Although the ME7 model of prion disease is not dominated by T cell responses, there is a trend towards increased numbers of T cells in WT mice, but no further increase of T cell frequencies during the course of pathology in PD-1 KO mice was observed, indicating that in terms of prion pathology T cell responses do not seem to contribute to disease phenotype in the absence of PD-1. This evidence concerns the gene PDCD1 and prion disease.