Challenges in retinal circuit regeneration: linking neuronal connectivity to circuit function

Recombinant Adeno-Associated Viral Vectors (rAAV)-Vector Elements in Ocular Gene Therapy Clinical Trials and Transgene Expression and Bioactivity Assays

Inherited retinal dystrophies and optic neuropathies cause chronic disabling loss of visual function. The development of recombinant adeno-associated viral vectors (rAAV) gene therapies in all disease fields have been promising, but the translation to the clinic has been slow. The safety and efficacy profiles of rAAV are linked to the dose of applied vectors. DNA changes in the rAAV gene cassette affect potency, the expression pattern (cell-specificity), and the production yield. Here, we present a library of rAAV vectors and elements that provide a workflow to design novel vectors. We first performed a meta-analysis on recombinant rAAV elements in clinical trials (2007-2020) for ocular gene therapies. We analyzed 33 unique rAAV gene cassettes used in 57 ocular clinical trials. The rAAV gene therapy vectors used six unique capsid variants, 16 different promoters, and six unique polyadenylation sequences. Further, we compiled a list of promoters, enhancers, and other sequences used in current rAAV gene cassettes in preclinical studies. Then, we give an update on pro-viral plasmid backbones used to produce the gene therapy vectors, inverted terminal repeats, production yield, and rAAV safety considerations. Finally, we assess rAAV transgene and bioactivity assays applied to cells or organoids in vitro, explants ex vivo, and clinical studies.

Development of Cellular and Tissue-based Products for Retinal Regenerative Medicine

Since the discovery of induced pluripotent stem cells (iPSCs) generation, much progress has been made in the fields of medical and pharmaceutical research, such as cell transplantation therapy. We have generated retinal cells and tissues, including retinal pigment epithelia (RPE), from human iPSCs. The ability to produce iPSCs from patients allows for autologous transplantation without causing immune rejection. The autologous transplantation of iPSC-derived retinal pigment epithelial sheets to a patient with age-related macular degeneration was carried out in Japan in 2014 as a first-in-human clinical study. Biotechnology has enabled the development of a wide range of drugs, including cell-based drugs. We are currently developing iPSC-derived RPE sheets as next-generation cell-based drugs aimed at allogeneic transplantation utilizing iPSC banks of homozygotes of human leukocyte antigen at 3 loci. Regulatory science concerning cellular and tissue-based products is a vital matter associated with the realization of regenerative medicine. Here we review the most recent progress in retinal regeneration and drug development, as well as its future prospects.