Development of systemic immunity to glioblastoma multiforme using tumor cells genetically engineered to express the membrane-associated isoform of macrophage colony-stimulating factor.

We investigated the ability of Fischer rat T9 glioblastoma cells transduced with cDNA genes for the secreted (s) or membrane-associated (m) isoform of M-CSF to elicit an antitumor response when implanted into syngeneic animals. Intracranial (i.c.) implantation of 1 x 10(5) T9 cells expressing mM-CSF (T9/mM-CSF) resulted in 80% tumor rejection. Electron microscopy of the T9/mM-CSF tumor site, 2-4 days postimplantation, showed marked infiltration by macrophages, many of which were in physical contact with the T9/mM-CSF cells. Animals that rejected T9/mM-CSF cells were resistant to i.c. rechallenge with T9 cells, but not syngeneic MadB106 breast adenocarcinoma cells, suggesting that T9-specific immunity can be generated within the brain via the endogenous APCs. Intracranial injection of parental T9, vector control (T9/LXSN), or T9 cells secreting M-CSF (T9/sM-CSF) was 100% fatal. Subcutaneous injection of 1 x 10(7) T9/sM-CSF, T9/LXSN, or parental T9 cells resulted in progressive tumors. In contrast, T9/mM-CSF cells injected s.c. were destroyed in 7-10 days and animals developed systemic immunity to parental T9 cells. Passive transfer of CD3+ T cells from the spleens of immune rats into naive recipients transferred T9 glioma-specific immunity. In vitro, splenocytes from T9/mM-CSF-immunized rats specifically proliferated in response to various syngeneic glioma stimulator cells. However, only marginal T cell-mediated cytotoxicity was observed by these splenocytes in a CTL assay against T9 target cells, regardless of restimulation with T9 cells. Subcutaneous immunization with viable T9/mM-CSF cells was effective in eradicating i.c. T9 tumors.