| Summary: | The study of complex biological processes at a detailed level of understanding requires an in vivo model where pathological immunity can be experimentally introduced and manipulated. In human studies however, due to obvious ethical and technical constraints, these in vivo mechanisms cannot be studied. The development of humanised models has been an important advancement to aid in the effective translation of medical research into human disease mechanisms and pathogenesis into clinical application. This thesis aims to investigate the use of these model systems to explore the role of human T-cells and dendritic cells (DCs) in the regulation of human alloimmunity. The occurrence of Graft-versus-Host Disease (GvHD) is a prevalent and potentially lethal complication that develops following hematopoietic stem cell transplantation. Humanized mouse models of xenogeneic-GvHD based upon immunodeficient strains injected with human peripheral blood mononuclear cells (PBMC; “Hu-PBMC mice”) are important tools to study human immune function in vivo. The recent introduction of targeted deletions at the interleukin-2 common gamma chain (IL-2R!null), notably the NOD-scid IL-2R!null (NSG) and BALB/c-Rag2null IL-2R!null (BRG) mice, has led to improved human cell engraftment. Despite their widespread use, a comprehensive characterisation of engraftment and GvHD development in the Hu-PBMC NSG and BRG models has never been performed in parallel. Engrafted human lymphocyte populations in the peripheral blood, spleens,lymph nodes and bone marrow of these mice were investigated. Kinetics of engraftment differed between the two strains, in particular a significantly faster expansion of the human CD45+ compartment and higher engraftment levels of CD3+T-cells were observed in NSG mice, which may explain the faster rate of GvHD II development in this model. The pathogenesis of human GvHD involves anti-host effector cell reactivity and cutaneous tissue infiltration. Despite this, the presence of Tcell subsets and tissue homing markers has only recently been characterised in the peripheral blood of patients and has never been properly defined in Hu-PBMC models of GvHD. Engrafted human cells in NSG mice shows a prevalence of tissue homing cells with a T-effector memory (TEM) phenotype and high levels of cutaneous lymphocyte antigen (CLA) expression. Characterization of Hu-PBMC mice provides a strong preclinical platform for the application of novel immunotherapies targeting TEMcell driven GvHD. The second part of thesis investigates the immune regulatory role of human skin DC subsets both in vitro and in vivo. A better understanding of human skin immune homeostasis and its regulation by specialized subsets of tissue residing immune sentinels is required. Here, we identify an immunoregulatory tissue resident DC in dermis of human skin characterized by surface expression of CD141, CD14 and constitutive IL-10 secretion (CD141+ DDCs). CD141+ DDCs possess lymph node migratory capacity, induce T cell hypo-responsiveness, cross-present self-antigens to auto-reactive T-cells, and induce potent regulatory T cells that inhibit skin inflammation. Vitamin D3 promotes certain phenotypic and functional properties of tissue resident CD141+ DDCs from human blood DCs. These CD141+ DDC-like cells can be generated in vitro and once transferred in vivo have the capacity to inhibit xenograft versus host disease and tumour alloimmunity. These findings suggest that CD141+ DDCs play an essential role in maintenance of skin homeostasis and in the regulation of both systemic and tumour alloimmunity. Finally, vitamin D3-induced CD141+ DDC-like cells have potential clinical use for their capacity to induce immune tolerance.
|
|---|
