Introduction
Sickle cell disease is a genetic disorder that affects the hemoglobin in red blood cells. It is caused by a single point mutation in the gene encoding β-globin (HBB), leading to the production of sickle hemoglobin and impaired red-cell function. Patients with sickle cell disease often have vaso-occlusive events, progressive vasculopathy, and chronic hemolytic anemia. These are associated with complications and an increased risk of early death. Current supportive treatment options can only manage the disease without halting its progression.
Background
Sickle cell disease is a debilitating condition that affects millions of people worldwide. Current supportive treatment options can only manage the disease without halting its progression. HLA-matched sibling allogeneic hematopoietic stem-cell transplantation is a potentially curative treatment option, but it is limited by the fact that only a small percentage of patients have HLA-matched donors, and there is a risk of graft-versus-host disease and graft rejection, as well as the risk of transplantation-related death. Gene therapies that use autologous stem cells may overcome these hurdles and are advancing into clinical trials.
Methods
LentiGlobin for sickle cell disease (bb1111; lovotibeglogene autotemcel, Bluebird Bio) consists of the autologous transplantation of hematopoietic stem and progenitor cells (HSPCs) transduced with the BB305 lentiviral vector encoding a modified β-globin gene. This results in the production of an antisickling hemoglobin, HbAT87Q. HbAT87Q is a modified adult hemoglobin with an amino acid substitution (threonine to glutamine at position 87) designed to sterically inhibit polymerization of sickle hemoglobin. In this ongoing phase 1-2 study, the researchers optimized the treatment process in the initial 7 patients in Group A and 2 patients in Group B with sickle cell disease. Group C was established for the pivotal evaluation of LentiGlobin for sickle cell disease, and a more stringent inclusion criterion was adopted that required a minimum of four severe vaso-occlusive events in the 24 months before enrollment.
Results
In this unprespecified interim analysis, the researchers evaluated the safety and efficacy of LentiGlobin in 35 patients enrolled in Group C. Included in this analysis was the number of severe vaso-occlusive events after LentiGlobin infusion among patients with at least four vaso-occlusive events in the 24 months before enrollment and with at least 6 months of follow-up. As of February 2021, cell collection had been initiated in 43 patients in Group C; 35 received a LentiGlobin infusion, with a median follow-up of 17.3 months (range, 3.7 to 37.6). Engraftment occurred in all 35 patients. The median total hemoglobin level increased from 8.5 g per deciliter at baseline to 11 g or more per deciliter from 6 months through 36 months after infusion. HbAT87Q contributed at least 40% of total hemoglobin and was distributed across a mean (±SD) of 85±8% of red cells. Hemolysis markers were reduced. Among the 25 patients who could be evaluated, all had resolution of severe vaso-occlusive events, as compared with a median of 3.5 events per year (range, 2.0 to 13.5) in the 24 months before enrollment. Three patients had a nonserious adverse event related or possibly related to LentiGlobin that resolved within 1 week after onset. No cases of hematologic cancer were observed
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