Stem cell and cell reprogramming as regenerative medicine
Stem cell and cell reprogramming as regenerative medicine
Stem cell therapy and stem cell research have been a hotly debated topic over recent years. Most of us may have general understanding of the controversy, but we may be unaware of the specific issues surrounding stem cell therapy and its research. A trial on a patient with severe spinal injuries is the first to test a treatment that has huge potential to cure disease and disability. But it also highly controversial and considered unethical among many Christian and pro-life groups. Research in the stem cell field grew out of findings by Canadian scientists E.A McCulloch and James E. Till in the1960s (1,2).
Three types of mammalian stem cells are as follows:
Embryonic stem cells are isolated from the inner cell mass of blastocysts. A blastocyst is an early stage embryo- approximately four to five days old in humans and crossing of 50-150 cells. Embryonic stem cells are pluipotent and give rise during development to all derivatives of the three primary germ layers: ectoderm, endoderm and mesoderm, In other words, they can develop into each of the more than 200 cell types of the adult body when given sufficient necessary stimulation for a specific cell type. They do not contribute to the extra-embryonic membranes or the placenta (3).
Adult stem cells that are found in adult tissues. The term adult stem cell refers to any cell which is found in developed organism that has two properties: the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself. Pluripotent adult stem cells are rare and generally small in number of tissues including umbilical cord blood (3).
Fetal stem cells are primitive cell types found in the organs of fetuses. The classification of fetal stem cells remains unclear and this type of stem cell is currently often grouped into adult stem cell (3).
Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell. Totipotent or omnipotent stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable organism. These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent. Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells, i.e. cells derived from any of the germ layers. . Multipotent stem cells are partially differentiated, so that they can form a restricted number of tissue types. Multipotent stem cells can be found in the fetus, in numerous adult tissues and umbilical cord blood. The stem cells can become any tissue in the body, excluding placenta. Pluripotent embryonic stem cells originate as inner mass cells within blastocyst . Only the morula's cells are totipotent, able to become all tissues and a placenta (3).
Stem cells and progenitor cells in adult organisms act as repair system for the body, replenishing specialized cells, but also maintain the normal turnover of regenerative organs, such as blood, skin, or intestinal tissues. Human stem cell research is both a controversial as well as a cutting-edge technology. Medical researchers believe that stem cell therapy has the potential to dramatically change the treatment of human disease. A number of adult stem cell therapies already exist, particularly bone marrow transplants that are used to treat leukemia. On one hand it promises to revolutionize medicine while on the other hand it raises a host of ethical issues. A stem cell is capable of developing into other types of cells, like kidney cells, liver cells, heart cells, etc. Stem cells circulate and function to replace dysfunctional cells, naturally maintaining optimal health.
There are many advantages and disadvantages to stem cell therapy and research.
Advantages:
It provides medical benefits in the fields of therapeutic cloning and regenerative medicine.
It provides great potential for discovering treatments and cures to a plethora of diseases including Parkinson's disease, schizophrenia, Alzheimer's disease, Cancer, spinal cord injuries, diabetes and many more.
Limbs and organs could be grown in a lab from stem cells and then used in transplants or to help treat illnesses.
It will help scientists to learn about human growth and cell development.
Scientists and doctors will be able to test millions of potential drugs and medicine, without the use of animals or human testers. This necessitates a process of simulating the effect the drug has on a specific population of cells. This would tell if the drug is useful or has any problems.
Stem cell research also benefits the study of developmental stages that cannot be studied directly in a human embryo, which sometimes are linked with major clinical consequences such as birth defects, pregnancy loss and infertility. A more comprehensive understanding of normal development will ultimately allow the prevention or treatment of abnormal human development.
It holds the key to reversing the effects of aging and prolonging our lives. Stem cell research has already found many treatments that help slow the aging process, and a bonus of further stem cell research is a possible cure' for aging altogether.
The usage of adult stem cells to treat disease is that a patient's own cells could be used to treat a patient. Risks would be quite reduced because patients' bodies would not reject their own cells.
An advantage of using embryonic stem cells is that they can develop into any cell types of the body, and may then be more versatile than adult stem cells.
