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Using Prime Editing Guide Generator (PEGG) for high-throughput generation of prime editing sensor libraries.

Prime editing enables the generation of nearly any small genetic variant. However, the process of prime editing guide RNA (pegRNA) design is challenging and requires automated computational design tools. We developed Prime Editing Guide Generator (PEGG), a fast, flexible, and user-friendly Python package that enables the rapid generation of pegRNA and pegRNA-sensor libraries. Here, we describe the installation and use of PEGG (https://pegg.readthedocs.io) to rapidly generate custom pegRNA-sensor libraries for use in high-throughput prime editing screens.

Gene Editing

Dense RNA motif modifications enable robust in vivo prime editing and enhance efficiencies of diverse editing systems.

Prime editing holds promise for therapeutic applications. However, viral delivery of the prime editor presents challenges for clinical translation due to concerns regarding long-term expression. Meanwhile, systemic delivery using non-viral vectors has been limited by low efficiency, the need for repeated injections and reliance on doses that exceed clinically translatable levels. Here we develop engineered prime editing guide RNAs (pegRNAs) with densely modified RNA motifs and demonstrate their application for efficient in vivo prime editing. By systemically delivering the prime editor in RNA format via a single injection of lipid nanoparticles, we achieved nearly 70% editing efficiency in the bulk mouse liver, indicating successful editing of the majority of hepatocytes. Notably, a single injection at a clinically translatable lipid nanoparticle dose was sufficient to suppress target protein expression in vivo, resulting in a near 80-fold increase in editing efficiency compared with conventional end-modified pegRNAs. Furthermore, incorporating densely modified RNA motifs, including the widely used MS2 motif, proved broadly applicable across various RNA sequences and split RNA-guided genome editing platforms, resulting in up to an 11-fold increase in base editing efficiency. These findings present a generalizable approach for enhancing the therapeutic potential of prime editing and expanding the utility of RNA-based therapeutics.

Journal Article

Prime editing in bacteria with BacPE.

Programmable genome editing technologies have revolutionized the ability of researchers to alter the genomes of microorganisms in a straightforward and efficient manner, significantly advancing the field of microbiology. To date, several CRISPR-Cas-based genome-editing systems have been developed for use in E. coli, including CRISPR/Cas9, base editing, and prime editing technologies. In this chapter, we describe the design and experimental application of BacPE, a variant of prime editing technology optimized for E. coli. BacPE facilitates the introduction of point mutations, insertions, and deletions without the need for double-strand DNA breaks. We demonstrate that BacPE is a powerful tool for genome editing in E. coli and highlight its potential applicability to other bacterial species.

Gene Editing

Efficient prime editing in vivo and in vitro using lipid nanoparticles.

Prime editing is a versatile clinical genome editing method that enables precise substitutions, small insertions and deletions at specified locations in the genomes of living systems including human cells. Although non-viral lipid nanoparticle (LNP) delivery of RNA in vivo has become a preferred method for gene editing in animals and patients, its application to complex, three-component prime editing systems has yielded low editing efficiencies. Here we developed a systematic prime editing LNP (PE-LNP) optimization platform that addresses key bottlenecks in cargo design that limit editing efficiency. This generalizable workflow yielded PE-LNPs that can achieve 49% average in vivo prime editing in the bulk mouse liver with a single dose of 2 mg kg-1. We applied our workflow to the correction of PAH R408W, a cause of phenylketonuria, in a mouse model and achieved prime editing efficiencies and serum phenylalanine levels anticipated to be curative. We also show that PE-LNPs minimize off-target editing compared with DNA delivery methods, induce only transient elevation of liver enzymes and can be dosed repeatedly to improve editing efficiencies. These PE-LNP systems provide an attractive alternative to viral delivery by offering transient expression that minimizes off-target editing, no observed long-term toxicity and high levels of non-viral in vivo liver prime editing.

Animals

LDLR Variant Classification Through Activity-Normalized Prime Editing Screening.

