Peripheral immunization against malignant rat glioma can induce effective antitumor immunity in the brain

Using two malignant rat glioma cell lines, we tested to what extent peripheral immunization could affect tumor growth in the brain of syngeneic rats. Peripheral subcutaneous (s.c.) immunization was performed with autologous Newcastle-disease-virus (NDV)-infected or non-infected live tumor cells. Thus immunized rats or non-immunized controls were intracerebrally implanted with increasing numbers of the respective malignant glioma cells. Without immunization the mean survival time after intracerebral implantation of 1x10(4) TZ363 or RG2 glioma cells was 9 and 29 days respectively. After s.c. immunization with either NDV-infected or non-infected TZ363 cells only 25% or less of challenged animals developed tumors in the brain. Immunization with NDV only had no effect. In RG2 glioma, s.c. immunization had no effect on tumor growth in the central nervous system and on survival time, no matter what kind of vaccine was used. These results clearly show, that in principle the efferent arm of the anti-tumor response can be effective accross the blood-brain barrier and extend into the microenvironment of the central nervous system. Whether or not glioma lines can induce this immunity and respond to it, seems to depend on their individual immunobiological characteristics.