A Comparison of Techniques to Evaluate the Effectiveness of Genome Editing

Roadmap to discovery and early development of an mRNA loaded LNP formulation for liver therapeutic genome editing

INTRODUCTION

mRNA therapeutics were a niche area in drug development before COVID vaccines. They are now used in vaccine development, for non-viral therapeutic genome editing, in vivo chimeric antigen receptor T (CAR T) cell therapies and protein replacement.  mRNA is large, charged, and easily degraded by nucleases. It cannot get into cells, escape the endosome, and be translated to a disease-modifying protein without a delivery system such as lipid nanoparticles (LNPs).

AREAS COVERED

This article covers how to design, select, and develop an LNP for therapeutic genome editing in the liver. The roadmap is divided into selecting the right LNP for discovery via a design, make, test, and analyze cycle (DMTA). The design elements are focused on ionizable lipids in a 4-component LNP, and insights are provided for how to set an in vitro and in vivo testing strategy. The second section focuses on transforming the LNP into a clinical drug product and covers formulation, analytical development, and process optimization, with brief notes on supply and regulator strategies.

EXPERT OPINION

The perspective discusses the impact that academic-industry collaborations can have on developing new medicines for therapeutic genome editing in the liver. From the cited collaborations an enhanced understanding of intracellular trafficking, notably endosomal escape, and the internal structure of LNPs were attained and are deemed key to designing effective and safe LNPs. The knowledge gained will also enable additional assays and structural activity relationships, which would lead to the design of the next-generation delivery systems for nucleic acid therapies.

One-pot DTECT enables rapid and efficient capture of genetic signatures for precision genome editing and clinical diagnostics

The detection of genomic sequences and their alterations is crucial for basic research and clinical diagnostics. However, current methodologies are costly and time-consuming and require outsourcing sample preparation, processing, and analysis to genomic companies. Here, we establish One-pot DTECT, a platform that expedites the detection of genetic signatures, only requiring a short incubation of a PCR product in an optimized one-pot mixture. One-pot DTECT enables qualitative, quantitative, and visual detection of biologically relevant variants, such as cancer mutations, and nucleotide changes introduced by prime editing and base editing into cancer cells and human primary T cells. Notably, One-pot DTECT achieves quantification accuracy for targeted genetic signatures comparable with Sanger and next-generation sequencing. Furthermore, its effectiveness as a diagnostic platform is demonstrated by successfully detecting sickle cell variants in blood and saliva samples. Altogether, One-pot DTECT offers an efficient, versatile, adaptable, and cost-effective alternative to traditional methods for detecting genomic signatures.

CRISPR/Cas detection with nanodevices: moving deeper into liquid biopsy

The emerging field of liquid biopsy has garnered significant interest in precision diagnostics, offering a non-invasive and repetitive method for analyzing bodily fluids to procure real-time diagnostic data. The precision and accuracy offered by the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (CRISPR/Cas) technology have advanced and broadened the applications of liquid biopsy. Significantly, when combined with swiftly advancing nanotechnology, CRISPR/Cas-mediated nanodevices show vast potential in precise liquid biopsy applications. However, persistent challenges are still associated with off-target effects, and the current platforms also constrain the performance of the assays. In this review, we highlight the merits of CRISPR/Cas systems in liquid biopsy, tracing the development of CRISPR/Cas systems and their current applications in disease diagnosis particularly in liquid biopsies. We also outline ongoing efforts to design nanoscale devices with improved sensing and readout capabilities, aiming to enhance the performance of CRISPR/Cas detectors in liquid biopsy. Finally, we identify the critical obstacles hindering the widespread adoption of CRISPR/Cas liquid biopsy and explore potential solutions. This feature article presents a comprehensive overview of CRISPR/Cas-mediated liquid biopsies, emphasizing the progress in integrating nanodevices to improve specificity and sensitivity. It also sheds light on future research directions in employing nanodevices for CRISPR/Cas-based liquid biopsies in the realm of precision medicine.

