The density of CD10 corresponds to commitment and progression in the human B lymphoid lineage. PLoS One. 2010;5:e12954. [PMID: 20886092 PMCID: PMC2944886 DOI: 10.1371/journal.pone.0012954]

Terminal deoxynucleotidyl transferase and CD84 identify human multi-potent lymphoid progenitors

Lymphoid specification in human hematopoietic progenitors is not fully understood. To better associate lymphoid identity with protein-level cell features, we conduct a highly multiplexed single-cell proteomic screen on human bone marrow progenitors. This screen identifies terminal deoxynucleotidyl transferase (TdT), a specialized DNA polymerase intrinsic to VDJ recombination, broadly expressed within CD34+ progenitors prior to B/T cell emergence. While these TdT+ cells coincide with granulocyte-monocyte progenitor (GMP) immunophenotype, their accessible chromatin regions show enrichment for lymphoid-associated transcription factor (TF) motifs. TdT expression on GMPs is inversely related to the SLAM family member CD84. Prospective isolation of CD84lo GMPs demonstrates robust lymphoid potentials ex vivo, while still retaining significant myeloid differentiation capacity, akin to LMPPs. This multi-omic study identifies human bone marrow lymphoid-primed progenitors, further defining the lympho-myeloid axis in human hematopoiesis.

A comprehensive review of the literature on CD10: its function, clinical application, and prospects

CD10, a zinc-dependent metalloprotease found on the cell surface, plays a pivotal role in an array of physiological and pathological processes including cardiovascular regulation, immune function, fetal development, pain response, oncogenesis, and aging. Recognized as a biomarker for hematopoietic and tissue stem cells, CD10 has garnered attention for its prognostic potential in the progression of leukemia and various solid tumors. Recent studies underscore its regulatory significance and therapeutic promise in combating Alzheimer's disease (AD), and it is noted for its protective role in preventing heart failure (HF), obesity, and type-2 diabetes. Furthermore, CD10/substance P interaction has also been shown to contribute to the pain signaling regulation and immunomodulation in diseases such as complex regional pain syndrome (CRPS) and osteoarthritis (OA). The emergence of COVID-19 has sparked interest in CD10's involvement in the disease's pathogenesis. Given its association with multiple disease states, CD10 is a prime therapeutic target; inhibitors targeting CD10 are now being advanced as therapeutic agents. This review compiles recent and earlier literature on CD10, elucidating its physicochemical attributes, tissue-specific expression, and molecular functions. Furthermore, it details the association of CD10 with various diseases and the clinical advancements of its inhibitors, providing a comprehensive overview of its growing significance in medical research.

CD34+ myeloma cells with self-renewal activities are therapy-resistant and persist as MRD in cell cycle quiescence

Side population (SP) is known to include therapy-resistant cells in various cancers. Here, we analyzed SP using multiple myeloma (MM) samples. The SP accounted for 2.96% in MM cells from newly diagnosed MM (NDMM). CD34 was expressed in 47.8% of SP cells, but only in 2.11% of bulk MM cells. CD34+ MM cells expressed more immature cell surface markers and a gene signature than CD34- MM cells. CD34+ but not CD34- MM cells possessed clonogenic activities and showed long-term self-renewal activities in xenotransplantation assays. Similarly, whereas 2.20% of MM cells were CD34+ in NDMM (n = 38), this proportion increased to 42.6% in minimal residual disease (MRD) samples (n = 16) (p < 0.001) and to 17.7% in refractory/relapsed MM (RRMM) (n = 30) (p < 0.01). Cell cycle analysis showed that 24.7% of CD34+ MM cells from NDMM were in G0 phase while this proportion was 54.9% in MRD (p < 0.05) and 14.5% in RRMM, reflecting the expansion of MM. Together, CD34+ MM cells with long-term self-renewal activities persist as MRD in cell cycle quiescence or remain as therapy-resistant cells in RRMM, substantiating the necessity of targeting this population to improve clinical outcomes of MM.

CD34 expression does not correlate with immunophenotypic stem cell or progenitor content in human cord blood products

The CD34+ compartment of human cord blood contains a range of HSPC immunophenotypes, among which the Lin−CD34+CD38+CD127+ CLP is rare. There is no correlation between the frequencies of CD34+ cells and immunophenotypic HSC in umbilical cord blood products.

