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Endogenous neural stem/precursor cells (NPCs) are considered a functional reservoir for promoting tissue homeostasis and repair after injury, therefore regenerative strategies that mobilize these cells have recently been proposed. Despite evidence of increased neurogenesis upon acute inflammatory insults (e.g. ischaemic stroke), the plasticity of the endogenous brain stem cell compartment in chronic CNS inflammatory disorders remains poorly characterized. Here we show that persistent brain inflammation, induced by immune cells targeting myelin, extensively alters the proliferative and migratory properties of subventricular zone (SVZ)-resident NPCs in vivo leading to significant accumulation of non-migratory neuroblasts within the SVZ germinal niche. In parallel, we demonstrate a quantitative reduction of the putative brain stem cells proliferation in the SVZ during persistent brain inflammation, which is completely reversed after in vitro culture of the isolated NPCs. Together, these data indicate that the inflamed brain microenvironment sustains a non cell-autonomous dysfunction of the endogenous CNS stem cell compartment and challenge the potential efficacy of proposed therapies aimed at mobilizing endogenous precursors in chronic inflammatory brain disorders.

Adult multipotent neural stem/precursor cells (NPCs) have the capacity to self-renew and generate functional differentiated cells (e.g. neurons, astrocytes or oligodendrocytes) within discrete tissue-specific germinal niches, such as the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus of the hippocampus. Due to their intrinsic plasticity NPCs can be considered an essential part of the cellular mechanism(s) by which the central nervous system (CNS) tries to repair itself after an injury and, as a consequence, they also represents an attractive therapeutic tool for the treatment of neurological disorders. Here we will discuss not only the role of NPC-based transplantation therapies in multiple sclerosis (MS) but also recent data suggesting that endogenous NPCs, while contributing to CNS repair in MS, may also become the target of the disease itself.

UNLABELLED: Cortical reorganization occurring in multiple sclerosis (MS) patients is thought to play a key role in limiting the effect of structural tissue damage. Conversely, its exhaustion may contribute to the irreversible disability that accumulates with disease progression. Several aspects of MS-related cortical reorganization, including the overall functional effect and likely modulation by therapies, still remain to be elucidated. The aim of this work was to assess the extent of functional cortical reorganization and its brain structural/pathological correlates in Dark Agouti rats with experimental autoimmune encephalomyelitis (EAE), a widely accepted preclinical model of chronic MS. Morphological and functional MRI (fMRI) were performed before disease induction and during the relapsing and chronic phases of EAE. During somatosensory stimulation of the right forepaw, fMRI demonstrated that cortical reorganization occurs in both relapsing and chronic phases of EAE with increased activated volume and decreased laterality index versus baseline values. Voxel-based morphometry demonstrated gray matter (GM) atrophy in the cerebral cortex, and both GM and white matter atrophy were assessed by ex vivo pathology of the sensorimotor cortex and corpus callosum. Neuroinflammation persisted in the relapsing and chronic phases, with dendritic spine density in the layer IV sensory neurons inversely correlating with the number of cluster of differentiation 45-positive inflammatory lesions. Our work provides an innovative experimental platform that may be pivotal for the comprehension of key mechanisms responsible for the accumulation of irreversible brain damage and for the development of innovative therapies to reduce disability in EAE/MS. SIGNIFICANCE STATEMENT: Since the early 2000s, functional MRI (fMRI) has demonstrated profound modifications in the recruitment of cortical areas during motor, cognitive, and sensory tasks in multiple sclerosis (MS) patients. Experimental autoimmune encephalomyelitis (EAE) represents a reliable model of the chronic-progressive variant of MS. fMRI studies in EAE have not been performed extensively up to now. This paper reports fMRI studies in a rat model of MS with somatosensory stimulation of the forepaw. We demonstrated modifications in the recruitment of cortical areas consistent with data from MS patients. To the best of our knowledge, this is the first report of cortical remodeling in a preclinical in vivo model of MS.

