Gene Therapy

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Early stage clinical trials for the treatment of hemophilia A

INTRODUCTION

Hemophilia A is a severe bleeding disorder affecting about 1 in 5,000 males. The gold standard for prophylaxis and treatment of acute bleeding has been factor (F) VIII concentrate. A multitude of treatment modalities are now available and under clinical investigation.

AREAS COVERED

This review discusses ongoing/recently completed early-phase clinical trials registered on ClinicalTrials.gov in patients with hemophilia A through April 2022. These new pipeline therapies are focused on addressing the safety and efficacy of new factor-related products, non-factor related products, and gene therapy options for hemophilia.

EXPERT OPINION

Current standard of care effectively prevents and treats acute bleeding and has significantly improved the quality of life in hemophilia. The biggest challenges in the improvement of care are treatment-related burden and the burden of cost in developing countries. New drugs under development are likely to enter practice by the end of this decade and address many of the unmet needs particularly of those with severe disease. Data is limited in unique populations (e.g. congenital/inherited FVIII inhibitors, non-severe hemophilia A, women/girls with hemophilia and children) which are important areas for future research; additional clinical trials and long-term outcome data are necessary prior to incorporating these new therapies in our treatment arsenal.

Harnessing nucleic acid technologies for human health on earth and in space

Nucleic acid therapeutics are a versatile class of sequence-programmable drugs that offer a robust and clinically viable strategy to modulate expression or correct genetic defects contributing to disease. The majority of drugs currently on the market target proteins; however, proteins only represent a subset of possible disease targets. Nucleic acid therapeutics allow intuitive engagement with genome sequences providing a more direct way to target many diseases at their genetic root cause. Their clinical success depends on platform technologies which can support durable and well tolerated pharmacological activity in a given tissue. Nucleic acid drugs possess a potent combination of target specificity and adaptability required to advance drug development for many diseases. As these therapeutic technologies mature, their clinical applications can also expand access to personalized therapies for patients with rare or solo genetic diseases. Spaceflight crew members exposed to the unique hazards of spaceflight, especially those related to galactic cosmic radiation (GCR) exposure, represent another patient subset who may also benefit from nucleic acid drugs as countermeasures. In this review, we will discuss the various classes of RNA- and DNA-targeted nucleic acid drugs, provide an overview of their present-day clinical applications, and describe major strategies to improve their delivery, safety, and overall efficacy.

G-Quadruplex Linked DNA Guides Selective Transfection into Nucleolin-Overexpressing Cancer Cells

Gene therapy is a promising approach for treating tumors. Conventional approaches of DNA delivery depending on non-viral or viral vectors are unsatisfactory due to the concerns of biosafety and cell-targeting efficiency. The question how to deliver DNA into tumor cells efficiently and selectively is a major technological problem in tumor gene therapy. Here, we develop a vector-free gene transfer strategy to deliver genes effectively and selectively by taking advantage of targeting nucleolin. Nucleolin, a shuttle protein moving between cell membrane, cytoplasm and nuclei, is overexpressed in tumor cells. It has a natural ligand G-quadruplex (Gq). Gq-linked DNA (Gq-DNA) is likely to be internalized by ligand dependent uptake mechanisms independently of vectors after neutralizing negative charges of cell membrane by targeting nucleolin. This strategy is referred to as Gq-DNA transfection. Benefiting from its high affinity to nucleolin, Gq-DNA can be effectively delivered into nucleolin-positive tumor cells even nuclei. Gq-DNA transfection is characterized by low cytotoxicity, high efficiency, ease of synthesis, high stability in serum, direct access into nuclei, and specific nucleolin-positive tumor cell targeting.

Development of a New DHFR-Based Destabilizing Domain with Enhanced Basal Turnover and Applicability in Mammalian Systems

Destabilizing domains (DDs) are an attractive strategy allowing for positive post-transcriptional small molecule-regulatable control of a fusion protein's abundance. However, in many instances, the currently available DDs suffer from higher-than-desirable basal levels of the fusion protein. Accordingly, we redesigned the E. coli dihydrofolate reductase (ecDHFR) DD by introducing a library of ∼1200 random ecDHFR mutants fused to YFP into CHO cells. Following successive rounds of fluorescence-activated cell sorting, we identified six new ecDHFR DD clones with significantly enhanced proteasomal turnover in the absence of a stabilizing ligand, trimethoprim (TMP). One of these clones, designated as "C12", contained four unique missense mutations (W74R/T113S/E120D/Q146L) and demonstrated a significant 2.9-fold reduction in basal levels compared to the conventional ecDHFR DD (i.e., R12Y/G67S/Y100I). This domain was similarly responsive to TMP with respect to dose response and maximal stabilization, indicating an overall enhanced dynamic range. Interestingly, both computational and wet-lab experiments identified the W74R and T113S mutations of C12 as the main contributors toward its basal destabilization. However, the combination of all the C12 mutations was required to maintain both its enhanced degradation and TMP stabilization. We further demonstrate the utility of C12 by fusing it to IκBα and Nrf2, two stress-responsive proteins that have previously been challenging to regulate. In both instances, C12 significantly enhanced the basal turnover of these proteins and improved the dynamic range of regulation post stabilizer addition. These advantageous features of the C12 ecDHFR DD variant highlight its potential for replacing the conventional N-terminal ecDHFR DD and improving the use of DDs overall, not only as a chemical biology tool but for gene therapy avenues as well.

Anion-Exchange Chromatography at the Service of Gene Therapy: Baseline Separation of Full/Empty Adeno-Associated Virus Capsids by Screening of Conditions and Step Gradient Elution Mode

Gene therapy is opening unprecedented opportunities for novel therapeutic approaches. Based on the concept of rescuing function mutations by co-expressing the correct gene to allow biological functions to be restored, it requires the use of viral vectors to ensure the proper delivery of therapeutic genes. In this context, recombinant adeno-associated viruses (rAAV) are the most widely used vectors. Their biomanufacturing process requires the insertion of the therapeutic gene into the rAAV (full capsids). However, a percentage of rAAV that do not contain the desired gene (empty capsids), as well as partly filled capsids, might also be produced, potentially impacting the efficiency of the therapy. Therefore, the determination of the rAAV capsids’ full/empty ratio needs to be monitored to ensure consistent product quality and efficacy. Anion-exchange chromatography (AEX) can serve this need. In this contribution, thorough AEX method development, including a mobile phase, a stationary phase and gradient conditions, has highlighted its potential in supporting gene therapy. Taking advantage of the fact that viral capsids follow an “on/off” retention behavior, the application of a step gradient approach to the rAAV serotype 8 (rAAV8) allowed the unprecedented separation of rAAV8 full/empty capsids, with a resolution gain of 3.7 as compared to the resolution obtained with a fully optimized linear gradient. Finally, the developed analytical approach allowed a precise and accurate baseline separation and quantification of full and empty rAAV8 capsids, with the potential to be applied as a high-throughput quality control (QC) method.

