Induced pluripotent stem cells take small step away from viruses
October 6, 2008 by Aaron Cheung
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Induced pluripotent stem cells (iPS) are stem cells that are created by infecting adult skin cells with four different viruses that carry “pluripotency” factors. This means that the cells develop the characteristics of embryonic stem cells and have the ability to become any kind of cell.
iPS cells have significant advantages over embryonic stem cells as they bypass the ethical issues relating to the use of human embryos. However, one disadvantage of iPS is the use of retroviruses. These viruses do more than turn the adult skin cells into iPS cells. They also integrate themselves into the genome of these cells which makes them unsafe for therapy. Alterations in genes are the cause of many diseases, like cancer.
In a recent publication in Science Express, Scientists at the Harvard Stem Cell Institute, built on their previous discovery to creating iPS cells from skin cells, and significantly improved the method generating iPS cells using another class of virus known as Adenovirus.
Adenoviruses are better than retroviruses as they do not integrate into the genome but still deliver high levels of the proteins needed to create iPS cells. Using adenoviruses, the group led by Dr. Konrad Hochedlinger, found a way to create the desired stem cells, without the potential disease-causing risk.
However, adeno-iPS are not a perfect solution and cells did had one drawback; the efficiency of generating adeno-iPS cells were much lower (0.001~0.0001%) than using conventional retroviruses (0.01~0.1%). While this is a significant step towards generating iPS cells without side-effects, much work needs to be done to improve efficiency in creating them. Fortunately, other methods of generating integration-free iPS cells, such as chemicals, are promising.
This is part of what makes research as exciting as it is. There are always more solutions on the horizon.
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Rett Syndrome and induced Pluripotent Stem cells goes “Green”
June 17, 2009 by Aaron Cheung
Stem cell researchers at The Hospital for Sick Children have now devised a method, reported in the scientific journal Nature Methods, that will facilitate the generation of induced Pluripotent Stem (iPS) cells. I have previously blogged about the promise of iPS cells (see related articles). iPS cells are cells which have been reprogrammed from a differentiated somatic cell (such as your skin cells) to a pluripotent stem cell (like an embryonic stem cell, only that you don’t need to use embryos!). The generation of iPS cells is inherently very rare which occurs at a frequency of about 0.01% meaning you can generate about one iPS cell line out of hundred thousand cells. Out of which, many lines fail to satisfy the different rigorous tests necessary to be given the prestigious name of “iPS cell”.
A group led by Dr. James Ellis, and lead author Dr. Akitsu Hotta, at The Hospital for Sick Children has generated a reporter, named EOS, that will facilitate the generation of iPS cells for both mouse and human. The reporter has DNA elements (called promoters) that will drive the expression of a fluorescent protein (GFP) and an antibiotic resistance gene (puromycin) that will only turn on in pluripotent stem cells, but remain off in differentiated cells. Therefore, scientists can now generate iPS cells from different sources and the iPS cells will literally “light up with a green colour” once reprogramming has been achieved. Furthermore, by adding puromycin to your culture, it will keep the iPS cells in a pluripotent state as iPS cells will normally spontaneously differentiate.
To demonstrate the applicability of EOS, Ellis also derived iPS cells from patients who have a neurodevelopmental disorder called Rett Syndrome. Rett Syndrome is an Autism Spectrum Disorder which affects almost exclusively females at an incidence of 1 in 10,000 and is one of the leading causes of mental retardation in girls. These Rett Syndrome iPS cells were green when placed under a fluorescent microscope and Ellis demonstrated that neurons can be generated from these Rett Syndrome iPS cells, the cell type affected in Rett Syndrome.
In conclusion, the EOS reporter will facilitate the generation of iPS and will be particularly useful for new labs going into this rapidly developing field. Furthermore, Rett Syndrome iPS cells that were also generated in this study will be invaluable for future drug screens that may be beneficial to those with Rett Syndrome.
Article:
Hotta, A. et al. Isolation of human iPS cells using EOS lentiviral vectors to select for pluripotency. Nature Methods 6, 370–376 (2009).
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[...] Variegated embryonic stem cell Induced pluripotent stem cells (iPS) are stem cells that are created by infecting adult skin cells with four different viruses that carry “pluripotency” factors. This means that the cells develop the … Read More [...]
[...] Variegated embryonic stem cell Induced pluripotent stem cells (iPS) are stem cells that are created by infecting adult skin cells with four different viruses that carry “pluripotency” factors. This means that the cells develop the … Read More [...]
[...] in reprogramming mouse fibroblasts into mouse iPS cells (I have previously blogged about this here). However, neither of these breakthroughs have been achieved in the human system and furthermore, [...]