Presentation on theme: "STEM CELLS AND THE MYTH OF ETERNAL YOUTH: ADULT VERSUS EMBRYONIC STEM CELLS Dr. Marie - Louise Labat."— Presentation transcript:
STEM CELLS AND THE MYTH OF ETERNAL YOUTH: ADULT VERSUS EMBRYONIC STEM CELLS Dr. Marie - Louise Labat
The myth of eternal youth has always haunted humanity. Today, what is at stake is regenerative medicine using stem cells.
Stem cells are undifferentiated cells that given the right signals can differentiate to the many (more than 200) specialized cells that make up the organism. Stem cells have the ability to self-replicate for the lifetime of the organism.
Different types of stem cells are involved during human development and adult life.
Adapted from David Prentice Pluripotent Totipotent Embryonic germ (EG) cells Pluripotent Tissue stem cells Pluripotent/Multipotent Stem Cells Pluri/ Multi potent HUMAN DEVELOPMENTAL CONTINUUM Fetus
Distinguishing Features of Progenitor/Precursors Cells and Stem Cells. http://stemcells.nih.gov/info/scireport/chapter4.pdf
Human embryo at stage 8 cells (2 days) 8 totipotent stem cells
Human embryo at blastocyst stage 200-250 cells (4 to 5 days) (Pluripotent stem cells) Inner Mass
From G. Baker: http://www.city.ac.uk/cs/lecturenotes/neuro_biomedsciences.pdf
Then, gastrulation leads to the establishment of definitive germ layers (ectoderm, endoderm, and mesoderm) that harbour multipotent cells.
From Human Embryology, Larsen, DeBoeck University Ed, Bruxelles, Belgium, 1996
According to the classical dogma, pluripotency was thought to be lost after the blastocyst stage.
Therefore, so-called pluripotent embryonnic stem cells are extracted before gastrulation, from the inner mass of the blastocyst From ‘Science et Avenir’ 2002, n° 130, special issue
Martin G; Isolation of pluripotent cell lines from early mouse embryos. Proc Natl Acad Sci USA 1981; 78: 7634-7838.
Thomson JA, Istkovitz-Eldor J, Shapiro SS, Waknitz MA, Swiergel JJ, Marshall VS, Jones JM. Embryonic stem cell lines derived from the human blastocyst. Science 1998; 282: 1145-1147
The authors concluded that such human embryonic stem cells could be used for transplantation medicine, in order to cure: - Alzheimer’s disease - Parkinson’s disease - Juvenile type diabetes - Spinal cord injury
However, because extraction of the stem cells from the blastocysts leads to the destruction of a human embryo, a worldwide debate both ethical and political started.
From the time that the ovum is fertilized, a life is begun that is neither that of the father nor the mother, it is rather the life of a new human being with his own growth, it would never become human, if it were not human already. John-Paul II (Evangelium vitae)
The study by Thomson’s team was made using ‘supernumerary embryos’ donated by the parents after informed consent and after institutional review board approval.
But the question is: Whom do these embryos belong to, if not to themselves?
This question is linked to another one: When does human life begin ?
At an April 2002 press conference, Senator A. Specter (Penn) was asked by a reporter, within the context of embryonic stem cell research, when life begins. Senator Specter replied: « I haven’t found it helpful to get into the details. »
What are exactly these human embryonic stem cells?
First of all, their isolation is the direct consequence of in vitro fertilization and preimplantation diagnosis.
Sciences et Avenir, 2002; 130, Hors-série Preimplantation genetic diagnosis In vitro fertilized ovocyte In vitro culture Pipet One cells is taken Embryo between 6 to 12 cells One cell is sampled from each embryo fertilized and cultured in vitro Diagnostic test on each sampled cell Healthy embryos are selected for implantation in the uterus
1978: birth of the first baby by in vitro fertilization (IVF) in Great Britain. 1982: birth of a baby by in vitro fertilization in France. During the past 20 years, 100 000 babies were born in France by IVF. In 1998, more than 13 000 babies were born by IVF (1,8% of birth). This number is in constant increase, due to: 1. greater efficiency of ovary stimulation, 2. cryopreservation of embryos.
As a result, the human embryo became available for experimentation.
Human embryo (3 days old, 16 cells) Science et Avenir 2002; 130 Special issue
In fact, embryonic stem cells, at the heart of the present debate are not present as such in the embryo, they result from manipulations in the laboratory.
