Tu108 - An Integrated Single-cell Chromatin Landscape and Transcriptomic Map of Human Thymic Epithelium Identifies HIVEP3 as a New Player in the Control of Immune Tolerance

Lucas Brusselle – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Claire Usal – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Laurent Tesson – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Séverine Remy – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Severine Menoret – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Jeremie Poschmann – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Ignacio Anegon – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France; Matthieu Giraud – Nantes Université, INSERM, Center for Research in Transplantation and Translational Immunology, UMR 1064, F-44000 Nantes, France

Abstract Text: Promiscuous gene expression of tissue-restricted self-antigens (TRAs) by medullary epithelial cells of the thymus (mTECs) is crucial for the control of central T cell tolerance and autoimmunity. The crosstalk between developing thymocytes and mTECs sustains their maturation into mTEChi expressing a full repertoire of TRAs whose presentation ensures the purge of autoreactive T cells. mTEC maturation relies on NF-kB signaling and results in the expression of the autoimmune regulator (AIRE) that induces the expression of a wide array of TRAs. In addition, a significant amount of TRAs is expressed in the absence of AIRE and is influenced by the developmental stage of mTEC. Thus, to uncover the missing factors implicated in mTEChi maturation and TRA expression, we carried out a sc-ATAC sequencing on isolated TECs from human and mouse thymi. Remarkably, along with NF-kB we identified a strong conservation of open chromatin at HIVEP binding sites in human and mouse mTEChi, with specific accessibility at TRA genes, therefore indicating a role for HIVEP on the control of mTEChi development and TRA expression. Importantly, sc-RNAseq analyses of human TECs revealed that HIVEP3 is the sole HIVEP family member whose expression is exclusive to mTECs. Recently, we successfully created a Nfkb2-deficient rat model. Therefore, to assess the extent of Hivep3’s effect on central tolerance, individually and in combination with Nfkb2, we generated the first Hivep3-deficient rat line by CRISPR/Cas9 genome editing. Hence, we propose that HIVEP3 plays a key role in the regulation of immune tolerance through the control of mTEC maturation.