Replacing Cells - Biotechnology and Your Health: Pharmaceutical Applications - page 113

Blood-forming Stem Cells
Scientists have known for a long time that stem cells taken from the bone
marrow, the soft tissue inside the hollow part of most bones, can develop
into all the different types of blood cells. These blood-forming, or
hematopoietic, stem cells are now the most widely used stem cells in
medicine. Most types of blood cells survive for only a short time and the
hematopoietic stem cells are constantly replacing both themselves and the
dying blood cells. Blood-forming stem cells are normally present in very
small numbers in the blood, but will increase if a person is treated with
recombinant forms of protein growth factors (described in Chapter 5)
that dock onto a protein on the surface of the cells and trigger the cells to
divide and become mature blood cells. Another source of blood-forming
stem cells is the blood in a newborn's umbilical cord.
Hematopoietic stem cells are used to treat people whose own
blood-forming cells fail because of a rare condition called aplastic ane-
mia, or to help people who have been accidentally exposed to very high
doses of irradiation . Hematopoietic stem cells are most often used as
part of the treatment for certain forms of cancer. Sometimes cancer
patients are given very high doses of irradiation and/or chemotherapy
drugs that destroy the blood-forming stem cells in the bone marrow.
Transplants with the patient's own blood stem cells that were removed
before the treatment, or stem cells from a healthy donor, allow the
patient to recover. The transplant process is very simple: The cells in
a salt solution are slowly injected into a vein just like a blood trans-
fusion. If the blood stem cells come from a donor, then the donor and
the patient must share certain inherited proteins to make sure that
the donor's immune system cells will not attack the treated patient.
This condition, called graft versus host disease , can severely damage
the intestines, liver, and other organs, and may be fatal.
Multitalented Stem Cells
Recently, scientists have also become very interested in other, more
versatile, kinds of stem cells—stem cells that may be able to develop