ABSTRACT
Cross-presentation of normal self and candidate tumor Ags by bone marrow (BM)-derived APCs that have not been activated has been demonstrated as a major mechanism contributing to acquisition of tolerance by mature T cells that first encounter an Ag in the periphery (cross-tolerance). Following adoptive transfer of naive TCR-transgenic CD8(+) T cells into a host expressing a transgenic Ag that is a potentially targetable tumor Ag in normal hepatocytes as a self-Ag, we found that the majority of Ag-specific CD8(+) T cells were deleted, with the remaining cells rendered anergic. Studies in BM chimeric mice and with purified cell populations demonstrated that these events were not dependent on cross-presentation by BM-derived APCs including Kupffer cells or liver sinusoidal endothelial cells, and apparently can occur entirely as a consequence of direct recognition of Ag endogenously processed and presented by hepatocytes. Direct recognition of Ag-expressing hepatocytes in vivo induced a proliferative response and up-regulation of activation markers in responding CD8(+) T cells, but proliferating cells did not accumulate, with most cells rapidly eliminated, and the persisting T cells lost the capacity to proliferate in response to repeated Ag stimulation. The results suggest that parenchymal tissues may retain the capacity to directly regulate in vivo responses to self-Ags processed and presented in the context of class I MHC molecules.
Subject(s)
Autoantigens/immunology , CD8-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/metabolism , Cross-Priming/immunology , Liver/immunology , Liver/metabolism , Self Tolerance/immunology , Animals , Autoantigens/biosynthesis , Autoantigens/genetics , CD8-Positive T-Lymphocytes/cytology , CD8-Positive T-Lymphocytes/virology , Cell Line, Tumor , Cells, Cultured , Cross-Priming/genetics , Epitopes, T-Lymphocyte/immunology , Friend murine leukemia virus/immunology , Gene Products, gag/biosynthesis , Gene Products, gag/genetics , Gene Products, gag/immunology , Lymphocyte Depletion , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Transgenic , Resting Phase, Cell Cycle/genetics , Resting Phase, Cell Cycle/immunology , Self Tolerance/genetics , Serum Albumin/genetics , Serum Albumin/immunologyABSTRACT
CD8+ T cells can mediate eradication of established tumors, and strategies to amplify tumor-reactive T-cell numbers by immunization or ex vivo expansion followed by adoptive transfer are currently being explored in individuals with cancer. Generating effective CD8+ T cell-mediated responses to tumors is often impeded by T-cell tolerance to relevant tumor antigens, as most of these antigens are also expressed in normal tissues. We examined whether such tolerant T cells could be rescued and functionally restored for use in therapy of established tumors. We used a transgenic T-cell receptor (TCR) mouse model in which peripheral CD8+ T cells specific for a candidate tumor antigen also expressed in liver are tolerant, failing to proliferate or secrete interleukin (IL)-2 in response to antigen. Molecular and cellular analysis showed that these tolerant T cells expressed the IL-15 receptor alpha chain, and could be induced to proliferate in vitro in response to exogenous IL-15. Such proliferation abrogated tolerance and the rescued cells became effective in treating leukemia. Therefore, high-affinity CD8+ T cells are not necessarily deleted by encounter with self-antigen in the periphery, and can potentially be rescued and expanded for use in tumor immunotherapy.