Evolving therapies in neuronopathic LSDs: opportunities and challenges

Lysosomal storage disorders (LSD) are multisystemic progressive disorders caused by genetic mutations involving lysosomal function. While LSDs are individually considered rare diseases, the overall true prevalence of these disorders is likely higher than our current estimates. More than two third of the LSDs have associated neurodegeneration and the neurological phenotype often defines the course of the disease and treatment outcomes. Addressing the neurological involvement in LSDs has posed a significant challenge in the rapidly evolving field of therapies for these diseases. In this review, we summarize current approaches and clinical trials available for patients with neuronopathic lysosomal storage disorders, exploring the opportunities and challenges that have emerged with each of these.

Biocompatible Iron Oxide Nanoparticles for Targeted Cancer Gene Therapy: A Review

In recent years, gene therapy has made remarkable achievements in tumor treatment. In a successfully cancer gene therapy, a smart gene delivery system is necessary for both protecting the therapeutic genes in circulation and enabling high gene expression in tumor sites. Magnetic iron oxide nanoparticles (IONPs) have demonstrated their bright promise for highly efficient gene delivery target to tumor tissues, partly due to their good biocompatibility, magnetic responsiveness, and extensive functional surface modification. In this review, the latest progress in targeting cancer gene therapy is introduced, and the unique properties of IONPs contributing to the efficient delivery of therapeutic genes are summarized with detailed examples. Furthermore, the diagnosis potentials and synergistic tumor treatment capacity of IONPs are highlighted. In addition, aiming at potential risks during the gene delivery process, several strategies to improve the efficiency or reduce the potential risks of using IONPs for cancer gene therapy are introduced and addressed. The strategies and applications summarized in this review provide a general understanding for the potential applications of IONPs in cancer gene therapy.

Rational engineering of adeno-associated virus capsid enhances human hepatocyte tropism and reduces immunogenicity

OBJECTIVES

Gene therapy based on recombinant adeno-associated viral (rAAV) vectors has been proved to be clinically effective for genetic diseases. However, there are still some limitations, including possible safety concerns for high dose delivery and a decreasing number of target patients caused by the high prevalence of pre-existing neutralizing antibodies, hindering its application. Herein, we explored whether there was an engineering strategy that can obtain mutants with enhanced transduction efficiency coupled with reduced immunogenicity.

METHODS

We described a new strategy for AAV capsids engineering by combining alterations of N-linked glycosylation and the mutation of PLA2-like motif. With this combined strategy, we generated novel variants derived from AAV8 and AAVS3.

RESULTS

The variants mediated higher transduction efficiency in human liver carcinoma cell lines and human primary hepatocytes as well as other human tissue cell lines. Importantly, all the variants screened out showed lower sensitivity to neutralizing antibody in vitro and in vivo. Moreover, the in vivo antibody profiles of variants were different from their parental AAV capsids.

CONCLUSIONS

Our work proposed a new combined engineering strategy and engineered two liver-tropic AAVs. We also obtained several AAV variants with a higher transduction efficiency and lower sensitivity of neutralizing antibodies. By expanding the gene delivery toolbox, these variants may further facilitate the success of AAV gene therapy.

Impact of genetically modified organism requirements on gene therapy development in the EU, Japan, and the US

Advanced therapies are emerging as an important class of medicinal products; among these, gene therapies are advancing at an exceptional rate. However, one of the major challenges for gene therapies relates to the additional regulatory requirements for genetically modified organisms. In this paper, we provide an overview of the regulatory requirements for genetically modified organisms in the European Union, Japan, and the United States. We share our experience in managing these requirements and their impact on the adeno-associated virus gene therapies that are under development at Pfizer. Specifically, we discuss the relative complexity of the approval process and the impact of risk assessment expectations on the clinical development of genetically modified organisms. We also compare the regulatory processes and timelines of various regions based on our experience with adeno-associated viral vectors. Finally, we propose that genetically modified organisms, for which pathogenicity and replication competency are well controlled, should be regulated solely under medicinal product regulations and be exempt from additional requirements for genetically modified organisms. Even if an exemption is not implemented, it should still be possible to significantly reduce the sponsor and agency burden by simplifying and harmonizing documentation and data requirements as well as timelines for applications for genetically modified organisms.

The Arrival of Gene Therapy for Patients with Hemophilia A

Historically, the standard of care for hemophilia A has been intravenous administration of exogenous factor VIII (FVIII), either as prophylaxis or episodically. The development of emicizumab, a humanized bispecific monoclonal antibody mimicking activated FVIII, was a subsequent advance in treatment. However, both exogenous FVIII and emicizumab require repeated and lifelong administration, negatively impacting patient quality of life. A recent breakthrough has been the development of gene therapy. This allows a single intravenous treatment that could result in long-term expression of FVIII, maintenance of steady-state plasma concentrations, and minimization (or possibly elimination) of bleeding episodes for the recipient's lifetime. Several gene therapies have been assessed in clinical trials, with positive outcomes. Valoctocogene roxaparvovec (an adeno-associated viral 5-based therapy encoding human B domain-deleted FVIII) is expected to be the first approved gene therapy in European countries, including Italy, in 2022. Some novel challenges exist including refining patient selection criteria, managing patient expectations, further elucidation of the durability and variability of transgene expression and long-term safety, and the development of standardized 'hub and spoke' centers to optimize and monitor this innovative treatment. Gene therapy represents a paradigm shift, and may become a new reference standard for treating patients with hemophilia A.

