Session: 801. Gene Editing, Therapy and Transfer: Poster III
Hematology Disease Topics & Pathways:
sickle cell disease, HSCs, Diseases, Therapies, Adverse Events, Hemoglobinopathies, Biological Processes, Technology and Procedures, Cell Lineage, Xenograft models, erythropoiesis, gene editing, Study Population, flow cytometry, NGS
Here we describe the use of ABEs to recapitulate naturally occurring HPFH variants in hematopoietic stem cells (HSCs). We electroporated ABE7.10-single guide (sg) RNA ribonucleoprotein (RNP) complex into mobilized peripheral blood CD34+ hematopoietic stem and progenitor cells (HSPCs) to recreate 3 different HPFH variants in the HBG1/2 promoters (-198 T>C, -175 T>C and -113 A>G). Measured editing frequency was maximal on day 10 after electroporation and transferred to erythroid differentiation media. 20% editing efficiency was observed for the -198 site, 58% for -175 and 50% for -113. Indel frequencies were <2% at each of the three sites, reflecting a low rate of DSBs. Fetal hemoglobin levels in erythroid cells generated in vitro from A base-edited CD34+ HSPCs were 26±4% (-198 T>C), 60±10% (-175 T>C), and 42±7% (-113 A>G) versus14±2% in unedited control cells. Base editing at the -175 site in sickle cell disease (SCD) donor CD34+ HSPCs resulted in the induction of HbF to 55% in erythroid progeny compared to 6% in controls. After exposure to hypoxia (2% oxygen), reticulocytes generated from -175 T>C-edited CD34+ HSPCs exhibited sickling rates of 24%, compared to 52% in controls. Thus, creation of this variant, which generates a de novo binding site for the transcriptional activator TAL1, reactivates erythroid cell HbF to levels that inhibit sickle hemoglobin polymerization and cell sickling.
To assess base editing in HSCs, we used ABE RNP to modify the -175 site in SCD donor CD34+ HSPCs, followed by transplantation into NBSGW mice. The editing frequency in CD34+ HSPCs before transplantation was ~30% and declined to approximately 20% in bone marrow-repopulating donor cells at 16 weeks post-transplantation. Editing frequencies were similar in CD34+ donor cell–derived myeloid, erythroid, and B cells, indicating that hematopoietic differentiation was not altered. Bone marrow erythroblasts derived from base-edited and control CD34+ HSPCs exhibited similar maturation profiles and enucleation. Erythroblasts generated in vivo from SCD patient HSPCs exhibited 32±2% HbF compared to unedited controls (4±1%) (n=4, P>0.0001).
Our studies provide proof of concept that adenosine base editors can be used therapeutically for β-hemoglobinopathies. Specifically, generation of the -175 T>C HPFH mutation in patient HSCs followed by autologous transplantation represents a new therapeutic approach for SCD and β-thalassemia.
Disclosures: Yen: Beam Therapeutics: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Sharma: Spotlight Therapeutics: Consultancy; CRISPR Therapeutics: Other: Clinical Trial PI, Research Funding; Novartis: Other: Clinical Trial PI, Research Funding; Vertex Pharmaceuticals: Other: Clinical Trial PI, Research Funding. Liu: Pairwise Plants: Consultancy, Patents & Royalties; Editas Medicine: Consultancy, Patents & Royalties; Beam Therapeutics: Consultancy, Patents & Royalties; Prime Medicine: Consultancy, Patents & Royalties. Weiss: Beam Therapeuticcs: Consultancy, Current equity holder in private company; Esperion Therapeutics: Consultancy, Current equity holder in private company; Novartis: Consultancy, Current equity holder in private company; Cellarity Inc.: Consultancy, Current equity holder in private company; Rubius Inc.: Consultancy, Current equity holder in private company.
See more of: Oral and Poster Abstracts