Lentiviral haemopoietic stem-cell gene therapy in early-onset metachromatic leukodystrophy: an ad-hoc analysis of a non-randomised, open-label, phase 1/2 trial

BACKGROUND

Metachromatic leukodystrophy (a deficiency of arylsulfatase A [ARSA]) is a fatal demyelinating lysosomal disease with no approved treatment. We aimed to assess the long-term outcomes in a cohort of patients with early-onset metachromatic leukodystrophy who underwent haemopoietic stem-cell gene therapy (HSC-GT).

METHODS

This is an ad-hoc analysis of data from an ongoing, non-randomised, open-label, single-arm phase 1/2 trial, in which we enrolled patients with a molecular and biochemical diagnosis of metachromatic leukodystrophy (presymptomatic late-infantile or early-juvenile disease or early-symptomatic early-juvenile disease) at the Paediatric Clinical Research Unit, Ospedale San Raffaele, in Milan. Trial participants received HSC-GT, which consisted of the infusion of autologous HSCs transduced with a lentiviral vector encoding ARSA cDNA, after exposure-targeted busulfan conditioning. The primary endpoints of the trial are safety (toxicity, absence of engraftment failure or delayed haematological reconstitution, and safety of lentiviral vector-tranduced cell infusion) and efficacy (improvement in Gross Motor Function Measure [GMFM] score relative to untreated historical controls, and ARSA activity, 24 months post-treatment) of HSC-GT. For this ad-hoc analysis, we assessed safety and efficacy outcomes in all patients who had received treatment and been followed up for at least 18 months post-treatment on June 1, 2015. This trial is registered with ClinicalTrials.gov, number NCT01560182.

FINDINGS

Between April, 2010, and February, 2013, we had enrolled nine children with a diagnosis of early-onset disease (six had late-infantile disease, two had early-juvenile disease, and one had early-onset disease that could not be definitively classified). At the time of analysis all children had survived, with a median follow-up of 36 months (range 18-54). The most commonly reported adverse events were cytopenia (reported in all patients) and mucositis of different grades of severity (in five of nine patients [grade 3 in four of five patients]). No serious adverse events related to the medicinal product were reported. Stable, sustained engraftment of gene-corrected HSCs was observed (a median of 60·4% [range 14·0-95·6] lentiviral vector-positive colony-forming cells across follow-up) and the engraftment level was stable during follow-up; engraftment determinants included the duration of absolute neutropenia and the vector copy number of the medicinal product. A progressive reconstitution of ARSA activity in circulating haemopoietic cells and in the cerebrospinal fluid was documented in all patients in association with a reduction of the storage material in peripheral nerve samples in six of seven patients. Eight patients, seven of whom received treatment when presymptomatic, had prevention of disease onset or halted disease progression as per clinical and instrumental assessment, compared with historical untreated control patients with early-onset disease. GMFM scores for six patients up to the last follow-up showed that gross motor performance was similar to that of normally developing children. The extent of benefit appeared to be influenced by the interval between HSC-GT and the expected time of disease onset. Treatment resulted in protection from CNS demyelination in eight patients and, in at least three patients, amelioration of peripheral nervous system abnormalities, with signs of remyelination at both sites.

INTERPRETATION

Our ad-hoc findings provide preliminary evidence of safety and therapeutic benefit of HSC-GT in patients with early-onset metachromatic leukodystrophy who received treatment in the presymptomatic or very early-symptomatic stage. The results of this trial will be reported when all 20 patients have achieved 3 years of follow-up.

FUNDING

Italian Telethon Foundation and GlaxoSmithKline.

The future for treatment by bone marrow transplantation for adrenoleukodystrophy, metachromatic leukodystrophy, globoid cell leukodystrophy and Hurler syndrome

Within the past decade, bone marrow transplantation has been applied to over 200 patients worldwide with the intention of treating storage diseases. Bone marrow transplantation has provided a method for treatment of adrenoleukodystrophy, metachromatic leukodystrophy, globoid cell leukodystrophy and Hurler syndrome. After engraftment, significant improvement in the clinical course of each of these diseases occurs. Survival data of engrafted patients are superior to those of non-transplanted. Engraftment and the resulting enzymatic reconstitution are concordant. Outcomes based on neuropsychological tests indicate continued maintenance and in some cases increase in cognitive function. Magnetic resonance imaging as well as spectroscopic examinations of the brain provide further evidence that positive changes occur in the central nervous system following long-term engraftment. A better quality of life follows engraftment. Greater gains from use of bone marrow transplantation for these particular storage diseases will occur in the future. Earlier diagnosis will allow bone marrow transplantation in the presymptomatic stage at a younger age, providing an enhancement of positive effects noted from such treatment. At the same time, advances in bone marrow technology will serve to reduce the risk factors involved with the bone marrow transplantation process itself. These two factors taken together will be more than additive in providing benefits from use of bone marrow transplantation.

