Peripheral blood stem cell transplantation (bone marrow transplant) is a new technique in which stem cells are obtained from a patient's blood and used in bone marrow transplantation.
Stem cells are small, round cells with a squat nucleus and scant surrounding cytoplasm. They can perform what have been called "acts of biological resurrection" although they are unremarkable in appearance.
Stem cells, unlike other types of cells in the body, can reproduce forever, they can forgo immortality (in cell terms) and turn into an ordinary blood cell, a red blood cell (an erythrocyte), a white blood cell (a leukocyte), or a large cell (a megakaryocyte) that fragments into the platelets needed for blood to clot.
A relatively small number of stem cells can miraculously repopulate the whole bone marrow, provide an endless supply of stem cells, reconstitute the entire repertory of blood cells, and restore the immune system.
To recruit enough stem cells into the blood, stem cells are lured out of the bone marrow by a special regimen of drugs and coaxed into entering the peripheral blood (the blood stream).
The removal of the cells is termed pheresis or apheresis (from the Greek "aphairesis" for removal) because the blood is filtered through a machine and the stem cells are skimmed off. The stem cells then may be used right away for bone marrow transplant or stored in liquid nitrogen until needed.
Before the transplant is done, the patient receives high-dose chemotherapy and/or radiation therapy to destroy diseased cells (the leukemic cells, lymphoma cells, solid tumor cells, the diseased immune system cells in scleroderma, etc.). The stem cells are then infused into a vein of the patient, where they can produce new blood and immune cells and replace the cells destroyed by the treatment.