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3458 Lentiviral Gene Therapy with Low Dose Conditioning for X-Linked SCID Results in Complete Immune Reconstitution and No Evidence of Clonal ExpansionClinically Relevant Abstract

Program: Oral and Poster Abstracts
Session: 801. Gene Therapies: Poster II
Hematology Disease Topics & Pathways:
Research, clinical trials, Clinical Research, pediatric, Diseases, Immune Disorders, immunodeficiency, Therapies, Study Population, Human
Sunday, December 11, 2022, 6:00 PM-8:00 PM

Claire Booth, MBBS, PhD, MSc1*, Donald B. Kohn, MD2, Myriam Armant, PhD3*, Susan Prockop, MD4, Karen Buckland, PhD5*, Sharat Chandra, MBBS, MD6*, Shanmuganathan Chandrakasan, MD7, Kritika Chetty, MBBS8*, Colleen Dansereau, MSN, RN, CPN9*, Satiro de Oliveira, MD10*, John Everett11*, Diego León Rico, PhD8*, Wendy B. London, PhD12, Jin Hua Xu-Bayford13*, Theodore B. Moore, MD14, Nisha Nagarsheth, PhD15*, Suhag Parikh, MD16*, Dayna Terrazas, RN17*, Shanna L White18*, Axel Schambach, MD, PhD19*, Frederic D. Bushman, PhD20*, Adrian J. Thrasher, MBBS, PhD, FMedSci21*, David A. Williams, MD22 and Sung-Yun Pai, MD23

1Great Ormond Street Hospital, London, ENG, United Kingdom
2Broad Institute of Harvard and MIT, University of California - Los Angeles, Los Angeles, CA
3Boston Children's Hospital, Boston, MA
4Boston Children's Hospital/Dana Farber Cancer Institute, Boston, MA
5University College London/Great Ormond Street Hospital, London, United Kingdom
6Cancer and Blood Disease Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH
7Department of Pediatrics; Division of Hematology/Oncology, Emory University, Atlanta, GA
8UCL Great Ormond Street Institute of Child Health, London, United Kingdom
9Gene Therapy Program, Dana-Farber/Boston Children’s Cancer and Blood Disorders Center, Boston, MA
10Division of Hematology/Oncology, Department of Pediatrics, University of California, Los Angeles, Los Angeles, CA
11University of Pennsylvania, Pennsylvania
12Boston Children's Hospital, Harvard Medical School, Boston, MA
13Great Ormond Street Hospital For Children NHS Trust, London, GBR
14UCLA Division of Pediatric Hematology, University of California, Los Angeles, Los Angeles, CA
15National Cancer Institute, National Institutes of Health, Bethesda, MD
16Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA
17University of California, Los Angeles, Los Angeles, CA
18UCLA, Los Angeles
19Experimental Hematology, Hannover Medical School, Hannover, Germany
20Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
21UCL Great Ormond Street Institute of Child Health and Great Ormond Street Hospital NHS Trust, London, United Kingdom
22Dana-Farber/Boston Children’s Cancer & Blood Disorders Center, Division of Hematology/Oncology, Boston, MA
23National Cancer Institute, Center for Cancer Research, NIH, Bethesda, MD

Introduction: Gene therapy (GT) for X-linked severe combined immunodeficiency (SCID-X1) using a gamma (γ) retroviral vector resulted in robust T cell immune reconstitution but also insertional oncogenesis. A multi-institutional trial using a self-inactivating (SIN) γ-retroviral vector resulted in equivalent T cell immune reconstitution but no insertional oncogenesis to date (Hacein-Bey-Abina et al, NEJM 2014). In both trials, conditioning was only rarely used and therefore gene marking in B cells and neutrophils was negligible and reconstitution of NK cells was limited. To improve both the immune reconstitution and safety of GT for SCID-X1, we developed a lentiviral vector (LV) in which a codon optimized IL2RG transgene is driven by the elongation factor 1 alpha short promoter (EFS) and introduced low dose busulfan conditioning to enhance hematopoietic and multilineage expression of IL2RG. An international, multicenter, Phase 1/2 clinical trial (NCT03311503, NCT03601286) is currently underway to evaluate the safety and efficacy of LV mediated gene transfer using this vector.