Carboxymethyl chitosan prolongs adenovirus-mediated expression of IL-10 and ameliorates hepatic fibrosis in a mouse model

Effective and safe liver-directed gene therapy has great promise in treating a broad range of liver diseases. While adenoviral (Ad) vectors have been widely used for efficacious in vivo gene delivery, their translational utilities are severely limited due to the short duration of transgene expression and solicitation of host immune response. Used as a promising polymeric vehicle for drug release and nucleic acid delivery, carboxymethyl chitosan (CMC) is biocompatible, biodegradable, anti-microbial, inexpensive, and easy accessible. Here, by exploiting its biocompatibility, controlled release capability and anti-inflammatory activity, we investigated whether CMC can overcome the shortcomings of Ad-mediated gene delivery, hence improving the prospect of Ad applications in gene therapy. We demonstrated that in the presence of optimal concentrations of CMC, Ad-mediated transgene expression lasted up to 50 days after subcutaneous injection, and at least 7 days after intrahepatic injection. Histologic evaluation and immunohistochemical analysis revealed that CMC effectively alleviated Ad-induced host immune response. In our proof-of-principle experiment using the CCl4-induced experimental mouse model of chronic liver damage, we demonstrated that repeated intrahepatic administrations of Ad-IL10 mixed with CMC effectively mitigated the development of hepatic fibrosis. Collectively, these results indicate that CMC can improve the prospect of Ad-mediated gene therapy by diminishing the host immune response while allowing readministration and sustained transgene expression.

Aggregation-Induced Emission (AIE) and Magnetic Resonance Imaging Characteristics for Targeted and Image-Guided siRNA Therapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer and remains a global health challenge. Small interfering RNA (siRNA) is a promising therapeutic modality that blocks multiple disease-causing genes without impairing cell structures. However, siRNA therapeutics still have off-target proportion and lack effective quantitative analysis method in vivo. Thus, a novel theragnostic nanoparticle with dual-mode imaging is synthesized for targeted and image-guided siRNA therapy of HCC. Survivin siRNA is carried by Poly-ethylenimine (PEI) and interacted with T7-AIE/Gd NPs, which are self-assembled of DSPE-PEG-DTPA(Gd), DSPE-PEG-Mal, DSPE-PEG-PEI, and TPE. The resulting theragnostic nanoparticles exhibit lower toxicity and high therapeutic effect, and excellent T1-weighted magnetic resonance imaging (MRI) and aggregation-induced emission (AIE) imaging performance. Moreover, in vivo MRI and AIE imaging indicate that this kind of theragnostic nanoparticles rapidly accumulates in the tumor due to active targeting and enhanced permeability and retention (EPR) effects. Sur@T7-AIE-Gd suppresses HCC tumor growth by inducing autophagy and destabilizes DNA integrity in tumor cells. The results suggest that T7-AIE-Gd nanoparticles carrying Survivin siRNA with dual-mode imaging characteristics are promising for targeted and image-guided siRNA therapy of hepatocellular carcinoma.

Advanced Peptide Nanomedicines for Bladder Cancer Theranostics

Cancer is still a global public health problem. Although remarkable success has been achieved in cancer diagnosis and treatment, the high recurrence and mortality rates remain severely threatening to human lives and health. In recent years, peptide nanomedicines with precise selectivity and high biocompatibility have attracted intense attention in biomedical applications. In particular, there has been a significant increase in the exploration of peptides and their derivatives for malignant tumor therapy and diagnosis. Herein, we review the applications of peptides and their derivatives in the diagnosis and treatment of bladder cancer, providing new insights for the design and development of novel peptide nanomedicines for the treatment of bladder cancer in the future.

Stimuli-responsive nanoformulations for CRISPR-Cas9 genome editing

The CRISPR-Cas9 technology has changed the landscape of genome editing and has demonstrated extraordinary potential for treating otherwise incurable diseases. Engineering strategies to enable efficient intracellular delivery of CRISPR-Cas9 components has been a central theme for broadening the impact of the CRISPR-Cas9 technology. Various non-viral delivery systems for CRISPR-Cas9 have been investigated given their favorable safety profiles over viral systems. Many recent efforts have been focused on the development of stimuli-responsive non-viral CRISPR-Cas9 delivery systems, with the goal of achieving efficient and precise genome editing. Stimuli-responsive nanoplatforms are capable of sensing and responding to particular triggers, such as innate biological cues and external stimuli, for controlled CRISPR-Cas9 genome editing. In this Review, we overview the recent advances in stimuli-responsive nanoformulations for CRISPR-Cas9 delivery, highlight the rationale of stimuli and formulation designs, and summarize their biomedical applications.

Advances in Hemophilia A Management

Hemophilia A is an inherited insufficiency of Factor VIII (FVIII), one of the critical clotting factors. The gold standard for the management of moderate-to-severe hemophilia A is prophylaxis using regular replacement therapy with clotting factor concentrates. Compared with conventional treatment, extended half-life products reduce the burden of frequent factor replacement injections. Of note, up to 30% of patients with hemophilia A receiving prophylactic factor infusions develop "inhibitors," neutralizing anti-FVIII autoantibodies. Therapeutic options for patients with hemophilia A and inhibitors include the immune tolerance induction (ie, eradication of inhibitors) and the management of acute bleeds with bypassing agents and/or emicizumab. Emicizumab is a biphasic monoclonal antibody mimicking activated FVIII, approved for patients with hemophilia A with/without inhibitors. Gene therapy is an emerging therapy for hemophilia A, essentially curing patients with hemophilia A or transforming them to a milder phenotype by establishing continuous endogenous expression of FVIII after one-time treatment.

Inhibition of DYRK1A, via histone modification, promotes cardiomyocyte cell cycle activation and cardiac repair after myocardial infarction

BACKGROUND

While the adult mammalian heart undergoes only modest renewal through cardiomyocyte proliferation, boosting this process is considered a promising therapeutic strategy to repair cardiac injury. This study explored the role and mechanism of dual-specificity tyrosine regulated kinase 1A (DYRK1A) in regulating cardiomyocyte cell cycle activation and cardiac repair after myocardial infarction (MI).

METHODS

DYRK1A-knockout mice and DYRK1A inhibitors were used to investigate the role of DYRK1A in cardiomyocyte cell cycle activation and cardiac repair following MI. Additionally, we explored the underlying mechanisms by combining genome-wide transcriptomic, epigenomic, and proteomic analyses.

