Dominique Vanhecke

Signals from the IL-9 Receptor Are Critical for the Early Stages of Human Intrathymic T Cell Development

Highly purified human CD34+ hemopoietic precursor cells differentiate into mature T cells when seeded in vitro in isolated fetal thymic lobes of SCID mice followed by fetal thymus organ culture (FTOC). Here, this chimeric human-mouse FTOC was used to address the role of IL-9 and of the α-chain of the IL-9 receptor (IL-9Rα) in early human T cell development. We report that addition of the mAb AH9R7, which recognizes and blocks selectively the human high affinity α-chain of the IL-9R, results in a profound reduction of the number of human thymocytes. Analysis of lymphoid subpopulations indicates that a highly reduced number of cells undergo maturation from CD34+ precursor cells toward CD4+CD3−CD8−CD1+ progenitor cells and subsequently toward CD4+CD8+ double positive (DP) thymocytes. Addition of IL-9 to the FTOC resulted in an increase in cell number, without disturbing the frequencies of the different subsets. These data suggest that IL-9Rα signaling is critical in early T lymphoid development.

Human T lymphopoiesis. In vitro and in vivo study models.

Abstract: Successive Steps In T lymphocyte differentiation and T potential of human stem cells (HSC) can be tested in the following models: (a) the infusion of cells in NOD‐SCID MICE, (b) the injection of cells in renconstituted SCID/hu mice, (c) the differentiation of cells in fetal thymus organ culture (FTOC), and (d) on thymic stromal layers. using mixed human‐murine FTOC, we showed (a) TCRαβ, TCRγδ lymphocytes, NK cells, and dendritic cells complete their differentiation, (b) IL‐7Rα signaling and IL‐7 are essential, (c) a detailed phenotypic and functional analysis of discrete successive steps of positively selected thymocytes, (d) an efficient transduction of genes in HSC with persistent gene expression throughout the T‐lymphocyte differentiation, and (e) adaptation to submerging high oxygen culture increases the test sensitivity to a clonal assay. Other approaches are the in vivo SCID/hu reconstitution model. With this method small fragments of human fetal liver and thymus are implanted under the kidney capsule of an adult SCID mouse with result in an impressive human thymus organ, six months after transplantation. We use this model to study thymus T‐cell developmental kinetics, development of gene‐marked precursor cellsand thymic homing of precursor cells.

T Cell Development in the Human Thymus

T cell differentiation occurs in the thymus. In the thymus CD4+ helper cells and CD8αβ+ cytotoxic cells are generated under tight MHC control. Besides intrathymic T cell generation, T cells are generated outside the thymus. Peripheral expansion of mature T cells, which may or may not be antigen driven, is a major source of peripheral T cells, as well as de novo formation of T cells. Extrathymic T cell development mainly gives rise to CD4-CD8 double negative or CD8αα+TCRαβ+ and TCRγδ+ cells which reside mainly in bone marrow and epithelia.