Gates Package — page 816

Abstract Individuals with -thalassemia or Sickle Cell Disease and hereditary persistence of fetal hemoglobin (HPFH) possessing 30% HbF appear to be symptom-free. Here, we used a non-integrating HDAd5/35++ vector expressing a highly efficient and accurate version of an adenine base editor (ABE8e) to install, in vivo, a -113A>G HPFH mutation in the -globin promoters in "healthy" CD46/-YAC mice carrying the human -globin locus. Our in vivo hematopoietic stem cell (HSC) editing/selection strategy involves only subcutaneous and intravenous injections and does not require myeloablation and HSC transplantation. In vivo HSC base editing in CD46/-YAC mice resulted in >60% -113A>G conversion with 30% -globin of - globin expressed in 70% of erythrocytes. Importantly, no off-target editing at sites predicted by CIRCLESeq or in silico was detected. Furthermore, no critical alterations in the transcriptome of in vivo edited mice were found by RNA-seq. In vitro, in HSCs from -thalassemia and Sickle Cell Disease patients, transduction with the base editor vector mediated efficient -113 A>G conversion and reactivation of −globin expression with subsequent phenotypic correction of erythroid cells. Because our in vivo base editing strategy is safe and technically simple, it has the potential for clinical application in developing countries where hemoglobinopathies are prevalent.