FINDINGS

In adult mice subjected to MI, both conditional deletion and pharmacological inhibition of DYRK1A induced cardiomyocyte cell cycle activation and cardiac repair with improved cardiac function. Combining genome-wide transcriptomic and epigenomic analyses revealed that DYRK1A knockdown resulted in robust cardiomyocyte cell cycle activation (shown by the enhanced expression of many genes governing cell proliferation) associated with increased deposition of trimethylated histone 3 Lys4 (H3K4me3) and acetylated histone 3 Lys27 (H3K27ac) on the promoter regions of these genes. Mechanistically, via unbiased mass spectrometry, we discovered that WD repeat-containing protein 82 and lysine acetyltransferase 6A were key mediators in the epigenetic modification of H3K4me3 and H3K27ac and subsequent pro-proliferative transcriptome and cardiomyocyte cell cycle activation.

INTERPRETATION

Our results reveal a significant role of DYRK1A in cardiac repair and suggest a drug target with translational potential for treating cardiomyopathy.

FUNDING

This study was supported in part by grants from the National Natural Science Foundation of China (81930008, 82022005, 82070296, 82102834), National Key R&D Program of China (2018YFC1312700), Program of Innovative Research Team by the National Natural Science Foundation (81721001), and National Institutes of Health (5R01DK039308-31, 7R37HL023081-37, 5P01HL074940-11).

Targeted activation of HNF4α/HGF1/FOXA2 reverses hepatic fibrosis via exosome-mediated delivery of CRISPR/dCas9-SAM system

Aim: Hepatic fibrosis is one of the most common conditions worldwide, and yet no effective antifibrotic therapy is available. This study aimed to reverse hepatic fibrosis via exosome-mediated delivery of the CRISPR/dCas9-SAM system. Materials & methods: The authors constructed a modified-exosome delivery system targeting hepatic stellate cells (HSCs), and constructed the CRISPR/dCas9-SAM system inducing HSCs convert into hepatocyte-like cells in vitro and in vivo. Results: RBP4-modified exosomes could efficiently load and deliver the CRISPR/dCas9 system to HSCs. The in vitro CRISPR/dCas9 system induced the conversion from HSCs to hepatocyte-like cells via targeted activation of HNF4α/HGF1/FOXA2 genes. Importantly, in vivo targeted delivery of this system significantly attenuated CCl₄-induced hepatic fibrosis. Conclusion: Targeted activation of HNF4α/HGF1/FOXA2 reverses hepatic fibrosis via exosome-mediated delivery of the CRISPR/dCas9-SAM system, which provides a feasible antifibrotic strategy.

Immunomodulatory effect and safety of TNF-α RNAi mediated by oral yeast microcapsules in rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is a chronic autoimmune disease that requires long-term treatment and monitoring. Inhibition of inflammatory gene expression by gene therapy is a significant breakthrough in RA treatment, but the lack of a safe and effective gene delivery system hinders its application. Since oral administration can significantly reduce wound infection caused by parenteral administration, it also has the advantages of high patient compliance and convenience. Therefore, oral administration may be the best option for the treatment of this chronic disease. In this study, we developed a novel oral drug system by delivering tumor necrosis factor-α (TNF-α) short hairpin RNA (shRNA) mediated by non-pathogenic yeast to evaluate its regulation of systemic immune inflammation and safety in RA. Non-pathogenic yeast can resist the destruction of the gastrointestinal acid-base environment and can be recognized by the intestinal macrophages and act on systemic inflammatory lesions. Oral administration of yeast-mediated TNF-α shRNA significantly reduced the expression of TNF-α predominant pro-inflammatory factors in intestinal macrophages and joint synovium, and up-regulated the expression of anti-inflammatory cytokine IL-10 and M2 macrophages, systematically regulating the inflammatory response. This yeast-mediated oral gene delivery system can not only significantly inhibit knee joint synovial inflammation, but also has no toxic effects on peripheral blood and major organs. Therefore, yeast-mediated oral delivery of TNF-α shRNA may be used as a novel gene therapy strategy to treat RA through immunomodulating the mononuclear phagocyte system from the intestine to the joint synovium, and ultimately regulating systemic and local immune inflammation, providing new ideas for the clinical treatment of RA.

Phase 1-2 Trial of AAVS3 Gene Therapy in Patients with Hemophilia B

BACKGROUND

FLT180a (verbrinacogene setparvovec) is a liver-directed adeno-associated virus (AAV) gene therapy that uses a synthetic capsid and a gain-of-function protein to normalize factor IX levels in patients with hemophilia B.

METHODS

In this multicenter, open-label, phase 1-2 trial, we assessed the safety and efficacy of varying doses of FLT180a in patients with severe or moderately severe hemophilia B (factor IX level, ≤2% of normal value). All the patients received glucocorticoids with or without tacrolimus for immunosuppression to decrease the risk of vector-related immune responses. After 26 weeks, patients were enrolled in a long-term follow-up study. The primary end points were safety and efficacy, as assessed by factor IX levels at week 26.

RESULTS

Ten patients received one of four FLT180a doses of vector genomes (vg) per kilogram of body weight: 3.84×10¹¹ vg, 6.40×10¹¹ vg, 8.32×10¹¹ vg, or 1.28×10¹² vg. After receiving the infusion, all the patients had dose-dependent increases in factor IX levels. At a median follow-up of 27.2 months (range, 19.1 to 42.4), sustained factor IX activity was observed in all the patients except one, who resumed factor IX prophylaxis. As of the data-cutoff date (September 20, 2021), five patients had normal factor IX levels (range, 51 to 78%), three patients had levels from 23 to 43%, and one had a level of 260%. Of the reported adverse events, approximately 10% were related to FLT180a and 24% to immunosuppression. Increases in liver aminotransferase levels were the most common FLT180a-related adverse events. Late increases in aminotransferase levels occurred in patients who had received prolonged tacrolimus beyond the glucocorticoid taper. A serious adverse event of arteriovenous fistula thrombosis occurred in the patient with high factor IX levels.

CONCLUSIONS

Sustained factor IX levels in the normal range were observed with low doses of FLT180a but necessitated immunosuppression with glucocorticoids with or without tacrolimus. (Funded by Freeline Therapeutics; ClinicalTrials.gov numbers, NCT03369444 and NCT03641703; EudraCT numbers, 2017-000852-24 and 2017-005080-40.).