Central human B cell tolerance manifests with a distinctive cell phenotype and is enforced via CXCR4 signaling in hu-mice

Central B cell tolerance, the process restricting the development of many newly generated autoreactive B cells, has been intensely investigated in mouse cells while studies in humans have been hampered by the inability to phenotypically distinguish autoreactive and nonautoreactive immature B cell clones and the difficulty in accessing fresh human bone marrow samples. Using a human immune system mouse model in which all human Igκ⁺ B cells undergo central tolerance, we discovered that human autoreactive immature B cells exhibit a distinctive phenotype that includes lower activation of ERK and differential expression of CD69, CD81, CXCR4, and other glycoproteins. Human B cells exhibiting these characteristics were observed in fresh human bone marrow tissue biopsy specimens, although differences in marker expression were smaller than in the humanized mouse model. Furthermore, the expression of these markers was slightly altered in autoreactive B cells of humanized mice engrafted with some human immune systems genetically predisposed to autoimmunity. Finally, by treating mice and human immune system mice with a pharmacologic antagonist, we show that signaling by CXCR4 is necessary to prevent both human and mouse autoreactive B cell clones from egressing the bone marrow, indicating that CXCR4 functionally contributes to central B cell tolerance.

Development of LT-HSC-Reconstituted Non-Irradiated NBSGW Mice for the Study of Human Hematopoiesis In Vivo

Humanized immune system (HIS) mouse models are useful tools for the in vivo investigation of human hematopoiesis. However, the majority of HIS models currently in use are biased towards lymphocyte development and fail to support long-term multilineage leucocytes and erythrocytes. Those that achieve successful multilineage reconstitution often require preconditioning steps which are expensive, cause animal morbidity, are technically demanding, and poorly reproducible. In this study, we address this challenge by using HSPC-NBSGW mice, in which NOD,B6.SCID IL-2rγ-/-KitW41/W41 (NBSGW) mice are engrafted with human CD133+ hematopoietic stem and progenitor cells (HSPCs) without the need for preconditioning by sublethal irradiation. These HSPCs are enriched in long-term hematopoietic stem cells (LT-HSCs), while NBSGW mice are permissive to human hematopoietic stem cell (HSC) engraftment, thus reducing the cell number required for successful HIS development. B cells reconstitute with the greatest efficiency, including mature B cells capable of class-switching following allogeneic stimulation and, within lymphoid organs and peripheral blood, T cells at a spectrum of stages of maturation. In the thymus, human thymocytes are identified at all major stages of development. Phenotypically distinct subsets of myeloid cells, including dendritic cells and mature monocytes, engraft to a variable degree in the bone marrow and spleen, and circulate in peripheral blood. Finally, we observe human erythrocytes which persist in the periphery at high levels following macrophage clearance. The HSPC-NBSGW model therefore provides a useful platform for the study of human hematological and immunological processes and pathologies.

Nitric Oxide in the Control of the in vitro Proliferation and Differentiation of Human Hematopoietic Stem and Progenitor Cells

Hematopoietic stem and progenitor cell (HSPC) transplantation is the best-studied cellular therapy and successful in vitro control of HSPCs has wide clinical implications. Nitric oxide (NO) is a central signaling molecule in vivo and has been implicated in HSPC mobilization to the blood stream in mice. The influence of NO on HSPC behavior in vitro is, however, largely obscure due to the variety of employed cell types, NO administration systems, and used concentration ranges in the literature. Additionally, most studies are based on murine cells, which do not necessarily mimic human HSPC behavior. Thus, the aim of the present study was the systematic, concentration-dependent evaluation of NO-mediated effects on human HSPC behavior in vitro. By culture in the presence of the long-term NO donor diethylenetriamine/nitric oxide adduct (DETA/NO) in a nontoxic concentration window, a biphasic role of NO in the regulation of HSPC behavior was identified: Low DETA/NO concentrations activated classical NO signaling, identified via increased intracellular cyclic guanosine monophosphate (cGMP) levels and proteinkinases G (PKG)-dependent vasodilator-stimulated phosphoprotein (VASP) phosphorylation and mediated a pro-proliferative response of HSPCs. In contrast, elevated NO concentrations slowed cell proliferation and induced HSPC differentiation. At high concentrations, s-nitrosylation levels were elevated, and myeloid differentiation was increased at the expense of lymphoid progenitors. Together, these findings hint at a central role of NO in regulating human HSPC behavior and stress the importance and the potential of the use of adequate NO concentrations for in vitro cultures of HSPCs, with possible implications for clinical application of in vitro expanded or differentiated HSPCs for cellular therapies.

