The 3rd International Congress on

Rare Diseases

Gaucher disease (GD) is a lysosomal storage disorder caused by an inherited deficiency in the gene encoding glucocerebrosidase (GCase). The defective enzyme does not degrade sufficient glucocerebroside and it accumulates in macrophages throughout the body, producing Gaucher cells, the hallmark feature of GD.1 Enzyme replacement therapy is the standard treatment for GD patients. It reduces signs and symptoms, but it is not curative and restricts patients to lifelong infusions of the enzyme.1 Our work has been focused on development of a GCase lentiviral vector for correction of the genetic defect underlying GD. The first step in this process was creation of a viable model with pathology and clinical symptoms characteristic of type 1 GD. This was accomplished by conditionally deleting GCase exons 9–11 upon postnatal induction.2 In studies supported by AVROBIO, tThis mouse model was used to evaluate a clinical, Good Manufacturing Practices produced, single gene self-inactivating lentiviral vector (LV2) containing the glucocerebrosidase gene driven by the elongation factor 1α short (EFS) promoter.1,3 Lineage negative bone marrow cells were transduced with the LV2 vector and transplanted into irradiated GD type 1 mice, 2-3 months after induction of the gene deletion (early intervention) or 5-8 months after induction of disease (late intervention, when considerable splenomegaly has developed). Vector integration analysis demonstrated a typical lentiviral integration profile, with no integrations in high-risk proto-oncogenes and an oligoclonal integration site pattern.1,3 Mass spectrometric analysis of bone marrow, spleen, and liver demonstrated highly significant reductions in glucocerebroside accumulation in vector treated animals with both early and late intervention. Glucocerebroside levels were close to those in normal mice by 4 months after treatment. Histopathology demonstrated great reduction or disappearance of Gaucher cells in bone marrow and spleen by 4 months after vector treatment. In the late intervention study, hemoglobin and hematocrit were both normalized in vector treated animals.1,3 These data strongly support that gene therapy of GD type 1 mice using this clinical lentiviral vector is very efficient and demonstrates robust efficacy in the mouse disease model.

For many years, a number of neurodegenerative lysosomal storage diseases have been inaccessible to any therapy other than palliative care. Systemic enzyme replacement may not modify the course of the neurological phenotype although may improve patients’ lives by symptomatic relief. Recent clinical trials are now demonstrating acceptable safety and promising efficacy using various novel therapies such as delivery of molecules systemically or to the cerebrospinal fluid and gene therapies. Such treatments may not be early enough to prevent diseases which present very early in life and which present a precipitous clinical decline.

For these early-onset presentations, early intervention, perhaps even in the womb, may prevent or correct the neurological defect before irreversible damage is caused. The theoretical advantages of fetal gene therapy include i) targeting of progenitor or stem cells allowing for an equivalent effect at for a lower dose of vector ii) avoidance of immune response against the vector and transgenic protein and crucially iii) prevention of disease before irreversible pathological changes occur.  Several preclinical mouse studies have now demonstrated efficacy of fetal gene therapy in treating inherited genetic diseases. In this presentation I will examine some of these studies, explore theoretical advantages, and discuss the hurdles that might be faced in progressing such therapy to the clinic.

Pearson Syndrome (PS) is an ultra-rare mitochondrial disease with multisystemic  involvement, caused by de-novo mitochondrial DNA (mtDNA) deletions. No disease-modifying treatments are available for PS. Ex-vivo enrichment of functional mitochondria into various cells has been previously demonstrated, as has inter-cellular mitochondrial transfer. In preclinical models of mitochondrial and lysosomal disorders, hematopoietic stem and progenitor cells (HSCs) were shown to be capable of carrying and transferring normal organelles into diseased tissues, thereby altering disease phenotype. Here, we show enrichment of PS-derived HSCs with wild-type mitochondria, a process termed mitochondrial augmentation therapy (MAT).

We report a first in human study with a novel form of cellular therapy, MAT, in which we enrich HSCs with organelles encoding non-mutated version of the mtDNA sequence. We show the ability of MAT to improve in vitro PS-derived HSC function, and improvement in metabolic determinants, aerobic capacity and quality of life of three patients treated. Together, these preliminary clinical data suggest that MAT is safe, and may alter the clinical course for patients with mitochondrial deletions/mutations including PS. This methodology may prove to be a viable therapeutic intervention for additional mitochondrial disorders, and furthermore may be a prototype for other organelle transfer as well.