Current Landscape of Gene Therapy for the Treatment of Cardiovascular Disorders

Cardiovascular disorders (CVD) are the primary cause of death worldwide. Multiple factors have been accepted to cause cardiovascular diseases; among them, smoking, physical inactivity, unhealthy eating habits, age, and family history are flag-bearers. Individuals at risk of developing CVD are suggested to make drastic habitual changes as the primary intervention to prevent CVD; however, over time, the disease is bound to worsen. This is when secondary interventions come into play, including antihypertensive, anti-lipidemic, anti-anginal, and inotropic drugs. These drugs usually undergo surgical intervention in patients with a much higher risk of heart failure. These therapeutic agents increase the survival rate, decrease the severity of symptoms and the discomfort that comes with them, and increase the overall quality of life. However, most individuals succumb to this disease. None of these treatments address the molecular mechanism of the disease and hence are unable to halt the pathological worsening of the disease. Gene therapy offers a more efficient, potent, and important novel approach to counter the disease, as it has the potential to permanently eradicate the disease from the patients and even in the upcoming generations. However, this therapy is associated with significant risks and ethical considerations that pose noteworthy resistance. In this review, we discuss various methods of gene therapy for cardiovascular disorders and address the ethical conundrum surrounding it.

A Digital PCR Method Based on Highly Specific Taq for Detecting Gene Editing and Mutations

Digital PCR (dPCR) has great potential for assessing gene editing or gene mutation due to its ability to independently inspect each DNA template in parallel. However, current dPCR methods use a fluorescence-labeled probe to detect gene variation events, and their ability to distinguish variated sequences from the wild-type sequence is limited by the probe's tolerance to mismatch. To address this, we have developed a novel dPCR method that uses a primer instead of a probe to sense gene variation. The enhanced Taq DNA polymerase in the PCR system has a high mismatch sensitivity, which enables our dPCR method to distinguish gene mutations from wild-type sequences. Compared to current dPCR methods, our method shows superior precision in assessing gene editing efficiency and single-base DNA mutation. This presents a promising opportunity to advance gene editing research and rare gene mutation detection.

Genome editing is induced in a binary manner in single human cells

Even when precise nucleotide manipulations are intended, the outcomes of genome editing can be diverse, often including random insertions and deletions. The combinations and frequencies of these different outcomes in single cells are critical not only in the generation of genetically modified cell lines but also in the evaluation of the clinical effects of genome editing therapies. However, current methods only analyze cell populations, not single cells. Here, we utilized the Single Particle isolation System (SPiS) for the efficient isolation of single cells to systematically analyze genome editing results in individual human cultured cells. As a result, we discovered that genome editing induction has a binary nature, that is, the target alleles of cells tend to be all edited or not edited at all. This study enhances our understanding of the induction pattern of genome editing and provides a new strategy to analyze genome editing outcomes in single cells.

Visualizing the Genome: Experimental Approaches for Live-Cell Chromatin Imaging

Over the years, our vision of the genome has changed from a linear molecule to that of a complex 3D structure that follows specific patterns and possesses a hierarchical organization. Currently, genomics is becoming "four-dimensional": our attention is increasingly focused on the study of chromatin dynamics over time, in the fourth dimension. Recent methods for visualizing the movements of chromatin loci in living cells by targeting fluorescent proteins can be divided into two groups. The first group requires the insertion of a special sequence into the locus of interest, to which proteins that recognize the sequence are recruited (e.g., FROS and ParB-INT methods). In the methods of the second approach, "programmed" proteins are targeted to the locus of interest (i.e., systems based on CRISPR/Cas, TALE, and zinc finger proteins). In the present review, we discuss these approaches, examine their strengths and weaknesses, and identify the key scientific problems that can be studied using these methods.

