Hematopoietic stem cells differentiate into vascular cells that participate in the pathogenesis of atherosclerosis

Excessive accumulation of smooth-muscle cells (SMCs) has a key role in the pathogenesis of vascular diseases. It has been assumed that SMCs derived from the outer medial layer migrate, proliferate and synthesize extracellular matrix components on the luminal side of the vessel. Although much effort has been devoted to targeting migration and proliferation of medial SMCs, there is no effective therapy that prevents occlusive vascular remodeling. We show here that in models of post-angioplasty restenosis, graft vasculopathy and hyperlipidemia-induced atherosclerosis, bone-marrow cells give rise to most of the SMCs that contribute to arterial remodeling. Notably, purified hematopoietic stem cells differentiate into SMCs in vitro and in vivo. Our findings indicate that somatic stem cells contribute to pathological remodeling of remote organs, and may provide the basis for the development of new therapeutic strategies for vascular diseases through targeting mobilization, homing, differentiation and proliferation of bone marrow-derived vascular progenitor cells.

Disruption of the Bcl6 gene results in an impaired germinal center formation

The Bcl6 gene has been identified from the chromosomal translocation breakpoint in B cell lymphomas, and its products are expressed highly in germinal center (GC) B cells. To investigate the function of Bcl6 in lymphocytes, we have generated RAG1-deficient mice reconstituted with bone marrow cells from Bcl6-deficient mice (Bcl6(-/-)RM). Lymphogenesis in primary lymphoid tissues of Bcl6(-/-)RM is normal, and Bcl6(-/-)RM produced control levels of primary IgG1 antibodies specific to T cell-dependent antigens. However, GCs were not found in these mice. This defect was mainly due to the abnormalities of B cells. Therefore, Bcl6 is essential for the differentiation of GC B cells.

Bifurcation of osteoclasts and dendritic cells from common progenitors

Osteoclasts and dendritic cells are derived from monocyte/macrophage precursor cells; however, how their lineage commitment is regulated is unknown. This study investigated the differentiation pathways of osteoclasts and dendritic cells from common precursor cells at the single-cell level. Osteoclastogenesis induced by macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB ligand (RANKL) or tumor necrosis factor-alpha (TNF-alpha) is completely inhibited by addition of granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 at early stages of differentiation. GM-CSF-treated cells express both c-Fms and RANK and also low levels of CD11c and DEC205, which are detected on dendritic cells. Addition of GM-CSF also reduces expression of both c-Fos and Fra-1, which is an important event for inhibition of osteoclastogenesis. Overexpression of c-Fos by retroviral infection or induction in transgenic mice can rescue a failure in osteoclast differentiation even in the presence of GM-CSF. By contrast, differentiation into dendritic cells is inhibited by M-CSF, indicating that M-CSF and GM-CSF reciprocally regulate the differentiation of both lineages. Dendritic cell maturation is also inhibited when c-Fos is expressed at an early stage of differentiation. Taken together, these findings suggest that c-Fos is a key mediator of the lineage commitment between osteoclasts and dendritic cells. The lineage determination of osteoclast progenitors seen following GM-CSF treatment functions through the regulation of c-Fos expression.

Role for Bcl-6 in the generation and maintenance of memory CD8+ T cells

Naïve T cells proliferate and differentiate into memory cells after antigenic stimulation or in a lymphopenic environment. We showed here transient increases in memory phenotype CD8+ T cell numbers in the lymphopenic environment of spleens of very young mice. The magnitude of the increase correlated with Bcl-6 expression in the T cells. Bcl-6 controlled the generation and maintenance of antigen-specific memory phenotype CD8+ T cells in the spleens of immunized mice. These data suggest that Bcl-6, which is essential for memory B cell development in germinal centers, is a key molecule for the establishment not only of memory T cells but also of the peripheral T cell compartment in infancy.

