Browsing by Author "Schwessinger, R."

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Direct correction of haemoglobin E β-thalassaemia using base editors
(Nature Pub. Group, 2023) Badat, M.; Ejaz, A.; Hua, P.; Rice, S.; Zhang, W.; Hentges, L.D.; Fisher, C.A.; Denny, N.; Schwessinger, R.; Yasara, N.; Roy, N.B.A.; Issa, F.; Roy, A.; Telfer, P.; Hughes, J.; Mettananda, S.; Higgs, D.R.; Davies, J.O.J.
Haemoglobin E (HbE) β-thalassaemia causes approximately 50% of all severe thalassaemia worldwide; equating to around 30,000 births per year. HbE β-thalassaemia is due to a point mutation in codon 26 of the human HBB gene on one allele (GAG; glutamatic acid → AAG; lysine, E26K), and any mutation causing severe β-thalassaemia on the other. When inherited together in compound heterozygosity these mutations can cause a severe thalassaemic phenotype. However, if only one allele is mutated individuals are carriers for the respective mutation and have an asymptomatic phenotype (β-thalassaemia trait). Here we describe a base editing strategy which corrects the HbE mutation either to wildtype (WT) or a normal variant haemoglobin (E26G) known as Hb Aubenas and thereby recreates the asymptomatic trait phenotype. We have achieved editing efficiencies in excess of 90% in primary human CD34 + cells. We demonstrate editing of long-term repopulating haematopoietic stem cells (LT-HSCs) using serial xenotransplantation in NSG mice. We have profiled the off-target effects using a combination of circularization for in vitro reporting of cleavage effects by sequencing (CIRCLE-seq) and deep targeted capture and have developed machine-learning based methods to predict functional effects of candidate off-target mutations.
Genome editing of haemopoietic stem cells for treatment of thalassaemia
(Oxford University Press, 2019) Badat, M.; Mettananda, S.; Hua, P.; Schwessinger, R.; Hughes, J.; Higgs, D.; Davies, J.
AIM: Thalassaemia is commonly due to mutations at the beta globin (HBB) locus, and this causes transfusion dependent anaemia in severe cases. A key pathophysiological factor is the imbalance of alpha and beta globin production. This results in accumulation of excess alpha globin chains, which are toxic and cause cell death. Patients who co-inherit partial deletions of the alpha globin genes with beta thalassaemia usually have a mild phenotype and are transfusion independent. We aim to develop genome editing strategies of haemopoietic stem cells to exploit this for use as part of an autologous transplant to treat thalassaemia. METHODS: CRISPR-Cas9 was used to edit the most important enhancer of the alpha globin gene to elicit a controlled reduction in alpha globin expression. In silico methods were used to define the key sequences to delete to abrogate transcription factor binding. This allowed us to develop a strategy to disrupt single transcription factor binding sites using Cas9 ribonucleoprotein. RESULTS: Our in silico approaches allowed us to define three key transcription factor binding sites within the enhancer. We were able to achieve indel efficiencies in excess of 75% as measured by next generation sequencing. This resulted in a much more controlled reduction in alpha globin expression than was achieved by deletion of the whole enhancer. DISCUSSION: In silico prediction allows the identification of the sites within enhancers that allow genome editing to be used to reduce gene expression in a highly controlled manner.