We tested cortical motor evoked potentials (cMEPs) as a quantitative marker for in vivo monitoring of corticospinal tract damage in a murine multiple sclerosis model (experimental autoimmune encephalomyelitis, EAE). The cMEPs, previously standardized in naive C57BL/6 developing and adult mice, were studied longitudinally in adult EAE mice. Central conduction times (CCTs) increased significantly shortly before the earliest clinical signs developed (10 days postimmunization, dpi), with peak delay in acute EAE (20-40 dpi). In clinically stable disease (80 dpi), CCTs did not increase further, but cMEP amplitude declined progressively, with complete loss in >80% of mice at 120 dpi. Increase in CCT correlated with presence of inflammatory infiltrates and demyelination in acute EAE, whereas small or absent cMEPs were associated with continuing axonal damage in clinically-stabilized disease and beyond (>80 dpi). These results demonstrate that cMEPs are a useful method for monitoring corticospinal tract function in chronic-progressive EAE, and provide insight into the pathological substrate of the condition.

Cell renewal in the adult central nervous system (CNS) is limited, and is blocked in inflammatory brain conditions. We show that both neurogenesis and oligodendrogenesis of adult neural progenitor cells in mice are blocked by inflammation-associated (endotoxin-activated) microglia, but induced by microglia activated by cytokines (IL-4 or low level of IFN-gamma) associated with T-helper cells. Blockage was correlated with up-regulation of microglial production of tumor necrosis factor-alpha. The effect induced by IL-4-activated microglia was mediated, at least in part, by insulin-like growth factor-I. The IL-4-activated microglia showed a bias towards oligodendrogenesis whereas the IFN-gamma-activated microglia showed a bias towards neurogenesis. It thus appears that microglial phenotype critically affects their ability to support or impair cell renewal from adult stem cell.

Gene therapy protocols aimed to deliver therapeutic molecules into the central nervous system may represent an alternative therapeutic strategy in patients affected by inflammatory demyelinating diseases of the central nervous system where systemic therapies have shown limited therapeutic efficacy possibly owing to the blood-brain barrier, a major obstacle for the entry of therapeutic molecules into the central nervous system.Among inflammatory demyelinating diseases of the central nervous system, gene therapy approaches have been so far developed almost exclusively for multiple sclerosis. However, the chronic/relapsing nature of the disease, the restriction to the central nervous system of the pathological process as well as the necessity to inhibit the ongoing inflammatory process but also to foster endogenous remyelinating pathways, have posed several questions which still need to be properly addressed for the development of a successful gene therapy strategy in multiple sclerosis patients.The gene therapy approaches for multiple sclerosis have been so far developed and tested only in rodents and monkeys with experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis. The results of these studies clearly indicate that the delivery of therapeutic genes within the central nervous system is superior to the peripheral delivery. In particular, the intracerebral delivery of genes coding for anti-inflammatory and/or neurotrophic molecules, using gene vectors derived from non-replicative viruses, showed to inhibit not only the detrimental function of blood-borne mononuclear effector cells but also to foster proliferation and differentiation of surviving oligodendrocytes within demyelinated areas. Here, we summarize the most recent findings of this novel area of research.

Several bioengineering approaches have been proposed for peripheral nervous system repair, with limited results and still open questions about the underlying molecular mechanisms. We assessed the biological processes that occur after the implantation of collagen scaffold with a peculiar porous micro-structure of the wall in a rat sciatic nerve transection model compared to commercial collagen conduits and nerve crush injury using functional, histological and genome wide analyses. We demonstrated that within 60 days, our conduit had been completely substituted by a normal nerve. Gene expression analysis documented a precise sequential regulation of known genes involved in angiogenesis, Schwann cells/axons interactions and myelination, together with a selective modulation of key biological pathways for nerve morphogenesis induced by porous matrices. These data suggest that the scaffold's micro-structure profoundly influences cell behaviors and creates an instructive micro-environment to enhance nerve morphogenesis that can be exploited to improve recovery and understand the molecular differences between repair and regeneration.

