What Are Stem Cells?

[Vik]

What Are Stem Cells?

Research on stem cells is advancing knowledge about how an organism develops from a single cell and how healthy cells can replace damaged cells in adult organisms.



Definition of Stem Cells
Stem cells have two important characteristics that distinguish them from other types of cells. Firstly they are unspecialized cells and secondly, under certain physiologic or experimental conditions, they can be induced to become cells with special functions.

All stem cells have three general properties

• They are unspecialized;
• They can give rise to specialized cell types;
• They are capable of dividing and renewing themselves for long periods

Stem cells may replicate many times in a process called proliferation. If the resulting cells continue to be unspecialized, the cells are said to be capable of long-term self-renewal. Also, stem cells do not have any tissue-specific structures, therefore unspecialized stem cells can give rise to specialized cells, including heart muscle cells, blood cells, or nerve cells by a process called differentiation.

Blood stem cells are one of several types of stem cell. Healthy blood stem cells are vital because they replace our supply of red blood cells, white blood cells, and platelets. Red blood cells carry oxygen throughout the body, white blood cells fight infection, and platelets clot blood (control bleeding) when the skin or other tissue is cut.

When a person's blood stem cells become diseased or cancerous, it is a life-threatening situation. Often, the only hope for a cure is a blood stem cell transplant, which replaces the patient's diseased cells with healthy new cells. For the transplant to be a success these cells must match the patient's own cells as closely as possible.

The cells used in blood stem cell transplants come from three main sources: bone marrow, peripheral (or circulating) blood, and the umbilical cord of newborn babies (cord blood). In the case of bone marrow and peripheral blood stem cells, an adult donor donates the cells. Umbilical cord blood stem cells are collected when a baby is born and are stored for future use.
Donating cord blood poses no risk or pain to mother or baby. Also, there is a lower risk of graft-versus-host disease post-transplant using cord blood stem cells than with other types of blood stem cell transplants, allowing for less than perfect matches of HLA type (Human Leukocyte Antigen typing) which determines whether a patient has a suitable donor for stem cell transplant.

[Vik]

All About Stem Cells

Stem cells, those white wisps of cells that separate during laboratory processing, have become the answer to over 45 diseases and are projected to be able to treat many more. More parents are considering the option of banking their newborn's umbilical cord blood as insurance against certain diseases, but it's hard to stay abreast of the scientific earful of information on the topic of cord blood banking. Let this be your resource when making that important decision.



Adult Stem Cells: Stem cells that are harvested from mature human tissue.

To help make your decision, you should first familiarize yourself with the many concepts that lie behind cord blood banking.
What Are Stem Cells?
Literally, many cells in your body 'stem' from these primitive, undifferentiated stem cells. Stem cells have two characteristics that separate them from the other cells in your body:

1. proliferation: stem cells have the ability to renew themselves over long periods of time through the process of cell division.
2. differentiation: originally, stem cells are unspecialized, mononuclear cells; under certain conditions that can be scientifically manipulated, a signal will coax the stem cell to become a specialized cell, such as an auditory hair cell or a pumping heart muscle cell.

More Information on Stem Cells
Those used in stem cells research primarily derive from two sources: there are embryonic stem cells and adult stem cells.

1. human embryonic stem cells: scientists use a donated human embryo that is no longer needed for in vitro fertilization (IVF) with the informed consent of the donor; the inner cell mass of the 4-day old embryo, or blastocyte, is then cultured in Petri dishes for approximately six months until they produce a 'cell line' containing millions of stem cells.
2. 2. adult stem cells: these are taken from mature tissue in 'adults'; your baby's umbilical cord blood also falls into the 'adult' stem cell category, and therefore scientists sometimes name this category 'somatic' stem cells. There are three tissues from which stem cells are usually harvested:
   • umbilical cord blood
   • bone marrow
   • peripheral blood

What Sets Cord Blood Apart from Adult Stem Cells?
Although umbilical cord blood is defined as adult or somatic stem cells, because it is younger in nature, there are several factors that make it unique.

1. primitive: because cord blood stem cells are younger, they have more plasticity, meaning they can give rise to a greater variety of specialized cells. They have also been less affected by damaging environmental toxins that change the DNA, and so more likely are healthier cells. Lastly, because they are young, they can better integrate into the recipient patient and are less likely to cause graft vs. host disease (GvHD) or cell rejection.
2. stem cell-rich: approximately one liter of umbilical cord blood is collected, and among that 1-2% of the mononuclear cells are stem cells. This makes cord blood one of the richest sources of stem cells. It is also easier to separate stem cells in cord blood. While adult stem cells can be found in numerous mature tissues, they are found in lesser quantities and are harder to locate.
3. availability: cord blood banking means that it will always be immediately available, unlike other adult stem cell transplants such as bone marrow.

