Base Editing (ABE8e) for HBB c.79G>A (p.Glu27Lys) in Sickle cell disease (HBB p.Glu6Val)

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Sickle cell disease (HBB p.Glu6Val) targeting the HBB c.79G>A (p.Glu27Lys) variant (Pathogenic, missense variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: Blood/HSC. Therapeutic goal: Correct the HBB c.20A>T (p.Glu7Val, HbS) mutation at chr11:5227002 to restore normal adult beta-globin and prevent sickling-related vaso-occlusion and hemolytic anemia.. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Medium, immunogenicity Low.

1. Molecular basis: HBB NM_000518.5(HBB):c.79G>A (p.Glu27Lys) is classified as Pathogenic (ClinVar variation ID 3777010). Molecular consequence: missense variant. Protein change: E27K, V24F. 2. Epidemiology: Over 500,000 infants are born with sickle cell disease annually worldwide, with high prevalence and mortality concentrated in sub-Saharan Africa, India, and the Middle East; approximately 100,000 affected individuals live in the United States (PAPER-04, WEB-01). 3. Standard of care: Chronic management with hydroxyurea to raise HbF, transfusion programs and iron chelation, pain crisis management, and allogeneic hematopoietic stem cell transplantation for selected patients; access to hydroxyurea and comprehensive care remains limited in many low- and middle-income countries (PAPE 4. Pipeline: Multiple curative-intent therapies are in late-stage development or approved, including ex vivo gene addition and genome-editing approaches targeting HBB or BCL11A (e.g., CRISPR-Cas9-based products like CASGEVY), alongside small molecules and supportive agents; most are in phase II/III or early comm 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting HBB c.79G>A (p.Glu27Lys) with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically.
2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed.
3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.