Cellular aggregates in bone marrow cultures of patients with acute myeloid leukemia.

We describe the incidence and morphology of cellular aggregates which may develop in 8 day bone marrow (BM) cultures of patients with acute myeloid leukemia (AML). Aggregates formed in at least one BM culture from 50% (20/39) of the AML group. They developed irrespective of the patient's status (i.e. stages M1-M4), FAB type, and presence of colony stimulating factor (CSF). All aggregates were composed of macrophages, plasma cells, and cells of the myelocyte series surrounding a core of adipocytes and collagen fibrils. The percentage of blasts and promyelocytes in the plated BM aspirate governed the final composition of the aggregate. Patients in Stages M3 or M4 with FAB types M1 or M2 formed aggregates with a high proportion of myelocytic cells; aggregates of all other AML patients were composed predominantly of macrophages and plasmacytes. Aggregates appeared to form as a result of attraction of cells in the medium toward the stroma cell core. Furthermore, the development of aggregates in the absence of exogenous CSF, suggested that stromal cells excreted a factor with CSF-like activity. The results indicate that cellular aggregates in AML-BM cultures reflect the important role of BM stroma in creating microenvironments which enhance the development of hemopoietic stem cells.