Plasmacytoid dendritic cells mediate glioma regression and immunological memory in a syngeneic rat model. Free

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Rapid rates of tumor mutation and tumor recurrence post-glioma resection hinder the long-term efficacy of current treatment modalities. In a large syngeneic rat model of glioma we tested whether Flt3L and HSV1-TK expression would induce intra-tumoral recruitment of dendritic cells capable of antigen presentation. Fifteen and twenty-two days after tumor implantation, treatment with adenovirus (Ad) encoding Flt3L and HSV1-TK induced infiltration of plasmacytoid Dendritic cells, B cells, macrophages, and NK cells. Plasmacytoid DCs isolated from treated tumors were capable of in vitro antigen uptake and did not express MHC II or CD86 on their cell surface suggestive of an immature phenotype. PDCs induced in vitro allogenic T cell proliferation suggesting that they can present antigen to T cells. Tumor antigen specific T cells were detected by IFNγ elispot. We examined long-term efficacy of Flt3L and TK treatment to prevent tumor recurrence. 100% of animals rechallenged with GBM in the contralateral hemisphere, 60 days after primary GBM implantation survived long term and exhibited INFγ secreting, tumor antigen specific Tcells. Immunological memory responses to CNS-1 tumors were dependent on the presence of CD8+ cells as their depletion abrogated survival. Since pDCs serve as the major secretory cell for IFNα, we aimed to test if this cytokine would elicit similar effects as Flt3L. In a small tumor model IFNα alone was sufficient to induce 50% survival. However in a large tumor model IFNα was not effective. When IFNα was expressed with TK in tumor bearing rats ~50% survival was observed in a large tumor model. Expression of IFNα alone or with TK in naïve rat brain resulted in extensive damage to the striatum, dramatic weight loss, leukopenia and the infiltration of CD68, CD8 and MHCII expressing cells into the brain. Unlike Ad-Flt3L/Ad-TK, use of Ad-IFNα induced gross neuropathological abnormalities to the striatum and severe systemic adverse side effects. In conclusion, Ad-Flt3L/Ad-TK treatment of glioma induces infiltration of antigen presenting cells capable of inducing adaptive immune responses without toxic side effects and warrant further development of this therapeutic approach for the implementation of a clinical trial for GBM. Funding: NIH/NINDS Grant 1R01 NS44556.01; 1R21-NSO54143.01; 1UO1 NS052465.01 to M.G.C.; NIH/NINDS Grants 1 RO1 NS 054193.01; RO1 NS 42893.01, U54 NS045309-01 and 1R21 NS047298-01 to P.R.L. The Bram and Elaine Goldsmith and the Medallions Group Endowed Chairs in Gene Therapeutics to PRL and MGC, respectively, The Linda Tallen & David Paul Kane Foundation Annual Fellowship and the Board of Governors at CSMC. GDK is supported by NIH/NINDS 1F32 N50503034-01. M.C is supported by NIH/NINDS 1F32 NS058156.01.