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Disruptive non-disruptive applications of CRISPR/Cas9.
The bacterial type II Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR Associated (Cas) systems, and in particular Streptococcus pyogenes CRISPR-Cas9, have been broadly applied to edit the genome of bacterial and eukaryotic cells. Cas9, which is an RNA-guided programmable nuclease, is a powerful tool for disrupting protein-coding genes. Cas9 cleaves target sites to generate a double-strand break (DSB) that is repaired via an error-prone repair process, leading to insertion/deletion mutations and gene knockouts. However, Cas9 can also be used to modulate genome function without gene disruption, enabling base editing, transcriptional and epigenetic reprogramming, genome imaging, cellular barcoding, genetic recording, and genetic computation.
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Elimination of CaMKIIδ Autophosphorylation by CRISPR-Cas9 Base Editing Improves Survival and Cardiac Function in Heart Failure in Mice.
BACKGROUND: Cardiovascular diseases are the main cause of worldwide morbidity and mortality, highlighting the need for new therapeutic strategies. Autophosphorylation and subsequent overactivation of the cardiac stress-responsive enzyme CaMKIIδ (Ca2+/calmodulin-dependent protein kinase IIδ) serves as a central driver of multiple cardiac disorders. METHODS: To develop a comprehensive therapy for heart failure, we used CRISPR-Cas9 adenine base editing to ablate the autophosphorylation site of CaMKIIδ. We generated mice harboring a phospho-resistant CaMKIIδ mutation in the germline and subjected these mice to severe transverse aortic constriction, a model for heart failure. Cardiac function, transcriptional changes, apoptosis, and fibrosis were assessed by echocardiography, RNA sequencing, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, and standard histology, respectively. Specificity toward CaMKIIδ gene editing was assessed using deep amplicon sequencing. Cellular Ca2+ homeostasis was analyzed using epifluorescence microscopy in Fura-2-loaded cardiomyocytes. RESULTS: Within 2 weeks after severe transverse aortic constriction surgery, 65% of all wild-type mice died, and the surviving mice showed dramatically impaired cardiac function. In contrast to wild-type mice, CaMKIIδ phospho-resistant gene-edited mice showed a mortality rate of only 11% and exhibited substantially improved cardiac function after severe transverse aortic constriction. Moreover, CaMKIIδ phospho-resistant mice were protected from heart failure-related aberrant changes in cardiac gene expression, myocardial apoptosis, and subsequent fibrosis, which were observed in wild-type mice after severe transverse aortic constriction. On the basis of identical mouse and human genome sequences encoding the autophosphorylation site of CaMKIIδ, we deployed the same editing strategy to modify this pathogenic site in human induced pluripotent stem cells. It is notable that we detected a >2000-fold increased specificity for editing of CaMKIIδ compared with other CaMKII isoforms, which is an important safety feature. While wild-type cardiomyocytes showed impaired Ca2+ transients and an increased frequency of arrhythmias after chronic β-adrenergic stress, CaMKIIδ-edited cardiomyocytes were protected from these adverse responses. CONCLUSIONS: Ablation of CaMKIIδ autophosphorylation by adenine base editing may offer a potential broad-based therapeutic concept for human cardiac disease.
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Directed Evolution of OgeuIscB With Enhanced Activity in Human Cells.
The miniature RNA-guided endonuclease IscB, as the evolutionary progenitor of Cas9, is attracting increased attention for genome editing due to its compact size and suitability for in vivo delivery. However, the poor editing efficiency of IscB in eukaryotic cells presents a significant challenge to its widespread application in precise site-specific human genome editing. In this study, we employed structure-guided rational design and protein engineering to optimize OgeuIscB, resulting in the identification of enIscB-F138R, which further enhanced editing activity up to 3.49-fold in mammalian cells compared to the high-activity OgeuIscB variant enIscB. Furthermore, we engineered an enIscB-F138R nickase-based adenine base editor, termed miABE-F138R, exhibiting enhanced base editing efficiency relative to miABE. To illustrate the practical applications of miABE-F138R, we applied it to rectify the prevalent R560C mutation in Pde6β associated with autosomal recessive retinitis pigmentosa, resulting in a significant improvement in activity compared to miABE. In conclusion, enIscB-F138R and miABE-F138R offer adaptable platforms for genome editing with potential significance in future biomedical applications.
