In vivo modulation of T cell responses and protective immunity by TCR antagonism during infection.

Infectious agents are known to express altered peptide ligands that antagonize T cells in vitro; however, direct evidence of TCR antagonism during infection is still lacking, and its importance in the context of infection remains to be established. In this study, we used a murine model of infection with recombinant Listeria monocytogenes and addressed three issues that are critical for assessing the role of TCR antagonism in the modulation of the immune response. First, we demonstrated that the antagonist peptide efficiently inhibited the ability of the agonist to prime naive TCR-transgenic T cells in vivo. Second, we showed clonal memory T cells were antagonized during recall responses, resulting in loss of protective immunity. Lastly, we observed that even in the context of a polyclonal response, TCR antagonism greatly inhibits the agonist-specific response, leading to altered hierarchy of immunodominance and reduced T cell memory and protective immunity. These results provide direct evidence of clonal TCR antagonism of naive and memory CD8 T cells during infection and demonstrate the effect of TCR antagonism on protective immunity. Thus, agonist/antagonist interactions may play an important role in determining the immunodominance and repertoire of T cell targets, and evaluation of immune responses and vaccine strategies may require examination of not only agonists but also antagonists and their interactions during an infection.