Interferon-γ resistance and immune evasion in glioma develop via Notch-regulated co-evolution of malignant and immune cells

Immune surveillance is critical to prevent tumorigenesis. Gliomas evade immune attack, but the underlying mechanisms remain poorly understood. We show that glioma cells can sustain growth independent of immune system constraint by reducing Notch signaling. Loss of Notch activity in a mouse model of glioma impairs MHC-I and cytokine expression and curtails the recruitment of anti-tumor immune cell populations in favor of immunosuppressive tumor-associated microglia/macrophages (TAMs). Depletion of T cells simulates Notch inhibition and facilitates tumor initiation. Furthermore, Notch-depleted glioma cells acquire resistance to interferon-γ and TAMs re-educating therapy. Decreased interferon response and cytokine expression by human and mouse glioma cells correlate with low Notch activity. These effects are paralleled by upregulation of oncogenes and downregulation of quiescence genes. Hence, suppression of Notch signaling enables gliomas to evade immune surveillance and increases aggressiveness. Our findings provide insights into how brain tumor cells shape their microenvironment to evade immune niche control.

An In Vivo CRISPR Screen Identifies Stepwise Genetic Dependencies of Metastatic Progression

Blood-borne metastasis of breast cancer involves a series of tightly regulated sequential steps, including the growth of a primary tumor lesion, intravasation of circulating tumor cells (CTC), and adaptation in various distant metastatic sites. The genes orchestrating each of these steps are poorly understood in physiologically relevant contexts, owing to the rarity of experimental models that faithfully recapitulate the biology, growth kinetics, and tropism of human breast cancer. Here, we conducted an in vivo loss-of-function CRISPR screen in newly derived CTC xenografts, unique in their ability to spontaneously mirror the human disease, and identified specific genetic dependencies for each step of the metastatic process. Validation experiments revealed sensitivities to inhibitors that are already available, such as PLK1 inhibitors, to prevent CTC intravasation. Together, these findings present a new tool to reclassify driver genes involved in the spread of human cancer, providing insights into the biology of metastasis and paving the way to test targeted treatment approaches.

SIGNIFICANCE

A loss-of-function CRISPR screen in human CTC-derived xenografts identifies genes critical for individual steps of the metastatic cascade, suggesting novel drivers and treatment opportunities for metastatic breast cancers.

Local progenitor cells shape the neoplastic vasculature and promote brain tumor growth

e14044

Background: Aggressive brain tumors like glioblastoma depend on support by their local environment. While the role of tumor-associated myeloid cells on glioblastoma progression is well-documented, we have only partial knowledge of the pathological impact of glioblastoma -parenchymal progenitor cells. Methods: We investigated the glioblastoma microenvironment with transgenic lineage-tracing models ( nestin-creER2, R26-tdTomato and sox2-creER2,R26-tdTomato), intravital imaging, single-cell transcriptomics, immunofluorescence and flow-cytometry as well as histopathology and characterized a previously unknown tumor-associated progenitor cell. In functional experiments, we studied the knockout of the transcription factor SOX2 in these tumor-associated cells. Results: Lineage-traced cells from mouse glioblastoma were obtained by flow-cytometry and single cell transcriptomes compared to established gene expression data from brain tumor parenchymal cells. The traced tumor-associated cells had a transcriptomic profile largely resembling myeloid cells and expressed microglia-/macrophage-markers on the protein-level. However, transgenic models and bone-marrow chimera revealed that the traced cells were clearly distinct from microglia or macrophages. The traced tumor associated cells with a myeloid expression profile derived from a SOX2-dependent progenitor cell. Consequently, conditional Sox2-knockout ablated the entire myeloid-like cell population. Remarkably, this tumor-associated cell population had a large impact on disease-progression causing significant reduction of glioblastoma –vascularization to 53%, changing vascular function and leading to a decrease in tumor volume to 42% as compared to controls. The myeloid-like progenitor cells were identified in human brain tumors by immunofluorescence and in scRNA-seq data. Conclusions: We identified a previously unacknowledged population of tumor-associated progenitor cells with a myeloid-like expression profile that transiently appeared during glioblastoma growth. These progenitors have strong impact on glioblastoma progression and point towards a new and promising therapeutic target in order to support anti-angiogenic regimen in glioblastoma.

TAMEP are brain tumor parenchymal cells controlling neoplastic angiogenesis and progression

Aggressive brain tumors like glioblastoma depend on support by their local environment and subsets of tumor parenchymal cells may promote specific phases of disease progression. We investigated the glioblastoma microenvironment with transgenic lineage-tracing models, intravital imaging, single-cell transcriptomics, immunofluorescence analysis as well as histopathology and characterized a previously unacknowledged population of tumor-associated cells with a myeloid-like expression profile (TAMEP) that transiently appeared during glioblastoma growth. TAMEP of mice and humans were identified with specific markers. Notably, TAMEP did not derive from microglia or peripheral monocytes but were generated by a fraction of CNS-resident, SOX2-positive progenitors. Abrogation of this progenitor cell population, by conditional Sox2-knockout, drastically reduced glioblastoma vascularization and size. Hence, TAMEP emerge as a tumor parenchymal component with a strong impact on glioblastoma progression.

Oncogenic and Tumor-Suppressive Functions of NOTCH Signaling in Glioma

Although the role of NOTCH signaling has been extensively studied in health and disease, many questions still remain unresolved. Being crucial for tissue homeostasis, NOTCH signaling is also implicated in multiple cancers by either promoting or suppressing tumor development. In this review we illustrate the context-dependent role of NOTCH signaling during tumorigenesis with a particular focus on gliomas, the most frequent and aggressive brain tumors in adults. For a long time, NOTCH has been considered an oncogene in glioma mainly by virtue of its neural stem cell-promoting activity. However, the recent identification of NOTCH-inactivating mutations in some glioma patients has challenged this notion, prompting a re-examination of the function of NOTCH in brain tumor subtypes. We discuss recent findings that might help to reconcile the controversial role of NOTCH signaling in this disease, and pose outstanding questions that still remain to be addressed.

