Current Gene Therapy - Volume 14, Issue 6, 2014

The Wiskott-Aldrich Syndrome (WAS) is a monogenic X-linked primary immunodeficiency characterised also by thrombocytopenia, eczema, and a high susceptibility to develop tumours and autoimmunity. WAS patients have a severely reduced life expectancy, unless they undergo a successful HLA-matched haematopoietic stem cell (HSC) transplantation. However, several WAS patients lack a compatible donor and complications, such as autoimmunity, can arise in a significant fraction of HSC transplanted patients. Administration of WAS gene-corrected autologous HSC represents an alternative therapeutic approach, potentially applicable to all WAS patients. To this aim, several gene therapy approaches for WAS using initially γ-retroviral vectors (RVs) and subsequently HIV-based lentiviral vectors (LVs) have been developed. In the present review, we will first describe the results of the preclinical studies conducted in the murine model of WAS and then discuss the outcome of different phase I/II clinical trials using RV or LV- transduced HSC. Both gene therapy approaches led to restored WASP expression, correction of functional defects and clinical improvement. While RV-mediated gene therapy was associated with a high occurrence of leukaemia, results obtained in the first patients treated with LV-based HSC gene therapy indicate a safer risk-benefit profile.

Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) syndrome is a rare autoimmune disease due to mutations in the gene encoding for Forkhead box P3 (FOXP3), a transcription factor fundamental for the function of thymus-derived (t) regulatory T (Treg) cells. The dysfunction of Treg cells results in the development of devastating autoimmune manifestations affecting multiple organs, eventually leading to premature death in infants, if not promptly treated by hematopoietic stem cell transplantation (HSCT). Novel gene therapy strategies can be developed for IPEX syndrome as more definitive cure than allogeneic HSCT. Here we describe the therapeutic approaches, alternative to HSCT, currently under development. We described that effector T cells can be converted in regulatory T cells by LVmediated FOXP3-gene transfer in differentiated T lymphocytes. Despite FOXP3 mutations mainly affect a highly specific T cell subset, manipulation of stem cells could be required for long-term remission of the disease. Therefore, we believe that a more comprehensive strategy should aim at correcting FOXP3-mutated stem cells. Potentials and hurdles of both strategies will be highlighted here.

Over the last few years, the transfer of therapeutic genes via gammaretro- or lentiviral vector systems has proven its virtue as an alternative treatment for a series of genetic disorders. The number of approved phase I/II clinical trials, especially for rare diseases, is steadily increasing, but the overall hurdles to become a broadly acceptable therapy remain numerous. The efforts by clinicians and basic scientists have tremendously improved the knowledge available about feasibility and biosafety of gene therapy. Nonetheless, despite the generation of a plethora of clinical and preclinical safety data, we still lack sufficiently powerful assays to predictively assess the exact levels of toxicity that might be observed in any given clinical gene therapy. Insertional mutagenesis is one of the major concerns when using integrating vectors for permanent cell modification, and the occurrence of adverse events related to genotoxicity, in early gene therapy trials, has refrained the field of gene therapy from emerging further. In this review, we provided a comprehensive overview on the basic principles and potential co-factors concurring in the generation of adverse events reported in gene therapy clinical trials using integrating vectors. Additionally, we summarized the available systems to assess genotoxicity at the preclinical level and we shed light on the issues affecting the predictive value of these assays when translating their results into the clinical arena. In the last section of the review we briefly touched on the future trends and how they could increase the safety of gene therapy employing integrating vector technology to take it to the next level.

Haemophagocytic lymphohistiocytosis (HLH) describes a severe and often fatal immunodysregulatory disorder caused primarily by the uncontrolled activation and proliferation of T cells and macrophages. A number of genetic defects mainly involving defective granule exocytosis and effector cell cytotoxicity have been identified and well characterised at the molecular and cellular level. These conditions have limited therapeutic options and given the predominant restriction of the causative gene to the haematopoietic system, they have become attractive targets for haematopoietic cell gene therapy. Pre clinical studies in murine models of HLH due to perforin deficiency have shown correction of the disease phenotype as a result of autologous haematopoietic stem cell (HSC) gene transfer using lentiviral vectors. In a murine model of X-linked lymphoproliferative disease (XLP1), HSC gene transfer is able to correct the immunological manifestations of the disease. These encouraging murine studies have led to further work to develop clinically applicable strategies. An alternative approach is to correct defective T cells as this approach is safer than HSC gene therapy and may allow early control of the HLH through the engraftment of functional gene modified effector T cells. Both strategies are now in development and a gene therapy option for certain genetic forms of HLH may soon enter clinical trials.

