Intra-tumoral dendritic cells increase efficacy of peripheral vaccination by modulation of glioma microenvironment

Pilot data showed that adding intratumoral (IT) injection of dendritic cells (DCs) prolongs survival of patients affected by glioblastoma multiforme (GBM) treated by subcutaneous (SC) delivery of DCs. Using a murine model resembling GBM, we investigated the immunological mechanisms underlying this effect. C57BL6/N mice received brain injections of GL261 glioma cells. Seven days later, mice were treated by 3 SC injectionsof DCs with or without 1 IT injection of DCs. DC maturation, induced by pulsing with GL261 lysates, was necessary to develop effective immune responses. IT injection of pulsed (pDC), but not unpulsed DCs (uDC), increased significantly the survival, either per se or in combination with SC-pDC (P < .001 vs controls). Mice treated by IT-pDC plus SC-pDC survived longerthan mice treated by SC-pDC only (P 5 .03). Injected pDC were detectable in tumor parenchyma, but not in cervical lymph nodes. In gliomas injected with ITpDC, CD81 cells were significantly more abundant and Foxp31 cells were significantly less abundant than in other groups. Using real-time polymerase chain reaction, we also found enhanced expression of IFN-gand TNF-a and decreased expression of transforming growth factor-beta (TGF-b) and Foxp3 in mice treated with SC-pDC and IT-pDC. In vitro, pDC produced more TNF-a than uDC: addition of TNF-a to the medium decreased the proliferation of glioma cells. Overall, the results suggest that IT-pDC potentiates theanti-tumor immune response elicited by SC-pDC by pro-immune modulation of cytokines in the tumor microenvironment, decrease of Treg cells, and direct inhibition of tumor proliferation by TNF-a.