In situ transduction of stromal cells and thymocytes upon intrathymic injection of lentiviral vectors

Young adult mice were injected in the thymus with lentiviral vectors expressing eGFP or the hemaglutinin of the Influenza virus under the control of the ubiquitous phospho glycerate kinase promoter. Thymi were examined 5 to 90 days thereafter directly under a UV-light microscope and by flow cytometry. Intrathymic injection of lentiviral vectors predominantly results in infection of stromal cells that could be detected for at least 3 months. Importantly, hemaglutinin expression by thymic stromal cells mediated negative selection of thymocytes expressing the cognate T-cell receptor. In addition and despite the low multiplicity of infection, transduced thymocytes were also detected, even 30 days after injection.Our results demonstrate that intrathymic delivery of a lentiviral vector is an efficient means for stable expression of a foreign gene in the thymus. This new method of gene delivery may prove useful for induction of tolerance to a specific antigen and for gene therapy of severe combined immunodeficiencies.The thymus is a bilobate organ derived from embryonic endoderm and mesoderm differentiation and is located just above the heart (reviewed in [1]). It is the primary organ for maturation of T cells. This process involves the interaction between developing thymocytes and thymic stromal cells. Thymic stromal cells which forms the thymic architecture, have been classified according to their anatomical localization. They encompass a very diverse array of cell types, including cortical and medullar epithelial cells, fibroblasts, macrophages and dendritic cells (reviewed in [2]). Stromal cells control the differentiation of haematopoietic precursors derived from the liver or the bone marrow into T lymphocytes: T-cell differentiation is defined by the acquisition of maturation markers such as CD4, CD8 and the T-cell receptor complex (TCR), which conditions the reactivity of immature thymocytes with thymic stromal cells. The early thymocyte progenitors entering the thy