Modulation of peripheral T cell responses by unconventional antigen-presenting cells: role of plasmacytoid dendritic cells in anti-tumor immunity and lymphatic endothelial cells in autoimmunity

Abstract

The aim of this thesis was to characterize the role of plasmacytoid dendritic cells (pDCs) and lymphatic endothelial cells (LECs) in the modulation of peripheral T cell responses, with a particular focus on MHC class II-restricted antigen presentation. Depending on the immunological context, pDC MHCII-mediated antigen-presenting functions can be either tolerogenic or immunogenic. For instance, pDCs are maintained in a tolerogenic state by the tumor microenvironment. In the first part of this thesis, we asked the question whether tumor-associated pDCs could undergo a tolerogenic-to-immunogenic reprogramming following the intratumoral administration of CpG-B, a TLR9 ligand, along with a model MHC-II-restricted tumor antigenic peptide. LECs from lymph nodes (LN-LECs) were shown to impact peripheral CD8+ T cell responses, as antigen-presenting cells (APCs). Emerging evidence is in favor of a role for LN-LECs in CD4+ T cell tolerance to MHC-II-restricted antigens, although this phenomenon is still a matter of debate. In the second part of this thesis, we sought to determine the contribution of LN-LECs as MHC-II-restricted APCs to autoreactive CD4+ T cell responses in experimental autoimmune encephalomyelitis, a mouse model for multiple sclerosis.