The pluripotent cells extracted from the inner mass of the blastocyst are manipulated in the laboratory to give rise to cell lines that proliferate indefinitely Science et Avenir 2002, n°130, special issue
Manipulation of embryonic stem cells in the laboratory
- - After dissociation of the inner mass of human blastocysts, the cells are first grown on a feeder layer of irradiated mouse embryonic fibroblasts, - after 9 to 15 days of culture, the outgrowth are harvested and replated, - cell lines are selected by their prolonged undifferentiated proliferation characteristics while retaining the ability to differentiate into the three embryonic germ-layers.
. CyThera (California) 9 ES Cell International (Australia) 6 Geron Corporation (California) 7 University of Göteborg (Sweden) 19 Maria Biotech Co (Korea) 3 Miz Medi Hospital (Korea) 1 National Center for Biological Science (India) 3 Pochon CHA University (Korea) 2 Reliance Life Sciences, Bombay (India) 7 Technion University, Haifa (Israel) 4 University of California SF (California) 2 Wisconsin Alumni Research Foundation 5 Bresagen, Inc (Georgia, USA) 4 Human embryonic stem cell lines approved by President Bush for federally funded research (August 9, 2001)
These cells lines, created for possible future disease treatments were grown on mouse fibroblasts. That could expose humans to animal virus their immune system couldn’t fight, the U.S. medical ethics panel said on November 2003.
Attempts are made to grow human embryonic stem cell lines without using a feeder layer of mouse fibroblasts and without using fetal calf serum Amit M, Shariki C, Margulets V, Itskovitz-Eldor J Feeder and serum-free culture of human embryonic stem cells. Biol Reprod 2004; 70: 837-45
According to the US National Institutes of Health (NIH), only 11 cell lines can really be considered (some were discarded because contaminated by viruses, or cross-contaminated, or because they were not really stem cells, or for ethical reasons).
One of these cells lines, that had received the agreement of the NIH, that was considered as stable and devoid of chromosome abnormalities was used as a reference. It was widely distributed in 150 laboratories all around the world. This reference cell line was recently shown by Draper and Smith, to be instable and to present an excess of chromosome 12 and 17.
Draper JS, Smith K, et al Recurrent gain of chromosome 17 q and 12 in cultured human embryonic stem cells. Nat Biotechnol 2004; 22: 53-54
108th congress of Office of Legislative Policy and Analysis Ronald McKay National Institute of Neurological Disorders and Stroke May 22, 2003 « There is clear evidence that human ES cells will form teratomas, complex mixtures of different cells, but much less is known about efficiently generating specific cell type … »
In fact, it is difficult to differentiate embryonic stem cells toward one direction only: Schuldiner M, Yanuka O, Itskovitz- Taylor J et al. Effect of eight growth factors on the differentiation of cells derived from human embryonic stem cells. Proc Natl Acad Sci 2000; 97: 11307
Even the pioneer of human embryonic stem cell research, J. A. Thomson, does not believe any more in the therapeutic use of human embryonic stem cells.
In december 1998, J. A. Thomson testified before the American Senate that human embryonic stem cells were going to cure: - Alzheimer’s disease - Parkinson’s disease - Juvenile type diabetes - Spinal cord lesions
On June 2002, J. D. Thomson stated at the « Workshop on the Basic Biology of Mammalian Stem Cells » organized by the National Institute of General Medical Sciences : ‘ in the next decade, relatively few clinical trials in « cell therapy » will be initiated with human embryonic stem cells, due to safety concerns and possible immune interference … Forecasting that stem cells would have a greater impact on understanding the roots of disease rather than on treatment’
Indeed, that last proposition: ‘… stem cells would have a greater impact on understanding the roots of disease rather than on treatment’ could not have motivated the associations of patients to back research on human embryonic stem cells.
A similar evolution can be noted in the statements of the other pionnier J. Gearhardt who derived in 1998 pluripotent cell lines from germ cells from human embryos.
November 19, 2002, J. Gearhart stated in the Washington Fax, the official press organ of the National Institutes of Health: « Embryonic and fetal stem cells likely will never be used as part of disease therapy, but research into both embryonic and fetal stem cells is critical and will provide scientists with vital informations that will enable treatments.
