Stem Cell Research: New Way To Make Stem Cells Avoids Risk Of Cancer

The new work was accomplished using a plasmid, a circle of DNA, and cells from the foreskins of newborns. "The plasmids carry all the needed transgenes, but don't integrate into the host DNA, they just float around as episomes" in the cell, Thomson says.

The plasmids replicate, but they do so somewhat inefficiently, Thomson explains, so that after they perform the job of reprogramming, they can subsequently be weeded out, leaving the induced cells free of any exotic genetic material. "Once the transgenes have done their job and are no longer needed, one can merely recover induced pluripotent stem cells that have lost their episomes."

The resulting cells, says Thomson, are remarkably similar to embryonic stem cells and show the same capacity to proliferate indefinitely in culture and diversify into all the cell types of the human body.

"The recent discovery that adult cells could be reprogrammed to iPS cells that resemble embryonic stem cells opened up tremendous potential for regenerative medicine," says Marion Zatz of the National Institute of Health's National Institute of General Medical Sciences, which partially funded the new work. "However, the early methods posed significant risks in using iPS cells in a clinical setting. This latest discovery by Thomson's group of a new method for generating iPS cells without inserting viral vectors into the cells' genetic material is a major advance toward safely reprogramming cells for clinical use."

Thomson notes that researchers have developed other promising approaches using mouse cells, and previously had removed most of the vector and exogenous gene sequences from human-induced pluripotent stem cells. However, those efforts did not succeed in removing all of the genetic artifacts of reprogramming, which could still result in mutations in induced cells.

"Given the rapid pace of the field, it won't be surprising if there are several alternative methods for producing vector and transgene free cells very soon," says Thomson. "However, it will be essential to determine which of these methods most consistently produces induced pluripotent stem cells with the fewest genetic abnormalities. Any problems would impact research, drug development and possible transplantation therapies."

Junying Yu, Kejin Hu, Kim Smuga-Otto, Shulan Tian, Ron Stewart, Igor I. Slukvin and James A. Thomson. Human Induced Pluripotent Stem Cells Free of Vector and Transgene Sequences. Science, March 26, 2009

Journal reference:

   1. Junying Yu, Kejin Hu, Kim Smuga-Otto, Shulan Tian, Ron Stewart, Igor I. Slukvin and James A. Thomson. Human Induced Pluripotent Stem Cells Free of Vector and Transgene Sequences. Science, March 26, 2009

Adapted from materials provided by University of Wisconsin-Madison, via EurekAlert!, a service of AAAS.
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University of Wisconsin-Madison (2009, March 26). Stem Cell Research: New Way To Make Stem Cells Avoids Risk Of Cancer. ScienceDaily. Retrieved March 27, 2009,
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