Development of a universal antibiotic resistance screening reporter for improving efficiency of cytosine and adenine base editing

Base editing has emerged as a revolutionary technology for single nucleotide modifications. The cytosine and adenine base editors (CBEs and ABEs) have demonstrated great potential in clinical and fundamental research. However, screening and isolating target-edited cells remains challenging. In the current study, we developed a universal Adenine and Cytosine Base-Editing Antibiotic Resistance Screening Reporter (ACBE-ARSR) for improving the editing efficiency. To develop the reporter, the CBE-ARSR was first constructed and shown to be capable of enriching cells for those that had undergone CBE editing activity. Then, the ACBE-ARSR was constructed and was further validated in the editing assays by four different CBEs and two versions of ABE at several different genomic loci. Our results demonstrated that ACBE-ARSR, compared to the reporter of transfection (RoT) screening strategy, improved the editing efficiency of CBE and ABE by 4.6- and 1.9-fold on average, respectively. We found the highest CBE and ABE editing efficiencies as enriched by ACBE-ARSR reached 90% and 88.7%. Moreover, we also demonstrated ACBE-ARSR could be employed for enhancing simultaneous multiplexed genome editing. In conclusion, both CBE and ABE activity can be improved significantly using our novel ACBE-ARSR screening strategy, which we believe will facilitate the development of base editors and their application in biomedical and fundamental research studies.

Multiplex knockout of trichome-regulating MYB duplicates in hybrid poplar using a single gRNA

As the focus for CRISPR/Cas-edited plants moves from proof-of-concept to real-world applications, precise gene manipulation will increasingly require concurrent multiplex editing for polygenic traits. A common approach for editing across multiple sites is to design one guide RNA (gRNA) per target; however, this complicates construct assembly and increases the possibility of off-target mutations. In this study, we utilized one gRNA to target MYB186, a known positive trichome regulator, as well as its paralogs MYB138 and MYB38 at a consensus site for mutagenesis in hybrid poplar (Populus tremula × P. alba INRA 717-1B4). Unexpected duplications of MYB186 and MYB138 resulted in eight alleles for the three targeted genes in the hybrid poplar. Deep sequencing and polymerase chain reaction analyses confirmed editing across all eight targets in nearly all of the resultant glabrous mutants, ranging from small indels to large genomic dropouts, with no off-target activity detected at four potential sites. This highlights the effectiveness of a single gRNA targeting conserved exonic regions for multiplex editing. Additionally, cuticular wax and whole-leaf analyses showed a complete absence of triterpenes in the trichomeless mutants, hinting at a previously undescribed role for the nonglandular trichomes of poplar.

Genetic correction of concurrent α- and β-thalassemia patient-derived pluripotent stem cells by the CRISPR-Cas9 technology

BACKGROUND

Thalassemia is a genetic blood disorder characterized by decreased hemoglobin production. Severe anemia can damage organs and severe threat to life safety. Allogeneic transplantation of bone marrow-derived hematopoietic stem cell (HSCs) at present represents a promising therapeutic approach for thalassemia. However, immune rejection and lack of HLA-matched donors limited its clinical application. In recent years, human-induced pluripotent stem cells (hiPSCs) technology offers prospects for autologous cell-based therapy since it could avoid the immunological problems mentioned above.

METHODS

In the present study, we established a new hiPSCs line derived from amniotic cells of a fetus with a homozygous β41-42 (TCTT) deletion mutation in the HBB gene and a heterozygous Westmead mutation (C > G) in the HBA2 gene. We designed a CRISPR-Cas9 to target these casual mutations and corrected them. Gene-corrected off-target analysis was performed by whole-exome capture sequencing. The corrected hiPSCs were analyzed by teratoma formation and erythroblasts differentiation assays.

RESULTS

These mutations were corrected with linearized donor DNA through CRISPR/Cas9-mediated homology-directed repair. Corrections of hiPSCs were validated by sequences. The corrected hiPSCs retain normal pluripotency. Moreover, they could be differentiated into hematopoietic progenitors, which proves that they maintain the multilineage differentiation potential.