However, the worlwide ethical and political debate continues without taking into account these new informations. Most of the politicians are convinced that embryonic stem cells are, for sure, going to cure Alzheimer’s disease, diabetes, Parkinson’s disease, etc. …
« Research …if conducted in a true scientific way and if it respects moral law, cannot be in conflict with faith. » John-Paul II (Gaudium et spes, n 36 )
Concerning research on embryonic stem cells, clearly the research has not been well conducted.
While this debate on human embryonic stem cells was going on, major changes in our knowledge about stem cells present in adults occured.
According to the classical dogma, it was thought, that pluripotent stem cells were completely lost after the blastocyst stage. Now it is know that pluripotent stem cells are still present in adult life. They are called organ stem cells or adult stem cells, because being present in the adult.
Adapted from David Prentice Pluripotent Totipotent Embryonic germ (EG) cells Pluripotent Tissue stem cells Pluripotent/Multipotent Stem Cells Pluri/ Multip otent HUMAN DEVELOPMENTAL CONTINUUM Fetus
Until these past few years, adult stem cells were known only in permanently renewing tissues, such as blood, skin, gastrointestinal tract, and bone. They were thought to have the same embryological origin as the tissue in which they are hidden.
Now, adult stem cells have been found in every organ where it has been looked for them, including brain. They are also present bone marrow, blood and cord blood.
Adult organ stem cells are not involved in organogenesis. They are responsible for normal tissue renewal and for regeneration following damage.
Organ (adult) stem cells are reserve stem cells which keep embryonic characteristics during all the life of the individual. They seed the different organs, where they normally remain quiescent until, in response to precise signals, they proliferate and differentiate to insure the integrity of the organism.
Their origin is the neural crest. (Labat et al. Biomed and Pharmacotherapy, 2000)
Organ stem cells present in the adult share similarities with embryonic stem cells: both are able to proliferate and to differentiate into all kinds of cellular types i.e. they are pluripotent.
But, there are major differences between adult and embryonic stem cells: contrarily to embryonic stem cells, adult stem cells are mastered cells that the adult organism knows how to control.
Adult stem cells show their potential of proliferation and differentiation only in response to precise signals. Their role is tissue repair, that, like every immunological reaction, has to be initiated, to develop and to know how to end.
That means that adult stem cells are tightly controlled.
Many mechanisms are probably involved in that control. One of them involves a particular subset of T lymphocytes called phagic T lymphocytes because of their unique mode of action. This has been evidenced studying organ stem cells present in adult blood.
Adult stem cells present in blood constitute, together with stem cells hidden in the organs, a single pool of pluripotent stem cells in homeostatic equilibrium.
In vitro Characterization of the normal circulating stem cells Before adhesion, they look like monocytes: they stain for non specific esterases activity they express CD14+ and CD68+ markers They express constitutively HLA-DR molecules
Once they have adhered,they give rise to cells with different phenotypes, among them fibroblast- like cells They express collagen 1, collagen, 3, procollagen 1, and fibronecti, while still expressing monocyte markers.
The normal stem cells are almost quiescent. Once they have adhered and started to differentiate, their time-life is short. They activate a special subpopulation of CD4+T lymphocytes called phagic T lymphocytes (PTLs). Phagic T lymphocytes adhere to the differentiated stem cell, penetrate inside them. As a result, the differentiated stem cell is destroyed.
A B A.Adhesion of phagic T lymphocytes to the stem cell that started to differentiate. B.Penetration of a phagic T lymphocyte into the stem cell.
Phagic T ymphocytes present inside the stem cell that has started to differentiate
‘Explosion of the stem cell under the action of phagic T lymphocytes’ Labat et al. Biomed and Pharmacother 2001;
Only normal stem cells are destroyed by phagic T lymphocytes when they start to differentiate out of a repair purpose (for instance, when tissue repair is completed).
It is a beneficial exception to self tolerance, in order to terminate the repair process and to avoid the development of diseases such as fibrosis or malignant proliferation.
Two major changes are observed when the blood is drawned from patients with fibrosis and/or malignant proliferations: 1. the organ stem cells proliferate indefinitely, 2. they escape phagic T lymphocytes control and as a consequence they accumulate in vitro giving rise to a tissue that evokes the pathology.
