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 × 10⁶ 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 <1-month post-EDIT-301 infusion. Patients 1–2 with TDT were 3- and <1-months post-EDIT-301 infusion, respectively.

Neutrophil and platelet engraftment were achieved after a mean (range) of 25 (23–29) and 27 (19–37) days in Patients 1–4 with SCD and on Day 23 and 26 in Patient 1 with TDT, respectively.

There were no VOEs in SCD patients post-EDIT-301 infusion, compared with a mean (range) of 4.2 (3.0–5.5) VOEs/year in the 2 years before enrollment (n=6). Following EDIT-301 infusion, Hb levels rapidly increased to 14.2 (12.4–15.7) g/dL by Month 4 (n=4), reaching the normal physiological range, from a mean (range) of 10.5 (8.5–11.9) g/dL at baseline (n=5). By Month 4, the mean (range) HbF concentration was 6.8 (5.7–7.6) g/dL and HbF was >40% (n=4); Patients 3 and 4 had >50% HbF. Percentage of F-cells and MCH-F/F-cell also increased. Key markers of hemolysis improved or normalized in all patients with SCD.

Patient 1 with TDT had a HbF concentration of 7.2 g/dL by Month 3, stopped receiving RBC transfusions 20 days after EDIT-301 infusion, and remained transfusion free through the 3-month period. Patient 2 with TDT also showed early improvements.

The safety profile of EDIT-301 in both SCD and TDT was consistent with myeloablative conditioning with busulfan. No serious AEs were reported after EDIT-301 infusion.

Conclusion: These data demonstrated successful engraftment, a rapid and sustained normalization of Hb as early as 4 months after infusion, an increase in HbF and percentage of F-cells, resolution of VOEs (SCD) and transfusion independence (TDT). In addition, there were improvements in key markers of hemolysis (SCD) and a favorable safety profile in EDIT-301-treated patients. EDIT-301 treatment showed promising results for the first clinical use of AsCas12a in both SCD and TDT patients after gene editing of the γ-globin gene (HBG1/2) promoters. These findings support further investigation of EDIT-301 in the RUBY and EdiThal trials. Updated data with additional outcomes will be presented.