Why Are Stem Cells Important?Perhaps most importantly, stem cells make us. The inner mass of cells in the blastocyte is rich in stem cells-stem cells that will one day form a heart, lungs, muscle tissue, hair, etc.

Stem cells are like the backbone of the immune system; they sit waiting for something to go wrong, and ten they jump into action. Stem cells found in bone marrow will differentiate into mature cells that make up the immune system. For example, stem cells reside in the skin's basal layer and at the base of follicles where they form a protective layer against cuts and infections. Brain stem cells help form nerve connections. In other words, stem cells throughout the body help regulate your health.

Since 1998, stem cells have also been cultured and manipulated in order to treat diseases, such as leukemia. Scientists estimate that research will one day allow stem cells to be used to treat Diabetes, Parkinson's, spinal cord injuries, heart diseases and many other devastating diseases.

[Vik]

Embryonic vs. Adult Stem Cells

Fundamentals of Adult Stem Cells
Within our bodies, the adult stem cells found in various tissues and organs function as part of our immune system. This means they primarily replace our body’s supply of life-giving and disease-fighting blood. Specifically, they differentiate into red and white blood cells and platelets

.

• red blood cells: carry oxygen through our blood stream
• white blood cells: fight infection
• platelets: clot our blood when skin is cut in order to prevent profuse bleeding

When certain diseases, such as leukemia, damage our blood’s ability to replenish a healthy blood supply, transplants of healthy stem cells can be the answer. There are a few main sources of healthy stem cells that physicians turn to for transplants.

Bone Marrow
Bone marrow, the spongy material found in our bones, is the probably the richest source of adult (excluding cord blood) stem cells. Bone marrow transplants have been used to treat genetic disorders, immune system disorders and blood disorders such as aplastic anemia and leukemia.

Peripheral Blood Stem Cells
While peripheral blood is not as rich a source of stem cells, the donor can be given 'growth factor' drugs that increase the amount of stem cells. These stem cells are then separate from the donor's blood; this is called the apharesis phase.

pro: unlike bone marrow transplants, no anesthesia is used on the donor

con: there is an increased risk of graft vs. host disease (GVHD)

Umbilical Cord Blood
The first cord blood transplant was performed in 1988, and has spurred a flurry of activity in the area. Umbilical cord blood has many benefits that bone marrow transplants and peripheral blood stem cells lack. It's painless to extract, and once it's banked, it's readily available for transplant needs. There are a host of diseases that cord blood can treat, making it a leader in cell-based regenerative therapy. Because it's a source of more primitive stem cells, there is a lower risk of GVHD. Because of this lower risk, it is possible to treat patients with less perfect HLA (Human Leukocyte Antigens) matches.

Also, because the costs of cord blood transplants are lower, medical insurance companies prefer cord blood banking to bone marrow; there are even companies that will allow you to do cord blood banking for free if you meet their 'case of need' criteria (visit our company listings and information page). Lastly, you can choose whether you prefer banking your baby's cord blood or donating it to a community bank. Banking with a private company means the cord blood will be stored for your own personal use. Donating to a community bank is an act of good will; it will allow patients in need to use your baby's life-giving stem cells to treat their diseases. Community banks are also popping up throughout the country, which means you have more banks close to home. Some of these banks even give you priority to your baby's cord blood in case of your need.

While genetic diseases can be transmitted through cord blood, the cord blood bank you choose will alert you to the presence of any abnormalities they find in the blood. Another concern with cord blood is that the amount collected usually can treat a child or a small adult (approximately 110 lbs). While currently, cord blood can be stored and kept fresh for only 15 years, science is pushing the years your cord blood stays viable.

While cord blood is technically an 'adult' or 'somatic' stem cell source, it is often distinguished from the adult stem cell category. Because cord blood is a source of younger stem cells, it looms somewhere between adult stem cells and embryonic stem cells, offering the benefits of each category.

Embryonic Stem Cell Basics
Embryonic stem cells are cultured in a Petri dish using the spare fertilized eggs of in vitro fertilization (IVF). These eggs are donated with the informed consent of the donors. Many moral and ethical questions arise in embryonic stem cell research; this is especially true of fetal stem cell research, the use of older embryos. The issue lies in scientists making their own embryos from scratch for use in stem cell research.