Polyreactive (auto)antibodies are frequently found in healthy subjects and are bona fide considered to be nonpathogenic. However, autoreactive B cells and circulating (auto)antibodies have been associated with several neurological syndromes, including demyelinating disorders. Whether these antibodies can have a real impact on disease development is still a matter of debate. Here, we briefly summarize some of the most recently published data on both the deleterious and the protective effects of antibodies in autoimmune demyelinating disorders of the central nervous system.

Transplanted neural stem/precursor cells possess peculiar therapeutic plasticity and can simultaneously instruct several therapeutic mechanisms in addition to cell replacement. Here, we interrogated the therapeutic plasticity of neural stem/precursor cells after their focal implantation in the severely contused spinal cord. We injected syngeneic neural stem/precursor cells at the proximal and distal ends of the contused mouse spinal cord and analysed locomotor functions and relevant secondary pathological events in the mice, cell fate of transplanted neural stem/precursor cells, and gene expression and inflammatory cell infiltration at the injured site. We used two different doses of neural stem/precursor cells and two treatment schedules, either subacute (7 days) or early chronic (21 days) neural stem/precursor cell transplantation after the induction of experimental thoracic severe spinal cord injury. Only the subacute transplant of neural stem/precursor cells enhanced the recovery of locomotor functions of mice with spinal cord injury. Transplanted neural stem/precursor cells survived undifferentiated at the level of the peri-lesion environment and established contacts with endogenous phagocytes via cellular-junctional coupling. This was associated with significant modulation of the expression levels of important inflammatory cell transcripts in vivo. Transplanted neural stem/precursor cells skewed the inflammatory cell infiltrate at the injured site by reducing the proportion of 'classically-activated' (M1-like) macrophages, while promoting the healing of the injured cord. We here identify a precise window of opportunity for the treatment of complex spinal cord injuries with therapeutically plastic somatic stem cells, and suggest that neural stem/precursor cells have the ability to re-programme the local inflammatory cell microenvironment from a 'hostile' to an 'instructive' role, thus facilitating the healing or regeneration past the lesion.

Emerging evidence points to reactive glia as a pivotal factor in Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mouse model of basal ganglia injury, but whether astrocytes and microglia activation may exacerbate dopaminergic (DAergic) neuron demise and/or contribute to DAergic repair is presently the subject of much debate. Here, we have correlated the loss and recovery of the nigrostriatal DAergic functionality upon acute MPTP exposure with extensive gene expression analysis at the level of the ventral midbrain (VM) and striata (Str) and found a major upregulation of pro-inflammatory chemokines and wingless-type MMTV integration site1 (Wnt1), a key transcript involved in midbrain DAergic neurodevelopment. Wnt signaling components (including Frizzled-1 [Fzd-1] and β-catenin) were dynamically regulated during MPTP-induced DAergic degeneration and reactive glial activation. Activated astrocytes of the ventral midbrain were identified as candidate source of Wnt1 by in situ hybridization and real-time PCR in vitro. Blocking Wnt/Fzd signaling with Dickkopf-1 (Dkk1) counteracted astrocyte-induced neuroprotection against MPP(+) toxicity in primary mesencephalic astrocyte-neuron cultures, in vitro. Moreover, astroglial-derived factors, including Wnt1, promoted neurogenesis and DAergic neurogenesis from adult midbrain stem/neuroprogenitor cells, in vitro. Conversely, lack of Wnt1 transcription in response to MPTP in middle-aged mice and failure of DAergic neurons to recover were reversed by pharmacological activation of Wnt/β-catenin signaling, in vivo, thus suggesting MPTP-reactive astrocytes in situ and Wnt1 as candidate components of neuroprotective/neurorescue pathways in MPTP-induced nigrostriatal DAergic plasticity.

