PD-1 preserves skin cancer immunity in CD8 T cells.

A mouse model was developed to study the role of PD-1 in maintaining peripheral tolerance towards skin-specific antigens. PD-1 prevented tissue-infiltrating antigen-specific effector CD8 T cells from acquiring a pathogenic differentiation state, secreting effector molecules, and gaining access to epidermal antigen-expressing cells. In the absence of PD-1, epidermal antigen-expressing cells were eliminated by antigen-specific CD8 T cells, resulting in local pathology. The study supports a model of peripheral T cell tolerance in which PD-1 allows antigen-specific effector CD8 T cells to co-exist with antigen-expressing cells in tissues without immunopathology.