TLR engagement induces ARID3a in human blood hematopoietic progenitors and modulates IFNα production

The DNA binding protein AT-rich interacting domain 3a (ARID3a)2 is expressed in healthy human hematopoietic cord blood progenitors where its modulation influences myeloid versus B lineage development. ARID3a is also variably expressed in subsets of adult peripheral blood hematopoietic progenitors where the consequences of ARID3a expression are unknown. In B lymphocytes, Toll-like receptor (TLR)3 signaling induces ARID3a expression in association with Type I interferon inflammatory cytokines. We hypothesized that TLR ligand stimulation of peripheral blood hematopoietic progenitors would induce ARID3a expression resulting in interferon production, and potentially influencing lineage decisions. Our data revealed that the TLR9 agonist CpG induces ARID3a expression with interferon alpha synthesis in human hematopoietic progenitors. However, ARID3a expression was not associated with increased B lineage development. These results demonstrate the need for further experiments to better define how pathogen-associated responses influence hematopoiesis.

ARID3a expression in human hematopoietic stem cells is associated with distinct gene patterns in aged individuals

Background

Immunologic aging leads to immune dysfunction, significantly reducing the quality of life of the elderly. Aged-related defects in early hematopoiesis result in reduced lymphoid cell development, functionally defective mature immune cells, and poor protective responses to vaccines and pathogens. Despite considerable progress understanding the underlying causes of decreased immunity in the elderly, the mechanisms by which these occur are still poorly understood. The DNA-binding protein ARID3a is expressed in a subset of human hematopoietic progenitors. Inhibition of ARID3a in bulk human cord blood CD34⁺ hematopoietic progenitors led to developmental skewing toward myeloid lineage at the expense of lymphoid lineage cells in vitro. Effects of ARID3a expression in adult-derived hematopoietic stem cells (HSCs) have not been analyzed, nor has ARID3a expression been assessed in relationship to age. We hypothesized that decreases in ARID3a could explain some of the defects observed in aging.

Results

Our data reveal decreased frequencies of ARID3a-expressing peripheral blood HSCs from aged healthy individuals compared with young donor HSCs. Inhibition of ARID3a in young donor-derived HSCs limits B lineage potential, suggesting a role for ARID3a in B lymphopoiesis in bone marrow-derived HSCs. Increasing ARID3a levels of HSCs from aged donors in vitro alters B lineage development and maturation. Finally, single cell analyses of ARID3a-expressing HSCs from young versus aged donors identify a number of differentially expressed genes in aged ARID3A-expressing cells versus young ARID3A-expressing HSCs, as well as between ARID3A-expressing and non-expressing cells in both young and aged donor HSCs.

Conclusions

These data suggest that ARID3a-expressing HSCs from aged individuals differ at both molecular and functional levels compared to ARID3a-expressing HSCs from young individuals.

Immunogenetics of marsupial B-cells

Marsupials and eutherians are mammals that differ in their physiological traits, predominately their reproductive and developmental strategies; eutherians give birth to well-developed young, while marsupials are born highly altricial after a much shorter gestation. These developmental traits also result in differences in the development of the immune system of eutherian and marsupial species. In eutherians, B-cells are the key to humoral immunity as they are found in multiple lymphoid organs and have the unique ability to mediate the production of antigen-specific antibodies in the presence of extracellular pathogens. The development of B-cells in marsupials has been reported and hypothesised to be similar to that of eutherians, except that haematopoiesis occurs in the liver, postpartum, until the bone marrow fully matures. In eutherians, specific genes are linked to specific stages in B-cell development, maturation, and differentiation processes, and have been identified including immunoglobulins (heavy and light chains), cluster of differentiation markers (CD10, 19, 34 and CD79α/β), signal transduction molecules (BTK, Lyn and Syk) and transcriptional regulators (EBF1, E2A, and Pax5). This review aims to discuss the known similarities and differences between marsupial and eutherian B-cells, in regards to their genetic presence, homology, and developmental stages, as well as to highlight the areas requiring further investigation. By enhancing our understanding of the genes that are involved with B-cells in the marsupial lineage, it will, in turn, aid our understanding of the marsupial immune system and support the development of specific immunological reagents for research and wildlife conservation purposes.

