Linda’s daughter has heart disease, Sylvia’s husband Alzheimer’s. Joe’s neighbor has Parkinson’s, Jesse’s nephew is paralyzed. All of these people long for medical research to develop cures for debilitating disease and injuries.
In light of this longing, people want to know, Should stem cell research be allowed or shouldn’t it? Did President George W. Bush make the right decision in allowing federal funds to go toward research on already existing embryonic stem cells? And, what other types of stem cell research can be done? Conflict and perplexity characterize discussions of this ethical quagmire.
The news media typically portray those who value human life as human life from the moment of conception as radicals opposed to scientific advances and indifferent to human suffering. What kind of response can bridge the gap between those in favor of virtually any form of biomedical advance with the potential to alleviate suffering and those who recognize that biotechnology has the potential to devalue and abuse human life? Can Christians participate in the stem cell debate in a way that expresses care and compassion—a way that might appeal to skeptics and seekers?
No thoughtful response is possible without an understanding of the basic science behind stem cell research. The following paragraphs offer a brief overview, and a ray of hope.
More than two hundred different types of cells make up the human body. These different cell types interact to form the wide range of tissues found in the human body. Specialized tissue cells develop from more generalized cells through the process of cell differentiation. Generalized cells that give rise to differentiated cells are called stem cells. When a stem cell divides it produces two daughter cells: one a stem cell and the other a cell that develops into a specialized cell. This characteristic of stem cell division makes stem cells “self-renewing.”
Scientists know of three types of stem cells: unipotent stem cells capable of developing into a single specialized cell type; pluripotent stem cells capable of developing into a few closely related cell types and totipotent stem cells capable of developing into any cell type found in the adult organism. The presence of stem cells in an adult allows some tissues to regenerate throughout a human’s lifetime. Unfortunately, some adult tissues lack stem cells, and, therefore, cannot regenerate when impaired or in response to aging. After a heart attack, the damaged cardiac muscle cannot be replaced since adult heart tissue lacks stem cells.
Scientists have long regarded unipotent and pluripotent stem cells as the only stem cell types in adults. Totipotent cells are found exclusively in the early stages of embryonic development immediately after fertilization occurs. After fertilization, the zygote (the fertilized egg), rapidly divides several times. The resulting cells, called blastomeres, all have the potential to develop into the various tissues comprising the human body. They are totipotent. Shortly after this embryonic stage, the cells begin to differentiate, sealing their developmental fate to a specific cell type. The only cells capable of developing into all tissue types are blastomeres.
Biochemical researchers looking for treatments for devastating conditions such as heart disease or spinal cord injuries are pursuing cell replacement therapies—the implanting of healthy tissue in place of damaged tissue. Few sources for replacement tissue currently exist. Researchers hope that totipotent blastomeres can be cultured in the lab and coaxed to develop into the different tissue types needed for tissue replacement. However, state-of-the-art techniques result in destruction of the embryos supplying these blastomeres.
Herein lies the source of controversy in the stem cell debate. Many people view the destruction of the viable embryos from which totipotent blastomeres are harvested as nothing less than the taking of human life. They question whether this end truly justifies the means. Biomedical researchers, on the other hand, see no other source of totipotent stem cells. These scientists, especially those who do not necessarily share the perspective that man is made in God’s image, become frustrated by ethical objections that delay important experiments necessary to develop technology capable of alleviating human suffering. Even more perplexing to them are objections to the use of “leftover” human embryos produced by in vitro fertilization. After all, embryos no longer needed for the procedure are slated for destruction. Many Christians do not see this use as an acceptable compromise. They see it, instead, as utter disregard for “unwanted” but immeasurably valuable human life.
Some very recent scientific advances have the potential to virtually dissolve this ethical quagmire. Until now, developmental biology has regarded adult stem cells as having only restricted capability to develop into specific tissue types. Scientists have viewed cell differentiation as mostly irreversible. However, current work suggests that this paradigm will soon be overthrown.
A team of scientists from Canada’s McGill University recently isolated a unique type of stem cell from the skin of adult and juvenile mice. The McGill scientists coaxed these stem cells to develop into neurons, smooth muscle, and adipocyte (fat) cells. This work holds twofold significance. Biomedical researchers previously thought that adult stem cells could only develop into cell types of the same tissue lineage, but these cells developed into cell types representing different tissue lineages. Though not totipotent, these stem cells manifested developmental potential beyond that of typical pluripotent stem cells. Secondly, these unique multipotent stem cells derive from the skin making them easily accessible. The human scalp may actually possess this type of adult stem cell.
Another team of scientists has recovered adult stem cells from the bone marrow of mice—cells that developed into lung, skin, stomach, and intestine cells. Yet another team has isolated mouse brain tissue stem cells with the capacity to develop into nonneural tissues. These studies usher in an important paradigm shift in stem cell research that may well eliminate the demand for embryonic stem cells.
Another mouse study overthrows an additional long-held paradigm in developmental biology—namely, that some tissue types lack the capacity to regenerate after injury. Investigators from the Wister Institute in Philadelphia discovered a mouse with the amazing capacity to regenerate heart muscle tissue. In mammals, damage to cardiac tissue leads to the formation of nonfunctional scar tissue. Yet when their hearts were damaged, these mice displayed limited scar tissue buildup and produced replacement cardiac tissue. Understanding the molecular and genetic framework for this remarkable property holds potential for pharmaceutical treatment not only to repair damage from heart disease, but perhaps to repair damaged nerve tissue as well.
These thrilling advances, as well as new ones anticipated in the future, will likely lead to a shift in the focus of stem cell research. While continuing to oppose destruction of human embryos, the Christian community can and should aggressively support additional funding for stem cell research with the same goal as the scientific community—alleviating human suffering.
Daughters, husbands, neighbors, and nephews—loved individuals—all deserve compassion and the best of ethical research. On this common point of human dignity everyone can agree.
For a primer on stem cell research posted by the National Institutes of Health see http://stemcells.nih.gov/info/basics/ [28 April 2009].