CRISPR-Cas12a Gene Editing of HBG1 and HBG2 Promoters to Treat β-Thalassemia

Renizgamglogene autogedtemcel (reni-cel) is an investigational clustered regularly interspaced short palindromic repeats (CRISPR)-Cas12a gene-edited autologous hematopoietic stem-cell therapy. The therapy was designed to disrupt the BCL11A binding sites in the HBG1 and HBG2 promoters to reactivate fetal hemoglobin production for the treatment of transfusion-dependent β-thalassemia.

We conducted a phase 1-2, multicenter, open-label, single-group study of reni-cel in participants 18 to 35 years of age with transfusion-dependent β-thalassemia. The participants received myeloablative conditioning with busulfan before reni-cel infusion. The primary end points were neutrophil engraftment by 42 days after infusion and frequency and severity of adverse events. Participants were monitored for hemoglobin-related measures and transfusion independence. The study was terminated early on the basis of the sponsor's reassessment of clinical development priorities. Results of an analysis that was not prespecified are reported.

Nine participants with transfusion-dependent β-thalassemia (four β⁰/β⁰ or β⁰/β⁰-like and five non-β⁰/β⁰ genotypes) received reni-cel and were included in the analysis. The median duration of postinfusion follow-up was 17.5 months (range, 3.8 to 23.4), and six participants could be evaluated for transfusion independence at 12 months or more. All the participants had neutrophil and platelet engraftment by 42 days after infusion. Rapid increases in total and fetal hemoglobin levels resulted in each of the nine participants being transfusion-free at their last follow-up visit. The six participants who could be evaluated at 12 months or later were transfusion-independent. The mean total and fetal hemoglobin levels were greater than 12 g per deciliter and greater than 11 g per deciliter, respectively, between months 6 and 18. A total of 69 grade 3 or 4 adverse events with onset or worsening during or after reni-cel infusion were reported in the nine participants. Six serious adverse events (infections, pyrexia, or pneumonitis) were reported in four participants. Adverse events were generally consistent with myeloablative conditioning. One patient had decreased lymphocyte counts attributed to reni-cel.

Treatment with reni-cel resulted in rapid neutrophil engraftment, an increase in fetal hemoglobin expression, and transfusion independence. These data support further investigation of Cas12a gene editing of the promoters of HBG1 and HBG2 in the treatment of transfusion-dependent β-thalassemia. (Funded by Editas Medicine; EdiThal ClinicalTrials.gov number, NCT05444894.).