Viral Vectors Cause Harmful Mutations
Stem cells could significantly help in the treatment of various serious diseases, but their collection from human embryos is almost inextricable ethical dilemma. Fortunately, science is now so advanced that it is possible to take common body cells from adults and to make stem-like cells out of them. After that, from those new stem cells, all the other types of body cells could be derived. During this process, genetically modified viruses are commonly used to deliver genes that control the cell nucleus and are inserted into the chromosomes. After that, the genes that make cells pluripotent or reprogrammed are activated, making the stem cell from which it is now possible to make any type cell.
Let’s simplify this process by an example. Four years ago, U.S. scientists took skin cells of 82-year old patient who suffered from severe sclerosis. With the help of genetically modified viruses the cells were then reprogrammed into neurons responsible for motor processes. So, the cells that scientists "created" from simulated stem cells could help them in the understanding and treatment of many diseases. Being said that the patient receives his own cells, the risk of a reaction of the immune system is eliminated, and therefore, doctors are hoping that this approach will lead to success in future cell transplantation therapies. However, although at first glance it does not seem like it, the whole procedure contains some significant drawbacks. For example, it appears that the process of reprogramming cells destabilize the genome and causes various mutations. If you are trying to cure the patient with stem cells that will cause harmful mutations in its genome, then the whole process is ultimately useless.
The New Method
Last year, Dr. Pei Duanying from the Chinese Academy of Sciences with the group of co-workers published a research paper in which they presented a pretty interesting research on human urine. Specifically, Pei and his colleagues concluded that urine contains cells like skin cells (which came in the urine from the renal tubules) that can be successfully reprogrammed into neurons, glial cells, liver cells and heart muscle cells. After a year of intensive work, Chinese scientists have mastered the process and made it faster, more efficient and more reliable.
In the latest study, the cells were isolated from urine samples of three donors (donors were 10, 25 and 37 years old) and were converted into stem cells, from which neurons were developed. After that, the reprogrammed cells were grown in petri dishes, and developed in mature neurons that can generate nerve impulses. From the stem cells, they have also made oligodendrocytes and astrocytes, the two types of glial cells, which are found in the human brain. Once they raised the desired cells, neurons and astrocytes were transplanted into the brains of newborn rats, and a month later they noticed that their grown cells are still alive in the bodies of animals. While this is in itself quite a success, the researchers emphasize that the actual critical period is yet to come - it is necessary to see how long this cells can survive and, in particular, could they be incorporated into the neural network and become fully functional.
This is not the first time that one cell type was converted to another, and that the cells had not previously been brought into pluripotent stage. Two years ago, scientists at Stanford University directly transformed connective tissue cells into neurons in mice. However, this technique still has several important advantages compared to those used by the Stanford team.
Instead of using a virus as a vector for reprogrammed genes, Chinese researchers used a tiny piece of bacterial DNA that can replicate itself. This approach not only speeds up the whole process, but also eliminates the need to reprogram the genes integrated into the chromosome. This process has often caused genetic mutations, and that way made the whole idea of reprogramming cells unusable. However, it is still not clear whether the reprogrammed cells using bacterial DNA are less prone to mutations and what the real benefits of this approach are.
Of the remaining benefits of this new approach we should emphasize the fact that it makes the whole procedure of the creation of new cells much easier and much less invasive. This simply stems from the fact that cell samples now can be derived from urine and not from blood or biopsy. The next step for researchers is to create neuronal cells from urine collected from patients with Alzheimer's, Parkinson's and other neurodegenerative diseases. Since the whole approach was developed precisely in order to treat these conditions, it is crucial to find out whether and how this non-viral way of reprogramming cells affects the incidence of harmful mutations in the genome of the patient.