Abstract
Neuroblastoma (NB) is one of the few tumors known to undergo spontaneous regression. Its progression, however, often leads to bone marrow (BM) metastasis. Proliferation and differentiation of human NB cells may be regulated in vitro by a variety of biologic agents, some of which are released by low-density BM and peripheral blood (PB) cells. Little is known regarding BM cell-derived control of NB cell growth and differentiation. The proliferative and differentiative responses of NB cells, to BM cell-, and to PB cell-derived conditioned medium (CM) were evaluated in comparison to cytokine-induced responses. CM from unstimulated cultures of low density BM and PB cells, from healthy donors, from newborn infants, and from NB patients, significantly and reproducibly stimulate NB cell growth in vitro. The intensity of CM-induced stimulation was not attained by recombinant human tumor necrosis factor (rhTNF), interferon (rhIFN), or granulocyte-monocyte colony stimulating factor (rhGM-CSF); and although epidermal growth factor (rhEGF) and transforming growth factor alpha (rhTGF alpha) were strongly stimulatory, neutralizing antibodies against each of these agents did not affect CM-derived activity. In contrast to growth stimulation, differentiation of CM-treated NB cells, was reproducibly suppressed, as reflected in abrogation of neuronal cell morphology as well as of neurofilament and neuron specific enolase expression. Spontaneous regression of NB tumors, on one hand and BM metastasis on the other may be associated with the extent and nature of the NB cell response to regulatory activity released by BM and PB cells.
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