STEM CELL RESEARCH + HUMAN CLONING
In recent years, stem cell research and related bioethical issues have posed new ethical challenges. As science, technology, and medicine continue to advance, human life must be respected and protected at every stage and in every condition.
What are stem cells?
A stem cell is an unspecialized cell with two unique abilities:
to become different types of cells, such as heart, blood, or nerve cells
to self-renew, dividing and creating more stem cells
Stem cells are found in many places throughout the body. They usually function to replace dead cells and repair damaged tissues. In young organisms (embryos), stem cells give rise to the different organs and tissues of the body as it develops.
Some stem cells are multipotent, which means that they can become only a limited number of cell types—usually cells within a specific tissue type. Stem cells found in the adult body (adult stem cells) are usually multipotent. Other stem cells are pluripotent, which means that they can theoretically become all of the cells types of the body. These cells are found in young embryos (embryonic stem cells).
Scientists seek to harvest stem cells in order to use them for research and medical therapies. Scientists aim to transform stem cells into the tissue types targeted by disease or injury and transplant them into patients’ bodies, where they can work to repair damaged organs and body systems.
Types of stem cells
Adult (or non-embryonic) stem cells (ASCs): These stem cells have traditionally been called “adult stem cells” even though they are present in both adults and children. ASCs are found in various tissues such as bone marrow, skin, and fat. They are also found in umbilical cord blood, placentas, and amniotic fluid. No harm is done to people when ASCs are extracted from them for research or therapies.
Embryonic stem cells (ESCs): These cells are found in the “inner cell mass” portion of a young embryo about five days after fertilization, which is called a blastocyst. ESC researchers derive the stem cells from the embryo and culture them in the laboratory.
Most embryos used for ESC research were created through in vitro fertilization (IVF) at fertility clinics and then donated for research (because they were “left over” and the parents did not want to implant them). Embryos can also be created by cloning (somatic cell nuclear transfer) specifically in order to derive their stem cells. These stem cells are sought because they would be genetically (nearly) identical to a patient. (See “Human cloning” below.)
ESC research is unethical because it requires killing the embryo in order to derive the stem cells. Human ESCs were first derived at the University of Wisconsin in 1998. Stem cells from cloned human embryos were first derived by a team of Oregon scientists in 2013.
Induced pluripotent stem cells (iPSCs): In a major breakthrough, researchers in 2007 announced that they had taken adult cells and genetically “reprogrammed” them to become pluripotent stem cells, virtually equivalent to ESCs. These induced pluripotent stem cells seem to offer the same theoretical benefits as ESCs from cloned embryos—they can be taken from a patient’s own body, so they are genetically matched to that patient—but they do not require the destruction of human embryos or human cloning. Japanese scientist Shinya Yamanaka won a Nobel Prize in 2012 for his discovery of the iPSC technique.
In 1996 Dr. Ian Wilmut famously used the cloning process called somatic cell nuclear transfer (SCNT) to create Dolly the sheep, the first adult mammal created by that method. In SCNT, the nucleus of an egg is removed and replaced with the nucleus from a somatic cell (a body cell other than an egg or sperm cell). The DNA from the somatic cell gives the egg a full complement of 46 chromosomes. The egg is then stimulated using electricity or chemicals, and, if successful, it begins dividing as a new embryo. The new organism is genetically virtually identical to the individual from whom the somatic cell was taken.
After the first isolation of human ESCs in 1998, researchers envisioned using SCNT to create cloned human embryos whose ESCs could be extracted for research and therapies. By using somatic cells from patients (people suffering from diseases or conditions that stem cells might help treat), cloned embryos could be created whose stem cells would be genetically matched to those patients, possibly preventing rejection by the immune system. (See “The benefits of stem cells” below.) Human cloning offered the chance to create “patient-specific” pluripotent stem cells.
Traditionally, a distinction has been made between “reproductive cloning” and “therapeutic cloning.” In reproductive cloning, the embryo created by SCNT would be implanted in a woman’s uterus with the intention that it develop toward maturity and become a fetus, infant, child, and so on. Almost everyone opposes human cloning for this purpose.
