Generation of cytotoxic immune responses against a rat glioma by in vivo priming and secondary in vitro stimulation with tumor cells.

Cytotoxic T lymphocyte (CTL) responses to most antigens are generated by in vivo priming and secondary stimulation with antigen in vitro. The present studies were designed to determine whether that strategy could be used to stimulate development of CTL against brain tumors. Rats were primed with one of two tumors, RT2, an astrocytoma, or 9L, a gliosarcoma, and Corynebacterium parvum. Spleen cells from primed rats were stimulated with tumor cells and interleukin-2 in vitro to generate CTL. CTL generated against RT2 killed RT2 and 9L, but not allogeneic or histopathologically unrelated tumor cells, suggesting that the killing was brain tumor-specific and major histocompatibility complex gene product-restricted. Similar results were obtained with rats primed and secondarily stimulated with 9L. Specific cytotoxic cells only developed when syngeneic brain tumor cells were used for both priming and secondary stimulation. The cytotoxic cell populations were composed of OX-19+ T cells with a mixed CD4/CD8 phenotype. Controls consisting of spleen cells from unprimed or primed rats tested before culture exhibited low levels of cytotoxicity against brain tumor targets. Culturing unprimed or primed cells with interleukin-2 alone stimulated cell proliferation, but the cells that grew out exhibited only low levels of cytotoxicity for brain tumor cells. Cell populations exhibited consistent cytotoxicity against natural killer cell targets. None of the cell populations killed lymphokine-activated killer cell targets. The results demonstrated that brain tumor-specific CTL could be produced by priming in vivo followed by secondary stimulation with brain tumor cells in vitro. The results further demonstrated that RT2 and 9L share antigens that both induce and serve as target structures for specific cytotoxic cells.