Hematopoietic stem cells are used in bone marrow transplant and have the ability to self renew in the marrow and to differentiate into the full complement of cell types found in blood.

They were first adult stem cells to be discovered.

Heamatopoietic cells are found in the bone marrow a, fetal liver, fetal spleen, umbilical cord and placental blood.

The cells are discovered nearly four decades ago but their ability to grow and  generate tissues other than those of the blood system has recently come into light. this property is called plasticity. therefore it is hoped that we might be able to grow many lines of stem cells from these hematopoietic cells.

There are encouraging studies that report this.

If possible this would avoid the risk graft versus host disease associated with embronic stem cell tissues.

They differ in number and type differentiated cell types they can become.

Differentiation Capacity

While embryonic stem cells can become all cell types of the body because they are pluripotent, adult stem cells are  limited to differentiating into their tissue of origin.

Growth

Embryonic stem cells can be grown relatively easily in culture. Adult stem cells are rare  and isolating these cells from an adult tissue is difficult. Moreover ways to increase their population in cell culture is yet to be found.

This is an important difference, as large numbers of cells are needed for stem cell replacement therapies.

Rejection Chances

Embryonic and adult stem cells may differ in the likelihood of being rejected after transplantation. Though not supported by any scientific evidence, adult stem cells, and tissues derived from them, are currently believed less likely to initiate rejection after transplantation. This is because a patient’s own cells could be expanded in culture, coaxed into assuming a specific cell type  and then reintroduced into the patient.

The use of adult stem cells and tissues derived from the patient’s own adult stem cells would mean that the cells are less likely to be rejected by the immune system.

This represents a significant advantage, as immune rejection can be circumvented only by continuous administration of immunosuppressive drugs, and the drugs themselves may cause seroius side effects.

The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found.

They are also termed as  somatic stem cell. The origin of adult stem cells in mature tissues is unknown.

Adult stem cells have been found in many more tissues than they once thought possible. In right environment, certain kinds of adult stem cells seem to have the ability to differentiate into a number of different cell types, given the right conditions. If this is possible under lab conditions, these cells may become the basis of therapies for many serious common diseases.

About 40 years ago, researchers discovered that the bone marrow contains at least two kinds of stem cells. One population, called hematopoietic stem cells, forms all the types of blood cells in the body. A second population, called bone marrow stromal cells, generate bone, cartilage, fat, and fibrous connective tissue.

There are a very small number of stem cells in each tissue.They may remain non-dividing for many years until they are activated by disease or tissue injury.

The adult tissues reported to contain stem cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin and liver.

Struggle, however is to  grow adult stem cells in cell culture and manipulate them to generate specific cell types so they can be used to treat injury or disease.

How To Identify Adult Stem Cells?

One or more of the following three methods are used to identify adult stem cells

1. Labeling the cells in a living tissue with molecular markers and then determining the specialized cell types they generate
2. Removing the cells from a living animal, labeling them in cell culture, and transplanting them back into another animal to determine whether the cells repopulate their tissue of origin
3. Isolating the cells, growing them in cell culture, and manipulating them, often by adding growth factors or introducing new genes, to determine what differentiated cells types they can become.

Stem cells are present in most multi-cellular organisms.

The two broad types of mammalian stem cells are

• Embryonic stem cells
  These cells are isolated from the inner cell mass of blastocysts in embryo.In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues.
• Adult stem cells
  These are found in adult tissues and participate in  repair system for the body, replenish specialized cells and maintain the normal turnover of regenerative organs, such as blood, skin or intestinal tissues.

Stem cells can now be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture.

Highly plastic adult stem cells from a variety of sources, including umbilical cord blood and bone marrow, are routinely used in medical therapies. Embryonic cell lines and autologous embryonic stem cells generated through therapeutic cloning are promising candidates for future therapies.