Highly water-dispersible PCN nanosheets as light-controlled lysosome self-promoting escape type non-cationic gene carriers for tumor therapy

The construction of non-viral gene delivery faces two major challenges: cytotoxicity caused by high cationic charge units and easy degradation by lysosomes. Herein, highly water-dispersible polymeric carbon nitride (PCN) nanosheets were utilized as the core to construct a light-controlled non-cationic gene delivery system with sufficient lysosomal escape ability. In this system, these nanosheets exhibited efficient DNA condensation, outstanding biocompatibility, transfection tracking, light responsiveness and high transfection efficiency. Once PCN-DNA was taken up by the tumor cells, the accumulated ROS generated by photosensitizers (PSs) under light irradiation would destroy the structure of lysosomes, promote the escape of PCN-DNA and increase the efficiency of gene transfection. Simultaneously, the gene transfection process could be tracked in real time through fluorescence imaging technology, which was conducive to investigate the transfection mechanism. In vitro and in vivo experiments further confirmed that PCN nanosheets loaded with the P53 gene were beneficial to the regeneration of the P53 apoptotic pathway, increased tumor sensitivity to PSs, and further induced tumor cell apoptosis. In summary, the highly water-dispersible PCN nanosheets were applied to light-controlled self-escaping gene delivery for the first time, and tumor gene therapy was successfully realized.

Potential disease-modifying therapies for Huntington's disease: lessons learned and future opportunities

Huntington's disease is the most frequent autosomal dominant neurodegenerative disorder; however, no disease-modifying interventions are available for patients with this disease. The molecular pathogenesis of Huntington's disease is complex, with toxicity that arises from full-length expanded huntingtin and N-terminal fragments of huntingtin, which are both prone to misfolding due to proteolysis; aberrant intron-1 splicing of the HTT gene; and somatic expansion of the CAG repeat in the HTT gene. Potential interventions for Huntington's disease include therapies targeting huntingtin DNA and RNA, clearance of huntingtin protein, DNA repair pathways, and other treatment strategies targeting inflammation and cell replacement. The early termination of trials of the antisense oligonucleotide tominersen suggest that it is time to reflect on lessons learned, where the field stands now, and the challenges and opportunities for the future.

Synthetic Helical Polypeptide as a Gene Transfection Enhancer

The relatively low transfection efficiency limits further application of polymeric gene carriers. It is imperative to exploit a universal and simple strategy to enhance the gene transfection efficiency of polymeric gene carriers. Herein, we prepared a cationic polypeptide poly(γ-aminoethylthiopropyl-l-glutamate) (PALG-MEA, termed PM) with a stable α-helical conformation, which can significantly improve the gene transfection efficiency of cationic polymers. PM can be integrated into polymeric gene delivery systems noncovalently through electrostatic interactions. With the assistance of PM, polymeric gene delivery systems exhibited excellent cellular uptake and endosomal escape, thereby enhancing transfection efficiency. The transfection enhancement effect of PM was applicable to a variety of cationic polymers such as polyethylenimine (PEI), poly-l-lysine (PLL), and polyamidoamine (PAMAM). The ternary gene delivery system PM/pshVEGF/PEI exhibited an excellent antitumor effect against the B16F10 tumor model. Moreover, we demonstrated that PM could also enhance the delivery of gene editing systems (sgRNA-Cas9 plasmids). This work provides a facile and effective strategy for constructing polymeric gene delivery systems with a high transfection efficiency.

MSD-based assays facilitate a rapid and quantitative serostatus profiling for the presence of anti-AAV antibodies

Adeno-associated virus (AAV) vector applications are often limited by capsid-directed humoral immune responses, mainly through neutralizing antibodies (NAbs), which are present throughout the human population due to natural AAV infections. Currently, antibody levels are often quantified via ELISA-based protocols or by cellular NAb assays and less frequently by in vivo NAb assays in mice. These methods need optimization for each serotype and are often not applicable to AAV variants with poor in vitro transduction. To tackle these limitations, we have established Meso Scale Discovery (MSD)-based assays for the quantification of binding antibodies (BAbs) and NAbs against the three most commonly used AAV serotypes, AAV2, AAV8, and AAV9. Both assays detect anti-AAV-IgG1-3 with high sensitivity and consistency as shown in a screen of sera from 40 healthy human donors. Subsequently, BAb and NAb titers were determined for identification of seronegative animals in a non-human primate (NHP) cohort. Moreover, the MSD-based BAb assay protocol was extended to a panel of 14 different AAV serotypes. In summary, our platform allows a rapid and quantitative assessment of the immunological properties of any natural or engineered AAV variant irrespective of transduction efficiency and enables high-throughput screens.

Emerging Therapies for Hepatocellular Carcinoma (HCC)

Hepatocellular carcinoma (HCC) arises from hepatocytes and accounts for 90% of primary liver cancer. According to Global Cancer Incidence, Mortality and Prevalence (GLOBOCAN) 2020, globally HCC is the sixth most common cancer and the third most common cause of cancer-related deaths. Reasons for HCC prognosis remaining dismal are that HCC is asymptomatic in its early stages, leading to late diagnosis, and it is markedly resistant to conventional chemo- and radiotherapy. Liver transplantation is the treatment of choice in early stages, while surgical resection, radiofrequency ablation (RFA) and trans arterial chemoembolization (TACE) are Food and Drug Administration (FDA)-approved treatments for advanced HCC. Additional first line therapy for advanced HCC includes broad-spectrum tyrosine kinase inhibitors (TKIs), such as sorafenib and lenvatinib, as well as a combination of immunotherapy and anti-angiogenesis therapy, namely atezolizumab and bevacizumab. However, these strategies provide nominal extension in the survival curve, cause broad spectrum toxic side effects, and patients eventually develop therapy resistance. Some common mutations in HCC, such as in telomerase reverse transcriptase (TERT), catenin beta 1 (CTNNB1) and tumor protein p53 (TP53) genes, are still considered to be undruggable. In this context, identification of appropriate gene targets and specific gene delivery approaches create the potential of gene- and immune-based therapies for the safe and effective treatment of HCC. This review elaborates on the current status of HCC treatment by focusing on potential gene targets and advanced techniques, such as oncolytic viral vectors, nanoparticles, chimeric antigen receptor (CAR)-T cells, immunotherapy, and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), and describes future prospects in HCC treatment.

