Androgen ablation mitigates tolerance to a prostate/prostate cancer-restricted antigen

To understand the T cell response to prostate cancer, we created transgenic mice that express a model antigen in a prostate-restricted pattern and crossed these animals to TRAMP mice that develop spontaneous prostate cancer. Adoptive transfer of prostate-specific CD4 T cells shows that, in the absence of prostate cancer, the prostate gland is mostly ignored. Tumorigenesis allows T cell recognition of the prostate gland--but this recognition is tolerogenic, resulting in abortive proliferation and ultimately in hyporesponsiveness at the systemic level. Androgen ablation (the most common treatment for metastatic prostate cancer) was able to mitigate this tolerance--allowing prostate-specific T cells to expand and develop effector function after vaccination. These results suggest that immunotherapy for prostate cancer may be most efficacious when administered after androgen ablation.

CD4 cell priming and tolerization are differentially programmed by APCs upon initial engagement

Bone marrow-derived APCs present both parenchymal-self and pathogen-derived Ags in a manner that elicits either T cell tolerization or immunity, respectively. To study the parameters that confer tolerogenic vs immunogenic APC function we used an adoptive transfer system in which naive TCR transgenic hemagglutinin (HA)-specific CD4(+) T cells are either tolerized upon encountering HA expressed constitutively as a parenchymal self-Ag (self-HA) or primed to express effector function upon encountering transiently expressed vaccinia-derived HA (viral-HA). When the duration of viral-HA presentation was extended for the period required to elicit tolerization toward self-HA, CD4 cell tolerization to viral-HA did not occur. Furthermore, CD4 cells exhibited both phenotypic as well as functional differences during early stages of tolerization and priming, suggesting that these divergent differentiation processes are programmed soon after the initial APC-CD4 cell interaction. When mice expressing self-HA were infected with an irrelevant vaccinia, CD4 cell tolerization still occurred, indicating that priming vs tolerization cannot be explained by pathogen-induced third parties (i.e., non-APCs) that act directly on CD4 cells. Taken together, these results suggest that CD4 cell tolerization to parenchymal self-Ags and priming to pathogen-derived Ags are initiated by functionally distinct APCs.