"Therapeutic Cloning:" What It's Done For

    Cell division in the human experiments has thus far not proceeded past the four-cell stage. Further cell divisions would produce, by the fourth or fifth day of development, a hollow blastocyst of roughly 100 cells. The blastocyst includes a group of cells, the inner cell mass, that would eventually develop into a fetus. Dissociation of the blastocyst, extraction and culture of the inner cell mass would provide stem cells for major organ systems, such as nerve cells, blood cells, pancreatic islets, and cardiac muscle cells.

    Potential applications include cloning of a patient's own cells in a donated egg, so that the genotype of the stem cells will be identical to that of the patient. This might for example assist in successful transplantation of blood-forming cells into the bone marrow, following radiation therapy to kill cancerous cells, so as to start a new hematopoetic cell line free of cancer.


Text & Figures © 2001 by Scientific American; additional commentary © 2004 by Steven M. Carr