Memory B cells without somatic hypermutation are generated from Bcl6-deficient B cells

After immunization with T cell-dependent antigens, the high-affinity B cells selected in germinal centers differentiate into memory B cells or long-lived antibody-forming cells. However, a role for germinal centers in development of these B lineage cells is still controversial. We show here that Bcl6-deficient B cells, which cannot develop germinal centers, differentiated into IgM and IgG1 memory B cells in the spleen but barely differentiated into long-lived IgG1 antibody-forming cells in the bone marrow. Mutation in the V-heavy gene was null in these memory B cells. Therefore, Bcl6 and germinal center formation are essential for somatic hypermutation, and generation of memory B cells can occur independently of germinal center formation, somatic hypermutation, and Ig class switching.

Application of Highly Immunocompromised Mice for the Establishment of Patient-Derived Xenograft (PDX) Models

Patient-derived xenograft (PDX) models are created by engraftment of patient tumor tissues into immunocompetent mice. Since a PDX model retains the characteristics of the primary patient tumor including gene expression profiles and drug responses, it has become the most reliable in vivo human cancer model. The engraftment rate increases with the introduction of Non-obese diabetic Severe combined immunodeficiency (NOD/SCID)-based immunocompromised mice, especially the NK-deficient NOD strains NOD/SCID/interleukin-2 receptor gamma chain(IL2Rγ)null (NOG/NSG) and NOD/SCID/Jak3(Janus kinase 3)null (NOJ). Success rates differ with tumor origin: gastrointestinal tumors acquire a higher engraftment rate, while the rate is lower for breast cancers. Subcutaneous transplantation is the most popular method to establish PDX, but some tumors require specific environments, e.g., orthotropic or renal capsule transplantation. Human hormone treatment is necessary to establish hormone-dependent cancers such as prostate and breast cancers. PDX mice with human hematopoietic and immune systems (humanized PDX) are powerful tools for the analysis of tumor-immune system interaction and evaluation of immunotherapy response. A PDX biobank equipped with patients' clinical data, gene-expression patterns, mutational statuses, tumor tissue architects, and drug responsiveness will be an authoritative resource for developing specific tumor biomarkers for chemotherapeutic predictions, creating individualized therapy, and establishing precise cancer medicine.

High-affinity monoclonal IgA regulates gut microbiota and prevents colitis in mice

Immunoglobulin A (IgA) is the main antibody isotype secreted into the intestinal lumen. IgA plays a critical role in the defence against pathogens and in the maintenance of intestinal homeostasis. However, how secreted IgA regulates gut microbiota is not completely understood. In this study, we isolated monoclonal IgA antibodies from the small intestine of healthy mouse. As a candidate for an efficient gut microbiota modulator, we selected a W27 IgA, which binds to multiple bacteria, but not beneficial ones such as Lactobacillus casei. W27 could suppress the cell growth of Escherichia coli but not L. casei in vitro, indicating an ability to improve the intestinal environment. Indeed W27 oral treatment could modulate gut microbiota composition and have a therapeutic effect on both lymphoproliferative disease and colitis models in mice. Thus, W27 IgA oral treatment is a potential remedy for inflammatory bowel disease, acting through restoration of host-microbial symbiosis.

Transplanted hematopoietic stem cells from bone marrow differentiate into neural lineage cells and promote functional recovery after spinal cord injury in mice

Recovery in central nervous system disorders is hindered by the limited ability of the vertebrate central nervous system to regenerate lost cells, replace damaged myelin, and re-establish functional neural connections. Cell transplantation to repair central nervous system disorders is an active area of research, with the goal of reducing functional deficits. Recent animal studies showed that cells of the hematopoietic stem cell (HSC) fraction of bone marrow transdifferentiated into various nonhematopoietic cell lineages. We employed a mouse model of spinal cord injury and directly transplanted HSCs into the spinal cord 1 week after injury. We evaluated functional recovery using the hindlimb motor function score weekly for 5 weeks after transplantation. The data demonstrated a significant improvement in the functional outcome of mice transplanted with hematopoietic stem cells compared with control mice in which only medium was injected. Fluorescent in situ hybridization for the Y chromosome and double immunohistochemistry showed that transplanted cells survived 5 weeks after transplantation and expressed specific markers for astrocytes, oligodendrocytes, and neural precursors, but not for neurons. These results suggest that transplantation of HSCs from bone marrow is an effective strategy for the treatment of spinal cord injury.

c-MYC overexpression with loss of Ink4a/Arf transforms bone marrow stromal cells into osteosarcoma accompanied by loss of adipogenesis