BACKGROUND: Inherited variants in the LDL (low-density lipoprotein) receptor (LDLR) gene are the most common cause of familial hypercholesterolemia, significantly increasing coronary artery disease risk. Early identification of pathogenic LDLR variants enables prompt lipid-lowering therapy and cascade testing of at-risk relatives; however, most LDLR variants observed in the population have uncertain or absent clinical classifications, leaving many patients without actionable information. METHODS: We developed the first activity-normalized prime editing screening pipeline to measure the impact of 5184 LDLR coding variants on LDL-cholesterol (LDL-C) uptake. Each prime editing guide RNA is paired with a genotypic outcome reporter to correct for variable editing efficiency, overcoming a key limitation of previous pooled genome editing screens. A statistical framework further improves variant effect estimates by jointly analyzing all missense variants at each amino acid position. RESULTS: We show that prime editing of the reporter construct correlates with endogenous variant installation frequency, validating the activity normalization approach. The resulting scores capture a continuous spectrum of functional effects, robustly separate pathogenic versus benign ClinVar variants, and show concordance with LDL-C levels in UK Biobank participants. We calibrate functional evidence strengths to the ACMG/AMP variant interpretation framework, enabling integration into a clinical variant classification workflow. By combining functional, computational, population, and contextual evidence, 322 of 434 LDLR variants currently classified as variants of uncertain significance, conflicting, or absent from ClinVar appear to meet evidence thresholds for reclassification and can be prioritized for expert review, substantially expanding the pool of actionable variant classifications. The screen also reveals a cluster of gain-of-function variants in LDLR class A repeat 5, at least some of which enhance LDL-C uptake through increased apolipoprotein B interaction, with implications for therapeutic genome editing. Last, prime editing uniquely detects splice-altering coding variants missed by cDNA-based screens and pathogenicity predictors, revealing an advantage of endogenous variant installation. CONCLUSIONS: Altogether, activity-normalized prime editing provides a scalable framework for LDLR variant classification that substantially expands the proportion of variants with evidence for genetic diagnosis and reveals novel biology with therapeutic relevance.

CRISPR screening

From feasibility to predictability: prime editing redefines precision breeding in plants.

Originally developed in mammalian systems as a genome editing strategy without double-strand breaks, prime editing (PE) has been adapted for precise genome modifications. However, its deployment revealed key limitations, including reduced efficiency, strong locus dependency, low germline transmission, and somatic chimerism. Consequently, diverse PE variants have emerged, resulting in fragmented landscape of architectures with context-dependent and inconsistent performance. This review consolidates these advances and outlines emerging design principles behind plant PE systems. It evaluates optimization strategies at multiple levels, discusses their applications in monocots and eudicots, and highlights persistent bottlenecks and future directions, including AI-guided protein engineering and improved delivery strategies. These advances position PE as a rapidly evolving platform toward enabling precision breeding in plants.

cis-regulatory engineering

Discovery and Engineering of a Rat Endogenous Retrovirus Reverse Transcriptase for Efficient Prime Editing.

CRISPR-based prime editors (PEs) install precise edits into genomic DNA without generating double-strand breaks. Their editing efficiency is highly dependent on reverse transcriptases (RTs), but efficient RT candidates remain limited. Here, we identified 19 novel active RTs by screening 558 candidates. Among them, RERV-RT, derived from Rattus norvegicus, exhibited the highest activity. Through structure-guided engineering and deep mutational scanning, we developed an optimized variant, enRERV-RT, which outperforms conventional M-MLV-RT-based PE systems by 1.20-fold in mammalian and plant cells, and by 1.88-fold at hard-to-edit loci, while enabling precise multiplex editing of functionally relevant genes. Additionally, we developed a high-throughput platform, TRAP-seq-PE, to systematically evaluate prime editor performance. Across diverse mutation types, we found that PE systems based on enRERV-RT exhibited higher editing efficiencies than those based on M-MLV-RT. Collectively, our work establishes a versatile, high-efficiency PE system, thereby facilitating advances in clinical gene therapy and precise crop breeding.

Animals

Development of a highly efficient prime editing platform for cucurbits enables breeding of multi-disease-resistant cucumber.

