Intratumoral infiltration of plasmacytoid dendritic cells elicits immunological memory in a recurrent, syngeneic rat model of glioma Free

965

Tumor recurrence post-resection of glioblastoma multiforme (GBM) hinders the long-term efficacy of current treatment modalities. We tested the hypothesis that in a large syngeneic rat model of glioma, intra-tumoral expression of the immunostimulant, FMS-like tyrosine kinase 3 ligand (Flt3L) and conditionally cytotoxic HSV1-TK followed by treatment with ganciclovir (GCV) would induce dendritic cell recruitment into the tumor mass with concomitant release of tumor antigen for uptake and antigen presentation. If anti-tumor immunity initiated by this combined treatment initiates a Th1 immune response, long-term protection from tumor recurrence would be observed. Upon analysis 15 and 22 days after CNS-1 tumor implantation followed by treatment with adenovirally delivered Flt3L and HSV1-TK (+gancyclovir; GCV), we demonstrated infiltration of plasmacytoid dendritic cells (pDCs), B cells, macrophages, and NK cells within the tumor mass. PDCs isolated from treated tumors were capable of in vitro and in vivo antigen uptake and induced in vitro proliferation of T cells. These results suggest their capacity to act as antigen presenting cells. This combined treatment resulted in 80% survival and prevented the growth of a second tumor implanted in the contra lateral hemisphere in all long-term survivors. Immunological memory responses to CNS-1 tumors were dependent on the presence of CD8+ T cells at the time of rechallenge. Rapid rates of tumor mutation can limit immune mediated treatment efficacy. To test whether Flt3L and HSV1-TK treatment would be able to prevent tumor escape by recognizing tumor neo-antigens, CNS1 tumor survivors were rechallenged with CNS1 cells expressing hemagglutanin A (HA), a surrogate tumor neo-antigen. Rechallenge with CNS1-HA resulted in long-term survival and induction of an anti-HA immune response not observed in animals implanted with wild type CNS1 cells. Animals implanted with CNS1 tumors displayed amphetamine induced rotational preference, following tumor elimination, behavioral abnormalities resolved completely and fine motor skills were not disrupted. Neuropathological evaluation of long-term survivors after rechallenge shows low levels of immune infiltration restricted to the immediate tumor injection sites. In summary, Flt3L and HSV1-TK treatment GBM in rats induces infiltration of antigen presenting cells capable of inducing long term immunological memory.

Financial Support:

Funded by the NINDS grant # RO1 NS4456.01, RO3 TW006273-01 to MGC; NINDS grant #RO1 NS42893, U54 4 NS04-5309, and R21 NS47298 to PRL; the Linda Tallen & David Paul Kane Foundation; the Bram and Elaine Goldsmith Endowed Chair to PRL; the Medallions Group Endowed Chair to MGC and the BOG at CSMC. GDK is supported by NINDS F32 NS0503034-01.