The development of cancer is due to the growth and proliferation of transformed normal cells. Recent evidence suggests that the nature of oncogenic stress and the state of the cell of origin critically affect both tumorigenic activity and tumor histological type. However, this mechanistic relationship in mesenchymal tumors is currently largely unexplored. To clarify these issues, we established a mouse osteosarcoma (OS) model through overexpression of c-MYC in bone marrow stromal cells (BMSCs) derived from Ink4a/Arf (-/-) mice. Single-cell cloning revealed that c-MYC-expressing BMSCs are composed of two distinctly different clones: highly tumorigenic cells, similar to bipotent-committed osteochondral progenitor cells, and low-tumorigenic tripotent cells, similar to mesenchymal stem cells (MSCs). It is noteworthy that both bipotent and tripotent cells were capable of generating histologically similar, lethal OS, suggesting that both committed progenitor cells and MSCs can become OS cells of origin. Shifting mesenchymal differentiation by depleting PPARγ in tripotent MSC-like cells and overexpressing PPARγ in bipotent cells affected cell proliferation and tumorigenic activity. Our findings indicate that differentiation potential has a key role in OS tumorigenic activity, and that the suppression of adipogenic ability is a critical factor for the development of OS.

DNA polymerase theta is preferentially expressed in lymphoid tissues and upregulated in human cancers

DNA polymerase theta (Pol theta) is a recently identified family A polymerase that contains an intrinsic helicase domain. Drosophila Pol theta mutants are hypersensitive to bifunctional DNA crosslinking agents and exhibit an elevated frequency of spontaneous chromosomal aberrations, suggesting a role for Pol theta in repair of DNA interstrand crosslinks and in the general maintenance of genome stability. To investigate a possible involvement of Pol theta in tumorigenesis, we have examined its expression in various normal and malignant tissues. Paired tumor and adjacent nontumorous tissues from patients with lung (n = 27), stomach (n = 28) and colon (n = 26) cancer, as well as 26 normal human tissues, were examined for Pol theta expression by RT-PCR, Northern or Western blot analysis. Pol theta was predominantly expressed in primary lymphoid organs including the fetal liver, thymus and bone marrow where lymphocyte progenitors undergo V(D)J rearrangements of their antigen receptor genes. In addition, Pol theta expression was upregulated in germinal center B cells, in which class switch recombination of the immunoglobulin genes occurs. Examination of Pol theta expression in matched cancer specimens revealed that Pol theta was barely detectable in the nontumorous tissues but was upregulated in 17 of 27 (63%) lung, 11 of 28 (39%) stomach and 20 of 26 (77%) colon cancers. Moreover, patients with high levels of Pol theta expression had a significantly poorer clinical outcome compared with those expressing low levels of Pol theta. These results implicate that Pol theta may have a specialized function in lymphocytes and that its overexpression may contribute to tumor progression.

Targeting Excessive EZH1 and EZH2 Activities for Abnormal Histone Methylation and Transcription Network in Malignant Lymphomas

Although global H3K27me3 reprogramming is a hallmark of cancer, no effective therapeutic strategy for H3K27me3-high malignancies harboring EZH2^WT/WT has yet been established. We explore epigenome and transcriptome in EZH2^WT/WT and EZH2^WT/Mu aggressive lymphomas and show that mutual interference and compensatory function of co-expressed EZH1 and EZH2 rearrange their own genome-wide distribution, thereby establishing restricted chromatin and gene expression signatures. Direct comparison of leading compounds introduces potency and a mechanism of action of the EZH1/2 dual inhibitor (valemetostat). The synthetic lethality is observed in all lymphoma models and primary adult T cell leukemia-lymphoma (ATL) cells. Opposing actions of EZH1/2-polycomb and SWI/SNF complexes are required for facultative heterochromatin formation. Inactivation of chromatin-associated genes (ARID1A, SMARCA4/BRG1, SMARCB1/SNF5, KDM6A/UTX, BAP1, KMT2D/MLL2) and oncovirus infection (HTLV-1, EBV) trigger EZH1/2 perturbation and H3K27me3 deposition. Our study provides the mechanism-based rationale for chemical dual targeting of EZH1/2 in cancer epigenome.