Id4 Downstream of Notch2 Maintains Neural Stem Cell Quiescence in the Adult Hippocampus

Neural stem cells (NSCs) in the adult mouse hippocampal dentate gyrus (DG) are mostly quiescent, and only a few are in cell cycle at any point in time. DG NSCs become increasingly dormant with age and enter mitosis less frequently, which impinges on neurogenesis. How NSC inactivity is maintained is largely unknown. Here, we found that Id4 is a downstream target of Notch2 signaling and maintains DG NSC quiescence by blocking cell-cycle entry. Id4 expression is sufficient to promote DG NSC quiescence and Id4 knockdown rescues Notch2-induced inhibition of NSC proliferation. Id4 deletion activates NSC proliferation in the DG without evoking neuron generation, and overexpression increases NSC maintenance while promoting astrogliogenesis at the expense of neurogenesis. Together, our findings indicate that Id4 is a major effector of Notch2 signaling in NSCs and a Notch2-Id4 axis promotes NSC quiescence in the adult DG, uncoupling NSC activation from neuronal differentiation.

Apelin-induced cardioprotection against ischaemia/reperfusion injury: roles of epidermal growth factor and Src

AIM

Apelin, the ligand of the G-protein-coupled receptor (GPCR) APJ, exerts a post-conditioning-like protection against ischaemia/reperfusion injury through activation of PI3K-Akt-NO signalling. The pathway connecting APJ to PI3K is still unknown. As other GPCR ligands act through transactivation of epidermal growth factor receptor (EGFR) via a matrix metalloproteinase (MMP) or Src kinase, we investigated whether EGFR transactivation is involved in the following three features of apelin-induced cardioprotection: limitation of infarct size, suppression of contracture and improvement of post-ischaemic contractile recovery.

METHOD

Isolated rat hearts underwent 30 min of global ischaemia and 2 h of reperfusion. Apelin (0.5 μm) was infused during the first 20 min of reperfusion. EGFR, MMP or Src was inhibited to study the pathway connecting APJ to PI3K. Key components of RISK pathway, namely PI3K, guanylyl cyclase or mitochondrial K⁺ -ATP channels, were also inhibited. Apelin-induced EGFR and phosphatase and tensing homolog (PTEN) phosphorylation were assessed. Left ventricular pressure and infarct size were measured.

RESULTS

Apelin-induced reductions in infarct size and myocardial contracture were prevented by the inhibition of EGFR, Src, MMP or RISK pathway. The involvement of EGFR was confirmed by its phosphorylation. However, neither direct EGFR nor MMP inhibition affected apelin-induced improvement of early post-ischaemic contractile recovery, which was suppressed by Src and RISK inhibitors only. Apelin also increased PTEN phosphorylation, which was removed by Src inhibition.

CONCLUSION

While EGFR and MMP limit infarct size and contracture, Src or RISK pathway inhibition suppresses the three features of cardioprotection. Src does not only transactivate EGFR, but also inhibits PTEN by phosphorylation thus playing a crucial role in apelin-induced cardioprotection.

Notch2 Signaling Maintains NSC Quiescence in the Murine Ventricular-Subventricular Zone

Neurogenesis continues in the ventricular-subventricular zone (V-SVZ) of the adult forebrain from quiescent neural stem cells (NSCs). V-SVZ NSCs are a reservoir for new olfactory bulb (OB) neurons that migrate through the rostral migratory stream (RMS). To generate neurons, V-SVZ NSCs need to activate and enter the cell cycle. The mechanisms underlying NSC transition from quiescence to activity are poorly understood. We show that Notch2, but not Notch1, signaling conveys quiescence to V-SVZ NSCs by repressing cell-cycle-related genes and neurogenesis. Loss of Notch2 activates quiescent NSCs, which proliferate and generate new neurons of the OB lineage. Notch2 deficiency results in accelerated V-SVZ NSC exhaustion and an aging-like phenotype. Simultaneous loss of Notch1 and Notch2 resembled the total loss of Rbpj-mediated canonical Notch signaling; thus, Notch2 functions are not compensated in NSCs, and Notch2 is indispensable for the maintenance of NSC quiescence in the adult V-SVZ.

Glypican-2 levels in cerebrospinal fluid predict the status of adult hippocampal neurogenesis

Adult hippocampal neurogenesis is a remarkable form of brain plasticity through which new neurons are generated throughout life. Despite its important roles in cognition and emotion and its modulation in various preclinical disease models, the functional importance of adult hippocampal neurogenesis in human health has not been revealed because of a lack of tools for monitoring adult neurogenesis in vivo. Therefore, we performed an unbiased proteomics screen to identify novel proteins expressed during neuronal differentiation using a human neural stem cell model, and we identified the proteoglycan Glypican-2 (Gpc2) as a putative secreted marker of immature neurons. Exogenous Gpc2 binds to FGF2 and inhibits FGF2-induced neural progenitor cell proliferation. Gpc2 is enriched in neurogenic regions of the adult brain. Its expression is increased by physiological stimuli that increase hippocampal neurogenesis and decreased in transgenic models in which neurogenesis is selectively ablated. Changes in neurogenesis also result in changes in Gpc2 protein level in cerebrospinal fluid (CSF). Gpc2 is detectable in adult human CSF, and first pilot experiments with a longitudinal cohort indicate a decrease over time. Thus, Gpc2 may serve as a potential marker to monitor adult neurogenesis in both animal and human physiology and disease, warranting future studies.

A Tumor Suppressor Function for Notch Signaling in Forebrain Tumor Subtypes

In the brain, Notch signaling maintains normal neural stem cells, but also brain cancer stem cells, indicating an oncogenic role. Here, we identify an unexpected tumor suppressor function for Notch in forebrain tumor subtypes. Genetic inactivation of RBP-Jκ, a key Notch mediator, or Notch1 and Notch2 receptors accelerates PDGF-driven glioma growth in mice. Conversely, genetic activation of the Notch pathway reduces glioma growth and increases survival. In humans, high Notch activity strongly correlates with distinct glioma subtypes, increased patient survival, and lower tumor grade. Additionally, simultaneous inactivation of RBP-Jκ and p53 induces primitive neuroectodermal-like tumors in mice. Hence, Notch signaling cooperates with p53 to restrict cell proliferation and tumor growth in mouse models of human brain tumors.

