A major obstacle to widespread therapeutic use of human embryonic stem cells is this nasty tendency for a few of them to turn "Frankenstein" on us. Out of the tens of millions of pluripotent cells used in therapy, cells that have been "programmed" by scientists to become any type of specified adult tissue, a few go rogue and become dangerous tumors called teratomas when transplanted into patients. So, researchers at Stanford University, writing in the journal Nature Biotechnology, describe a method to get rid of the cells that can become teratomas before they are used in humans.This deals with a recently detected problem: the fact that stem cells have far more mutations on them than we'd like a problem first detected in March:
"The ability to do regenerative medicine requires the complete removal of tumor-forming cells from any culture that began with pluripotent cells," Stanford's Irving Weissman said in a release. "We've used a combination of antibodies to weed out the few undifferentiated cells that could be left in the 10 or 100 million differentiated cells that make up a therapeutic dose."
The article mentions a couple of studies into the genome of induced pluripotent stem (iPS) cells, which are adult cells that have been reprogrammed into stem cells. They, in turn, could be transformed into any type of tissue. Researchers at the University of California, San Diego, sequenced the gene-coding portion of the genome in 22 iPS cell lines that had been reprogrammed. "Every cell line we looked at, we found single [genetic-letter] mutations in the protein-coding region, an average of six mutations per cell line," Zhang told Technology Review. A disproportionate number of the mutations appeared in genes involved in cell growth or in genes that have been previously linked to cancer.This is a Big Deal, as the use of stem cells promises many breakthroughs in reconstructive medicine.
Basically, in a mature body, these unprogrammed cells migrate to a place where a cell is needed, and based on the local environment, are programmed to become the type of cell needed. This is the mechanism by which patients who have had bone-marrow transplants gradually become genetically identical to the donor - as described in an earlier post.
Our bodies are not so much objects, as processes. We are performance art, rather than a static display, changing slightly from day to day. And our somatic identity is not determined by our genes, it's a construct where genes are part of the process, not the whole story.
I've had to write an extensive chapter on this issue (amongst the many others involved in Evolution), and the distinction between Genotype and Phenotype for my PhD thesis. It's the Phenotype that determines the "Fitness" of an entity in a population, but the Genotype that determines what characteristics are transmitted to the next generation. The Phenotypes of the next generation are influenced by more than just genes, but the environment too. Many phenotypes can result from a single genotype - just ask any pair of Identical Twins. They comprise a clone, genetically identical, yet the bodies have subtle differences. Genes don't so much define the body, as define the range of possible bodies, and the chances of various characteristics manifesting, depending on foetal environment. Two genetically identical foetusses in two different host mothers may differ considerably.