Capturing B type acute lymphoblastic leukemia cells using two types of antibodies

One way to monitor minimal residual disease (MRD) is to screen cells for multiple surface markers using flow cytometry. In order to develop an alternative microfluidic based method, isolation of B type acute lymphoblastic cells using two types of antibodies should be investigated. The immunomagnetic beads coated with various antibodies are used to capture the B type acute lymphoblastic cells. Single beads, two types of beads and surface immobilized antibody were used to measure the capture efficiency. Both micro and nanosize immunomagnetic beads can be used to capture B type acute lymphoblastic cells with a minimum efficiency of 94% and maximum efficiency of 98%. Development of a microfluidic based biochip incorporating immunomagnetic beads and surface immobilized antibodies for monitoring MRD can be an alternative to current cost and time inefficient laboratory methods. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2737, 2019.

Single-cell analysis reveals the continuum of human lympho-myeloid progenitor cells

The hierarchy of human hemopoietic progenitor cells that produce lymphoid and granulocytic-monocytic (myeloid) lineages is unclear. Multiple progenitor populations produce lymphoid and myeloid cells, but they remain incompletely characterized. Here we demonstrated that lympho-myeloid progenitor populations in cord blood - lymphoid-primed multi-potential progenitors (LMPPs), granulocyte-macrophage progenitors (GMPs) and multi-lymphoid progenitors (MLPs) - were functionally and transcriptionally distinct and heterogeneous at the clonal level, with progenitors of many different functional potentials present. Although most progenitors had the potential to develop into only one mature cell type ('uni-lineage potential'), bi- and rarer multi-lineage progenitors were present among LMPPs, GMPs and MLPs. Those findings, coupled with single-cell expression analyses, suggest that a continuum of progenitors execute lymphoid and myeloid differentiation, rather than only uni-lineage progenitors' being present downstream of stem cells.

Role of B Cell Development Marker CD10 in Cancer Progression and Prognosis

The human CD10 antigen is a single pass, type II transmembrane, 100 kD cell surface glycoprotein belonging to peptidase M13 family. Identified in common acute lymphoblastic leukemia as a cancer specific antigen, CD10 is a cell surface ectoenzyme widely expressed on different types of cells. Earlier, it was used only as a cell surface marker to identify and differentiate between haematological malignancies. Later, reported to be present in various malignancies, it is thought to play significant role in cancer development and progression. Regulated expression of CD10 is necessary for angiogenesis and so forth. However its expression level is found to be deregulated in different cancers. In some cancers, it acts as tumor suppressor and inhibits tumor progression whereas in others it has tumor promoting tendency. However, its role in tumorigenesis remains unclear. This review summarises structural features, functions, and probable role of CD10 in cancer development.

Human B-1 and B-2 B Cells Develop from Lin-CD34+CD38lo Stem Cells

The B-1 B cell population is an important bridge between innate and adaptive immunity primarily because B-1 cells produce natural Ab. Murine B-1 and B-2 cells arise from distinct progenitors; however, in humans, in part because it has been difficult to discriminate between them phenotypically, efforts to pinpoint the developmental origins of human B-1 and B-2 cells have lagged. To characterize progenitors of human B-1 and B-2 cells, we separated cord blood and bone marrow Lin^-CD34⁺ hematopoietic stem cells into Lin^-CD34⁺CD38^lo and Lin^-CD34⁺CD38^hi populations. We found that transplanted Lin^-CD34⁺CD38^lo cells, but not Lin^-CD34⁺CD38^hi cells, generated a CD19⁺ B cell population after transfer into immunodeficient NOD.Cg-Prkdc^scid Il2rg^tm1wjl/SxJ neonates. The emergent CD19⁺ B cell population was found in spleen, bone marrow, and peritoneal cavity of humanized mice and included distinct populations displaying the B-1 or the B-2 cell phenotype. Engrafted splenic B-1 cells exhibited a mature phenotype, as evidenced by low-to-intermediate expression levels of CD24 and CD38. The engrafted B-1 cell population expressed a VH-DH-JH composition similar to cord blood B-1 cells, including frequent use of VH4-34 (8 versus 10%, respectively). Among patients with hematologic malignancies who underwent hematopoietic stem cell transplantation, B-1 cells were found in the circulation as early as 8 wk posttransplantation. Altogether, our data demonstrate that human B-1 and B-2 cells develop from a Lin^-CD34⁺CD38^lo stem cell population, and engrafted B-1 cells in humanized mice exhibit an Ig-usage pattern comparable to B-1 cells in cord blood.

