Frank J.T. Staal
Leiden University Medical Center -Netherlands
Title: Stem cell based gene therapy for Recombinase deficient-SCID
Biography
Biography: Frank J.T. Staal
Abstract
Recombinase-activating gene (RAG) deficient SCID patients lack B and T lymphocytes due to the inability to rearrange immunoglobulin and T-cell receptor genes. The two RAG genes are acting as a required dimer to initiate gene recombination. Gene therapy is a valid treatment alternative for RAG-SCID patients, who lack a suitable bone marrow donor, but developing such therapy for RAG1/2 has proven challenging.Hence, we tested clinically relevant lentiviral SIN vectors with different internal promoters (UCOE, PGK, MND, and UCOE-MND) driving codon optimized versions of the RAG1 or RAG2 genes to ensure optimal expression. We used Rag1-/- or Rag2-/-mice as a preclinical model for RAG-SCID to assess the efficacy of the various vectors at low vector copy number. In parallel, the-conditioning regimen in these mice was optimized using busulfan instead of commonly used total body irradiation.We observed that B and T cell reconstitution directly correlated with RAG1 and RAG2 expression. Mice receiving low Rag1/2 expression showed poor immune reconstitution; however high Rag1/2 expression resulted in a lymphocyte reconstitution comparable to mice receiving wild type stem cells. Efficiency and safety of our clinical RAG1 lentivirus batch was assessed in Rag1-/- mice model showing that functional restoration of RAG1-deficiency can be achieved with clinically acceptable vectors. Additionally, RAG1-SCID patient CD34+ cells transduced with our clinical RAG1 vector and transplanted into NSG mice led to fully restored human B and T cell development. Together with favourable safety data, these results substantiate a clinical trial for RAG1 SCID which is planned for late 2018.