Characterization of normal peripheral blood T- and B-cell colony-forming cells: growth factors(s) and accessory cell requirements for their in vitro proliferation.

The biological properties of normal peripheral lymphoid precursors were studied using separate colony assays for T- and B-cell colony-forming cells (T-CFC and B-CFC, respectively). Cell fractions, selected by complement-mediated cytotoxicity with monoclonal antibodies, were cultured in methylcellulose using different sources of growth factors containing (PHA-LCM2 and PHA-LCM7) or not (PHA-TCM) Interleukin-2 (IL-2). Well-differentiated T-cell colonies were only observed with IL-2-containing conditioned media (CM). Normal T-CFC displayed either an immature (E-T11-OKT3-Ia-) or mature (E+) phenotype, were quiescent cells presenting different radiosensitivity (D0 = 80 and 155 rads, respectively). B-CFC displayed the E-T11-OKT3-B1-Ia+ surface phenotype, were in DNA synthesis and were more radioresistant (D0 = 300 rads) than T-CFC. B-cell colonies could be obtained in the presence of allogeneic irradiated T cells and PHA-TCM, but not with IL-2-containing CM. When E-T11-OKT3- cells were seeded with PHA-TCM supplemented with increasing amounts of semipurified IL-2 in the presence of a fixed number of irradiated T cells, the B-cell colony growth (as assessed by the frequency of sIg+ colony cells) progressively decreased whereas that of T-cell colonies increased. IL-2-free CM (PHA-TCM) was able to induce T-cell colony growth from E-T11-OKT3- cells but addition of allogeneic irradiated T cells induced B-cell colony formation in a dose-dependent manner. Conversely, T cells enhanced T-cell colony growth in the presence of IL-2-containing CM. Furthermore, adherent cell depletion of E-T11-OKT3- cells inhibited T- but not B-cell colony growth. These results taken together suggest that T- and B-cell colonies derive from different progenitor cells which have different growth factor(s) and accessory cell requirements and indicate that T-cell colony growth is associated with inhibition of B-cell colony formation.