Abstract
This paper describes and discusses the various types of human stem cells, including those in early-stage embryos (the blastocyst) and those present in adult tissue, explaining the practical uses of the various types in the medical field, where stem cells can be used to repair damaged tissue and organs. Although the adult stem cell types offer fewer possibilities for medical applications than the embryonic type, their use is less ethically controversial because it does not require destruction of a living albeit very early stage embryo. Research into stem cell applications is finding improved techniques. These include the treatment of acute leukemia that was once a fatal disease but is increasingly treatable using stem cell therapy in the form of bone marrow transplants, progressively increasing the survival rates for leukemia patients. In conclusion it is recommended that because stem cell technology and therapy is potentially so important for future treatment of diseases, such research should not only be continued but expanded in scope.
Stem Cells
Introduction
This paper discusses and researches the various types of stem cells, the research in hand to use them to treat leukemia and the prognosis for greater probability of survival by regenerating a damaged immune system.
What Are Stem Cells?
An easily understood explanation of stem cells is provided in “Definition: What are Stem Cells?” (2007) published by the University of Minnesota (UMN). They are defined as human cells that are “blank”, meaning that they can potentially develop into any of the many specialized cell types which comprise the majority of the cells in the human body. Those specialized or differentiated cells are different to the stem cells which are undifferentiated. Examples of differentiated cells are red blood cells which are designed to hold and transport oxygen, and a white blood cell which is specially equipped to fight off disease.
Stem Cell Types
The UMN article explains that there are two basic types of stem cells, known either as Pluripotent or Multipotent. The Pluripotent stem cell type is found in early-stage embryos and can develop into all the cell types present in the human body; these may include cells found in organs such as the brain or heart and in bone and skin tissue. The Multipotent stem cells are found only in adults or in the umbilical cords of newborn babies. Their capacity for development is more limited, in that they can only develop into cells comprising the organ system that they came from. Hence one such cell from bone marrow can only develop into one of three types: a red or white blood cell or a blood platelet. It cannot develop into other types such as a brain cell or skin tissue cell.
In addition to those two basic types of stem cells, there is a third type known as Induced Pluripotent stem cells or IPSCs (alternative name reprogrammed stem cells). According to Cox (Aug. 2012), these are similar to the embryonic or Pluripotent type found in early stage embryos, but are in fact created from adult (specialized) cells in the laboratory, using a technique discovered as recently as 2006.
Further, there are three other “potency” classifications of stem cells as described by Crosta (2008-2013). These are Totipotent – having the ability to different into every possible cell type (cells from the earliest few divisions after fertilization), Oligopotent – cells able to differentiate into a few other cells (e.g. adult lymphoid or myeloid stem cells); and Unipotent – cells that can only differentiate into the same type (e.g. adult muscle stem cells).
An important aspect of the 2006 discovery is that whereas stem cell research using cells extracted from embryos is the subject of considerable controversy because it effectively involves destroying an embryo that has been artificially fertilized at 5-14 days (“Definition: What are Stem Cells?, 2007), research using IPSCs is not so controversial. Note that the research usually uses “extra” embryos that have been created in an in vitro fertilization (IVF) clinic, following the implantation of one embryo in the woman subject (Crosta, 2008-2013).
As explained by Crosta, those very early stage embryos (4 to 5 days) begin as a single cell called a zygote at fertilization. It then goes through a series of divisions (first 2, then 4, then 8, then 16, etc) and this developing cell mass is referred to at this stage as a blastocyst. It comprises an inner mass (embryoblast), which would normally go on to grow into a complete adult organism, and an outer mass (trophoblast) which would develop as the placenta. It is that inner mass from which stem cells can be harvested by placing it in culture dish. Those stem cells then divide and replicate themselves as undifferentiated cells
Part of the reason why using adult stem cells does not attract the same controversy is that adult (or stomatic) stem cells exist in all of our bodies following embryonic development and can be found in the different human tissues types – in organs like the brain and the liver, and in bone marrow, blood and blood vessels, muscular tissue and the skin (Crosta). A characteristic feature of these stem cells is that they remain in a non-dividing condition unless activated due to a disease or an injury to the host. Also, they are able to divide and/or renew themselves indefinitely, having the ability to create cell types from the organ that contains them, or even to regenerate the complete organ. Whilst there are thoughts that they may have limited differentiation abilities according to the tissue type in which they originated, there are possibilities that they may be able to differentiate and become other cell types, too.