Alterations of brain metabolites in metachromatic leukodystrophy as detected by localized proton magnetic resonance spectroscopy in vivo

The brain morphology and chemistry of seven children with late infantile (4/7) and juvenile (3/7) forms of metachromatic leukodystrophy (MLD) were investigated by magnetic resonance imaging (MRI) and localized proton magnetic resonance spectroscopy (MRS). Patients who were examined at least 6 months after the onset of symptoms (6/7) had severe leukodystrophic changes on MRI. Proton MRS revealed a marked reduction of the neuronal marker N-acetylaspartate in white and grey matter and elevated lactate in demyelinated areas. In contrast to other leukodystrophies MLD patients showed a generalized increase of brain myo-inositol (2- to 3-fold in white matter), indicating a specific role in the pathophysiology of demyelination in MLD.

Generation of Human Induced Pluripotent Stem Cell-Derived Bona Fide Neural Stem Cells for Ex Vivo Gene Therapy of Metachromatic Leukodystrophy

Allogeneic fetal‐derived human neural stem cells (hfNSCs) that are under clinical evaluation for several neurodegenerative diseases display a favorable safety profile, but require immunosuppression upon transplantation in patients. Neural progenitors derived from patient‐specific induced pluripotent stem cells (iPSCs) may be relevant for autologous ex vivo gene‐therapy applications to treat genetic diseases with unmet medical need. In this scenario, obtaining iPSC‐derived neural stem cells (NSCs) showing a reliable “NSC signature” is mandatory. Here, we generated human iPSC (hiPSC) clones via reprogramming of skin fibroblasts derived from normal donors and patients affected by metachromatic leukodystrophy (MLD), a fatal neurodegenerative lysosomal storage disease caused by genetic defects of the arylsulfatase A (ARSA) enzyme. We differentiated hiPSCs into NSCs (hiPS‐NSCs) sharing molecular, phenotypic, and functional identity with hfNSCs, which we used as a “gold standard” in a side‐by‐side comparison when validating the phenotype of hiPS‐NSCs and predicting their performance after intracerebral transplantation. Using lentiviral vectors, we efficiently transduced MLD hiPSCs, achieving supraphysiological ARSA activity that further increased upon neural differentiation. Intracerebral transplantation of hiPS‐NSCs into neonatal and adult immunodeficient MLD mice stably restored ARSA activity in the whole central nervous system. Importantly, we observed a significant decrease of sulfatide storage when ARSA‐overexpressing cells were used, with a clear advantage in those mice receiving neonatal as compared with adult intervention. Thus, we generated a renewable source of ARSA‐overexpressing iPSC‐derived bona fide hNSCs with improved features compared with clinically approved hfNSCs. Patient‐specific ARSA‐overexpressing hiPS‐NSCs may be used in autologous ex vivo gene therapy protocols to provide long‐lasting enzymatic supply in MLD‐affected brains. Stem Cells Translational Medicine2017;6:352–368

Juvenile metachromatic leukodystrophy 10 years post transplant compared with a non-transplanted cohort

Metachromatic leukodystrophy (MLD) is a rare inborn error of metabolism leading to severe neurological symptoms and early death. Hematopoietic SCT (HSCT) is considered a treatment option, but results are inconsistent and comparison with natural history is practically missing. We compare a girl with juvenile MLD 10 years after allogeneic HSCT not only with her untreated sister, but also with a large cohort of untreated patients. The girl received HSCT at the age of 5 years when first motor signs appeared. Over 10 years she was stable with respect to her clinical course and gained cognitive abilities. Magnetic resonance imaging (MRI) showed clear regression of white matter changes and magnetic resonance spectroscopy (MRS) demonstrated a reversal of the initial choline increase and N-acetyl-aspartate (NAA) decrease. Only axonal demyelinating neuropathy showed some progression. Her gross motor function and MRI-scores were clearly better compared with her sister and the cohort of untreated patients. Difference to her sister became apparent only 4 years after HSCT. We conclude that HSCT, early in the course of disease, can lead to stabilization of juvenile MLD with a course clearly different from the natural history. HSCT may prevent disease progression, if performed sufficient time before loss of walking, which typically initiates rapid deterioration.