Tumor cell-derived angiopoietin-like protein ANGPTL2 is a critical driver of metastasis

Strategies to inhibit metastasis have been mainly unsuccessful in part due to insufficient mechanistic understanding. Here, we report evidence of critical role for the angiopoietin-like protein 2 (ANGPTL2) in metastatic progression. In mice, Angptl2 has been implicated in inflammatory carcinogenesis but it has not been studied in human tumors. In patients with lung cancer, elevated levels of ANGPTL2 expression in tumor cells within the primary tumor were associated with a reduction in the period of disease-free survival after surgical resection. Transcription factors NFATc, ATF2, and c-Jun upregulated in aggressive tumor cells promoted increased Angptl2 expression. Most notably, tumor cell-derived ANGPTL2 increased in vitro motility and invasion in an autocrine/paracrine manner, conferring an aggressive metastatic tumor phenotype. In xenograft mouse models, tumor cell-derived ANGPTL2 accelerated metastasis and shortened survival whereas attenuating ANGPTL2 expression in tumor cells-blunted metastasis and extended survival. Overall, our findings showed that tumor cell-derived ANGPTL2 drives metastasis and provided an initial proof of concept for blockade of its action as a strategy to antagonize the metastatic process.

Circulating CD14(+) CD16(+) monocyte levels predict tissue invasive character of cholangiocarcinoma

Chronic inflammation as a risk factor for cancer development is driven in part by monocyte/macrophages, which in many cancers exhibit pro-tumorigenic activity. In this study we identified elevation in CD14(+) CD16(+) , a minor blood monocyte subpopulation in cholangiocarcinoma (CCA) patients, compared to normal and biliary disease patient specimens. Tumour association was suggested by the observation that this elevated level decreased to normal after tumour resection. Moreover, the elevated level of CD14(+) CD16(+) monocytes in CCA patient blood correlated with degree of MAC387-positive (recent blood-derived macrophage migrant-specific marker) tumour-associated macrophage infiltration as determined by immunohistochemistry. These CD14(+) CD16(+) monocytes were suggested to enhance tumour progression as this subpopulation possesses (i) high expression of adhesion molecules (CD11c, CD49d, and CD54) and scavenger receptor (CD163), which enable them to adhere strongly to endothelial cells, and (ii) that peripheral blood monocytes from CCA patients express high levels of growth and angiogenic factor-related genes (epiregulin, VEGF-A and CXCL3). Elevation of peripheral CD14(+) CD16(+) monocyte levels was associated with features associated with poor prognosis CCA parameters (non-papillary type and high number of tissue macrophages). These data indicate that the CD14(+) CD16(+) monocytes from CCA patients with pro-tumorigenic characteristics may associate with rapid tumour progression and poor patient outcome. If confirmed in subsequent studies, the level of CD14(+) CD16(+) monocytes may serve as a marker for disease activity in CCA patients and serve as a target for pathogenic macrophage specific drug development.

Granulocyte colony-stimulating factor (G-CSF) mobilizes bone marrow-derived cells into injured spinal cord and promotes functional recovery after compression-induced spinal cord injury in mice

The aim of the present study was to elucidate the effects of granulocyte colony-stimulating factor (G-CSF)-mediated mobilization of bone marrow-derived stem cells on the injured spinal cord. Bone marrow cells of green fluorescent protein (GFP) transgenic mice were transplanted into lethally irradiated C57BL/6 mice. Four weeks after bone marrow transplantation, spinal cord injury was produced by a static load (20 g, 5 min) at T8 level. G-CSF (200 microg/kg/day) was injected subcutaneously for 5 days. Immunohistochemistry for GFP and cell lineage markers was performed to evaluate G-CSF-mediated mobilization of bone marrow-derived cells into injured spinal cord. Hind limb locomotor recovery was assessed for 6 weeks. Immunohistochemistry revealed that G-CSF increased the number of GFP-positive cells in injured spinal cord, indicating that bone marrow-derived cells were mobilized and migrated into injured spinal cord. The numbers of double positive cells for GFP and glial markers were larger in the G-CSF treated mice than in the control mice. Luxol Fast Blue staining revealed that G-CSF promoted white matter sparing. G-CSF treated mice showed significant recovery of hind limb function compared to that of the control mice. In conclusion, G-CSF showed efficacy for spinal cord injury treatment through mobilization of bone marrow-derived cells.

