Chronic viral infections exhibit great phenotypic T-cell heterogeneity and T-cell phenotypes predominantly found during latent infection are: hepatitis C virus (HCV) (CCR7+CD27+CD28+), EBV (CCR7−CD27+CD28+), human immunodeficiency virus (HIV) (CD45RA−CCR7−CD27+CD28+) [36], and CMV (CD45RA+CCR7−CD27−CD28−) [35,37,38]. This evidence concerns the gene CD28 and viral infectious disease.