Using Clustered Regularly Interspaced Short Palindromic Repeats gene editing to induce permanent expression of fetal hemoglobin in β-thalassemia and sickle cell disease: A comparative meta-analysis

Abstract

β-hemoglobinopathies like sickle cell disease (SCD) and β-thalassemia are characterized by differing mutations in the hemoglobin subunit beta gene (HBB). These disorders vary in phenotypic presentation and severity, with more severe manifestations leading to transfusion dependence along with associated complications such as infection and iron overload. β-hemoglobinopathies symptoms rapidly worsen after birth as the levels of fetal hemoglobin (HbF) begin to decline. To reverse this decline, current treatment plans typically involve the use of pharmacological agents such as hydroxyurea to raise expression levels of HbF. However, these treatments only result in transient effects and must be consistently administered. Gene editing technologies such as CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats- CRISPR associated protein) offer the opportunity to create novel treatments which can raise HbF expression with potential permanent effects. Two gene targets, B-cell lymphoma/leukemia 11A gene (BCL11A) and the promoter regions of gamma globin genes (HBG1/2), have been identified to significantly increase HbF protein expression. In order to differentiate the effectiveness of BCL11A and HBG1/2 editing, a meta-analysis was performed by first identifying 119 studies for inclusion based on the search terms terms “β-Thalassemia,” “beta-thal” “sickle cell disease,” “SCD,” and “CRISPR.” Following application of exclusion and inclusion criteria, we performed analysis on 8 peer-reviewed published studies from 2018 to 2021 were included in the study. Forest plots were generated using R (version 4.1.2). Primary comparative analysis shows HBG1/2 had a significantly (p < 0.01)greater impact on induction of HbF expression compared to BCL11A. This analysis leads us to conclude that HBG1/2 merits further investigation as a possible gene editing target for treatment of SCD and β-thalassemia.

Global, regional, and national burden of thalassemia, 1990–2021: a systematic analysis for the global burden of disease study 2021

“… 34 , 35 Innovative therapeutic approaches have garnered attention. 36 , 37 Particularly methods regulating BCL11A gene expression, which show promise in potentially enabling patients to achieve long-term transfusion independence, 38 , 39 Additionally, the use of Luspatercept has been proven to effectively improve ineffective erythropoiesis associated with thalassemia. 40 However, these novel treatments are still in development and pose new challenges in terms of safety, cost-effectiveness, and economic burden.…”

Pharmacogenomics of Drugs Used in β-Thalassemia and Sickle-Cell Disease: From Basic Research to Clinical Applications

“…In addition, GWAS-identified single nucleotide polymorphisms (SNPs) have been mapped within the erythroid enhancer of the BCL11A gene [84]. This was a key contribution to the development of the pharmacogenomics of β-thalassemia, especially after the development of gene editing protocols that were able to demonstrate that the disruption of discrete portions of the BCL11A enhancer are associated with a reduction in the expression of BCL11A and an increase in γ-globin gene expression and HbF production [90][91][92]. More recently, Antoniou et al have used base editing to generate a large variety of mutations within the −200 region of the γ-globin gene promoters [91].…”

“…For instance, Roy et al studied the influence of BCL11A, HBS1L-MYB, and HBBP1 single nucleotide polymorphisms (in addition to the HBG2 XmnI polymorphism) on the levels of endogenous production of HbF and found a significant association of HbF levels with rs2071348 (BCL11A) and rs4895441 (HBS1L-MYB), respectively. The HBG2 XmnI polymorphism showed the strongest association [76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95]. An extensive description of SNPs associated with high production of HbF is outside the objectives of the present review that is mainly focused on the most relevant (in our opinion) DNA polymorphisms considered in published pharmacogenomic studies on β-thalassemia and SCD.…”

Therapeutic Relevance of Inducing Autophagy in β-Thalassemia

“…Figure 3 depicts additional approaches to reduce the imbalanced α-globin/β-like globin ratio in β-thalassemia. Evidently, γ-globin gene activation and fetal hemoglobin (HbF) induction can be obtained either by CRISPR-Cas9 gene editing, targeting γ-globin gene repressors or the binding sequences presenting the γ-globin gene promoter (Figure 3, approach "B") [37][38][39], or by exposure of β-thalassemic erythroid cells to a variety of HbF inducers, (Figure 3C) as reviewed elsewhere [40][41][42] (Figure 3, approach "C"). Finally, a decrease in the excess free α-globin chains can be achieved in erythroid cells by the activation (or potentiation) of autophagy (as outlined in Figure 3, approach "D"), and is reported in several studies [43][44][45][46][47][48].…”