Saturday, December 19, 2009

Stem Cell Technology

A stem cell is a "blank" cell/ precursor cell that can give rise to multiple tissue types such as a skin, muscle, or nerve cell. A stem cell is essentially the building block of the human body.

Properties of stem Cells

Stem Cells are very unique cells. Stem Cells have the amazing ability to develop into several distinct cell types in the body. Stem Cells can be used as a repair system for the body. Stem Cells can theoretically divide without limit in a living organism in order to replenish various types of cells. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function (i.e. a muscle cell, a red blood cell, a brain cell, etc.).

Unique properties of stem cells

Stem cells are capable of dividing and renewing themselves for long periods; They are “unspecialized” and they can give rise to specialized cell types. A stem cell is "uncommitted," until it receives a signal to develop into a specialized cell.
Asymmetric division of stem cells - Stem cells have the ability to divide asymmetrically . One portion of the cell division becomes a differentiated cell while the other becomes another stem cell.
Stem cells are unspecialized - A stem cell does not have any tissue-specific structures that allow it to perform specialized functions. A stem cell cannot work with its neighbors to pump blood through the body (like a heart muscle cell); It cannot carry molecules of oxygen through the bloodstream (like a red blood cell); and it cannot fire electrochemical signals to other cells that allow the body to move (like a nerve cell).
Stem cells are capable of dividing and renewing themselves for long periods - Stem cells may replicate many times. When cells replicate themselves many times it is called proliferation. The stem cells that proliferate for many months in the laboratory can yield millions of cells. Stem cells are capable of long-term self-renewal.
Stem cells can give rise to specialized cells - When unspecialized stem cells give rise to specialized cells, the process is called differentiation. There are signals inside and outside cells that trigger stem cell differentiation. The internal signals are controlled by a cell's genes. The external signals include chemicals secreted by other cells, physical contact with neighboring cells, and certain molecules in the microenvironment.
Stem cells exist in both embryos and adults - In embryos, stem cells function to generate new organs and tissues. In adults, they function to replace cells during the natural course of cell turnover.
Distinguishing Features of Progenitor/Precursor Cells and Stem Cells - A stem cell is an unspecialized cell that develops into a variety of specialized cell types. A stem cell divides and gives rise to one additional stem cell and a specialized cell. Example: a hematopoietic stem cell produces a second generation stem cell and a neuron.
A progenitor cell (a precursor cell) is unspecialized that is capable of undergoing cell division and yielding two specialized cells. Example: a myeloid progenitor/precursor cell undergoing cell division to yield two specialized cells (a neutrophil and a red blood cell).

Embryonic Stem Cells

Embryonic Stem Cells are derived from embryos that develop from eggs that have been fertilized in vitro. Embryonic Stem Cells are never derived from eggs fertilized inside of a woman's body. 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.
They are capable of undergoing an unlimited number of symmetrical divisions without differentiating (long-term self-renewal). They exhibit and maintain a stable, full (diploid), normal complement of chromosomes (karyotype). Pluripotent ES cells can give rise to differentiated cell types that are derived from all three primary germ layers of the embryo (endoderm, mesoderm, and ectoderm).

Adult type stem cells

Adult stem cells are undifferentiated cells. They are found in small numbers in most adult tissues. They can also be extracted from umbilical cord blood. They are also called “somatic stem cells.”They are multipotent in nature. They give rise to a closely related family of cells within the tissue. An example is hematopoietic stem cells, which form all the various cells in the blood.
Sources of adult stem cells
Umbilical Cords, Placentas and Amniotic Fluid - Adult type stem cells can be derived from various pregnancy-related tissues.
Adult Tissues - In adults, stem cells are present within the bone marrow, liver, epidermis, retina, skeletal muscle, intestine, brain, dental pulp and elsewhere.
Cadavers - Neural stem cells have been removed from specific areas in post-mortem human brains as late as 20 hours following death.