These findings have consequences in terms of transplantation: Donor adult stem cells have to match the tissue type of the host: - not to avoid rejection, as is the case for specialized cells, - but to allow their control by phagic T lymphocytes.
In fact, recent studies showed that adult stem cells are not rejected when transplanted into mismatching recipient. Adult organ stem cells are said to be ‘invisible’ to the immune system of the host.
Hori J, NG TF, Shatos M, Klassen H, Streilein JW, Young MJ. Neural progenitor cells lack immunogenicity and resist destruction as allografts. Stem Cells 2003; 21: 405-416
Saito T, Kuang J-Q, Bittira B, Al-Khaldi A, Chiu RC-J. Xenotransplant Cardiac Chimera: Immune tolerance of adult stem cells. Ann Thorac Surg 2002; 74: 19-24
This immune ‘invisibility’ is also a property of embryonic stem cells.
This is an important finding since human therapeutic cloning was precisely proposed to avoid the supposed inevitable rejection of stem cells coming from incompatible supernumeray embryos.
Human therapeutic cloning was proposed soon after Dolly the first cloned sheep was presented to the public.
Dolly was presented to the public on February 1997. It was the first animal cloned with the genetic material taken from adult cells.
Isolation of the adult nucleus Nucleus of the adult cell Enucleated ovocyte Ovocyte Nucleus extracted from the ovocyte In vitro culture THERAPEUTIC CLONING REPRODUCTIVE CLONING Ovocyte with the adult nucleus Muscle cells Skin cells Blood cells Neurons Pipette Therapeutic and reproductive cloning Sciences et avenir 2002 ; N° 130 Special Issue adult Adult cell Implantation of the ovocyte containing the adult nucleus in the womb of a foster mother Embryonic stem cells under the influence of hormones or vitamins
When such ‘therapeutic cloning’ was proposed, it was simply assumed that transplantation rules for embryonic stem cells should be the same as for specialized cells.
It is now known that it is not the case: Fändrich F, Dresske B, Bader M and Schulze M Embryonic stem cells share immune- privileged features relevant for tolerance induction. J Mol Med 2002; 80: 343-350
These findings were confirmed by studies from the Robarts Research Institute in Canada: Li L, Baroja ML, Majumdar A, Chadwick K, Rouleau A, Gallacher L, Ferber I, Lebkowski J, Martin T, Madrenas J, Bhatia M Human embryonic stem cells possess immune-privileged properties Stem Cells 2004; 22: 448-456
In addition, the adult organism cannot control stem cells coming from a 5 day old embryon (either ‘supernumerary embryo or cloned embryo). The ability to be controlled by phagic T lymphocytes is, indeed, acquired during the development of the immune system. It is a property of adult stem cells that distinguish them from embryonic stem cells.
That explain, in part, why embryonic stem cells grow into teratoma and/or teratocarcinoma when they are transplanted in an adult organism.
That is also in agreement with the fact that when these mouse teratocarcinoma cells are reinjected in a five day old normal mouse embryo, they mix with the cells of the inner mass and behave normally. Reimplanted in a mouse uterus, this 5 day old embryo develops to give birth to a normal mouse.
Because embryonic stem cells are not rejected when transplanted into mismatching recipients, the reason why human therapeutic cloning was proposed disappears. Logically the debate should have stopped. Despite these new findings, the political debate still goes on.
Contrarily to embryonic stem cells, adult stem cells have already been successfully used in clinical trials.
Horwitz EM, Prockop et al. Transplantability and therapeutic effects of bone marrow-derived mesenchymal cells in children with osteogenesis imperfecta. Nat Med 1999; 309-313
The beneficial effect was confirmed in 2002 Horwitz EM et al. Isolated allogeneic bone marrow-derived mesenchymal cells engraft and stimulate growth in children with osteogenesis imperfecta: implications for cell therapy of bone. Proc Natl Acad Sci USA 2002; 99: 8932-8937
Succesful treatment of infarcted myocardium by bone marrow graft Germany Wollert KC, Meyer GP, Lotz J, Ringes-Lichtenberg S, Lippolt P, Breidenbach C, Fichtner S, Korte T, Hornig B, Messingr D, Arseniev L, Hertenstein B, Ganser A, Drexler H. Intracoronary autologous bone-marrow cell transfer after myocardial infarction: the BOOST randomised controlled trial. Lancet 2004; 364: 141-8 Stamm C, Westphal B, Kleine HD, Petzsch M, Kittner C, Klinge H, Schumichen C, Nienaber CA, Freund M, Steinhoff G. Autologous bone-marrow stem-cell transplantation for myocardial regeneration. Lancet 2003; 361: 45-46.