Inflammation-driven senescence-associated secretory phenotype in cancer-associated fibroblasts enhances peritoneal dissemination

In the tumor microenvironment, senescent non-malignant cells, including cancer-associated fibroblasts (CAFs), exhibit a secretory profile under stress conditions; this senescence-associated secretory phenotype (SASP) leads to cancer progression and chemoresistance. However, the role of senescent CAFs in metastatic lesions and the molecular mechanism of inflammation-related SASP induction are not well understood. We show that pro-inflammatory cytokine-driven EZH2 downregulation maintains the SASP by demethylating H3K27me3 marks in CAFs and enhances peritoneal tumor formation of gastric cancer (GC) through JAK/STAT3 signaling in a mouse model. A JAK/STAT3 inhibitor blocks the increase in GC cell viability induced by senescent CAFs and peritoneal tumor formation. Single-cell mass cytometry revealed that fibroblasts exist in the ascites of GC patients with peritoneal dissemination, and the fibroblast population shows p16 expression and SASP factors at high levels. These findings provide insights into the inflammation-related SASP maintenance by histone modification and the role of senescent CAFs in GC peritoneal dissemination.

Granulocyte Colony-Stimulating Factor Attenuates Neuronal Death and Promotes Functional Recovery After Spinal Cord Injury in Mice

Granulocyte colony-stimulating factor (G-CSF) is a protein that stimulates differentiation, proliferation, and survival of granulocytic lineage cells. Recently, a neuroprotective effect of G-CSF was reported in a model of cerebral infarction. The aim of the present study was to elucidate the potential therapeutic effect of G-CSF for spinal cord injury (SCI) in mice. We found that G-CSF is neuroprotective against glutamate-induced cell death of cerebellar granule neurons in vitro. Moreover, we used a mouse model of compressive SCI to examine the neuroprotective potential of G-CSF in vivo. Histologic assessment with cresyl violet staining revealed that the number of surviving neurons in the injured spinal cord was significantly increased in G-CSF-treated mice. Immunohistochemistry for neuronal apoptosis revealed that G-CSF suppressed neuronal apoptosis after SCI. Moreover, administration of G-CSF promoted hindlimb functional recovery. Examination of signaling pathways downstream of the G-CSF receptor suggests that G-CSF might promote functional recovery by inhibiting neuronal apoptosis after SCI. G-CSF is currently used in the clinic for hematopoietic stimulation, and its ongoing clinical trial for brain infarction makes it an appealing molecule that could be rapidly placed into trials for patients with acute SCI.

Current status of treatment for primary effusion lymphoma

Primary effusion lymphoma (PEL) is a rare and aggressive B-cell non-Hodgkin's lymphoma that usually presents with malignant effusions without tumor masses. An extracavitary or solid variant of PEL has also been described. Human herpes virus 8/Kaposi sarcoma-associated herpes virus (HHV-8/KSHV) is universally associated with the pathogenesis of PEL. More than 70% of cases occur with concurrent Epstein-Barr virus infection, but its relation to the pathogenesis is unknown. Patients are found in the context of immunosuppressive states (HIV-1 infection, post-organ transplantation). PEL is usually treated with CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone)-like chemotherapy with antiretroviral therapy if HIV-1 is positive. However, it is generally resistant to chemotherapy with a short median survival of less than 6 months. The optimal treatment for PEL has not been established yet. More intensive chemotherapy, such as dose-adjusted EPOCH (DA-EPOCH; etoposide, prednisone, vincristine, cyclophosphamide and doxorubicin) and CDE (cyclophosphamide, doxorubicin, etoposide) are expected to show a favorable prognosis. Recently, the molecular steps in KSHV/HHV-8-driven oncogenesis have begun to be revealed, and molecular targeting therapies such as proteasome, NF-κB, cytokines and surface antigens would provide evidence for their clinical use.