Using a mouse model of spinal injury, Michal Schwartz and colleagues tested the effect of macrophages on the recovery process and demonstrate an important anti-inflammatory role for a subset of infiltrating monocyte-derived macrophages that is dependent upon their expression of interleukin 10., Background Although macrophages (MΦ) are known as essential players in wound healing, their contribution to recovery from spinal cord injury (SCI) is a subject of debate. The difficulties in distinguishing between different MΦ subpopulations at the lesion site have further contributed to the controversy and led to the common view of MΦ as functionally homogenous. Given the massive accumulation in the injured spinal cord of activated resident microglia, which are the native immune occupants of the central nervous system (CNS), the recruitment of additional infiltrating monocytes from the peripheral blood seems puzzling. A key question that remains is whether the infiltrating monocyte-derived MΦ contribute to repair, or represent an unavoidable detrimental response. The hypothesis of the current study is that a specific population of infiltrating monocyte-derived MΦ is functionally distinct from the inflammatory resident microglia and is essential for recovery from SCI. Methods and Findings We inflicted SCI in adult mice, and tested the effect of infiltrating monocyte-derived MΦ on the recovery process. Adoptive transfer experiments and bone marrow chimeras were used to functionally distinguish between the resident microglia and the infiltrating monocyte-derived MΦ. We followed the infiltration of the monocyte-derived MΦ to the injured site and characterized their spatial distribution and phenotype. Increasing the naïve monocyte pool by either adoptive transfer or CNS-specific vaccination resulted in a higher number of spontaneously recruited cells and improved recovery. Selective ablation of infiltrating monocyte-derived MΦ following SCI while sparing the resident microglia, using either antibody-mediated depletion or conditional ablation by diphtheria toxin, impaired recovery. Reconstitution of the peripheral blood with monocytes resistant to ablation restored the lost motor functions. Importantly, the infiltrating monocyte-derived MΦ displayed a local anti-inflammatory beneficial role, which was critically dependent upon their expression of interleukin 10. Conclusions The results of this study attribute a novel anti-inflammatory role to a unique subset of infiltrating monocyte-derived MΦ in SCI recovery, which cannot be provided by the activated resident microglia. According to our results, limited recovery following SCI can be attributed in part to the inadequate, untimely, spontaneous recruitment of monocytes. This process is amenable to boosting either by active vaccination with a myelin-derived altered peptide ligand, which indicates involvement of adaptive immunity in monocyte recruitment, or by augmenting the naïve monocyte pool in the peripheral blood. Thus, our study sheds new light on the long-held debate regarding the contribution of MΦ to recovery from CNS injuries, and has potentially far-reaching therapeutic implications. Please see later in the article for Editors' Summary, Editors' Summary Background Every year, spinal cord injuries paralyze about 11,000 people in the US. The spinal cord, which contains bundles of nervous system cells called neurons, is the communication highway between the brain and the body. Messages from the brain travel down the spinal cord to control movement, breathing and other bodily functions; messages from the skin and other sensory organs travel up the spinal cord to keep the brain informed about the body. The bones of the spine normally protect the spinal cord but, if these are broken or displaced, the spinal cord can be cut or compressed, which interrupts the information flow. Damage near the top of the spinal cord paralyzes the arms and legs (tetraplegia); damage lower down paralyzes the legs only (paraplegia). Spinal cord injuries also cause other medical problems, including the loss of bladder and bowel control. Currently, there is no effective treatment for spinal cord injuries, which usually cause permanent disability because the damaged nerve fibers rarely regrow. Why Was This Study Done? After a spinal cord injury, immune system cells called macrophages accumulate at the injury site. Some of these macrophages—so-called monocyte-derived macrophages—come into (infiltrate) the spinal cord from the blood in response to the injury, whereas others—microglia—are always in the nervous system. Although macrophages are essential for wound healing in other parts of the body, it is unclear whether they have good or bad effects in the spinal cord. Many experts believe that immune system cells hinder healing in the spinal cord and should be suppressed or eliminated, but other scientists claim that macrophages secrete factors that stimulate nerve regrowth. Furthermore, although some macrophages elsewhere in the body have proinflammatory (potentially deleterious) effects, others have anti-inflammatory (beneficial) effects. So do the infiltrating monocyte-derived macrophages and the resident microglia (which are proinflammatory) have different functions at spinal cord injury sites? In this study, the researchers try to answer this important question. What Did the Researchers Do and Find? The researchers bruised a small section of the spinal cord of adult mice and then investigated the effect of infiltrating monocyte-derived macrophages on the recovery process. Monocyte-derived macrophages and microglia cannot be distinguished using standard staining techniques so to study their behavior after spinal cord injury the researchers introduced labeled monocyte-derived macrophages into their experimental animals by using adoptive transfer (injection of genetically labeled monocytes into the animals) or by making bone marrow chimeras. In this second technique, the animals' monocyte-derived macrophages (but not their microglia) were killed by irradiating the animals before injection of genetically labeled bone marrow, the source of monocytes. Using these approaches, the researchers found that monocyte-derived macrophages collected at the margins of spinal cord injury sites whereas microglia accumulated throughout the sites. When the pool of monocyte-derived macrophages in the mice was increased by adoptive transfer or by using a technique called “CNS-specific vaccination,” more monocyte-derived macrophages infiltrated the injury site and the animals' physical recovery from injury improved. Conversely, removal of the infiltrating monocyte-derived macrophages from the injury site reduced the animals' physical recovery. Other experiments indicated that the infiltrating monocyte-derived macrophages have a beneficial, local anti-inflammatory effect that is dependent on their expression of interleukin-10 (an anti-inflammatory signaling molecule). What Do These Findings Mean? These findings provide new information about the contribution of monocyte-derived macrophages to spontaneous recovery from spinal cord injury, a contribution that has long been debated. In particular, the findings suggest that this subset of macrophages (but not the resident microglia) has a beneficial effect on spinal cord injuries that is mediated by their production of the anti-inflammatory molecule interleukin-10. The findings also show that the effect of these monocyte-derived macrophages can be boosted, at least in mice. Although results obtained in experiments done in animals do not always accurately reflect what happens in people, this new understanding of the different functions of microglia and infiltrating monocyte-derived macrophages after injury to the spinal cord may eventually lead to the development of better treatments for spinal cord injuries. Additional Information Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000113. The MedlinePlus encyclopedia provides information about spinal cord injuries (in English and Spanish) The US National Institute of Neurological Disorders and Stroke provides detailed information about spinal cord injury, including information on current research into the problem (in English and Spanish) MedlinePlus provides an interactive tutorial on spinal cord injury and a list of links to additional information (in English and Spanish)

