title: An ectopic stromal implant model for hematopoietic reconstitution and in vivo evaluation of bone marrow niches.
abstract: In adults, hematopoiesis takes places in the bone marrow, where specialized niches containing mesenchymal nonhematopoietic cells (stroma) harbor the hematopoietic stem cell (HSC). These niches are responsible and essential for the maintenance of HSCs. Attempts to expand HSCs fail to  keep the general properties of stem cells, which depend on several niche components difficult to reproduce in in vitro culture systems. Here, we describe a methodology for in vivo study of hematopoietic stroma. We use stroma-loaded macroporous microcarriers implanted in the subcutaneous tissue  of experimental animals and show that the ectopic stroma implant (ESI) is able to support hematopoiesis. Moreover, lethally irradiated mice can be rescued by ESI preloaded with HSCs, showing that they function as an ectopic bone marrow. ESI is also shown as a good system to study the role  of different niche components. As an example, we used stromas lacking connexin 43 (Cx43) and confirm the importance of this molecule in the maintenance of the HSC niche in vivo. We believe ESI can work as an ectopic bone marrow allowing in vivo testing of different niches components and opening  new avenues for the treatment of a variety of hematologic conditions particularly when stromal cell defects are the main cause of disease.
authors.affiliation: Banco de Sangue de Cordão Umbilical e Placentário, Centro de Transplante de Medula óssea, Instituto Nacional de Câncer, Rio de Janeiro, Brazil.
authors.forename: Flávio Henrique
authors.initials: FH
authors.lastname: Paraguassú-Braga
authors.forename: Ana Paula G
authors.initials: AP
authors.lastname: Alves
authors.forename: Isabella Maria Alvim Andrade
authors.initials: IM
authors.lastname: Santos
authors.forename: Martin
authors.initials: M
authors.lastname: Bonamino
authors.forename: Adriana
authors.initials: A
authors.lastname: Bonomo
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology*; D002478:Cells, Cultured; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism; D006410:Hematopoiesis; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D023421:Models, Animal; D055153:Stem Cell Niche; D017154:Stromal Cells / Q000166:cytology* / Q000378:metabolism; D014916:Whole-Body Irradiation
chemical_list: D018031:Connexin 43