Clonaid’s claim to have produced the first human clones propelled the ethical debate about human cloning to the headlines last December. Given this fanfare, the debate has tended to focus on reproductive cloning—the use of cloning to generate a human being—and its bizarre societal and familial side effects. What deserves greater attention, however, is therapeutic cloning, a (potential) cloning application considered far more important to the biomedical and scientific communities and one far more ethically challenging.
Though fraught with problems, reproductive cloning at least strives to reproduce a human being and, in principle, preserves the value of human life. Therapeutic cloning, on the other hand, creates human embryos merely as a source of embryonic stem cells. Some in the biomedical community hope to develop techniques to generate replacement tissues from these embryonic stem cells. Implanting replacement tissue into damaged and diseased organs would provide the opportunity to treat and possibly cure many dreaded diseases and debilitating injuries. Tragically, however, in order to harvest stem cells from human embryos, the embryos must be destroyed. Crudely put, therapeutic cloning looks to generate human embryos solely for the body parts they can provide.
Recent and ongoing research suggests an alternative approach that can achieve the same goal (repair of damaged or diseased organs) without destroying human embryos. One such approach, called “xenotransplantation” (the transplantation of living cells, tissues, and organs from one species to another species), turns to pigs as a source of organs for human transplants.
To date, a number of obstacles have hindered pig-to-human xenotransplantation. The chief one is hyper-acute rejection (HAR)—the rejection of pig organs by the human recipient. HAR occurs because the sugar groups on the surface of pig and human cells differ.
A recent breakthrough, however, offers the hope that HAR can be overcome. An international research team genetically engineered pig cells that lacked a functional form of the gene that codes for a key enzyme involved in the production of the cell surface sugars that cause HAR. The researchers then used these cells as the source of genetic material to clone pigs with organs that lacked the sugar groups responsible for HAR. In fact, the research team oversaw the birth of four normal, healthy piglets with organs suitable for human transplants.
With this advance, the biomedical community takes one more step toward successful xenotransplantation. The step forward in science also can be a step forward in ethics. Though the science of cloning presents opportunity to exploit and devalue human life, it may, on the other hand, provide the means to alleviate significant human suffering in a way that upholds the sanctity of human life.
- Practical implementation of reproductive cloning suffers significant problems. To date, all animal clones have experienced severe health problems in utero, at the time of birth and throughout life. The scientific community expects the same for human clones. Currently, cloning is a “hit-and-miss” endeavor. Most cloning attempts fail, with success rates varying from 0 to about 4%. This means that hundreds of human embryos would die to achieve a single live human clone birth. Those two factors make attempts to clone humans for reproductive purposes ethically troubling.
- Pig organ size and physiology are comparable to that of humans.
- Carol J. Phelps et al., “Production of a-1, 3-Galactosyltransferase-Deficient Pigs,” Science 299 (2003), 411-4.