CONCLUSIONS

We designed sgRNAs and demonstrated that these sgRNAs facilitating the CRISPR-Cas9 genomic editing system could be applied to correct concurrent α- and β-thalassemia in patient-derived hiPSCs. In the future, these corrected hiPSCs can be applied for autologous transplantation in patients with concurrent α- and β-thalassemia.

RNA-Guided AsCas12a- and SpCas9-Catalyzed Knockout and Homology Directed Repair of the Omega-1 Locus of the Human Blood Fluke, Schistosoma mansoni

The efficiency of the RNA-guided AsCas12a nuclease of Acidaminococcus sp. was compared with SpCas9 from Streptococcus pyogenes, for functional genomics in Schistosoma mansoni. We deployed optimized conditions for the ratio of guide RNAs to the nuclease, donor templates, and electroporation parameters, to target a key schistosome enzyme termed omega-1. Programmed cleavages catalyzed by Cas12a and Cas9 resulted in staggered- and blunt-ended strand breaks, respectively. AsCas12a was more efficient than SpCas9 for gene knockout, as determined by TIDE analysis. CRISPResso2 analysis confirmed that most mutations were deletions. Knockout efficiency of both nucleases markedly increased in the presence of single-stranded oligodeoxynucleotide (ssODN) template. With AsCas12a, ssODNs representative of both the non-CRISPR target (NT) and target (T) strands were tested, resulting in KO efficiencies of 15.67, 28.71, and 21.43% in the SpCas9 plus ssODN, AsCas12a plus NT-ssODN, and AsCas12a plus T-ssODN groups, respectively. Trans-cleavage against the ssODNs by activated AsCas12a was not apparent in vitro. SpCas9 catalyzed more precise transgene insertion, with knock-in efficiencies of 17.07% for the KI_Cas9 group, 14.58% for KI_Cas12a-NT-ssODN, and 12.37% for KI_Cas12a-T-ssODN. Although AsCas12a induced fewer mutations per genome than SpCas9, the phenotypic impact on transcription and expression of omega-1 was similar for both nucleases.

A detection method for the capture of genomic signatures: From disease diagnosis to genome editing

Variations in the genetic information originate from errors during DNA replication, error-prone repair of DNA damages, or genome editing. The most common approach to detect changes in DNA sequences employs sequencing technologies. However, they remain expensive and time-consuming, limiting their utility for routine laboratory experiments. We recently developed DinucleoTidE Signature CapTure (DTECT). DTECT is a marker-free and versatile detection method that captures targeted dinucleotide signatures resulting from the digestion of genomic amplicons by the type IIS restriction enzyme AcuI. Here, we describe the DTECT protocol to identify mutations introduced by CRISPR-based precision genome editing technologies or resulting from genetic variation. DTECT enables accurate detection of mutations using basic laboratory equipment and off-the-shelf reagents with qualitative or quantitative capture of signatures.

Multiplexed bioluminescence-mediated tracking of DNA double-strand break repairs in vitro and in vivo

The dynamics of DNA double-strand break (DSB) repairs including homology-directed repair and nonhomologous end joining play an important role in diseases and therapies. However, investigating DSB repair is typically a low-throughput and cross-sectional process, requiring disruption of cells and organisms for subsequent nuclease-, sequencing- or reporter-based assays. In this protocol, we provide instructions for establishing a bioluminescent repair reporter system using engineered Gaussia and Vargula luciferases for noninvasive tracking of homology-directed repair and nonhomologous end joining, respectively, induced by SceI meganuclease, SpCas9 or SpCas9 D10A nickase-mediated editing. We also describe complementation with orthogonal DSB repair assays and omics analyses to validate the reporter readouts. The bioluminescent repair reporter system provides longitudinal and rapid readout (~seconds per sample) to accurately and efficiently measure the efficacy of genome-editing tools and small-molecule modulators on DSB repair. This protocol takes ~2-4 weeks to establish, and as little as 2 h to complete the assay. The entire bioluminescent repair reporter procedure can be performed by one person with standard molecular biology expertise and equipment. However, orthogonal DNA repair assays would require a specialized facility that performs Sanger sequencing or next-generation sequencing.

