Annalisa Lattanzi

Widespread enzymatic correction of CNS tissues by a single intracerebral injection of therapeutic lentiviral vector in leukodystrophy mouse models

Leukodystrophies are rare diseases caused by defects in the genes coding for lysosomal enzymes that degrade several glycosphingolipids. Gene therapy for leukodystrophies requires efficient distribution of the missing enzymes in CNS tissues to prevent demyelination and neurodegeneration. In this work, we targeted the external capsule (EC), a white matter region enriched in neuronal projections, with the aim of obtaining maximal protein distribution from a single injection site. We used bidirectional (bd) lentiviral vectors (LV) (bdLV) to ensure coordinate expression of a therapeutic gene (beta-galactocerebrosidase, GALC; arylsulfatase A, ARSA) and of a reporter gene, thus monitoring simultaneously transgene distribution and enzyme reconstitution. A single EC injection of bdLV.GALC in early symptomatic twitcher mice (a murine model of globoid cell leukodystrophy) resulted in rapid and robust expression of a functional GALC protein in the telencephalon, cerebellum, brainstem and spinal cord. This led to global rescue of enzymatic activity, significant reduction of tissue storage and decrease of activated astroglia and microglia. Widespread protein distribution and complete metabolic correction were also observed after EC injection of bdLV.ARSA in a mouse model of metachromatic leukodystrophy. Our data indicated axonal transport, distribution through cerebrospinal fluid flow and cross-correction as the mechanisms contributing to widespread bioavailability of GALC and ARSA proteins in CNS tissues. LV-mediated gene delivery of lysosomal enzymes by targeting highly interconnected CNS regions is a potentially effective strategy that, combined with a treatment able to target the PNS and peripheral organs, may provide significant therapeutic benefit to patients affected by leukodystrophies.

Therapeutic benefit of lentiviral-mediated neonatal intracerebral gene therapy in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) is an inherited lysosomal storage disease caused by β-galactocerebrosidase (GALC) deficiency. Gene therapy (GT) should provide rapid, extensive and lifetime GALC supply in central nervous system (CNS) tissues to prevent or halt irreversible neurologic progression. Here we used a lentiviral vector (LV) to transfer a functional GALC gene in the brain of Twitcher mice, a severe GLD model. A single injection of LV.GALC in the external capsule of Twitcher neonates resulted in robust transduction of neural cells with minimal and transient activation of inflammatory and immune response. Importantly, we documented a proficient transduction of proliferating and post-mitotic oligodendroglia, a relevant target cell type in GLD. GALC activity (30–50% of physiological levels) was restored in the whole CNS of treated mice as early as 8 days post-injection. The early and stable enzymatic supply ensured partial clearance of storage and reduction of psychosine levels, translating in amelioration of histopathology and enhanced lifespan. At 6 months post-injection in non-affected mice, LV genome persisted exclusively in the injected region, where transduced cells overexpressed GALC. Integration site analysis in transduced brain tissues showed no aberrant clonal expansion and preferential targeting of neural-specific genes. This study establishes neonatal LV-mediated intracerebral GT as a rapid, effective and safe therapeutic intervention to correct CNS pathology in GLD and provides a strong rationale for its application in this and similar leukodystrophies, alone or in combination with therapies targeting the somatic pathology, with the final aim of providing an effective and timely treatment of these global disorders.

Specific Determination of β-Galactocerebrosidase Activity via Competitive Inhibition of β-Galactosidase

BACKGROUNDnThe determination of cellular beta-galactocerebrosidase activity is an established procedure to diagnose Krabbe disease and monitor the efficacy of gene/stem cell-based therapeutic approaches aimed at restoring defective enzymatic activity in patients or disease models. Current biochemical assays for beta-galactocerebrosidase show high specificity but generally require large protein amounts from scanty sources such as hematopoietic or neural stem cells. We developed a novel assay based on the hypothesis that specific measurements of beta-galactocerebrosidase activity can be performed following complete inhibition of beta-galactosidase activity.nnnMETHODSnWe performed the assay using 2-7.5 microg of sample proteins with the artificial fluorogenic substrate 4-methylumbelliferone-beta-galactopyranoside (1.5 mmol/L) resuspended in 0.1/0.2 mol/L citrate/phosphate buffer, pH 4.0, and AgNO(3). Reactions were incubated for 30 min at 37 degrees C. Fluorescence of liberated 4-methylumbelliferone was measured on a spectrofluorometer (lambda(ex) 360 nm, lambda(em) 446 nm).nnnRESULTSnAgNO(3) was a competitive inhibitor of beta-galactosidase [inhibition constant (K(i)) = 0.12 micromol/L] and completely inhibited beta-galactosidase activity when used at a concentration of 11 micromol/L. Under this condition, the beta-galactocerebrosidase activity was preserved and could be specifically and accurately measured. The assay can detect beta-galactocerebrosidase activity in as little as 2 microg cell protein extract or 7.5 microg tissue. Assay validation was performed using (a) brain tissues from wild-type and twitcher mice and (b) murine GALC(-/-) hematopoietic stem cells and neural precursor cells transduced by GALC-lentiviral vectors.nnnCONCLUSIONSnThe procedure is straightforward, rapid, and reproducible. Within a clinical context, our method unequivocally discriminated cells from healthy subjects and Krabbe patients and is therefore suitable for diagnostic applications.

