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Development of a ß-Globin Gene Replacement Strategy as a Therapeutic Approach for ß-Hemoglobinopathies

ABSTRACT: β-hemoglobinopathies are the most common genetic disorders worldwide. In sickle cell disease (SCD) a single mutation (E6V) in the b-globin (HBB) gene results in dysfunctional hemoglobin protein, while in β-thalassemia, over 300 mutations distributed across the HBB gene are known to reduce the production of β-globin and cause severe anemia. A genetic engineering approach that replaces the whole HBB gene is an ideal strategy to rescue HBB expression for most genotypes but is technically challenging as the insert cannot be homologous to the endogenous gene and codon-optimized, intron-less sequences may not reconstitute adequate HBB levels. Here, we developed a novel approach for a “one-size-fits-all" HBB gene repair strategy using CRISPR-Cas9 which successfully addresses these problems. First, our DNA donor design avoids sequence homology through a diverged HBB coding sequence and second, incorporates heterologous introns from the fetal g-globin gene, further reducing homology to endogenous HBB while mimicking its intron composition. Screening DNA donors with various heterologous globin introns, polyadenylation signals and truncated sequences, identified a heterologous intron DNA donor that highly expresses β-globin and rescued β-globin expression in two in vitro hemoglobinopathy models in hematopoietic stem and progenitor cells (HSPCs). Furthermore, healthy donor HSPCs modified with this HBB gene replacement approach showed successful engraftment in immunodeficient mice at 16 weeks. In summary, we developed a universal HBB gene replacement strategy that results in physiological b-globin production, offering a potential differentiated approach for treating patients with β-thalassemia, SCD or compound heterozygous individuals.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE229212 | GEO | 2024/04/01

REPOSITORIES: GEO

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Project description:Background: The thalassemias are highly diverse at both the molecular and clinical levels. Many of the HBB mutations that result in β-thalassemia are missense mutations in the coding region of the β-globin gene, but a few cause alternative splicing, and interfere with normal processing of the β-globin transcripts. Transcriptome profiling in individuals affected with β-thalassemia, especially in individuals who carry novel mutations in the HBB, may improve our understanding of the heterogeneity and molecular mechanisms of the disease. Methods: Members of a family with a daughter affected with thalassemia intermedia, although her mother was not clinically affected, were examined for physical characteristics, hematological parameters and β-globin gene sequences. We also characterized genome-wide gene expression in the family using RT-qPCR and high-throughput RNA-sequencing mRNA expression profiling of blood. Results: Clinical findings, hematological indices, DNA and RNA sequence analysis of individuals with β-thalassemia, including the description of a novel mutation in the β-globin gene, which introduces a cryptic donor splice site. More than 300 genes are differentially expressed in β-thalassemic blood with many of the DEGs involved in pathways relevant to the clinical management of β-thalassemia. β-thalassemia shows important similarities and differences with sickle cell disease at the transcriptome level. Conclusions: We described the down-regulation of the β-globin gene in β-thalassemia by RNA-sequencing analysis using a sample from an affected individual and her mother, who have a novel mutation in the HBB that creates a cryptic donor splice site. The daughter has a typical β-thalassemia allele as well, and an unexpectedly severe phenotype. The DEGs are enriched in pathways that are directly or indirectly related to β-thalassemia such as hemopoiesis, heme biosynthesis, response to oxidative stress, inflammatory responses, immune responses, control of circadian rhythm, apoptosis, and other cellular activities. We compare our findings with published results of RNA-Sequencing analysis of sickle cell disease (SCD) and erythroblasts from a KLF1-null neonate with hydrops fetalis, and recognize similarities and differences in their transcriptional expression patterns.

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Development of a ß-Globin Gene Replacement Strategy as a Therapeutic Approach for ß-Hemoglobinopathies

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