Base Editing (ABE8e) for HBB c.79G>A (p.Glu27Lys) in Beta-thalassemia major

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Beta-thalassemia major 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 pathogenic HBB alleles and/or disrupt BCL11A erythroid enhancer to restore effective beta-globin or fetal hemoglobin expression and achieve transfusion independence in beta-thalassemia major.. 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: Approximately 60,000 symptomatic beta-thalassemia births annually worldwide, with highest prevalence in the Mediterranean, Middle East, South and Southeast Asia; beta-thalassemia major presents in infancy with severe anemia and is universally transfusion-dependent without curative therapy. 3. Standard of care: Lifelong regular red blood cell transfusions plus iron chelation; selected patients may receive allogeneic HSCT. Adjuncts include luspatercept to reduce transfusion burden. 4. Pipeline: Approved gene-addition (betibeglogene autotemcel) and gene-editing (exagamglogene autotemcel) therapies for transfusion-dependent beta-thalassemia; multiple Phase I/II/III trials of HbF inducers, small molecules, and next-generation gene-editing or gene-therapy approaches ongoing. 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.