Slow progression of juvenile metachromatic leukodystrophy 6 years after bone marrow transplantation

Metachromatic leukodystrophy refers to a group of genetic neurologic diseases caused by deficiencies of the enzyme arylsulfatase A and the resulting accumulation of sulfatides in white matter. Bone marrow transplantation has been advocated as a treatment in an attempt to correct the enzyme deficiency. Such a transplant was performed in 1991 in a 16-year-old girl with a form of late juvenile metachromatic leukodystrophy caused by a homozygous P426L mutation in the arylsulfatase A gene. Engraftment was prompt and resulted in constant enzymatic normalization of circulating lymphocytes. The elevated urinary excretion of sulfatides remained unaffected. Clinical findings up until transplantation consisted of gait disturbances, impairment of cognitive functioning, and deterioration in school performance over several years. During a 6-year follow-up period, the patient's condition was subject to major fluctuations but, on the whole, findings showed slow neurologic and neurophysiologic deterioration. The clinical course observed after bone marrow transplantation probably more or less reflects the natural course expected in this form of late-onset metachromatic leukodystrophy.

Haematopoietic stem cell transplantation does not retard disease progression in the psycho-cognitive variant of late-onset metachromatic leukodystrophy

Haematopoietic stem cell transplantation has an unproven role in the management of late-onset metachromatic leukodystrophy: theoretically justified through the engraftment of enzyme-replete haematopoietic progenitors and restoration of capacity for sulphatide catabolism in neural tissue through enzyme recapture, the long-term outcome is unknown. The rarity of the psycho-cognitive variant and slow progression of late-onset disease impairs evaluation of treatment. We report detailed clinical and neuropsychological assessments after haematopoietic stem-cell transplantation in a patient with a late-onset psycho-cognitive form of metachromatic leukodystrophy. Cognitive decline, indistinguishable from the natural course of the disease, was serially documented over 11 years despite complete donor chimaerism and correction of leukocyte arylsulphatase A to wild type values; subtle motor deterioration was similarly noted and progressive cerebral volume loss was evident upon magnetic resonance imaging. Sensory nerve conduction deteriorated 17 months post-transplantation with apparent stabilisation at 11-year review. Haematopoietic stem-cell transplantation was ineffective for this rare attenuated variant of metachromatic leukodystrophy. In the few patients identified pre-symptomatically or with early-phase disease, clear recommendations are lacking; when transplantation is considered, umbilical cord blood grafts from enzyme-replete donors with adjunctive mesenchymal stem cell infusions from the same source may be preferable. Improved outcomes will depend on enhanced awareness and early diagnosis of the disease, so that promising interventions such as genetically modified, autologous stem cell transplantation have the best opportunity of success.

Arylsulfatase-A in umbilical cord blood: gestational age and mode of delivery do not influence enzyme activity

The possibility of using umbilical cord blood for transplantation in several enzyme deficiencies has received increasing attention because of the availability of cord blood, the reduced incidence of post-transplantation complications, such as graft-versus-host disease and the possible accomplishment of good corrective results following transplantation, even in cases of greater HLA disparity. The use of hematopoietic stem cells from unrelated donors is even more highly recommended for the treatment of inherited enzyme deficiencies, because it might reduce the risk of the transplanted cells originating from a carrier of the defect, which might have an inadequate corrective ability. Our study was designed to elucidate whether the gestational age and mode of delivery influences the arylsulfatase-A activity in the umbilical cord blood. Enzyme activities proved to be similar in the four populations studied (full-term normal spontaneous vaginal delivery, full-term caesarean section, preterm normal spontaneous vaginal delivery and preterm caesarean section). Therefore, umbilical cord blood samples seem to be suitable for transplantation in metachromatic leukodystrophy, regardless of gestational age and mode of delivery. Moreover, our results are the first published data on normal values for arylsulfatase-A activity in human umbilical cord blood.