Protoplast-Based Method for Genome Editing in Tetraploid Potato

The cultivated potato is tetraploid with four probably equivalent loci for each gene. A potato variety is furthermore commonly genetically heterogeneous and selected based on a beneficial genetic context which is maintained by clonal propagation. When introducing genetic changes by genome editing it is then desirable to achieve edits in all four loci for a certain gene target. This is in order to avoid crosses to achieve homozygosity for edited gene loci and at the same time reduce risk of inbreeding depression. In such a context transient transfection of protoplasts for the introduction of mutations, avoiding stable insertion of foreign DNA, would be very attractive. The protocol of this chapter has been shown to be applicable for the introduction of mutations by DNA vectors containing expression cassettes of TALEN, Cas9, and Cas9 deaminase fusions together with sgRNA expression cassettes on either single or separate vectors. Furthermore, the protoplast-based system has been shown to work very efficiently for mutations introduced by in vitro-produced and transfected RNP (ribonucleoprotein) complexes.

A multiplexed bioluminescent reporter for sensitive and non-invasive tracking of DNA double strand break repair dynamics in vitro and in vivo

Tracking DNA double strand break (DSB) repair is paramount for the understanding and therapeutic development of various diseases including cancers. Herein, we describe a multiplexed bioluminescent repair reporter (BLRR) for non-invasive monitoring of DSB repair pathways in living cells and animals. The BLRR approach employs secreted Gaussia and Vargula luciferases to simultaneously detect homology-directed repair (HDR) and non-homologous end joining (NHEJ), respectively. BLRR data are consistent with next-generation sequencing results for reporting HDR (R2 = 0.9722) and NHEJ (R2 = 0.919) events. Moreover, BLRR analysis allows longitudinal tracking of HDR and NHEJ activities in cells, and enables detection of DSB repairs in xenografted tumours in vivo. Using the BLRR system, we observed a significant difference in the efficiency of CRISPR/Cas9-mediated editing with guide RNAs only 1-10 bp apart. Moreover, BLRR analysis detected altered dynamics for DSB repair induced by small-molecule modulators. Finally, we discovered HDR-suppressing functions of anticancer cardiac glycosides in human glioblastomas and glioma cancer stem-like cells via inhibition of DNA repair protein RAD51 homolog 1 (RAD51). The BLRR method provides a highly sensitive platform to simultaneously and longitudinally track HDR and NHEJ dynamics that is sufficiently versatile for elucidating the physiology and therapeutic development of DSB repair.

High-throughput assessment of mutations generated by genome editing in induced pluripotent stem cells by high-resolution melting analysis

BACKGROUND AND AIMS

Genome editing of induced pluripotent stem cells (iPSCs) holds great potential for both disease modeling and regenerative medicine. Although clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 provides an efficient and precise genome editing tool, iPSCs are especially difficult to transfect, resulting in a small percentage of cells carrying the desired correction. A high-throughput method to identify edited clones is required to reduce the time and costs of such an approach.

METHODS

Here we assess high-resolution melting analysis (HRMA), a simple and efficient real-time polymerase chain reaction-based method, and compare it with more commonly used assays.

RESULTS AND CONCLUSIONS

Our data show that HRMA is a robust and highly sensitive method, allowing the cost-effective and time-saving screening of genome-edited iPSCs. Samples can be prepared directly from 96-well microtiter plates for high-throughput analysis, and amplicons can be further analyzed with downstream techniques for further confirmation, if needed.