Embryonic stem cells have the capacity to replicate themselves, a process called proliferation. At about six months, cultured embryonic stem cells have created millions of new stem cells. Embryonic stem cells can proliferate for a year or more in the laboratory.

With those countless stem cells, scientists have the potential ability to create various specialized cells. This is because embryonic stem cells are pluripotent, or they have the ability to transform into virtually any cell. Ideally, these specialized cells will be able to treat a number of diseases and disorders in the future including diabetes, Parkinson's disease, heart disease, spinal cord injuries and vision and hearing loss. However, scientists haven't yet perfected the growing and differentiating process for embryonic stem cells. As a result, embryonic stem cells can sometimes differentiate spontaneously, which, currently, could cause serious repercussions if the stem cells were used to treat people. Throughout the world, though, there is continuous research being done on embryonic stem cells with new discoveries being made every day about how to best use these stem cells.

[vamanjani]

Dear Vik,
Hats off for the finest cotribution on stem cell transplant. I can imagine, what pain you must have taken to subsribe such minute details in such an efficient manner.
May God bless you and that you remain hale and hearty . Congratulations.
Vaman Jani

[vamanjani]

PERIPHERAL BLOOD STEM CELL TRANSPLANTATION
In the past few years, an increasing number of PBSCT are being performed. The procedure is similar to BMT except for differences in the method of collection of the stem cells and slight changes in the engraftment potential. It is well known that the peripheral blood contains a small percent of stem cells, approximately 0.1%. This number can be increased by administration of colony stimulating factors, like G-CSG and GM-CSF.
For allogenic donors, administration of colony stimulating factors, like G-CSF for 4 to 5 days results in a high circulating stem cells which can be collected by a cell-separator. The procedure requires venous access and takes two to four hours. The donor nedd not be admitted, does not require anesthesia and is spared the pain of marrow aspiration.
CORD BLOOD STEM CELL TRANSPLANTATION
Plancental blood, which is routinely discarded in clinical practice, is potentially a vast supply of allogeneic fetal hematopoietic stem cells. Cord blood stem cells have distinctive advantages which include
a) ENRICHED PROPORTION OF IMMATURE STEM CELLS
B) HIGHER CLONOGENIC GROWTH ADVANTAGE
C) INCREASED CELL CYCLE RATE
D) AUTOCRINE GROWTH FACTORS PRODUCTION AND
E) INCREASED TELOMERE LENGTH.
The small number and relative immaturity of naive T cells of cord blood lmphocytes is expected to reduce the risk and severity of graft versus host disease. The activation pattern of cord blood T cells is less in magnitude than that nin adult counterparts.
The main limitation of cord blood transplants is the limited number of nucleated cells availabale in a unit. As compared to bone marrow transplantation, the time for engraftment in a cord blood transplantation is much longer, taking month for neutrophilic engraftment and more than fifty days for platelet engraftment. There is also a higher incidence of nonengraftment. This leads to a high transplant related mortality.
It is estimated that 170,000 cord blood units have been cryopreserved in cord blood banks worldwide and about 4500 CBTs have been performed. Majority of these have been unrelated CBTs, mainly in children. The main indication of CBTs is in those cases where there is no HLA identical sibling donor available, and the disease is potentially fatal like a relapsed acute leukaemia or severe aplastic anemia. There is very limited experience with unrelated CBT in Thalassaemia major. The only other advantage of a related CBT is a lower incidence of GVHD at the cost of a higher transplant related mortality due to delayed engraftment.
THALASSAEMIA AND CORD BLOOD TANSPLANT
Cord blood transplants have been reported in Thalassaemia patients, but no large series has been pblished for evaluation of prognostic factors. In a series of CBT in hemoglobinopaties from related cord blood, sustained engraftment was seen in only 5 out of 10 cases. In contrast, with conventional BMT using HLA identical siblings as donors, event free survival of 94% was seen in class 1 cases. In a large series of related CBTs in thalassaemia and sickle cell anemia, 33 patients with thalassaemia, 7 patients (21%) did not have sustained engraftment.
The high incidence of graft rejection after related cord blood transplantation suggest that it is not the procedure of choice. The reasons for the graft rejection are the limited number of nucleated cells available for transplantation. Moreover, the procedure of cord blood transplantation is more complicated than a BMT, as it takes longer for engraftment and initial mortality is higher.
Once CBT is rejected, subsequent BMT from the same donor is likely to be less successful, as presensitiation would lead to a higher risk of rejection.

Vaman Jani