Reni-Cel, an Investigational AsCas12a Gene-Edited Cell Medicine, Led to Sustained Hemoglobin Normalization and Increased Fetal Hemoglobin in Patients with Severe Sickle Cell Disease Treated in the RUBY Trial

Introduction: Sickle cell disease (SCD) is a genetic blood disorder caused by a pathogenic variant in the β-globin gene. Sustained increases in fetal hemoglobin (HbF, α2γ2) can reduce or eliminate SCD symptoms, including vaso-occlusive events (VOEs). Renizgamglogene autogedtemcel (reni-cel) is an investigational gene-edited autologous hematopoietic stem cell medicine comprised of CD34⁺ cells edited at the distal CCAAT box (-118 to -113) of the promoter regions of the γ-globin genes (HBG1/2) with a highly specific and efficient, proprietary gene-editing nuclease, AsCas12a. These edits mimic naturally occurring variants of hereditary persistence of HbF in the HBG1/2 promoters and reactivate γ-globin expression, resulting in sustained and clinically meaningful production of HbF. In preclinical studies, editing this genomic region in CD34⁺ cells from patients with SCD led to ≥80% editing, robust HbF production, and significantly reduced sickling of erythroid progeny. The ongoing RUBY trial (NCT04853576) is a Phase I/II/III, multicenter, open-label, single-arm study evaluating safety, tolerability, and efficacy of reni-cel in patients with severe SCD. Interim clinical data are reported; updated data will be presented.

Methods: Eligible patients must be 12–50 years and have a diagnosis of severe SCD, defined as ≥2 severe VOEs per year in the 2 years prior to informed consent. After plerixafor mobilization, autologous CD34⁺ hematopoietic stem and progenitor cells are collected by apheresis and edited at the HBG1/2 promoters. Patients then undergo myeloablative conditioning with pharmacokinetically adjusted busulfan and receive a single infusion of reni-cel (≥3 × 10⁶ CD34⁺ cells/kg). Patients are monitored for engraftment, allelic editing levels, VOEs, total hemoglobin (Hb), HbF production, percentage of F-cells, mean HbF concentration/F-cell (MCH-F/F-cell), markers of hemolysis, and adverse events (AEs) for 24 months and then followed in a long-term study for an additional 13 years.

Results: As of June 28, 2024, 21 patients with SCD had received reni-cel. Median (range) age was 28 (18–41) years, 52.4% were female, 95.2% had the β^S/β^S genotype, and the majority (95.2%) were Black or African American. Patients were a median (range) of 8.0 (0.6–24.1) months post-reni-cel infusion, with 7 patients having >1 year follow-up. Neutrophil and platelet engraftment were achieved after a median (range) of 23.0 (15–29) and 24.5 (18–51) days, respectively (n=20). After reni-cel infusion, patients achieved early correction of anemia, with durable normalization of total Hb; mean (standard deviation [SD]) total Hb was 14.2 (2.0) g/dL at Month 6 (n=10) and was maintained through last follow-up. Mean (SD) percentage of HbF was 48.2% (3.4%) by Month 6 (n=12) and was sustained at >40% through last follow-up. The percentage of F-cells and MCH-F/F-cell increased early, and MCH-F/F-cell was sustained above the anti-sickling threshold of 10 pg/F-cell through last follow-up. Markers of hemolysis, including absolute reticulocyte count, indirect bilirubin, lactate dehydrogenase, and haptoglobin, improved or normalized by Month 6 and were generally maintained over time. All patients were VOE-free post-reni-cel infusion as of the data cutoff date, compared with a mean (SD) of 4.9 (2.8) severe VOEs/year in the 2 years before enrollment (n=21). Patients showed sustained high levels of allelic editing in both peripheral blood nucleated cells and bone marrow–derived CD34⁺ cells, with mean (SD) editing levels of 80.9% (5.9% [n=4]) and 86.9% (4.1% [n=3]) at Month 12, respectively. The safety profile of reni-cel was consistent with myeloablative conditioning with busulfan. No serious AEs related to reni-cel were reported.

Conclusions: Reni-cel treatment showed promising results for gene editing at the HBG1/2 promoters, with early Hb normalization and durable increases in HbF. The data also demonstrate an early increase in the percentage of F-cells, improvements in markers of hemolysis, sustained high levels of editing, resolution of VOEs, and a favorable safety profile, with successful engraftment in all patients. These findings, which are based on a larger cohort of patients and additional outcomes, build on clinical evidence that support the continued investigation of reni-cel in the RUBY trial.