Neuroblastoma (NB), a tumor of the sympathetic nervous system, is the most common extracranial solid tumor in children. NB-derived gangliosides inhibit the functional activity of T and natural killer cells, contribute to tumor-induced bone marrow suppression, and cause multiple alterations of hematopoiesis, resulting in pancytopenia. However, the role of gangliosides in the regulation of dendritic cell (DC) generation (dendropoiesis) has not been studied. Using murine and human NB cell lines, we demonstrated that coincubation of murine bone marrow progenitors or human CD34+ progenitor cells with NB cells resulted in a significant inhibition of dendropoiesis in vitro up to 90%. The number of DCs was assessed by FACScan determination of CD83+ or CD11c+ cells coexpressing MHC class II and CD86 molecules. In addition, inhibition of antigen-presenting properties of DCs cultured in the presence of NB cells was observed in allogeneic mixed leukocyte reaction (33,508 +/- 1,613 cpm for control DCs versus 17,428 +/- 152 cpm for NB-treated DCs; P < 0.05). Treatment of NB cells with 10 microM DL-threo-1-phenyl-2-decanolylamine-3-morpholino-1-propanol HCl, an inhibitor of glucosylceramide synthase, markedly abrogated ganglioside synthesis and was accompanied by blockade of NB ability to inhibit dendropoiesis. Furthermore, purified gangliosides added to DC cultures significantly inhibited DC generation. The percentage of CD83+ cells decreased from 51.8 +/- 6.1% in the control group to 12.9 +/- 2.7% in cultures treated with GD2 (P < 0.05). Thus, our results demonstrate that NB-derived gangliosides inhibit the generation of functionally active DCs and may play a role in tumor-induced immunosuppression and subsequent tumor escape from immune recognition and elimination.