Human memory T cell pools proliferate and differentiate at varying rates that are determined
by the frequency of lifelong antigenic re-encounter with different specific antigens. An
important question concerning immunity is whether certain specific pools of memory T cells
are driven to exhaustion in elderly subjects, a pertinent point in view of increasing human life
expectancy. An emerging consensus is that cytomegalovirus (CMV), a β-herpesvirus with a
prevalence of 60–90% worldwide, is an agent that induces specific T cells to extreme …

E vidence is accumulating that old individuals are more susceptible to infection with
organisms to which they were previously immune, indicating that there might be a limit to the
persistence of immune memory. The prevailing concept is that defects in memory T-cell
populations result from inexorable end-stage differentiation as a result of repeated lifelong
antigenic challenge. We discuss here mechanisms that might constrain the persistence of
memory T cells and consider whether humans will suffer from memory T-cell exhaustion as …