Development of a recombinant adenovirus vector production system free of replication-competent adenovirus by utilizing a packaging size limit of the viral genome

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

Viral-Vector-Delivered Anti-Angiogenic Therapies to the Eye

Pathological vessel growth harms vision and may finally lead to vision loss. Anti-angiogenic gene therapy with viral vectors for ocular neovascularization has shown great promise in preclinical studies. Most of the studies have been conducted with different adeno-associated serotype vectors. In addition, adeno- and lentivirus vectors have been used. Therapy has been targeted towards blocking vascular endothelial growth factors or other pro-angiogenic factors. Clinical trials of intraocular gene therapy for neovascularization have shown the treatment to be safe without severe adverse events or systemic effects. Nevertheless, clinical studies have not proceeded further than Phase 2 trials.

Gene therapy for monogenic liver diseases: clinical successes, current challenges and future prospects

Over the last decade, pioneering liver-directed gene therapy trials for haemophilia B have achieved sustained clinical improvement after a single systemic injection of adeno-associated virus (AAV) derived vectors encoding the human factor IX cDNA. These trials demonstrate the potential of AAV technology to provide long-lasting clinical benefit in the treatment of monogenic liver disorders. Indeed, with more than ten ongoing or planned clinical trials for haemophilia A and B and dozens of trials planned for other inherited genetic/metabolic liver diseases, clinical translation is expanding rapidly. Gene therapy is likely to become an option for routine care of a subset of severe inherited genetic/metabolic liver diseases in the relatively near term. In this review, we aim to summarise the milestones in the development of gene therapy, present the different vector tools and their clinical applications for liver-directed gene therapy. AAV-derived vectors are emerging as the leading candidates for clinical translation of gene delivery to the liver. Therefore, we focus on clinical applications of AAV vectors in providing the most recent update on clinical outcomes of completed and ongoing gene therapy trials and comment on the current challenges that the field is facing for large-scale clinical translation. There is clearly an urgent need for more efficient therapies in many severe monogenic liver disorders, which will require careful risk-benefit analysis for each indication, especially in paediatrics.

Current Experimental Studies of Gene Therapy in Parkinson's Disease

Parkinson's disease (PD) was characterized by late-onset, progressive dopamine neuron loss and movement disorders. The progresses of PD affected the neural function and integrity. To date, most researches had largely addressed the dopamine replacement therapies, but the appearance of L-dopa-induced dyskinesia hampered the use of the drug. And the mechanism of PD is so complicated that it's hard to solve the problem by just add drugs. Researchers began to focus on the genetic underpinnings of Parkinson's disease, searching for new method that may affect the neurodegeneration processes in it. In this paper, we reviewed current delivery methods used in gene therapies for PD, we also summarized the primary target of the gene therapy in the treatment of PD, such like neurotrophic factor (for regeneration), the synthesis of neurotransmitter (for prolong the duration of L-dopa), and the potential proteins that might be a target to modulate via gene therapy. Finally, we discussed RNA interference therapies used in Parkinson's disease, it might act as a new class of drug. We mainly focus on the efficiency and tooling features of different gene therapies in the treatment of PD.

Infectious bursal disease virus as a replication-incompetent viral vector expressing green fluorescent protein

Infectious bursal disease virus (IBDV) has been established as a replication-competent viral vector capable of carrying an epitope at multiple loci in the genome. To enhance the safety and increase the insertion capacity of IBDV as a vector, a replication-incompetent IBDV vector was developed in the present study. The feasibility of replacing one of the viral gene loci, including pvp2, vp3, vp1, or the polyprotein vp243, with the sequence of green fluorescent protein (GFP) was explored. A method combining TCID₅₀ and immunoperoxidase monolayer assay (IPMA) determined the most feasible locus for gene replacement to be pvp2. The genomic segment containing gfp at the pvp2 locus was able to be encapsidated into IBDV particles. Furthermore, the expression of GFP in GFP-IBDV infected cells was confirmed by Western blotting and GFP-IBDV particles showed similar morphology and size to that of wildtype IBDV by electron microscopy. By providing the deleted protein in trans in a packaging cell line (pVP2-DF1), replication-incompetent GFP-IBDV particles were successfully plaque-quantified. The gfp sequence from the plaque-forming GFP-IBDV in pVP2-DF1 was confirmed by RT-PCR and sequencing. To our knowledge, GFP-IBDV developed in the present study is the first replication-incompetent IBDV vector which expresses a foreign protein in infected cells without the capability to produce viral progeny. Additionally, such replication-incompetent IBDV vectors could serve as bivalent vaccine vectors for conferring protection against infections with IBDV and other economically important, or zoonotic, avian pathogens.

