Enrichment of c-kit(+) Lin(-) haemopoietic progenitor cells that commit themselves to extrathymic T cells in in vitro culture of appendix mononuclearcells

The appendix as well as the small intestine have recently been found to car ry c-kit(+) stem cells which give rise to extrathymic T cells. In this stud y, the properties of c-kit(+) stem cells in the appendix of mice were furth er characterized. When appendix mononuclear cells (MNC) were cultured in th e presence of stem cell factor, interleukin-3, interleukin-6 and erythropoi etin on a methylcellulose culture plate, the population of c-kit(dull) Lin( -) and that of c-kit(hi) Lin(-) cells expanded. Morphological study reveale d that these c-kit(hi) Lin(-) cells were basophilic granular cells (possibl y mast cells). Both populations of cultured appendix MNC were then injected into severe combined immunodeficient mice or cultured with Tst-4 thymic st roma cells. These in vivo and in vitro studies demonstrated that c-kit(dull ) Lin(-) cells were oligopotent haemopoietic progenitor cells which gave ri se to extrathymic T cells, while c-kit(hi) Lin(-) cells lacked haemopoietic progenitor cell activity. In contrast to c-kit(+) stem cells in the bone m arrow, those in the appendix did not give rise to myeloid cells and convent ional thymic T cells under any of the conditions tested. The present result s suggest that the appendix primarily comprises c-kit(+) cells which give r ise to basophilic granular cells and extrathymic T cells and that such c-ki t(+) cells have the ability to replicate themselves in culture in vitro.