Repetitive busulfan administration after hematopoietic stem cell gene therapy associated with a dominant HDAC7 clone in a nonhuman primate

Models and Methods for Evaluating Regeneration of Spermatogenesis After Cytotoxic Treatments

Cytotoxic exposure, predominantly during radiation and/or chemotherapy treatment for cancer, interferes with fertility in men. While moderate doses cause temporary azoospermia allowing eventual recovery of spermatogenesis, higher doses of sterilizing agents can cause permanent sterility by killing the spermatogonial stem cells (SSCs). In this chapter, the methods involved in the following aspects of cytotoxic regeneration are described: (i) designing rodent and non-human primate models for regeneration of spermatogenesis after cytotoxic treatment by radiation and chemotherapy; (ii) analysis of SSCs with respect to the impact of the cytotoxic treatment, including analysis of spermatogonial clones, scoring the testicular section to analyze the extent of spermatogenic recovery, preparation of testicular and epididymal sperm, and collection of semen in non-human primates for sperm analysis; and (iii) preparation and delivery of a GnRH antagonist and steroids for enhancement or induction of spermatogonial differentiation, leading to the regeneration of spermatogenesis, largely applicable in the rat model.

Barcoding of Macaque Hematopoietic Stem and Progenitor Cells: A Robust Platform to Assess Vector Genotoxicity

Gene therapies using integrating retrovirus vectors to modify hematopoietic stem and progenitor cells have shown great promise for the treatment of immune system and hematologic diseases. However, activation of proto-oncogenes via insertional mutagenesis has resulted in the development of leukemia. We have utilized cellular bar coding to investigate the impact of different vector designs on the clonal behavior of hematopoietic stem and progenitor cells (HSPCs) during in vivo expansion, as a quantitative surrogate assay for genotoxicity in a non-human primate model with high relevance for human biology. We transplanted two rhesus macaques with autologous CD34+ HSPCs transduced with three lentiviral vectors containing different promoters and/or enhancers of a predicted range of genotoxicities, each containing a high-diversity barcode library that uniquely tags each individual transduced HSPC. Analysis of clonal output from thousands of individual HSPCs transduced with these barcoded vectors revealed sustained clonal diversity, with no progressive dominance of clones containing any of the three vectors for up to almost 3 years post-transplantation. Our data support a low genotoxic risk for lentivirus vectors in HSPCs, even those containing strong promoters and/or enhancers. Additionally, this flexible system can be used for the testing of future vector designs.

Ex vivo gene transfer and correction for cell-based therapies

Cell-based therapies are fast-growing forms of personalized medicine that make use of the steady advances in stem cell manipulation and gene transfer technologies. In this Review, I highlight the latest developments and the crucial challenges for this field, with an emphasis on haematopoietic stem cell gene therapy, which is taken as a representative example given its advanced clinical translation. New technologies for gene correction and targeted integration promise to overcome some of the main hurdles that have long prevented progress in this field. As these approaches marry with our growing capacity for genetic reprogramming of mammalian cells, they may fulfil the promise of safe and effective therapies for currently untreatable diseases.

Differential Secondary Reconstitution of In Vivo-Selected Human SCID-Repopulating Cells in NOD/SCID versus NOD/SCID/γ chain Mice

Humanized bone-marrow xenograft models that can monitor the long-term impact of gene-therapy strategies will help facilitate evaluation of clinical utility. The ability of the murine bone-marrow microenvironment in NOD/SCID versus NOD/SCID/γ chain^null mice to support long-term engraftment of MGMT^P140K-transduced human-hematopoietic cells following alkylator-mediated in vivo selection was investigated. Mice were transplanted with MGMT^P140K-transduced CD34⁺ cells and transduced cells selected in vivo. At 4 months after transplantation, levels of human-cell engraftment, and MGMT^P140K-transduced cells in the bone marrow of NOD/SCID versus NSG mice varied slightly in vehicle- and drug-treated mice. In secondary transplants, although equal numbers of MGMT^P140K-transduced human cells were transplanted, engraftment was significantly higher in NOD/SCID/γ chain^null mice compared to NOD/SCID mice at 2 months after transplantation. These data indicate that reconstitution of NOD/SCID/γ chain^null mice with human-hematopoietic cells represents a more promising model in which to test for genotoxicity and efficacy of strategies that focus on manipulation of long-term repopulating cells of human origin.