labs and it was shown that the iPS cells in humans were almost identical to original embryonic stem cells (ES cells) that are responsible for the creation of all structures in a fetus. An important feature of iPS cells is that they can be generated with cells taken from an adult, which would circumvent many of the ethical problems associated with working with ES cells. These iPS cells also have potential in creating and examining new disease models and developing more efficient drug treatments. Another feature of these cells is that they provide researchers with a human cell sample, as opposed to simply using an animal with similar DNA, for drug testing.
One major problem with iPS cells is the way in which the cells are reprogrammed. Using gene-carrying viruses has the potential to cause iPS cells to develop into cancerous cells. Also, an implant made using undifferentiated iPS cells, could cause a teratoma to form. Any implant that is generated from using these iPS cells would only be viable for transplant into the original subject that the cells were taken from. In order for these iPS cells to become viable in therapeutic use, there are still many steps that must be taken.
In the future, researchers hope that induced pluripotent cells may be used to treat other diseases. Pluripotency is a crucial part of disease treatment because iPS cells are capable of differentiation in a way that is very similar to embryonic stem cells which can grow into fully differentiated tissues. iPS cells also demonstrate high telomerase activity and express human telomerase reverse transcriptase, a necessary component in the telomerase protein complex. Also, iPS cells expressed cell surface antigenic markers expressed on ES cells. Also, doubling time and mitotic activity are cornerstones of ES cells, as stem cells must self-renew as part of their definition. As said, iPS cells are morphologically similar to embryonic stem cells. Each cell has a round shape, a large nucleolus and a small amount of cytoplasm. One day, the process may be used in practical settings to provide a fundamental way of regeneration.
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