An enhancer haplotype may influence BCL11A expression levels and the response to hydroxyurea in β-thalassemia patients

Therapeutic promise of CRISPR-Cas9 gene editing in sickle cell disease and β-thalassemia: A current review

Sickle cell disease (SCD and β-thalassemia (BT) affects millions of people worldwide. In addition, around 500,000 infants are born with SCD and 60,000 people are diagnosed with BT every year. Mutations in the hemoglobin subunit beta (HBB) gene are responsible for causing both BT and SCD. Indeed, the diversity of potential mutations in the HBB gene elucidates the diversity in clinical severity observed in individuals with BT and related morbidities. On the other hand, SCD takes place because of the alteration in a single amino acid at position 6 in the beta-globin chain, where a base substitution occurs from glutamic acid to valine, which eventually results in abnormal sickle hemoglobin. Conventional therapies for BT and SCD including pharmaceutical drugs and blood transfusion might temporarily improve the clinical severity of these diseases, however these therapies cannot cure the diseases. CRISPR-Cas9 (CC9) is revolutionizing genome engineering, offering promising therapeutic avenues for genetic diseases. Therefore, CC9-mediated gene therapy provides great hope in the treatment of both BT and SCD. CC9-mediated gene therapy has already demonstrated its effectiveness in correcting both SCD and BT-causing mutations. Moreover, CC9-mediated gene editing was found to be effective in reactivating the expression of hemoglobin F (HbF) and regulating LRF and BCL11A. A number of clinical trials with CC9 gene-edited therapies are being carried out to elucidate their potential in treating BT and SCD. Genetics and pathophysiological mechanisms of SCD and BT, the mechanism of CC9-mediated gene editing, and common delivery methods of the CC9 system have been discussed in this review. Moreover, an in-depth discussion on applications and the current status of CC9-mediated gene editing in SCD and BT along with current challenges and future perspectives have been provided.

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.

CRISPR/Cas9, a promising approach for the treatment of β-thalassemia: a systematic review

The CRISPR/Cas9 technique is easily programmable, fast, more powerful, and efficient at generating a mutation compared to previous gene therapy methods. β-thalassemia is the most common autosomal recessive disorder worldwide. Appropriate genomic changes in the β gene can be modified to alleviate the symptoms of the disease using the CRISPR/Cas9 system. PubMed/Medline, Scopus, Web of Science, and SID databases were searched in Persian and English from February 2000 to September 2022. Finally, 39 articles had inclusion criteria which were reviewed by two separate individuals. Among the reviewed articles, articles were divided into three categories. In the first group, studies attemped to increase the expression of γ-globin and production of hemoglobin F. The strategy of second group of studies were the reduction of the α-globin chain to prevent hemolysis of RBCs by accumulation of excessive α-globins. The third group corrected the mutations causing β-thalassemia. Studies have shown that the genome of β-thalassemia patients can be modified using the CRISPR/Cas9 technique, and this approach might be promising for the treatment of β-thalassemia.

Omics Studies in Hemoglobinopathies

Hemoglobinopathies include all genetic diseases of hemoglobin and are grouped into thalassemia syndromes and structural hemoglobin variants. The β-thalassemias constitute a group of severe anemias with monogenic inheritance, caused by β-globin gene mutations. This review is focused on omics studies in hemoglobinopathies and mainly β-thalassemia, and discusses genomic, epigenomic, transcriptomic, proteomic and metabolomic findings. Omics analyses have identified various disease modifiers with an impact on disease severity and efficacy of treatments. These modifiers have contributed to the understanding of globin genes regulation/hemoglobin switching and the development of novel therapies. How omics data and their integration can contribute to efficient patient stratification, therapeutic management, improvements in existing treatments and application of novel personalized therapies is discussed.

CRISPR-based strategies for studying regulatory elements and chromatin structure in mammalian gene control

The development of high-throughput methods has enabled the genome-wide identification of putative regulatory elements in a wide variety of mammalian cells at an unprecedented resolution. Extensive genomic studies have revealed the important role of regulatory elements and genetic variation therein in disease formation and risk. In most cases, there is only correlative evidence for the roles of these elements and non-coding changes within these elements in pathogenesis. With the advent of genome- and epigenome-editing tools based on the CRISPR technology, it is now possible to test the functional relevance of the regulatory elements and alterations on a genomic scale. Here, we review the various CRISPR-based strategies that have been developed to functionally validate the candidate regulatory elements in mammals as well as the non-coding genetic variants found to be associated with human disease. We also discuss how these synthetic biology tools have helped to elucidate the role of three-dimensional nuclear architecture and higher-order chromatin organization in shaping functional genome and controlling gene expression.