The Transcription Factor ARID3a Is Important for In Vitro Differentiation of Human Hematopoietic Progenitors

We recently reported that the transcription factor ARID3a is expressed in a subset of human hematopoietic progenitor stem cells in both healthy individuals and in patients with systemic lupus erythematosus. Numbers of ARID3a(+) lupus hematopoietic stem progenitor cells were associated with increased production of autoreactive Abs when those cells were introduced into humanized mouse models. Although ARID3a/Bright knockout mice died in utero, they exhibited decreased numbers of hematopoietic stem cells and erythrocytes, indicating that ARID3a is functionally important for hematopoiesis in mice. To explore the requirement for ARID3a for normal human hematopoiesis, hematopoietic stem cell progenitors from human cord blood were subjected to both inhibition and overexpression of ARID3a in vitro. Inhibition of ARID3a resulted in decreased B lineage cell production accompanied by increases in cells with myeloid lineage markers. Overexpression of ARID3a inhibited both myeloid and erythroid differentiation. Additionally, inhibition of ARID3a in hematopoietic stem cells resulted in altered expression of transcription factors associated with hematopoietic lineage decisions. These results suggest that appropriate regulation of ARID3a is critical for normal development of both myeloid and B lineage pathways.

Differential expression of the transcription factor ARID3a in lupus patient hematopoietic progenitor cells

Although hematopoietic stem/progenitor cells (HSPCs) are used for transplantation, characterization of the multiple subsets within this population in humans has lagged behind similar studies in mice. We found that expression of the DNA-binding protein, ARID3a, in mouse stem cells was important for normal development of hematopoietic lineages; however, progenitors expressing ARID3a in humans have not been defined. We previously showed increased numbers of ARID3a(+) B cells in nearly half of systemic lupus erythematosus (SLE) patients, and total numbers of ARID3a(+) B cells were associated with increased disease severity. Because expression of ARID3a in those SLE patients occurred throughout all B cell subsets, we hypothesized that ARID3a expression in patient HSPCs might also be increased relative to expression in healthy controls. Our data now show that ARID3a expression is not limited to any defined subset of HSPCs in either healthy controls or SLE patients. Numbers of ARID3a(+) HSPCs in SLE patients were increased over numbers of ARID3a(+) cells in healthy controls. Although all SLE-derived HSPCs exhibited poor colony formation in vitro compared with controls, SLE HSPCs with high numbers of ARID3a(+) cells yielded increased numbers of cells expressing the early progenitor marker, CD34. SLE HSPCs with high numbers of ARID3a(+) cells also more readily generated autoantibody-producing cells than HSPCs with lower levels of ARID3a in a humanized mouse model. These data reveal new functions for ARID3a in early hematopoiesis and suggest that knowledge regarding ARID3a levels in HSPCs could be informative for applications requiring transplantation of those cells.

Early B lymphocyte development: Similarities and differences in human and mouse

B lymphocytes differentiate from hematopoietic stem cells through a series of distinct stages. Early B cell development proceeds in bone marrow until immature B cells migrate out to secondary lymphoid tissues, such as a spleen and lymph nodes, after completion of immunoglobulin heavy and light chain rearrangement. Although the information about the regulation by numerous factors, including signaling molecules, transcription factors, epigenetic changes and the microenvironment, could provide the clinical application, our knowledge on human B lymphopoiesis is limited. However, with great methodological advances, significant progress for understanding B lymphopoiesis both in human and mouse has been made. In this review, we summarize the experimental models for studies about human adult B lymphopoiesis, and the role of microenvironment and signaling molecules, such as cytokines, transforming growth factor-β superfamily, Wnt family and Notch family, with point-by-point comparison between human and mouse.

