Regulation of hematopoietic stem cells by bone marrow stromal cells

•Stromal cell populations in the bone marrow microenvironment regulate hematopoiesis. •Current evidence supports a perivascular HSC niche. •Endothelial cells and CXCL12+ mesenchymal progenitors are key components of the HSC niche. •CXCL12 and SCF are key niche signals that regulate HSCs. Hematopoietic stem cells (HSCs) reside in specialized microenvironments (niches) in the bone marrow. The stem cell niche is thought to provide signals that support key HSC properties, including self-renewal capacity and long-term multilineage repopulation ability. The stromal cells that comprise the stem cell niche and the signals that they generate that support HSC function are the subjects of intense investigation. Here, we review the complex and diverse stromal cell populations that reside in the bone marrow and examine their contribution to HSC maintenance. We highlight recent data suggesting that perivascular chemokine CXC ligand (CXCL)12-expressing mesenchymal progenitors and endothelial cells are key cellular components of the stem cell niche in the bone marrow. Hematopoietic stem cells (HSCs) reside in specialized microenvironments (niches) in the bone marrow. The stem cell niche is thought to provide signals that support key HSC properties, including self-renewal capacity and long-term multilineage repopulation ability. The stromal cells that comprise the stem cell niche and the signals that they generate that support HSC function are the subjects of intense investigation. Here, we review the complex and diverse stromal cell populations that reside in the bone marrow and examine their contribution to HSC maintenance. We highlight recent data suggesting that perivascular chemokine CXC ligand (CXCL)12-expressing mesenchymal progenitors and endothelial cells are key cellular components of the stem cell niche in the bone marrow.