Functional and genetic characterization of three cell lines derived from a single tumor of an Opisthorchis viverrini-associated cholangiocarcinoma patient

Three cholangiocarcinoma (CCA) cell line-formerly named, M156, M213 and M214 have been intensively used with discrepancy of their tumor origins. They were assumed to be originated from three different donors without authentication. To verify the origins of these cell lines, the short tandem repeat (STR) analysis of the currently used cell lines, the cell stocks from the establisher and the primary tumor of a CCA patient were performed. Their phenotypic and genotypic originality were compared. The currently used 3 CCA cell lines exhibited similar STR as CCA patient ID-M213 indicating the same origin of these cells. The cell stocks from the establisher, however, revealed the same STR of M213 and M214 cells, but not M156. The misidentification of M214 and M156 is probably due to the mislabeling and cross-contamination of M213 cells during culture. These currently used cell lines were renamed as KKU-213A, -213B and -213C, for the formerly M213, M214 and M156 cells, respectively. These cell lines were established from a male with an intrahepatic mass-forming CCA stage-4B. The tumor was an adenosquamous carcinoma with the liver fluke ova granuloma in evidence. All cell lines had positive CK19 with differential CA19-9 expression. They exhibited aneuploidy karyotypes, distinct cell morphology, cell growth, cytogenetic characteristic and progressive phenotypes. KKU-213C formed a adenosquamous carcinoma, whereas KKU-213A and KKU-213B formed poorly- and well-differentiated squamous cell carcinomas in xenografted mice. mRNA microarray revealed different expression profiles among these three cell lines. The three cell lines have unique characteristics and may resemble the heterogeneity of tumor origin.

PolyI:C-Induced, TLR3/RIP3-Dependent Necroptosis Backs Up Immune Effector-Mediated Tumor Elimination In Vivo

Double-stranded RNA directly acts on fibroblast and myeloid lineages to induce necroptosis as in TNFα. Here, we investigated whether this type of cell death occurred in cancer cells in response to polyinosinic-polycytidylic acid (polyI:C) and the pan-caspase inhibitor z-Val-Ala-Asp fluromethyl ketone (zVAD). We found that the colon cancer cell line CT26 is highly susceptible to necroptosis, as revealed by staining with annexin V/propidium iodide. CT26 cells possess RNA sensors, TLR3 and MDA5, which are upregulated by interferon (IFN)-inducing pathways and linked to receptor-interacting protein kinase (RIP) 1/3 activation via TICAM-1 or MAVS adaptor, respectively. Although exogenously added polyI:C alone marginally induced necroptosis in CT26 cells, a combined regimen of polyI:C and zVAD induced approximately 50% CT26 necroptosis in vitro without secondary effects of TNFα or type I IFNs. CT26 necroptosis depended on the TLR3-TICAM-1-RIP3 axis in the tumor cells to produce reactive oxygen species, but not on MDA5, MAVS, or the caspases/inflammasome activation. However, the RNA-derived necroptosis was barely reproduced in vivo in a CT26 tumor-implanted Balb/c mouse model with administration of polyI:C + zVAD. Significant shrinkage of CT26 tumors was revealed only when polyI:C (100 μg) was injected intraperitoneally and zVAD (1 mg) subcutaneously into tumor-bearing mice that were depleted of cytotoxic T lymphocytes and natural killer cells. The results were confirmed with immune-compromised mice with no lymphocytes. Although necroptosis-induced tumor growth retardation appears mechanistically complicated and dependent on the injection routes of polyI:C and zVAD, anti-caspase reagent directed to tumor cells will make RNA adjuvant immunotherapy more effective by modulating the formation of the tumoricidal microenvironment and dendritic cell-inducing antitumor immune system.

Hematopoietic stem cell and marrow stromal cell for spinal cord injury in mice

We compared the effects of hematopoietic stem cell and marrow stromal cell transplantation for spinal cord injury in mice. From green fluorescent protein transgenic mouse bone marrow, lineage-negative, c-kit- and Sca-1-positive cells were sorted as hematopoietic stem cells and plastic-adherent cells were cultured as marrow stromal cells. One week after injury, hematopoietic stem cells or marrow stromal cells were injected into the lesioned site. Functional recovery was assessed and immunohistochemistry was performed. In the hematopoietic stem cell group, a portion of green fluorescent protein-positive cells expressed glial marker. In the marrow stem cell group, a number of green fluorescent protein and fibronectin-double positive cells were observed. No significant difference was observed in the recovery between both groups. Both hematopoietic stem cells and marrow stromal cells have the potential to restore the injured spinal cord and to promote functional recovery.

