International Conference onStem Cells, Regenerative Medicine and Tissue Engineering

Title: Stem cell-based gene therapy for Recombinase deficient-SCID

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, given the high expression levels needed, especially for RAG1.

We tested clinically relevant lentiviral SIN vectors with 8 different internal promoters 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 numbers. In parallel, the conditioning regimen in these mice was optimized using busulfan instead of commonly used total body irradiation. To minimize the risks of insertional mutagenesis, we have chosen to aim for VCN around one, to avoid multiple integrations in the same stem cell clone. This preclinical program resulted, surprisingly, in different promoter choices in the LV vectors for RAG1 and RAG2.

A clinical trial for RAG1-SCID has been initiated, while for RAG2 a clinical batch vector has been generated in preparation for a Phase/II trial in 2024. Two patients have thus far been included in the RAG1-SCID trial, with excellent clinical and immunological results. Importantly, we aim for multicentre, international trials with various clinical sites in Europe, Asia, and Australia. For several countries, including Spain, Poland, and Turkey, clinical centers have been added, from where patients’ stem cells will be sent to Leiden, genetically modified, and after QC returned to these centers as cryopreserved IMP. Thus, the paradigm of this consortium (cells travel, while patients stay home) has become realistic and should be of use for other gene therapy trials for rare diseases.

Biography:

Prof Dr Frank J.T. Staal obtained his bachelor's and master's degrees (both cum laude) in Medical Biology at Utrecht University. He obtained his PhD degree (1993) at the Department of Genetics, Stanford University School of Medicine under the supportive guidance of professors Leonard and Leonore Herzenberg where was taught the intricacies of flow cytometry. His thesis dealt with transcriptional regulation of HIV expression in T-lymphocytes and involved many functional flow cytometric assays and cell sorting experiments. In 1993 he became a postdoctoral fellow at the Netherlands Cancer Institute for 2 years, after which he moved back to Utrecht University as a fellow of the Royal Academy of Sciences (KNAW) in the laboratory of Professor Hans Clevers. In 2000 he was recruited to Erasmus Medical Center (EMC) Rotterdam to start his laboratory on human T cell development and became an assistant professor. In 2004 he was appointed associate professor at EMC and expanded his research to Wnt signaling in blood stem cells and T cells, as well as to gene therapy for immune disorders. In 2008 he was recruited to the Leiden University Medical Center (LUMC) and became a full professor of Molecular Stem Cell biology. His research focuses on stem cell biology and lymphocyte development, including thymus biology. He has brought stem cell-based gene therapy for several types of SCID to the clinic, in an expanding portfolio that includes immune deficiencies and lysosomal storage diseases. Staal coordinates several large European and national consortia in the area of clinical gene therapy.