Longterm maintenance of human naive T cells through in situ homeostasis in lymphoid tissue sites.

Naïve T cells develop in the thymus and coordinate immune responses to new antigens; however, mechanisms for their long-term persistence over the human lifespan remain undefined. Here, we investigated human naïve T cell development and maintenance in primary and secondary lymphoid tissues obtained from individual organ donors aged 3 months-73 years. In the thymus, the frequency of double-positive thymocytes declined sharply in donors over age 40 coincident with reduced recent thymic emigrants (RTE) in lymphoid tissues, while naïve T cells were functionally maintained predominantly in lymph nodes (LN). Analysis of TCR clonal distribution by CDR3 sequencing of naïve CD4 ⁺ and CD8 ⁺ T cells in spleen and LNs reveal site-specific clonal expansions of naïve T cells from individuals >40 years of age with minimal clonal overlap between lymphoid tissues. We also identified biased naïve T cell clonal distribution within specific lymph nodes based on VJ usage. Together these results suggest prolonged maintenance of naïve T cells through in situ homeostasis and retention in lymphoid tissue.