Disadvantages:
The use of embryonic stem cells for research involves the destruction of blastocysts formed from laboratory-fertilized human eggs. For those people who believe that life begins at conception, the blastocyst is a human life and to destroy it is immoral and unacceptable.
Like any other new technology, it is also completely unknown what the long term effects of such an interference with nature could materialize.
Embryonic stem cells may not be the solution for all ailments.
According to a new research stem cell therapy was used on heart disease patients. It was found that it can make their coronary arteries become narrower.
A disadvantage of most adult stem cells is that they are pre-specialized, for instance, blood stem cells make only blood, and brain stem cells make only brain cells.
A disadvantage of embryonic stem cells is that they are derived from embryos that are not a patient's own and the patient's body may reject them.
The results of the procedure, carried out by privately funded US company Geron, will be awaited eagerly around the by doctors and scientists working in regenerative medicines. If a success, it could be the catalyst to open up stem treatments from nerve damage, to Alzheimer's disease to diabetes. Professor Chris Mason, an expert in regenerative medicine at University College of London, said it marked the dawn of the stem cell age'. He also stated that this pivotal clinical trial is a major morale boost for scientists, clinicians and most of all patients by finally commencing the transformation of stem cells from a scientific curiosity into advanced health care.
Millions of embryonic stem cells, which come from human embryos left over from fertility treatments, are injected into the damaged area. The hope is that they will travel to the site of the damaged tissue and help the tissue regenerate. Thomas Okarma, chief executive of Geron, said that it is a milestone for the field of human embryonic stem cell-based therapies.
Embryonic stem cells are master cells found in human embryos, which give rise to more than 200 specialized types of tissue in the adult body, and can be grown into any kind of tissue to replace cells damaged by injury or disease. Use of embryonic stem cells is controversial because they must be harvested from human embryos that are destroyed in the process. This has raised moral objection from those who believe that embryos have the same right as humans and see the treatment as unethical. At long last researchers have proved that they can make human embryonic stem cells (hESCs) without destroying embryos. This may got round some moral objections to embryo research, but more importantly it has brought to light a substance that should help cell stem cell researchers improve their craft (4). That substance is laminin a protein found in the basement membranes underlying layers of skin. It made all the difference to work by Lanza and his team at Advanced Cell Technology, a company in Worcester, Massachusetts, who reported creating hESCs from human embryos without destroying them. Lanza proved that hESCs could be generated from blastomeres, but none of the embryos he took them from survived. Also, just 2 per cent of his blastomeres generated hESCs, so large numbers of embryos were needed. But when laminin was added to the dishes in which the embryos were grown, the majority of them survived the removal of blastomere, and 20 to 50 per cent of the blastomeres went on to generate hESCs- about the same success rare as when taking hESCs directly from embryos. Laminine appears to stop newly extracted blastomeres from turning into useless trophectoderm cells from which placenta originates, and instead encourages them to turn into hESCs.
New techniques circumvent a road block to the production of embryonic stem cell-like lines from adult tissue. Such reprogrammed cell lines should be much safer to use for therapy. Shinya Yamanaka's amazing discovery (5) that cells from differentiated tissues can be reprogrammed into induced pluripotent stem (iPS) cells- cells that can potentially differentiate into any cell type- has transformed research in stem- cell biology and regenerative medicine. Transgenic expression of just four defined transcription factors (c-Myc, Klf4, Oct4 and Sox2) is sufficient to reprogram somatic cells to a pluripotent state virus-free integration of reprogramming genes, followed by their removal. Woltjen et al (6) and Kaji et al (7) combined powerful technologies, developed independently, to overcome many of the difficulties others encountered in attempting virus-free reprogramming. These groups also made use of the virally derived 2A- peptide sequence to create multi-protein expression vectors incorporating all of the reprogramming genes. Instead of retroviruses or plasmids, however, they used the piggyback transposon/transposase gene-delivery system. This vector can easily integrate into the genome. But more importantly, the integrated DNA can also be removed from the genome- through transient expression of the transposase enzyme- in a highly efficient and seamless fashion, leaving no trace of the integration in the genome of the iPS cells. The use of the 2A peptide is crucial, not just because it allows delivery of all of the required reprogramming genes in a single construct, but also because it makes complete excision of the foreign constructs much easier (6,7)
Vierbuchen et al (8) maintain the pace of this research by describing a potential innovation for generating disease-specific and patient-specific tissues of the central nervous system (CNS) that does not rely on stem cells. The route to possible regenerative-medicine-based treatment of CNS disorders such as epilepsy, stroke and Parkinson's disease may have taken another unexpected turn. They reported that mouse and human fibroblasts can be reprogrammed to a pluripotent state with a combination of four transcription factors. Starting from a pool of 19 candidate genes, they (8) identified a combination of only three factors, AscI1, Brn2 and Myt1I, that suffice to rapidly and efficiently convert mouse embryonic and postnatal fibroblasts into functional neurons in vitro. These induced neuronal (iN) cells express multiple neuron-specific proteins, generate action potentials and form functional synapses.
