Persistent IL-10 production is required for glioma growth suppressive activity by Th1-directed effector cells after stimulation with tumor lysate-loaded dendritic cells.

Injection of dendritic cells (DC) pulsed with tumor antigens is a novel treatment strategy against malignancies, and aims to elicit anti-tumoral cell-mediated immune responses. We studied the in vitro proliferative responses and cytokine production in T cell cultures after 2 stimulations with autologous DC loaded with tumor lysates derived from glioblastoma multiforme (GBM) cells in the presence of recombinant interleukin (rIL)-6/rIL-12 in the first, and rIL-2/rIL-7 in the second stimulation. After the second stimulation, T cells were co-cultured with glioblastoma (GBM) cells and tumor growth suppression by T cells was assessed using a MTT assay. Although loaded DC induced a significant shift towards T helper cell type 1 (Th1) cytokine production as compared to unloaded DC, persistent interleukin (IL)-10 production by T cells both at the end of 2 stimulations with loaded DC and during the effector phase was also required for their tumor suppressive activity. A stronger glioma growth suppressive activity by T cells stimulated with tumor lysate-loaded DC than by control T cells, cultured with unloaded DC, was seen only if the relative IL-10 production after two stimulations with loaded DC was at least 40% of the IL-10 production after two stimulations with unloaded DC. If less than 40% IL-10 was produced in the experimental condition compared to the control condition, T cells also lost their tumor growth suppressive activity. Addition of rIL-10 during stimulation increased the suppressive activity on tumor cell viability and interferon (IFN)-gamma production by T cells that showed Th1 response upon stimulation with loaded DC. The data point towards the production of both IFN-gamma and IL-10 by responding effector T cells, and towards an immune modulatory rather than immune suppressive role of IL-10 to generate anti-tumoral effector T cells against GBM.