Surface antigens on hematopoietic stem cells (HSCs) enable prospective isolation and characterization. Here, we compare the cell-surface phenotype of hematopoietic repopulating cells from murine yolk sac, aorta-gonad-mesonephros, placenta, fetal liver, and bone marrow with that of HSCs derived from the in vitro differentiation of murine embryonic stem cells (ESC-HSCs). Whereas c-Kit marks all HSC populations, CD41, CD45, CD34, and CD150 were developmentally regulated: the earliest embryonic HSCs express CD41 and CD34 and lack CD45 and CD150, whereas more mature HSCs lack CD41 and CD34 and express CD45 and CD150. ESC-HSCs express CD41 and CD150, lack CD34, and are heterogeneous for CD45. Finally, although CD48 was absent from all in vivo HSCs examined, ESC-HSCs were heterogeneous for the expression of this molecule. This unique phenotype signifies a developmentally immature population of cells with features of both primitive and mature HSC. The prospective fractionation of ESC-HSCs will facilitate studies of HSC maturation essential for normal functional engraftment in irradiated adults.
Primary central nervous system (CNS) lymphoma (PCNSL) is a diffuse large B-cell lymphoma (DLBCL) confined to the CNS. A genome-wide gene expression comparison between PCNSL and non-CNS DLBCL was performed, the latter consisting of both nodal and extranodal DLBCL (nDLBCL and enDLBCL), to identify a "CNS signature." Pathway analysis with the program SigPathway revealed that PCNSL is characterized notably by significant differential expression of multiple extracellular matrix (ECM) and adhesion-related pathways. The most significantly up-regulated gene is the ECM-related osteopontin (SPP1). Expression at the protein level of ECM-related SPP1 and CHI3L1 in PCNSL cells was demonstrated by immunohistochemistry. The alterations in gene expression can be interpreted within several biologic contexts with implications for PCNSL, including CNS tropism (ECM and adhesion-related pathways, SPP1, DDR1), B-cell migration (CXCL13, SPP1), activated B-cell subtype (MUM1), lymphoproliferation (SPP1, TCL1A, CHI3L1), aggressive clinical behavior (SPP1, CHI3L1, MUM1), and aggressive metastatic cancer phenotype (SPP1, CHI3L1). The gene expression signature discovered in our study may represent a true "CNS signature" because we contrasted PCNSL with wide-spectrum non-CNS DLBCL on a genomic scale and performed an in-depth bioinformatic analysis.