Dynamic activity of miR-125b and miR-93 during murine neural stem cell differentiation in vitro and in the subventricular zone neurogenic niche

Several microRNAs (miRNAs) that are either specifically enriched or highly expressed in neurons and glia have been described, but the identification of miRNAs modulating neural stem cell (NSC) biology remains elusive. In this study, we exploited high throughput miRNA expression profiling to identify candidate miRNAs enriched in NSC/early progenitors derived from the murine subventricular zone (SVZ). Then, we used lentiviral miRNA sensor vectors (LV.miRT) to monitor the activity of shortlisted miRNAs with cellular and temporal resolution during NSC differentiation, taking advantage of in vitro and in vivo models that recapitulate physiological neurogenesis and gliogenesis and using known neuronal- and glial-specific miRNAs as reference. The LV.miRT platform allowed us monitoring endogenous miRNA activity in low represented cell populations within a bulk culture or within the complexity of CNS tissue, with high sensitivity and specificity. In this way we validated and extended previous results on the neuronal-specific miR-124 and the astroglial-specific miR-23a. Importantly, we describe for the first time a cell type- and differentiation stage-specific modulation of miR-93 and miR-125b in SVZ-derived NSC cultures and in the SVZ neurogenic niche in vivo, suggesting key roles of these miRNAs in regulating NSC function.

Pervasive supply of therapeutic lysosomal enzymes in the CNS of normal and Krabbe‐affected non‐human primates by intracerebral lentiviral gene therapy

Metachromatic leukodystrophy (MLD) and globoid cell leukodystrophy (GLD or Krabbe disease) are severe neurodegenerative lysosomal storage diseases (LSD) caused by arylsulfatase A (ARSA) and galactosylceramidase (GALC) deficiency, respectively. Our previous studies established lentiviral gene therapy (GT) as a rapid and effective intervention to provide pervasive supply of therapeutic lysosomal enzymes in CNS tissues of MLD and GLD mice. Here, we investigated whether this strategy is similarly effective in juvenile non‐human primates (NHP). To provide proof of principle for tolerability and biological efficacy of the strategy, we established a comprehensive study in normal NHP delivering a clinically relevant lentiviral vector encoding for the human ARSA transgene. Then, we injected a lentiviral vector coding for the human GALC transgene in Krabbe‐affected rhesus macaques, evaluating for the first time the therapeutic potential of lentiviral GT in this unique LSD model. We showed favorable safety profile and consistent pattern of LV transduction and enzyme biodistribution in the two models, supporting the robustness of the proposed GT platform. We documented moderate inflammation at the injection sites, mild immune response to vector particles in few treated animals, no indication of immune response against transgenic products, and no molecular evidence of insertional genotoxicity. Efficient gene transfer in neurons, astrocytes, and oligodendrocytes close to the injection sites resulted in robust production and extensive spreading of transgenic enzymes in the whole CNS and in CSF, leading to supraphysiological ARSA activity in normal NHP and close to physiological GALC activity in the Krabbe NHP, in which biological efficacy was associated with preliminary indication of therapeutic benefit. These results support the rationale for the clinical translation of intracerebral lentiviral GT to address CNS pathology in MLD, GLD, and other neurodegenerative LSD.

Optimization of CRISPR/Cas9 Delivery to Human Hematopoietic Stem/Progenitor Cells for Therapeutic Genomic Rearrangements

Editing the β-globin locus in hematopoietic stem cells is an alternative therapeutic approach for gene therapy of β-thalassemia and sickle cell disease. Using the CRISPR/Cas9 system, we genetically modified human hematopoietic stem and progenitor cells (HSPCs) to mimic the large rearrangements in the β-globin locus associated with hereditary persistence of fetal hemoglobin (HPFH), a condition that mitigates the clinical phenotype of patients with β-hemoglobinopathies. We optimized and compared the efficiency of plasmid-, lentiviral vector (LV)-, RNA-, and ribonucleoprotein complex (RNP)-based methods to deliver the CRISPR/Cas9 system into HSPCs. Plasmid delivery of Cas9 and gRNA pairs targeting two HPFH-like regions led to high frequency of genomic rearrangements and HbF reactivation in erythroblasts derived from sorted, Cas9+ HSPCs but was associated with significant cell toxicity. RNA-mediated delivery of CRISPR/Cas9 was similarly toxic but much less efficient in editing the β-globin locus. Transduction of HSPCs by LVs expressing Cas9 and gRNA pairs was robust and minimally toxic but resulted in poor genome-editing efficiency. Ribonucleoprotein (RNP)-based delivery of CRISPR/Cas9 exhibited a good balance between cytotoxicity and efficiency of genomic rearrangements as compared to the other delivery systems and resulted in HbF upregulation in erythroblasts derived from unselected edited HSPCs.