Rational engineering of a functional CpG-free ITR for AAV gene therapy

Inverted terminal repeats (ITRs) are the only wild-type components retained in the genome of adeno-associated virus (AAV) vectors. To determine whether ITR modification is a viable approach for AAV vector engineering, we rationally deleted all CpG motifs in the ITR and examined whether CpG elimination compromises AAV-vector production and transduction. Modified ITRs were stable in the plasmid and maintained the CpG-free nature in purified vectors. Replacing the wild-type ITR with the CpG-free ITR did not affect vector genome encapsidation. However, the vector yield was decreased by approximately 3-fold due to reduced vector genome replication. To study the biological potency, we made micro-dystrophin (μDys) AAV vectors carrying either the wild-type ITR or the CpG-free ITR. We delivered the CpG-free μDys vector to one side of the tibialis anterior muscle of dystrophin-null mdx mice and the wild-type μDys vector to the contralateral side. Evaluation at four months after injection showed no difference in the vector genome copy number, microdystrophin expression, and muscle histology and force. Our results suggest that the complete elimination of the CpG motif in the ITR does not affect the biological activity of the AAV vector. CpG-free ITRs could be useful in engineering therapeutic AAV vectors.

Immune regulatory effect of osteopontin gene therapy in a murine model of multi-drug resistant pulmonary tuberculosis

Tuberculosis (TB) has been for many years a major public health problem since treatment is long and sometimes ineffective favoring the increase of multi-drug-resistant mycobacteria (MDR). Gene therapy is a novel and effective tool to regulate immune responses. In this study we evaluated the therapeutic effect of an adenoviral vector codifying osteopontin (AdOPN), a molecule known for their roles to favour Th1 and Th17 type-cytokine expression which are crucial in TB containment. A single-dose of AdOPN administration in BALB/c mice suffering late progressive pulmonary MDR-TB, produced significant lower bacterial load and pneumonia, due to higher expression of IFN-γ, IL-12 and IL-17 in coexistence with increase of granulomas in number and size, resulting in higher survival, in contrast with mice treated with the control adenovirus that codify the green fluorescent protein (AdGFP). Combined therapy of AdOPN with a regimen of 2nd line antibiotics produced a better control of bacterial load in lung during the first days of treatment, suggesting that AdOPN can shorten chemotherapy. Taken together, gene therapy with AdOPN leads to higher immune responses against TB infection, resulting in a new potential treatment against pulmonary TB that can co-adjuvant chemotherapy.

Gene Therapy for Acquired and Genetic Cholestasis

Cholestatic diseases can be caused by the dysfunction of transporters involved in hepatobiliary circulation. Although pharmacological treatments constitute the current standard of care for these diseases, none are curative, with liver transplantation being the only long-term solution for severe cholestasis, albeit with many disadvantages. Liver-directed gene therapy has shown promising results in clinical trials for genetic diseases, and it could constitute a potential new therapeutic approach for cholestatic diseases. Many preclinical gene therapy studies have shown positive results in animal models of both acquired and genetic cholestasis. The delivery of genes that reduce apoptosis or fibrosis or improve bile flow has shown therapeutic effects in rodents in which cholestasis was induced by drugs or bile duct ligation. Most studies targeting inherited cholestasis, such as progressive familial intrahepatic cholestasis (PFIC), have focused on supplementing a correct version of a mutated gene to the liver using viral or non-viral vectors in order to achieve expression of the therapeutic protein. These strategies have generated promising results in treating PFIC3 in mouse models of the disease. However, important challenges remain in translating this therapy to the clinic, as well as in developing gene therapy strategies for other types of acquired and genetic cholestasis.

Genetic Medicine for Hearing Loss: OTOF as Exemplar

Millions of people worldwide have disabling hearing loss because one of their genes generates an incorrect version of some specific protein the ear requires for hearing. In many of these cases, delivering the correct version of the gene to a specific target cell within the inner ear has the potential to restore cochlear function to enable high-acuity physiologic hearing. Purpose: In this review, we outline our strategy for the development of genetic medicines with the potential to treat hearing loss. We will use the example of otoferlin gene (OTOF)-mediated hearing loss, a sensorineural hearing loss due to autosomal recessive mutations of the OTOF gene.

A dynamic DNA nanosponge for triggered amplification of gene-photodynamic modulation

Nucleic acid therapeutics has reached clinical utility through modulating gene expression. As a potential oligonucleotide drug, DNAzyme has RNA-cleaving activity for gene silencing, but faces challenges due to the lack of a safe and effective delivery vehicle and low in vivo catalytic activity. Here we describe DNAzyme-mediated gene regulation using dynamic DNA nanomaterials with intrinsic biocompatibility, stability, tumor-targeted delivery and uptake, and self-enhanced efficacy. We assemble programmable DNA nanosponges to package and deliver diverse nucleic acid drugs and therapeutic agents such as aptamer, DNAzyme and its cofactor precursor, and photosensitizer in one pot through the rolling circle amplification reaction, formulating a controllable nanomedicine using encoded instructions. Upon environmental stimuli, DNAzyme activity increases and RNA cleavage accelerates by a supplementary catalytic cofactor. In addition, this approach induces elevated O2 and 1O2 generation as auxiliary treatment, achieving simultaneously self-enhanced gene-photodynamic cancer therapy. These findings may advance the clinical trial of oligonucleotide drugs as tools for gene modulation.

Liver-directed lentiviral gene therapy corrects hemophilia A mice and achieves normal-range factor VIII activity in non-human primates

Liver gene therapy with adeno-associated viral (AAV) vectors delivering clotting factor transgenes into hepatocytes has shown multiyear therapeutic benefit in adults with hemophilia. However, the mostly episomal nature of AAV vectors challenges their application to young pediatric patients. We developed lentiviral vectors, which integrate in the host cell genome, that achieve efficient liver gene transfer in mice, dogs and non-human primates, by intravenous delivery. Here we first compare engineered coagulation factor VIII transgenes and show that codon-usage optimization improved expression 10-20-fold in hemophilia A mice and that inclusion of an unstructured XTEN peptide, known to increase the half-life of the payload protein, provided an additional >10-fold increase in overall factor VIII output in mice and non-human primates. Stable nearly life-long normal and above-normal factor VIII activity was achieved in hemophilia A mouse models. Overall, we show long-term factor VIII activity and restoration of hemostasis, by lentiviral gene therapy to hemophilia A mice and normal-range factor VIII activity in non-human primate, paving the way for potential clinical application.

“Lentiviral gene therapy to the liver establishes stable long-term normal to supra-normal coagulation factor VIII activity in mouse models of hemophilia A and in non-human primates, representing a potential new treatment option for people with hemophilia A.”.