Molecular diversity subdivides the adult forebrain neural stem cell population

Neural stem cells (NSCs) in the ventricular domain of the subventricular zone (V-SVZ) of rodents produce neurons throughout life while those in humans become largely inactive or may be lost during infancy. Most adult NSCs are quiescent, express glial markers, and depend on Notch signaling for their self-renewal and the generation of neurons. Using genetic markers and lineage tracing, we identified subpopulations of adult V-SVZ NSCs (type 1, 2, and 3) indicating a striking heterogeneity including activated, brain lipid binding protein (BLBP, FABP7) expressing stem cells. BLBP(+) NSCs are mitotically active components of pinwheel structures in the lateral ventricle walls and persistently generate neurons in adulthood. BLBP(+) NSCs express epidermal growth factor (EGF) receptor, proliferate in response to EGF, and are a major clonogenic population in the SVZ. We also find BLBP expressed by proliferative ventricular and subventricular progenitors in the fetal and postnatal human brain. Loss of BLBP(+) stem/progenitor cells correlates with reduced neurogenesis in aging rodents and postnatal humans. These findings of molecular heterogeneity and proliferative differences subdivide the NSC population and have implications for neurogenesis in the forebrain of mammals during aging.

Notching up neural stem cell homogeneity in homeostasis and disease

Adult neural stem cells (NSCs) are perceived as a homogeneous population of cells that divide infrequently and are capable of multi-lineage differentiation. However, recent data revealed that independent stem cell lineages act in parallel to maintain neurogenesis and provide a cellular source for tissue repair. In addition, even within the same lineage, the stem and progenitor cells are strikingly heterogeneous including NSCs that are dormant or mitotically active. We will discuss these different NSC populations and activity states with relation to their role in neurogenesis and regeneration but also how these different stem cells respond to aging. NSCs depend on Notch signaling for their maintenance. While Notch-dependence is a common feature among NSC populations, we will discuss how differences in Notch signaling might contribute to adult NSC heterogeneity. Understanding the fate of multiple NSC populations with distinct functions has implications for the mechanisms of aging and regeneration.

GABA suppresses neurogenesis in the adult hippocampus through GABAB receptors

Adult neurogenesis is tightly regulated through the interaction of neural stem/progenitor cells (NSCs) with their niche. Neurotransmitters, including GABA activation of GABAA receptor ion channels, are important niche signals. We show that adult mouse hippocampal NSCs and their progeny express metabotropic GABAB receptors. Pharmacological inhibition of GABAB receptors stimulated NSC proliferation and genetic deletion of GABAB1 receptor subunits increased NSC proliferation and differentiation of neuroblasts in vivo. Cell-specific conditional deletion of GABAB receptors supports a cell-autonomous role in newly generated cells. Our data indicate that signaling through GABAB receptors is an inhibitor of adult neurogenesis.

A modified RMCE-compatible Rosa26 locus for the expression of transgenes from exogenous promoters

Generation of gain-of-function transgenic mice by targeting the Rosa26 locus has been established as an alternative to classical transgenic mice produced by pronuclear microinjection. However, targeting transgenes to the endogenous Rosa26 promoter results in moderate ubiquitous expression and is not suitable for high expression levels. Therefore, we now generated a modified Rosa26 (modRosa26) locus that combines efficient targeted transgenesis using recombinase-mediated cassette exchange (RMCE) by Flipase (Flp-RMCE) or Cre recombinase (Cre-RMCE) with transgene expression from exogenous promoters. We silenced the endogenous Rosa26 promoter and characterized several ubiquitous (pCAG, EF1α and CMV) and tissue-specific (VeCad, αSMA) promoters in the modRosa26 locus in vivo. We demonstrate that the ubiquitous pCAG promoter in the modRosa26 locus now offers high transgene expression. While tissue-specific promoters were all active in their cognate tissues they additionally led to rare ectopic expression. To achieve high expression levels in a tissue-specific manner, we therefore combined Flp-RMCE for rapid ES cell targeting, the pCAG promoter for high transgene levels and Cre/LoxP conditional transgene activation using well-characterized Cre lines. Using this approach we generated a Cre/LoxP-inducible reporter mouse line with high EGFP expression levels that enables cell tracing in live cells. A second reporter line expressing luciferase permits efficient monitoring of Cre activity in live animals. Thus, targeting the modRosa26 locus by RMCE minimizes the effort required to target ES cells and generates a tool for the use exogenous promoters in combination with single-copy transgenes for predictable expression in mice.

Newborn interneurons in the accessory olfactory bulb promote mate recognition in female mice

In the olfactory bulb of adult rodents, local interneurons are constantly replaced by immature precursors derived from the subventricular zone. Whether any olfactory sensory process specifically relies on this cell renewal remains largely unclear. By using the well known model of mating-induced imprinting to avoid pregnancy block, which requires accessory olfactory bulb (AOB) function, we demonstrate that this olfactory memory formation critically depends on the presence of newborn granule neurons in this brain region. We show that, in adult female mice, exposure to the male urine compounds involved in mate recognition increases the number of new granule cells surviving in the AOB. This process is modulated by male signals sensed through the vomeronasal organ and, in turn, changes the activity of the downstream amygdaloid and hypothalamic nuclei involved in the pregnancy block response. Chemical depletion of newly generated bulbar interneurons causes strong impairment in mate recognition, thus resulting in a high pregnancy failure rate to familiar mating male odors. Taken together, our results indicate that adult neurogenesis is essential for specific brain functions such as persistent odor learning and mate recognition.

Quiescent and active hippocampal neural stem cells with distinct morphologies respond selectively to physiological and pathological stimuli and aging

New neurons are generated in the adult hippocampus throughout life by neural stem/progenitor cells (NSCs), and neurogenesis is a plastic process responsive to external stimuli. We show that canonical Notch signaling through RBP-J is required for hippocampal neurogenesis. Notch signaling distinguishes morphologically distinct Sox2(+) NSCs, and within these pools subpopulations can shuttle between mitotically active or quiescent. Radial and horizontal NSCs respond selectively to neurogenic stimuli. Physical exercise activates the quiescent radial population whereas epileptic seizures induce expansion of the horizontal NSC pool. Surprisingly, reduced neurogenesis correlates with a loss of active horizontal NSCs in aged mice rather than a total loss of stem cells, and the transition to a quiescent state is reversible to rejuvenate neurogenesis in the brain. The discovery of multiple NSC populations with Notch dependence but selective responses to stimuli and reversible quiescence has important implications for the mechanisms of adaptive learning and also for regenerative therapy.

