title: Children are not little adults: just ask their hematopoietic stem cells.
abstract: HSCs differ during ontogeny in some important parameters, including anatomic site of residence and cell cycling characteristics. In this issue of the JCI, Bowie et al. show that postnatal HSCs as well as fetal liver HSCs in mice are active in the cell cycle at much higher rates than that of adult HSCs; however, this increased frequency of cycling abruptly ceases 4 weeks after birth (see the related article beginning on page 2808). The cycling postnatal HSCs expressed high levels of CXC chemokine ligand 12 (CXCL12, also known as stromal cell-derived factor 1 [SDF-1]), a chemokine previously implicated in stem cell trafficking to the marrow cavity and shown to be expressed by cells within the hematopoietic microenvironment. These cells also possessed an engraftment defect impeding reconstitution in irradiated recipient mice, which was reversible by pretransplant administration of antagonists of the CXCL12 receptor, CXCR4. Such agents are currently clinically available, suggesting that this approach could be used to improve stem cell transplantation and engraftment.
authors.affiliation: Division of Experimental Hematology, Cincinnati Children's Research Foundation and Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA. david.williams@cchmc.org
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
authors.forename: Haiming
authors.initials: H
authors.lastname: Xu
authors.forename: Jose A
authors.initials: JA
authors.lastname: Cancelas
mesh_terms: D000328:Adult; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000037:antagonists & inhibitors / Q000235:genetics; D002648:Child; D006410:Hematopoiesis / Q000502:physiology; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D006413:Hematopoietic System / Q000166:cytology* / Q000196:embryology / Q000254:growth & development; D006801:Humans; D008099:Liver / Q000166:cytology / Q000196:embryology; D051379:Mice; D008954:Models, Biological
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; C515256:Cxcl12 protein, mouse