Two separate defects affecting true naive or virtual memory T cell precursors combine to reduce naive T cell responses with aging.

Naive T cell responses are eroded with aging. We and others have recently shown that unimmunized old mice lose ? 70% of Ag-specific CD8 T cell precursors and that many of the remaining precursors acquire a virtual (central) memory (VM; CD44(hi)CD62L(hi)...