CD4 and Alzheimer disease: Recently, the first report of changes in PD-1/PD-L1 expression in earlier stages of AD was published, where PD-L1 expression was upregulated in certain subsets of T cells in individuals with mild AD (CDR stage 1; CD3+CD56+ T cells and CD4+CD25+ T cells) and moderate AD (CDR stage 2; CD4+ and CD8+ T cells) (90).