Cho, Hyun-II

Abstract Tumor antigen-specific T-cell tolerance is a critical element of tumor escape. It is known that MDSC can induce antigen-specific CD8+ T cell tolerance in an experimental system with adoptive transfer of transgenic T cells. In this study we addressed the critical question whether a similar phenomenon can be observed in a "natural" non-transgenic experimental model. Balb/C mice were subcutaneously inoculated with two different tumor cell lines, a derivative A2L2 cell line, which expresses high levels of HER2/neu and the parental cell line 66.3. HER2/neu specific CD8+T cells were generated by immunization of mice with peptide. MDSC were able to tolerize antigen-specific T cells in vivo if they were collected from A2L2 but not from 66.3 tumor-bearing mice indicating the tumor-specific nature of T cell tolerance induced by MDSC. Next we investigated the type of signaling caused by MDSC in CD8+T cells that could lead to tolerance. MDSC dramatically reduced the ability of CD8+ T cells to respond to the specific peptide. However, study of various signaling molecules using different experimental systems and tests found that MDSC did not induce negative signaling in T cells. This conclusion was confirmed in adoptive transfer experiments with CD8+T cells expressing dual TCR: LCMV glycoprotein peptide gp33-41 and OVA-derived H-2Kb-restricted peptide ova257-264. We found that MDSC loaded with peptide specific for one TCR induced tolerance only against that specific epitope but CD8+ T cells retained the ability to respond to the peptide specific for the other TCR expressed on the same cell.