Bone marrow transplantation was the original term used to describe the collection and transplantation of hematopoietic stem cells, but with the demonstration that peripheral blood and umbilical cord blood are also useful sources of stem cells, hematopoietic cell transplantation (HCT) has become the preferred generic term for this process. HCT is used to treat patients with an abnormal but nonmalignant lymphohematopoietic system by replacing it with one from a normal donor. HCT is also used to treat malignancy by allowing the administration of higher doses of myelosuppressive therapy than would otherwise be possible, and in the setting of allogeneic HCT, by conferring an immunologic graft-versus-tumor effect. The use of HCT has been increasing, both because of its efficacy in selected diseases and because of increasing availability of donors.
The Center for International Blood and Marrow Transplant Research (http://www.cibmtr.org) estimates that worldwide about 70,000 transplants were performed in 2016. The frequency of transplantation varied widely from country to country with a close association of transplant rates with Gross National Income (GNI)/capita. However, even among countries with similar GNIs/capita, there are substantial differences between countries and regions concerning the frequency of transplantation, disease indications, and choice of donor type.
THE HEMATOPOIETIC STEM CELL
Several features of the hematopoietic stem cell make transplantation clinically feasible, including its remarkable regenerative capacity, its ability to home to the marrow space following intravenous injection, and the ability of the stem cell to be cryopreserved (Chap. 92). Transplantation of a single stem cell can replace the entire lymphohematopoietic system of an adult mouse. In humans, transplantation of a small percentage of a donor’s bone marrow volume regularly results in complete and sustained replacement of the recipient’s entire lymphohematopoietic system, including all red cells, granulocytes, B and T lymphocytes, and platelets, as well as cells comprising the fixed macrophage population, including Kupffer cells of the liver, pulmonary alveolar macrophages, osteoclasts, Langerhans cells of the skin, and brain microglial cells. The ability of the hematopoietic stem cell to home to the marrow following intravenous injection is mediated, in part, by an interaction between CXCL12, also known as stromal cell–derived factor 1, produced by marrow stromal cells and the alpha-chemokine receptor CXCR4 found on stem cells. Homing is also influenced by the interaction of cell-surface molecules, termed selectins, including E- and L-selectin, on bone marrow endothelial cells with ligands, termed integrins, such as VLA-4, on early hematopoietic cells. Human hematopoietic stem cells can survive freezing and thawing with little, if any, damage, making it possible to remove and store a portion of the patient’s own bone marrow for later reinfusion following treatment of the patient with high-dose myelotoxic therapy.
HCT can be described according to the relationship between the patient and the donor and by the anatomic source of stem cells. In ~1% of cases, patients have ...