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Fetal Hemoglobin Modulation in Sickle Cell Disease: βs Haplotypes, Key Polymorphisms Identified by GWAS, and Advances in γ-Globin Editing: An Updated Overview.
Fetal hemoglobin (HbF) plays a central role in mitigating the pathophysiological effects of sickle cell disease (SCD). Understanding the genetic determinants influencing HbF expression is essential for identifying the factors contributing to its modulation. This review provides an updated synthesis of evidence on HbF modulation, focusing on βs haplotypes and their molecular characterization through Sanger sequencing, polymorphisms consistently associated with HbF levels in genome-wide association studies (GWAS), and recent advances in gene editing targeting HbF expression. An integrative review (2016-2025) was conducted using PubMed/MEDLINE, Scopus, and Web of Science, encompassing original research, experimental studies, systematic reviews, and genomic analyses. Key regulatory loci such as BCL11A, HBS1L-MYB (HMIP), and the HBB cluster explain a significant proportion of HbF variability across populations. Furthermore, additional variants in KLF1, NFIX, BACH2, and ZBTB7A have emerged as potential modulators in specific cohorts. Regarding advances in γ-globin editing, "prime editing", although still in the experimental phase, has recently emerged as an innovative approach capable of introducing multiple HPFH-like mutations within γ-globin promoters, expanding future therapeutic possibilities in SCD. This review also provides a comparative overview of prime editing and other gene-editing strategies for HbF modulation, such as CRISPR-Cas9 and Base editing. Collectively, this work outlines the current landscape of HbF modulation and provides an informative basis for future research aimed at advancing precision-oriented therapeutic strategies in sickle cell disease.
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Eliminating predictable DNA off-target effects of cytosine base editor by using dual guiders including sgRNA and TALE.
Predictable DNA off-target effect is one of the major safety concerns for the application of cytosine base editors (CBEs). To eliminate Cas9-dependent DNA off-target effects, we designed a novel effective CBE system with dual guiders by combining CRISPR with transcription activator-like effector (TALE). In this system, Cas9 nickase (nCas9) and cytosine deaminase are guided to the same target site to conduct base editing by single-guide RNA (sgRNA) and TALE, respectively. However, if nCas9 is guided to a wrong site by sgRNA, it will not generate base editing due to the absence of deaminase. Similarly, when deaminase is guided to a wrong site by TALE, base editing will not occur due to the absence of single-stranded DNA. In this way, Cas9- and TALE-dependent DNA off-target effects could be completely eliminated. Furthermore, by fusing TALE with YE1, a cytidine deaminase with minimal Cas9-independent off-target effect, we established a novel CBE that could induce efficient C-to-T conversion without detectable Cas9- or TALE-dependent DNA off-target mutations.
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CRISPR-Cas9 cytidine and adenosine base editing of splice-sites mediates highly-efficient disruption of proteins in primary and immortalized cells.
CRISPR-Cas9 cytidine and adenosine base editors (CBEs and ABEs) can disrupt genes without introducing double-stranded breaks by inactivating splice sites (BE-splice) or by introducing premature stop (pmSTOP) codons. However, no in-depth comparison of these methods or a modular tool for designing BE-splice sgRNAs exists. To address these needs, we develop SpliceR ( http://z.umn.edu/spliceR ) to design and rank BE-splice sgRNAs for any Ensembl annotated genome, and compared disruption approaches in T cells using a screen against the TCR-CD3 MHC Class I immune synapse. Among the targeted genes, we find that targeting splice-donors is the most reliable disruption method, followed by targeting splice-acceptors, and introducing pmSTOPs. Further, the CBE BE4 is more effective for disruption than the ABE ABE7.10, however this disparity is eliminated by employing ABE8e. Collectively, we demonstrate a robust method for gene disruption, accompanied by a modular design tool that is of use to basic and translational researchers alike.