Human lymphoid development in the absence of common γ-chain receptor signaling

Despite the power of model systems to reveal basic immunologic mechanisms, critical differences exist between species that necessitate the direct study of human cells. Illustrating this point is the difference in phenotype between patients with SCID caused by mutations affecting the common γ-chain (γc) cytokine signaling pathway and mice with similar mutations. Although in both species, null mutations in either IL-2RG (which encodes γc), or its direct downstream signaling partner JAK3, result in T and NK cell deficiency, an associated B cell deficiency is seen in mice but not in humans with these genetic defects. In this study, we applied recent data that have revised our understanding of the earliest stages of lymphoid commitment in human bone marrow (BM) to determine the requirement for signaling through IL-2RG and JAK3 in normal development of human lymphoid progenitors. BM samples from SCID patients with IL-2RG (n = 3) or JAK3 deficiency (n = 2), which produce similar "T-NK-B+" clinical phenotypes, were compared with normal BM and umbilical cord blood as well as BM from children on enzyme treatment for adenosine deaminase-deficient SCID (n = 2). In both IL-2RG- and JAK3-SCID patients, the early stages of lymphoid commitment from hematopoietic stem cells were present with development of lymphoid-primed multipotent progenitors, common lymphoid progenitors and B cell progenitors, normal expression patterns of IL-7RA and TLSPR, and the DNA recombination genes DNTT and RAG1. Thus, in humans, signaling through the γc pathway is not required for prethymic lymphoid commitment or for DNA rearrangement.

A feeder-free differentiation system identifies autonomously proliferating B cell precursors in human bone marrow

The peripheral B cell compartment is maintained by homeostatic proliferation and through replenishment by bone marrow precursors. Because hematopoietic stem cells cycle at a slow rate, replenishment must involve replication of precursor B cells. To study proliferation of early human B cell progenitors, we established a feeder cell-free in vitro system allowing the development of B cells from CD34(+) hematopoietic stem cells up to the stage of immature IgM(+) B cells. We found that pro-B and pre-B cells generated in vitro can proliferate autonomously and persist up to 7 wk in culture in the absence of signals induced by exogenously added cytokines. Nevertheless, addition of IL-7 enhanced pre-B cell expansion and inhibited maturation into IgM(+) B cells. The B cell precursor subsets replicating in vitro were highly similar to the bone marrow B cell precursors cycling in vivo. The autonomous proliferation of B cell precursor subsets in vitro and their long-term persistence implies that proliferation during pro-B and pre-B cell stages plays an important role in the homeostasis of the peripheral B cell compartment. Our in vitro culture can be used to study defects in B cell development or in reconstitution of the B cell pool after depletion and chemotherapy.

Early events in lymphopoiesis: an update

PURPOSE OF REVIEW

Cells of the immune system are replaced in large numbers throughout life, and the underlying mechanisms have been extensively studied. Whereas the pace of discovery in this area is unprecedented, many questions remain, particularly with respect to lymphocyte formation.

RECENT FINDINGS

While transcription factors have long been a focus of investigation, microRNAs are also being implicated in lymphopoiesis. Lymphocytes are normally replaced in correct proportion to other blood cells, but ratios change dramatically during infections. Long-standing issues relating to T versus B lineage divergence remain but have been enriched with remarkable new findings about thymus seeding. There are indications that at least some age-related changes in lymphopoiesis may be reversible. Finally, knowledge obtained from studies of mice is slowly being extended to humans.

SUMMARY

We can now appreciate that new lymphoid progenitors are drawn from a heterogeneous collection of hematopoietic stem cells through asynchronous patterns of gene expression. Complex interactions then occur between the gene products, preparing lymphoid progenitors to respond to environmental cues. Whereas unique markers describe the process of lymphocyte formation in humans, fundamental information now available should suggest ways to promote rebound from chemotherapy or transplantation and reverse declines associated with aging.

