Bone Marrow Transplantation after Nonmyeloablative Treosulfan Conditioning Is Curative in a Murine Model of Sickle Cell Disease

Abstract

Allogeneic hematopoietic stem cell transplantation (HSCT) can be curative for patients with sickle cell disease (SCD). However, morbidity associated with myeloablative conditioning and graft-versus-host disease has limited its utility. To this end, autologous HSCT for SCD using lentiviral gene-modified bone marrow (BM) or peripheral blood stem cells has been undertaken, although toxicities of fully ablative conditioning with busulfan and incomplete engraftment have been encountered. Treosulfan, a busulfan analog with a low extramedullary toxicity profile, has been used successfully as part of a myeloablative conditioning regimen in the allogeneic setting in SCD. To further minimize toxicity of conditioning, noncytotoxic monoclonal antibodies that clear stem cells from the marrow niche, such as anti-c-Kit (ACK2), have been considered. Using a murine model of SCD, we sought to determine whether nonmyeloablative conditioning followed by transplantation with syngeneic BM cells could ameliorate the disease phenotype. Treosulfan and ACK2, in a dose-dependent manner, decreased BM cellularity and induced cytopenia in SCD mice. Conditioning with treosulfan alone at nonmyeloablative dosing (3.6 g/kg), followed by transplantation with syngeneic BM donor cells, permitted long-term mixed-donor chimerism. Level of chimerism correlated with improvement in hematologic parameters, normalization of urine osmolality, and improvement in liver and spleen pathology. Addition of ACK2 to treosulfan conditioning did not enhance engraftment. Our data suggests that pretransplant conditioning with treosulfan alone may allow sufficient erythroid engraftment to reverse manifestations of SCD, with clinical application as a preparative regimen in SCD patients undergoing gene-modified autologous HSCT.

GBT021601 improves red blood cell health and the pathophysiology of sickle cell disease in a murine model

“…GBT021601 also dose dependently decreased reticulocytes in SS mice (Figure 4B), and treatment with GBT021601 150 mg/kg achieved the same level of reticulocytes as that observed in the bone marrow-transplanted SS mice expressing curative levels of HbA (>60% HbA). 11 Consistent with improving anaemia, GBT021601 caused a dose-dependent increase in RBC counts (Figure 4C), normalizing that and other haematological parameters at the 150 mg/kg dose (Table 3). Importantly, erythropoietin levels remained low (Figure 4D) with GBT021601 treatment.…”

“…In this study, mean steady‐state Hb occupancies of approximately 30%–40% at C min and 70% at C max and a significant decrease in RBC sickling, spleen weight and haemolysis were observed after oral QD administration of GBT021601 150 mg/kg in SS mice. Notably, GBT021601 increased Hb in SS mice compared with that observed in wild‐type mice (C57BL/6) and decreased reticulocytes to the same level as that observed in the bone marrow–transplanted SS mice expressing curative levels of HbA (>60% HbA) 11 . Additionally, GBT021601 improved RBC deformability, maturation and half‐life in SS mice.…”

“… Note : Reference interval values for all C57BL6 RBC parameters were previously reported 19,20 . Reference interval values for all AA, AS and SS RBC parameters were previously reported 5,11,17 . Absolute reticulocyte reference values were calculated as the product of % reticulocytes and RBC counts.…”

“…19,20 Reference interval values for all AA, AS and SS RBC parameters were previously reported. 5,11,17 Absolute reticulocyte reference values were calculated as the product of % reticulocytes and RBC counts. n = 6, 6, 6, 4 and 5 mice for the 0, 20, 40, 75 and 150 mg/kg, respectively, GBT021601-dosed groups for all parameters.…”

Development and characterization of a preclinical total marrow irradiation conditioning-based bone marrow transplant model for sickle cell disease

“…Furthermore, in TMI (8:2) dose escalation, although no sustained engraftment was seen when 5 and 10 million donor cells were used, 25 million donor BM cells resulted in sustained engraftment, suggesting that increased dose could create space for donor HSC to home; however, sustained engraftment was possible only with higher donor BM cells. Similarly, in a previous study in SCD mice, increasing donor cell numbers from 10 to 50 million did not improve chimerism in nonmyeloablative Treosulfan conditioning; however, chimerism increased only when the conditioning dose of treosulfan was increased (27). Therefore, increased dose to the BM using TMI was also essential along with increased donor BM cells for sustained engraftment.…”