Cover Credit: The equine model of post-traumatic osteoarthritis is a powerful tool to translate therapeutic effects of intra-articular therapies, specifically gene therapies, in people. The equine model used here and described within this issue, demonstrates optimal doses of scAAVIL-1ra that have maximal anti-inflammatory effects but also identifies doses of vector that are either too high resulting in nonoptimal synovial capsule changes or doses that are too low that do not control inflammation within the joint. This highly relevant pre-clinical model of osteoarthritis will inform intra-articular dosing regimens in people due to the similarities between horses and humans regarding joint anatomy, physiology and osteoarthritis disease progression.

Cover Credit: The remarkable tools of modern genetics have the potential to reduce costs of gene-based therapies and make them accessible to all who need them. The high prices for some recently approved therapies underscore the uncertain success of that goal. Cover created with BioRender.com by Caitlin Wheeler (PhD Candidate), Division of Human Genetics, National Health Laboratory Service and School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, South Africa, Bioengineering and Integrated Genomics Group, Council for Scientific and Industrial Research, Pretoria, South Africa.

Cover Credit: Recombinant adeno-associated virus 9 (rAAV9) successfully transduced corneal limbal stem cells (LSCs) in a mouse model of the childhood blindness aniridia.

Aniridia is a congenital blindness with unmet therapeutic needs. The success of gene therapy for aniridia may depend on the presence of functional LSCs in the cloudy aniridic corneas and whether rAAV can transduce them for gene-therapy delivery. Both these concerns were unknown, and thus were addressed by our study. Confocal microscopy images of wild type (left panel) and aniridic (right panel) corneal flat mounts, 7 months after direct-to-cornea injections of rAAV9 encoding Cre recombinase, resulted in tdTomato stripes indicative of successful LSC transduction in both wild-type and aniridic corneas. Thus, rAAV9 capsid is a good candidate for use in future aniridia gene-therapy development.

Cover Credit: Gene Therapy to reduce astrogliosis in ALS motor cortex. Astrogliosis and microgliosis contribute to upper motor neuron degeneration in ALS, especially within the context of TDP-43 pathology. The image shows that cortical component of ALS can be modulated by intrathecal injection of AAV9 expressing HGF gene under the control of a novel and engineered promoter. This gene therapy approach significantly reduces astrogliosis and microgliosis that occurs in the ALS motor cortex with TDP-43 pathology.

Cover Credit: Transgene expression along retinal ganglion cell axons. Recombinant adeno-associated viral vectors (AAVs) have the capacity for efficient gene transfer in the retina. The strength and cell-selectivity of transgene expression are influenced by promoters. The cover article of this Gene Therapy issue investigated the impact of five short promoters on AAV2-mediated transgene expression in mice and ex vivo human retinal ganglion cells. The accompanying image illustrates a horizontal brain section of a mouse that received intravitreal injection of AAV2-SYN-eGFP. Notably, transgene expression is observed in the axons of retinal ganglion cells along the visual pathway.

Cover Credit: Mouse brain prefrontal cortex transduced with a mixture of AAV vectors.

The world population is aging and the prevalence of diseases affecting the nervous system is on the rise. Gene transfer with AAV vectors is a promissing “one and done” approach to target and treat disease-relevant brain areas.

To further increase the efficacy and safety of AAV-based brain gene therapies, it is important to better understand and optimize vector dosing, biodistribution and transgene expression at the single-cell level. The authors developed a simple tool to quantify with single-cell resolution, the number of incoming AAV genomes co-expressed in vivo in the mouse brain. The image shows brain prefrontal cortex co-transduced with a mixture of three AAV vectors expressing different fluorescent reporter proteins in green, blue and red. Neurons are labelled in purple, and when all three vectors transduce the same cell and co-express their genomes, neurons are labelled in white.

Cover Credit: Gene therapy for patients with advanced neovascular age-related macular degeneration has reached clinical trial phases by introducing sFLT01. htsFLT01 gene construct is a novel anti-angiogenic tool with promising improvements compared to existing treatments. The critical properties of htsFLT01 molecule were maintained in desired limits post hinge deletion process when compared to sFLT01 protein. While, hinge shrinkage led to increased flexibility, stability and safety profile and decreased antigenicity of the htsFLT01 molecule. The image shows confocal microscopy of retinal vasculature in P16 mice, 2 weeks after AAV2-htsFLT01 intravitreal delivery. The presence of isolectin-positive dots in htsFLT01 treated eyes was the result of attenuation and impaired vascular formation due to anti-angiogenic effects of htsFLT01 protein.

Cover credit: Purkinje cells transduced by AAV9 following intracisternal delivery in rats. The image shows a rat Purkinje cell transduced by a single-stranded AAV9-EGFP delivered to the cisterna magna next to the untransduced granule cell layer stained by Neu N.