Third, stem cells can give rise to specialized cells a process called differentiation. Scientists are attempting to understand the signals that trigger the differentiation in stem cells. These signals are both internal and external. The cell’s genes control the internal signals and intersperse them across the DNA which carry coded instructions for all the functions and structures of the cell. The external signals differentiate the cells by including chemicals secreted by other cells, physical contact with neighboring cells and certain molecules in the microenvironment.
Although the term stem cell is often referred to as the cells in the adult organism that renew tissue, the most basic and unusual of the stem cells are found in the early stage embryo. These embryonic stem (ES) cells have the special ability to develop into nearly any cell type, unlike the adult stem cells. Embryonic germ (EG) cells which originate from primordial reproductive cells of the developing fetus have similar properties of the ES cells. It is the unique versatility of the ES and EG cells from the early stage embryo and cadaver fetal tissue that offer scientists the possibility to generate more specialized cells or tissues, which could allow the generation of new cells used to treat injuries or diseases like Alzheimer’s, Parkinson’s, heart disease and kidney failure. Also, scientists believe these cells could be the means for understanding the earliest stages for human development and important tool in developing life saving drugs and cell replacement therapies to treat disorders caused by early cell death or impairment.
Human stem cells can be derived from the following sources:
- Human fetal tissue after elective abortion (EG cells)
- Human embryos that are created by in vitro fertilization (IVF) and that are no longer needed by couples being treated for infertility (ES cells)
- Human embryos that are created by IVF with gamaetes donated for the sole purpose of providing research material (ES cells)
- Potentially, human (or hybrid) embryos generated asexually by somatic cell nuclear transfer or similar cloning techniques where the nucleus of an adult human cell is introduced into an enucleated human or animal ovum (ES cells).
The successful isolation and culture of ES and EG cells have caused a longstanding ethical controversy about the research of human embryos and cadaver fetal material. The controversy arises from differing moral views regarding elective abortion and the use embryos for research. This brings both a challenge and opportunity to the ethical debate. The challenge concerns both important and morally contested questions about the beginning of life. The opportunity brings forth but another serious public discussion about the importance that this biomedical science discovery offers to improve human welfare and the quality of life.
While most would agree that human embryos deserve respect as a form of human life, disagreements arise regarding both what form of such respect should take and what level of protection is required at different stages of embryonic development. This embryo research is bound to raise serious concerns between two important ethical commitments to cure disease and to protect human life. Some believe that the embryo has the moral status of a person from the moment of conception, and research that would destroy the embryo is considered wrong and should not take place. Others believe arriving at an ethically acceptable policy ion the arena involves a complex balancing of a number of important ethical issues.
For most, the resolution of these ethical issues depends to some degree on the source of the stem cells. The use of cadaver fetal tissue to derive EG stem cells is usually the most accepted. With respect to ES stem cells, most draw an ethical distinction between the two types of embryos. The first referred to as the research embryo, an embryo created through IVF provided solely for research purposes. Many have expressed that the federal government should not fund research that involves creating such embryos.
The second type of embryo is created for infertility treatment, but is now intended to be discarded because it is unsuitable or no longer needed for such treatment. The use of these embryos raises fewer ethical questions because it does not alter their final disposition.
