Imagine being able to grow any kind of human tissue in the laboratory and using it to replace the damaged cells of someone suffering from diseases such as Parkinson’s, Alzheimer’s or muscular dystrophy.
Within a decade or two that science fictional dream could be reality, thanks to a breakthrough last week that scientists have been pursuing for 17 years: the successful culturing of human embryonic stem cells.
Stem cells are undifferentiated cells that are unlike any specific adult cell but have the potential to form any of them. They also have the potential to grow indefinitely in the laboratory. Together, those facts raise the possibility of growing unlimited supplies of any human tissue.
Two different teams of scientists announced last week that they had succeeded in culturing human embryonic stem cells: one from Johns Hopkins University, led by Dr. John Gearhart, and one from the University of Wisconsin at Madison, led by Dr. James Thomson.
The Johns Hopkins team searched small samples of non-living human fetal tissue for “primordial germ cells”–cells which would have eventually become sperm or eggs. Carefully nourished, these cells developed into stem cells.
The University of Wisconsin team harvested stem cells from surplus embryos created for, and willingly donated by, couples using in vitro fertilization. The embryos were at the late blastocyst stage, the equivalent of five to six days after conception, when they consist of about 140 cells in the shape of a hollow ball.
Getting the stem cells to grow wasn’t as simple as plopping them in a petri dish. At Johns Hopkins, for example, the primordial germ cells had to be nurtured on a “feeder layer” of mouse connective tissue cells, within a broth of nutrients and several highly specialized growth factors. But at both universities, stem cells were not only kept alive, but were observed to spontaneously change into cartilage, bone, muscle, neural and gut cells.
Scientists hope, with further study, to eventually be able to direct stem cells to turn into a specific type of tissue. Stem cells don’t age, which means that, properly nourished and guided, they could theoretically generate an endless supply of human tissue.
The first use of the technology will probably be for more quickly screening chemicals as possible medicines. Researchers could test chemicals on laboratory-grown tissue to judge their potential and problems.
But more exciting still is the possibility of growing new tissue for transplantation into patients. And endless supply of laboratory-grown tissue, genetically altered to limit the risk of rejection, would ease the problem of a shortage of donors, and the lab-grown cells could be used to treat numerous ailments, from juvenile diabetes to stroke to heart attack to spinal-cord damage.
The ability to culture stem cells will also teach us more about the process of human development, by enabling us to observe processes we can’t study in living embryos. This could lead to new treatments for infertility and ways to prevent miscarriages and birth defects.
Researchers caution that therapeutic uses are still years away, but you can bet this is about to become one of the hottest fields of medical research–which raises ethical questions.
Both research teams received corporate rather than government funding, because the U.S. government is legally forbidden to provide funding for experiments involving human fetal or embryonic tissue. That’s because many people feel it is disrespectful or even morally wrong to use cells from a human embryo for research or medical purposes. Many people see even a 140-cell blastocyst as a new human being, entitled to all the rights of any other human being. Other people believe that embryos are merely potential human beings, and have no moral standing. Many others’ belief falls somewhere in between.
Stem-cell culturing raises the uncomfortable specter of scientists creating embryos in the laboratory just for the purpose of generating stem cells. On the other hand, in vitro fertilization invariably leads to surplus embryos which are currently either destroyed or kept frozen. Society accepts this as an unavoidable side-effect of the otherwise laudable process of providing children to couples who might otherwise remain infertile. Since those embryos already exist and would otherwise be destroyed, why not make use of them for another laudable process: that of providing treatment for disease?
In light of the promising medical possibilities opened up by the successful culturing of human embryonic stem cells, I think society’s eventual answer will be, “No reason at all.”
