Prime Editing for Inherited Retinal Diseases

Abstract

Inherited retinal diseases (IRDs) are chronic, hereditary disorders that lead to progressive degeneration of the retina. Disease etiology originates from a genetic mutation—inherited or de novo—with a majority of IRDs resulting from point mutations. Given the plethora of IRDs, to date, mutations that cause these dystrophies have been found in approximately 280 genes. However, there is currently only one FDA-approved gene augmentation therapy, Luxturna (voretigene neparvovec-rzyl), available to patients with RPE65-mediated retinitis pigmentosa (RP). Although clinical trials for other genes are underway, these techniques typically involve gene augmentation rather than genome surgery. While gene augmentation therapy delivers a healthy copy of DNA to the cells of the retina, genome surgery uses clustered regularly interspaced short palindromic repeats (CRISPR)-based technology to correct a specific genetic mutation within the endogenous genome sequence. A new technique known as prime editing (PE) applies a CRISPR-based technology that possesses the potential to correct all twelve possible transition and transversion mutations as well as small insertions and deletions. EDIT-101, a CRISPR-based therapy that is currently in clinical trials, uses double-strand breaks and nonhomologous end joining to remove the IVS26 mutation in the CEP290 gene. Preferably, PE does not cause double-strand breaks nor does it require any donor DNA repair template, highlighting its unparalleled efficiency. Instead, PE uses reverse transcriptase and Cas9 nickase to repair mutations in the genome. While this technique is still developing, with several challenges yet to be addressed, it offers promising implications for the future of IRD treatment.

Base and Prime Editing in the Retina—From Preclinical Research toward Human Clinical Trials

“…However, there are still many challenges to overcome before these gene editing technologies will be available to treat human patients with IRDs. One challenge that is still being addressed is having an efficient gene editing system for areas of the genome that are difficult to access or target, as IRDs can be attributed to over 280 genes [ 34 ]. To target them all would be costly, unfeasible, and inefficient.…”

“…Since many of the IRDs are monogenic and can be attributed to a single point mutation, base and prime editors hold great promise for gene editing without the high potential for off-target effects from the traditional CRISPR/Cas9 double-strand break methods [ 34 ]. In particular, split-intein [ 35 ] AAV delivery is promising for the use of delivering base and prime editors directly to the gene of interest to permanently correct the mutation.…”

Antiviral Targeting of Varicella Zoster Virus Replication and Neuronal Reactivation Using CRISPR/Cas9 Cleavage of the Duplicated Open Reading Frames 62/71

“…A possible initial application of AAV-mediated gene editing as an antiviral strategy could be for VZV-induced retinal diseases. The retina has been a prime target for advancing AAV-mediated gene therapy strategies, and there are promising results from both animal models and human studies that AAV-mediated delivery can restore vision loss for specific inherited defects [99]. VZV replication in the retinal tissues is known to result in rare but devastating blinding diseases such as peripheral outer retinal necrosis (PORN), acute retinal necrosis (ARN) and chorioretinitis [100].…”

CRISPR/Cas therapeutic strategies for autosomal dominant disorders

“…Off-target effects remain a considerable safety concern with DSB approaches, and high levels of adeno-associated virus (AAV) integration have been observed in Cas9-induced DSBs (28,29). Therefore, DSB-independent iterations of CRISPR/Cas technology that exhibit high editing efficiencies and have better safety profiles need to be extensively evaluated as potential therapeutics (30).…”

“…While prime editing may have a slightly higher indel rate, it has a substantial increase in flexibility, does not lead to bystander mutations, and is less reliant on ideal PAM positioning (33). For an in-depth overview of base and prime editing, see recent reviews (30,34,35).…”