Project 3 The perinatal thymus plays a unique role in promoting central tolerance. Central tolerance results from negative selection of autoreactive conventional T cells (Tconv) and differentiation of regulatory T cells (Treg). Notably, Tregs selected during the perinatal period are more autoreactive and are uniquely required for life- long protection against autoimmunity. Perinatal Tconv cells are also more autoreactive and have unique molecular and functional properties compared with their juvenile/adult counterparts. Both negative selection and Treg induction occur when thymocytes encounter auto-antigens presented by medullary thymic epithelial cells (mTECs) or hematopoietic antigen presenting cells (HAPCs), including dendritic cells (DCs). TECs and thymic HAPCs undergo profound changes during the perinatal to juvenile transition. The rationale for RP3 is that thymic HAPCs are distinct in cellular composition and molecular profiles in the perinatal period, when thymic selection is critical for differentiation of the first wave of Tconv cells and establishment of self-tolerance. We will test the hypothesis that unique properties of mTECs and HAPCs in the perinatal period create an altered environment for central tolerance induction and are responsible for selection of Tconv and Treg cells with increased self-reactivity and age-specific functional properties.
In Aim 1, we will use single cell transcriptional profiling (scRNA-seq) and multiplex imaging to identify the cellular, transcriptional, and organizational changes that occur in mouse and human HAPCs over the perinatal to juvenile transition which could impact central tolerance.
In Aim 2, we will use phenotypic analyses, transcriptional profiling, genetic models, and functional assays to identify the APCs responsible for selecting tissue-protective Treg in the perinatal period. We will also determine whether CCR7-mediated cross-talk with TECs alters the DC compartment in perinatal mice, with downstream consequences for Treg selection.
In Aim 3, we will determine if negative selection is impaired in perinates in response to antigens across a range of affinities. Live-cell 2- photon microscopy will be used to determine if distinct APCs induce negative selection in the perinatal period. RP3 has multiple points of intersection with all Projects and Cores. We will use scRNA-seq to identify altered molecular signatures of HAPCs in mice and humans (with Cores B and C) during the perinatal to juvenile transition that could impact central tolerance. Parallel data from RP1 and RP2 will provide a comprehensive map of changes in TECs and thymic stromal cells over the perinatal to juvenile transtition that could to alter central tolerance. We will also collaborate with the Manley lab (RP2) for MiCasa analysis to reveal organizational changes in the thymic environment during the perinatal to juvenile transition. Results generated in RP3 are integral to achieving the overall Program goals of elucidating mechanisms by which thymic stromal properties alter Treg and Tconv cell differentiation and selection in the perinatal period, with implications for devising rational therapeutic strategies to safely enhance T cell output.