Retrovirus vector-mediated correction and cross-correction of lysosomal alpha-mannosidase deficiency in human and feline fibroblasts

Promoter considerations in the design of lentiviral vectors for use in treating lysosomal storage diseases

More than 50 lysosomal storage diseases (LSDs) are associated with lysosomal dysfunctions with the frequency of 1:5,000 live births. As a result of missing enzyme activity, the lysosome dysfunction accumulates undegraded or partially degraded molecules, affecting the entire body. Most of them are life-threatening diseases where patients could die within the first or second decade of life. Approximately 20 LSDs have the approved treatments, which do not provide the cure for the disorder. Therefore, the delivery of missing genes through gene therapy is a promising approach for LSDs. Over the years, ex vivo lentiviral-mediated gene therapy for LSDs has been approached using different strategies. Several clinical trials for LSDs are under investigation.Ex vivo lentiviral-mediated gene therapy needs optimization in dose, time of delivery, and promoter-driven expression. Choosing suitable promoters seems to be one of the important factors for the effective expression of the dysfunctional enzyme. This review summarizes the research on therapy for LSDs that has used different lentiviral vectors, emphasizing gene promoters.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

Diffusion Tensor Imaging for Assessing Brain Gray and White Matter Abnormalities in a Feline Model of α-Mannosidosis

α-Mannosidosis (AMD) is an autosomal recessively inherited lysosomal storage disorder affecting brain function and structure. We performed ex vivo and in vivo diffusion tensor imaging (DTI) on the brains of AMD-affected cats to assess gray and white matter abnormalities. A multi-atlas approach was used to generate a brain template to process the ex vivo DTI data. The probabilistic label method was used to measure fractional anisotropy (FA), mean diffusivity, axial diffusivity, and radial diffusivity values from gray and white matter regions from ex vivo DTI. Regional analysis from various regions of the gray matter (frontal cortex, cingulate gyrus, caudate nucleus, hippocampus, thalamus, and occipital cortex), and white matter (corpus callosum, corticospinal tract, cerebral peduncle, external and internal capsule) was also performed on both ex vivo and in vivo DTI. Ex vivo DTI revealed significantly reduced FA from both gray and white matter regions in AMD-affected cats compared to controls. Significantly reduced FA was also observed from in vivo DTI of AMD-affected cats compared to controls, with lower FA values observed in all white matter regions. We also observed significantly increased axial and radial diffusivity values in various gray and white matter regions in AMD cats from both ex vivo and in vivo DTI data. Imaging findings were correlated with histopathologic analyses suggesting that DTI studies can further aid in the characterization of AMD by assessing the microstructural abnormalities in both white and gray matter.

Hematopoietic stem cell gene therapy for the multisystemic lysosomal storage disorder cystinosis

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders (LSDs). The defective gene is CTNS encoding the lysosomal cystine transporter, cystinosin. Cystine accumulates in all tissues and leads to organ damage including end-stage renal disease. Using the Ctns(-/-) murine model for cystinosis, we tested the use of hematopoietic stem and progenitor cells (HSPC) genetically modified to express a functional CTNS transgene using a self-inactivating-lentiviral vector (SIN-LV). We showed that transduced cells were capable of decreasing cystine content in all tissues and improved kidney function. Transduced HSPC retained their differentiative capabilities, populating all tissue compartments examined and allowing long-term expression of the transgene. Direct correlation between the levels of lentiviral DNA present in the peripheral blood and the levels present in tissues were demonstrated, which could be useful to follow future patients. Using a new model of cystinosis, the DsRed Ctns(-/-) mice, and a LV driving the expression of the fusion protein cystinosin-enhanced green fluorescent protein (eGFP), we showed that cystinosin was transferred from CTNS-expressing cells to Ctns-deficient adjacent cells in vitro and in vivo. This transfer led to cystine decreases in Ctns-deficient cells in vitro. These data suggest that the mechanism of cross-correction is possible in cystinosis.

Over-expression of human lysosomal alpha-mannosidase in mouse embryonic stem cells

Alpha-mannosidosis is a lysosomal storage disorder characterised by the lysosomal accumulation of mannose-containing oligosaccharides and a range of pathological consequences, caused by a deficiency of the lysosomal enzyme alpha-mannosidase. One of the major features of alpha-mannosidosis is progressive neurological decline, for which there is no safe and effective treatment. Implantation of stem cells into the central nervous system has been proposed as a potential therapy for these disorders. We report the construction and characterisation of mouse embryonic stem cell lines for the sustained over-expression of recombinant human lysosomal alpha-mannosidase (rhalphaM). Two vectors (involving recombinant human alpha-mannosidase expression driven by either the chicken beta-actin promoter/CMV enhancer or by the elongation factor 1-alpha promoter) were constructed and used to transfect mouse D3 embryonic stem cells. Selected clonal cell lines were isolated and tested to evaluate their expression of recombinant human alpha-mannosidase. Stem cell clones transfected with the chicken beta-actin promoter/CMV enhancer maintained rhalphaM expression levels throughout differentiation. This expression was not markedly elevated above background. In contrast, the vector incorporating the elongation factor 1-alpha promoter facilitated substantial over-expression of alpha-mannosidase when analysed out to 21 days of differentiation in stably transfected cell lines. The highest expressing cell line was found to qualitatively retain a similar differentiation potential to untransfected cells, and to secrete alpha-mannosidase that could mediate a reduction in the level of oligosaccharides stored by human alpha-mannosidosis skin fibroblasts. These results suggest potential for the use of this cell line for investigation of a stem cell therapy approach to treat alpha-mannosidosis.

