Core Viewpoint - CRISPR/Cas9 gene editing technology has emerged as a groundbreaking tool in the biomedical field, showcasing significant potential in basic research and translational medicine, yet it faces critical technical challenges that need to be addressed [2]. Group 1: Technical Challenges of CRISPR/Cas9 - The first challenge is the precision and safety of editing, as CRISPR/Cas9 relies on double-strand breaks (DSB) or single-strand breaks (SSB) in the genome, which can lead to non-homologous end joining (NHEJ) repair pathways, potentially causing genomic instability and cytotoxic effects [2]. - The second challenge involves the efficient insertion of long DNA fragments, as existing gene editing tools primarily target short DNA sequences, and the key repair mechanism, homologous directed repair (HDR), is limited to specific cell cycle phases, making it difficult to achieve precise insertion of long DNA (kilobase scale) in mammalian cells [2]. Group 2: Development of New Gene Editing Tools - A research team from Nanjing Medical University and the University of Science and Technology of China developed a new gene editing tool, Cas9-EcRecE, which significantly improves the efficiency of precise insertion of long DNA fragments (kilobase scale) in mammalian cells [3]. - The study also introduced a safe gene editing tool, dCas9-EcRecTE, which does not rely on DNA double-strand breaks, providing new technical support for safe and efficient gene editing [3][12]. Group 3: Enhancements in HDR Efficiency - The research team previously demonstrated that phage-derived SSAP-RecT can significantly enhance the efficiency of kilobase-scale DNA fragment insertion in mammalian cells, leading to the development of the REDIT technology and dCas9-SSAP, although these technologies still have room for improvement [7]. - The team optimized the homologous repair template, protein nuclear localization signals, and developed a mini version of EcRecE, achieving approximately 20% HDR efficiency in HEK293T cells, providing a feasible solution for in vivo gene editing [9]. Group 4: RED-CRISPR System - A new system called RED-CRISPR, based on the λ phage homologous recombination system (Redα/Redβ), enhances CRISPR/Cas9-mediated precise editing of long DNA fragments (kilobase scale) [16]. - The RED-CRISPR system achieved approximately 20% HDR efficiency in HEK293T cells and demonstrated significantly reduced off-target editing events and chromosomal translocation events, indicating higher safety and potential clinical application value [20]. Group 5: Applications and Future Prospects - The RED-CRISPR system has shown effectiveness in various biomedical applications, including the construction of large transgenic animal models, CAR-T cell preparation, and precise correction of pathogenic gene mutations [21]. - The system achieved a 44.3% efficiency in precise knock-in of a 2 kb expression cassette in T cells, significantly outperforming the Cas9 group and demonstrating its potential for clinical translation [21].

Core Insights - A research team from Mie University and other institutions in Japan has successfully utilized gene editing technology to remove the extra 21st chromosome from cells of patients with Down syndrome, confirming the results in a publication in the Proceedings of the National Academy of Sciences [1][2] Group 1: Research Methodology - The team extracted fibroblasts from the skin of Down syndrome patients to cultivate induced pluripotent stem cells (iPS cells) [2] - They developed three types of iPS cells, each with one of the three 21st chromosomes deleted, and constructed a CRISPR/Cas9 system to target and cut the extra chromosome at multiple sites [2] - The CRISPR/Cas9 system achieved a removal accuracy of up to 37.5% for the target 21st chromosome [2] Group 2: Findings and Implications - Analysis of the modified iPS cells showed that their characteristics, including gene expression patterns, cell proliferation rates, and reactive oxygen handling, had returned to normal [2] - The CRISPR/Cas9 system was also confirmed to be effective in removing chromosomes from differentiated cells, such as fibroblasts and non-dividing cells [2] Group 3: Future Directions - The technology is currently in the concept validation stage through in vitro cell experiments and has some limitations [2] - Future research will focus on developing safer chromosome removal techniques that do not rely on cutting [2]