During the last decades the definition and notion of stem cells changed significantly due to new features and characteristics that have been always detailed. Not to go into the scientific debates, stem cells can be characterized as an undifferentiated cell population, able to maintain itself and to differentiate into different cell types. Initially regional/adult (tissue specific) stem cells were considered to produce only cells of their tissue and embryonic stem cells give rise to all cells of the body. But according to the results of the latest research the conception of trans-differentiation was put in to life. There are data that blood stem cells can differentiate into liver and nerve stem cells.

    Stem cells are the main cell resource for such rapidly renewing tissues as blood and epithelium. But stem cells can be found in tissues with low cell turnover. Here they account for their repair (physiological and reparative regeneration). Such cells are in dormant state and are activated only due to specific signals, such as organ injury. Stem cells are represented in low quantity in the tissue and maintain the undifferentiated state due to their peculiar micro-environment. After activation and division tissue specific stem cells give rise to daughter cells, the offspring that proliferate (goes through several division terms) and differentiate, repairing the injured site or supplying the cell population of rapidly renewing tissue. The asymmetric division is believed to be the reason of one stem and one daughter cell derivation maintaining the population, instead of two daughter cells obtainment.

    Nowadays the idea of stem cell obtainment from adult differentiated cells is alluring. One of the methods of autologous embryonic cells obtainment is based on the technique of differentiated somatic (not gamete cell) cell nuclear transfer into the non-fertilized oocyte (ovum). After that, it is stimulated to development and on the blastocyst stage embryonic stem cells are isolated. These cells are genetically identical to the somatic cell donor. The second method implies specific factors usage. These factors bring differentiated cells to the stage of «“stemmness”». Such cells were called induced pluripotent stem cells (iPS) and have all the features of ESC.

    Due to their differentiation potential, the ability to self-renew and repair tissues, stem cells draw the attention of practicing doctors to use this material with the aim of different tissues and organs repair.