As is the case for embryo-derived stem cells, application of reprogrammed human induced pluripotent stem cells is limited by our understanding of lineage specification. Here Bhatia (9) demonstrated the ability to generate progenitors and mature cells of the haematopoietic fate directly from human dermal fibroblasts without establishing pluripotency. Ectopic expression of OCT4 (also called POU5F1)-activated hematopoietic transcription factors, together with specific cytokine treatment, allowed generation of cells expressing the pan-leukocyte marker CD45. These unique fibroblast-derived cells gave rise to granulocytic, monocytic, megakaryocytic and erythroid lineages, and demonstrated in vivo engraftment capacity. They (9) noted that adult haematopoietic programs are activated, consistent with bypassing the pluripotent state to generate blood fate: this is distinct from hematopoiesis involving pluripotent stem cells, where embryonic programs are activated. These findings demonstrated restoration of multipotency from human fibroblasts, and suggested an alternative approach to cellular reprogramming for autologous cell-replacement therapies that avoids complications associated with the use of human pluripotent stem cells.
Scientists have coaxed adult human skin into producing blood, a breakthrough that could offer an alternative source of the vital fluid to cancer patients or those undergoing surgery. What's more, the procedure is simple- there is no need to first convert the skin cells (which actually deliver the different types of cells), a step that is essential to other such processes (9).
The scientists- led by Mickie Bhatia, director of McMaster's Stem Cell and Cancer Research Institute at the Michael G. DeGroote School of Medicine, and main author of the study- found that a protein called OCT4 can reprogramme skin stem cells obtained from a patch of human skin into blood without resorting to any intermediary steps. They further refined the process by adding several other growth factors, which improve the efficiency (9). Normally, blood is produced in the bone marrow. For scientific and therapeutic applications, in recent times, blood cells have also been harvested from preserved umbilical cords and placentas. This has given rise to whole new industry that works towards preserving cord blood for future use. Bhatia hopes that clinical trials will begin in 2012.
The most efficient stem cells are embryonic stem cells which, as the name suggests, are derived from human embryos. Apart from ethical issues, there are biological concerns that the cells might be rejected when transplanted into an adult and also that their source is limited. Truly, the controversy over cell reprogramming research will continue to rage furiously. We hope there is some novel scientific innovation of human cell reprogramming in the future, it could be quickly applied to the creation of disease-specific cells for disease modeling and regenerative drug discovery, and to understanding the genetic and epigenetic mechanisms that determine the cell fate.
References:
Becker A.J, McCulloch E.A, Till J.E, Nature, 197:452-454 (1963).
Siminovitch L, McCulloch E.A, Till J.E, J.Cell.Comp.Physiol, 62: 327-336 (1963).
http://en.wikipedia.org/wiki/Stem_cell_research
Coghlan. A . NewScientist, 19th January, 2008
Takahashi, K and Yamanaka, S. Cell, 126:663-676(2006).
Woltjen, K et al. Nature, 458: 766-770 (2009).
Kaji, K et al. Nature, 458: 771-775 (2009).
Vierbuchen, T et al. Nature, 463: 1035-1041 (2010).
Szabo, E. et al. Nature, 468: 521-526 (2010).
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