The use of viral vectors to promote repair after spinal cord injury

Spinal cord injury (SCI) is a devastating event that can permanently disrupt multiple modalities. Unfortunately, the combination of the inhibitory environment at a central nervous system (CNS) injury site and the diminished intrinsic capacity of adult axons for growth results in the failure for robust axonal regeneration, limiting the ability for repair. Delivering genetic material that can either positively or negatively modulate gene expression has the potential to counter the obstacles that hinder axon growth within the spinal cord after injury. A popular gene therapy method is to deliver the genetic material using viral vectors. There are considerations when deciding on a viral vector approach for a particular application, including the type of vector, as well as serotypes, and promoters. In this review, we will discuss some of the aspects to consider when utilizing a viral vector approach to as a therapy for SCI. Additionally, we will discuss some recent applications of gene therapy to target extrinsic and/or intrinsic barriers to promote axon regeneration after SCI in preclinical models. While still in early stages, this approach has potential to treat those living with SCI.

Gene therapy for neuromuscular disorders: prospects and ethics

Most childhood neuromuscular disorders are caused by mutations causing abnormal expression or regulation of single genes or genetic pathways. The potential for gene therapy, gene editing and genetic therapies to ameliorate the course of these conditions is extraordinarily exciting, but there are significant challenges associated with their use, particularly with respect to safety, efficacy, cost and equity. Engagement with these novel technologies mandates careful assessment of the benefits and burdens of treatment for the patient, their family and their society. The examples provided by spinal muscular atrophy and Duchenne muscular dystrophy illustrate the potential value and challenges of gene and genetic therapies for paediatric neurological conditions. The cost and complexity of administration of these agents is a challenge for all countries. Jurisdictional variations in availability of newborn screening, genetic diagnostics, drug approval and reimbursement pathways, treatment and rehabilitation will affect equity of access, nationally and internationally. These challenges will best be addressed by collaboration by governments, pharma, clinicians and patient groups to establish frameworks for safe and cost-effective use of these exciting new therapies.

Drug delivery systems for RNA therapeutics

RNA-based gene therapy requires therapeutic RNA to function inside target cells without eliciting unwanted immune responses. RNA can be ferried into cells using non-viral drug delivery systems, which circumvent the limitations of viral delivery vectors. Here, we review the growing number of RNA therapeutic classes, their molecular mechanisms of action, and the design considerations for their respective delivery platforms. We describe polymer-based, lipid-based, and conjugate-based drug delivery systems, differentiating between those that passively and those that actively target specific cell types. Finally, we describe the path from preclinical drug delivery research to clinical approval, highlighting opportunities to improve the efficiency with which new drug delivery systems are discovered.

Utility of the DHFR-based destabilizing domain across mouse models of retinal degeneration and aging

The Escherichia coli dihydrofolate reductase (DHFR) destabilizing domain (DD) serves as a promising approach to conditionally regulate protein abundance in a variety of tissues. To test whether this approach could be effectively applied to a wide variety of aged and disease-related ocular mouse models, we evaluated the DHFR DD system in the eyes of aged mice (up to 24 months), a light-induced retinal degeneration (LIRD) model, and two genetic models of retinal degeneration (rd2 and Abca4^−/− mice). The DHFR DD was effectively degraded in all model systems, including rd2 mice, which showed significant defects in chymotrypsin proteasomal activity. Moreover, trimethoprim (TMP) administration stabilized the DHFR DD in all mouse models. Thus, the DHFR DD-based approach allows for control of protein abundance in a variety of mouse models, laying the foundation to use this strategy for the conditional control of gene therapies to potentially treat multiple eye diseases.

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Destabilizing domains (DDs) confer conditional control of ocular protein abundance

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The DHFR DD is effectively turned over and stabilized in aged mouse’s retina

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DHFR DDs perform well in environmental and genetic retinal degenerative models

The MIR100HG/miR-29a-3p/Tab1 axis modulates TGF-β1-induced fibrotic changes in type II alveolar epithelial cells BLM-caused lung fibrogenesis in mice

Transforming growth factor (TGF)-β1-induced fibrotic changes in alveolar epithelium is a critical event in pulmonary fibrosis. Herein, we recognized that lncRNA mir-100-let-7a-2-mir-125b-1 cluster host gene (MIR100HG) was abnormally upregulated within human idiopathic pulmonary fibrosis (IPF) lung tissue, bleomycin (BLM)-caused pulmonary fibrotic model mice and TGF-β1-stimulated mice type II alveolar epithelial cells. In vivo, MIR100HG knockdown attenuated BLM-caused lung fibrogenesis in mice; in vitro, MIR100HG knockdown attenuated TGF-β1-induced fibrotic changes in mice type II alveolar epithelial cells. Through direct binding, MIR100HG knockdown upregulated microRNA-29a-3p (miR-29a-3p) expression; through serving as competing endogenous RNA for miR-29a-3p, MIR100HG knockdown downregulated TGF-beta activated kinase 1/MAP3K7 binding protein 1 (Tab1) expression. Finally, under TGF-β1 stimulation, Tab1 knockdown attenuated TGF-β1-induced fibrotic changes and partially attenuated the effects of miR-29a-3p inhibition. In conclusion, we demonstrated the aberrant upregulation of lncRNA MIR100HG in BLM-caused lung fibrogenesis and TGF-β1-stimulated MLE 12 cells. The MIR100HG/miR-29a-3p/Tab1 axis could modulate TGF-β1-induced fibrotic changes in type II alveolar epithelial cells and, thus, might be promising targets for pulmonary fibrosis therapy.

The first gene therapy for RPE65 biallelic dystrophy with voretigene neparvovec-rzyl in Brazil

PURPOSE

To report the first Brazilian patient with RPE65 deficiency-inherited retinal dystrophy (RPE65-IRD) treated with voretigene neparvovec-rzyl (VN).

METHODS

An adult patient with Leber congenital amaurosis-2 with a homozygous mutation in the RPE65 gene (p.Phe83Leu) was treated bilaterally with VN. The clinical and surgical aspects are described. The baseline and 4-month postoperative ophthalmologic examinations included measurement of the best-corrected visual acuity (BCVA), full-field stimulus threshold (FST) test, Octopus 900 semiautomated kinetic visual fields (VFs), and microperimetry.

