An in vitro demonstration of the ability of human bone marrow stromal elements to sustain granulocytopoiesis.

The ability of human bone marrow particles to produce a microenvironment conducive to granulocytopoiesis was tested by culturing them in vitro without an exogenous source of colony stimulating activity (CSA). Granulocytopoiesis in this system was confirmed by the following observations: (1) presence of mitotic figures in promyelocytes and myelocytes; (2) early disappearance of mature granulocytes, followed by their reemergence after 4 days in culture, and (3) presence of immature granulocytes even after 10-14 days in culture. Although no exogenous source of CSA was added to the culture plates, a probable endogenous source was the dense accumulation of stromal elements in the core of particles; these cells may generate sufficiently high local levels of CSA to stimulate and nurture granulocyte proliferation and maturation.