Natural killer (NK) cell activity in human long-term bone marrow cultures (LTBMC): effects of interleukin-2 (IL-2) and granulocyte-macrophage colony-stimulating factor (GM-CSF) on the progenitor cells.

Human bone marrow-derived progenitor cells were studied in a long-term bone marrow culture system (LTBMC) dependent on an autologous stroma cell layer. The establishment of the stromal cell layer was facilitated by using marrow obtained from small pieces of sternum, which was cultured for 4 weeks without addition of exogenous growth factors. After this period, the response of LTBMC to two different cytokines [recombinant human interleukin-2 (rhIL-2) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF)] was investigated. Our results show proliferation in response to both cytokines and induction of differentiation of cells able to bind IL-2 and/or GM-CSF again. The two cytokines also generate cells responding to rhGM-CSF by colony formation. However, a difference with respect to morphology, phenotype and cytotoxic function of cells in the LTBMC, was noted between the two cytokines. Cells with large granular lymphocyte (LGL) morphology and cytotoxic activity against K562 and Daudi were generated only in the rhIL-2-supplemented LTBMC. This was compatible with a higher frequency of cells expressing the CD56+ phenotype in the IL-2-stimulated LTBMC as compared to the GM-CSF supplemented LTBMC. Our results also demonstrate the existence of a population of myeloid progenitor cells (CD33+) with ability to bind IL-2 in fresh bone marrow (BM).