Current Gene Therapy - Volume 18, Issue 2, 2018

Tay-Sachs disease, caused by impaired β-N-acetylhexosaminidase activity, was the first GM2 gangliosidosis to be studied and one of the most severe and earliest lysosomal diseases to be described. The condition, associated with the pathological build-up of GM2 ganglioside, has acquired almost iconic status and serves as a paradigm in the study of lysosomal storage diseases. Inherited as a classical autosomal recessive disorder, this global disease of the nervous system induces developmental arrest with regression of attained milestones; neurodegeneration progresses rapidly to cause premature death in young children. There is no effective treatment beyond palliative care, and while the genetic basis of GM2 gangliosidosis is well established, the molecular and cellular events, from diseasecausing mutations and glycosphingolipid storage to disease manifestations, remain to be fully delineated. Several therapeutic approaches have been attempted in patients, including enzymatic augmentation, bone marrow transplantation, enzyme enhancement, and substrate reduction therapy. Hitherto, none of these stratagems has materially altered the course of the disease. Authentic animal models of GM2 gangliodidosis have facilitated in-depth evaluation of innovative applications such as gene transfer, which in contrast to other interventions, shows great promise. This review outlines current knowledge pertaining the pathobiology as well as potential innovative treatments for the GM2 gangliosidoses.

Mucopolysaccharidosis type II or Hunter syndrome is an X-linked lysosomal storage disease caused by a mutation in the gene encoding the lysosomal enzyme iduronate-2-sulfatase. The consequent enzyme deficiency causes a progressive, multisystem accumulation of glycosaminoglycans, which is the cause of the clinical manifestations involving also Central Nervous System for patients with the severe form of disease. The limits of the currently available therapies for Hunter syndrome, hematopoietic stem cell transplantation and recombinant enzyme replacement therapy, mainly regarding brain achievement, have encouraged several studies which recognized gene therapy as a potential therapeutic option for this condition. In vitro studies firstly aimed at the demonstration that viral vector- mediated IDS gene expression could lead to high levels of enzyme activity in transduced cells. The encouraging results obtained allowed the realization of many preclinical studies investigating the utilization of gene therapy vectors in animal models of Mucopolysaccharidosis II, together with a phase I clinical trial approved for Hunter patients affected by the mild form of the disease. Together to in vivo studies in which recombinant vectors are directly administered, systematically or by direct injection into Central Nervous System, also ex vivo gene therapy, consisting in transplantation of autologous hematopoietic stem cells, modified in vitro, into the animal or patient, has been tested. A wider clinical application of the results obtained so far is essential to ensure that gene therapy can be definitively validated as a therapeutic option available and usable for this rare but life-threatening disorder.

Fabry's disease is a genetic disorder of X-linked inheritance caused by mutations in the alpha galactosidase A gene resulting in deficiency of this lysosomal enzyme. The progressive accumulation of glycosphingolipids, caused by the inadequate enzymatic activity, is responsible of organ dysfunction and thus of clinical manifestations. In the presence of a high clinical suspicion, a careful physical examination and specific laboratory tests are required, finally diagnosis of Fabry's disease is confirmed by the demonstration of absence or reduced alpha-galactosidase A enzyme activity in hemizygous men and gene typing in heterozygous females; in fact the performance of enzymatic activity assay alone in women is inconclusive. Measurement of the biomarkers Gb3 and Lyso Gb3 in biological specimens may facilitate diagnosis. Because of its multisystemic involvement Fabry's disease may present a large spectrum of clinical manifestations as acroparesthesias, hypohidrosis, angiokeratomas, signs and symptoms of cardiac, renal, cerebrovascular involvement (renal insufficiency, proteinuria, left ventricular hypertrophy, strokes). Enzyme replacement therapy with recombinant α- galactosidase A is actually the specific therapy for Fabry disease. Early beginning of this treatment has shown beneficial effects in particular in cardiac and renal disease, a less efficacy it has been reported in central nervous system involvement. ERT has shown to be associated to a significant reduction of Gb3 accumulation in several tissues, in particular heart and kidney; moreover it improves pain related quality of life. Next generation lysosomal storage disorder treatment is based on new strategic approaches as stem cell based therapy, pharmacological chaperones, viral gene therapy; concerning Fabry's disease, it has been recently addressed to great interest this last innovative method, that is to say viral gene therapy, for delivering recombination enzyme into main involved tissues; promising results have been reported in animal models. Great efforts have been made and are still required in this field in order to make available a more effective, safer, advantageous therapeutic strategy for patients with Fabry's disease.

