Neuroblastoma (NB) is the most common childhood solid tumor. Although spontaneous regression can occur in patients <1-year old, 70% of patients over the age of 1 year have a high-risk and difficult-to-treat NB. Cell type heterogeneity is observed either in the morphological appearance of NB tumors or in cell lines isolated from tumor specimens. NB consists of two principal neoplastic cell types: i) neuroblastic or N-type (undifferentiated cells); and ii) stromal or S-type (differentiated cells). As NB cells seem to have the capacity to differentiate spontaneously in vivo and in vitro, their heterogeneity could affect treatment outcome, in particular the response to apoptosis induced by chemotherapy. Therefore, it is important to understand the underlying process governing changes in differentiation in order to improve treatment response and NB patient outcome and the neoplastic population in IMR-32 represented a good model for such a study. Results showed that this cell line was extremely heterogeneous and highly variable in its stage of differentiation and we demonstrated that sedimentation field flow fractionation (SdFFF) permitted the isolation of 2 N-phenotypes and contributed to the understanding of the IMR-32 cell population dynamics. The first N-phenotype forms a pool of quiescent undifferentiated cells while the second one was able to proliferate (incorporation of BrdU) and also give rise to adherent S-type cells (PSA-N-CAM+ and N-CAM+). The results could also suggest a close interaction between these different cellular phenotypes to create the IMR-32 cell lineage.

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