Comparison of embryonic and adult stem cells

Advantages of Embryonic Stem Cell 

1. Flexible - appear to have the potential to make any cell.
2. Immortal - one embryonic stem cell line can potentially provide an endless supply of cells with defined characteristics.
3. Availability - embryos from in vitro fertilization clinics.
Disadvantages of Embryonic Stem Cell
Difficult to differentiate uniformly and homogeneously into a target tissue.
Immunogenic - embryonic stem cells from a random embryo donor are likely to be rejected after transplantation
Tumorigenic - capable of forming tumors or promoting tumor formation.
Destruction of developing human life.

Advantages of Adult Stem Cell

Adult stem cells from bone marrow and umbilical cords appear to be as flexible as the embryonic type
  • Somewhat specialized - inducement may be simpler. 
  • Not immunogenic - recipients who receive the products of their own stem cells will not experience immune rejection. 
  • Relative ease of procurement - some adult stem cells are easy to harvest (skin, muscle, marrow, fat) 
  • Non-tumorigenic-tend not to form tumors. 
  • No harm done to the donor.

Disadvantages of Adult stem cells

1.Limited quantity - can sometimes be difficult to obtain in large numbers.
2. Finite - may not live as long as embryonic stem cells in culture.
3. Less flexible - may be more difficult to reprogram to form other tissue types

Potential sources of stem cells

Fetal tissue that becomes available after an abortion. Excess embryos from assisted reproductive technologies such as commonly used in fertility clinics. Embryos created through in vitro fertilization specifically for research purpose, and embryos created asexually as a result of the transfer of a human somatic cell nucleus to an egg with its own nucleus removed. Other sources of stem cells are those from umbilical cord blood, and bone marrow. In addition, neural stem cells, haematopoetic stem cells and mesenchymal stem cells can be harvested from fetal blood and fetal tissue.

Classification of stem cells based on level of differentiation

Totipotent stem cells - The fertilized egg is said to be totipotent from the Latin totus, meaning “entire”. It has the potential to generate all the cells and tissues that make up an embryo. It supports embryonic development in utero.
Pluripotent stem cells - are descendants of the totipotent stem cells of the embryo. These cells develop about four days after fertilization. They can differentiate into any cell type, except for totipotent stem cells and the cells of the placenta. “Pluri” is derived from the Latin plures means several or many. Thus, pluripotent cells have the potential to give rise to any type of cell.
  Multipotent stem cells - are descendents of pluripotent stem cells and antecedents of specialized cells in particular tissues. For example, hematopoietic stem cells, which are found primarily in the bone marrow, give rise to all of the cells found in the blood, including red blood cells, white blood cells, and platelets.
Unipotent stem cells - a term that is usually applied to a cell in adult organisms, means that the cells in question are capable of differentiating along only one lineage. "Uni" is derived from the Latin word unus, which means one.
Umbilical cord stem cells - Blood from the placenta and umbilical cord that are left over after birth is a rich source of hematopoietic stem cells. These so-called umbilical cord stem cells have been shown to be able to differentiate into bone cells and neurons, as well as the cells lining the inside of blood vessels. Cord blood stem cells have been used to treat 70 different diseases, including leukemia, lymphoma, and inherited diseases (of red blood cells, the immune system, and certain metabolic abnormalities). Cord blood collection is a safe, simple procedure that poses no risk to the mother or newborn baby.

Stem Cell therapy.

  • Treatment of neural diseases such as Parkinson's disease, Huntington’s disease and Alzheimer's disease. 
  • Stem cells could be used to repair or replace damaged neurons.
  • Repair of damaged organs such as the liver and pancreas. 
  • Treatments for AIDS. 
Stem cell transplantation (SCT) is the term now used in preference to bone marrow transplantation (BMT). When a patient's bone marrow fails to produce new blood cells, for whatever reason, he or she will develop anaemia, be prone to frequent, persistent infections and may develop serious bleeding problems. In order to restore blood cell production a patient may be given healthy stem cells.
Intense chemotherapy in cancer patients damages a person’s bone marrow, where the stem cells for blood reside. Depleted of a fresh supply of blood cells, the patient is left vulnerable to infection, anemia and bleeding. These side effects of chemotherapy are often treated with a bone marrow transplant.

1 comment:

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