AbstractMouse models in which tumors arise spontaneously due to the transgenic expression of an oncoprotein provide an opportunity to test approaches that target the immune-mediated control of tumor progression. In this report we investigated the role of SV40 Tag-specific CD8+ T cells in the control of advanced choroid plexus tumor progression using large tumor Ag (Tag) transgenic mice. Since mice of the SV11 line are tolerant to the immunodominant SV40 Tag-derived CTL epitopes, mice with advanced stage tumors were reconstituted with naive C57BL/6 spleen cells following a low dose of γ-irradiation. This led to the priming of CTLs specific for the H2-Kb-restricted epitope IV by the endogenous Tag and a significant increase in the life span of Tag transgenic mice. Epitope IV-specific CD8+ T cells accumulated and persisted in the brains and tumors of SV11 mice, as determined by analysis with epitope-specific MHC class I tetramers. Brain-infiltrating epitope IV-specific T cells were capable of producing IFN-γ as well as lysing syngeneic Tag-transformed cells in vitro. In addition, the adoptive transfer of spleen cells from Tag-immune C57BL/6 mice resulted in a dramatic increase in the control of tumor progression in SV11 mice and was associated with the accumulation of CD8+ T cells specific for multiple Tag epitopes in the brain. These results indicate that the control of advanced stage spontaneous choroid plexus tumors is associated with the induction of a strong and persistent CD8+ T cell response to Tag.