53. From GWAS To the Clinic: Genome-Editing the Human BCL11A Erythroid Enhancer for Fetal Globin Elevation in the Hemoglobinopathies
Authors: Andreas Reik, Kai-Hsin Chang, Jeff Vierstra, Nikoletta Psatha, Sandra Stehling-Sun, Yuanyue Zhou, Colleen M. O'Neil, Andrea Mich, Jeffrey C. Miller, Gary Lee, Siyuan Tan, Haiyan Jiang, George Stamatoyannopoulos, Thalia Papayannopoulou, Edward J. Rebar, Philip D. Gregory, John A. Stamatoyannopoulos, Fyodor D. Urnov
Journal: Molecular Therapy (2015)

We describe here a fundamentally novel way to approach the development of a therapeutic: use of data from genome-wide association studies (GWAS) as a guide to create, in a targeted fashion, a disease-ameliorating genotype in the patient's own cells. We exemplify this by focusing on the hemoglobinopathies, β-thalassemia and sickle cell disease (SCD): in both cases elevated levels of fetal hemoglobin (HbF) have been shown to lessen or eliminate disease symptoms. Thus, reversing HbF silencing in patients is an attractive strategy for the development of therapies. To this end, GWAS data pointed to loss-of-function variants in the erythroid-specific enhancer of the fetal globin repressor, BCL11A, as causative for HbF elevation. While such regulatory elements are challenging to affect in a clinical setting via a conventional small molecule approach, the development of genome editing with engineered nucleases allows, in principle, a targeted intervention at the DNA level to disable enhancer function. Here, we reduce this notion to practice. The BCL11A enhancer consists of three separate cis-regulatory elements spanning a total of~1,500 bp that together drive erythroid-specific expression of BCL11A and lead to a silencing of fetal hemoglobin post-birth. Guided in part by fine-scale in vivo protein-DNA interaction data, we performed a reverse-genetic analysis of the enhancer at its endogenous location in the physiologically relevant cell type, primary human erythroid cells, using zinc finger nucleases (ZFNs). We developed highly optimized ZFNs that yield 60-80% target locus editing in human mobilized peripheral blood CD34 cells. Remarkably, we find that the ZFN-driven ablation of a single 5 bp element, GATAA, resident in the enhancer reproducibly elevates fetal globin in erythroid progeny of these CD34 cells to levels indistinguishable from those resulting from an essentially complete ZFN-driven coding knockout of BCL11A itself. We demonstrate high-efficiency ZFN-driven marking at the enhancer in peripheral blood mobilized CD34 cells at clinical scale production in a GMP-compliant setting, observe the successful engraftment and differentiation of genome-edited cells in an immunodeficient mouse model, and use an unbiased deep-sequencing based assay to comprehensively characterize the nucleus-wide specificity profile of ZFN action. Together these data illustrate the feasibility of using findings from genome-wide association studies to pursue novel therapeutic approaches in monogenic disease. In particular, our work supports the further development of fetal globin elevation via the targeted genome editing of the BCL11A erythroid-specific enhancer in both peripheral blood- and bone marrow-derived CD34 cells as a potential treatment for the hemoglobinopathies.