Α genetic fusion construct between the tetanus toxin C fragment and the lysosomal acid hydrolase β-glucuronidase expresses a bifunctional protein with enhanced secretion and neuronal uptake

The neurotropic atoxic fragment of tetanus toxin has been used as a carrier for transporting macromolecules into neurons but all studies to date have tested cytosolic proteins. In this study we investigated the effect of a genetic addition of the tetanus toxin C fragment sequence to a lysosomal enzyme which contains a signal sequence for insertion into the membrane-bound compartment and must be extensively modified in the endoplasmic reticulum (ER) and Golgi to attain functionality. In-frame fusion constructs between the atoxic C fragment and beta-glucuronidase were compared with the wild-type enzyme for: (i) enzymatic activity; (ii) heat stability; (iii) pH dependence; (iv) specific activity; (v) apparent molecular mass and (vi) receptor-mediated uptake by fibroblasts and neurons. The modified proteins had biochemical properties similar to wild-type enzyme but exhibited different enzyme secretion profiles. Addition of the secreted fusion enzyme to cultures of primary neurons showed significantly increased neuronal uptake of the modified protein compared with the wild-type, demonstrating the bifunctionality of the chimeric molecule.

Gene transfer strategies for correction of lysosomal storage disorders

Lysosomal storage diseases (LSDs) represent a large group of monogenic disorders of metabolism, which affect approximately 1 in 5000 live births. LSDs result from a single or multiple deficiency of specific lysosomal hydrolases, the enzymes responsible for the luminal catabolization of macromolecular substrates. The consequent accumulation of undigested metabolites in lysosomes leads to polysystemic dysfunction, including progressive neurologic deterioration, mental retardation, visceromegaly, blindness, and early death. In general, the residual amount of functional enzyme in lysosomes determines the severity and age at onset of the clinical symptoms, implying that even modest increases in enzyme activity might affect a cure. A key feature on which therapy for LSDs is based is the ability of soluble enzyme precursors to be secreted by one cell type and reinternalize by neighboring cells via receptor-mediated endocytosis and routed to lysosomes, where they function normally. In principle, somatic gene therapy could be the preferred treatment for LSDs if the patient's own cells could be genetically modified in vitro or in vivo to constitutively express high levels of the correcting enzyme and become the source of the enzyme in the patient. Both ex vivo and in vivo gene transfer methods have been experimented with for gene therapy of lysosomal disorders. Several of these methods have proved efficient for the transfer of genetic material into deficient cells in culture and reconstitution of enzyme activity. However, the same methods applied to humans or animal models have been giving inconsistent results, the bases of which are not fully understood. A broader knowledge of disease pathogenesis, facilitated by available, faithful animal models of LSDs, coupled to the development of better gene transfer systems as well as the understanding of vector host interactions will make somatic gene therapy for these devastating and complex diseases the most suitable therapeutic approach.

T-cell-depleted peripheral blood stem cell transplantation for alpha-mannosidosis

Alpha-mannosidosis (alpha-mannosidosis) is a lysosomal storage disease characterized by accumulation of oligosaccharides in various tissues leading to symptoms such as coarse facial features, dysostosis multiplex, hearing disabilities, mental developmental delay and skeletal involvement (dysostosis multiplex). Without treatment, the severe infantile onset form of this autosomal recessive disease leads to progressive neurodegeneration and sometimes to early death. Stem cell transplantation has been shown to be an effective treatment. In the five patients published so far, correction of skeletal abnormalities and improvement of neuropsychological capabilities have been observed. We report the first patient who received a T-cell-depleted peripheral blood stem cell transplantation (PBSCT) for alpha-mannosidosis. The diagnosis of alpha-mannosidosis was made at the age of 14 months. At the age of 24 months, he underwent PBSCT with T-cell depletion by CD34-positive selection from his HLA phenotypically identical mother. Conditioning was carried out with busulfan (20 mg/kg), cyclophosphamide (200 mg/kg), OKT3 and methylprednisolone. The patient is alive and well 27 months after PBSCT and has made significant developmental progress. The pattern of urinary oligosaccharides has returned to almost normal. CD34-positive-selected PBSCT is a feasible option to reduce risk for GVHD for these patients.

