All of the hundreds of different cell types it takes to make you, each doing dramatically different things, share the exact same cookbook—the same genome. It's like a massive four-star restaurant with every chef using a copy of The Joy of Cooking. Making all those cell types requires the genome to be dog-eared or tabbed—marking genes for reading or silencing.
Embryonic stem cells are made from a few dozen cells in an early embryo before all these markings have been made. Tricking these cells into dividing creates a stem-cell line made of billions of cells that can become any cell type in the body. Each year thousands of extra embryos are created for in-vitro fertilization, only to be destroyed with bleach and dumped down the drain when insurance stops paying for their storage. So why not use these excess embryos to make and then farm a bank of stem-cell lines—one to match every transplantation type? The president, with his towering moral compass, deemed this idea too evil to consider. As a result, scientists have been scrambling to discover an alternative way of making "embryonic" stem cells without destroying an embryo—allowing the saved embryos to be bleached and dumped down the drain, as God apparently desires.
The Holy Grail is to "reprogram" an adult cell by somehow removing all the markings. We can do this with adult cells from a mouse. By putting the nucleus—the genome's home—of an adult cell in an unfertilized egg that has had its half-nucleus removed, the adult cell's genome can be wiped clean enough to make an embryonic stem cell line. Great! Except this technique can also be used for cloning, is horrifically inefficient, and requires a tremendous amount of unfertilized eggs—cells that are expensive to acquire, dangerous to collect, and incredibly delicate.
This brings us to three scientific papers that came out this month. Two groups—one in Japan, another at MIT—showed that adult mouse cells can become embryonic stem cell-like after adding four genes, two of which are known cancer-causing genes, and selecting for the rare cell where it worked. Great! Except, would you want cells with two added cancer-causing genes injected into you? The third paper described a way of re-using eggs from in-vitro fertilization that absolutely cannot become a baby—fertilized by two sperm, for example—to reprogram an adult cell's nuclei to be like embryonic stem cells. But will the reusing of doomed embryos still be too morally icky to be accepted?
Most importantly, all of this promising work is in mice. Mice are not little people. It is not clear that adult human cells can be reprogrammed; there is only one hint in all the scientific literature. The tricks that work in mice have failed so far with human cells. Reprogramming human cells is a worthy goal, but we're not as close as you've been led to believe. Expect wild distortions of the mouse work in the future as the human embryonic stem-cell bills are vetoed repeatedly.