The prime editing (PE) system is a precise genome editing technology that works efficiently in monocots; however, its application is limited by low editing efficiency in dicots, particularly Cucurbitaceae and Solanaceae plants. Here, we first significantly improved the transformation efficiency by introducing spectinomycin in cucurbits, then used the tomato elongation factor 1-alpha (SlEF1α) promoter to enhance PE protein expression, and incorporated the Csy4 ribonuclease to process pegRNAs, collectively addressing multiple constraints limiting PE efficiency in cucurbits. The optimized PE systems, particularly Csy4-PE6d, achieved an average desired editing frequency of 80.83% at targeted loci in cucumber via stable genetic transformation, with frequencies reaching up to 100% at certain sites. Moreover, Csy4-PE6d generated homozygous edits in 36.43% of transgenic lines and demonstrated robust editing activity in melon, pumpkin, and potato. Using the Csy4-PE6d tool, we generated heritable edited cucumber lines with dual resistance to bacterial angular leaf spot and downy mildew by targeting the CsSGR gene. Collectively, this optimized system substantially enhances PE efficiency in Cucurbit crops, providing an effective solution to common challenges such as low editing efficiency and limited heritability in these species.

Disease Resistance

Efficient homologous replacement and deletion of large genomic fragments through template-jumping prime editing in rice.

Homologous replacement of genomic sequences with large DNA fragments (> 100 bp) holds great potential for crop breeding, yet an efficient method to achieve such edits is lacking in plants. Here, in rice, we developed template-jumping prime editing (TJ-PE), a recently reported PE strategy for large targeted insertion, as an efficient tool for homologous replacement with DNA fragments ranging from dozens to hundreds of base pairs, and using TJ-PE, we replaced genomic fragments of up to 340 bp with homologous fragments of the same length. In addition, our TJ-PE tool also enabled precise deletion of 944- to 2024-bp fragments in rice, with efficiencies of up to 34.6% for c. 2000-bp precise deletions. Collectively, this study expands the editing scope of PE in rice and establishes TJ-PE as a generalist tool for precise deletion and replacement of large DNA fragments.

Oryza

Prime Editing for p47phox-Deficient Chronic Granulomatous Disease.

Chronic granulomatous disease (CGD) is a severe monogenic immunodeficiency caused by damaging variants in genes required for microbicidal NADPH oxidase activity. Autosomal recessive p47phox-deficient CGD (p47-CGD) is predominantly caused by a two-nucleotide deletion in exon 2 (delGT) of NCF1. We developed PM359, an autologous CD34+ hematopoietic stem-cell therapy in which prime editing is used to correct delGT. Two participants received PM359 after myeloid conditioning with busulfan: neutrophils and platelets engrafted promptly in both patients. Adverse events were consistent with myeloid conditioning with busulfan. NADPH oxidase activity was observed in neutrophils within 1 month and was maintained for 6 months and 4 months as of the last follow-up visit in Participants 1 and 2, respectively. These results support further investigation of prime editing of CD34+ cells to treat p47-CGD. (Funded by Prime Medicine; ClinicalTrials.gov number, NCT06559176.).

Adolescent

Identifying critical lysines in mammalian histone H3 with high-throughput CRISPR prime editing.

Histone post-translational modifications are fundamental to genome regulation, yet dissecting the functions of individual histone marks in mammals remains challenging due to the presence of multiple histone gene copies. Here we develop a high-throughput clustered regularly interspaced short palindromic repeats (CRISPR) prime editing platform enabling precise, reversible and combinatorial mutagenesis of canonical and noncanonical histone H3 genes within their native genomic context. Using systematic lysine-to-arginine substitutions benchmarked against synonymous controls, we identify key residues, including H3K4, H3K9, H3K14, H3K18 and H3K79, whose mutation compromises fitness in mouse embryonic stem cells. We further show that H3K56, linked to genome stability in yeast and Drosophila, has a conserved role in mammalian cells. Through analysis of selected double mutants, we uncover functional crosstalk across residues, with combinations such as H3K27R + H3K36R impairing stem cell self-renewal and altering transcription. Altogether, this study establishes a functional map of histone H3 lysines in mammals and provides a broadly applicable platform for systematic dissection of chromatin regulation.

