'Induced stem cells' are stem cells artificially derived from somatic cells by epigenetic reprogramming. In accordance to the degree of cell dedifferentiation caused by induced reprogramming they are distinguished and subdivided as: totipotent, induced pluripotent stem cells (iPSc) and obtained by so-called direct reprogramming < ref name=" Li "> Li Qian, Yu Huang, C. Ian Spencer, Amy Foley, Vasanth Vedantham, Lei Liu, Simon J. Conway, Ji-dong Fu & Deepak Srivastava. (2012) In vivo reprogramming of murine cardiac fibroblasts into induced cardiomyocytes. Nature, 2012; DOI: 10.1038/nature11044 </ ref> < ref name=" Eva"> Eva Szabo, et al & Mickie Bhatia (2010) Direct conversion of human fibroblasts to multilineage blood progenitors. Nature 468, 521-526 </ ref> < ref name=" Jem"> Jem A. Efe, et al & Sheng Ding (2011) Conversion of mouse fibroblasts into cardiomyocytes using a direct reprogramming strategy Nature Cell Biology 13, 215-222 </ ref> < ref name=" Ernesto"> Ernesto Lujan, Soham Chanda, Henrik Ahlenius, Thomas C. Südhof and Marius Wernig (2012) Direct conversion of mouse fibroblasts to self-renewing, tripotent neural precursor cells. PNAS Published online before print January 30, 2012, doi: 10.1073/pnas.1121003109 </ ref> < ref name=" Marc"> Marc Thier, Philipp Wörsdörfer, Yenal B. Lakes, et al. (2012) Direct Conversion of Fibroblasts into Stably Expandable Neural Stem Cells. Cell Stem Cell, 22 March 2012, doi: 10.1016/j.stem.2012.03.003 </ ref> < ref name=" Han"> Han DW, Tapia N., Hermann A., et al. & Schöler H.R. (2012) Direct Reprogramming of Fibroblasts into Neural Stem Cells by Defined Factors. Cell Stem Cell, April 6, 2012, doi: 10.1016/j.stem.2012.02.021 </ ref> induced progenitor (multipotent or unipotent) stem cells.
Currently, there are three ways to reprogram somatic cells into pluripotent stem cells < ref name=" Yamanaka"> Yamanaka S, Blau HM. (2010) Nuclear reprogramming to a pluripotent state by three approaches. Nature. , 465 (7299) :704-712. </ ref> These are:
- Transplantation of nuclei taken from somatic cells into a fertilized egg from which the nucleus is removed prior < ref name=" Gurdon"> Gurdon J. B. and Ian Wilmut (2011) Nuclear Transfer to Eggs and Oocytes Cold Spring Harb Perspect Biol; 3: a002659 </ ref> or, in the case of human eggs, where the removal of the nucleus breaks further division of the oocyte, just fertilized egg with the nucleus < ref name=" Scott"> Scott Noggle et al. & Dieter Egli (2011) Human oocytes reprogram somatic cells to a pluripotent state Nature 478 (7367), 70-75 doi: 10.1038/nature10397 </ ref>;
- Fusion of somatic cells with embryonic pluripotent stem cells < ref name=" Do"> Do JT, et al. (2007) Erasure of cellular memory by fusion with pluripotent cells. Stem Cells 25:1013-1020 </ ref> and
- Modification of somatic cells, inducing its transformation into a stem cell, using: the genetic material encoding reprogramming protein factors < ref name=" Takahashi"> Takahashi K, Tanabe K, Ohnuki M, Narita M, Ichisaka T, Tomoda K, Yamanaka S. (2007) Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell; 131 (5) :861-872. </ Ref> < ref name=" Wei ">Wei Wang, et al. and Pentao Liu (2011) Rapid and efficient reprogramming of somatic cells to induced pluripotent stem cells by retinoic acid receptor gamma and liver receptor homolog 1. PNAS 2011; published ahead of print October 11, 2011, doi: 10.1073/pnas.1100893108 </ ref> < ref name=" Laure ">Laure Lapasset et al. and Jean-Marc Lemaitre (2011) Rejuvenating senescent and centenarian human cells by reprogramming through the pluripotent state Genes Dev. 25: 2248-2253; doi: 10.1101/gad.173922.111 </ ref>; recombinant proteins < ref name=" Hongyan">Hongyan Zhou, Shili Wu, Jin Young Joo, et al & Sheng Ding (2009) Generation of Induced Pluripotent Stem Cells Using Recombinant Proteins . Cell Stem Cell; 4 (5), 381-384. doi: 10.1016/j.stem.2009.04.005 </ ref>; microRNA < ref name=" Li">Li, Z. and Rana, T. M. (2012) Using MicroRNAs to Enhance the Generation of Induced Pluripotent Stem Cells. Current Protocols in Stem Cell Biology. 20:4 D.4.1-4D.4.14. DOI: 10.1002/9780470151808.sc04a04s20 </ ref> < ref name=" Anokye ">Anokye-Danso F, Trivedi CM, Juhr D, Gupta M, Cui Z, Tian Y, Zhang Y, Yang W, Gruber PJ, Epstein JA, Morrisey EE. (2011) Highly Efficient miRNA-Mediated Reprogramming of Mouse and Human Somatic Cells to Pluripotency. Cell Stem Cell; 8 (4) :376-88 </ ref> < ref name=" Norikatsu ">Norikatsu Miyoshi, et al. & Masaki Mori (2011) Reprogramming of Mouse and Human Cells to Pluripotency Using Mature MicroRNAs. Cell Stem Cell. 8 (6), 633-638. </ ref> <ref> Tilanthi M. Jayawardena, Bakytbek Egemnazarov, Elizabeth A. Finch, et al, & Victor J. Dzau (2012) MicroRNA-Mediated In Vitro and In Vivo Direct Reprogramming of Cardiac Fibroblasts to Cardiomyocytes doi: 10.1161/CIRCRESAHA.112.269035 </ ref> and low-molecular biologically active substances < ref name=" Jem "> Jem A. Efe and Sheng Ding (2011) The evolving biology of small molecules: controlling cell fate and identity Phil. Trans. R. Soc. B August 12, 2011 366:2208-2221; doi: 10.1098/rstb.2011.0006 </ ref>,< ref name=" Stadtfeld ">Stadtfeld M, Apostolou E, Ferrari F et al. & Hochedlinger K.(2012) Ascorbic acid prevents loss of Dlk1-Dio3 imprinting and facilitates generation of all-iPS cell mice from terminally differentiated B cells. Nat Genet. 44(4):398-405, S1-2. doi: 10.1038/ng.1110 </ ref>.