The Research Projects (RP) of this comprehensive discovery-based P01 seek to identify specific changes in the transcriptional profiles and signaling pathways that control thymic epithelial cell (TEC), stromal cell, and thymic hematopoietic antigen presenting cell (HAPC) compartment dynamics and lineage hierarchies during the transition from perinatal thymus expansion to juvenile/adult homeostasis. Studies in the RPs will focus on murine models, but the questions they seek to address require comparison of mouse and human thymus biology across the perinatal to juvenile transition. However, human thymus tissue is not readily available at most institutions and cross-species comparisons are not always straight-forward. In addition, the emphasis of this P01 on deciphering heterogeneity in mostly non-overlapping cellular subsets of TECs (RP1, RP2), other stromal cells, (RP2), and HAPCs (RP3) mean that data relevant to all three RPs can potentially be obtained from each human tissue studied. Integration of this centralized Human Thymus Core into the P01 has resolved these issues. Core C services will allow RP 1-3 to address the knowledge gaps regarding translation of their mouse data and previously unstudied aspects of human thymus biology, via three focused specific aims/Service Tasks: 1) Procurement and processing of human thymus tissues from healthy donors to meet project-specific translation needs; 2) Enrichment and immunophenotyping of TECs, other stromal cells, and HAPCs to validate human equivalent markers analogous to those identified in mice in RP 1-3; and 3) Molecular analysis of thymic stromal cells and HAPC subsets through generation of standardized, quality- controlled single cell (sc) and bulk RNA-seq data from sorted human thymus populations for analysis by Core B. In addition to providing critical services to the RPs, the comprehensive database of gene expression in subsets of TEC, stromal cells, and HAPCs from human thymus that will be generated by this Core will be a significant new resource for both human and mouse thymus research communities.