Resident regulatory T cells reflect the immune history of individual lymph nodes.

Regulatory T cells (Treg) are present in lymphoid and non-lymphoid tissues where they restrict immune activation, prevent autoimmunity and regulate inflammation. Treg in non-lymphoid tissues are typically resident, while those in lymph nodes (LNs) are considered to recirculate. However, Treg in LNs are not a homogenous population and circulation kinetics of different Treg subsets are poorly characterized. Furthermore, whether Treg can acquire memory T cell properties and persist for extended periods after their activation in LNs is unclear. Here, we used in situ labeling with a stabilized photoconvertible protein to uncover turnover rates of Treg in LNs in vivo . We found that while the majority of Treg in LNs recirculate, 10-20% are memory-like resident cells that remain in their respective LNs for weeks to months. Single cell RNA sequencing revealed that LN-resident cells are a functionally and ontogenetically heterogeneous population and share the same core residency gene signature with conventional CD4 + and CD8 + T cells. Resident cells in LNs did not actively proliferate and did not require continuous TCR signaling for their residency. Yet, resident and circulating Treg had distinct TCR repertoires, and each LN contained exclusive clonal subpopulations of resident Treg. Our results demonstrate that, similar to conventional T cells, Treg can form resident memory-like populations in LNs after adaptive immune responses. Specific and local suppression of immune responses by resident Treg in draining LNs might provide new therapeutic opportunities for the treatment of local chronic inflammatory conditions.