Progression of T cell lineage restriction in the earliest subpopulation of murine adult thymus visualized by the expression of lck proximal promoter activity

The proximal promoter of lck directs gene expression exclusively in T cells. To investigate the developmental regulation of the lck proximal promoter activity and its relationship to T cell lineage commitment, a green fluorescence protein (GFP) transgenic (Tg) mouse in which the GFP expression is under the control of the proximal promoter of lck was created. In the adult GFP-Tg mice, >90% of CD4(+)CD8(+) and CD4(+)CD8(-) thymocytes, and the majority of CD4(-)CD8(+) and CD4(-)CD8(-) [double-negative (DN)] thymocytes were highly positive for GFP. Slightly lower but substantial levels of expression of GFP was also observed in mature splenic T cells. No GFP(+) cells was detected in non-T lineage subsets, including mature and immature B cells, CD5(+) B cells, and NK cells, indicating a preserved tissue specificity of the promoter. The earliest GFP(+) cells detected were found in the CD44(+)CD25(-) DN thymocyte subpopulation. The developmental potential of GFP(-) and GFP(+) cells in the CD44(+)CD25(-) DN fraction was examined using in vitro culture systems. The generation of substantial numbers of alphabeta and gammadelta T cells as well as NK cells was demonstrated from both GFP(-) and GFP(+) cells. However, no development of B cells or dendritic cells was detected from GFP(+) CD44(+)CD25(-) DN thymocytes. These results suggest that the progenitors expressing lck proximal promoter activity in the CD44(+)CD25(-) DN thymocyte subset have lost most of the progenitor potential for the B and dendritic cell lineage. Thus, progression of T cell lineage restriction in the earliest thymic population can be visualized by lck proximal promoter activity, suggesting a potential role of Lck in the T cell lineage commitment.

BAZF, a novel Bcl6 homolog, functions as a transcriptional repressor

The BCL6 gene, which has been identified from the chromosomal translocation breakpoint in B-cell lymphomas, functions as a sequence-specific transcriptional repressor. We cloned a novel Bcl6-homologous gene, BAZF (encoding Bcl6-associated zinc finger protein). The predicted amino acid sequence of BAZF indicated that the BTB/POZ domain and the five repeats of the Krüppel-like zinc finger motif are located in the NH2-terminal region and the COOH-terminal region, respectively. BAZF associated with Bcl6 at the BTB/POZ domain and localized in the nucleus. Since zinc finger motifs of BAZF were 94% identical to those of Bcl6 at the amino acid level, BAZF bound specifically to the DNA-binding sequence of Bcl6 and functioned as a transcriptional repressor. The repressor activity was associated with both the BTB/POZ domain and the middle portion of BAZF. The 17-amino-acid sequence in the middle portion was completely conserved between BAZF and Bcl6, and the conserved region was critical for the repressor activity. Expression of BAZF mRNA, like that of Bcl6 mRNA, was induced in activated lymphocytes as an immediate-early gene. Therefore, the biochemical character of BAZF is similar to that of Bcl6 although the tissue expression pattern of BAZF differs from that of Bcl6. This is apparently the first report of a gene family whose members encode zinc finger proteins with the BTB/POZ domain.

Early development of human hematopoietic and acquired immune systems in new born NOD/Scid/Jak3null mice intrahepatic engrafted with cord blood-derived CD34 + cells

An animal model in which the human immune system can be reconstituted is necessary to study acquired immunity in vivo. We report here a novel model, the NOD/SCID/JAK3(null) mouse, for the human immune system's development. Newborn mice transplanted with human cord blood CD34(+) cells intrahepatically, developed human T and B cells, and myeloid and plasmacytoid dendritic cells. The T and B cells had a naïve to memory phenotype, and included plasma cells. The human acquired immune system can be reconstituted from CD34(+) cells in NOD/SCID/JAK3(null) mice. This model is a powerful tool for the study of human immunity.