Integration and sensory experience-dependent survival of newly-generated neurons in the accessory olfactory bulb of female mice

Newborn neurons generated by proliferative progenitors in the adult subventricular zone (SVZ) integrate into the olfactory bulb circuitry of mammals. Survival of these newly-formed cells is regulated by the olfactory input. The presence of new neurons in the accessory olfactory bulb (AOB) has already been demonstrated in some mammalian species, albeit their neurochemical profile and functional integration into AOB circuits are still to be investigated. To unravel whether the mouse AOB represents a site of adult constitutive neurogenesis and whether this process can be modulated by extrinsic factors, we have used multiple in vivo approaches. These included fate mapping of bromodeoxyuridine-labelled cells, lineage tracing of SVZ-derived enhanced green fluorescent protein-positive engrafted cells and neurogenesis quantification in the AOB, in both sexes, as well as in females alone after exposure to male-soiled bedding or its derived volatiles. Here, we show that a subpopulation of SVZ-derived neuroblasts acquires proper neurochemical profiles of mature AOB interneurons. Moreover, 3D reconstruction of long-term survived engrafted neuroblasts in the AOB confirms these cells show features of fully integrated neurons. Finally, exposure to male-soiled bedding, but not to its volatile compounds, significantly increases the number of new neurons in the AOB, but not in the main olfactory bulb of female mice. These data show SVZ-derived neuroblasts differentiate into new functionally integrated neurons in the AOB of young and adult mice. Survival of these cells seems to be regulated by an experience-specific mechanism mediated by pheromones.

Isolation and manipulation of mammalian neural stem cells in vitro

Neural stem cells are potentially a source of cells not only for replacement therapy but also as drug vectors, bringing bioactive molecules into the brain. Stem cell-like cells can be isolated readily from the human brain, thus, it is important to find culture systems that enable expansion in a multipotent state to generate cells that are of potential use for therapy. Currently, two systems have been described for the maintenance and expansion of multipotent progenitors, an adhesive substrate bound and the neurosphere culture. Both systems have pros and cons, but the neurosphere may be able to simulate the three-dimensional environment of the niche in which the cells reside in vivo. Thus, the neurosphere, when used and cultured appropriately, can expand and provide important information about the mechanisms that potentially control neural stem cells in vivo.

Vitiligo pathogenesis: autoimmune disease, genetic defect, excessive reactive oxygen species, calcium imbalance, or what else?

The pathobiology of vitiligo has been hotly disputed for as long as one remembers, and has been a magnet for endless speculation. Evidently, the different schools of thought--ranging, e.g. from the concept that vitiligo essentially is a free-radical disorder to that of vitiligo being a primary autoimmune disease--imply very different consequences for the best therapeutic strategies that one should adopt. As a more effective therapy for this common, often disfiguring pigmentary disorder is direly needed, we must strive harder to settle the pathogenesis debate definitively--on the basis of sound experimental evidence, rather than by a war of dogmatic theories. Recognizing, however, that it is theories which tend to guide our experimental designs and choice of study parameters, the various pathogenesis theories on the market deserve to be critically, yet unemotionally re-evaluated. This Controversies feature invites you to do so, and to ask yourself: is there something important or worthwhile exploring in other pathogenesis scenarios than those already favoured by you that may help you improve your own study design, next time you have a fresh look at vitiligo? Vitiligo provides a superb model for the study of many fundamental problems in skin biology and pathology. Therefore, even if it later turns out that, as far as your own vitiligo pathogenesis concept is concerned, you have barked-up the wrong tree most of the time, chances are that you shall anyway have generated priceless new insights into skin function along the way.

Maternal deprivation and early handling affect density of calcium binding protein-containing neurons in selected brain regions and emotional behavior in periadolescent rats

Adverse early life experiences can induce neurochemical changes that may underlie modifications in hypothalamic-pituitary-adrenal axis responsiveness, emotionality and cognition. Here, we investigated the expression of the calcium binding proteins (CBPs) calretinin, calbindin and parvalbumin, which identify subpopulations of GABAergic neurons and serve important functional roles by buffering intracellular calcium levels, following brief (early handling) and long (maternal deprivation) periods of maternal separation, as compared with non-handled controls. CBP-expressing neurons were analyzed in brain regions related to stress and anxiety. Emotionality was assessed in parallel using the social interaction test. Analyses were carried out at periadolescence, an important phase for the development of brain areas involved in stress responses. Our results indicate that density of CBP-immunoreactive neurons decreases in the paraventricular region of deprived rats but increases in the hippocampus and lateral amygdala of both early-handled and deprived rats when compared with controls. Emotionality is reduced in both early-handled and deprived animals. In conclusion, early handling and deprivation led to neurochemical and behavioral changes linked to stress-sensitive brain regions. These data suggest that the effects of early experiences on CBP containing neurons might contribute to the functional changes of neuronal circuits involved in emotional response.

cAMP response element-binding protein regulates differentiation and survival of newborn neurons in the olfactory bulb

The transcription factor cAMP response element-binding protein (CREB) is involved in multiple aspects of neuronal development and plasticity. Here, we demonstrate that CREB regulates specific phases of adult neurogenesis in the subventricular zone/olfactory bulb (SVZ/OB) system. Combining immunohistochemistry with bromodeoxyuridine treatments, cell tracer injections, cell transplants, and quantitative analyses, we show that although CREB is expressed by the SVZ neuroblasts throughout the neurogenic process, its phosphorylation is transient and parallels neuronal differentiation, increasing during the late phase of tangential migration and decreasing after dendrite elongation and spine formation. In vitro, inhibition of CREB function impairs morphological differentiation of SVZ-derived neuroblasts. Transgenic mice lacking CREB, in a null CREM genetic background, show reduced survival of newborn neurons in the OB. This finding is further supported by peripheral afferent denervation experiments resulting in downregulation of CREB phosphorylation in neuroblasts, the survival of which appears heavily impaired. Together, these findings provide evidence that CREB regulates differentiation and survival of newborn neurons in the OB.

