Clinical Results of the Drepaglobe Trial for Sickle Cell Disease Patients

Abstract

In sickle cell disease (SCD), the β6 Glu→Val substitution leads to sickle hemoglobin (HbS) polymerization and red blood cell (RBC) sickling. Transplantation of autologous, genetically modified hematopoietic stem/progenitor cells (HSPCs) represents a promising therapeutic option for patients lacking a compatible donor. We previously designed a lentiviral vector (βAS3 LV) expressing a potent anti-sickling βAS3 globin and demonstrated its safety and efficacy in SCD patient cells (Weber et al., 2018). In vitro and in vivo preclinical studies demonstrated the safety and efficacy of a gene therapy (GT) protocol based on the efficient transduction of plerixafor-mobilized SCD HSPCs by βAS3 LV. Based on these results a Phase 1/2 clinical trial (NCT03964792) started in January 2020. Three homozygous SCD patients (P1, P2 and P3) were recruited. Before GT, patients suffered from severe SCD symptoms that were not controlled despite of a strict adherence to the treatment. Plerixafor-mobilized HSPCs were transduced achieving a VCN of 0.9±0.2 in liquid culture, 1.6±0.3 in BFU-E and 0.8±0.2 in CFU-GM. The patients were hypertransfused to reach HbS levels <30%. After busulphan-based myeloablative conditioning, they received a drug product 6 to 8.1x 10 6 per kg. Here, for the 3 patients we report the follow-up of 18 (P1), 10 (P2) and 6 (P3) months. No drug-related severe adverse events were observed. Importantly, no sign of clonal hematopoiesis was detected by NGS sequencing performed on the graft before and after transduction. Despite of the similar VCN in the drug product, gene marking in peripheral blood mononuclear cells was variable and ranged between 0.2 and 0.6, as measured at the last follow-up (0.4 in P1, 0.6 in P2 and 0.2 in P3). These results pinpoint the difficulty to estimate the gene marking, self-renewal and engraftment potential of HSCs in the grafts. P1 and P2 clinically benefit from the GT treatment despite they presented non-severe vaso-occlusive crises (VOCs) not requiring hospitalization (two for P1 at month 6 and 14 and one in P2 at month 8 post-GT). Despite the rapid resolution of these episodes, P1 started hydroxyurea at month 10 and stopped it at month 16. P2 initiated a phlebotomy program to treat liver iron overload and decrease viscosity. Intravascular hemolysis improved in P1 and P2, as shown by a decrease in plasma hemoglobin and heme, and an increase in hemopexin (HPX). Interestingly, in P1 a mild worsening occurred at the time of VOC. In P1 and P2, total bilirubin, a marker of extravascular hemolysis, decreased post-GT. Deformability, measured using osmoscan, improved in P1 and to a lesser extent in P2; however, both still exhibited some degree of dehydration compared to normal RBCs (Fig. 1). Adhesion to thrombospondin decreased after GT with an increase during VOC in P1 or prior the VOC in P2 (Fig. 1). In both patients, markers of inflammation (e.g., C reactive protein) and reticulocyte counts decreased upon GT. An in vitro sickling assays was performed for P1 and showed significant improvement, reaching a frequency of sickling cells similar to SCD heterozygous carriers (from 88% before GT to 45% 6 months post-GT). The GT treatment was not effective in P3 due to the modest intake and rapid decline of gene modified cells. In P1 and P2, who were no longer on transfusions, HbAS3 levels correlated with the VCN (2.1 g/dl for P1 and 3.3 g/dl for P2) and the therapeutic Hb accounted for 21.5%, and 28.7% of the total hemoglobins, respectively. For P3, who remained transfusion-dependent, this frequency was <3% due to the low VCN and the presence of the transfusion-derived Hb. Notably, total Hb concentration was only 8.1 g/dl in P2 before the treatment and reached 11.4 g/dl at the last follow-up, suggesting a better survival of RBCs derived from genetically modified HSPCs. Furthermore, in P1 and P2, HbAS3 levels were significantly higher in mature RBCs compared to reticulocytes, indicating a survival advantage of βAS3 globin-expressing cells. Overall, these clinical data indicate a variable efficacy of the DREPAGLOBE GT treatment, which likely depends on the extent of gene marking achieved in HSCs in vivo and on the engraftment capability of genetically modified HSCs in SCD patients' bone marrow. Single-cell RNA-seq analysis of HSPCs and evaluation of the bone marrow niche in SCD patients will aid to define critical parameters for achieving successful outcomes in GT clinical trials for SCD. Figure 1 Figure 1. Disclosures Joseph: bluebird bio: Consultancy. El Nemer: Hemanext: Consultancy. Bartolucci: INNOVHEM: Other: Co-founder; AGIOS: Consultancy; GBT: Consultancy; Bluebird: Consultancy, Research Funding; Jazz Pharma: Other: Lecture fees; Fabre Foundation: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Lecture fees, Steering committee, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy; Hemanext: Consultancy; Addmedica: Consultancy, Other: Lecture fees, Research Funding; Emmaus: Consultancy. Cavazzana: Smart Immune: Other: co-founder.

Clinical genome editing to treat sickle cell disease—A brief update

“…The clinical product, LentiGlobin BB305 (Figure 1B), entails autologous HSCs transduced with an LV that encodes an anti-sickling variant of β-globin, known as βA-T87Q (mimicking the inhibitory effect of HbF on HbS polymerization). The recently published results confirmed stable βA-T87Q expression upon engraftment as well as reduced hemolysis, absence of VOC, and transfusion-independency (13,14). A phase III clinical study (NCT04293185) with 35 SCD patients as well as a long-term follow-up study (NCT04628585) were opened in 2020.…”

Sickle Cell Disease in Children and Adolescents: A Review of the Historical, Clinical, and Public Health Perspective of Sub-Saharan Africa and Beyond

“…Gene therapy broadly takes a variety of approaches including addition of a helpful gene, often using a lentiviral vector, gene knockdown (e.g., BCL11A silencing), direct globin gene editing to rectify the mutation (changing the HbS-encoding gene to HbA-encoding gene), and gene editing of elements that regulate globin, to at least partially reverse the normal hemoglobin switching from HbF to HbA (e.g., by targeting the BCL11A gene) [ 193 , 194 ]. Recently published pilot studies have shown that single treatment using gene therapy techniques results in sustained production of HbA in most RBCs and increased total Hb and HbF levels, reduces hemolysis, and completely resolves severe vaso-occlusive events [ 195 , 196 ], whereas variable findings have been documented in other studies [ 197 , 198 ]. Several other pilot studies are underway to primarily assess the feasibility, safety, and efficacy of gene therapy in patients with severe SCD [ 198 – 200 ].…”

Hematopoietic Stem Cell Gene-Addition/Editing Therapy in Sickle Cell Disease

“…Though 2/3 patients received treatment benefits, therapeutic amelioration correlated with VCN, reflective of engraftment capability. Patient 3 remained transfusion dependent due to low VCN and <3.0% therapeutic Hb [ 73 ]. A different study out of the University of California, Los Angeles, is using the β AS3 -FB carrying the β AS3 -globin gene and including an enhancer-blocking insulator in the 3′LTR (the footprint II (FII) of chicken HS4 insulator and human T-cell receptor blocking element alpha/delta 1 (BEAD-1) insulator).…”