Stem Cell Reprogramming and Therapeutic Applications
Reprogramming Adult Cells to Pluripotency
Can terminally differentiated adult cells be reprogrammed to become pluripotent?
- Yes, this was demonstrated by semi-starving cells from a mammary cell donor, effectively reversing their maturation (dedifferentiation). The process involved taking an enucleated egg from a donor and fusing it with the mammary cell. The resulting cell was cultured to form an embryo, which was then implanted into a surrogate sheep. This sheep carried the embryo to term and gave birth to Dolly.
- This method allows for the cloning of mammals.
- A terminally differentiated adult cell can be reprogrammed to become pluripotent by manipulating and semi-starving the cells, causing them to alter their gene expression profiles.
Embryonic Stem (ES) Cells
- Embryonic Stem cells are highly plastic cells capable of differentiating into any cell type in the body.
- They are found in embryos, specifically during the zygote to blastocyst stage (3-5 days).
- The inner cell mass within the blastocyst gives rise to all the different tissue cells of the embryo, while the outer cells form the placenta.
- Embryonic Stem (ES) cells are derived from the inner cell mass when it is removed and cultured.
- The removal of stem cells from the blastocyst results in the destruction of the embryo.
- ES cells are pluripotent, meaning they can become any of the 220 different cell types in the body.
- Researchers have developed techniques for creating stem cells without using human eggs or embryos, potentially resolving ethical concerns in the field.
Induced Pluripotent Stem (iPS) Cells
- c-myc is an oncogene when overexpressed.
Potential Uses of iPS Cells
- The initial goal was to reverse the aging of patient cells and transform them into cells of interest. This would allow for targeted drug delivery through cell culture instead of systemic administration.
- The procedure involves replacing damaged cells with healthy, differentiated cells derived from the patient’s own iPS cells.
- This procedure is expensive and time-consuming. There are risks involved, such as the potential for incomplete differentiation, which could lead to the introduction of cells capable of becoming any cell type in the body.
Dolly the Sheep
Dolly was genetically identical to the mammary cell donor. Removing the nucleus from the egg cell donor allowed the nucleus from the mammary cell donor to direct the development of all cells in Dolly’s body.
Generating iPS Cells
Skin cells were treated with four genes: Oct4, Sox2, c-myc, and Klf4. These genes act on the DNA to activate specific regions, generating cells similar to embryonic stem cells.
Induced Pluripotent Stem (iPS) cells are produced by treating mature cells, such as fibroblasts, with genes that “dedifferentiate” them to a pluripotent stage, similar to an embryonic stem cell. Viral vectors, such as retroviruses, are generally used for gene transfer. The transformed cells become morphologically and biochemically similar to pluripotent stem cells, with the advantage of representing autologous cells in therapeutic applications.