Transgenic mice for in vivo epigenome editing with CRISPR-based systems.

CRISPR-Cas9 technologies have dramatically increased the ease of targeting DNA sequences in the genomes of living systems. The fusion of chromatin-modifying domains to nuclease-deactivated Cas9 (dCas9) has enabled targeted epigenome editing in both cultured cells and animal models. However, delivering large dCas9 fusion proteins to target cells and tissues is an obstacle to the widespread adoption of these tools for in vivo studies. Here, we describe the generation and characterization of two conditional transgenic mouse lines for epigenome editing, Rosa26:LSL-dCas9-p300 for gene activation and Rosa26:LSL-dCas9-KRAB for gene repression. By targeting the guide RNAs to transcriptional start sites or distal enhancer elements, we demonstrate regulation of target genes and corresponding changes to epigenetic states and downstream phenotypes in the brain and liver in vivo, and in T cells and fibroblasts ex vivo. These mouse lines are convenient and valuable tools for facile, temporally controlled, and tissue-restricted epigenome editing and manipulation of gene expression in vivo.

CRISPR-Cas9 DNA Base-Editing and Prime-Editing.

Many genetic diseases and undesirable traits are due to base-pair alterations in genomic DNA. Base-editing, the newest evolution of clustered regularly interspaced short palindromic repeats (CRISPR)-Cas-based technologies, can directly install point-mutations in cellular DNA without inducing a double-strand DNA break (DSB). Two classes of DNA base-editors have been described thus far, cytosine base-editors (CBEs) and adenine base-editors (ABEs). Recently, prime-editing (PE) has further expanded the CRISPR-base-edit toolkit to all twelve possible transition and transversion mutations, as well as small insertion or deletion mutations. Safe and efficient delivery of editing systems to target cells is one of the most paramount and challenging components for the therapeutic success of BEs. Due to its broad tropism, well-studied serotypes, and reduced immunogenicity, adeno-associated vector (AAV) has emerged as the leading platform for viral delivery of genome editing agents, including DNA-base-editors. In this review, we describe the development of various base-editors, assess their technical advantages and limitations, and discuss their therapeutic potential to treat debilitating human diseases.

Non-Viral Delivery of CRISPR/Cas Cargo to the Retina Using Nanoparticles: Current Possibilities, Challenges, and Limitations.

The discovery of the CRISPR/Cas system and its development into a powerful genome engineering tool have revolutionized the field of molecular biology and generated excitement for its potential to treat a wide range of human diseases. As a gene therapy target, the retina offers many advantages over other tissues because of its surgical accessibility and relative immunity privilege due to its blood-retinal barrier. These features explain the large advances made in ocular gene therapy over the past decade, including the first in vivo clinical trial using CRISPR gene-editing reagents. Although viral vector-mediated therapeutic approaches have been successful, they have several shortcomings, including packaging constraints, pre-existing anti-capsid immunity and vector-induced immunogenicity, therapeutic potency and persistence, and potential genotoxicity. The use of nanomaterials in the delivery of therapeutic agents has revolutionized the way genetic materials are delivered to cells, tissues, and organs, and presents an appealing alternative to bypass the limitations of viral delivery systems. In this review, we explore the potential use of non-viral vectors as tools for gene therapy, exploring the latest advancements in nanotechnology in medicine and focusing on the nanoparticle-mediated delivery of CRIPSR genetic cargo to the retina.

The Potential Benefit of Expedited Development and Approval Programs in Precision Medicine.

BACKGROUND: Increased understanding of the molecular causes of disease has begun to fulfill the promise of precision medicine with the development of targeted drugs, particularly for serious diseases with unmet needs. The drug approval regulatory process is a critical component to the continued growth of precision medicine drugs and devices. To facilitate the development and approval process of drugs for serious unmet needs, four expedited approval programs have been developed in the US: priority review, accelerated approval, fast track, and breakthrough therapy programs. METHODS: To determine if expedited approval programs are fulfilling the intended goals, we reviewed drug approvals by the US Food and Drug Administration (FDA) between 2011 and 2017 for new molecular entities (NMEs). RESULTS: From 2011 through 2017, the FDA approved 250 NMEs, ranging from 27 approvals in 2013 to 46 in 2017. The NME approvals spanned 22 different disease classes; almost one-third of all NMEs were for oncology treatments. CONCLUSIONS: As these pathways are utilized more, additional legislative changes may be needed to re-align incentives to promote continued development of innovative drugs for serious unmet needs in a safe, efficacious, and affordable manner.

Is subretinal AAV gene replacement still the only viable treatment option for choroideremia?

INTRODUCTION: Choroideremia is an X-linked inherited retinal degeneration resulting from mutations in the CHM gene, encoding Rab escort protein-1 (REP1), a protein regulating intracellular vesicular transport. Loss-of-function mutations in CHM lead to progressive loss of retinal pigment epithelium (RPE) with photoreceptor and choriocapillaris degeneration, leading to progressive visual field constriction and loss of visual acuity. Three hundred and fifty-four unique mutations have been reported in CHM. While gene augmentation remains an ideal therapeutic option for choroideremia, other potential future clinical strategies may exist. AREAS COVERED: The authors examine the pathophysiology and genetic basis of choroideremia. They summarize the status of ongoing gene therapy trials and discuss CHM mutations amenable to other therapeutic approaches including CRISPR/Cas-based DNA and RNA editing, nonsense suppression of premature termination codons, and antisense oligonucleotides for splice modification. The authors undertook a literature search in PubMed and NIH Clinical Trials in October 2020. EXPERT OPINION: The authors conclude that AAV-mediated gene augmentation remains the most effective approach for choroideremia. Given the heterogeneity of CHM mutations and potential risks and benefits, genome-editing approaches currently do not offer significant advantages. Nonsense suppression strategies and antisense oligonucleotides are exciting novel therapeutic options; however, their clinical viability remains to be determined.

