The Raji-A2 SEB T cell assay models the activation of an antigen-experienced T cell population, predominantly CD4+PD-1+ T cells, by APCs while the killing studies with insulin-specific CD8+ T cell clones model the recognition of self-peptide HLA on pancreatic islet β cells by autoreactive CD8+ T cells and ensuing β cell destruction that occurs in type 1 diabetes. This evidence concerns the gene PDCD1 and type 1 diabetes mellitus.