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Enrichment of c‐kit+ Lin− haemopoietic progenitor cells that commit themselves to extrathymic T cells in in vitro culture of appendix mononuclear cells

The appendix as well as the small intestine have recently been found to carry c‐kit+ stem cells which give rise to extrathymic T cells. In this study, the properties of c‐kit+ stem cells in the appendix of mice were further characterized. When appendix mononuclear cells (MNC) were cultured in the presence of stem cell factor, interleukin‐3, interleukin‐6 and erythropoietin on a methylcellulose culture plate, the population of c‐kitdull Lin− and that of c‐kithi Lin− cells expanded. Morphological study revealed that these c‐kithi Lin− cells were basophilic granular cells (possibly mast cells). Both populations of cultured appendix MNC were then injected into severe combined immunodeficient mice or cultured with Tst‐4 thymic stroma cells. These in vivo and in vitro studies demonstrated that c‐kitdull Lin− cells were oligopotent haemopoietic progenitor cells which gave rise to extrathymic T cells, while c‐kithi Lin− cells lacked haemopoietic progenitor cell activity. In contrast to c‐kit+ stem cells in the bone marrow, those in the appendix did not give rise to myeloid cells and conventional thymic T cells under any of the conditions tested. The present results suggest that the appendix primarily comprises c‐kit+ cells which give rise to basophilic granular cells and extrathymic T cells and that such c‐kit+ cells have the ability to replicate themselves in culture in vitro.