Dynamics of therapeutic gene delivery to sensory neurons of the trigeminal ganglion

Abstract

The development of novel therapies to treat diseases of the nervous system requires a multidisciplinary approach. Recent advances in gene therapy technologies have made it possible to accurately edit genomes in vivo. Editing of genomes allow scientists to replace defected cellular genes with fully functional genes to treat neurodegenerative diseases, or promote mutagenesis of essential viral genes from pathogenic viruses to inhibit infection and disease. One such pathogen, herpes simplex virus (HSV), evades antiviral immunity by establishing latency in peripheral neurons that persist as intranuclear episomes. Upon viral reactivation, HSV can cause recurrent disease and transmission to new hosts. Disruption of essential HSV genes in the infected sensory neuron can prevent reactivation. The basic principle of gene therapy requires efficient delivery and expression of therapeutic genes in target cells using a safe and reliable vector system appropriate for the treatment. Viruses are natural gene delivery systems, and hence, they can be employed as therapeutic gene vectors. To determine the dynamics of therapeutic gene delivery and expression in sensory neurons of the trigeminal ganglion, we used a viral vector derived from adeno-associated virus (AAV) in a mouse model. We found that AAV serotype 1 (AAV-1) trafficked to the trigeminal ganglion (TG) after intradermal injection in the mouse whiskerpad. Furthermore, AAV-1, 5, 7, 8, 9, which have diverse cellular tropisms, trafficked to the trigeminal ganglion from the whiskerpad with similar efficiency. After trafficking to the TG in just 3 days, the level of AAV genomes in the TG remained constant for at least 28-days post inoculation. We determined that 5x1011 AAV vector genomes provided the highest level of AAV-mediated transgene expression in neurons, in vivo. Importantly, we achieved at least 50% transduction efficiency of neurons in the TG after whiskerpad injection. Moreover, the level of transgene expression was sustained for at least 28-days post inoculation. We showed that AAVs co-transduced the same neuron, which enabled delivery of multiple genes to same the target cell. In addition, we demonstrated that AAV-1 co-infect neurons that was infected with HSV-1. Understanding the parameters necessary for AAV-mediated gene transfer to neurons in the trigeminal ganglion will allow a gene therapy approach to treat HSV-1 infected neurons, and likely other diseases that directly affect or are mediated by sensory neurons in the nervous system.