Differentiation of Thy 1-bearing cells from progenitors in long-term bone marrow cultures.

Lone-term marrow cultures, established according to the technique described by Dexter, contain a colony-forming cell (CFU-T) that produces Thy 1-positive progeny after stimulation with PHA-induced conditioned medium from human leukocytes. When 10(-7) M hydrocortisone is added to the medium for the long-term cultures CFU-T can be maintained in vitro for at least 16 weeks. Cells from individual colonies lack precursors for cytotoxic lymphocytes but can provide nonspecific help required for the generation of cytotoxic lymphocytes.