Zinc Finger Nuclease-Mediated Disruption Of The Bcl11a Erythroid Enhancer Results In Enriched Biallelic Editing, Increased Fetal Hemoglobin, And Reduced Sickling In Erythroid Cells Derived From Sickle Cell Disease Patients

High fetal hemoglobin (HbF) levels are associated with decreased severity and mortality in sickle cell disease (SCD) and beta thalassemia (BT). We have developed a novel gene-edited cell therapy using autologous hematopoietic stem and progenitor cells (HSPCs) that have been genetically modified with zinc finger nucleases (ZFNs) to reactivate HbF expression. The ZFNs target the binding motif of GATA1 (GATAA) within an intronic erythroid-specific enhancer (ESE) of BCL11A, which encodes a major transcriptional repressor of HbF. Previously, we reported successful ZFN-mediated editing of the BCL11A ESE and reactivation of HbF in both dual (granulocyte colony-stimulating factor (G-CSF) and plerixafor) and single plerixafor mobilized HSPCs(Holmes 2017, Moran 2018). Both related drug candidates, ST-400 and BIVV003, are currently in phase 1/2a clinical trials for transfusion-dependent BT (NCT03432364) and SCD (NCT03653247), respectively. Here, we performed extensive genetic and phenotypic characterization of ZFN-edited HSPCs from healthy and SCD donors.