Dynamic but Unified Changes in the Perinatal Thymus Promote Distinct Waves of Treg Generation 2254735

Abstract

Abstract Introduction The thymic environment enforces tolerance by inducing autoreactive T cells to either undergo negative selection or divert to the regulatory T cell (Treg) lineage. We previously found that coordinated transcriptional changes occur in thymic stromal cells and antigen-presenting cells (APCs) as the thymus transitions from neonatal growth to juvenile homeostasis: the first wave (P0-P3) of neonatal growth is accompanied by E2F transcriptional activity, while the second wave, at the “transitional” ages of P7-P14, is characterized by elevated Type I/III interferon signaling and altered antigen presentation. Concomitantly, two distinct waves of Tregs are generated, with the first wave expressing high levels of CTLA-4 and PD-1, and the second wave expressing elevated CD5 and GITR —functional markers of heightened Treg suppressive capacity. These findings raise the question of whether the age of thymocytes and/or the thymus generates phenotypically distinct and uniquely suppressive Tregs in perinates. Methods We performed heterochronic Treg generation assays on live thymic slices, as well as in vitro Treg generation assays to distinguish the contributions of the age of thymocytes versus the thymic environment on Treg selection in perinates. Results We find that both the perinatal age of CD4 single-positive thymocytes (CD4SPs) and the perinatal environment drive expression of key effector markers on Tregs (i.e. PD-1, GITR, and CD5). Perinatal CD4SPs are intrinsically biased towards Treg generation, while in vivo Treg phenotypes are largely driven by the age of the thymus environment. Conclusion Two phenotypically distinct waves of Tregs, first PD-1hi/CTLA-4hi followed by CD5hi/GITRhi, are promoted by both the thymic environment and a CD4SP-intrinsic capacity for Treg generation in perinates. These results provide significant insight into the selection of unique perinatal Treg subsets and reveal more phenotypic heterogeneity than previously described. Funding Source NIH P01 Topic Categories Hematopoiesis and Immune System Development (HEM)