Frequently Asked Questions
Q: Are stem cells currently used in therapies today?
A: Blood stem cells are currently the stem cells most commonly used for therapy: doctors have been transferring blood stem cells by bone marrow transplant for more than 40 years. Advanced techniques for collecting or “harvesting” blood stem cells are now used to treat leukemia, lymphoma and several inherited blood disorders, among others. Cord blood, like bone marrow, is stored as a source of blood stem cells and is being used experimentally as an alternative to bone marrow in transplantation.
Work has also been done using stem cells in skin and hair grafts. In addition, new clinical uses of stem cells are being tested therapeutically for the treatment of neurologic abnormalities, musculoskeletal abnormalities, cardiac disease, liver disease, autoimmune and metabolic disorders (amyloidosis), chronic inflammatory diseases (lupus) and other advanced cancers. However, these new therapies have been offered only to a very limited number of patients.
A: Nuclear transfer, as therapeutic cloning is also known, is a method for making embryonic stem cells that involves transferring the nucleus from any cell in the body, say a skin cell, into an egg that has had its own nucleus removed. This egg is coaxed in the lab into developing as if it had been fertilized, dividing until it has formed an early embryo, from which embryonic stem cells can then be generated. These cells are genetically identical to the donor skin cell.
Reproductive cloning, as was done with Dolly the Sheep, would involve implanting an egg generated by nuclear transfer into the womb of an animal, resulting in offspring with an identical genetic makeup as the donor cell. The overwhelming consensus of the world’s scientific and medical communities is that human reproductive cloning should be totally banned. Children’s is in complete agreement with that consensus.
Q: Are the induced pluripotent stem cells produced from skin cells identical to embryonic stem cells?
A: Both iPS cells and embryonic stem cells can potentially form any cell type in the body. But while the two kinds of cells are very similar, they are actually not identical. For example, one report showed that a few thousand genes in the skin-based stem cells were not activated to the same degree that they are in embryonic stem cells. Future work will no doubt continue to refine these techniques and may bring the two cell types even closer to one another. Children’s scientists are actively working in this area.
Q: I’ve heard that the stem cells produced through genetic reprogramming usually became cancerous. Is this true?
A: The first studies using this technique were conducted using mouse cells. In those experiments, a significant number of cancers formed in experimental laboratory animals. While it is unknown whether or not similarly produced human cells would also cause cancer, it is important to point out that the cells described in these scientific experiments are not intended for use in therapies. Rather, they are very early, scientific studies along a path that we trust will lead to future cellular therapeutics. They are a foundation that needs to be improved upon and refined.
Q: Does the ability to reprogram cells to a pluripotent state mean we no longer need embryonic stem cell research?
A: We at Children’s Hospital Boston believe that cellular reprogramming and embryonic stem cell research must advance in parallel to bring cell therapy to the clinic as quickly as possible. The lab of George Q. Daley, MD, PhD, Director of the Stem Cell Transplantation Program, is one of the few in the world to simultaneously pursue a variety of strategies, including nuclear transfer, the use of donor eggs and embryos, and the use of unfertilized eggs alone, in addition to cellular reprogramming. Each of these strategies has its own applications, answers certain kinds of questions, and is informing the strategies, quickening the pace of the research overall. For example, lessons learned through nuclear transfer experiments might provide insights into improving the safety of induced pluripotent cell (iPS cells).
Q: What is parthenogenesis?
A: Parthenogenesis is a method of reproduction in some organisms in which the female can generate offspring without the contribution of a male, creating a viable embryo from an unfertilized egg. It doesn’t occur in most species of animals, but researchers have been able to induce unfertilized mouse eggs to develop into embryos through a series of chemical treatments. Embryonic stem cells can then be generated.
Q: Could parthenogenesis be used to generate cells for medical use?
A: Potentially, but not yet. To date, human parthenogenetic embryonic stem cells have been created in just a few labs worldwide.
In addition, before stem cells made from eggs alone are used in patients, potential safety concerns must be addressed. Embryonic stem cells created through parthenogenesis have altered expression of certain genes that are “imprinted.” We all have about 50 imprinted genes, which are expressed (turned on or off) based on whether they come from our mother or our father. Because parthenogenetic embryonic stem cells are made from eggs only, they carry no paternally imprinted genes, and instead carry two copies of maternally imprinted genes. Altered expression of imprinted genes has been linked with cancer and poor growth in some tissues and prevents such embryos from developing very far.
Q: So why are parthenogenetic embryonic stem cells important?
A: One of our goals in stem cell research is to make embryonic stem cells that match the tissue type of a particular patient, so that they wouldn’t be rejected by the immune system. One way to do this is through nuclear transfer, which brings the patient’s cells into an egg whose own DNA has been removed. But this hasn’t yet been done successfully in humans and the process is very inefficient. Parthenogenesis is much more efficient; for decades, many groups have been able to generate healthy and functional embryonic stem cells using parthenogenesis in animals.
Once created, these cells could be used by patients donating their own eggs, or by a close relative. In addition, parthenogenetic embryonic stem cells could be genetically typed to match the major histocompatibility complex genes (those responsible for tissue matching) of different groups of patients, making them useful to many more people. This opens up the prospect of making a “panel” of egg-derived embryonic stem cells that would carry different combinations of histocompatibility genes that would match a significant percentage of people needing transplants.
Q: Why not just use adult stem cells?
A: The ultimate goal of pluripotent stem cell research is, in fact, to use these cells to generate adult stem cells for medical use. Currently, the only type of adult stem cell therapy in routine clinical use is blood stem cell transplant to treat leukemia, lymphoma, and various genetic diseases of the blood. Other types of adult stem cells are only beginning to be isolated from different tissues and have only been used therapeutically in small numbers of patients.
Although bone marrow transplants have saved many lives, they require a matched donor, and the majority of people who need a bone marrow transplant cannot find one. If the donor is only a partial match, patients must face aggressive and toxic therapy to prevent immune rejection and graft-versus-host disease. This harsh treatment can sometimes be fatal.
We at Children’s believe that pluripotent stem cells can potentially be used to make adult stem cells safer for use in transplants, starting with blood stem cell transplants. We have good evidence in animals that pluripotent stem cells can be used to make different kinds of adult stem cells. These adult stem cells would be genetically matched to the patient because they are derived from his or her own cells, and no donor would be needed.
Q: If embryonic stem cells have so much promise, why haven’t they led to any cures?
A: Human embryonic stem cells were first made only in 1998. The science has moved at a rapid pace in the short time since that initial breakthrough, but much work remains before we can know for certain how such cells might best contribute to better therapies. We hope this work will address the many diseases for which no therapy currently exists, or in which limited access to tissue donors prevent individuals from obtaining life saving therapies.