Brutes or Angels: Human Possibility in the Age of Biotechnology

2. Stem Cells: Embryos, Therapeutic Cloning, and Personhood

2 Stem Cells Embryos, Therapeutic Cloning, and Personhood It is doubtful that natural sexual reproduction, with its risk of sexually transmitted disease, its high abnormality rate in the resulting children , and its gross inefficiency in terms of the death and destruction of embryos, would ever have been approved by regulatory bodies if it had been invented as a reproductive technology rather than simply “found” as part of our evolved biology. —John Harris, Enhancing Evolution: The Ethical Case for Making Better People Not since Copernicus and Galileo removed Earth from the center of the universe and Charles Darwin placed the ori­ gin of humans and other animals on equal footing has a scientific discovery created more po­ liti­ cal, religious , and social controversy than the 1998 generation of human embryonic stem cells (ESCs). In that year James Thomson and his coworkers at the University of Wisconsin described how they used very early human embryos to obtain cells that could revolutionize medicine. Thomson’s work was honored in 1999 by the Ameri­ can Association for the Advancement of Science as the Breakthrough of the Year, “a rare discovery that profoundly changes the practice or interpretation of science or its implications for society” (1999, 2238). Since 1998, cell biologists working with human ESCs in laboratories worldwide have laid the groundwork for regenerative medicine, a new field that will someday cure now incurable diseases, repair tissue damaged by strokes, heart attacks, and accidents, and offer humans longer, more ac- 38 / Chapter 2 tive lives. This chapter is about the science of stem cells, the new medical treatments they promise, and the ethical dilemmas they raise. Three categories of stem cells occur naturally in humans and other mammals: ESCs, adult stem cells, and embryonic germ cells. In this chapter we examine each of these stem cell types for their biology and clinical potential and for the ethical issues their use raises. We also look at induced pluripo­ tent stem (iPS) cells, cells that do not occur naturally but are products of the laboratory. These iPS and RiPS cells shook up the world of stem cell research in late 2007 and 2010, respectively, because they behave very much like ESCs and do not involve destroying human embryos. As we will see though, iPS cells carry ethical issues of their own. The goal of this chapter is to facilitate the formation of informed opinions and decisions about stem cells and their use. To this end, we consider six questions: 1. Where do ESCs, adult stem cells, embryonic germ cells, and iPS cells come from and what do they do? 2. What are the potential health benefits from each type of stem cell? 3. What is therapeutic cloning, how is it related to ESC research, and why do it? 4. What ethical issues are raised by stem cell research, the clinical use of stem cells, and therapeutic cloning? 5. How do persons from different religious traditions and cultures and ethicists view the moral status of human embryos? 6. How should benefits from new biotechnologies be distributed and biotechnology research be prioritized? Stem Cells: The Biology Occurrence, Normal Functions, and Clinical Uses of Stem Cells Stem cells get their name from the fact that they can generate specialized types of cells, just as the growing tip of a plant stem gives rise to root, branch, leaf, and flower cells. In fact, some stem cells can generate all 252 Stem Cells / 39 types of cells in the human body. Ancestral lines for the trillions of cells in the human body originate in a small group of pluripotent (having a plurality of developmental potentials) stem cells present in very young embryos and, ultimately, from the fertilized egg cell itself. In most cells, mitotic cell division produces two identical daughter cells. But when a stem cell divides, it produces two kinds of cells: (1) another cell like itself and (2) a progenitor cell committed to producing specialized cells via subsequent cell divisions (fig. 2.1). The stepwise specialization accompanying cell division that produces cells dedicated to specific tasks is called cell differentiation. Examples of differentiated cells include oxygen-­ carrying red blood cells, electrical signal-­conducting nerve cells, contracting muscle cells, and insulin-­ producing pancreatic cells. Development of an entire plant or animal from a single fertilized egg, wound healing, and the daily replacement of worn-­ out blood and skin cells are examples of what stem cell division and subsequent cell...