The chemokines CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC regulate lymphocyte chemotaxis, mediate vascular pericyte proliferation, and act as angiostatic agents, thus inhibiting tumor growth. These multiple activities are apparently mediated by a unique G protein–coupled receptor, termed CXCR3. The chemokine CXCL4/PF4 shares several activities with CXCL9, CXCL10, and CXCL11, including a powerful angiostatic effect, but its specific receptor is still unknown. Here, we describe a distinct, previously unrecognized receptor named CXCR3-B, derived from an alternative splicing of the CXCR3 gene that mediates the angiostatic activity of CXCR3 ligands and also acts as functional receptor for CXCL4.Human microvascular endothelial cell line-1 (HMEC-1), transfected with either the known CXCR3 (renamed CXCR3-A) or CXCR3-B, bound CXCL9, CXCL10, and CXCL11, whereas CXCL4 showed high affinity only for CXCR3-B. Overexpression of CXCR3-A induced an increase of survival, whereas overexpression of CXCR3-B dramatically reduced DNA synthesis and up-regulated apoptotic HMEC-1 death through activation of distinct signal transduction pathways. Remarkably, primary cultures of human microvascular endothelial cells, whose growth is inhibited by CXCL9, CXCL10, CXCL11, and CXCL4, expressed CXCR3-B, but not CXCR3-A. Finally, monoclonal antibodies raised to selectively recognize CXCR3-B reacted with endothelial cells from neoplastic tissues, providing evidence that CXCR3-B is also expressed in vivo and may account for the angiostatic effects of CXC chemokines.

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Depletion of podocytes, common to glomerular diseases in general, plays a role in the pathogenesis of glomerulosclerosis. Whether podocyte injury in adulthood can be repaired has not been established. Here, we demonstrate that in the adult human kidney, CD133ϩCD24ϩ cells consist of a hierarchical population of progenitors that are arranged in a precise sequence within Bowman's capsule and exhibit heterogeneous potential for differentiation and regeneration. Cells localized to the urinary pole that expressed CD133 and CD24, but not podocyte markers (CD133ϩCD24ϩPDXϪ cells), could regenerate both tubular cells and podocytes. In contrast, cells localized between the urinary pole and vascular pole that expressed both progenitor and podocytes markers (CD133ϩCD24ϩPDXϩ) could regenerate only podocytes. Finally, cells localized to the vascular pole did not exhibit progenitor markers, but displayed phenotypic features of differentiated podocytes (CD133ϪCD24ϪPDXϩ cells). Injection of CD133ϩCD24ϩPDXϪ cells, but not CD133ϩCD24ϩPDXϩ or CD133-CD24Ϫ cells, into mice with adriamycin-induced nephropathy reduced proteinuria and improved chronic glomerular damage, suggesting that CD133ϩCD24ϩPDXϪ cells could potentially treat glomerular disorders characterized by podocyte injury, proteinuria, and progressive glomerulosclerosis. Glomerular diseases account for 90% of ESRD at a cost of $20 billion/yr in the United States. 1 The traditional glomerular disease classification encompasses a bewildering array of descriptive pathologic entities and their clinical counterparts. However, converging evidence suggests that podocyte depletion, secondary to toxic, genetic, immune, infectious, oxidant, metabolic, hemodynamic, and other mechanisms, is a common determining factor that can result in a broad spectrum of clinical syndromes. As long as the podocyte loss is limited, restitution or repair is possible. By contrast, 20 to 40% podocyte loss results in a scarring response, until at greater than 60% podocyte loss glomeruli become globally sclerotic and nonfiltering. These stages of podocyte depletion are accompanied by corresponding degrees of proteinuria and, as an increasing proportion of glomeruli become involved, by measurable reduction in the clearance function of the kidney. [1][2][3] To what extent podocytes can be replaced at all during adult life, and if so, how and at what rate, is still unclear. Indeed, mature podocytes have limited capacity to divide in situ and display all phenotypic and functional features of highly spe-

Recent studies implicated the existence in adult human kidney of a population of renal progenitors with the potential to regenerate glomerular as well as tubular epithelial cells and characterized by coexpression of surface markers CD133 and CD24. Here, we demonstrate that CD1331CD241 renal progenitors can be distinguished in distinct subpopulations from normal human kidneys based on the surface expression of vascular cell adhesion molecule 1, also known as CD106. CD1331CD241CD1061 cells were localized at the urinary pole of Bowman's capsule, while a distinct population of scattered CD1331CD241CD1062 cells was localized in the proximal tubule as well as in the distal convoluted tubule.