Dicer functions as an antiviral system against human adenoviruses via cleavage of adenovirus-encoded noncoding RNA

In various organisms, including nematodes and plants, RNA interference (RNAi) is a defense system against virus infection; however, it is unclear whether RNAi functions as an antivirus system in mammalian cells. Rather, a number of DNA viruses, including herpesviruses, utilize post-transcriptional silencing systems for their survival. Here we show that Dicer efficiently suppresses the replication of adenovirus (Ad) via cleavage of Ad-encoding small RNAs (VA-RNAs), which efficiently promote Ad replication via the inhibition of eIF2α phosphorylation, to viral microRNAs (mivaRNAs). The Dicer knockdown significantly increases the copy numbers of VA-RNAs, leading to the efficient inhibition of eIF2α phosphorylation and the subsequent promotion of Ad replication. Conversely, overexpression of Dicer significantly inhibits Ad replication. Transfection with mivaRNA does not affect eIF2α phosphorylation or Ad replication. These results indicate that Dicer-mediated processing of VA-RNAs leads to loss of activity of VA-RNAs for enhancement of Ad replication and that Dicer functions as a defence system against Ad in mammalian cells.

Preferable sites and orientations of transgene inserted in the adenovirus vector genome: The E3 site may be unfavorable for transgene position

The adenovirus vector (AdV) can carry two transgenes in its genome, the therapeutic gene and a reporter gene, for example. The E3 insertion site has often been used for the expression of the second transgene. A transgene can be inserted at six different sites/orientations: E1, E3 and E4 sites, and right and left orientations. However, the best combination of the insertion sites and orientations as for the titers and the expression levels has not sufficiently been studied. We attempted to construct 18 AdVs producing GFP or LacZ gene driven by the EF1α promoter and Cre gene driven by the α-fetoprotein promoter. The AdV containing GFP gene at E3 in the rightward orientation (GFP-E3R) was not available. The LacZ-E3R AdV showed 20-fold lower titer and 50-fold lower level of fiber mRNA than the control E1L AdV. Notably, we found four aberrantly spliced mRNAs in the LacZ-E3L/R AdVs, probably explaining their very low titers. Although the transgene expression levels in the E4R AdVs were about threefold lower than those in the E1L AdVs, their titers are comparable with that of E1L AdVs. We concluded that E1L and E4R sites/orientations are preferable for expressing the main target gene and a second gene, respectively.

Viral vectors for gene delivery to the central nervous system

The potential benefits of gene therapy for neurological diseases such as Parkinson's, Amyotrophic Lateral Sclerosis (ALS), Epilepsy, and Alzheimer's are enormous. Even a delay in the onset of severe symptoms would be invaluable to patients suffering from these and other diseases. Significant effort has been placed in developing vectors capable of delivering therapeutic genes to the CNS in order to treat neurological disorders. At the forefront of potential vectors, viral systems have evolved to efficiently deliver their genetic material to a cell. The biology of different viruses offers unique solutions to the challenges of gene therapy, such as cell targeting, transgene expression and vector production. It is important to consider the natural biology of a vector when deciding whether it will be the most effective for a specific therapeutic function. In this review, we outline desired features of the ideal vector for gene delivery to the CNS and discuss how well available viral vectors compare to this model. Adeno-associated virus, retrovirus, adenovirus and herpesvirus vectors are covered. Focus is placed on features of the natural biology that have made these viruses effective tools for gene delivery with emphasis on their application in the CNS. Our goal is to provide insight into features of the optimal vector and which viral vectors can provide these features.