Effective identification of CRISPR/Cas9-induced and naturally occurred mutations in rice using a multiplex ligation-dependent probe amplification-based method

A multiplex ligation-dependent probe amplification (MLPA)-based method was developed and successfully utilized to efficiently detect both CRISPR/Cas9-induced and naturally occurred mutations in rice. The site-specific nuclease-based CRISPR/Cas9 system has emerged as one of the most efficient genome editing tools to modify multiple genomic targets simultaneously in various organisms, including plants for both fundamental and applied researches. Screening for both on-target and off-target mutations in CRISPR/Cas9-generated mutants at the early stages is an indispensable step for functional analysis and subsequent application. Various methods have been developed to detect CRISPR/Cas9-induced mutations in plants. Still, very few have focused on the detection of both on- and off-targets simultaneously, let alone the detection of natural mutations. Here, we report a multiplex capable method that allows to detect CRISPR/Cas9 induced on- and off-target mutations as well as naturally occurred mutation based on a multiplex ligation-dependent probe amplification (MLPA) method. We demonstrated that unlike other methods, the modified target-specific MLPA method can accurately identify any INDELs generated naturally or by the CRISPR/Cas9 system and that it can detect natural variation and zygosity of the CRISPR/Cas9-generated mutants in rice as well. Furthermore, its high sensitivity allowed to define INDELs down to 1 bp and substitutions to a single nucleotide. Therefore, this sensitive, reliable, and cheap method would further accelerate functional analysis and marker-assisted breeding in plants, including rice.

Microbial Base Editing: A Powerful Emerging Technology for Microbial Genome Engineering

Genome engineering is crucial for answering fundamental questions about, and exploring practical applications of, microorganisms. Various microbial genome-engineering tools, including CRISPR/Cas-enhanced homologous recombination (HR), have been developed, with ever-improving simplicity, efficiency, and applicability. Recently, a powerful emerging technology based on CRISPR/Cas-nucleobase deaminase fusions, known as base editing, opened new avenues for microbial genome engineering. Base editing enables nucleotide transition without inducing lethal double-stranded (ds)DNA cleavage, adding foreign donor DNA, or depending on inefficient HR. Here, we review ongoing efforts to develop and apply base editing to engineer industrially and clinically relevant microorganisms. We also summarize bioinformatics tools that would greatly facilitate guide (g)RNA design and sequencing data analysis and discuss the future challenges and prospects associated with this technology.

Computational Tools and Resources Supporting CRISPR-Cas Experiments

The CRISPR-Cas system has become a cutting-edge technology that revolutionized genome engineering. The use of Cas9 nuclease is currently the method of choice in most tasks requiring a specific DNA modification. The rapid development in the field of CRISPR-Cas is reflected by the constantly expanding ecosystem of computational tools aimed at facilitating experimental design and result analysis. The first group of CRISPR-Cas-related tools that we review is dedicated to aid in guide RNA design by prediction of their efficiency and specificity. The second, relatively new group of tools exploits the observed biases in repair outcomes to predict the results of CRISPR-Cas edits. The third class of tools is developed to assist in the evaluation of the editing outcomes by analysis of the sequencing data. These utilities are accompanied by relevant repositories and databases. Here we present a comprehensive and updated overview of the currently available CRISPR-Cas-related tools, from the perspective of a user who needs a convenient and reliable means to facilitate genome editing experiments at every step, from the guide RNA design to analysis of editing outcomes. Moreover, we discuss the current limitations and challenges that the field must overcome for further improvement in the CRISPR-Cas endeavor.