559. Induction of Fetal Hemoglobin in Adult Erythroblasts by Genome Editing of the Beta-Globin Locus

Sickle cell disease (SCD) and β-thalassemia are severe anemias characterized by abnormal or reduced production of hemoglobin β-chains. Autologous transplantation of genetically corrected hematopoietic stem cells (HSC) is an attractive therapeutic alternative for patients lacking a compatible HSC donor. Naturally occurring, large deletions in the β-globin locus result in increased fetal hemoglobin (HbF) expression (HPFH, Hereditary Persistence of Fetal Hemoglobin), a condition that mitigates the clinical severity of β-hemoglobinopathies. Here, we integrated BCL11A and GATA1 transcription factor binding site analysis and HPFH mutational data to identify potential HbF silencers in the β-globin locus. Based on this analysis, we designed a CRISPR/Cas9 strategy to disrupt a 13-kb genomic region commonly deleted in HPFH, which includes the Δ- and β-globin genes and putative intergenic HbF silencers, and achieved efficient targeted deletion in erythroid cell lines by plasmid, RNA and lentiviral delivery of the CRISPR/Cas9 nuclease system. RT-PCR showed a dramatic increase in γ-globin mRNA levels in modified adult hematopoietic stem progenitor cells (HSPC)-derived erythroid cell lines (HUDEP-2). FACS and HPLC analysis demonstrated reactivation of HbF and a concomitant decrease in HbA expression. Cell morphology, erythroid marker profile, total Hb levels and erythroid maturation were unaffected, consistent with the asymptomatic phenotype of adult HPFH carriers. The same strategy was tested in primary human erythroblasts by lentiviral transduction of adult CD34+ HSPCs followed by in vitro erythroid differentiation in liquid and clonogenic cultures. Deletion of potential HbF silencers resulted in a 35% increase in γ-globin expression compared to basal levels in primary human erythroblasts as measured by HPLC, suggesting that these sequences could serve as targets for therapeutic genome editing for HbF induction in β-hemoglobinopathies. We are currently testing the efficiency of our CRISPR/Cas9-based strategy in patient-derived HSPCs. Overall, this study contributes to the knowledge of the mechanisms underlying fetal to adult Hb switching, and provides clues for a therapeutic strategy for SCD and β-thalassemia.

135. Optimization of Dual-gRNA Lentiviral Vectors for Targeted Genomic Deletions

CRISPR-Cas9 technology is a powerful tool for genome editing based therapeutic approaches. Despite its potential, the delivery of Cas9 components into primary cells, such as hematopoietic stem progenitor cells (HSPC), is still a major challenge. In addition, several applications - e.g. the use of Cas9-nickase and the generation of genomic deletions/inversions - require the delivery and expression of two different gRNA. Lentiviral vectors (LV) can efficiently transduce HSPC, but the presence and the orientation of direct repeated elements in the gRNA expression cassettes can potentially trigger recombination events that affect vector stability. To address this issue, we designed different LV encoding for two gRNA pairs, which generate deletions of different size (3 and 13 kb) in the beta-globin gene cluster. gRNA expression was driven by murine and human U6 promoters, having little sequence similarity, to avoid potential recombination events of the LV genome. To further reduce LV rearrangements and optimize expression levels, gRNA cassettes were positioned in different orientations with respect to each other (LV Inward, Tandem and Outward). We compared LV from different vector batches in HCT116 cells and we observed that Tandem configuration resulted in higher viral titers and infectivity, although this difference was not statistically significant. Analysis of proviral integrity on genomic DNA of transduced cells showed the intact dual-gRNA cassette and no sign of recombination for all the LV configurations. To understand if different orientations could affect gRNA expression (measured by RT-qPCR) and consequently deletion/inversion efficiency, we co-transduced erythroleukemic K562 cells with LV-Cas9-Blast and the three different LV. Surprisingly, LV Inward showed poor gRNA expression, negligible deletion and inversion frequency and low efficiency of InDel formation at each gRNA target site (2.4 % and 6.8%). Conversely, LV Tandem and Outward configurations allowed efficient cell transduction and significant and comparable levels of gRNA expression. As a results, we observed a good deletion frequency (11.0% ±1.8 of total alleles for LV Tandem and 12.3 % ± 2.5 for LV Outward), a lower proportion of inversions events (5.4% ±1.3 for LV Tandem and 3.8 % ± 0.4 for LV Outward) and up to 58% of InDels events at each gRNA target sites. Comparable results were also obtained in adult HSPC-derived erythroid cell line (HUDEP-2). Overall, our study indicates LV Tandem and LV Outward as promising tools for genome editing of primary cells; both vectors are now being evaluated in primary HSPC.