Chain formation and glial tube assembly in the shift from neonatal to adult subventricular zone of the rodent forebrain

The subventricular zone (SVZ) is regarded as an embryonic germinal layer persisting at the end of cerebral cortex neurogenesis and capable of generating neuronal precursors throughout life. The two distinct compartments of the adult rodent forebrain SVZ, astrocytic glial tubes and chains of migrating cells, are not distinguishable in the embryonic and early postnatal counterpart. In this study we analyzed the SVZ of mice and rats around birth and throughout different postnatal stages, describing molecular and morphological changes which lead to the typical structural arrangement of adult SVZ. In both species studied, most changes occurred during the first month of life, the transition being slightly delayed in mice, in spite of their earlier development. Important modifications affected the glial cells, eventually leading to glial tube assembly. These changes involved an overall reorganization of glial processes and their mutual relationships, as well as gliogenesis occurring within the SVZ which gives rise to glial cell subpopulations. The neuroblast cell population remained qualitatively quite homogeneous throughout all the stages investigated, changes being restricted to the relationships among cells and consequent formation of chains at about the third postnatal week. Electron microscopy showed that chain formation is not directly linked to glial tube assembly, generally preceding the occurrence of complete glial ensheathment. Moreover, chain and glial tube formation is asymmetric in the medial/lateral aspect of the SVZ, being inversely related. The attainment of an adult SVZ compartmentalization, on the other hand, seems linked to the pattern of expression of adhesion and extracellular matrix molecules.

Neurogenesis in the subependymal layer of the adult rat: a role for neuroactive derivatives of progesterone

The subependymal layer (SEL) of the adult mammalian brain provides a continuous supply of newborn cells that migrate to the olfactory bulb (OB) where they differentiate into interneurons. These newly generated cells migrate tangentially to the OB within a dense meshwork of astrocytic cells, organized to form tangentially oriented channels (glial tubes). The central nervous system is able to synthesize a variety of steroids. Among these, we analyzed the effects of progesterone (P) and its neuroactive metabolites dihydroprogesterone (DHP) and tetrahydroprogesterone (THP), administered by intraventricular injection, on the SEL of the adult rat. We found that THP and DHP, but not their precursor P, modify glial tubes organization and decrease immunoreactivity for glial associated proteins in SEL astrocytes. Moreover P metabolites reduce the proliferative activity within the SEL.

Effects of progesterone derivatives, dihydroprogesterone and tetrahydroprogesterone, on the subependymal layer of the adult rat

Indirect evidence suggests that in the subependymal layer (SEL) steroid hormones could be partially involved in the modulation of neurogenesis, but little or nothing is known about a direct effect of these molecules on this cellular system. The possible effect of progesterone (P) and/or its neuroactive metabolites, dihydroprogesterone (DHP) and tetrahydroprogesterone (THP), on the two cellular components of the SEL (i.e., proliferating/migrating neuroblasts and protoplasmic astrocytes) has been analyzed in adult male rat. P, DHP, and THP were administered by intraventricular injections and after 2 days the SEL was analyzed by immunohistochemistry by using anti-glial fibrillary acidic protein (GFAP) and anti-vimentin antibodies, to label the glial compartment, anti-polysialylated form of the neural cell adhesion molecule (PSA-NCAM), anti-Stathmin, and anti-beta III Tubulin antibodies to label the migrating neuroblasts. Furthermore, the newly formed cells were identified by using intraventricular injections of 5-bromo-2'-deoxyuridine (BrdU) detected immunohistochemically. Our results demonstrate that DHP and THP treatments drastically decrease the number of BrdU-labeled cells within the SEL. THP, DHP, and to a lesser extent P, administrations also induce molecular and structural modifications of the SEL glial compartment. On the whole, the present results indicate that neuroactive derivatives of P (i.e., DHP and THP) exert direct effects on adult neurogenesis, strongly affecting both neuroblasts and astrocytes of the SEL.

Cytotoxic T-lymphocyte responses in melanoma through in vitro stimulation with the Melan-A peptide analogue A27L: a qualitative analysis

Modifications in tumour antigen-derived epitopes that stabilize the major histocompatibility complex (MHC)-peptide complex result in enhanced stimulatory capacity and improved immunogenicity of the altered peptide. These epitope analogues are attractive candidates for the development of peptide-based vaccine trials. Any modification, however, in tumour antigens may induce T-cell responses that could either fail to react against the naturally occurring peptides or represent only a subset of the total antigen-specific repertoire. In the present study, we performed a critical analysis of the ability of cytotoxic T-lymphocyte (CTL) clones, derived from two melanoma patients through stimulation with the A27L peptide analogue, to cross-react with the naturally processed Melan-A/MART-1 (Melan-A) peptides in terms of T-cell receptor (TCR) affinity, functional avidity and fine antigen specificity. We found that all the A27L-specific clones analysed possessed a very low avidity for the natural Melan-A peptides, and that their binding affinity for human leukocyte antigen (HLA) tetramers complexed with both the modified and the natural Melan-A peptides did not strictly correlate with their functional avidity. We also observed that these clones were able to cross-recognize both natural Melan-A peptides in one patient, but only one peptide in the second patient. We discuss the capability of the A27L peptide analogue to stimulate all the available Melan-A-specific repertoire.

Sexually dimorphic neurogenesis is topographically matched with the anterior accessory olfactory bulb of the adult rat

The accessory olfactory bulb (AOB) is a sexually dimorphic structure of the vomeronasal system, which plays a role in the control of sexual behaviors. In adult rats, we have demonstrated previously that the migrating neuroblasts of the subependymal layer (SEL) directed to the main olfactory bulb (MOB) also reach the AOB. To tackle the relation between sexual dimorphism and targeted cell migration, we quantified the neo-neurogenesis in the AOB of adult rats of both sexes. Our results confirm a morphological sexual dimorphism in the AOB granular layer volumes. We showed that the number of newly generated cells reaching the AOB in both sexes was considerable, even if lower than those directed to the MOB. Moreover, we demonstrated that the rate of neurogenesis in the anterior AOB of the two sexes was significantly different.

