ABSTRACT
PURPOSE: alpha-Galactosylceramide (alpha-GalCer)-stimulated human Valpha24 natural killer T (NKT) cells exert antitumor activity against some leukemia in a CD1d dependent and TCR-mediated manner, but could not kill CD1d-negative neuroblastoma (NB) cells. There are few reports about the direct antitumor effect of highly secreted cytokines by these cells on activation. In this study, using a cell-free supernatant (SPN) collected from plate bound hCD1d/alphaGalCer tetramers-stimulated NKT cells, we examined whether they could be helpful in the immunotherapeutic treatment of NB. METHODS: Cells were cultured in IMDM. The cytokines produced by NKT cells were measured with Cytometric Bead Array (CBA) analysis. Cell viability was evaluated by calcein-AM fluorescence with digital image microscopy scanning (DIMSCAN). The percentage of specific apoptosis was calculated by flow cytometric detection of apoptosis using annexin V and 7-AAD. RESULTS: The activated NKT cells secreted high levels of IL-2, INF-gamma, TNF-alpha. The SPN was significantly cytotoxic against four out of eight tested NB cell lines, through mainly apoptosis as evidenced by annexin-V staining and inhibition with the pretreatment of pancaspase blocker. This apoptosis was significantly inhibited when anti-TNF-alpha and anti-IFN-gamma neutralizing mAbs were used separately and it was completely abolished when the two mAbs were combined. CONCLUSION: IFN-gamma and TNF-alpha produced by NKT cells could exert synergistically direct anti-tumor activity through apoptosis on some NB cell lines.