Hematopoietic stem cell transplantation

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Hematopoietic stem cell (HSC) transplantation is a rapidly evolving technique that offers a potential cure for hematologic cancers (leukemias, lymphomas, myeloma) and other hematologic disorders (eg, primary immunodeficiency, aplastic anemia, myelodysplasia). HSC transplantation is also sometimes used for solid tumors (eg, some germ cell tumors) that respond to chemotherapy. (See also Overview of Transplantation.)
HSC transplantation contributes to a cure by

Restoring bone marrow after myeloablative cancer-eradicating treatments
Replacing abnormal bone marrow with normal bone marrow in nonmalignant hematologic disorders

HSC transplantation may be autologous (using the patient#39;s own cells) or allogeneic (using cells from a donor). Stem cells may be harvested from

Bone marrow
Peripheral blood
Umbilical cord blood

Peripheral blood has largely replaced bone marrow as a source of stem cells, especially in autologous HSC transplantation, because stem cell harvest is easier and neutrophil and platelet counts recover faster. Umbilical cord HSC transplantation has been restricted mainly to children because there are too few stem cells in umbilical cord blood for an adult. A potential future source of stem cells is induced pluripotent stem cells (certain cells taken from adults and reprogrammed to act like stem cells).
There are no contraindications to autologous HSC transplantation.
Contraindications to allogeneic HSC transplantation are relative and include age gt; 50, previous HSC transplantation, and significant comorbidities.
Allogeneic HSC transplantation is limited mainly by lack of histocompatible donors. A human leukocyte antigen (HLA)-identical sibling donor is ideal, followed by an HLA-matched sibling donor. Because only one fourth of patients have such a sibling donor, mismatched related or matched unrelated donors (identified through international registries) are often used. However, long-term disease-free survival rates may be lower than those with HLA-identical sibling donors.
The technique for umbilical cord HSC transplantation is still in its infancy, but it is gaining interest. About 20,000 cord blood transplantations have been done since the procedure was introduced in 1989. Because cord blood contains immature stem cells, HLA matching appears less crucial than for the other types of hematopoietic stem cell transplantation. One concern about the procedure is the antigen-inexperienced nature of immune cells in cord blood, leading to a higher percentage of naive T cells, which increases risk of reactivating infections with cytomegalovirus or Ebstein-Barr virus.