The Feline Genome Project

The compilation of a dense gene map and eventually a whole genome sequence (WGS) of the domestic cat holds considerable value for human genome annotation, for veterinary medicine, and for insight into the evolution of genome organization among mammals. Human association and veterinary studies of the cat, its domestic breeds, and its charismatic wild relatives of the family Felidae have rendered the species a powerful model for human hereditary diseases, for infectious disease agents, for adaptive evolutionary divergence, for conservation genetics, and for forensic applications. Here we review the advantages, rationale, and present strategy of a feline genome project, and we describe the disease models, comparative genomics, and biological applications posed by the full resolution of the cat's genome.

Comparative genome organization of human, murine, and feline MHC class II region

To study comparative molecular dynamics in the genesis of the major histocompatibility complex (MHC), we determined a complete nucleotide sequence spanning 758,291 bp of the domestic cat (Felis catus) extended and classical class II region. The feline class II MHC includes 44 genes (31 predicted to be expressed) which display DNA sequence homology and ordered gene synteny with human HLA and mouse H2, in extended class II and centromere proximal regions (DM to DO) of the classical class II region. However, remarkable genomic alterations including gene gain and loss plus size differentials of 250 kb are evident in comparisons of the cat class II with those of human and mouse. The cat MHC lacks the entire DQ region and retains only relict pseudogene homologs of DP genes, compensated by expansion and reorganization of seven modern DR genes. Repetitive gene families within the feline MHC comprise 35% of the feline MHC with very different density and abundance of GC levels, SINES, LINES, STRs, and retro-elements from the same repeats in human and mouse MHC. Comparison of the feline MHC with the murine and human MHC offers a detailed view of the consequences of genome organization in three mammalian lineages.

Histopathology, electrodiagnostic testing, and magnetic resonance imaging show significant peripheral and central nervous system myelin abnormalities in the cat model of alpha-mannosidosis

Alpha-mannosidosis is a disease caused by the deficient activity of alpha-mannosidase, a lysosomal hydrolase involved in the degradation of glycoproteins. The disease is characterized by the accumulation of mannose-rich oligosaccharides within lysosomes. The purpose of this study was to characterize the peripheral nervous system (PNS) and central nervous system (CNS) myelin abnormalities in cats from a breeding colony with a uniform mutation in the gene encoding alpha-mannosidase. Three affected cats and 3 normal cats from 2 litters were examined weekly from 4 to 18 wk of age. Progressively worsening neurological signs developed in affected cats that included tremors, loss of balance, and nystagmus. In the PNS, affected cats showed slow motor nerve conduction velocity and increased F-wave latency. Single nerve fiber teasing revealed significant demyelination/remyelination in affected cats. Mean G-ratios of nerves showed a significant increase in affected cats compared to normal cats. Magnetic resonance imaging of the CNS revealed diffuse white matter signal abnormalities throughout the brain of affected cats. Quantitative magnetization transfer imaging showed a 8%-16% decrease in the magnetization transfer ratio in brain white matter of affected cats compared to normal cats, consistent with myelin abnormalities. Histology confirmed myelin loss throughout the cerebrum and cerebellum. Thus, histology, electrodiagnostic testing, and magnetic resonance imaging identified significant myelination abnormalities in both the PNS and CNS that have not been described previously in alpha-mannosidosis.

Retrovirus-mediated gene transfer and galactocerebrosidase uptake into twitcher glial cells results in appropriate localization and phenotype correction

Galactocerebrosidase (GALC) is deficient in all tissues from human patients and animal models with globoid cell leukodystrophy (GLD) or Krabbe disease. The deficiency results in decreased lysosomal catabolism of certain galactolipids including galactosylceramide and psychosine that are synthesized maximally during myelination. According to current theories, the accumulation of psychosine in humans and animals with GLD induces oligodendrocyte degeneration and myelination ceases. Transduction of oligodendrocytes from twitcher mice with a retroviral vector containing the GALC cDNA can correct the enzyme deficiency in these cells. Our data show that twitcher astrocytes and oligodendrocytes can internalize exogenous GALC, as well as donate the enzyme to the mutant glial cells. Antibodies against human GALC localized the GALC antigen in retrovirally transduced cells and cells receiving enzyme via cell to cell secretion and uptake to the lysosomal fraction. In fact immunocytochemical studies in transduced oligodendrocytes revealed that the GALC colocalizes in vesicles lysosomal-associated membrane protein-2 (LAMP2) (+). Moreover, labeling cells with anti-GALC and a marker for oligodendrocytes demonstrated that, upon differentiation, transduced, twitcher oligodendrocytes attained the normal branched process configuration, while untransduced cells show only abnormal morphology. Phenotype correction in mutant oligodendrocytes has also been observed after enzyme transfer. These studies indicate that GALC activity supplied to cultured oligodendrocytes from twitcher mice by different methods can correct the pathological phenotype of these cells.