Human thymic epithelial cells maintain long-term survival of clonogenic myeloid and erythroid progenitor cells in vitro

Precursor cells that migrate into the thymus are still multipotent. Therefo re, thymic epithelial cells (TECs) may provide microenvironments not only f or T-cell development, but also for maintenance of multipotent precursor ce lls until they undergo T-cell commitment. In the present study, we performe d long-term cultures of CD34(+) bone-marrow (BM) cells on TEC lines that we re derived from cortical epithelial cells of post-natal thymus, to investig ate whether human TECs could maintain long-term nonlymphoid haematopoiesis. Haematopoietic cells maintained in direct contact with established TEC lin es were able to generate clonogenic progeny to both myeloid and erythroid c ells for periods in excess of 5 weeks. Their abilities to support colony-fo rming units of granulocytes-macrophages (CFU-GM) and burst-forming units of erythroids (BFU-E) were almost equal to those of BM stromal cells. We obse rved similar results by using cloned TEC lines derived by limiting dilution , as well as those by using parental TEC lines, Colony-forming activities w ere maintained even when haematopoietic progenitor cells were physically se parated from TEC lines and cultured on microporous membrane. These observat ions indicate that haematopoiesis maintained in TEC-contact long-term cultu res may depend on soluble factors produced by TEC lines. Our results sugges t that thymic cortical epithelial cells have the ability to support not onl y the differentiation of haematopoietic cells, but also long-term survival of clonogenic myeloid/erythroid progenitor cells.