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Highly efficient base editing at PCSK9 and normal human embryo development.
Cas9-based tools enable programmable DNA lesions for studying repair outcomes, gene function and genome correction. In human embryos, Cas9-induced DNA double-stranded breaks are genotoxic, causing frequent aneuploidy and large deletions1,2. Here, we evaluate DNA repair outcomes at nicks and mismatches introduced by base editors at the PCSK9 and HBG loci in human embryos. Delivering ABE8e(V106W) as a protein at fertilization achieved editing at all PCSK9 alleles, supporting development to the blastocyst stage and the derivation of homozygous edited stem cell lines. No insertions or deletions were detected, although rare on-target chromosome breakages and chromosomal abnormalities occurred. Furthermore, editing at bystander and off-target sites was mosaic, and the introduction of the editor as mRNA caused frequent embryo arrest due to guide-independent deaminase activity. Thus, in contrast to Cas9-induced DNA breaks, base-editor-induced lesions are efficiently repaired. However, undesirable consequences for the genome and development can occur, currently precluding the clinical use of base editing in reproduction.
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Adenine base editor-mediated correction of the common and severe IVS1-110 (G>A) β-thalassemia mutation.
β-Thalassemia (BT) is one of the most common genetic diseases worldwide and is caused by mutations affecting β-globin production. The only curative treatment is allogenic hematopoietic stem/progenitor cells (HSPCs) transplantation, an approach limited by compatible donor availability and immunological complications. Therefore, transplantation of autologous, genetically-modified HSPCs is an attractive therapeutic option. However, current gene therapy strategies based on the use of lentiviral vectors are not equally effective in all patients and CRISPR/Cas9 nuclease-based strategies raise safety concerns. Thus, base editing strategies aiming to correct the genetic defect in patients' HSPCs could provide safe and effective treatment. Here, we developed a strategy to correct one of the most prevalent BT mutations (IVS1-110 [G>A]) using the SpRY-ABE8e base editor. RNA delivery of the base editing system was safe and led to ∼80% of gene correction in the HSPCs of patients with BT without causing dangerous double-strand DNA breaks. In HSPC-derived erythroid populations, this strategy was able to restore β-globin production and correct inefficient erythropoiesis typically observed in BT both in vitro and in vivo. In conclusion, this proof-of-concept study paves the way for the development of a safe and effective autologous gene therapy approach for BT.
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Improving the Cpf1-mediated base editing system by combining dCas9/dead sgRNA with human APOBEC3A variants.
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In vivo CRISPR base editing of PCSK9 durably lowers cholesterol in primates.
Gene-editing technologies, which include the CRISPR-Cas nucleases1-3 and CRISPR base editors4,5, have the potential to permanently modify disease-causing genes in patients6. The demonstration of durable editing in target organs of nonhuman primates is a key step before in vivo administration of gene editors to patients in clinical trials. Here we demonstrate that CRISPR base editors that are delivered in vivo using lipid nanoparticles can efficiently and precisely modify disease-related genes in living cynomolgus monkeys (Macaca fascicularis). We observed a near-complete knockdown of PCSK9 in the liver after a single infusion of lipid nanoparticles, with concomitant reductions in blood levels of PCSK9 and low-density lipoprotein cholesterol of approximately 90% and about 60%, respectively; all of these changes remained stable for at least 8 months after a single-dose treatment. In addition to supporting a 'once-and-done' approach to the reduction of low-density lipoprotein cholesterol and the treatment of atherosclerotic cardiovascular disease (the leading cause of death worldwide7), our results provide a proof-of-concept for how CRISPR base editors can be productively applied to make precise single-nucleotide changes in therapeutic target genes in the liver, and potentially in other organs.
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