Dendritic cell counts and their subsets during treatment of multiple myeloma.

Human dendritic cells have distinct roles in the regulation of immunity. In this study we analysed the kinetics and the proportion of myeloid and plasmacytoid subsets of dendritic cells (DC) in peripheral blood of 15 patients with multiple myeloma (MM) before and during treatment that included autologous transplantation. Control group of 15 healthy volunteers was evaluated by using the same approaches. Flowcytometric determination of relative and absolute cell counts in unmanipulated peripheral blood was based on the expression of surface antigens CD83 and HLA-DR. Depending on the expression of CD11c or CD123, we divided these cells into CD11c+ dendritic cells type 1 (DC1) and CD123+ DC type 2 (DC2). Significant differences were found in initial relative counts of CD83+ cells and of the DC2 subtype between the group of controls and the group of patients before treatment. In absolute counts, there was a difference only in the DC2 subtype. After induction treatment (vincristine, doxorubicin, and dexamethasone), the mean percentage of CD83+ DC and the DC1 percentage were significantly higher than initially, but there was no significant difference in absolute counts. Administration of G-CSF again increased the total DC numbers. Intermediate DC counts were found in the apheresis products. After engraftment, we found the highest relative DC numbers, but absolute counts were not very high because of leukopenia. Within six months after transplantation, normal relative and absolute DC counts were found in patients. Untreated patients with MM have significantly lower relative numbers of peripheral blood DC in comparison with healthy volunteers. The highest number of total DC was found after engraftment. The DC1/DC2 ratio showed relative predominance of DC1 subtype and the lowest DC1/DC2 ratio was found in the apheresis products. DC counts comparable with those of healthy volunteers were found in patients six months after transplantation.