Perin EC, Dohamnn HF, Borojevic R, Silva SA, Sousa AL, Mesquita CT, Rossi MI, et al. Transendocardial, autologous bone marrow cell transplantation for severe, chronic ischemic heart failure. Circulation 2003; 107: 2294-302 Strauer BE, Brehm M, Zeus T, Kostering M, Hernandez A et al. Repair of infarcted myocardium by autologous intracoronary mononuclear bone marrow transplantation in humans. Circulation 2002; 106: 1913-8
China Tse HF, Kwong Y-L, Chan JKF, Lo G, Ho C-L, Lau C-P Angiogenesis in ischaemic myocardium by intramyocardial bone marrow mononuclear cell implantation. The Lancet; 2003: 47-49
Transplantation of bone marrow stem cells for cutaneous wound healing Badavias EV, Falanga V Treatment of chronic wounds with bone-marrow derived cells. Arch Dermatol 2003; 139: 510-516
Corneal graft with highly promising clinical capabilities have been grown from limbal stem cells. Nishida K, Yamato M, Hayashida Y, Watanabe K, Maeda N, Watanabe H et al. Functional bioengineered corneal epithelial sheet grafts from corneal stem cells expanded in vivo on a temperature-responsive cell culture surface Transplantation 2004; 77: 379-385
Transplantation of limbal stem cells in blind patients Wylegala E, Tarnawska D, Wroblewska EM Limbal stem cell transplantation from HLA-compatible living donor. Long term observation. Klin Oczna 2003; 105: 378-83
Implantation of autologous neural stem cells in a patient with Parkinson disease by Dr. Michel Levesque, Los Angeles A beneficial effect of 83% was reported in September 2002, in the absence of additional medication.
Treatment of spinal cord injury by transplantation of stem cells from the olfactory mucosa: In Portugal (Dr. Carlos Lima), 11 patients around the world have been already treated by such procedure with some functional improvement.
The cord blood : a rich source of stem cells (from the baby) Cord blood contains hematopoietic and organ stem cells that both belong to the category of adult stem cells.
Dr. Nice Gardini from the ‘Centro de Criopreservazione’ (Forli, Italy) reported in July 2004 that for the first time a french woman was successfully treated for leukemia by transfusion of cord blood from an italian baby.
For other diseases than leukemia, preliminary results from animal studies, using cord blood organ stem cells, are promising.
-We have to discover what these adult stem cells really are..- We have to learn how they are controlled. The mechanism shown here is probably only one among many others. - We have to understand why these control mechanisms fail in pathological situations of fibrosis and chondrosarcoma
The research on adult stem cells despite its rapid progress is still in infancy. It remains to discover what stem cell therapy really is.
That is necessary to insure an efficient and safe therapeutic use.
At the present time, it appears that only adult stem cells can be used for stem cells therapy because the organism knows how to control them.
If the research had been well conducted, the rules governing embryonic stem cells transplantation should have been studied in mice before claiming a potential therapeutic use.
Peter Medawar, Nobel Price 1958 studied on mice the transplantation rules for specialized tissues, so helpful for humankind.
In 1998, in his testimony in front of the American Senate, Dr John Thomson, proposed 3 main utilisations for the human embryonic stem cells he just isolated: - 1. to cure degenerative diseases - 2. to better understand human embryo development - 3. to test new drugs.
« The biomedical industry is critical and growing component of New Jersey’s economy, and would be significantly diminished by limitations imposed on stem cell research » Senate of New Jersey (USA) September 30, 2002
Embryonic stem cells lines, either coming from ‘supernumerary embryos’ or cloned embryos are patentable intellectual property. In the case of adult stem cells, in most cases autologous grafts are performed.
Ideology does not necessarily lead to scientific truth. When Louis Pasteur discovered microorganisms, he had against him all the ones who wanted to believe in spontaneous generation.
The multiplication of interdisciplinary exchanges along with philosophical and theological reflection will foster the work of truth and respect for the mystery of human being John Paul II (november 2001)