Background: Several methods have been investigated to effectively and safely transmit genes that stimulate cells to release therapeutic factor VIII (FVIII) and factor IX (FIX) into the circulation of people with hemophilia (PWH). Objective: To review the role of gene therapy (GT) in PWH. Methods: A Cochrane Library and PubMed (MEDLINE) search related to the role of GT in hemophilia was analyzed. Results: The most promising vectors for hemophilia GT are adeno-associated virus (AAV) and lentivirus. Several gene methods are available to lessen risks related to random vector integration and insertional mutagenesis, based on designer nucleases or CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR associated system). However, off-target issues need to be more meticulously and widely evaluated. Some clinical studies on hemophilia B based on AAV have obtained transitory or subtherapeutic levels of FIX expression. Another problem is possible transitory liver toxicity. Therefore, to reduce unintentional immune responses, transitory immunosuppression must be used, particularly when administering high-vector doses. Codon-optimized FVIII or FIX transgenes are able to promote clotting factor expression levels. The inclusion of a hyper-active gain-of-function R338L mutation in the FIX gene (FIX-R338L [FIX Padua]) makes the procedure more effective. Conclusion: Achieving a safe and efficient remedy for hemophilia A and B by means of GT vector engineering needs further improvement. No randomized or quasi-randomized clinical trials of GT for hemophilia have been found. Given it is in its incipient period, there is need for well-designed clinical trials to evaluate the long-term practicability, efficacy and risks of GT for PWH.

Genome editing mediated by Clustered Regularly Interspaced Palindromic Repeats (CRISPR) and its associated proteins (Cas) has recently been considered to be used as efficient, rapid and site-specific tool in the modification of endogenous genes in biomedically important cell types and whole organisms. It has become a predictable and precise method of choice for genome engineering by specifying a 20-nt targeting sequence within its guide RNA. Firstly, this review aims to describe the biology of CRISPR system. Next, the applications of CRISPR–Cas9 in various ways, such as efficient generation of a wide variety of biomedically important cellular models as well as those of animals, modifying epigenomes, conducting genome-wide screens, gene therapy, labelling specific genomic loci in living cells, metabolic engineering of yeast and bacteria and endogenous gene expression regulation by an altered version of this system were reviewed.

Objective: Our previous phase I clinical trial has confirmed the safety of Adenovirus carrying Hepatocyte Growth Factor gene (Ad-HGF) by intracoronary administration for treating severe coronary artery disease. This study was performed to evaluate the safety and efficacy of Ad-HGF by percutaneous endocardial injection for treating post-infarct heart failure. Methods: A total of 30 patients (15 in the experimental group and 15 in the control group) with postinfarct heart failure who were not indicated to revascularization and had received the optimal standardized medication therapy were included in the study. Percutaneous endocardial Ad-HGF gene transfer was injected with a catheter-based intramyocardial delivery system in the experimental group. Safety parameters were measured and compared between baseline and follow-ups in the experimental group. The Mean Difference (MD) of efficacy parameters from baseline to 6-month follow-up was measured in both groups and compared with each other. Results: No one suffered from serious adverse events in the experimental group during the 6-month follow-up. The experimental group revealed significant lower left ventricular end-diastolic dimension (LVDd) (68.5 vs. 65.8 MD: -2.69±1.08, P=0.03) and higher LVEF of both echocardiograph (35.2 vs. 39.3, MD: 4.05±0.86, P=0.0005) and single photon emission computed tomography (27.7 vs. 30.6, MD: 2.9±0.8, P=0.003) in the 6-month follow-up than that in the baseline, but the control group did not (P>0.05). Compared to the control group, the experimental group showed significant improvement ranges of lower LVDd (2.6 vs. -2.69, MD: -5.3±1.4, P=0.0009) and higher echocardiographic LVEF (-2 vs. 4.05, MD: 6.1±1.6, P=0.0008) from baseline to 6-month follow-up. Conclusion: Percutaneous endocardial administration of Ad-HGF is safe and potentially efficient in improving LVEF and lowering LVDd of patients with post-infarct heart failure.