Comparative characteristics of human stem cells

Stem cell (SC) therapy is one of the most perspective methods of clinical medicine; SC containing products are actively investigated in clinical trials, while some of them are already officially approved for treatment in many countries worldwide. So quickly developing direction of modern medicine should be properly reflected in educational programs of medical universities, providing basic understanding of SC subtypes, their properties and potential risks. The purpose of this review is to perform comparative analysis of SC types, methods of their procurement and perspectives of their employment. SCs could be divided into groups according to the age of the donor organism. Embryonic SCs are isolated from blastocyst, obtained as a result of extracorporeal fertilization, cloning, semicloning or parthenogenesis (androgenetic and gynogenetic SCs). Fetal SCs could be isolated from embryonic and fetal tissues before the birth or from miscarriages and abortion material (including ectopic pregnancy). Among fetal there is and especial group of perinatal extraembryonic SCs which are obtained from extraembryonic organs (umbilical cord, amnion, placenta) after the birth; among them hematopoietic, mesenchymal, epithelial and decidual cells are distinguished. Adult (somatic, tissue specific) SCs could be isolated from different tissues and organs of adult organism throughout the life; their properties depend on the place of their localization and age of the donor. Additionally, SCs could be created artificially from mature cells by modification of gene expression; they are united in the group of induced pluripotent SCs. Every group of SCs is not homogenous and has its advances and drawbacks, analyzed in this review. Also, application of exosomes produced by stem cells as an alternative of cellular therapy is considered.