immunology allergic disorders
Hematopoietic Stem Cell Transplantation
Introduction
Hematopoietic stem cell (HSC) transplantation is a rapidly evolving technique that offers a potential cure for hematologic cancers ( Overview of Leukemia , (See also Overview of Transplantation .) Hematopoietic stem cell 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 Hematopoietic stem cell transplantation may be autologous (using the patient'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 hematopoietic stem cell transplantation, because stem cell harvest is easier and neutrophil and platelet counts recover faster. Umbilical cord hematopoietic stem cell 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 hematopoietic stem cell transplantation. Contraindications to allogeneic hematopoietic stem cell transplantation are relative and include Age>50 Previous hematopoietic stem cell transplantation Significant comorbidities (eg, renal failure) Allogeneic hematopoietic stem cell 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 hematopoietic stem cell transplantation is still in its infancy, but it is gaining interest. 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 that immune cells in cord blood do not have experience with the viruses responsible for latent infections, leading to a higher percentage of naive T cells and thus increased vulnerability to reactivation of cytomegalovirus or Epstein-Barr virus infection. 