Safe and effective superoxide dismutase 1 silencing using artificial microRNA in macaques

Gene Therapy Tools for Brain Diseases

Neurological disorders affecting the central nervous system (CNS) are still incompletely understood. Many of these disorders lack a cure and are seeking more specific and effective treatments. In fact, in spite of advancements in knowledge of the CNS function, the treatment of neurological disorders with modern medical and surgical approaches remains difficult for many reasons, such as the complexity of the CNS, the limited regenerative capacity of the tissue, and the difficulty in conveying conventional drugs to the organ due to the blood-brain barrier. Gene therapy, allowing the delivery of genetic materials that encodes potential therapeutic molecules, represents an attractive option. Gene therapy can result in a stable or inducible expression of transgene(s), and can allow a nearly specific expression in target cells. In this review, we will discuss the most commonly used tools for the delivery of genetic material in the CNS, including viral and non-viral vectors; their main applications; their advantages and disadvantages. We will discuss mechanisms of genetic regulation through cell-specific and inducible promoters, which allow to express gene products only in specific cells and to control their transcriptional activation. In addition, we will describe the applications to CNS diseases of post-transcriptional regulation systems (RNA interference); of systems allowing spatial or temporal control of expression [optogenetics and Designer Receptors Exclusively Activated by Designer Drugs (DREADDs)]; and of gene editing technologies (CRISPR/Cas9, Zinc finger proteins). Particular attention will be reserved to viral vectors derived from herpes simplex type 1, a potential tool for the delivery and expression of multiple transgene cassettes simultaneously.

Design of AAV Vectors for Delivery of RNAi

Adeno-associated viral vectors have emerged as an important tool for human gene therapy, having demonstrated high transduction efficiency in a broad range of target tissues, a good safety profile in animal models and human clinical trials, and prospective long-lasting gene expression. First discovered 20 years ago, RNA interference (RNAi) has become another important tool for human gene therapy, enabling scientists to move on from classical gene transfer to gene silencing approaches, or combinations thereof. In this chapter, we describe a simple step-by-step method that will allow gene silencing novices to design their own artificial miRNAs against a target of their choice, clone these miRNAs into an AAV-based vector, and rapidly screen for highly efficient artificial miRNAs. The described method takes into consideration recent advances in the field including miRNA processing from various cellular miRNA backbones, choice between polymerase II and III promoters, and the potential impact of these factors on toxicity as it relates to off-targeting and to saturation of the endogenous RNAi machinery.

Intrathecal Delivery of AAV Vectors in Cynomolgus Macaques for CNS Gene Therapy and Gene Expression Analysis in Microdissected Motor Neurons

This protocol describes a method of delivering adeno-associated viral (AAV) vectors to the intrathecal space of nonhuman primates for CNS-directed gene therapy. It includes the surgical implantation of the catheter, vector infusion, necropsy, laser-capture microdissection of motor neurons, and gene expression analysis. This method allows efficient and reproducible delivery, and would be of interest to test gene therapy vectors for the treatment of disorders of the central nervous system of nonhuman primates. This protocol was tested in cynomolgus macaques and may be adapted for AAV delivery to different species of large animals.