Several Phase I/II clinical trials aiming at the correction of X-linked CGD by gene transfer into hematopoietic stem cells (HSCs) have demonstrated the therapeutic potential of gene modified autologous HSCs for the treatment of CGD. Resolution of therapy-resistant bacterial and fungal infections in liver, lung and spinal canal of CGD patients were clearly documented in all trials. However, clinical benefits were not sustained over time due to the failure of gene transduced cells to engraft long-term. Moreover, severe adverse effects were observed in some of the treated patients due to insertional mutagenesis leading to the activation of growth promoting genes and to myeloid malignancy. These setbacks fostered the development of novel safety and efficacy improved vectors that have already entered or are about to enter the clinics. Meanwhile, ongoing research is constantly refining the CGD disease phenotype, including the definition of factors that may explain the unique engraftment phenotype observed in CGD gene therapy trials. This review provides a condensed overview on the current knowledge of the molecular pathomechanisms and clinical manifestations of CGD and summarizes the lessons learned from clinical gene therapy trials, the preclinical progress in vector design and the future perspectives for the gene therapy of CGD.

Generation and precise genetic correction of patient-derived hiPSCs have great potential in regenerative medicine. Such targeted genetic manipulations can now be achieved using gene-editing nucleases. Here, we report generation of cystic fibrosis (CF) and Gaucher’s disease (GD) hiPSCs respectively from CF (homozygous for CFTRΔF508 mutation) and Type II GD [homozygous for β-glucocerebrosidase (GBA) 1448T>C mutation] patient fibroblasts, using CCR5- specific TALENs. Site-specific addition of loxP-flanked Oct4/Sox2/Klf4/Lin28/Nanog/eGFP gene cassette at the endogenous CCR5 site of patient-derived disease-specific primary fibroblasts induced reprogramming, giving rise to both monoallele (heterozygous) and biallele CCR5-modified hiPSCs. Subsequent excision of the donor cassette was done by treating CCR5-modified CF and GD hiPSCs with Cre. We also demonstrate site-specific correction of sickle cell disease (SCD) mutations at the endogenous HBB locus of patient-specific hiPSCs [TNC1 line that is homozygous for mutated β- globin alleles (βS/βS)], using HBB-specific TALENs. SCD-corrected hiPSC lines showed gene conversion of the mutated βS to the wild-type βA in one of the HBB alleles, while the other allele remained a mutant phenotype. After excision of the loxP-flanked DNA cassette from the SCD-corrected hiPSC lines using Cre, we obtained secondary heterozygous βS/βA hiPSCs, which express the wild-type (βA) transcript to 30-40% level as compared to uncorrected (βS/βS) SCD hiPSCs when differentiated into erythroid cells. Furthermore, we also show that TALEN-mediated generation and genetic correction of disease-specific hiPSCs did not induce any off-target mutations at closely related sites.

Epigenetics means gene expression alterations which occur due to the biochemical changes of the nucleotides modifying structure of DNA rather than the changes in the genetic code itself as in case of mutations. The epigenome, consisting of chromatin and its modifications, acts as a link between the inherited genome and the changes imposed by the environment. Over the past decade, there has been mounting evidence suggestive of associations between epigenetic modifications and various human conditions such as aging, and most common human diseases viz. cancer, cardiovascular diseases, diabetes, rheumatoid arthritis, HIV etc and the clearest evidence as the central mechanism for common multifactorial diseases, has been identified with the factors involved in the inflammatory response. Periodontal disease, basically an immune-inflammatory affliction, being a multifactorial complex disease, owing to its high prevalence, chronicity and wide ranging systemic effects, essentially calls for a better comprehension of the underlying disease mechanisms, so as to develop and decipher the novel methodologies to combat this disease. The current paper aims to visualize periodontal disease from an epigenetic perspective, featuring the contemporary evidence supported literature and tends to explore the possibilities to find some explanations for perio-systemic health links, individualized and improvised diagnostic tools for earlier detection and ways to halt the disease and help regeneration and reconstruction of the lost periodontal attachment apparatus with the biology based approaches.