Stem cells are cells found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian scientists Ernest A. McCulloch and James E. Till in the 1960s.

The two broad types of mammalian stem cells are: 1- embryonic stem cells that are isolated from the inner cell mass of blastocysts; and 2- adult stem cells that are found in adult tissues.

In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing specialized cells, but also 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 stem cell research has been plagued by moral and legal problems. In addition, early transplantation work with embryonic cells indicates that the transplanted cells create tumors, a critical setback for long-term work.

Thus far, the approximate 70 therapies that use adult stem cells successfully use stem cells derived from the bone marrow. This process, called bone marrow apheresis, requires drilling holes in the hip bone and extracting about one quart of bone marrow and blood and separating the stem cells from it. This is costly (over $100,000), painful, and about 5% of the people die from infection and related problems. It is the last thing you would prefer to do after a heart attack, but since it works, it is being used.

Now, everyone's goal is to avoid such a difficult treatment by take circulating blood that can be easily removed (called peripheral blood) and use that to regenerate needed tissue. However, circulating blood is not rich enough in stem cells to regenerate tissue; it would take too much blood to be provide a therapeutic amount of cells.

Ultimately, the goal is to take blood from the arm, as simple as one would give a blood sample, and use that blood to grow (referred to as "expand") the cells to a therapeutic amount of cells. It's not easy to do, and the researchers that are able to do so may change the course of medical treatment as we know it.