Rapid loss of adoptively transferred tumor-specific CD8(+) T cells (T(CD8)) following Ag recognition in the periphery and their limited accumulation within the tumor stroma reduces the effectiveness of T cell-based immunotherapy. To better understand the role of T(CD8) in the control of autochthonous tumors, we have used mice of the RIP1-Tag4 lineage that develop pancreatic beta cell tumors due to expression of the SV40 large T Ag from the rat insulin promoter. We previously showed that the kinetics of functional T(CD8) tolerance varies toward two distinct epitopes derived from T Ag. Epitope I ((206)SAINNYAQKL(215))-specific T(CD8) are rapidly deleted whereas T(CD8) targeting epitope IV ((404)VVYDFLKC(411)) persist over the lifetime of tumor-bearing animals. In this report, we show that the conditioning of tumor-bearing RIP1-Tag4 mice with agonistic anti-CD40 Ab induces extensive expansion of naive epitope I-specific TCR transgenic (TCR-I) T cells in this tolerogenic environment and delays their loss from the host. In addition, functional TCR-I T cells intensively infiltrate pancreatic tumors, resulting in increased survival of RIP1-Tag4 mice. These results suggest that a similar approach could effectively enhance T cell-based immunotherapies to cancer when targeting other highly tolerogenic epitopes.