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This has permitted, for the first time in a large animal model, tracking of individual stem and progenitor cell clones via insertion site analysis, an advantage over competitive transplantation studies, which cannot firmly evaluate the number or life span of individual clones contributing to hematopoiesis.Retroviral tracking studies in mice suggest that stable hematopoiesis may be dominated by a small number of clones, but these studies have been limited by insensitive detection methods, low numbers of transplanted stem cells, and limited life span of immunodeficient mice.Critical characteristics such as homing to the marrow microenvironment are also difficult to model in vitro.
However, over the past several years, retroviral transduction of non-human primate repopulating cells has significantly improved, allowing tracking of multiple individual stem cell clones in this large animal model.Autologous transplantation studies in non-human primates have just begun and have the potential to shed light on controversial issues such as the number of clones contributing to stable hematopoiesis, clonal succession, and lineage commitment, as well as the effect of clinically relevant manipulations such as cytokines, chemotherapy, and radiation on hematopoiesis.These approaches will have significant impact in studying various aspects of stem cell biology including the phenomenon of stem cell plasticity.Retroviral insertion site analysis following transplantation of marked hematopoietic stem cells (HSCs) is a powerful method for studying hematopoiesis in vivo.High-level gene transfer efficiency was achieved in murine models in the late 1980s, but early human gene transfer protocols into hematopoietic stem and progenitor cells using the murine methodology showed consistently poor results.
Gene marking protocols designed to track the fate of transduced cells, without therapeutic intent, were the first clinical gene transfer studies carried out in humans. (1990) determining the fate of tumor infiltrating lymphocytes using retroviral gene transduction first demonstrated the feasibility and safety of human gene marking studies.