AsCas12a Gene Editing of HBG1/2 Promoters with EDIT-301 Results in Rapid and Sustained Normalization of Hemoglobin and Increased Fetal Hemoglobin in Patients with Severe Sickle Cell Disease and Transfusion-Dependent Beta-Thalassemia

Background: Sickle cell disease (SCD) and transfusion-dependent β-thalassemia (TDT) are hereditary blood disorders caused by mutations in the β-globin gene. Clinical evidence has demonstrated that increased fetal hemoglobin (HbF, α2γ2) can reduce or eliminate SCD and TDT complications. EDIT-301, an investigational gene-edited autologous hematopoietic stem cell medicine, has a unique genomic modification that mimics naturally occurring mutations of hereditary persistence of fetal hemoglobin in the γ-globin gene ( HBG1/2) promoters. These mutations reactivate γ-globin expression and increase HbF production. EDIT-301 is manufactured with a highly efficient and specific, proprietary gene editing nuclease, AsCas12a. In preclinical studies, edited CD34 + cells from patients with SCD or TDT increased HbF production in red blood cells (RBCs) sufficient for a therapeutic effect, including reduced sickling (SCD) and improved erythropoiesis (TDT). Aim: RUBY (NCT04853576) and EdiThal (NCT05444894) are Phase I/II, multicenter, open-label, single-arm studies evaluating the safety, efficacy, and tolerability of EDIT-301 in patients with severe SCD and TDT, respectively. As of June 28, 2023, 7 SCD patients and 2 TDT patients have received EDIT-301 treatment. Preliminary clinical efficacy and safety data are reported. Methods: Patients aged 18-50 years with severe SCD (defined as ≥2 severe vaso-occlusive events [VOEs] per year in the 2 years prior to informed consent [IC]) and patients aged 18-35 years with TDT (defined as at least 100 mL/kg/year or 10 U/year of packed RBC transfusions in the 2 years prior to IC) were eligible to enroll in RUBY and EdiThal, respectively. Autologous CD34 + hematopoietic stem and progenitor cells collected by apheresis after plerixafor (RUBY) or plerixafor + filgrastim (EdiThal) mobilization were edited at the HBG1/2 promoters with AsCas12a. After myeloablative conditioning with busulfan, patients received a single infusion of EDIT-301 (a minimum of 3 × 10 6 CD34 + cells/kg), and were monitored for engraftment, total hemoglobin (Hb), HbF, mean HbF concentration/F-cell (MCH-F/F-cell), percentage of F-cells, markers of hemolysis, transfusion requirement, VOEs (SCD only), and adverse events (AEs) for 24 months. Results: Based on a data cut of June 28, 2023, Patients 1-4 with SCD were 12-, 9-, 4-, and 4-months post-EDIT-301 infusion, respectively. Patients 5-7 with SCD were