Background: The systemic injection of neural stem/precursor cells (NPCs) provides remarkable amelioration of the clinicopathological features of experimental autoimmune encephalomyelitis (EAE). This is dependent on the capacity of transplanted NPCs to engage concurrent mechanisms of action within specific microenvironments in vivo. Among a wide range of therapeutic actions alternative to cell replacement, neuroprotective and immune modulatory capacities of transplanted NPCs have been described. However, lacking is a detailed understanding of the mechanisms by which NPCs exert their therapeutic plasticity. This study was designed to identify the first candidate that exemplifies and sustains the immune modulatory capacity of transplanted NPCs. Methodology/Principal Findings: To achieve the exclusive targeting of the peripheral immune system, SJL mice with PLP-induced EAE were injected subcutaneously with NPCs and the treatment commenced prior to disease onset. NPC-injected EAE mice showed significant clinical improvement, as compared to controls. Exogenous NPCs lacking the expression of major neural antigens were reliably (and for long-term) found at the level of draining lymph nodes, while establishing sophisticated anatomical interactions with lymph node cells. Importantly, injected NPCs were never found in organs other than lymph nodes, including the brain and the spinal cord. Draining lymph nodes from transplanted mice showed focal upregulation of major developmental stem cell regulators, such as BMP-4, Noggin and Sonic hedgehog. In lymph nodes, injected NPCs hampered the activation of myeloid dendritic cells (DCs) and steadily restrained the expansion of antigen-specific encephalitogenic T cells. Both ex vivo and in vitro experiments identified a novel highly NPC-specific-BMP-4-dependent-mechanism hindering the DC maturation. Conclusion/Significance: The study described herein, identifies the first member of the TGF beta/BMP family of stem cell regulators as a novel tolerogenic factor released by NPCs. Full exploitation of this pathway as an efficient tool for vaccination therapy in autoimmune inflammatory conditions is underway. Background: The systemic injection of neural stem/precursor cells (NPCs) provides remarkable amelioration of the clinicopathological features of experimental autoimmune encephalomyelitis (EAE). This is dependent on the capacity of transplanted NPCs to engage concurrent mechanisms of action within specific microenvironments in vivo. Among a wide range of therapeutic actions alternative to cell replacement, neuroprotective and immune modulatory capacities of transplanted NPCs have been described. However, lacking is a detailed understanding of the mechanisms by which NPCs exert their therapeutic plasticity. This study was designed to identify the first candidate that exemplifies and sustains the immune modulatory capacity of transplanted NPCs. Methodology/Principal Findings: To achieve the exclusive targeting of the peripheral immune system, SJL mice with PLP-induced EAE were injected subcutaneously with NPCs and the treatment commenced prior to disease onset. NPC-injected EAE mice showed significant clinical improvement, as compared to controls. Exogenous NPCs lacking the expression of major neural antigens were reliably (and for long-term) found at the level of draining lymph nodes, while establishing sophisticated anatomical interactions with lymph node cells. Importantly, injected NPCs were never found in organs other than lymph nodes, including the brain and the spinal cord. Draining lymph nodes from transplanted mice showed focal upregulation of major developmental stem cell regulators, such as BMP-4, Noggin and Sonic hedgehog. In lymph nodes, injected NPCs hampered the activation of myeloid dendritic cells (DCs) and steadily restrained the expansion of antigen-specific encephalitogenic T cells. Both ex vivo and in vitro experiments identified a novel highly NPC-specific-BMP-4-dependent-mechanism hindering the DC maturation. Conclusion/Significance: The study described herein, identifies the first member of the TGF beta/BMP family of stem cell regulators as a novel tolerogenic factor released by NPCs. Full exploitation of this pathway as an efficient tool for vaccination therapy in autoimmune inflammatory conditions is underway.

