In vitro studies on lymphocyte differentiation. II. Generation of terminal deoxynucleotidyl transferase-positive cells in long-term cultures of mouse bone marrow.

The enzyme TdT is the earliest known marker of lymphocytic differentiation in rodents. Cells containing this enzyme were demonstrated in suspension cultures of mouse bone marrow cells that had been maintained in vitro for periods of 7 to 45 days. The cells were detected by immunofluorescence using purified antibodies to homogeneous TdT. Between 0.04 and 2.0% of cultured bone marrow cells from a variety of mouse strains were positive. More than 40% of the TdT-positive cells incorporated 3H-thymidine during a 20-min pulse. Surface Ig and Thy-1 antigens were not detected on the TdT-positive cells. The prevalence of TdT-positive cells was decreased 10-fold in cultures that had been treated with 10(-6) M hydrocortisone 24 hr before harvesting. The results indicate that lymphoid progenitor cells can be generated in vitro.