Successful treatment of metachromatic leukodystrophy using bone marrow transplantation of HoxB4 overexpressing cells

Macrophage transplantation rescues RNASET2-deficient leukodystrophy by replacing deficient microglia in a zebrafish model

RNASET2-deficient leukodystrophy is a rare infantile white matter disorder mimicking a viral infection and resulting in severe psychomotor impairments. Despite its severity, there is little understanding of cellular mechanisms of pathogenesis and no treatments. Recent research using the rnaset2 mutant zebrafish model has suggested that microglia may be the drivers of the neuropathology, due to their failure to digest apoptotic debris during neurodevelopment. Therefore, we developed a strategy for microglial replacement through transplantation of adult whole kidney marrow-derived macrophages into embryonic hosts. Using live imaging, we revealed that transplant-derived macrophages can engraft within host brains and express microglia-specific markers, suggesting the adoption of a microglial phenotype. Tissue-clearing strategies revealed the persistence of transplanted cells in host brains beyond embryonic stages. We demonstrated that transplanted cells clear apoptotic cells within the brain, as well as rescue overactivation of the antiviral response otherwise seen in mutant larvae. RNA sequencing at the point of peak transplant-derived cell engraftment confirms that transplantation can reduce the brain-wide immune response and particularly, the antiviral response, in rnaset2-deficient brains. Crucially, this reduction in neuroinflammation resulted in behavioral rescue-restoring rnaset2 mutant motor activity to wild-type (WT) levels in embryonic and juvenile stages. Together, these findings demonstrate the role of microglia as the cellular drivers of neuropathology in rnaset2 mutants and that macrophage transplantation is a viable strategy for microglial replacement in the zebrafish. Therefore, microglia-targeted interventions may have therapeutic benefits in RNASET2-deficient leukodystrophy.

Treatment of adult metachromatic leukodystrophy model mice using intrathecal administration of type 9 AAV vector encoding arylsulfatase A

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by an arylsulfatase A (ARSA) deficiency and characterized by severe neurological symptoms resulting from demyelination within the central and peripheral nervous systems. We investigated the feasibility and efficacy of intrathecal administration of a type 9 adeno-associated viral vector encoding ARSA (AAV9/ARSA) for the treatment of 6-week-old MLD model mice, which are presymptomatic, and 1-year-old mice, which exhibit neurological abnormalities. Immunohistochemical analysis following AAV9/ARSA administration showed ARSA expression within the brain, with highest activities in the cerebellum and olfactory bulbs. In mice treated at 1 year, alcian blue staining and quantitative analysis revealed significant decreases in stored sulfatide. Behaviorally, mice treated at 1 year showed no improvement in their ability to traverse narrow balance beams as compared to untreated mice. By contrast, MLD mice treated at 6 weeks showed significant decreases in stored sulfatide throughout the entire brain and improved ability to traverse narrow balance beams. These findings suggest intrathecal administration of an AAV9/ARSA vector is a promising approach to treating genetic diseases of the central nervous system, including MLD, though it may be essential to begin therapy before the onset of neurological symptoms.

Identification of candidate biomarkers in converting and non-converting clinically isolated syndrome by proteomics analysis of cerebrospinal fluid

Multiple sclerosis (MS) often starts in the form of clinically isolated syndrome (CIS) and only some of the CIS patients progress to relapsing-remitting MS (RRMS). Biomarkers to predict conversion from CIS to MS are thus greatly needed for making correct treatment decisions. To identify a predictive cerebrospinal fluid (CSF) protein, we analyzed the first-attack CSF samples of CIS patients who converted (CIS-MS) (n = 23) and did not convert (CIS-CIS) (n = 19) to RRMS in a follow-up period of 5 years using proteomics analysis by liquid chromatography tandem-mass spectrometry (LC-MS/MS) and verified by ELISA. Label-free differential proteomics analysis of CSF ensured that 637 proteins were identified and 132 of these proteins were found to be statistically significant. Further investigation with the ingenuity pathway analysis (IPA) software led to identification of three pathway networks mostly comprised proteins involved in inflammatory response, cellular growth and tissue proliferation. CSF levels of four of the most differentially expressed proteins belonging to the cellular proliferation network function, chitinase-3-like protein 1 (CHI3L1), tumor necrosis factor receptor superfamily member 21 (TNFRSF21), homeobox protein Hox-B3 (HOXB3) and iduronate 2-sulfatase (IDS), were measured by ELISA. CSF levels of HOXB3 were significantly increased in CIS-MS patients. Our results indicate that cell and tissue proliferation functions are dysregulated in MS as early as the first clinical episode. HOXB3 has emerged as a potential novel biomarker which might be used for prediction of CIS-MS conversion.

