Different contribution of EBV and CMV infections in very long-term carriers to age-related alterations of CD8+ T cells

Aging is accompanied by a complex dynamics of CD8⁺ T cell subsets whose origin is unclear. To evaluate the impact of Epstein-Barr virus (EBV) and cytomegalovirus (CMV) chronic infections on CD8⁺ T cells in far advanced age, we studied CD8⁺ T cells frequencies and phenotype in nonagenarians and centenarians by HLA-A*0201- and HLA-B*0702- tetramers incorporating epitopes specific of both viruses along with viral replication. The results demonstrate that EBV and CMV infections induce quantitatively and qualitatively different CD8⁺ T-cell responses in advanced aging. The frequency and absolute number of CD8⁺ T cells specific for one lytic and two latent EBV-epitopes, were relatively low and mostly included within CD8⁺ CD28⁺ cells. By contrast, CMV infection was characterized by highly variable numbers of CD8⁺ T cells specific for two differently restricted CMV-epitopes that, in some subjects, were strikingly expanded. Moreover, the great majority of anti-CMV CD8⁺ T cells did not bear CD28 antigen. Notwithstanding the expansion of CMV-specific CD8⁺ lymphocytes, CMV-DNA detection in blood samples was invariably negative. Altogether, we suggest that CMV, but not EBV, can sustain chronic activation of the HLA-class I restricted effector arm in elderly that might have detrimental effects on age-associated diseases.