Circulating Hematopoietic Stem Cell Transplantation

Circulating blood normally contains a subpopulation of self-renewing, pluripotent hematopoietic stem cells. The number of these cells in the circulation is usually quite low, but if they are increased deliberately with mobilizing therapies, they can be harvested efficiently in sufficient numbers for transplantation using apheresis techniques. Transplantation of mobilized hematopoietic stem cells, derived from the blood in both the autologous and allogeneic settings, provides faster marrow function recovery than transplantation of nonmobilized blood-derived stem cells or marrow-derived stem cells. Allogeneic transplants are performed if the recipient's marrow is malignant, as in myelogenous leukemia, and needs to be replaced or if a patient with genetic disorder, such as an immune deficiency, requires a new immune system generated from a new bone marrow for survival. Early studies of blood-derived stem-progenitor cell transplantation to lethally irradiated animal models were successful but clinical investigations required the development of techniques to collect the cells in large numbers, previously identified as necessary for successful marrow-derived hematopoietic stem cell transplantation. Five years passed before the next report of clinical attempts at blood-derived stem-progenitor cell transplantation using nonleukemic cells appeared. When the second marrow transplant also failed, collecting marrow from the donor a third time in a short period was problematic, so granulocyte colony-stimulating factor (G-CSF) was administered to this donor and mobilized blood stem cells were collected and infused.