Large-scale discovery of potent, compact and erythroid specific enhancers for gene therapy vectors.

Gene expression during cell development and differentiation is orchestrated by distal regulatory elements that precisely modulate cell selective gene activity. Gene therapy vectors leverage these elements for precise spatiotemporal transgene expression. Here, we develop a one-shot approach to screen candidate regulatory sequences from large-scale epigenomics data for programmable transgene expression within gene therapy viral vectors. We assess a library of 15,000 short sequences derived from developmentally active elements during erythropoiesis using a clinically relevant reporter vector. These elements display a gradient of transcriptional enhancer activity in erythroid cells, with high cell type restriction and developmental stage specificity. Finally, replacing the canonical β-globin μLCR with a compact enhancer in a β-thalassemia lentiviral vector successfully corrects the thalassemic phenotype in patient-derived hematopoietic and stem and progenitor cells (HSPCs), while increasing viral titers and cell transducibility. Our approach provides further insights into enhancer biology with wider implications for human gene therapy.