Peripheral tolerance to tumor antigens is a major obstacle in antitumor immunity. Among the possible mechanisms are presentation of tissue-derived proteins by quiescent dendritic cells, suppression by regulatory immune cells and secretion of factors that suppress T cells leading to anergy or deletion. To investigate anti-tumor immune responses, Tumor (B16 transfected with ovalbumin) bearing mice were transferred with admixed naïve splenocytes from pmel-1 and OT-I.GFP mice. At several time points, cells were isolated from mice and tested. Tumor growth sufficiently induce proliferation and effector phenotype acquisition of pmel-1 and OT-I.GFP cells in the draining lymph nodes (T-DLNs). Pmel-1 cells were unable to mediate tumor regression and show impaired capacity of killing target cells or secretion of IFNγ. Within the tumor, pmel-1 cells proliferated extensively while their frequencies were decreasing rapidly. In contrast, OT-I.GFP cells were able to mediate tumor regression and killing capacity both in the tumor and in the periphery. While OT-I.GFP cells in the DLNs proliferated at low rates, extensive proliferation was detected in the tumor. Suggesting that tolerance followed by elimination of pmel-1 T cells develops already in the T-DLNs; indicating that lack of anti-tumor response efficacies are not solely due to general immunosuppressive mechanisms in the tumor microenvironment. Recently, we tested the involvement of the lymph node stroma in mediating CD8 T cell peripheral tolerance. We demonstrated that LN-resident lymphatic endothelial cells express peripheral tissue antigens and directly present the melanocyte protein PMEL17/gp100, to pmel-1 cells, resulting in their deletion, thus preventing a protective immune response.