Checkpoints to the Brain: Directing Myeloid Cell Migration to the Central Nervous System

Myeloid cells are a unique subset of leukocytes with a diverse array of functions within the central nervous system during health and disease. Advances in understanding of the unique properties of these cells have inspired interest in their use as delivery vehicles for therapeutic genes, proteins, and drugs, or as "assistants" in the clean-up of aggregated proteins and other molecules when existing drainage systems are no longer adequate. The trafficking of myeloid cells from the periphery to the central nervous system is subject to complex cellular and molecular controls with several 'checkpoints' from the blood to their destination in the brain parenchyma. As important components of the neurovascular unit, the functional state changes associated with lineage heterogeneity of myeloid cells are increasingly recognized as important for disease progression. In this review, we discuss some of the cellular elements associated with formation and function of the neurovascular unit, and present an update on the impact of myeloid cells on central nervous system (CNS) diseases in the laboratory and the clinic. We then discuss emerging strategies for harnessing the potential of site-directed myeloid cell homing to the CNS, and identify promising avenues for future research, with particular emphasis on the importance of untangling the functional heterogeneity within existing myeloid subsets.

Delivering drugs to the central nervous system: an overview

Developing therapies for the brain is perhaps the greatest challenge facing modern medicine today. While a great many potential therapies show promise in animal models, precious few make it to approval or are even studied in human patients. The particular challenges to the translation of neurotherapeutics to the clinic are many, but a major barrier is difficulty in delivering therapeutics into the brain. The goal of this workshop was to present ways to deliver therapeutics to the brain, including the limitations of each method, and describe ways to track their delivery, safety, and efficacy. Solving the problem of delivery will aid translation of therapeutics for patients suffering from neurodegeneration and other disorders of the brain.

Long-term correction of biochemical and neurological abnormalities in MLD mice model by neonatal systemic injection of an AAV serotype 9 vector

As both the immune system and the blood-brain barrier (BBB) are likely to be developmentally immature in the perinatal period, neonatal gene transfer may be useful for the treatment of lysosomal storage disease (LSD) with neurological involvements such as metachromatic leukodystrophy (MLD). In this experiment, we examined the feasibility of single-strand adeno-associated viral serotype-9 (ssAAV9)-mediated systemic neonatal gene therapy of MLD mice. ssAAV9 vector expressing human arylsulfatase A (ASA) and green fluorescent protein (GFP) (ssAAV9/ASA) was injected into the jugular vein of newborn MLD mice. High levels of ASA expression were observed in the muscle and heart for at least 15 months. ASA was continuously secreted into plasma without development of antibodies against ASA. Global gene transfer into the brain and spinal cord (SC), across the BBB, and long-term ASA expression in the central nervous system were detected in treated mice. Significant inhibition of the accumulation of sulfatide (Sulf) in the brain and cervical SC was confirmed by Alcian blue staining and biochemical analysis of the Sulf content. In a behavior test, treated mice showed a greater ability to traverse narrow balance beams than untreated mice. These data clearly demonstrate that MLD mice model can be effectively treated through neonatal systemic injection of ssAAV9/ASA.

