Cell-factor interaction and factor-dependant long-term growth of human T-progenitor cells

Specific cell-factor interactions provide a basic mechanism for differentiation of myeloid and lymphoid cells. Evidence at the present time indicates that factor-producing cells, factor and factor-responding cells are integrated into an interacting network to produce various specific differentiatied functions. To elucidate the mechanisms of such interactions in the differentiation of T lymphocyte, a systematic study was carried out to characterize a liquid suspension culture system for T progenitor cells from human peripheral blood or bone marrow. T progenitor cells were assayed either by their membrane properties or by their ability to form colonies in semisolid media. T lymphocyte growth stimulators (TL-GS) were isolated from phytohemagglutin (PHA)-stimulated human T lymphocyte conditioned medium. TL-GS were capable of selectively supporting growth for four months or longer of T progenitor cells. This system should facilitate the study of cell-factor interactions mediating the proliferation and differentiation of T lymphocytes.