A characterization of T lymphocyte colony-forming cells (TL-CFC) in human bone marrow.

T lymphocyte colony-forming cells (TL-CFC) present in the peripheral blood of healthy individuals have been studied by several investigators but an analysis of the properties of marrow TL-CFC is still lacking. The experiments reported here represent a first attempt to define some characteristic of marrow TL-CFC, in direct comparison with blood TL-CFC, using density gradients, rosette tests and stimulation of DNA synthesis. It was found that marrow TL-CFC and blood TL-CFC have different density properties. Both populations were characterized by distinct profiles with peaks at 1 . 07 g/ml and 1 . 065 g/ml respectively. In marrow as well as blood striking similarities between the density distributions of TL-CFC and E rosette-forming cells (E-RFC) were found. From E rosette Ficoll separation experiments it became clear that TL-CFC in bone marrow, as well as in blood, represent a subgroup of the E-RFC population. A marked dissociation was observed between the quantitative values of thymidine incorporation and colony responses following stimulation with PHA. The most prominent findings was that light-dense bone marrow-subfractions, which were virtually negative in PHA mitogen (DNA-synthesis) tests, still gave rise to relatively large numbers of T lymphocyte colonies after stimulation with PHA. On the contrary, in blood, T lymphocyte colonies could be grown exclusively from density fractions which were positive in PHA mitogen stimulation tests. Apparently, characteristics differences exist between marrow and blood TL-CFC.