Expression of VEGFR-2 and AC133 by circulating human CD34+ cells identifies a population of functional endothelial precursors

Abstract

Emerging data suggest that a subset of circulating human CD34+ cells have phenotypic features of endothelial cells. Whether these cells are sloughed mature endothelial cells or functional circulating endothelial precursors (CEPs) is not known. Using monoclonal antibodies (MoAbs) to the extracellular domain of the human vascular endothelial receptor-2 (VEGFR-2), we have shown that 1.2 ± 0.3% of CD34+ cells isolated from fetal liver (FL), 2 ± 0.5% from mobilized peripheral blood, and 1.4 ± 0.5% from cord blood were VEGFR-2+. In addition, most CD34+VEGFR-2+ cells express hematopoietic stem cell marker AC133. Because mature endothelial cells do not express AC133, coexpression of VEGFR-2 and AC133 on CD34+ cells phenotypically identifies a unique population of CEPs. CD34+VEGFR-2+ cells express endothelial-specific markers, including VE-cadherin and E-selectin. Also, virtually all CD34+VEGFR-2+ cells express the chemokine receptor CXCR4 and migrate in response to stromal-derived factor (SDF)-1 or VEGF. To quantitate the plating efficiency of CD34+ cells that give rise to endothelial colonies, CD34+ cells derived from FL were incubated with VEGF and fibroblast growth factor (FGF)-2. Subsequent isolation and plating of nonadherent FL-derived VEGFR-2+ cells with VEGF and FGF-2 resulted in differentiation of AC133+VEGFR-2+ cells into adherent AC133−VEGFR-2+Ac-LDL+(acetylated low-density lipoprotein) colonies (plating efficiency of 3%). In an in vivo human model, we have found that the neo-intima formed on the surface of left ventricular assist devices is colonized with AC133+VEGFR-2+ cells. These data suggest that circulating CD34+ cells expressing VEGFR-2 and AC133 constitute a phenotypically and functionally distinct population of circulating endothelial cells that may play a role in neo-angiogenesis.

Platelet‐derived growth factor promotes ex vivo expansion of CD34+ cells from human cord blood and enhances long‐term culture‐initiating cells, non‐obese diabetic/severe combined immunodeficient repopulating cells and formation of adherent cells

“…Our study demonstrated that PDGF significantly enhanced the development of adherent cells and clusters from enriched cord blood CD34 + cells. Some adherent cells were endothelial in nature as revealed by the positive VE-adherin expression and they were probably developed from endothelial cell precursors (Peichev et al, 2000) present in the fresh cord blood in a minute quantity (Nieda et al, 1997). Bone marrow stromal cells and cord endothelial cells have been known to enhance the expansion of SCID repopulation cells and long-term haematopoietic progenitor cells respectively (Ye et al, 1994;Yamaguchi et al, 2001).…”

Critical assessment of the efficiency of CD34 and CD133 antibodies for enrichment of rabbit hematopoietic stem cells

“…For example, vascular endothelial growth factor receptor-2-positive endothelial progenitors are AC133 epitope-positive and AC133 epitope expression is rapidly downregulated during maturation. 47 Down-regulation of AC133 and AC141 epitope expression was also observed upon differentiation of the colon carcinoma cell line Caco-2. 48 AC133 1 AC141 1 CD34 2 CD45 2 cells isolated by FACS from fresh human fetal brain tissue initiated neurosphere cultures, and the progeny of clonogenic cells could differentiate into both neurons and glial cells.…”

Integrative molecular and developmental biology of adult stem cells

“…These cells possess an even broader range of differentiation potential than MSCs (Reyes et al, 2001;Reyes et al, 2002;Jiang et al, 2002a). MAPCs can apparently differentiate not only into all MSC-derived cell types (including skeletal muscle-like cells) but also into CD34 + CD133 + VEGFR-2 + VE-cadherin + cells that have properties of endothelial progenitors (Peichev et al, 2000;Quirici et al, 2001). While MAPCs could not be induced to differentiate into hematopoietic cells in vitro under the conditions employed (but see below), they are capable of differentiating in vitro into nonmesodermal cell types, such as hepatocyte-like cells (Schwartz et al, 2002) and cells having characteristics of midbrain neurons (Jiang et al, 2003).…”