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Read this article to learn about the embryonic stem cell engineering and its applications, limitations and ethical issues.
The cells of the body, when grown in culture generally maintain their original character. Thus, liver cells behave like liver cells, and keratinocytes as keratinocytes.
This is possible since each type of specialized cell has a memory of its developmental history. Stem cells are undifferentiated cells that can divide continuously (indefinitely) to produce daughter cells. The daughter cells undergo differentiation into particular cell types.
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Embryonic stem (ES) cells are an extraordinary class of stem cells that can proliferate indefinitely in culture, as they possess very high developmental potential. The cultured ES cells when put back into the animal can develop into different cell types and tissues. This depends on the site at which they are introduced. For instance, ES cells in liver adopt the character and behaviour of normal liver cells.
ES Cell Cultures to Produce Differentiated Cells:
The ES cells obtained from an early mouse embryo can be cultured indefinitely. The cultures may be continued as monolayers or allowed to form aggregates called embryoid bodies. The cells of the embryoid bodies can specialize and differentiate under suitable conditions (by using various combinations of signal proteins) into different cells (Fig. 40.5). For instance, when treated with certain growth factors, ES cells can form astrocytes and oligodendrocytes. These are the main types of glial cells of the central nervous system.
Cultured ES cells, appropriately treated with growth factors, when injected into the brain can serve as progenitors of glial cells. Thus, it is possible to correct a mouse deficient in myelin-forming oligodendrocytes. The grafted cells are capable of forming myelin sheaths around axons lacking them.
Human Embryonic Stem Cell Research:
It was in 1998, researchers for the first time reported the establishment of human embryonic stem cell lines. These cells, existing indefinitely in culture, are capable of giving rise to any human cell type.
Applications of Human ES Cells:
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The applications of human embryonic stem cell research are extraordinary.
Some of them are listed below:
i. Corrections of disorders with loss of normal cells- diabetes, Alzheimer’s disease, Parkinson’s disease. This can be achieved by appropriate cell therapy.
ii. Engineering and replacement of various tissues.
iii. For the discovery of new drugs, and testing safety of drugs.
iv. To study the development of humans.
Limitations of Human ES Cells:
There are several practical and technical difficulties associated with ES cell cultures and their utility. It is recently (2004) found that contamination with medium (the most commonly used being animal-derived media) created immunological complications when such cells are utilized for therapeutic purposes in humans.
This contamination is identified to be due to a non- human molecule namely N-glycolylneuraminic acid. It is suggested that for human ES cell cultures, products of animal origin of any kind should not be used. An ideal alternative is to use human embryo- derived connective tissue cells as the feeder layer in ES cell cultures.
Ethical Issues of ES Cell Research:
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Many people object to growing of human embryos in the laboratories, even if it is limited to the early stages of development. Some countries have, in fact, banned the use of Government funds for human embryo research. However, some private companies are conducting/financing research on human embryonic cells.
There are many serious ethical, legal and political issues surrounding human ES cell research. This is in addition to the enormous technical difficulties. If may take some more years before the appropriate applications of ES cell research to human welfare becomes a reality.
