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

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Beta-thalassemia 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 loss-of-function HBB mutations or functionally reprogram the HBB/LCRB locus (e.g., via fetal hemoglobin induction) to restore sufficient β-globin production and achieve durable transfusion ind. 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: Beta-thalassemia (ORPHA:848) is an autosomal recessive disorder caused by reduced (β+) or absent (β0) synthesis of the β-globin chains of adult hemoglobin. Orphanet reports a global prevalence on the order of 1–9 per 1,000,000 in the general population, but carrier frequencies are much higher (up to 3. Standard of care: Current standard of care for transfusion-dependent beta-thalassemia combines regular red blood cell transfusions and iron chelation. Thalassaemia International Federation (TIF) guidelines describe initiation of transfusions early in life, with schedules tailored to maintain pre-transfusion Hb around 4. Pipeline: The therapeutic pipeline for beta-thalassemia is among the most advanced in monogenic diseases. Lentiviral gene addition targeting autologous hematopoietic stem and progenitor cells (HSPCs), exemplified by betibeglogene autotemcel (Zynteglo), has demonstrated high rates of durable transfusion indepe 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.