621. Immunological Memory in a Syngeneic Model of Recurrent and Multifocal Glioblastoma
Authors: Gwendalyn D. King, James F. Curtin, Chunyan Liu, Catherine Bresee, Sarah B. Honig, Jeffery M. Zirger, Nico VanRooijen, Antoni Ribas, Robert Pechnick, Pedro R. Lowenstein, Maria G. Castro
Journal: Molecular Therapy (2006)

Lack of novel and efficacious treatments for glioma make it an attractive candidate for treatment by gene therapy. Expression of the conditional cytotoxic Ad-HSV1-TK plus GCV and the immune stimulatory molecule, i.e., Flt3L, induces complete glioma regression of a large, syngeneic, intracranial, CNS1 tumor model in 70% of the tumor bearing rats. Tumor regression is mediated by helper T-cells and macrophages. We sought to characterize the early immunological mediators of anti-tumor immune responses and to examine long-term efficacy of Ad-HSV1-TK+GCV and Ad-Flt3L treatment. Immune cells' infiltration during tumor regression was examined five and twelve days after treatment. Our data showed increased infiltration of NK and macrophages five days, plasmacytoid DCs five and twelve days, and B cells twelve days after treatment. As measured by IFN gamma release upon in vitro stimulation, CTLs were also induced. The combined therapy resolved the primary treated tumor mass and a distant, untreated tumor mass in 50% of animals. Induction of immunological memory was also elicited by the combined therapy as measured by adoptive transfer and tumor rechallenge paradigms. Depletion of CD8+ T cells at rechallenge, blocked immune memory responses resulting in death of the rechallenged animals. Systemic cellular immune-surveillance as determined by delayed type hypersensitivity was present 8 months after initial tumor implantation in the treated animals. Animals surviving over 8 months from initial tumor implantation displayed no behavioral abnormalities or widespread inflammation in the brain. Glioma treatment using Ad-HSV1-TK and AdFlt3L in rats induced anti-tumor innate and adaptive immune responses capable of eliminating disseminated disease and inducing long-term memory without overt adverse side effects. Lack of novel and efficacious treatments for glioma make it an attractive candidate for treatment by gene therapy. Expression of the conditional cytotoxic Ad-HSV1-TK plus GCV and the immune stimulatory molecule, i.e., Flt3L, induces complete glioma regression of a large, syngeneic, intracranial, CNS1 tumor model in 70% of the tumor bearing rats. Tumor regression is mediated by helper T-cells and macrophages. We sought to characterize the early immunological mediators of anti-tumor immune responses and to examine long-term efficacy of Ad-HSV1-TK+GCV and Ad-Flt3L treatment. Immune cells' infiltration during tumor regression was examined five and twelve days after treatment. Our data showed increased infiltration of NK and macrophages five days, plasmacytoid DCs five and twelve days, and B cells twelve days after treatment. As measured by IFN gamma release upon in vitro stimulation, CTLs were also induced. The combined therapy resolved the primary treated tumor mass and a distant, untreated tumor mass in 50% of animals. Induction of immunological memory was also elicited by the combined therapy as measured by adoptive transfer and tumor rechallenge paradigms. Depletion of CD8+ T cells at rechallenge, blocked immune memory responses resulting in death of the rechallenged animals. Systemic cellular immune-surveillance as determined by delayed type hypersensitivity was present 8 months after initial tumor implantation in the treated animals. Animals surviving over 8 months from initial tumor implantation displayed no behavioral abnormalities or widespread inflammation in the brain. Glioma treatment using Ad-HSV1-TK and AdFlt3L in rats induced anti-tumor innate and adaptive immune responses capable of eliminating disseminated disease and inducing long-term memory without overt adverse side effects.