Expression and hydroxyurea-triggered induction of EGFP upon CRISPR/Cas9-mediated integration into the γ-globin gene of K562 cells

Detection of CRISPR/Cas9-Mediated Fetal Hemoglobin Reactivation in Erythroblasts Derived from Cord Blood-Hematopoietic Stem Cells

Reactivation of the fetal hemoglobin (HbF) in adult erythroid cells via genome editing is a strategy for the treatment of β-thalassemia and sickle cell disease. In related reports, the reactivation of HbF is regularly examined in erythroblasts which are generated from the adult CD34+ hematopoietic stem and progenitor cells (HSPCs). However, the procurement of adult HSPCs, either from the bone-marrow (BM) or from mobilized peripheral-blood (mPB), is difficult. Cord-blood (CB) is a readily available source of HSPCs. CB-HSPCs, however, produce high quantities of HbF following differentiation into the erythroid lineage-a potential drawback in such studies. Here, we have edited the BCL11A enhancer (a well-characterized HbF-quantitative trait loci or QTL) via CRISPR/Cas9 in order to determine whether HbF reactivation could be detected in CB-HSPC-derived erythroblasts. In the edited erythroblasts, insertion/deletion (indel) frequencies of 74.0-80.4% and BCL11A RNA reduction levels of 92.6 ± 5.1% (P < 0.0001) were obtained. In turn, the γ/β-globin transcript ratios were increased from 11.3 ± 1.1-fold to 77.1 ± 2.0-fold, i.e., by 6.8-fold (P < 0.0001)-and the HbF% levels increased from 34.3% in the control population to 43.5% in the BCL11A edited erythroblasts. Our results suggest that γ-globin/HbF reactivation via genome editing can be detected in CB-HSPCs generated erythroblasts-rendering CB-HSPCs a useful model for similar studies.

Improving Homology-Directed Repair in Genome Editing Experiments by Influencing the Cell Cycle

Genome editing is currently widely used in biomedical research; however, the use of this method in the clinic is still limited because of its low efficiency and possible side effects. Moreover, the correction of mutations that cause diseases in humans seems to be extremely important and promising. Numerous attempts to improve the efficiency of homology-directed repair-mediated correction of mutations in mammalian cells have focused on influencing the cell cycle. Homology-directed repair is known to occur only in the late S and G2 phases of the cell cycle, so researchers are looking for safe ways to enrich the cell culture with cells in these phases of the cell cycle. This review surveys the main approaches to influencing the cell cycle in genome editing experiments (predominantly using Cas9), for example, the use of cell cycle synchronizers, mitogens, substances that affect cyclin-dependent kinases, hypothermia, inhibition of p53, etc. Despite the fact that all these approaches have a reversible effect on the cell cycle, it is necessary to use them with caution, since cells during the arrest of the cell cycle can accumulate mutations, which can potentially lead to their malignant transformation.

Challenges of CRISPR-Based Gene Editing in Primary T Cells

Adaptive T-cell immunotherapy holds great promise for the successful treatment of leukemia, as well as other types of cancers. More recently, it was also shown to be an effective treatment option for chronic virus infections in immunosuppressed patients. Autologous or allogeneic T cells used for immunotherapy are usually genetically modified to express novel T-cell or chimeric antigen receptors. The production of such cells was significantly simplified with the CRISPR/Cas system, allowing for the deletion or insertion of novel genes at specific locations within the genome. In this review, we describe recent methodological breakthroughs that were important for the conduction of these genetic modifications, summarize crucial points to be considered when conducting such experiments, and highlight the potential pitfalls of these approaches.