Pluripotent stem cells (PSCs) such as embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC) can give rise to any fetal or adult cell type and have the ability to self-renew indefinitely.
In contrast to human embryonic stem cells (ESCs) which develop during embryogenesis from the inner cell mass of the human blastocyst, induced pluripotent stem cells (iPSCs) are pluripotent cells artificially derived from an already differentiated cell type by process called reprogramming. Reprogramming is achieved by introducing stem cell-specific transcription factors into a pre-mature or mature somatic cell type.
The resulting iPSCs phenotypically and functionally resemble embryonic stem cells (ESCs), e.g. they can indefinitely self-renew in culture and have the potential to differentiate into cell types from all three germ layers i.e. any cell type. However, it remains to be assessed in more detail, whether they can be considered fully identical to natural pluripotent cells.
The Power of iPSCs
Due to their ESC-like capabilities, iPSCs are a powerful tool for many developmental or disease-related applications. As they can be “made” from a person’s own skin or blood, reprogramming can provide a source of patient-specific, genetically identical cells that would not be rejected by the immune system.
Potential application comprise:
- Basic research: iPSCs can help scientists to further identify mechanisms of development or disease pathogenesis.
- Human disease models: Cells derived from human iPSCs could serve as novel human disease models for performing in vitro drug screening and toxicity studies. Patient-specific iPSC-derived cells may help to evaluate drug effects on individual genomic differences.
- Regenerative medicine: Moreover, iPSCs also hold great potential for being a new tool in regenerative medicine, e.g. for the treatment of degenerative diseases, including diabetes, Parkinson’s and a number of cardiovascular diseases. They could serve as a renewable source of material for producing therapeutic cells for transplantation. Because they can be derived from any individual, iPSCs may be useful for generating autologous therapeutic cells for transplantation for replacing damaged or diseased cells.
The raise of iPSCs makes the usage of pluripotent stem cells independent from the availability of embryonic cells and thus independent of ethic controversy and patient-/tissue-matching issues.
iPSC Generation
For human cells, iPSC generation by cellular reprogramming was first described in 2007 by two independent research groups (Yu J et al. (2007) Science 318 (5858): 1917–1920; Takahashi K et al. (2007) Cell 131 (5): 861–872). In 2012, Sir John Gurdon and Shinya Yamanaka were honored with the Nobel Prize for “the discovery that mature cells can be reprogrammed to become pluripotent” (
https://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/press.html).
Induced PSCs can simply be generated in the lab via introducing stem cell specific transcription factors into primary somatic cells by either viral transduction or non-viral transfection. Typical reprogramming factors used in different combinations are Oct4, Sox2, Klf4, c-Myc, Nanog and Lin28. Expression of these factors in various adult cell types including fibroblasts, peripheral blood mononuclear cells (PBMCs), fibroblasts or CD34+ hematopoietic progenitor was shown to be able reverting those cells back into a pluripotent stem cell state.
NucleofectorTM Technology for iPSC Generation
For the generating iPSCs from a somatic cell, one needs to introduce the relevant transcription factors into the cell to be reprogrammed. Initially, these reprogramming factors were delivered into the somatic cell by retroviral transduction, thereby diminishing their applicability to the clinic because of the permanent integration into the genome. Potential inactivation of tumor suppressor genes by random integration and long-term presence of reprogramming factors may give rise to tumor growth.
Thus, researcher have explored alternatives by using non-integrating RNA viruses or non-viral delivery of episomal vectors or even mRNA. Lonza’s NucleofectorTM Technology has been demonstrated to be a convenient, efficient, and cost-effective non-viral alternative for iPSC generation and is currently being used by leading scientists around the world.
