Bone Marrow Stem Cell Gene Therapy of Arylsulfatase A-Deficient Mice, Using an Arylsulfatase A Mutant That Is Hypersecreted from Retrovirally Transduced Donor-Type Cells

Abstract

Arylsulfatase A (ASA)-deficient mice represent an animal model for the fatal lysosomal storage disease metachromatic leukodystrophy, which is characterized by widespread intralysosomal deposition of sulfatide. Bone marrow stem cell gene therapy in mice, using a retroviral vector mediating expression of wild-type human ASA, has the potential to ameliorate the visceral pathology, but improves the prevailing brain disease and neurologic symptoms only marginally. One factor that influences the efficacy of bone marrow transplantation therapy in lysosomal storage diseases is the secretion level of the therapeutic enzyme from donor-type cells. Here we test the potential of a hypersecreted glycosylation variant of ASA. Although this mutant lacks mannose 6-phosphate residues it is taken up by cells by a mannose 6-phosphate receptor-independent pathway and causes partial metabolic correction of ASA-deficient mouse cells. Retrovirally mediated transfer of the mutant cDNA into ASA-deficient mice results in the sustained expression of the transgene. Serum levels argue for an increased secretion of the glycosylation mutant also in vivo. Tissue levels were reduced to 2% in liver and up to 40% in kidney compared with animals treated with the wild-type enzyme, indicating reduced endocytosis. Thus, the limited uptake of the variant enzyme outweighs the putative advantageous effect of improved supply. Although the mutant enzyme is able to correct the metabolic defect partially, histological examinations did not reveal any reduction of sulfatide storage in treated animals. Surprisingly, analysis of neurologic symptoms indicated a significant improvement of the gait pattern.

Correction of metachromatic leukodystrophy in the mouse model by transplantation of genetically modified hematopoietic stem cells

“…By performing detailed neurophysiological studies of MLD mice, we found significant impairments of central and peripher-al motor conduction (MCV reduction, increased F wave, MEP and CCT latencies), which provide useful functional parameters to monitor disease progression and therapeutic efficacy, and were not evaluated or assessable in previous studies (3,25,47,48). Behavioral tests demonstrated a clear decline in motor learning and coordination in aging MLD mice.…”

“…Previous transplantation studies using retroviral vector-transduced BM cells failed to observe significant benefits in NS pathology and functional parameters in MLD mice (47,48). It is likely that the successful outcome of our approach was dependent on the efficient HSC transduction and robust gene expression in their vascular and extravascular progeny reached by the optimized LVs and conditions used in this study.…”

Gene therapy for the neurological manifestations in lysosomal storage disorders

“…The most extensive studies have been performed in a model of metachromatic leukodystrophy and initially used donor cells modifi ed by fi rst-generation ␥ -retroviral vectors which demonstrated a modest correction of the neuropathology in the mouse model ( 150 ). Subsequent studies using more effi cient lentiviral-based vectors that transduced a greater number of the donor hematopoietic stem cells and that resulted in the secretion of higher levels of the enzyme (i.e., arylsulfatase A) completely prevented the development of neuropathology and behavioral abnormalities in mice ( 141,151 ).…”

Potential of mesenchymal stem cells in gene therapy approaches for inherited and acquired diseases

“…The proteins included the Escherichia coli β-galactosidase [15,40], GFP [14,18,19] and red fluorescent protein (DsRed) [19], as well as many therapeutic proteins, including coagulation factors VIII [12,16,17] and IX [41][42][43], IL-3 [15,44,45] and IL-7 [46], human growth hormone [41], human erythropoietin (hEPO) [47] and murine erythropoietin (mEPO) [48], arylsulfatase A [49,50], tyrosine hydroxylase GTP cyclohydrolase I [13,51], α-L-iduronidase [52], β-hexosaminidase A [53] and bone morphogenetic protein (BMP) [54]. It remains to be determined how MSCs perform relative to other mammalian expression systems, such as Chinese hamster ovary cells, in terms of transgene expression levels.…”