Harvesting Embryonic Stem Cells

The techniques used in harvesting embryonic stem cells are being continually refined so as to arrive at a process that will not be cumbersome for researchers. Recent advances have made it possible to harvest embryonic stem cells without sacrificing embryos and these are indeed welcome developments.

Conventionally embryonic stem cells are harvested by destroying the human embryo in a process called somatic cell nuclear transfer (SCNT). However the objections regarding destroying the human embryo even though it was only 5-7 days old, have forced researchers to come up with alternate techniques for harvesting embryonic stem cells.

In summary, there are three main techniques used to harvest embryonic stem cells

* Somatic cell nuclear transfer (SCNT)

* Altered Nuclear Transfer (ANT)

* Blastomere Extraction

Somatic Cell Nuclear Transfer (SCNT)
Somatic cell nuclear transfer (SCNT) is a laboratory technique that is widely used for harvesting stem cells for research purposes. Here a somatic cell, which is any cell from the body other than a sperm or an egg, is used. The nucleus of this somatic cell is transferred into an egg cell, whose nucleus has also been removed.

After the somatic nucleus is transferred into the egg cell, the host cell then reprograms the cell nucleus. This altered cell is then stimulated by shock and begins to divide producing a blastocyst. The latter is an early stage embryo having about 100 cells. The blastocyst is destroyed between 5 and 7 days and stem cells are harvested for research purposes.

The fact that the resulting embryo must be sacrificed has raised ethical hackles among the scientific community. That is why alternate methods, which do not require the destruction of the embryo, are being explored.

Altered Nuclear Transfer (ANT)
Altered nuclear transfer (ANT) is a proposed technological approach to obtain embryonic stem cells without destroying the embryo. This technique is being advocated by William B. Hurlbut as an alternative to the conventional SCNT.

Dr Hurlbut proposed this method, which prevents an embryo from being formed. The biological entities that are created using this technique do have the properties of embryonic stem cells, but are not the predecessors of living organisms per se.

In a landmark paper, Dr Hurlbut and colleagues write, "Using the techniques of somatic cell nuclear transfer (SCNT), but with the intentional alteration of the nucleus before transfer, we could construct a biological entity that, by design and from its very beginning, lacks the attributes and capacities of a human embryo."

Such a method has the potential to produce the embryonic stem cells required for research. This method also bypasses the ethical dilemma generated from the necessity of having to destroy the embryo to harvest stem cells.

Blastomere Extraction
This technique was propounded by Robert Lanza and colleagues at the Advanced Cell Technologies (ACT). In a paper in the November 2006 issue of Nature, Dr Lanza proposed that a single blastomere (cell) is removed from a eight-stage blastocyst (inner mass of the embryo) and is cultured to from an embryonic stem cell.

This means the embryo itself is not harmed in any way and can go on to grow into a full human being without any problems. However this is a controversial technique as some researchers argue that it is not possible for an embryo to grow normally following the extraction of a single cell.

In summary, the above mentioned techniques of harvesting embryonic stem cells are not perfect. Scientists are working to refine these methods so as to arrive at a technique that is morally as well as ethically acceptable to the society.


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