No abstract

The human tyrosinase-derived peptide YMDGTMSQV is presented on the surface of human histocompatibility leukocyte antigen (HLA)-A*0201+ melanomas and has been suggested to be a tumor antigen despite the fact that tyrosinase is also expressed in melanocytes. To gain information about immunoreactivity and self-tolerance to this antigen, we established a model using the murine tyrosinase-derived homologue of this peptide FMDGTMSQV, together with transgenic mice expressing the HLA-A*0201 recombinant molecule AAD. The murine peptide was processed and presented by AAD similarly to its human counterpart. After immunization with recombinant vaccinia virus encoding murine tyrosinase, we detected a robust AAD-restricted cytotoxic T lymphocyte (CTL) response to FMDGTMSQV in AAD transgenic mice in which the entire tyrosinase gene had been deleted by a radiation-induced mutation. A residual response was observed in the AAD+tyrosinase+ mice after activation under certain conditions. At least some of these residual CTLs in AAD+tyrosinase+ mice were of high avidity and induced vitiligo upon adoptive transfer into AAD+tyrosinase+ hosts. Collectively, these data suggest that FMDGTMSQV is naturally processed and presented in vivo, and that this presentation leads to substantial but incomplete self-tolerance. The relevance of this model to an understanding of the human immune response to tyrosinase is discussed.

The expansion of CD8+ T cells in response to Ag can be characterized as either dependent or independent of CD4+ T cells. The factors that influence this dichotomy are poorly understood but may be dependent upon the degree of inflammation associated with the Ag. Using dendritic cells derived from MHC class II-deficient mice to avoid interaction with CD4+ T cells in vivo, we have compared the immunogenicity of peptide-pulsed dendritic cells stimulated with molecules associated with infection to those stimulated via CD40. In the absence of CD4+ T cell help, the expansion of primary CD8+ T cells after immunization with TNF-α- or poly(I:C)-stimulated dendritic cells was minimal. In comparison, LPS- or CpG-stimulated dendritic cells elicited substantial primary CD8+ T cell responses, though not to the same magnitude generated by immunization with CD40L-stimulated dendritic cells. Remarkably, mice immunized with any stimulated dendritic cell population generated fully functional recall CD8+ T cells without the aid of CD4+ T cell help. The observed hierarchy of immunogenicity was closely correlated with the expression of CD70 (CD27L) on the stimulated dendritic cells, and Ab-mediated blockade of CD70 substantially prevented the CD4+ T cell-independent expansion of primary CD8+ T cells. These results indicate that the expression of CD70 on dendritic cells is an important determinant for helper-dependence of primary CD8+ T cell expansion and provide an explanation for the ability of a variety of pathogens to stimulate primary CD8+ T cell responses in the absence of CD4+ T cells.

We have established that the route of immunization with peptide-pulsed, activated DC leads to memory CD8+ T cells with distinct distributions in lymphoid tissues, which determines the ability to control tumors growing in different body sites. Both intravenous (i.v.) and subcutaneous (s.c.) immunization induced memory T cells in spleen and control of metastatic-like lung tumors. s.c. immunization also induced memory T cells in lymph nodes (LNs), imparting protection against subcutaneously growing tumors. In contrast, i.v. immunization-induced memory was restricted to spleen and failed to impart protective immunity against subcutaneously growing tumors. Memory cell distribution and tumor control were both linked to injection route–dependent localization of DCs in lymphoid compartments. Using peripheral LN–ablated mice, these LNs were shown to be essential for control of subcutaneously growing tumors but not lung metastases; in contrast, using immunized asplenic mice, we found that the spleen is necessary and sufficient for control of lung tumors, but unnecessary for control of subcutaneously growing tumors. These data demonstrate the existence of a previously undescribed population of splenic-resident memory CD8 T cells that are essential for the control of lung metastases. Thus, regional immunity based on memory T cell residence patterns is an important factor in DC-based tumor immunotherapy.