ABOUT STEM CELL

STEM CELL THERAPY

Stem cells are those cells that have the capability of self-renewal and differentiation. Stem cells are classified based on the type of differentiated cell they can reproduce. Pluripotent stem cells can make all cells of the embryo, including germ cells and cells derived from ectodermal, mesodermal and endodermal germ cell lines. (See 'Types of stem cells' above.)Embryonic stem cells are typically derived from the preimplantation blastocyst (7 to 10 days before fertilization). Adult stem cells typically derive from tissue formed beyond 10 to 14 days post fertilization, and are called “somatic” stem cells when derived from non-germ cell tissue. It is unclear whether adult stem cells are present in all tissues, such as pancreatic islet cells. Since 2006, it has been possible to create induced pluripotent stem cells by “reprogramming,” a process that involves gene transplantation into mature cells, with reversion to a pluripotent state. Induced pluripotent stem (iPS) cells provide the potential to create a specific tissue in tissue culture derived from an entirely other somatic cell. The potential for therapeutic use is great, although the need for genetic manipulation in the process limits the transference clinical application at the present time. (See 'Induced pluripotent stem cells (iPS)' above.)Stem cells present current and future opportunities for several different clinical applications. Hematopoietic stem cell replacement is currently a robust intervention for a number of hematologic conditions. Burn therapy, bone grafting and corneal transplant tissues are examples of other current uses of stem cell generated tissue. Tissue replacement treatment for other conditions (retinal disease, Parkinson disease, myocardial infarction) is in development. Concerns about the technology include integrating the transplanted cells into complex cell networks, oncogenesis of the transplant material, and the ability to generate the correct target cell types in the right stage of differentiation. (See 'Clinical applications: cell replacement' above.)Stem cell transplantation may have the ability to modify diseased tissue in a paracrine fashion, without actual engraftment. Drugs directed at endogenous tissue stem cells may modify tissue response to injury. Finally, stem cells may generate tissue to be used as laboratory models for the study of diseases where obtaining live tissue is otherwise difficult or not possible. (See 'Other clinical applications' above.)Ethical concerns have been raised regarding stem cell research. The use of induced pluripotent cells may mitigate concerns about disruption of embryos, but several other concerns remain to be addressed.