Cassava breeding and agronomy in Asia: 50 years of history and future directions

In Asia, cassava (Manihot esculenta) is cultivated by more than 8 million farmers, driving the rural economy of many countries. The International Center for Tropical Agriculture (CIAT), in partnership with national agricultural research institutes (NARIs), instigated breeding and agronomic research in Asia, 1983. The breeding program has successfully released high-yielding cultivars resulting in an average yield increase from 13.0 t ha-1 in 1996 to 21.3 t ha-1 in 2016, with significant economic benefits. Following the success in increasing yields, cassava breeding has turned its focus to higher-value traits, such as waxy cassava, to reach new market niches. More recently, building resistance to invasive pests and diseases has become a top priority due to the emergent threat of cassava mosaic disease (CMD). The agronomic research involves driving profitability with advanced technologies focusing on better agronomic management practices thereby maintaining sustainable production systems. Remote sensing technologies are being tested for trait discovery and large-scale field evaluation of cassava. In summary, cassava breeding in Asia is driven by a combination of food and market demand with technological innovations to increase the productivity. Further, exploration in the potential of data-driven agriculture is needed to empower researchers and producers for sustainable advancement.

Detection of Marker-Free Precision Genome Editing and Genetic Variation through the Capture of Genomic Signatures

Genome editing technologies have transformed our ability to engineer desired genomic changes within living systems. However, detecting precise genomic modifications often requires sophisticated, expensive, and time-consuming experimental approaches. Here, we describe DTECT (Dinucleotide signaTurE CapTure), a rapid and versatile detection method that relies on the capture of targeted dinucleotide signatures resulting from the digestion of genomic DNA amplicons by the type IIS restriction enzyme AcuI. DTECT enables the accurate quantification of marker-free precision genome editing events introduced by CRISPR-dependent homology-directed repair, base editing, or prime editing in various biological systems, such as mammalian cell lines, organoids, and tissues. Furthermore, DTECT allows the identification of oncogenic mutations in cancer mouse models, patient-derived xenografts, and human cancer patient samples. The ease, speed, and cost efficiency by which DTECT identifies genomic signatures should facilitate the generation of marker-free cellular and animal models of human disease and expedite the detection of human pathogenic variants.

A qPCR method for genome editing efficiency determination and single-cell clone screening in human cells

CRISPR/Cas9 technology has been widely used for targeted genome modification both in vivo and in vitro. However, an effective method for evaluating genome editing efficiency and screening single-cell clones for desired modification is still lacking. Here, we developed this real time PCR method based on the sensitivity of Taq DNA polymerase to nucleotide mismatch at primer 3' end during initiating DNA replication. Applications to CRISPR gRNAs targeting EMX1, DYRK1A and HOXB13 genes in Lenti-X 293 T cells exhibited comprehensive advantages. Just in one-round qPCR analysis using genomic DNA from cells underwent CRISPR/Cas9 or BE4 treatments, the genome editing efficiency could be determined accurately and quickly, for indel, HDR as well as base editing. When applied to single-cell clone screening, the genotype of each cell colony could also be determined accurately. This method defined a rigorous and practical way in quantify genome editing events.

A transient reporter for editing enrichment (TREE) in human cells

Current approaches to identify cell populations that have been modified with deaminase base editing technologies are inefficient and rely on downstream sequencing techniques. In this study, we utilized a blue fluorescent protein (BFP) that converts to green fluorescent protein (GFP) upon a C-to-T substitution as an assay to report directly on base editing activity within a cell. Using this assay, we optimize various base editing transfection parameters and delivery strategies. Moreover, we utilize this assay in conjunction with flow cytometry to develop a transient reporter for editing enrichment (TREE) to efficiently purify base-edited cell populations. Compared to conventional cell enrichment strategies that employ reporters of transfection (RoT), TREE significantly improved the editing efficiency at multiple independent loci, with efficiencies approaching 80%. We also employed the BFP-to-GFP conversion assay to optimize base editor vector design in human pluripotent stem cells (hPSCs), a cell type that is resistant to genome editing and in which modification via base editors has not been previously reported. At last, using these optimized vectors in the context of TREE allowed for the highly efficient editing of hPSCs. We envision TREE as a readily adoptable method to facilitate base editing applications in synthetic biology, disease modeling, and regenerative medicine.