Editas Medicine's CRISPR-Cas12a Therapy Achieves Functional Cure in 27 of 28 Sickle Cell Patients as RUBY Trial Results Land in NEJM
The RUBY trial of renizgamglogene autogedtemcel (reni-cel), a one-time CRISPR-Cas12a gene-editing therapy, showed that 27 of 28 patients with severe sickle cell disease had no painful crises after treatment, with hemoglobin levels normalizing to 13.8 g/dL by six months.
Overview
A gene-editing therapy that modifies a patient’s own blood-forming stem cells has produced what researchers are calling a functional cure for severe sickle cell disease. Results from the multicenter RUBY trial, published in the New England Journal of Medicine on April 1, 2026, showed that 27 of 28 patients treated with renizgamglogene autogedtemcel (reni-cel) experienced no painful vaso-occlusive crises after a single infusion of the gene-edited cells.
Reni-cel, developed by Editas Medicine, is the first therapy to use CRISPR-Cas12a technology in a clinical setting for sickle cell disease, distinguishing it from the Cas9-based approach used by Vertex Pharmaceuticals’ Casgevy, which received FDA approval in late 2023 for patients aged 12 and older.
How the Therapy Works
Sickle cell disease is caused by a mutation in the beta-globin gene that produces abnormal hemoglobin, causing red blood cells to deform into a rigid crescent shape. These sickled cells block blood flow, triggering episodes of severe pain known as vaso-occlusive crises and progressively damaging organs.
Reni-cel targets the promoter regions of the HBG1 and HBG2 genes using CRISPR-Cas12a to disrupt binding sites for BCL11A, a transcription factor that normally silences fetal hemoglobin production after infancy. By editing these promoter sequences, the therapy reactivates fetal hemoglobin production, which prevents red blood cells from sickling.
The process begins with collecting a patient’s hematopoietic stem cells, editing them ex vivo, and then reinfusing them after the patient undergoes myeloablative conditioning with busulfan chemotherapy to clear existing bone marrow and make room for the modified cells.
Trial Design and Results
The RUBY trial is a Phase 1-2, multicenter, open-label, single-group study that enrolled patients aged 12 to 50 with severe sickle cell disease who had experienced at least two severe vaso-occlusive events per year in the preceding two years. As of the data cutoff on October 29, 2024, 28 patients had received a single infusion of reni-cel.
The headline finding was striking: 27 of 28 patients had no vaso-occlusive events after infusion. Among the 18 patients with at least six months of follow-up data, the mean total hemoglobin level rose from a baseline of 9.8 g/dL to 13.8 g/dL at six months — a level within the normal range for adults without sickle cell disease. Mean fetal hemoglobin increased from 2.5 percent at baseline to 48.1 percent after treatment, and those levels remained stable over time.
Dr. Rabi Hanna, the study’s lead author at Cleveland Clinic Children’s, which treated four of the 28 patients, said the results represent a meaningful step forward. “Our aim has been to achieve a functional cure to help prevent any future damage caused by sickle cell disease, and these latest results are compelling,” Hanna said.
Safety Profile
Adverse events observed in the trial were consistent with those expected from myeloablative busulfan-based conditioning and autologous hematopoietic stem-cell transplantation, according to the NEJM paper. Unlike allogeneic bone marrow transplants, which require a matched donor and carry risks of graft-versus-host disease and immune rejection, reni-cel uses a patient’s own cells. Hanna noted that a key advantage of the CRISPR-Cas12a approach is that there is no rejection risk, differentiating it from traditional transplant procedures.
Context and Significance
Sickle cell disease affects approximately 100,000 people in the United States and millions worldwide, predominantly in communities of African, Mediterranean, Middle Eastern, and South Asian descent. While Casgevy became the first CRISPR-based treatment approved for the disease in December 2023, it uses Cas9 technology and is currently authorized only for patients aged 12 and older. Vertex has announced plans to submit regulatory filings for Casgevy in children aged 5 to 11 in the first half of 2026.
Reni-cel’s use of Cas12a rather than Cas9 represents a distinct gene-editing approach. Cas12a recognizes different DNA sequences and produces staggered cuts rather than the blunt cuts made by Cas9, which some researchers believe may offer advantages in editing precision at certain genomic loci.
The RUBY trial is still ongoing, and Editas Medicine has not yet announced a timeline for seeking regulatory approval. The Phase 1-2 design means the therapy would likely need additional pivotal data before it could be submitted to the FDA for consideration.