Enhancement of anti-tumor immunity specific to murine glioma by vaccination with tumor cell lysate-pulsed dendritic cells engineered to produce interleukin-12.

Aim: The aim of this study was to develop an immunotherapy specific to a malignant glioma by examining the efficacy of glioma tumor-specific cytotoxic T lymphocytes (CTL) as well as the anti-tumor immunity by vaccination with dendritic cells (DC) engineered to express murine IL-12 using adenovirus-mediated gene transfer and pulsed with a GL26 glioma cell lysate (AdVIL-12/DC+GL26) was investigated. EXPERIMENT1: For measuring CTL activity, splenocytes were harvested from the mice immunized with AdVIL-12/DC+GL26 and restimulated with syngeneic GL26 for 7 days. The frequencies of antigen-specific cytokine-secreting T cell were determined with mIFN-gamma ELISPOT. The cytotoxicity of CTL was assessed in a standard 51Cr-release assay. For the protective study in the subcutaneous tumor model, the mice were vaccinated subcutaneously (s.c) with 1x10(6) AdVIL-12/DC+GL26 in the right flanks on day -21, -14 and -7. On day 7, the mice were challenged with 1x10(6) GL26 tumor cells in the shaved left flank. For a protective study in the intracranial tumor model, the mice were vaccinated with 1x10(6) AdVIL-12/DC+GL26 s.c in the right flanks on days -21, -14 and -7. Fresh 1x10(4) GL26 cells were inoculated into the brain on day 0. To prove a therapeutic benefit in established tumors, subcutaneous or intracranial GL26 tumor-bearing mice were vaccinated s.c with 1x10(6) AdVIL-12/DC+GL26 on day 5, 12 and 19 after tumor cell inoculation.

Results: Splenocytes from the mice vaccinated with the AdVIL-12/DC+GL26 showed enhanced induction of tumor-specific CTL and increased numbers of IFN-gamma: secreting T cells by ELISPOT. Moreover, vaccination of AdVIL-12/DC+GL26 enhanced the induction of anti-tumor immunity in both the subcutaneous and intracranial tumor models.

Conclusions: These preclinical model results suggest that DC engineered to express IL-12 and pulsed with a tumor lysate could be used in a possible immunotherapeutic strategy for malignant glioma.