Specific cytotoxic T lymphocyte responses against Melan-A/MART1, tyrosinase and gp100 in vitiligo by the use of major histocompatibility complex/peptide tetramers: the role of cellular immunity in the etiopathogenesis of vitiligo

Vitiligo is a common skin disease characterized by the presence of well circumscribed, depigmented, milky white macules devoid of identifiable melanocytes. Although the detection of circulating anti-melanocytic antibodies and of infiltrating lymphocytes at the margin of lesions supports the view that vitiligo is an autoimmune disorder, its etiology remains unknown. In particular, it is still a matter of debate whether the primary pathogenic role is exerted by humoral or cellular abnormal immune responses. In this study, the presence of specific cytotoxic T lymphocyte responses against the melanocyte differentiation antigens Melan-A/MART1, tyrosinase, and gp100 in vitiligo patients have been investigated by the use of major histocompatibility complex/peptide tetramers. High frequencies of circulating melanocyte-specific CD8+ T cells were found in all vitiligo patients analyzed. These cells exerted anti-melanocytic cytotoxic activity in vitro and expressed skin-homing capacity. In one patient melanocyte-specific cells were characterized by an exceptionally high avidity for their peptide/major histocompatibility complex ligand. These findings strongly suggest a role for cellular immunity in the pathogenesis of vitiligo and impact on the common mechanisms of self tolerance.

Diverse expansion potential and heterogeneous avidity in tumor-associated antigen-specific T lymphocytes from primary melanoma patients

While tumor-associated antigen (TAA)-specific CD8(+) T lymphocytes have been detected in metastatic melanoma patients, immune response in early disease phases has not yet been carefully evaluated. We looked for circulating cytotoxic T lymphocytes (CTL) directed against Melan-A / MART1, tyrosinase, gp100 and MAGE-3 antigens in patients with a diagnosis of primary cutaneous melanoma by using fluorescent HLA-A2 tetramers. In five out of six cases high numbers of CD8(+)/tetramer(+) cells could be detected by flow cytometry, and in four patients lymphocyte populations specific for two different melanoma antigens (Melan-A/MART1 and tyrosinase) were contemporaneously present. The TAA-specific cells could represent as much as 1/220 T lymphocytes in the circulating CD8(+) population. When tetramers were used to monitor the in vitro expansion of TAA-specific CTL precursors upon antigen-specific stimulation, a diverse expansion potential was evidenced in CTL from the different donors and, more strikingly, in CTL specific for the different TAA. Melan-A/MART1-specific CTL clones derived from two patients exhibited a broad range of avidity. Only the highest avidity clones, representing about 50 % of the cases analyzed, were tumor specific. By correlating tetramer staining with clone avidity, we found that tetramer fluorescence intensity could represent a good indicator of TCR affinity, but not of overall clone avidity.

Kinetics of GATA-3 gene expression in early polarizing and committed human T cells

Different transcription factors have been shown to control the transition of naive T cells into T helper 1 (Th1)/Th2 subsets. The T-cell-specific transcription factor GATA-3 is known to be selectively expressed in murine developing Th2 cells and to exert a positive action on Th2-specific cytokine production. Investigating GATA-3 gene regulation in human T cells we have found that naive T cells highly express GATA-3, and during early T2 or T1 polarization, respectively, they either maintain or quickly down-regulate expression. In developing T2 cells, as well as in committed Th2 cell lines and clones, we found a positive correlation among GATA-3, interleukin (IL)-5 and IL-4 gene expression kinetics, supporting the positive action of GATA-3 on Th2-specific cytokine production. A possible relationship between GATA-3 gene expression and the down-regulation of the IL-12 receptor (beta2-chain; IL-12Rbeta2) gene was evident only in the early phases of T2 polarization (within 24 hr), and not demonstrated at later times. During T-cell commitment the presence of IL-4 in the culture was essential to maintain or enhance GATA-3 transcription, while IL-12 was not necessary for full repression of GATA-3. Finally, we showed selective GATA-3 up-regulation in human Th2 cell lines and clones and the maintainance of a low basal level of GATA-3 expression in Th1 cells upon activation.

Increased frequency of RAG-expressing, CD4(+)CD3(low) peripheral T lymphocytes in patients with defective responses to DNA damage

Accumulating evidence indicates that peripheral lymphocyte variants with altered antigen receptor expression may be capable of expressing recombination-activating genes (RAG). We and others recently observed functional RAG gene products in mature T cells with defective TCR expression (MacMahan and Fink, Immunity 1998. 9: 637 - 647; Lantelme et al., J. Immunol., 2000. 164: 3455 - 3459). Here, the association between TCR expression and RAG activity was assessed further in lymphocytes from patients with defective responses to DNA damage. We show that T cells with altered TCR surface expression are present in increased numbers in these patients and that they express RAG genes. The finding of RAG gene expression by TCR variants suggests the possibility that secondary V(D)J rearrangements could be induced in these cells to rescue their defective phenotype and cellular function. Moreover, as V(D)J recombination has been implicated in chromosome translocations involving antigen receptor genes, we discuss a possible relationship between altered TCR expression, RAG activity and the frequent lymphoma-specific translocations observed in these patients.

Cutting edge: recombinase-activating gene expression and V(D)J recombination in CD4+CD3low mature T lymphocytes

The recombinase-activating genes, RAG-1 and RAG-2, can be expressed by a subset of B cells within germinal centers, where they mediate secondary V(D)J rearrangements. This receptor revision mechanism could serve either receptor diversification or tolerance-induced functions. Alternatively, it might rescue those cells the receptors of which have been damaged by somatic mutation. Less is known about the occurrence of similar mechanisms in T cells. Here we show that mature T cells with defective TCR surface expression can express RAG genes and are capable of initiating secondary V(D)J rearrangements. The possibility that a cell rescue mechanism based on the generation of a novel Ag receptor might be active in peripheral T cells is envisaged.

Re-expression of RAG-1 and RAG-2 genes and evidence for secondary rearrangements in human germinal center B lymphocytes

V(D)J recombination occurs in immature B cells within primary lymphoid organs. However, recent evidence demonstrated that the recombination activating genes RAG-1 and RAG-2 can also be expressed in murine germinal centers (GC) where they can mediate secondary rearrangements. This finding raises a number of interesting questions, the most important of which is what is the physiological role, if any, of secondary immunoglobulin (Ig) gene rearrangements. In the present report, we provide evidence that human GC B cells that have lost surface immunoglobulin re-express RAG-1 and RAG-2, suggesting that they may be able to undergo Ig rearrangement. Furthermore, we describe two mature B cell clones in which secondary rearrangements have possibly occurred, resulting in light chain replacement. The two clones carry both kappa and lambda light chains productively rearranged, but fail to express the x chain on the cell surface due to a stop codon acquired by somatic mutation. Interestingly, the analysis of the extent of somatic mutations accumulated by the two light chains might suggest that the lambda chain could have been acquired through a secondary rearrangement. Taken together, these data suggest that secondary Ig gene rearrangements leading to replacement may occur in human GC and may contribute to the peripheral B cell repertoire.

