BACKGROUND: We are undertaking dendritic cell (DC) therapy against glioma stem-like cells (GSCs) with concomitant maintenance chemotherapy using temozolomide (TMZ). In general, anti-cancer agents are known to suppress immune response in patients. TMZ also suppresses immunity by inducing lymphopenia and myelosuppression in malignant glioma patients. However, there has been no study about the effect of TMZ on DC function. In this study, we evaluate whether concomitant TMZ affects DC function in vitro. METHODS: We isolated human blood plasmacytoid DCs (pDCs) and myelocytoid DCs (mDCs) from healthy volunteers by flow cytometry. These DC subsets were cultured in flat-bottomed 96-well plates at 5 × 104 cells in the final 200 µl of medium per well for 24 h. In the first set of experiment, we assessed cytotoxic activity of TMZ on DCs at clinically relevant concentration. After 24 h, viable cells were measured by a trypan-blue exclusion test. We next measured the Toll-like receptor ligand (TLRL) -induced cytokine production by DCs in the presence of TMZ. DC subsets were stained with FITC-labeled anti-CD83 and PE-labeled anti-CD86 antibody and then analyzed by FACS calibur. We also measured secreted IL-12p40 and IFN-alpha concentration in the supernatant of the cultures by ELISA. RESULTS: Analysis of trypan-blue exclusion of the dead cells showed that over 300 microM of TMZ started to kill both DC subsets and there was no cytocidal effect at 100 microM, a clinically relevant concentration. Therefore, we thereafter used 10 microM to 300 microM for the following assays. We found that TMZ did not affect IFN-alpha production by pDCs and IL-12 production by mDCs in response to various TLRLs. In addition, up to 100 microM of concentration, TMZ did not influence the CD83 and CD86 expression on both DC subsets. CONCLUSIONS: Temozolomide did not significantly affect on DC function, suggesting that DC therapy and concomitant chemotherapy using TMZ may be possible, although further assessment in the clinical setting is necessary. In the presentation, we also would like to present preliminary data on interaction between DCs and two types of GSCs (proneural and mesenchymal). SECONDARY CATEGORY: n/a.