Comparative characteristics of human stem cells

Stem cell (SC) therapy is one of the most promising methods of clinical medicine. Although most stem cell-containing products are still being investigated in clinical trials, some of them are already approved for treatment in many countries. Therefore, modern medicine providing basic understanding of SC subtypes, their properties and potential risks should be incorporated in educational programs of medical universities. The aim of this review is to compare SC types, methods of their procurement, and perspectives of their use. Stem cells can be grouped according to the age of the donor organism. Embryonic SCs are those isolated from blastocysts, obtained from extracorporeal fertilization, cloning, semi-cloning or parthenogenesis (androgenetic and gynogenetic SCs). Fetal SCs are those isolated from embryonic and fetal tissues before birth or from miscarriage and abortion material (including ectopic pregnancies). Fetal SCs include a special group of perinatal extraembryonic SCs, which are obtained from extraembryonic organs (umbilical cord, amnion, placenta) after birth; among them hematopoietic, mesenchymal, epithelial and decidual cells are distinguished. Adult SCs (somatic or tissue specific) are isolated from different tissues and organs of adult organisms throughout their life. Their properties depend on their location and age of the donor. Additionally, induced pluripotent SCs are created artificially from mature cells by modification of gene expression. Every group of SCs is heterogenous and has its advantages and drawbacks analyzed in this review. Also considered in this review is the application of exosomes produced by stem cells as an alternative to cellular therapy.