Neural stem/precursor cells (NPCs) are broadly proposed as an alternative cell source to repair brain damage upon transplantation. NPC-driven brain repair has variably been shown in several pre-clinical models of neurological disorders. However, a comprehensive knowledge of the different mechanism(s) by which such cells exert their therapeutic potential is still lacking. While the replacement of lost or damaged cells was until a few years ago assumed to be the prime therapeutic mechanism of stem cells, it is now clear that transplanted somatic stem cells may simultaneously instruct several therapeutic mechanisms not confined to cell replacement on its own. Combining the overall therapeutic potential of NPCs in neurological disease, the concept of therapeutic plasticity has recently been proposed (Martino and Pluchino, 2006). The brain repair potential of transplanted stem cells in stroke-like conditions has solid pre-clinical evidence. It has been shown, with variable results, that NPCs—transplanted either systemically or intraparenchymally—display peculiar pathotropism toward specific sites of ischaemic damage, survive within the host for long periods of time, and establish a functional cross-talk with the different cell types of the (micro)environment. This NPC-dependent operational behaviour was first demonstrated to be capable of promoting CNS tissue recovery in mice with experimental bacterial collagenase-induced intracerebral haemorrage (ICH) (Jeong et al. , 2003) or acute middle cerebral artery occlusion-induced ischaemic stroke (Chu et al. , 2004). Interestingly, transplanted NPCs promoted significant functional …

