Abstract

Background

β-globin gene transfer has the potential for substantial clinical benefit in patients with sickle cell disease (SCD). LentiGlobin Drug Product (DP) contains autologous CD34+ hematopoietic stem cells (HSCs) transduced with the BB305 lentiviral vector (LVV), encoding β-globin with an anti-sickling substitution (T87Q). The safety and efficacy of LentiGlobin gene therapy is being evaluated in the ongoing Phase 1 HGB-206 study (NCT02140554). Results in the initial 7 patients treated with LentiGlobin DP from steady state bone marrow harvested (BMH) HSCs using original DP manufacturing process (Group A) demonstrated stable HbAT87Q production in all patients, but at levels below the anticipated target. The protocol was thus amended to include pre-harvest RBC transfusions, optimize myeloablation by targeting higher busulfan levels, and use a refined DP manufacturing process (Group B); additionally, HSC collection by plerixafor mobilization/apheresis was instituted (Group C). Data from patients in Group C, treated under the modified protocol with DPs manufactured from plerixafor-mobilized HSCs using the refined process, are reported here. Results in patients in Groups A and B are reported separately.

Methods

Patients with severe SCD (history of recurrent vaso-occlusive crisis, acute chest syndrome, stroke, or tricuspid regurgitant jet velocity of >2.5 m/s) were enrolled. Patients in Group C received ≥2 months of transfusions to reach Hb of 10 - 12 g/dL and <30% HbS before HSC collection. Patients received 240 μg/kg of plerixafor 4 - 6 hours before HSCs were collected by apheresis and CD34+ cells were transduced with the BB305 LVV at a central facility. Following myeloablative conditioning with busulfan, the DP was infused, and patients were monitored for adverse events (AEs), engraftment, peripheral blood (PB) vector copy number (VCN), HbAT87Q expression, and HbS levels. Summary statistics are presented as median (min - max).

Results

As of 15 May 2018, 11 Group C patients (age 25 [18 - 35] years) had undergone mobilization/apheresis, 9 patients had DP manufactured (median 1 cycle of mobilization [1 - 3]) and 6 patients had been treated. Cell dose, DP VCN and % transduced cells in the 6 treated patients were: 7.1 (3 - 8) x 106 CD34+ cells/kg, 4.0 (2.8 - 5.6) copies/diploid genome (c/dg) and 81 (78 - 88) % transduced cells. The median follow-up was 3.0 (1.2 - 6.0) months. Patients achieved neutrophil engraftment at a median of 19 (18 - 20) days. Platelet engraftment was achieved at a median of 28 (12 - 64) days in 4 patients; platelet engraftment was pending in 2 patients.

Two of 11 patients experienced 4 grade ≥3 AEs associated with plerixafor mobilization/HSC collection: 1 had vaso-occlusive pain and hypomagnesaemia, and the other had vaso-occlusive pain and non-cardiac chest pain. The toxicity profile from DP infusion to last follow-up in the 6 treated patients was consistent with myeloablative conditioning. Febrile neutropenia (n=5) and stomatitis (n=4) were the most common non-hematologic grade ≥3 AEs. Serious AEs were reported in 3 patients post-DP infusion: splenic hematoma, non-cardiac chest pain and mucosal inflammation. To date, there have been no DP-related AEs, graft failure, vector-mediated replication competent lentivirus, or clonal dominance.

In the 6 treated patients, PB VCN at last visit ranged from 1.4 - 2.9 c/dg. In the 3 patients with 3 months follow-up, total Hb levels were 11.7 g/dL, 9.8 g/dL and 9.2 g/dL, and HbAT87Q levels were 4.7 g/dL, 3.2 g/dL and 3.5 g/dL. One additional patient with 6 months follow-up was off transfusions and had total Hb of 14.2 g/dL, of which 62% (8.8 g/dL) was vector-derived HbAT87Q and 36% (5.1 g/dL) was HbS. All 4 patients had HbAT87Q (median 39%) levels higher than or equal to HbS (median 31%) at the 3-month visit.

Summary

HGB-206 protocol changes and refined DP manufacturing have improved the LentiGlobin DP characteristics resulting in significantly improved outcomes. In addition, the HbAT87Q expression is comparable to, or exceeds, HbS levels as early as 3 months post DP infusion. These data support the feasibility of plerixafor-mediated CD34+ cell collection in patients with severe SCD and the efficacy of gene therapy. The safety profile of LentiGlobin gene therapy remains consistent with single-agent busulfan conditioning. Additional data and longer follow-up will determine the clinical effect of increased HbAT87Q/HbS ratios.

Disclosures

Kanter:Global Blood Therapeutics: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; bluebird bio: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; Sancilio: Research Funding; NHLBI: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Apopharma: Research Funding; ASH: Membership on an entity's Board of Directors or advisory committees. Mapara:Incyte: Consultancy. Kwiatkowski:Novartis: Research Funding; bluebird bio: Consultancy, Honoraria, Research Funding; Apopharma: Research Funding; Terumo: Research Funding; Agios Pharmaceuticals: Consultancy, Research Funding. Schmidt:GeneWerk GmbH: Employment; German Cancer Research Center: Employment; bluebird bio: Consultancy. Miller:bluebird bio: Employment, Equity Ownership. Pierciey:bluebird bio: Employment, Equity Ownership. Shi:bluebird bio: Employment, Equity Ownership. Ribeil:bluebird bio: Employment, Equity Ownership. Asmal:bluebird bio: Employment, Equity Ownership. Thompson:Amgen: Research Funding; Celgene: Research Funding; Baxalta/Shire: Research Funding; bluebird bio: Consultancy, Research Funding; Novartis: Research Funding; Biomarin: Research Funding; La Jolla Pharmaceutical: Research Funding. Walters:Sangamo Therapeutics: Consultancy; bluebird bio: Research Funding; ViaCord Processing Lab: Other: Medical Director; AllCells Inc.: Other: Medical Director.

Author notes

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Asterisk with author names denotes non-ASH members.

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