RAG-1 and Ly6D independently reflect progression in the B lymphoid lineage

Common lymphoid progenitors (CLPs) are thought to represent major intermediates in the transition of hematopoietic stem cells (HSCs) to B lineage lymphocytes. However, it has been obvious for some time that CLPs are heterogeneous, and there has been controversy concerning their differentiation potential. We have now resolved four Flt3⁺ CLP subsets that are relatively homogenous and capable of forming B cells. Differentiation potential and gene expression patterns suggest Flt3⁺ CLPs lacking both Ly6D and RAG-1 are the least differentiated. In addition to B cells, they generate natural killer (NK) and dendritic cells (DCs). At the other extreme is a subset of the recently described Flt3⁺ Ly6D⁺ CLPs that have a history of RAG-1 expression and are B lineage restricted. These relatively abundant and potent CLPs were depleted within 48 hours of acute in vivo estrogen elevation, suggesting they descend from hormone regulated progenitors. This contrasts with the hormone insensitivity of other CLP subsets that include NK lineage progenitors. This progenitor heterogeneity and differentiation complexity may add flexibility in response to environmental changes. Expression of RAG-1 and display of Ly6D are both milestone events, but they are neither synchronized nor dependent on each other.

Mesenchymal stromal/stem cells markers in the human bone marrow

BACKGROUND AIMS

Mesenchymal stromal/stem cells (MSCs) can be isolated from human bone marrow (BM), expanded ex vivo and identified via numerous surface antigens. Despite the importance of these cells in regenerative therapy programs, it is unclear whether the cell membrane signature defining MSC preparations ex vivo is determined during culture or may reflect an in vivo counterpart. BM-MSC phenotype in vivo requires further investigation.

METHODS

To characterize cells in their natural BM environment, we performed multi-parametric immunohistochemistry on trabecular bone biopsy specimens from multiple donors and described cells by different morphology and micro-anatomic localization in relationship to a precise pattern of MSC antigen expression.

RESULTS

Microscopically examined high-power field marrow sections revealed an overlapping in vivo expression of antigens characterizing ex vivo expanded BM-MSCs, including CD10, CD73, CD140b, CD146, GD2 and CD271. Expanding this panel to proteins associated with pluripotency, such as Oct4, Nanog and SSEA-4, we were able to identify different cellular populations in the human trabecular bone and BM expressing different progenitor cell markers.

CONCLUSIONS

Targeting several multipotency and pluripotency markers, we found that the BM contains identifiable and distinct progenitor cells further justifying their introduction for a wide range of applications in regenerative medicine.

Adipocyte-derived soluble factor(s) inhibits early stages of B lymphopoiesis

B lymphopoiesis declines with age, and in rabbits this occurs by 8 wk of age. We found that CFU fibroblasts (CFU-Fs) in the bone marrow (BM) decrease 10-fold by a few weeks of age and that the CFU-Fs preferentially differentiate into adipocytes instead of osteoblasts. BM becomes filled with fat spaces during this time, making rabbit a unique model to study the effects of accelerated fat accumulation on B lymphopoiesis. We show that adipocytes of both rabbit and human secrete a soluble factor(s) that inhibits B lymphopoiesis, and we tested if this inhibition was due to effects on the BM stroma or hematopoietic progenitors. Pretreatment of BM mononuclear cells with adipocyte conditioned medium dramatically inhibited their differentiation into proB cells in cocultures with OP9 stromal cells. In contrast, pretreatment of OP9 stromal cells with adipocyte conditioned medium had no effect on B lymphopoiesis. Using human hematopoietic stem cells, we show that inhibition by the adipocyte-derived factor occurred at the common lymphoid progenitor to preproB cell stage. We propose that the age-related decline in B lymphopoiesis is due to a decrease in CFU-Fs, an increase in adipocytes, and an adipocyte-derived factor that blocks B lymphopoiesis at the common lymphoid progenitor to preproB cell stage.

Lymphoid priming in human bone marrow begins before expression of CD10 with upregulation of L-selectin

The expression of CD10 has long been used to define human lymphoid commitment. We report a unique lymphoid-primed population in human bone marrow that was generated from hematopoietic stem cells (HSCs) before the onset of CD10 expression and B cell commitment. This subset was identified by high expression of the homing molecule L-selectin (CD62L). CD10⁻CD62L^hi progenitors possessed full lymphoid and monocytic potential, but lacked erythroid potential. Gene expression profiling placed the CD10⁻CD62L^hi population at an intermediate stage of differentiation between HSCs and lineage-negative (Lin⁻) CD34⁺CD10⁺ progenitors. L-selectin was expressed on immature thymocytes and its ligands were expressed at the cortico-medullary junction, suggesting a possible role in thymic homing. These studies identify the earliest stage of lymphoid priming in human bone marrow.

