Rapid accumulation of adoptively transferred CD8\u3csup\u3e+\u3c/sup\u3e T cells at the tumor site is associated with long-term control of SV40 T antigen-induced tumors

We previously established a model to study CD8+ T cell (T CD8)-based adoptive immunotherapy of cancer using line SV11 mice that develop choroid plexus tumors in the brain due to transgenic expression of Simian Virus 40 large T antigen (Tag). These mice are tolerant to the three dominant TCD8-recognized Tag epitopes I, II/III and IV. However, adoptive transfer of spleen cells from naïve C57BL/6 (B6) mice prolongs SV11 survival following TCD8 priming against the endogenous Tag epitope IV. In addition, survival of SV11 mice is dramatically increased following transfer of lymphocytes from Tag-immune B6 mice. In the current study, we compared the kinetics and magnitude of Tag-specific TCD8 accumulation at the tumor site following adoptive transfer with a high dose of either Tag-immune or naïve donor cells or decreasing doses of Tag-immune lymphocytes. Following adoptive transfer of Tag-immune cells, epitope I- and IV-specific TCD8 accumulated to high levels in the brain of SV11 mice, peaking at 5-7 days, while epitope IV-specific TCD8 derived from naïve donors required three weeks to achieve peak levels. A similar delay in the peak of epitope IV-specific TCD8 accumulation was observed when tenfold fewer Tag-immune donor cells were administered, reducing control of tumor progression. These results suggest that efficient and prolonged control of established autochthonous tumors is associated with high-level early accumulation of adoptively transferred T cells. We also provide evidence that although multiple specificities are represented in the Tag immune donor lymphocytes, epitope IV-specific donor TCD8 play a predominant role in control of tumor growth. © 2007 Springer-Verlag

Inefficient Cross-Presentation Limits the Cd8+ T Cell Response to a Subdominant Tumor Antigen Epitope

CD8+ T lymphocytes (TCD8) responding to subdominant epitopes provide alternate targets for the immunotherapy of cancer, particularly when self-tolerance limits the response to immunodominant epitopes. However, the mechanisms that promote TCD8 subdominance to tumor Ags remain obscure. We investigated the basis for the lack of priming against a subdominant tumor epitope following immunization of C57BL/6 (B6) mice with SV40 large tumor Ag (T Ag)-transformed cells. Immunization of B6 mice with wild-type T Ag-transformed cells primes TCD8 specific for three immunodominant T Ag epitopes (epitopes I, II/III, and IV) but fails to induce TCD8 specific for the subdominant T Ag epitope V. Using adoptively transferred T CD8 from epitope V-specific TCR transgenic mice and immunization with T Ag-transformed cells, we demonstrate that the subdominant epitope V is weakly cross-presented relative to immunodominant epitopes derived from the same protein Ag. Priming of naive epitope V-specific TCR transgenic TCD8 in B6 mice required cross-presentation by host APC. However, robust expansion of these TCD8 required additional direct presentation of the subdominant epitope by T Ag-transformed cells and was only significant following immunization with T Ag-expressing cells lacking the immunodominant epitopes. These results indicate that limited cross-presentation coupled with competition by immunodominant epitope-specific TCD8 contributes to the subdominant nature of a tumor-specific epitope. This finding has implications for vaccination strategies targeting TCD8 responses to cancer. © 2005 The American Association of Immunologists, Inc