Histones

A quick guide to evaluating prime editing efficiency in mammalian cells.

According to the Clinvar database, modeling the diseases associated with pathogenic mutations requires the installation of base substitutions, small insertions or deletions. Prime editor (PE) was recently developed to precisely install any base substitutions and/or small insertions/deletions (indels) in mammalian cells and animals without requiring DSBs or donor DNA templates. PE also offers greater editing and targeting flexibility compared to other precision CRISPR editing methods because the versatile editing information is encoded in the reverse-transcription template of its prime editing guide RNA. However, optimal PE system selection and experimental design can be complex, and there are various factors that can affect PE efficiency. This chapter serves as a rapid entry-level guideline for the application of PE, providing an experimental framework for using PE at a specific genomic locus. RUNX1 was selected as a representative target site to illustrate the detailed methodology for constructing PE plasmids and the process of transfecting these plasmids into 293FT cells. We further examined the efficiency of PE-mediated genome editing in mammalian cells by using next-generation sequencing.

Gene Editing

CRISPR-Engineered CAR-T Cell Therapy for Epstein-Barr Virus-Associated Nasopharyngeal Carcinoma: A Review of Emerging Therapeutic Prospects.

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) remains a clinically challenging malignancy, particularly in recurrent or metastatic disease where durable responses to chemoradiotherapy and immune checkpoint blockade are limited. The viral aetiology of NPC provides a strong biological rationale for immune-based treatment; however, translation of chimaeric antigen receptor (CAR) T-cell therapy into this solid tumour setting is constrained by poor tumour trafficking, antigen heterogeneity, limited surface accessibility of EBV latent antigens, T-cell exhaustion, and an immunosuppressive tumour microenvironment. This review critically evaluates the emerging therapeutic prospects of CRISPR-engineered CAR-T cell therapy for EBV-associated NPC. It synthesises evidence on EBV latency biology, NPC immune evasion, solid-tumour CAR-T limitations, and genome-engineering strategies including conventional CRISPR-Cas9, base editing, prime editing, and double-strand-break-sparing targeted integration. Particular attention is given to genotoxicity, chromosomal rearrangements, chromosome loss, bystander and off-target editing, manufacturing heterogeneity, and the regulatory and biological barriers that currently separate technical feasibility from NPC-specific clinical implementation. Available clinical evidence from checkpoint blockade, EBV-specific adoptive T-cell therapy, base-edited CAR-T cells in haematologic malignancy, and early CRISPR-edited T-cell trials supports the feasibility of immune and genetic redirection but does not establish efficacy of a clinically validated CRISPR-engineered CAR-T platform for NPC. Future development should prioritise surface-accessible antigen validation, fit-for-purpose selection of editing technology, genomic safety, scalable manufacturing, and biomarker-driven early-phase trials.

Humans

The emerging impact of CRISPR and gene editing on global crop improvement.

The advent of CRISPR-based genome editing has revolutionized crop improvement, offering unprecedented precision and efficiency in modifying key agronomic traits. This review comprehensively examines the mechanisms, applications, and future potential of CRISPR technology in enhancing global crop production. CRISPR-Cas systems, originally identified as adaptive immune mechanisms in bacteria and archaea, have been repurposed for targeted genome editing in plants. The CRISPR-Cas9 system, in particular, has emerged as a powerful tool for introducing site-specific double-strand breaks, enabling precise genetic modifications. The three-stage process of adaptation, expression, and interference underlies the CRISPR mechanism, with guide RNAs directing Cas endonucleases to specific genomic loci. Advances in CRISPR technology have expanded its applications beyond gene knockouts, encompassing base editing, prime editing, and epigenome editing. These innovations have facilitated the development of crops with enhanced yield, stress tolerance, disease resistance, nutritional content, and post-harvest quality. However, challenges related to off-target effects, regulatory hurdles, ethical concerns, and public acceptance must be addressed to fully harness the potential of CRISPR in agriculture. Integration of CRISPR with other cutting-edge technologies, such as synthetic biology, artificial intelligence, and high-throughput phenotyping, holds immense promise for accelerating crop improvement efforts. As research continues to refine CRISPR tools and expand their applicability across diverse plant species, this transformative technology is poised to play a pivotal role in shaping a sustainable, resilient, and productive global food system for future generations.