Central nervous system (CNS) delivery of anti-inflammatory cytokines, such as interleukin 4 (IL4), holds promise as treatment for multiple sclerosis (MS). We have previously shown that short-term herpes simplex virus type 1-mediated IL4 gene therapy is able to inhibit experimental autoimmune encephalomyelitis (EAE), an animal model of MS, in mice and non-human primates. Here, we show that a single administration of an IL4-expressing helper-dependent adenoviral vector (HD-Ad) into the cerebrospinal fluid (CSF) circulation of immunocompetent mice allows persistent transduction of neuroepithelial cells and long-term (up to 5 months) CNS transgene expression without toxicity. Mice affected by chronic and relapsing EAE display clinical and neurophysiological recovery from the disease once injected with the IL4-expressing HD-Ad vector. The therapeutic effect is due to the ability of IL4 to increase, in inflamed CNS areas, chemokines (CCL1, CCL17 and CCL22) capable of recruiting regulatory T cells (CD4+CD69- CD25+Foxp3+) with suppressant functions. CSF delivery of HD-Ad vectors expressing anti-inflammatory molecules might represent a valuable therapeutic option for CNS inflammatory disorders.

Toll-like receptors participate in the inflammatory response and are now shown to act in neural precursor cells to regulate adult hippocampal neurogenesis. The dialogue between inflammatory components and neural precursor cells might have important consequences for central nervous system homeostasis and repair.

The well regulated activities of microglia and T cells specific to central nervous system (CNS) antigens can contribute to the protection of CNS neural cells and their renewal from adult neural stem/progenitor cells (aNPCs). Here we report that T cell-based vaccination of mice with a myelin-derived peptide, when combined with transplantation of aNPCs into the cerebrospinal fluid (CSF), synergistically promoted functional recovery after spinal cord injury. The synergistic effect was correlated with modulation of the nature and intensity of the local T cell and microglial response, expression of brain-derived neurotrophic factor and noggin protein, and appearance of newly formed neurons from endogenous precursor-cell pools. These results substantiate the contention that the local immune response plays a crucial role in recruitment of aNPCs to the lesion site, and suggest that similar immunological manipulations might also serve as a therapeutic means for controlled migration of stem/progenitor cells to other acutely injured CNS sites.

Spontaneous remyelination occurs in multiple sclerosis (MS) patients. However, this process is not robust enough to promote a functional and stable recovery of the myelin architecture in demyelinated areas of the central nervous system (CNS). As a consequence of this incomplete reparative process, the disease invariably progresses and patchy areas of demyelination-in which axonal damage and/or loss is a constant accompanying factor-increase over time and lead to the accumulation of irreversible neurological deficits. Thus, the development of cell-based therapies aimed to promote multifocal remyelination in MS represents one of the most challenging areas of investigation. Several cell-replacement strategies have been developed in the last few years. However, most of these therapeutic approaches-although consistently able to form new myelin sheaths around the transplantation site-are unrealistic owing to the multifocality of the demyelinating process and the inability to in vitro growth and differentiate large number of myelin-forming cells. Recently, promising cell-replacement therapies based on the use of stem cells have been proposed. However, before envisaging any potential human applications of such therapies we need to confront with some preliminary and still unsolved questions: (i) the ideal stem cell source for transplantation, (ii) the route of cell administration, (iii) the differentiation and persistence of stem cells into the targeted tissue and, last but not least, (iv) the functional and long-lasting integration of transplanted cells into the host tissue.

