S264: EDIT-301 SHOWS PROMISING PRELIMINARY SAFETY AND EFFICACY RESULTS IN THE PHASE I/II CLINICAL TRIAL (RUBY) OF PATIENTS WITH SEVERE SICKLE CELL DISEASE USING HIGHLY SPECIFIC AND EFFICIENT ASCAS12A ENZYME

Abstract

Background: EDIT-301, an investigational gene-edited autologous hematopoietic stem cell medicine, has a unique genomic modification at the γ-globin gene (HBG1/HBG2) promoters where multiple naturally occurring mutations for hereditary persistence of fetal hemoglobin (HPFH) reside to reactivate γ-globin expression and increase HbF production. EDIT-301 is manufactured using a highly efficient and specific, proprietary AsCas12a. In preclinical studies, editing of this region in CD34+ cells from patients with SCD led to ≥80% editing, robust HbF production, no off-target editing, and significantly reduced sickling of EDIT-301-derived erythroid progeny. Aims: The RUBY trial (NCT04853576), a Phase I/II, multicenter, open-label, single-arm study, evaluates the safety, tolerability, and efficacy of EDIT-301 in subjects with severe SCD. Four subjects have received EDIT-301 treatment. Preliminary clinical data on gene editing, safety, and efficacy are reported. Methods: Subjects 18–50 years old must have a diagnosis of severe SCD defined as ≥2 severe vaso-occlusive events (VOEs) per year in the 2-year period prior to informed consent. Autologous CD34+ hematopoietic stem and progenitor cells are collected by apheresis after plerixafor mobilization and edited at the HBG1/HBG2 promoter with AsCas12a. After myeloablative conditioning with busulfan, subjects received a single infusion of EDIT-301 (≥3 × 106 CD34+ cells/kg), and were monitored for engraftment, total hemoglobin (Hb), HbF production, mean HbF concentration/F-cell (MCH-F/F-cell), percentage of F-cells, markers of hemolysis, transfusion requirement, VOEs, and adverse events (AEs) for 24-months. Results: Editing of CD34+ cells using AsCas12a resulted in ≥80% editing in study participants’ cells (N=8). As of March 1, 2023, Subjects 1 and 2 are 8- and 4-months post-EDIT-301 infusion, respectively, and Subjects 3 and 4 are <1-month post-EDIT-301 infusion. Neutrophil and platelet engraftment were achieved within 23 and 19 days (Subject 1) and within 29 and 37 days (Subject 2) of EDIT-301 infusion, respectively. At last data points available, Subjects 1 and 2 had normal Hb concentrations, HbF levels >35% (Figure 1), MCH-F/F-cell >10.0 pg/F-cell, and no reported VOEs. Hb increased by 4.5 g/dL from baseline (BL) to 16.4 g/dL at 6 months (Subject 1) and increased by 3.6 g/dL from BL to 12.1 g/dL at 3 months post-EDIT-301 infusion (Subject 2). Percentage of F-cells was 96.5% at 6 months (Subject 1). All markers of hemolysis improved or normalized. Editing levels in peripheral blood nucleated cells were >80% in both subjects. The safety profile of EDIT-301 was consistent with myeloablative conditioning with busulfan, with no reported EDIT-301-related AEs and no serious adverse events (SAEs) after EDIT-301 infusion. Summary/Conclusion: These preliminary data demonstrate successful engraftment, a rapid and sustained increase in total Hb, HbF level, and percentage of F-cells, improvements in key markers of hemolysis, and a favorable safety profile in subjects treated with EDIT-301. These preliminary data demonstrated clinical proof of concept and are promising for the first clinical use of AsCas12a-based gene editing of the globin gene (HBG1/HBG2) promoters, thereby supporting further investigation of EDIT-301 in the RUBY clinical trial. Updated data will be presented.Keywords: Globin gene, Sickle cell disease, Gene therapy

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