STROMAL CELLS IN LONG-TERM CULTURES - KEYS TO THE ELUCIDATION OF HEMATOPOIETIC DEVELOPMENT

Long-term bone marrow cultures mirror many aspects of in vivo mammalia n hematopoiesis. Thus. these cultures have been used widely to analyze the complex interactions that regulate hematopoietic differentiation. Hematopoiesis in vivo and in vitro is dependent on stromal cells. a m ixture of support cells. In the past years numerous clonal stromal cel l lines derived from murine and human tissues have been isolated and c haracterized. The stromal cell lines have proved to be invaluable tool s for the elucidation of the molecular and cellular signals that gover n differentiation and self-renewal of hematopoietic cells. This review describes the salient features of marrow cultures with a focus on the isolation and characterization of stromal cell lines. We summarize ho w stromal cell lines have been crucial tools for the detection, isolat ion. and maintenance of rare pluripotent stem cells and B lineage cell s. Intriguing questions about the nature of stromal cells, their requi rements for growth and differentiation, and their histogeneic origin r emain areas for further investigation.