Advances and pitfalls of cell therapy in metabolic leukodystrophies

Leukodystrophies are a group of disorders characterized by myelin dysfunction, either at the level of myelin formation or maintenance, that affect the central nervous system (CNS) and also in some cases, to a lesser extent, the peripheral nervous system (PNS). Although these genetic-based disorders are generally rare, all together they have a significant impact in the society, with an estimated overall incidence of 1 in 7,663 live births. Currently, there is no cure for leukodystrophies, and the development of effective treatments remains challenging. Not only leukodystrophies generally progress very fast, but also most are multifocal needing the simultaneous targeting at multiple sites. Moreover, as the CNS is affected, the blood-brain barrier (BBB) limits the efficacy of treatment. Recently, interest on cell therapy has increased, and the leukodystrophies for which metabolic correction is needed have become first-choice candidates for cell-based clinical trials. In this review, we present and discuss the available cell transplantation therapies in metabolic leukodystrophies including fucosidosis, X-linked adrenoleukodystrophy, metachromatic leukodystrophy, Canavan disease, and Krabbe's disease. We will discuss the latest advances of cell therapy and its pitfalls in this group of disorders, taking into account, among others, the limitations imposed by reduced cell migration in multifocal conditions, the need to achieve corrective enzyme threshold levels, and the growing awareness that not only myelin but also the associated axonopathy needs to be targeted in some leukodystrophies.

Developing treatment options for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) represents a devastating lysosomal storage disease characterized by intralysosomal accumulation of the sphingolipid sulfatide in various tissues. Three types of the disease are currently distinguished: the late-infantile, which is the most commonly observed, the juvenile and the adult type. Demyelination represents the main histopathological feature of the disorder, leading to neurological impairment with no curative treatment currently available. Nevertheless, the increased scientific interest on the disease has led to the experimental use of innovative therapeutic approaches in animal models, aiming to provide an effective therapeutic regimen for human patients, as well. This paper provides an overview of developing treatment options among patients with MLD. Apart from hematopoietic stem cell transplantation, already in use for decades, other recent data discussed includes umbilical cord blood and stem cell transplantation, enzyme replacement therapy, gene therapy and autologous hematopoietic transplantation of genetically modified stem cells. Gene therapy with oligodedroglial, neural progenitor, embryonic and microencapsulated recombinant cells represents add-on treatment options still on experimental level.

Global gene transfer into the CNS across the BBB after neonatal systemic delivery of single-stranded AAV vectors

Central nervous system (CNS) disorders are important targets for gene therapy; however, delivery of therapeutic proteins and/or genes to the brain remains a major challenge due to the difficulty of efficiently delivering viral vectors across the blood-brain barrier (BBB). In the present work, we tested the ability of several single-stranded adeno-associated viral (ssAAV) serotypes to deliver transgenes to the brain and spinal cord in neonatal mice. We injected ssAAV vectors encoding GFP (serotype-1, -8, -9 and -10: 1.5×10(11) vector genomes each) into the jugular vein of neonatal mice and assessed GFP expression immunohistochemically. Strong GFP signals were detected in both the brain and spinal cord after injection of any of these serotypes. ssAAV serotype-9 mediated gene transfer was the most efficient. GFP expression was detected throughout the brain, including the cortex, cerebellum, olfactory bulb and brainstem and was sustained for at least 18months. Immunohistochemical staining showed that the GFP signals were detected in GFAP positive astrocytes, NeuN positive neurons, and Calbindin positive purkinje cells. Our data suggest that systemic neonatal injection of ssAAV is an effective strategy for delivering transgenes to target neuronal systems that are not accessible to viral vectors in adult animals. These vectors should prove highly useful for efficient and long-term overexpression or downregulation of genes in CNS and spinal cord and could be a useful means of treating genetic neurological diseases.

Therapeutic approaches for lysosomal storage diseases

The lysosomal storage disorders (LSDs) comprise a heterogeneous group of inborn errors of metabolism characterized by tissue substrate deposits, most often caused by a deficiency of the enzyme normally responsible for catabolism of various byproducts of cellular turnover. Individual entities are typified by involvement of multiple body organs, in a pattern reflecting the sites of substrate storage. It is increasingly recognized that one or more processes, such as aberrant inflammation, dysregulation of apoptosis and/or defects of autophagy, may mediate organ dysfunction or failure. Several therapeutic options for various LSDs have been introduced, including hematopoietic stem cell transplantation, enzyme replacement therapy and substrate reduction therapy. Additional strategies are being explored, including the use of pharmacological chaperones and gene therapy. Most LSDs include a variant characterized by primary central nervous system (CNS) involvement. At present, therapy of the CNS manifestations remains a major challenge because of the inability to deliver therapeutic agents across the intact blood-brain barrier. With improved understanding of underlying disease mechanisms, additional therapeutic options may be developed, complemented by various strategies to deliver the therapeutic agent(s) to recalcitrant sites of pathology such as brain, bones and lungs.