CD8 T lymphocytes have a fundamental role in ensuring the control of different types of intracellular pathogens including bacteria, parasites and most viruses. This control may fail due to several reasons. The current aggressive anti-cancer therapies (or rarely certain congenital immune deficiencies) induce CD8 depletion. After bone-marrow transplantation, long time periods are required to ensure T cell reconstitution particularly in the adult. This long lag-time is due to the long-time periods required for hematopoietic precursors to generate T lymphocytes and to a thymus insufficiency in the adult. However, even when CD8 T cells are present CD8 immune responses are not always adequate. Certain chronic infections, as HIV, induce CD8 dysfunction and it is yet unclear how to generate efficient CD8 memory responses conferring adequate protection. To address these questions this project aims 1) To find strategies ensuring the rapid reconstitution of the peripheral and the gut CD8 T cell compartments a) by studying the mechanisms involved HSC division and T cell commitment; b) by isolating and characterizing progenitors we previously described that are T cell committed and able of an accelerated CD8 reconstitution c) by developing new strategies that may allow stable thymus transplantation and continuous thymus T cell generation. 2) To determine the mechanics associated to efficient CD8 memory generation a) by evaluating cellular modifications that ensure the efficient division and the remarkable accumulation and survival of CD8 T cells during the adequate immune responses as compared to inefficient responses b) by studying CD8 differentiation into effector and memory cells in both conditions. These studies will use original experiment mouse models we develop in the laboratory, that allow to address each of these aims. Besides state of the art methods, they will also apply unique very advanced approaches we introduced and are the sole laboratory to perform.