Methods: A total of 14 patients have been enrolled. Two patients were withdrawn due to poor stem cell mobilization and collection and manufacturing are in progress for 3 patients. Nine patients have been infused, 8 receiving mobilized peripheral blood stem cells and 1 receiving bone marrow at an average age of 5.3 months (range 3.2-7.1). Hematopoietic stem cells (CD34+ cells) were transduced with the LV vector (using transduction enhancers in 7 products) and drug products were cryopreserved. Median cell dose was 9.06 x 10e6 CD34+ cells/kg (4.55-17.87) and median vector copy number (VCN) was 0.86 copies/diploid genome(dg) (0.67-2.79). Drug products were thawed and infused after 2 days of busulfan conditioning targeted to an AUC of 30 mg*h/L. All infants tolerated busulfan exposure without any significant toxicity.

Results: As of July 2022, all treated patients are alive with robust reconstitution of gene marked T cells with median follow up of 2.2 years (0.2-4.3). T cell reconstitution was rapid with median CD3+ T cell count 552 cells/uL (132-1160) at 3 months. Seven patients evaluable at 1 year had CD3+ (2377-4900 cells/uL) and CD4+ T cell counts (1507-3080 cells/uL) normal for age at 1-year post-GT (Figure 1). Gene marking in T cells was robust averaging 1.55-5.66 copies/dg. Evidence of thymic function includes rising naïve CD4+ T cells and maintenance of a normal CD4/CD8 ratio. Multilineage engraftment of gene modified cells is evident in B cells, neutrophils, and NK cells at last follow-up with stable VCN over time (ranges 0.43-2.05, 0.24-2.11, 1.98-3.61 respectively). In contrast to limited NK cell reconstitution seen in the absence of conditioning in prior trials, NK cell counts have been sustained in 6 of 7 patients with greater than 12 months of follow-up achieving values within the normal range for age (Figure 1). Six of these 7 patients have been able to stop immunoglobulin replacement, 4 of 4 who have completed a primary vaccine series show response, with the results of 2 further patients awaited. Insertion site analysis shows uniformly polyclonal repertoire with no evidence of clonal expansion.

Conclusion: In summary, gene therapy using a lentiviral vector and low dose busulfan conditioning resulted in robust and complete immune reconstitution correcting T, NK, and B cell defects characteristic of SCID-X1 with 100% survival and no gene therapy related adverse events.

Figure 1 Immune reconstitution in 7 patients treated with >1 year follow-up A) CD3+ T cells. B) CD4+ T cells. C) NK cells.

Disclosures: Booth: Orchard Therapeutics: Consultancy; Revolution Medicines: Research Funding; Sobi: Honoraria. Kohn: Cimeio Therapeutics: Consultancy; Innoskel: Consultancy; MyoGene Bio: Consultancy, Other: Membership on Scientific Advisory Board; Pluto Immunotherapeutics: Consultancy, Other: Membership on Scientific Advisory Board; Allogene Therapeutics: Consultancy, Other: Member of Scientific Advisory Board; ImmunoVec: Consultancy; TransformaTx: Consultancy. Prockop: Atara Biotherapeutics (through MSK): Other: Co-inventor of IP licensed to Atara. Dr Prockop transferred IP rights to MSK & has no personal financial interests in Atara. MSK has financial interests in Atara/IP interests related to this study, Research Funding; Jasper Therapeutics (through MSK): Research Funding; AlloVir (through MSK): Research Funding; Memorial Sloan Kettering Cancer Center (MSK): Other: Co-inventor of intellectual property transferred from Atara. Chandrakasan: Sobi, Inc.: Consultancy. de Oliveira: Bluebird Bio: Research Funding; Orchard Therapeutics: Research Funding. León Rico: Achilles Therapeutics: Ended employment in the past 24 months; Rocket Pharmaceuticals: Current Employment. London: Jubliant Draximage: Consultancy, Other: Data Safety Monitoring Board service; Merck: Consultancy, Other: Data Safety Monitoring Board service; ArQule: Consultancy, Other: Data Safety Monitoring Board service. Thrasher: Orchard Therapeutics: Consultancy; Rocket Pharmaceuticals: Consultancy; 4bio capital: Consultancy; Generation Bio: Consultancy, Current equity holder in publicly-traded company. Williams: Insertion Site Advisory Board, Biomarin: Consultancy; Scientific Advisory Board, Skyline Therapeutics: Consultancy; Chief Scientific Chair, Emerging Therapy Solutions: Consultancy; Scientific Advisory Board, Beam Therapeutics: Consultancy; Orchard Therapeutics: Other: Provides vector; Novartis: Consultancy, Other: Steering Committee (fees donated to NAPAAC); Insertion Site Analysis Advisory Board, Bluebird Bio: Consultancy; Bluebird: Consultancy, Other: Provides Vector; Novartis: Other: Provision of study materials, medical writing.

OffLabel Disclosure: Autologous CD34+ selection of HSC used for gene therapy is off-label.

*signifies non-member of ASH