Adenine Base Editor ABE7.10 Corrects Sickle Cell Disease HBB E6V Mutation in Patient-Derived Hematopoietic Stem Cells With >84% Editing Efficiency and Preserved Engraftment

This study investigates adenine base editor ABE7.10 correction of the sickle cell disease HBB E6V point mutation in patient-derived CD34+ hematopoietic stem and progenitor cells with assessment of editing efficiency, off-target profile, and xenograft engraftment within the context of hematology and genome editing, an area of growing scientific importance given its implications for SCD gene therapy clinical translation, base editing HSPC platform for hemoglobinopathies, and off-target safety framework for clinical-grade base editor development. Using mRNA electroporation of ABE7.10 into mobilized CD34+ HSPCs, deep amplicon sequencing for HBB A-to-G conversion at position 6, whole-genome sequencing for off-target SNVs (n=5 donors), and 16-week NSG xenograft with human chimerism and erythroid differentiation assessment, we examine ABE7.10 adenine base editor converting A•T to G•C at HBB codon 6 (glutamic acid E6V), reverting the sickle mutation (GAG→GTG) back to wild-type sequence without double-strand breaks, reducing genotoxicity risk vs. nuclease-based approaches while achieving therapeutically relevant editing in long-term repopulating HSCs in CD34+ HSPCs from 8 SCD donors; n=40 NSG xenograft mice (5 per donor) transplanted with edited or mock-treated cells; 16-week follow-up with bone marrow analysis drawn from Ridgemont Stem Cell Institute GMP-compatible electroporation facility with 4D-Nucleofector, Illumina MiSeq for amplicon sequencing, and NSG xenograft facility with 16-week engraftment assessment. Results indicate that mean A-to-G editing efficiency 84.2% at HBB codon 6 (range 78-91% across donors); bystander edits <2.4%; no enrichment of off-target SNVs above background in WGS; human chimerism 48.4% at 16 weeks; HbS/HbA ratio reduced from 100% to 18.4% in erythroid progeny (p < 0.001), with 84.2% editing efficiency; HbS reduced to 18.4%; 48.4% engraftment; no enriched off-targets as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to hematology and genome editing and carry actionable implications for the design of programs and policies targeting SCD gene therapy clinical translation, base editing HSPC platform for hemoglobinopathies, and off-target safety framework for clinical-grade base editor development.