CRISPR genome engineering for retinal diseases.

Novel gene therapy treatments for inherited retinal diseases have been at the forefront of translational medicine over the past couple of decades. Since the discovery of CRISPR mechanisms and their potential application for the treatment of inherited human conditions, it seemed inevitable that advances would soon be made using retinal models of disease. The development of CRISPR technology for gene therapy and its increasing potential to selectively target disease-causing nucleotide changes has been rapid. In this chapter, we discuss the currently available CRISPR toolkit and how it has been and can be applied in the future for the treatment of inherited retinal diseases. These blinding conditions have until now had limited opportunity for successful therapeutic intervention, but the discovery of CRISPR has created new hope of achieving such, as we discuss within this chapter.

Genome-Editing Strategies for Treating Human Retinal Degenerations.

Inherited retinal degenerations (IRDs) are a leading cause of blindness. Although gene-supplementation therapies have been developed, they are only available for a small proportion of recessive IRD mutations. In contrast, genome editing using clustered-regularly interspaced short palindromic repeats (CRISPR) CRISPR-associated (Cas) systems could provide alternative therapeutic avenues for treating a wide range of genetic retinal diseases through targeted knockdown or correction of mutant alleles. Progress in this rapidly evolving field has been highlighted by recent Food and Drug Administration clinical trial approval for EDIT-101 (Editas Medicine, Inc., Cambridge, MA), which has demonstrated efficacious genome editing in a mouse model of CEP290-associated Leber congenital amaurosis and safety in nonhuman primates. Nonetheless, there remains a significant number of challenges to developing clinically viable retinal genome-editing therapies. In particular, IRD-causing mutations occur in more than 200 known genes, with considerable heterogeneity in mutation type and position within each gene. Additionally, there are remaining safety concerns over long-term expression of Cas9 in vivo. This review highlights (i) the technological advances in gene-editing technology, (ii) major safety concerns associated with retinal genome editing, and (iii) potential strategies for overcoming these challenges to develop clinical therapies.

What Is the Price and Claimed Efficacy of Platelet-Rich Plasma Injections for the Treatment of Knee Osteoarthritis in the United States?

Platelet-rich plasma (PRP) injections are often used for the treatment of knee osteoarthritis (OA), despite clinical value and cost-effectiveness not being definitely established. PRP injections are considered as a potential means of reducing pain and improving function in patients with knee OA, in the hope of delaying or avoiding the need for surgical intervention. Centers that offer PRP injections usually charge patients out of pocket and directly market services. Therefore, the purpose of this study was to quantify the current (1) prices and (2) marketed clinical efficacy of autologous PRP injections for knee OA. A prospective cross-sectional study was performed based on 286 centers identified in the United States offering PRP injections for knee OA. A total of 179 (73.4%) centers were successfully contacted via e-mail or phone, using a simulated 52-year-old male patient with knee OA. Scripted questions were asked by the simulated patient to determine the current marketed prices and clinical efficacy, either reported as "good results" or "symptomatic improvement," claimed by each treating center. The mean price for a single unilateral knee same-day PRP injection was $714 with a standard deviation of $144 (95% confidence interval [CI]: $691-737, n = 153). The mean claim of clinical efficacy was 76% with a standard deviation of 11% (95% CI: 73.5-78.3%, n = 84). Out of the 84 clinics, 10 claimed "90 to 100% efficacy," 27 claimed "80 to 90%," 29 claimed "70 to 80%," 9 claimed "60 to 70%," 8 claimed "50 to 60%," and 1 claimed "40 to 60%." These findings provide a unique perspective on the PRP market for the treatment of knee OA that is valuable to physicians and health care providers in providing better education to patients on the associated costs and purported clinical benefits of PRP injections.

Horizon Scan Of Clinical Laboratories Offering Pharmacogenetic Testing.

Pharmacogenetic (PGx) testing involves the analysis of genes known to affect response to medications. The field has been projected as a leading application of personalized or precision medicine, but the use of PGx tests has been stymied, in part, by the lack of clinical evidence of utility and reported low provider awareness. Another factor is the availability of testing. The range and types of PGx tests available have not been assessed to date. In the period September 2017-January 2018 we analyzed the numbers and types of PGx tests offered by clinical testing laboratories in the US. Of the 111 such labs that we identified, we confirmed that 76 offered PGx testing services. Of these, 31 offered only tests for single genes; 30 offered only tests for multiple genes; and 15 offered both types of tests. Collectively, 45 laboratories offered 114 multigene panel tests covering 295 genes. The majority of these tests did not have any clinical guidelines. PGx tests vary in type and makeup, which presents challenges in appropriate test evaluation and selection for providers, insurers, health systems, and patients alike.