On the other hand, many researchers and advocates support therapeutic cloning, in which the human embryo created by SCNT is destroyed in order to extract stem cells for research and (potentially) therapies. This is the kind of human cloning that many researchers have pursued. The only difference between the two kinds is whether the cloned embryo is allowed to grow and develop (reproductive cloning) or is killed for research (therapeutic cloning).
Technical problems have hindered human “therapeutic cloning” research. One problem is that cloning requires a large number of human eggs, which must be harvested from women. This procedure poses risks to women’s health.
A cloning breakthrough finally arrived in 2013 when researchers at Oregon Health & Science University announced that they had successfully isolated stem cells from cloned human embryos. But the announcement came after breakthroughs in non-controversial stem cell research—especially the creation of iPSCs, which are also patient-specific pluripotent stem cells—had made the quest for human cloning seem unnecessary.
The therapeutic benefits of stem cells
Embryonic stem cells have often been touted as superior to adult stem cells because they are pluripotent—they can become virtually any kind of cell—and they have a greater capacity for proliferation (they can divide almost indefinitely). But this same flexibility and rapid growth have created serious obstacles to the use of ESCs for medical therapies. ESCs tend to form tumors when transplanted, and scientists have had difficulty coaxing ESCs into the right kind of differentiated cells. ESCs may also be rejected by a patient’s immune system because they are not genetically identical to the patient. Human cloning could possibly solve the rejection problem, but the other difficulties remain.
Some human clinical trials using ESCs are underway, but no successful treatments have yet been developed using embryonic stem cells.
Induced pluripotent stem cells are nearly identical to ESCs, so they tend to have both the same potential advantages and the same challenges. Like stem cells from cloned embryos, however, iPSCs can genetically match a patient and possibly avoid the problem of immune rejection. Moreover, creating iPSCs seems to be easier and more efficient than deriving ESCs from either IVF- or SCNT-produced embryos. So iPSCs may offer practical advantages over research with human embryos.
Adult stem cells are typically multipotent rather than pluripotent, but they have proven to be more flexible than expected. And they tend not to have the major problems that afflict ESCs. ASCs are more stable and do not form tumors, and they can be taken from a patient’s own body and then transplanted into sick or damaged tissue, avoiding the possibility of immune rejection. ASCs can also be taken from a tissue-matched donor.
Adult stem cells are the only kind that has successfully treated human patients. The stem cells contained in bone marrow, for example, have been treating people who suffer from leukemia and other diseases for decades. These bone marrow transplants have saved thousands of lives. Stem cells from umbilical cord blood have also treated thousands of patients. As of 2014, more than 60,000 people worldwide each year receive adult stem cell transplants. ASCs have now been used to treat dozens of different conditions, including arthritis, diabetes, lupus, multiple sclerosis, brain cancer, breast cancer, ovarian cancer, leukemia, lymphoma, heart disease, sickle cell anemia, stroke damage, Parkinson’s disease, and spinal cord injury. (Most of these therapies are treatments, not cures, however, and many adult stem cell treatments are experimental and are not yet generally approved and available.)
Funding should support adult stem cell research
ASCs are currently successfully treating diseases and offer hope for many more therapies in the future. ESCs have not yet produced any proven medical treatments, but they may still be useful for studying diseases and other research. These same benefits, however, can be achieved using iPSCs, which do not require the destruction of human embryos or human cloning. Embryonic stem cell research is both unethical and simply unnecessary to realize the promise of stem cell research.
The main political and public policy debate concerning stem cell research has involved its public funding. Both ESC and ASC research are currently funded by the federal government. Funding should be directed solely to ethical ASC and iPSC research, not research that requires the destruction of human life. In Minnesota, scientists at the University of Minnesota conduct stem cell research of all kinds. They should focus their efforts on ethical, effective research with ASCs and IPSCs.