Growth stimulation of colorectal carcinoma cells via the c-kit receptor is inhibited by TGF-beta 1

Activation of the receptor tyrosine kinase c-kit by the kit-ligand, also known as stem cell factor (SCF), is essential to melanocyte and germ cell development and during the early stages of hematopoiesis. Deregulated expression of c-kit has been reported in malignancies affecting these lineages, i.e., myeloid leukemias, melanomas, and germ cell tumors. In addition, c-kit and SCF are coexpressed in some breast and colorectal cancer (CRC) cells, raising the question of whether c-kit serves an autocrine role in normal or malignant epithelial tissues. In this study, we demonstrate that human colorectal carcinomas, but not normal colorectal mucosa cells, coexpress SCF and c-kit in situ. Expression of c-kit was also observed in mucosa adjacent to colorectal tumor tissue. Consistent with a growth-regulatory role of SCF in CRC cells, exogenous SCF stimulated anchorage-dependent and anchorage-independent growth in four out of five CRC cell lines. Exogenous transforming growth factor (TGF)-beta 1 added at nanomolar concentrations to HT-29 CRC cells, which express the type I, II, and III TGF-beta receptors, downregulated c-kit expression to background levels and inhibited c-kit-dependent proliferation. Similarly, TGF-beta 1 inhibited SCF-dependent proliferation of three first-passage CRC cell lines. In summary, expression of the potential autocrine SCF/ c-kit axis is a tumor-associated phenomenon in colorectal cancer that can be suppressed by TGF-beta 1 in TGF-beta-responsive CRC cells.

Growth stimulation of colorectal carcinoma cells via the c-kit receptor is inhibited by TGF-beta 1

Activation of the receptor tyrosine kinase c-kit by the kit-ligand, also known as stem cell factor (SCF), is essential to melanocyte and germ cell development and during the early stages of hematopoiesis. Deregulated expression of c-kit has been reported in malignancies affecting these lineages, i.e., myeloid leukemias, melanomas, and germ cell tumors. In addition, c-kit and SCF are coexpressed in some breast and colorectal cancer (CRC) cells, raising the question of whether c-kit serves an autocrine role in normal or malignant epithelial tissues. In this study, we demonstrate that human colorectal carcinomas, but not normal colorectal mucosa cells, coexpress SCF and c-kit in situ. Expression of c-kit was also observed in mucosa adjacent to colorectal tumor tissue. Consistent with a growth-regulatory role of SCF in CRC cells, exogenous SCF stimulated anchorage-dependent and anchorage-independent growth in four out of five CRC cell lines. Exogenous transforming growth factor (TGF)-beta 1 added at nanomolar concentrations to HT-29 CRC cells, which express the type I, II, and III TGF-beta receptors, downregulated c-kit expression to background levels and inhibited c-kit-dependent proliferation. Similarly, TGF-beta 1 inhibited SCF-dependent proliferation of three first-passage CRC cell lines. In summary, expression of the potential autocrine SCF/ c-kit axis is a tumor-associated phenomenon in colorectal cancer that can be suppressed by TGF-beta 1 in TGF-beta-responsive CRC cells.

A novel SH3-containing human gene family preferentially expressed in the central nervous system

The Src-homology-3 domain (SH3) is an evolutionarily conserved, 50- to 60-amino-acid module carried by intracellular proteins involved in the transduction of signals for cell polarization, motility, enzymatic activation, and transcriptional regulation. The SH3 drives protein-protein interactions through binding to proline-rich ligands. This function relies on the conserved secondary structure, whereas the SH3 primary structure is highly diverse. Taking advantage of the fact that the few conserved amino acids are clustered near the N- and C-terminal ends, we designed degenerate oligonucleotides spanning these two regions and screened by PCR a variety of normal and tumor tissues for the expression of SH3-containing transcripts. Using this strategy, we have identified a novel SH3-containing human gene family of six related transcripts that map to four different chromosomes. The SH3 domain lies at the C-terminal end and shows 56-50% amino acid homology to the C-terminal SH3 of Sem-5/Drk/GRB2. The N-terminal segment of this novel SH3GL (from SH3-containing Grb2-like) gene family does not resemble any known protein. Three of these transcripts are in-frame and show a peculiar tissue distribution: SH3GL2 is preferentially expressed in the brain, SH3GL3 in brain and testis, and SH3GL1 is ubiquitous.

Clonal predominance, but preservation of a polyclonal reservoir, in the normal alpha beta T-cell repertoire

We recently demonstrated that the peripheral gamma delta T-cell repertoire becomes oligoclonal with increasing age. Although this junctional homogeneity should not severely affect the ability of gamma delta T cells to respond to foreign antigens, we reasoned that a similar oligoclonal repertoire of alpha beta T cells would lead to a profound impairment of the MHC-restricted response. We used heteroduplex analysis in this research to study the clonal complexity of the peripheral alpha beta T-cell repertoire in human subjects and supply evidence for the presence of alpha beta clonal expansions. Clonal predominance in the alpha beta T-cell repertoire of normal subjects was not simply related to age, since the PBL of young donors also showed clonal expansions and did not always correlate with a numeric increase in the corresponding V beta family. However, the type of alpha beta expansion appears to be strikingly different from the gamma delta expansions. In the case of alpha beta T cells, even in the presence of clonal dominance, evidence for a residual polyclonal background was found in all the donors tested, irrespective of age. The observation that true oligoclonality is exceptionally rare among alpha beta T lymphocytes could mean that maintenance of a highly diversified reservoir of TCR is primary for these cells throughout life.

Restriction of the T-cell receptor V delta gene repertoire is due to preferential rearrangement and is independent of antigen selection

To determine whether the limited V gene usage by the T-cell receptor delta (TCRD) chain is dictated by preferential rearrangement or by antigen selection, we characterized and compared the TCRDV gene repertoire of the productive with that of the unproductive allele in 80 human TCRG/TCRD clones. Six different V genes were found on the expressed allele; two of them, provisionally named DV7 and DV8, have not been described before on the surface of TCRG/TCRD T cells. Overall, six V genes and six non-V elements were isolated from the unproductive allele. Interestingly, the same set of genes was rearranged both in the productive and in the unproductive chromosome. These findings seem to suggest that antigen-independent mechanisms play a major role in the restriction of the TCRDV gene repertoire.

