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Stem Cell Research & Human Cloning: Raising the Questions Scientific Research William S. Oetting, Ph.D. Department of Medicine - Genetics Institute of Human Genetics University of Minnesota Sources of Stem Cells Embryonic Stem Cells Inner Cell Mass Adult Stem Cells
Raising the Questions
William S. Oetting, Ph.D.
Department of Medicine - Genetics
Institute of Human Genetics
University of Minnesota
Embryonic Stem Cells
Inner Cell Mass
Adult Stem Cells
Normally in adult tissue
Adult Derived Embryonic Stem Cells
Inner Cell Mass
Embryonic Germ Cells
Germinal ridge of a 5-10 week fetus
Stem cell differentiates
Stem cell self-replicates
Stem cells have two important characteristics that distinguish them from other types of cells.
First, they are unspecialized cells that renew themselves for long periods through cell division. Stem cells do not age.
The second is that under certain physiologic or experimental conditions, they can be induced to become cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.
Totipotent stem cells can give rise to all the different types of cells in the body. A fertilized egg is considered totipotent.
Pluripotent stem cells can give rise to any type of cell in the body except those needed to develop a fetus.
Multipotent stem cells can give rise to multiple different cell types.
Embryonic stem cells are derived from embryos that develop from eggs that have been fertilized in vitro.
The embryos from which human embryonic stem cells are derived are typically four or five days old and are a hollow microscopic ball of cells called the blastocyst.
The inner cell mass is removed and the cells dissociated into single cells.
The cells are then plated on irradiated mouse cells.
The cells are then subcloned to maintain the cell line.
The developing fetus itself is the area marked as "ICM" (inner cell mass)
The blastocoel cavity in the center is marked as "C“
The trophectoderm cells that will form the placenta surround the cavity - one is marked with a "T"
ES cell colony
University of Wisconsin
Hematopoietic colony-forming cells derived from human embryonic stem cells
Dan S. Kaufman*, et al., PNAS, 98:10716-10721, 2001
REUBINOFF BE NAT BIOTECH 19:1134, 2001
ZHANG SC NAT BIOTECH 19:1129, 2001
KEHAT I JCI 108:407, 2001Human ES cell differentiates into multiple tissues in a culture dish
Controversy surrounding ES cells
Adult stem cells typically generate the cell types of the tissue in which they reside.
A blood-forming adult stem cell in the bone marrow, for example, normally gives rise to the many types of blood cells such as red blood cells, white blood cells and platelets.
It was initially thought that a blood-forming cell in the bone marrow — which is called a hematopoietic stem cell — could only give rise to hematopoietic cells.
Recently it has been shown that these cells can give rise to other tissues such as neurons, liver cells that can be made to produce insulin, and hematopoietic stem cells that can develop into heart muscle.
A number of organ specific stem cells have been identified including hematopoietic, endothelial, muscle, mesenchymal, neural, gastrointestinal, hepatic, and epidermal stem cells. In contrast to ES cells, adult stem cells are derived from adult tissue.
Hematopoietic stem cells have been used for transplantation.
Neural stem cells, present in fetal and adult brain, could be used for treatment of Parkinson's disease, Huntington's disease, Alzheimers disease, multiple sclerosis, and spinal cord injury.
Insulin producing islet cells to treat diabetes mellitus using the patient's own islet stem cells, or using ex vivo generated / expanded islet cells from allogeneic donors.
Endothelial stem cells in the blood and marrow of humans and animals could be used to induce neovascularization, or to prevent tumor angiogenesis.
Mesenchymal stem cells present in bone marrow are capable of generating cartilage and bone, are being tested for their ability to restore bone and cartilage defects
There are three main approaches to cell therapy in regenerative medicine
Allogeneic embryonic stem cells. While these stem cells are totipotent, they are not compatible with the patient’s DNA, thereby having a high risk of rejection by the patient’s immune system. The word allogeneic literally means “other DNA type”. The companies pursuing this strategy typically intend to address this problem trough administration of immunosuppressant drugs along with the cell therapy.
Autologous adult stem cells. These are stem cells taken from the patient and coaxed into replacement cells for the patients degenerative disease. While the resulting cells are of the patients own DNA, only a limited number of cell types can be created from these stem cells, thereby limiting the usefulness of this approach.
Autologous embryonic stem cells. ACT’s strategy is to use stem cells cloned directly from the patient’s own cells, thereby generating totipotent stem cells that are not rejected by the patient.
Human therapeutic cloning. Robert P. Lanza et al. Nature Medicine 5, 975 - 977 (1999)
The recipient oocyte is held by a glass pipette (left side of each frame), while a glass needle is used to remove the genetic material in the process of enucleation.
A cell containing the genetic material from the donor is placed inside the Zona Pellucida. An electrical pulse is then applied across the two cells, causing their membranes to fuse into one complete cell.
Controversy surrounding adult derived ES cells