With each new report of a technological breakthrough, stem cells both inspire hope in patients and incite ethical controversy. Some see stem cells as a potentially game-changing cure for currently terminal diseases; others see them as an unnecessary obsession of scientists who lack reverence for human life at its earliest stages. So, is this debate worth the time and energy? Yes, it is. Stem cells occupy a fundamental place in human biology and disease, which means, as an issue, they aren’t going away.
The reason scientists have focused so intensely on stem cells is because these cells sit at the beginning of an elaborate decision-tree that accounts for why our bodies are made up of hundreds of different types of cells, ranging from motor neurons to fat cells, despite the fact that nearly all of those cells carry exactly the same genetic material. The process of development from a single fertilized egg cell into a full-grown adult is possible because different types of cells make different decisions about what parts of our DNA should be active. A neuron is a neuron, and not a liver cell, because that neuron has a particular pattern of active DNA. This pattern of active DNA is achieved in stages, beginning with a stem cell and working down a DNA decision-tree until the final, specialized cell type is reached. In other words, nerve cells generally can’t produce other nerve cells; stem cells produce nerve cells—and fat cells, and everything else. Just as nobody becomes an adult without passing through childhood first, specialized cells that carry out specific jobs are created only by passing through a stem cell stage.
The fundamental position of stem cells in our biology means that as our understanding improves, so will our ability to manipulate human life at its very beginning.
The vital role of stem cells in creating each kind of specialized cell is why stem cells are a big focus of biomedical research. Many diseases could potentially be treated by transplanting freshly created supplies of specialized cells that have been damaged during the course of a disease: retinal cells in blindness caused by macular degeneration,skeletal muscle cells in muscular dystrophy, pancreatic cells in diabetes, neurons in spinal cord injuries, and dopamine-producing cells in Parkinson’s disease. To create new supplies of these different types of cells, you must begin with stem cells, and preferably stem cells that carry the DNA of the patient.
IN PRINCIPLE, THE PROCESS of treating diseases with stem cells made with a patient’s DNA will work something like this: 1) take easily available cells (like skin cells) from a patient with, say, Parkinson’s Disease, 2) transform the skin cells into stem cells, and then 3) coax those stem cells to become dopamine-secreting cells, which you can transplant back into the patient. If you’re really ambitious, you can edit the DNA of those cells to repair the Parkinson’s-causing mutation before transplanting them back into the patient. A second approach is to 1) take isolated DNA from a patient, 2) transplant that DNA into a donated human egg cell, 3) induce that egg cell to become an embryo and extract the stem cells, then 4) use those stem cells to create specialized cells that get transplanted back into the patient.
Both of these methods are being pursued by scientists, and neither one is, at this point, without risk. The process of directly creating stem cells from a patient’s skin cells involves mucking around with genes that can lead to cancer: you may cure one disease, only to produce another. The second process, transplanting a patient’s DNA into a donated egg cell, while much more reliable, requires donated egg cells, involves creating and destroying embryos, and is also the first step toward making cloned copies of human beings.
Neither of these approaches to creating stem cells will ultimately avoid the ethical controversies, because the fundamental position of stem cells in our biology means that as our understanding improves, so will our ability to manipulate human life at its very beginning. Scientists may soon be able to routinely create clinically usable stem cells without harvesting embryos, but as they become better at creating and manipulating stem cells, it will be easier than ever to create life from scratch outside of the womb. Creating customized human embryos for research and other applications will be routine, and cloning a human being will be a feat that won’t require the resources of an elite, well-funded research lab. And so, we will have to choose how to resolve the controversies—or not—but technology won’t do it for us.