Stem Cell Therapy for Leukemia
“Promising Stem Cell Therapy for Leukemia Patients” (Apr. 2013) describes how stem cell therapy in the form of bone marrow transplants gives today’s leukemia patients a chance of survival that did not exist years ago. Leukemia is a formerly fatal cancer of the blood-building cells in the bone marrow. To deal with the cancerous cells in the bone marrow, patients are given chemotherapy and radiotherapy prior to a bone marrow transplant, which is effectively the beginning of a new immune system. The newly-transplanted cells take over the task of producing healthy blood cells from the diseased ones, at the same time as attacking and destroying the leukemia cells. There are risks involved in that the new immune system comes from outside the patient’s body and can as a consequence also attack healthy patient tissues, a phenomenon called GvHD (Graft versus Host Disease). In severe cases that can cause organ failure. Up to 50 percent of bone marrow transplant patients are affected, and in some 20 percent of those (so 10 percent of the total), the damage caused is fatal. There is also an additional risk that around 20 percent of all leukemia patients can suffer a relapse following the transplant. However, to reduce the risks of GvHD, the physicians treat transplant patients with carefully measured doses of immunosuppressants, so as to suppress the immune system, but not too much, which could cause the attacks on the cancerous cells to be ineffective. Research is in hand to find ways to prevent GvHD, including using antibodies to treat the new cells prior to transplantation so that they will “tolerate” the healthy tissue cells as opposed to attacking them, in this way helping to increase the success rate of the bone marrow transplant procedures. Initial tests have shown the principles to be valid, and testing is currently underway using mice modified with a human immune system, moving on soon to a clinical study.
Giebel (Dec. 2013) published encouraging results of a study of autologous bone marrow transplants for 177 patients to treat Philadelphia-positive acute lymphoblastic leukemia (Ph+ALL), showing clear improvements in survival rates following the “introduction of tyrosine kinase inhibitors.” The study showed that the three-year survival rates increased with the more recent transplant dates as follows: 1996 to 2001: 16 percent; 2002 to 2006: 48 percent; 2007 to 2010: 57 percent. Further statistics from the study showed an even higher rate for a selected subgroup of the patients after three years, and that the more recent the transplant date, the better the survival rates have become; i.e. that the research resulting in refining the techniques is continuing to increase the likelihood of survival.
Conclusions and Recommendations
The research undertaken has shown that there are two main types of stem cells: embryonic (or Pluripotent ) and adult tissue (or Multipotent) stem cells, which have fewer development capabilities than the embryonic type. Research over recent years has shown there are potentially exciting possibilities for treating diseases using stem cell therapy, including the possibility of regenerating human organs instead of depending on transplant surgery. Survival rates for acute leukemia patients have increased with increasing knowledge and better techniques in the field of stem cells applications for bone marrow transplants. For that reason this writer recommends continuing and increasing that research to improve the prognosis even further for patients with leukemia, and widening the scope of the present research to develop and improve treatments for other life-threatening diseases, too.
References:
Cox, Claire. (Aug. 2012). “Stem cell research & therapy: types of stem cells and their current uses.” Euro Stem Cell. Retrieved from http://www.eurostemcell.org/factsheet/stem-cell-research-therapy-types-stem-cells-and-their-current-uses
Crosta, Peter. (2008-2013). “What are Stem Cells?” Medical News Today. Retrieved from http://www.medicalnewstoday.com/info/stem_cell/
“Definition: What are Stem Cells?” (2007). University of Minnesota: Academic Health Center. Retrieved from http://www.ahc.umn.edu/bioethics/prod/groups/ahc/@pub/@ahc/documents/asset/ahc_75703.pdf
Giebel, S. (Dec. 2013). “ASCT improved outcomes in Ph+ALL.” Eur J Cancer. 2013; doi:10.1016/j.ejca.2013.08.027. Retrieved from http://www.healio.com/hematology-oncology/hematologic-malignancies/news/online/%7Bb14f81e4-5e9e-4733-8ef0-29781584c7fe%7D/asct-improved-outcomes-in-phall
“Promising Stem Cell Therapy for Leukemia Patients.” (Apr. 2013). Science Daily. Retrieved from http://www.sciencedaily.com/releases/2013/04/130402091248.htm
