Limitations of mouse models for sickle cell disease conferred by their human globin transgene configurations.

We characterized the human β-like globin transgenes in two mouse models of sickle cell disease (SCD) and tested a genome-editing strategy to induce red blood cell fetal hemoglobin (HbF; α2γ2). Berkeley SCD mice contain four to 22 randomly arranged, fragmented copies of three human transgenes (HBA1, HBG2-HBG1-HBD-HBBS and a mini-locus control region) integrated into a single site of mouse chromosome 1. Cas9 disruption of the BCL11A repressor binding motif in the γ-globin gene (HBG1 and HBG2; HBG) promoters of Berkeley mouse hematopoietic stem cells (HSCs) caused extensive death from multiple double-strand DNA breaks. Long-range sequencing of Townes SCD mice verified that the endogenous Hbb genes were replaced by single-copy segments of human HBG1 and HBBS including proximal but not some distal gene-regulatory elements. Townes mouse HSCs were viable after Cas9 disruption of the HBG1 BCL11A binding motif but failed to induce HbF to therapeutic levels, contrasting with human HSCs. Our findings provide practical information on the genomic structures of two common mouse SCD models, illustrate their limitations for analyzing therapies to induce HbF and confirm the importance of distal DNA elements in human globin regulation. This article has an associated First Person interview with the first author of the paper.
Competing Interests: Competing interests M.J.W. is on advisory boards for Cellarity Inc., Novartis, Graphite Bio and Forma Therapeutics. J.Y. is an equity owner of Beam Therapeutics. The other authors declare no competing financial interests. A.S. is the site principal investigator of clinical trials for genome editing of sickle cell disease sponsored by Vertex Pharmaceuticals/CRISPR Therapeutics (NCT03745287) and Novartis (NCT04443907). The industry sponsors provide funding for the clinical trial, which includes salary support. A.S. has received consultant fees from Spotlight Therapeutics, Medexus Inc. and Vertex Pharmaceuticals. He has also received research funding from CRISPR Therapeutics and honoraria from Vindico Medical Education.
(© 2022. Published by The Company of Biologists Ltd.)