Early lymphoid development and microenvironmental cues in B-cell acute lymphoblastic leukemia

B-cell acute lymphoblastic leukemia (B-ALL) is a hematological disorder characterized by malignant and uncontrolled proliferation of B-lymphoid precursor cells in bone marrow. Over the last few years remarkable advances have been made in identifying genetic aberrations, patterns of abnormal transcriptional activity controlling early fate decisions and environmental cues that may influence leukemic development. In this review we focus on the structure of the early lymphoid system and the current knowledge about cell composition and function of the hematopoietic microenvironment that might control progenitor cell activity and lead to differentiation, proliferation and survival of developing B leukemic precursors. Learning the biology of special leukemic niches is central to understanding the pathogenesis of B-ALL and for the development of novel therapies.

Checkpoints of B cell differentiation: visualizing Ig-centric processes

The generation of antibody responses and B cell memory can only take place following multiple steps of differentiation. Key molecular processes during precursor B cell differentiation in bone marrow generate unique antibodies. These antibodies are further optimized via molecular modifications during immune responses in peripheral lymphoid organs. Multiple checkpoints ensure proper differentiation of precursor and mature B lymphocytes. Many of these checkpoints have been found disrupted in patients with a primary immunodeficiency. Based on studies in these patients and in mouse models, new insights have been generated in B cell differentiation and antibody responses. Still, in many patients with impaired antibody formation, it remains unclear how B cells are affected. In this perspective, we present 11 critical processes in B cell differentiation. We discuss how defects in these processes can result in impaired checkpoint selection and how they can be visualized in healthy subjects and patients with immunodeficiency or other immunological disease.

CD10 in the developing human kidney: immunoreactivity and possible role in renal embryogenesis

CD10 was first identified in tumor cells of acute lymphoblastic leukemia. Most studies on CD10 expression have dealt with tumor pathology. Since no data are available for specific role in the fetal kidney, this study aimed at investigating CD10 expression during the different phases of renal embryogenesis. To this end, the expression of CD10 was evaluated in the kidney of two human fetus and in three newborns. In both fetuses, immunostaining for CD10 was compartmentalized and mainly concentrated in the mid-deep cortex. Reactivity for CD10 was stronger in the glomerular epithelium, in proximal tubules and in metanephric mesenchymal cells. At 25 weeks of gestation, CD10 was also detected in the subcapsular regions, including some pretubular aggregates of cap mesenchymal cells and renal vesicles. At 34 weeks of gestation, we observed an increased immunoreactivity for CD10 in visceral and parietal glomerular epithelium. At 39 weeks of gestation, CD10 was also expressed in the collecting tubules and in the Henle loops. Our data show a strong expression of CD10 in all stage of human kidney development, characterized by dynamic changes and support the hypothesis that CD10 plays a relevant role in renal embryogenesis.

Phenotype and function of CD25-expressing B lymphocytes isolated from human umbilical cord blood

BACKGROUND

We have shown that approximately 30% of human peripheral blood B-cells express CD25. B cells expressing CD25 display a mature phenotype belonging to the memory B-cell population and have a better proliferative and antigen-presenting capacity. The aim of the present study was to characterize the CD25-expressing subset of B cells in human cord blood.

MATERIAL AND METHODS

Mononuclear cell fraction from human cord blood (n=34) and peripheral adult blood (n=22) was sorted into CD20+CD25+ and CD20+CD25- B-cell populations. Phenotype and function of these B-cell populations were compared using flow cytometry, proliferation, cytokine production, and immunoglobulin secretion.

RESULTS

CD25-expressing B cells are a limited population of cord blood mononuclear cells representing 5% of the CD20+ B cells. They are characterised by high expression of CD5 in cord blood and CD27 in adult blood. CD25-expressing B cells express a functional IL-2 receptor and high levels of CC-chemokine receptors and spontaneously produce antibodies of IgG and IgM subclass.

CONCLUSIONS

CD25 expression is a common denominator of a specific immunomodulatory B-cell subset ready to proliferate upon IL-2 stimulation, possibly ready to migrate and home into the peripheral tissue for further differentiation/action.