RESULTS

No complications developed in this patient. The BCVA remained stable. The full-field stimulus threshold test (FST) and VFs showed clinically significant improvements bilaterally. The patient reported significant improvements in the ability to perform daily activities, mainly for those requiring the VFs and vision in a low-luminescence environment.

CONCLUSIONS

The treatments were beneficial for this patient who was homozygous for RPE65 p.Phe83Leu. The first VN treatments in an adult Brazilian patient in clinical practice showed measurable improvements in visual outcomes that were meaningful for the patient's daily activities.

TRANSLATIONAL RELEVANCE

This case reinforces the clinical trial results and proves that the procedure is feasible in countries such as Brazil.

Silencing Gene-Engineered Injectable Hydrogel Microsphere for Regulation of Extracellular Matrix Metabolism Balance

Extracellular matrix (ECM) metabolism balance is essential for maintaining tissue structure and function. However, the complex crosstalk between the ECM, resident cellular, and tissue microenvironment makes long-term maintenance of ECM metabolism balance in an abnormal microenvironment difficult to achieve. Herein, an injectable circRNA silencing-hydrogel microsphere (psh-circSTC2-lipo@MS) is constructed by grafting circSTC2 silencing genes-loaded 1,2-dioleoyl-3-trimethylammonium-propane/cholesterol/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOTAP/Chol/DOPE) cationic liposomes on methacrylated hyaluronic acid (HAMA) microspheres via amide bonds, which could silence pathological genes in nucleus pulposus (NP) cells to regulate ECM metabolism balance in the nutrient-restricted microenvironment, thereby inhibiting intervertebral disc (IVD) degeneration. HAMA microspheres prepared by microfluidics displayed good degradability, swellability, and injectability. And lipoplexes can be efficiently loaded and released for 27 d through chemical grafting. Cocultured under nutrient-restricted conditions for 72 h, psh-circSTC2-lipo@MS significantly promotes the synthesis of ECM-related proteins and inhibits the secretion of ECM catabolism-related proteases in NP cells. In the rat IVD nutrient-restricted model, local injection of psh-circSTC2-lipo@MS promotes ECM synthesis and restored NP tissue after 8 weeks. In summary, this study confirms that psh-circSTC2-lipo@MS as a safe and controllable targeted gene delivery system has great potential in regulating the ECM metabolism balance under an abnormal microenvironment.

Towards gene therapy for IPEX syndrome

Immune dysregulation polyendocrinopathy enteropathy X linked (IPEX) syndrome is an uncurable disease of the immune system, with immune dysregulation that is caused by mutations in FOXP3. Current treatment options, such as pharmacological immune suppression and allogeneic hematopoietic stem cell transplantation, have been beneficial but present limitations, and their life‐long consequences are ill‐defined. Other similar blood monogenic diseases have been successfully treated using gene transfer in autologous patient cells, thus providing an effective and less invasive therapeutic. Development of gene therapy for patients with IPEX is particularly challenging because successful strategies must restore the complex expression profile of the transcription factor FOXP3, ensuring it is tightly regulated and its cell subset‐specific roles are maintained. This review summarizes current efforts toward achieving gene therapy to treat immune dysregulation in IPEX patients.

Gene Therapy of Chronic Limb-Threatening Ischemia: Vascular Medical Perspectives

A decade ago, gene therapy seemed to be a promising approach for the treatment of chronic limb-threatening ischemia, providing new perspectives for patients without conventional, open or endovascular therapeutic options by potentially enabling neo-angiogenesis. Yet, until now, the results have been far from a safe and routine clinical application. In general, there are two approaches for inserting exogenous genes in a host genome: transduction and transfection. In case of transduction, viral vectors are used to introduce genes into cells, and depending on the selected strain of the virus, a transient or stable duration of protein production can be achieved. In contrast, the transfection of DNA is transmitted by chemical or physical processes such as lipofection, electro- or sonoporation. Relevant risks of gene therapy may be an increasing neo-vascularization in undesired tissue. The risks of malignant transformation and inflammation are the potential drawbacks. Additionally, atherosclerotic plaques can be destabilized by the increased angiogenesis, leading to arterial thrombosis. Clinical trials from pilot studies to Phase II and III studies on angiogenic gene therapy show mainly a mixed picture of positive and negative final results; thus, the role of gene therapy in vascular occlusive disease remains unclear.

Advanced Therapy Medicinal Products' Translation in Europe: A Developers' Perspective

Advanced Therapy Medicinal Products (ATMPs) comprising cell, gene, and tissue-engineered therapies have demonstrated enormous therapeutic benefits. However, their development is complex to be managed efficiently within currently existing regulatory frameworks. Legislation and regulation requirements for ATMPs must strike a balance between the patient safety while promoting innovations to optimize exploitation of these novel therapeutics. This paradox highlights the importance of on-going dynamic dialogue between all stakeholders and regulatory science to facilitate the development of pragmatic ATMP regulatory guidelines.

Maybe you can turn me on: CRISPRa-based strategies for therapeutic applications

Since the revolutionary discovery of the CRISPR-Cas technology for programmable genome editing, its range of applications has been extended by multiple biotechnological tools that go far beyond its original function as “genetic scissors”. One of these further developments of the CRISPR-Cas system allows genes to be activated in a targeted and efficient manner. These gene-activating CRISPR-Cas modules (CRISPRa) are based on a programmable recruitment of transcription factors to specific loci and offer several key advantages that make them particularly attractive for therapeutic applications. These advantages include inter alia low off-target effects, independence of the target gene size as well as the potential to develop gene- and mutation-independent therapeutic strategies. Herein, I will give an overview on the currently available CRISPRa modules and discuss recent developments, future potentials and limitations of this approach with a focus on therapeutic applications and in vivo delivery.

CRISPR-based genome editing through the lens of DNA repair

Genome editing technologies operate by inducing site-specific DNA perturbations that are resolved by cellular DNA repair pathways. Products of genome editors include DNA breaks generated by CRISPR-associated nucleases, base modifications induced by base editors, DNA flaps created by prime editors, and integration intermediates formed by site-specific recombinases and transposases associated with CRISPR systems. Here, we discuss the cellular processes that repair CRISPR-generated DNA lesions and describe strategies to obtain desirable genomic changes through modulation of DNA repair pathways. Advances in our understanding of the DNA repair circuitry, in conjunction with the rapid development of innovative genome editing technologies, promise to greatly enhance our ability to improve food production, combat environmental pollution, develop cell-based therapies, and cure genetic and infectious diseases.