Unique properties of thymic antigen-presenting cells promote epigenetic imprinting of alloantigen-specific regulatory T cells

// Garima Garg 1 , Eirini Nikolouli 1 , Matthias Hardtke-Wolenski 2 , Aras Toker 1 , Naganari Ohkura 3,4 , Michael Beckstette 1 , Takahisa Miyao 5 , Robert Geffers 6 , Stefan Floess 1 , Norbert Gerdes 7,8 , Esther Lutgens 7,9 , Anke Osterloh 10 , Shohei Hori 5 , Shimon Sakaguchi 3,4 , Elmar Jaeckel 2 and Jochen Huehn 1 1 Department of Experimental Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany 2 Department of Gastroenterology, Hepatology, Endocrinology, Hannover Medical School, Hannover, Germany 3 Department of Experimental Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Japan 4 Department of Experimental Pathology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan 5 Laboratory for Immune Homeostasis, RIKEN Center for Integrative Medical Sciences, Yokohama City, Kanagawa, Japan 6 Genome Analytics, Helmholtz Centre for Infection Research, Braunschweig, Germany 7 Institute for Cardiovascular Prevention, Ludwig-Maximilians-University, Munich, Germany 8 Division of Cardiology, Pulmonology, and Vascular Medicine Medical Faculty, University Hospital Dusseldorf, Dusseldorf, Germany 9 Department of Medical Biochemistry, Academic Medical Center, University of Amsterdam, AZ, Amsterdam, The Netherlands 10 Department of Immunology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany Correspondence to: Jochen Huehn, email: // Keywords : regulatory T cells, thymic APCs, epigenetic modification, alloantigen-specificity, Immunology and Microbiology Section, Immune response, Immunity Received : October 15, 2016 Accepted : March 03, 2017 Published : March 15, 2017 Abstract Regulatory T cells (Tregs) are potential immunotherapeutic candidates to induce transplantation tolerance. However, stability of Tregs still remains contentious and may potentially restrict their clinical use. Recent work suggested that epigenetic imprinting of Foxp3 and other Treg-specific signature genes is crucial for stabilization of immunosuppressive properties of Foxp3 + Tregs, and that these events are initiated already during early stages of thymic Treg development. However, the mechanisms governing this process remain largely unknown. Here we demonstrate that thymic antigen-presenting cells (APCs), including thymic dendritic cells (t-DCs) and medullary thymic epithelial cells (mTECs), can induce a more pronounced demethylation of Foxp3 and other Treg-specific epigenetic signature genes in developing Tregs when compared to splenic DCs (sp-DCs). Transcriptomic profiling of APCs revealed differential expression of secreted factors and costimulatory molecules, however neither addition of conditioned media nor interference with costimulatory signals affected Foxp3 induction by thymic APCs in vitro . Importantly, when tested in vivo both mTEC- and t-DC-generated alloantigen-specific Tregs displayed significantly higher efficacy in prolonging skin allograft acceptance when compared to Tregs generated by sp-DCs. Our results draw attention to unique properties of thymic APCs in initiating commitment towards stable and functional Tregs, a finding that could be highly beneficial in clinical immunotherapy.