Base Editing (ABE8e) for HBB c.79G>A (p.Glu27Lys) in Sickle cell disease due to HBB rs334

Base Editing (ABE8e) via RNP electroporation (ex vivo) delivery is a rationale-driven therapeutic strategy for Sickle cell disease due to HBB rs334 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 rs334 sickle mutation in autologous HSCs to eliminate sickling and related complications. 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: Autosomal recessive hemoglobinopathy prevalent in individuals of African, Middle Eastern, and Indian descent; A allele frequency ~0.10 in African ancestries (BIOMNI-08). 3. Standard of care: Hydroxyurea, chronic transfusions with iron chelation, small molecules (voxelotor, crizanlizumab), and allogeneic HSCT as curative option but limited by donor availability and transplant risks (PAPER-01, PAPER-10, WEB-05). 4. Pipeline: Ex vivo gene-addition (betibeglogene autotemcel) and gene-editing therapies (exa-cel targeting BCL11A enhancer) have reached Phase III / BLA and regulatory review, demonstrating high rates of VOC/transfusion elimination (WEB-04, WEB-05, PAPER-03, PAPER-07, PAPER-08). 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.