S272: safety and efficacy of rm-001 in patients with transfusion-dependent β-thalassemia: early results from the ongoing of autologous hbg1/2 promoter-modified cd34+ hematopoietic stem and progenitor cells

Background: Reactivating fetal globin (HbF) is a promising treatment for β-hemoglobinopathies. Using gene editing to mimic these mutations should reactivate γ-globin in patients with transfusion-dependent β-thalassemia (TDT) and ameliorate the symptoms of patients. RM-001 is a novel cell therapy that uses non-viral, ex vivo CRISPR-Cas9 gene editing in autologous hematopoietic stem and progenitor cells (HSPCs) at the promoter of the γ-globin genes (HBG1/2) to disrupt the binding site of BCL11. Aims: Here, we present available safety and efficacy results from all patients that received RM-001 infusion from two ongoing clinical trials (ChiCTR2100053406 & ChiCTR2100052858), including a recent treated TDT patient (β0/β0) who also carries two α-globin genes deletion (--/αα). Methods: Patients (6–35 y of age) with TDT receiving packed red blood cell (pRBC) transfusions of ≥100 mL/kg/y or ≥10 units/y in the previous 2 y were eligible. Peripheral CD34+ HSPCs were collected by apheresis after mobilization with G-CSF and plerixafor. CD34+ cells were edited with CRISPR-Cas9 using a guide RNA specific for the binding site of BCL11A on the HBG1/2 promoter. Prior to RM-001 product infusion (day 0), patients received myeloablative conditioning with Busulfan from day-7 to day-3. Patients were monitored for stem cell engraftment/hematopoietic recovery, adverse events (AEs), Hb production, HbF and F-cell expression, and pRBC transfusion requirements. Bone marrow cells were obtained at 3, 6, 12 and 24 months after RM-001 infusion to measure the on-target allelic editing frequency using next-generation sequencing. Results: Data presented here for all 6 TDT patients have been treated with RM-001. As of February 28, 2023, patients were followed up for 2 to 15 months and 5 of them have been followed up more than 12 months. Five patients have β0/β0 genotype (CD17/CD41-42, n=1; CD41-42/CD41-42, n=4) and the other has β0/β+ genotype (CD41-42/IVS-II-654). In addition to β-thalassemia (CD41-42/CD41-42), the sixth patient (25yo) also carries two α-globin genes deletion (--SEA/αα). Patients had received a mean of 56.2 units/y pRBC transfusions (range: 39-79.6 units/y). All patients received a single dose of RM-001 cells, and achieved both neutrophil and platelet engraftments 2 to 3 weeks after RM-001 infusion (neutrophil: day 13-19, platelet: day 10-22). All patients ceased pRBC transfusions within 1 month after RM-001 infusion and achieved transfusion-independent (TI, total Hb continued ≥ 9g/dL) within 2 months (Figure). At 4 month post-RM-001 infusion, HbF reached 10g/dL in the first 5 patients and continuously maintained over this level through the reported period. At 2 month post-RM-001 infusion, the sixth patient had a total Hb of 11.7g/dL with 78.0% of HbF. The safety profile was generally consistent with busulfan myeloablation and autologous hematopoietic stem cell transplantation. No RM-001 related SAE report. Summary/Conclusion: The updated data reported here from 6 patients with TDT infused with RM-001 demonstrated clinically meaningful increases in total hemoglobin (Hb) and HbF levels. All patients stopped receiving pRBC transfusions within 1 month after RM-001 infusion and remained transfusion-free through the time of this analysis. The safety profile of RM-001 is generally consistent with myeloablative conditioning and autologous hematopoietic stem cell transplantation. These results strongly support continued investigation of RM-001 as a potential cure for patients with TDT. Submitted on behalf of the RM-001 Investigators.Keywords: Gene therapy, Thalassemia, Autologous hematopoietic stem cell transplantation