Stem cells

Cultivable pluripotent stem cells are under close attention of researchers all over the world due to their enormous potential for curing a vast range of human degenerative diseases, which demand tissue replacement therapy. These cells have two unique properties: they can transform into any known cell types in an organism, and they also are able to indefinitely proliferate in vitro with all their fantastic properties kept unchanged.

Embryonic stem cells were first isolated in 1980s from mouse embryos, and for more than 20 years remain an important instrument for studying gene functions. However, scientists are aware of serious limitations for using these cells in clinical practice. One of these limitations is immune incompatibility of differentiated cell products from alien lines of embryonic stem cells during transplantation.

Discovery of a new type of stem cells – induced pluripotent stem cells – was a groundbreaking event in the field of stem cell biology. These cells have some advantages over embryonic stem cells, for instance, they can be synthesized from own somatic cells of a patient and cause no problems with immunity. Well, these cells also aren’t a cure-all – they are highly mutagenic, their chromosome content is unstable, and they have higher immunogenic activity, than embryonic stem cells. From the other hand, induced pluripotent stem cells open wide prospects for modeling and studying many human diseases.

A serious problem, which needs to be solved, prevents pluripotent stem cells from being used in clinical practice – such cells tend to form teratomas, fast-growing teratoid tumors, which contain various types of differentiated cells. Even two embryonic stem cells, injected subcutaneously into mice, cause teratoma formation and death of animals. Transplants almost always contain traces of these cells, which means possible formation of abovementioned tumors – this means safe usage of these cells in medicine is still a dream.

Russian researchers suggest a solution for this problem – stable introduction of a suicide gene into genome of any type of stem cell. Genetic construction allows the gene to work only when a cell is in undifferentiated state, in other words, able to form tumors, and when a cell “switches” to safe mode, the suicide gene turns off. This technique, designed in the Russian laboratory and tested on mice, is already patented.

The technique is close to perfection – introduction of undifferentiated embryonic or induced stem cells into blood stream doesn’t result in tumor formation. After injection these cells are followed to a target organ or tissue, transform into necessary cell types, and unchanged cells are then destroyed by suicide genes inside recipient’s body without any harm to other types of cells.

However, integration of suicide genes into cell’s genome is not as easy, as one may think. There is a tiny possibility that these genes may disturb normal functioning of host cell genes, including those, which protect cell from transformation into a cancer cell. Moreover, activity of suicide gene can decrease, and control over tumorigenicity will be lost. The key to solving these problems is in synthetic chromosomes. Researchers are currently working on these chromosomes.

Source: Science & Technologies

Anna Kizilova