Gene Editing

Transforming Plant Viruses into Vectors for Next-Generation Agriculture-A Review.

Plant viral vectors have evolved from tools for transient gene expression into a versatile platform for precise genetic intervention, offering a rapid, transgene-free alternative to conventional crop transformation. This review critically assesses their engineering for scalable field application, moving beyond foundational techniques like virus-induced gene silencing (VIGS). We highlight how advanced vector design, including deconstructed genomes and synthetic regulatory circuits enhances cargo capacity, specificity, and biosafety. The integration of viral delivery with CRISPR-Cas systems has unlocked virus-induced genome editing (VIGE), base editing, and prime editing, enabling heritable trait modification without tissue culture. However, the transition from proof-of-concept in model plants to robust field technology hinges on overcoming critical bottlenecks: expanding host range through chimeric vectors, ensuring environmental containment, and developing scalable delivery methods such as nano-formulations or adjusted agroinfiltration protocols. We evaluate these delivery routes and emerging synergies with nanobiotechnology for targeted and efficient applications. While challenges in regulation, public perception, and large-scale production persist, the strategic engineering of viral vectors for stability, specificity, and safety positions them as a transformative, next-generation biotechnological input for achieving sustainable crop improvement and protection under changing climatic conditions.

Plant Viruses

Programmable enzymes for targeted gene insertion.

Genome editing technologies have advanced from nuclease-based reagents that generate programmed DNA double-strand breaks, which can cause deleterious effects, to next-generation reagents that perform controlled DNA modification through double-strand break-independent mechanisms, such as base editing and prime editing. Although these approaches enable precise small-scale sequence changes, methods for programmable insertion of large DNA cargos have been limited. The ability to write entire genes or large regions into the genome could transform the treatment of genetically heterogeneous disorders, for which numerous pathogenic variants underlie a common disease and mutation-specific editing strategies are impractical. Recent advances in computational genome mining have accelerated the discovery of naturally occurring enzymes with novel biochemical and functional properties, including recombinases and transposases capable of large-scale modifications. Moreover, directed evolution, rational engineering and expanded homologue discovery are enabling the repurposing and optimization of these systems for genome engineering. Here we review recent technology development efforts that harness diverse enzymes for kilobase-scale genome engineering, with a particular focus on CRISPR-associated transposase systems.

Journal Article

Genetically Modified and Gene-Edited Organisms-Objectives, Public Perception and Applications.

Genetic modification and genome editing have become important tools in agriculture, animal production, biotechnology, and human medicine, but their safety and societal acceptance remain subjects of debate. This review examines genetically modified (GM) and gene-edited organisms, distinguishing transgenesis from precision genome editing technologies, including CRISPR/Cas9, base editing, and prime editing. Representative applications in crops, livestock, pharmaceutical production, and xenotransplantation are discussed, together with their regulatory framework and public perception. Current scientific assessments indicate that approved GM foods are not inherently more hazardous to human health than their conventional counterparts when evaluated case by case. Potential benefits include improved nutritional quality, biofortification, disease resistance, increased agricultural efficiency, production of therapeutic proteins, and applications in animal health and medicine. Possible concerns include allergenicity, toxicity, unintended genetic or phenotypic effects, altered nutritional composition, environmental consequences, animal welfare issues, and uncertainties associated with long-term or large-scale deployment. Public acceptance varies substantially according to geographical region, application, cultural and ethical considerations, regulatory environment, scientific literacy, and institutional trust. Overall, GM and gene-edited organisms should not be considered a homogeneous category. Their benefits, risks, and societal acceptability depend on the specific organism, genetic modification, intended trait, and context of use, supporting a balanced, evidence-based, and case-specific approach.

acceptance