In degenerative disorders of the central nervous system (CNS), transplantation of neural multipotent (stem) precursor cells (NPCs) is aimed at replacing damaged neural cells. Here we show that in CNS inflammation, NPCs are able to promote neuroprotection by maintaining undifferentiated features and exerting unexpected immune-like functions. In a mouse model of chronic CNS inflammation, systemically injected adult syngeneic NPCs use constitutively activated integrins and functional chemokine receptors to selectively enter the inflamed CNS. These undifferentiated cells survive repeated episodes of CNS inflammation by accumulating within perivascular areas where reactive astrocytes, inflamed endothelial cells and encephalitogenic T cells produce neurogenic and gliogenic regulators. In perivascular CNS areas, surviving adult NPCs induce apoptosis of blood-borne CNS-infiltrating encephalitogenic T cells, thus protecting against chronic neural tissue loss as well as disease-related disability. These results indicate that undifferentiated adult NPCs have relevant therapeutic potential in chronic inflammatory CNS disorders because they display immune-like functions that promote long-lasting neuroprotection.

Spontaneous neural tissue repair occurs in patients affected by inflammatory and degenerative disorders of the central nervous system (CNS). However, this process is not robust enough to promote a functional and stable recovery of the CNS architecture. The development of cell-based therapies aimed at promoting brain repair, through damaged cell-replacement, is therefore foreseen. Several experimental cell-based strategies aimed at replacing damaged neural cells have been developed in the last 30 years. Although successful in promoting site-specific repair in focal CNS disorders, most of these therapeutic approaches have failed to foster repair in multifocal CNS diseases where the anatomical and functional damage is widespread. Stem cell-based therapies have been recently proposed and might represent in the near future a plausible alternative strategy in these disorders. However, before envisaging any human applications of stem cell-based therapies in neurological diseases, we need to consider some preliminary and still unsolved issues: (i) the ideal stem cell source for transplantation, (ii) the most appropriate route of stem cell administration, and, last but not least, (iii) the best approach to achieve an appropriate, functional, and long-lasting integration of transplanted stem cells into the host tissue.

Selective interference with immune processes in the central nervous system (CNS) is a very difficult task because of the limitations associated with the delivery of immuno modulatory molecules across the blood brain barrier. Systemic administration of immune-mediators, either by conventional routes or by intramuscularly or intravenous gene therapy, is hampered by severe side effects and alters immune-system functions also in peripheral organs. To overcome these problems, different gene therapy strategies have been developed to deliver immuno modulatory molecules directly within the central nervous system. The use of engineered CNS antigen-specific circulating cells as selective delivery vehicles, the direct injection of gene vectors into the brain parenchyma, or also the ependymal route, have been proposed as possible alternative gene therapy protocols to selectively interfere with immuno-pathological processes in the CNS. We will review the use of these CNS-targeted gene therapy protocols for the treatment of experimental autoimmune encephalomyelitis (EAE), the prototypical experimental immune-mediated disease of the CNS, and therefore discuss the relevance of these results for the therapy of multiple sclerosis (MS) the most common, immune-mediated, demyelinating disease of the CNS in humans.

Widespread demyelination and axonal loss are the pathological hallmarks of multiple sclerosis. The multifocal nature of this chronic inflammatory disease of the central nervous system complicates cellular therapy and puts emphasis on both the donor cell origin and the route of cell transplantation. We established syngenic adult neural stem cell cultures and injected them into an animal model of multiple sclerosis--experimental autoimmune encephalomyelitis (EAE) in the mouse--either intravenously or intracerebroventricularly. In both cases, significant numbers of donor cells entered into demyelinating areas of the central nervous system and differentiated into mature brain cells. Within these areas, oligodendrocyte progenitors markedly increased, with many of them being of donor origin and actively remyelinating axons. Furthermore, a significant reduction of astrogliosis and a marked decrease in the extent of demyelination and axonal loss were observed in transplanted animals. The functional impairment caused by EAE was almost abolished in transplanted mice, both clinically and neurophysiologically. Thus, adult neural precursor cells promote multifocal remyelination and functional recovery after intravenous or intrathecal injection in a chronic model of multiple sclerosis.