Molecular Therapy: Methods & Clinical Development (Jun 2018)

Preclinical Development of a Lentiviral Vector for Gene Therapy of X-Linked Severe Combined Immunodeficiency

  • Valentina Poletti,
  • Sabine Charrier,
  • Guillaume Corre,
  • Bernard Gjata,
  • Alban Vignaud,
  • Fang Zhang,
  • Michael Rothe,
  • Axel Schambach,
  • H. Bobby Gaspar,
  • Adrian J. Thrasher,
  • Fulvio Mavilio

Journal volume & issue
Vol. 9
pp. 257 – 269

Abstract

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X-linked severe combined immunodeficiency (SCID-X1) is caused by mutations in the interleukin-2 receptor γ chain gene (IL2RG), and it is characterized by profound defects in T, B, and natural killer (NK) cell functions. Transplantation of hematopoietic stem/progenitor cells (HSPCs) genetically corrected with early murine leukemia retrovirus (MLV)-derived gammaretroviral vectors showed restoration of T cell immunity in patients, but it resulted in vector-induced insertional oncogenesis. We developed a self-inactivating (SIN) lentiviral vector carrying a codon-optimized human IL2RG cDNA driven by the EF1α short promoter (EFS-IL2RG), and we tested its efficacy and safety in vivo by transplanting transduced Il2rg-deficient Lin− HSPCs in an Il2rg−/−/Rag2−/− mouse model. The study showed restoration of T, B, and NK cell counts in bone marrow and peripheral blood and normalization of thymus and spleen cellularity and architecture. High-definition insertion site analysis defined the EFS-IL2RG genomic integration profile, and it showed no sign of vector-induced clonal selection or skewing in primarily and secondarily transplanted animals. The study enables a phase I/II clinical trial aimed at restoring both T and B cell immunity in SCID-X1 children upon non-myeloablative conditioning. Keywords: gene therapy, immunodeficiency, SCID-X1, lentiviral vector, integration, genotoxicity