Analysis of RBC Properties in Patients with SCD Treated with Lentiglobin Gene Therapy

Introduction: Gene therapy is a highly promising therapeutic strategy in sickle cell disease (SCD). The Phase 1/2 HGB-205 (NCT02151526) clinical study in France is evaluating the safety and efficacy of LentiGlobin gene therapy, which consists of autologous CD34+ cells transduced with a lentiviral vector encoding a human β-globin gene with a point mutation (T87Q) that confers anti-sickling properties. Data from the first successfully treated patient have been published (Ribeil et al, 2017 NEJM). In order to establish the effect of β^AT87Q-globin production on red blood cell properties, we have analyzed membrane properties, hemolysis markers, morphology, hemoglobin content, and the extent of HbS polymerization.

Methods: Whole blood samples were obtained from 3 patients with SCD (1204, 1207 and 1208) treated in HGB-205 during their clinical follow-up. HbS polymerization level was assessed by O₂ dissociation and association curves and cell morphology. Membrane properties were evaluated by RBC density curves in phthalate gradient, deformability under increasing osmolality (LORRCA) and level of adherence to surfaces coated with thrombospondin (TSP), under increasing shear stress (from 0.5 to 5 dynes/cm²). Hemolytic level was determined by measurement of classical markers (LDH, bilirubin and haptoglobin). Hemoglobin contents of total RBCs and reticulocytes (CD71-positive cells sorted) were assessed by reverse-phase HPLC. Results were compared against untreated β^Sβ^S patients (n=11 for deformability assay, n=4 for adhesion assay) and healthy donors (n=10 for deformability assay, n=3 for adhesion assay).

Results: As of May 29 2018, follow-up, total Hb and HbA^T87Q contribution to total Hb for patients 1204, 1207 and 1208 were: 42, 18 and 15 months, 12.2, 8.4, and 10.4 g/dL, and 49.44, 7.77 and 26.99%, respectively. At approximately 30 months post-infusion patient 1204 developed vaso-occlusive pain following an episode of acute gastroenteritis, since then the patient has not had any vaso-occlusive episodes or acute chest syndrome (ACS). Patient 1207 had 2 episodes of ACS approximately 6 and 8 months after LentiGlobin gene therapy and has since been on chronic transfusions and hydroxyurea treatment; the patient subsequently experienced 1 vaso-occlusive pain episode. Patient 1208 has had no episodes of VOCs or ACS post LentiGlobin gene therapy. Dissociation and association of O2 curves for RBCs isolated from the 2 patients free of chronic transfusions (1204 and 1208) and performed 36 and 8 months post infusion, respectively, showed only a slight increase in P50 during re-oxygenation, indicating anti-sickling capability of transgenic HbA^T87Q and low levels of HbS polymerization. Density curves showed an overall normal RBC hydration at multiple time points during follow-up, with dense cells contributing 0-4% compared to a mean (±SD) of 12.8% (±7.8) in untreated patients. The deformability of RBCs from the 2 patients (1204 and 1208) evaluated in HGB-205 study was lower than observed for healthy donors but higher than for untreated SCD patients. Under controlled shear stress, TSP adherence was consistently lower for RBCs isolated from the 2 patients (1204 and 1208) in HGB-205 compared to untreated patients with SCD.

Slight intravascular hemolysis was observed for the 3 HGB-205 patients during follow-up, but the hemolytic levels improved compared to baseline. RP-HPLC analysis of total RBCs isolated at last visit showed an increase in βA^T87Q and a decrease in βS in comparison to reticulocytes, indicating an improved survival of RBCs expressing more anti-sickling β-globin transgene (Table 1). Data on deformability, distribution of fetal Hb and additional adhesion markers will be presented.

Conclusions: Our results suggest an improvement in RBC properties for 2 of 3 patients with SCD treated with LentiGlobin gene therapy in the HGB-205 clinical trial compared to non-treated patients with SCD, suggesting a promising potential of this treatment.

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