Dual receptor T-cells. Implications for alloreactivity and autoimmunity

Using monoclonal antibodies to human V alpha, we have estimated that up to one-third of mature T-cells express two V alpha chains as part of two functional and independent T-cell receptors. Cells belonging to this dual TCR subset may be specific for a broader range of antigens than cells with a single receptor. We discuss the possibility that dual receptor T-cells may be involved in alloreactivity and autoimmunity.

Normal T lymphocytes can express two different T cell receptor beta chains: implications for the mechanism of allelic exclusion

We have examined the extent of allelic exclusion at the T cell receptor (TCR) beta locus using monoclonal antibodies specific for V beta products. A small proportion (approximately 1%) of human peripheral blood T cells express two V beta as determined by flow cytometric analysis, isolation of representative clones, and sequencing of the corresponding V beta chains. Dual beta T cells are present in both the CD45R0+ and CD45R0- subset. These results indicate that dual beta expression is compatible with both central and peripheral selection. They also suggest that the substantial degree of TCR beta allelic exclusion is dependent only on asynchronous rearrangements at the beta locus, whereas the role of the pre-TCR is limited to signaling the presence of at least one functional beta protein.

kappa+lambda+ dual receptor B cells are present in the human peripheral repertoire

It is a common notion that mature B lymphocytes express either kappa or lambda light (L) chains, although the mechanism that leads to such isotypic exclusion is still debated. We have investigated the extent of L chain isotypic exclusion in normal human peripheral blood B lymphocytes. By three-color staining with anti-CD19, anti-kappa, and anti-lambda antibodies we could estimate that 0.2-0.5% of peripheral blood B cells from healthy adults express both kappa and lambda on the cell surface. The kappa+lambda+ cells were sorted, immortalized by Epstein-Barr virus, and five independent clones were characterized in detail. All clones express both kappa and lambda on the cell surface and produce immunoglobulin M that contain both kappa and lambda chains in the same molecule, i.e., hybrid antibodies. Sequencing of the L chains revealed in three out of five clones evidence for somatic mutations. It is interesting to note that among a panel of single receptor B cell clones we identified two lambda+ clones that carried a productively rearranged kappa, which was inactivated by a stop codon generated by somatic mutation. These findings indicate that dual receptor B lymphocytes can be found among mature antigen-selected B cells and suggest that somatic mutation can contribute to increase the degree of isotypic exclusion by inactivating a passenger, nonselected L chain.

T cell receptor V delta 2-C alpha transcripts are present in the thymus but virtually absent in the periphery

To investigate whether the V delta 2-(D)-J alpha gene configuration, characteristically associated with the major subset of acute lymphoblastic leukemias in humans, might have a physiologic role in T cell ontogeny, we have looked for V delta 2-C alpha transcripts in the thymus and peripheral blood of normal donors. Here we show by PCR analysis that these transcripts are virtually absent in the PBMC, whereas they are present in fetal and postnatal thymus. Interestingly, over 80% of 43 V delta 2-C alpha cDNAs randomly isolated from one postnatal thymus appeared to maintain an open reading frame. This suggests that in the thymus the V delta 2-C alpha products might be exposed to selective pressure. Furthermore, in two of three thymuses tested for J alpha usage, it was found overrepresented in a J alpha element (J alpha 58) located 2 kb downstream to a pseudo-J (J alpha 61), known to be a hot spot of recombination in alpha beta committed cells. A possible alternative pathway to alpha beta T cell differentiation via a V delta 2-J alpha intermediate is discussed.

T cell receptor V delta 2-C alpha transcripts are present in the thymus but virtually absent in the periphery

To investigate whether the V delta 2-(D)-J alpha gene configuration, characteristically associated with the major subset of acute lymphoblastic leukemias in humans, might have a physiologic role in T cell ontogeny, we have looked for V delta 2-C alpha transcripts in the thymus and peripheral blood of normal donors. Here we show by PCR analysis that these transcripts are virtually absent in the PBMC, whereas they are present in fetal and postnatal thymus. Interestingly, over 80% of 43 V delta 2-C alpha cDNAs randomly isolated from one postnatal thymus appeared to maintain an open reading frame. This suggests that in the thymus the V delta 2-C alpha products might be exposed to selective pressure. Furthermore, in two of three thymuses tested for J alpha usage, it was found overrepresented in a J alpha element (J alpha 58) located 2 kb downstream to a pseudo-J (J alpha 61), known to be a hot spot of recombination in alpha beta committed cells. A possible alternative pathway to alpha beta T cell differentiation via a V delta 2-J alpha intermediate is discussed.

An alternative approach to the assessment of gamma delta T-cell clonality in celiac disease intestinal lesions through cDNA heteroduplex analysis of T-cell receptor VJ junctions

We have investigated the clonality of the gamma delta T lymphocytes infiltrating the intestinal mucosa of CD patients and control subjects by means of a simple and powerful method based on the heteroduplex analysis of the TCR VJ junctions. Each V-specific TCR chain, amplified either from fresh biopsy material or intestinal T-cell-line cDNA, is denatured and renatured to allow the random reshuffling of the various strands carrying different junctional sequences, coamplified in the same reaction. The mismatched chains (heteroduplexes) are separated from the matched ones (homoduplexes) through polyacrylamide gel electrophoresis, and whenever one or more T-cell clones are emerging over the polyclonal background, discrete bands are visible by ethidium-bromide staining. Through this method, we have estimated the diversity of the V delta 1-3 chains and a newly described V gene (V delta 8) whose homologue in mice is abundantly expressed in gamma delta iLs. We demonstrate that the well-documented expansion of V gamma 1+ gamma delta lymphocytes in the jejunum of CD patients is polyclonal. Overall, the heteroduplex analysis on fresh intestinal and peripheral blood lymphocytes from both healthy and affected subjects shows a polyclonal pattern of all the V delta+ subsets. In contrast, most intestinal T-cell lines produce oligoclonal patterns, suggesting a dramatic in vitro selection effect. The cell expansion in culture is generally not required for the TCR heteroduplex analysis, which can therefore be applied to rapidly monitor the T-cell response in a variety of physiologic and autoimmune reactions, substituting the standard approach of TCR cloning and multiple VJ sequencing.