CRISPR gene editing in human cells
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CRISPR Gene Editing Technologies in Human Cells
CRISPR gene editing has revolutionized the ability to modify the human genome, with several CRISPR-associated proteins—such as Cas9, Cas12a (Cpf1), and Cas12b—enabling targeted changes in DNA with high efficiency and flexibility 126. These systems are widely used in research and are being developed for clinical applications, including gene therapy and disease modeling 29.
Cas9, Cas12a (Cpf1), and Cas12b: Key CRISPR Systems
The most commonly used CRISPR system in human cells is CRISPR-Cas9, which can efficiently introduce targeted double-strand breaks (DSBs) in DNA, leading to gene disruption or correction 237. Cas12a (Cpf1) and Cas12b are alternative nucleases with unique features. Cas12a has a T-rich PAM requirement, generates sticky ends, and shows lower off-target effects compared to Cas9, making it suitable for multiplex gene editing and regulation . Cas12b, after engineering for human cell compatibility, offers high specificity and robust editing, expanding the CRISPR toolbox for human genome engineering .
Applications of CRISPR Gene Editing in Human Cells
Disease Modeling and Therapeutic Potential
CRISPR gene editing is used to correct mutations responsible for genetic diseases such as Duchenne muscular dystrophy, hemophilia, β-thalassemia, and cystic fibrosis in human cells and animal models . It is also applied in immunology, for example, to engineer T cells for cancer immunotherapy or to target genes involved in HIV infection 25. In addition, CRISPR is combined with induced pluripotent stem cells (iPSCs) to create disease models and donor-specific tissues for transplantation 29.
Editing in Clinically Relevant Human Cells
CRISPR-Cas9 has been shown to efficiently disrupt genes in primary human hematopoietic stem and progenitor cells (HSPCs) and T cells, with minimal off-target effects, supporting its potential for cell-based therapies . High editing efficiencies and low off-target activity have also been demonstrated with optimized Cas12a (MAD7) systems in human immune cells, enabling efficient gene disruption and transgene integration for applications like CAR T cell therapy .
DNA Repair Pathways and Editing Outcomes
Mechanisms of DNA Repair
After CRISPR-induced DSBs, human cells repair DNA mainly through nonhomologous end joining (NHEJ), microhomology-mediated end joining (MMEJ), or homology-directed repair (HDR) . NHEJ is fast but error-prone, often resulting in small insertions or deletions (indels). HDR allows precise edits using a donor template but is less efficient and restricted to certain cell cycle phases . The choice of repair pathway influences the outcome and precision of gene editing .
Unintended Editing Outcomes and Safety Concerns
While CRISPR is highly effective, unintended outcomes such as large deletions, chromosomal rearrangements, and loss of heterozygosity can occur at on-target sites 3410. These structural variants are not always detected by standard sequencing methods and may have safety implications, especially in clinical settings 3410. Mosaicism and off-target effects have also been observed, particularly in early human embryos, highlighting the need for improved specificity and comprehensive validation of editing outcomes 810.
Advances in Detection and Optimization
Recent advances in sequencing technologies, such as long-read sequencing, have improved the detection of large structural variants and complex on-target mutations, providing a more complete picture of CRISPR editing outcomes in human cells 34. Optimization of guide RNAs, delivery methods, and the use of engineered nucleases with higher fidelity are ongoing strategies to enhance editing precision and safety 156.
Conclusion
CRISPR gene editing in human cells offers powerful tools for research, disease modeling, and potential therapies. Multiple CRISPR systems—Cas9, Cas12a, and Cas12b—provide flexibility and specificity for diverse applications. However, unintended editing outcomes, including large deletions and chromosomal changes, remain a concern, especially for clinical use. Continued research into DNA repair mechanisms, improved detection methods, and optimization of editing strategies are essential to maximize the benefits and minimize the risks of CRISPR gene editing in human cells 1234+6 MORE.
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