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

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Sickle cell disease 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 pathogenic HBB Glu7Val (sickle) mutation at chr11:5227002 to restore adult hemoglobin function and prevent hemolysis and vaso-occlusion, or disrupt erythroid BCL11A regulatory elements to . 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: ~100,000 affected individuals in the US and millions worldwide; highly prevalent in sub-Saharan Africa, India and the Middle East, with carrier frequencies >10% and birth prevalence >1% in some regions. 3. Standard of care: Newborn screening, vaccination, penicillin prophylaxis, hydroxyurea, chronic transfusions with iron chelation, and allogeneic hematopoietic stem cell transplantation for a minority with suitable donors; newer disease-modifying drugs (voxelotor, crizanlizumab, L-glutamine) provide partial benefit but 4. Pipeline: Multiple gene-addition and gene-editing programs targeting HBB or BCL11A: lentiviral gene therapy (betibeglogene autotemcel; Phase II/III and approval in some regions), ex vivo CRISPR/Cas9 editing of the BCL11A erythroid enhancer (exagamglogene autotemcel, exa-cel/Casgevy; Phase II/III leading to fi 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.