Interleukin-12-based immunotherapy against rat 9L glioma

Interleukin-12 (IL-12) may be useful for immunotherapy against gliomas because it can reverse the glioma-induced suppression of T-cell proliferation and interferon-gamma production. We postulated that peripheral infusion of IL-12 along with irradiated tumor cells can lead to immunological rejection of 9L glioma.

9L gliosarcoma flank tumors were established in syngeneic Fischer 344 rats. Osmotic minipumps delivered IL-12 subcutaneously, and irradiated 9L cells were injected on Days 0, 3, 7, 14, and 21. Tumor volumes were measured by a blinded observer. For tumor rechallenge, animals initially cured of 9L flank tumors received either another implantation of flank tumor or a stereotactic injection of 10(6) 9L cells into the right striatum. Delayed-type hypersensitivity was measured after injecting 10(6) irradiated 9L tumor cells into the right pinnae.

Tumor growth curves were significantly different between treated and control animals. Among the animals that received 1 ng per day of IL-12, 40% did not develop any measurable tumors at all. A combination of irradiated 9L cells and IL-12 was necessary for optimal effect. Cured animals rejected future flank tumors. All animals rechallenged with intraparenchymal brain tumors survived, whereas control animals all died by Day 22. Delayed-type hypersensitivity measurements showed a specific and long-lasting response against 9L cells.

Continuous administration of the lymphokine IL-12, in the presence of irradiated tumor cells for antigen presentation, circumvents the need for gene transfection for generating tumor cell vaccines. We have demonstrated that the combination of IL-12 and irradiated tumor cells can lead to regression of 9L flank tumors and resistance to future flank and central nervous system tumor challenges.