AbstractsBiology & Animal Science

Tese de doutoramento, Medicina (Imunologia Clínica), Universidade de Lisboa, Faculdade de Medicina, 2016 Regulatory T Cells (Treg), constitutively expressing the transcription factor Foxp3/FOXP3, play a crucial role in maintaining self-tolerance, assuming particular relevance in the context of autoimmunity. Adoptive transfer of Treg has been shown to be highly efficient in the prevention and treatment of autoimmunity in rodents and clinical trials exploring Treg-based adoptive therapy in Type I Diabetes (T1D) are currently ongoing. These therapies require large numbers of Treg, stressing the importance of a better knowledge of the molecular and cellular requirements for human thymic and peripheral Treg development. Moreover, widespread application of Treg-based therapy dealt with several limitations regarding the stability and function of in vitro expanded populations for in vivo use. The creation of efficient protocols enabling stable FOXP3 acquisition by human non-regulatory cells could overcome the limited availability of thymus-derived (t)Treg and would facilitate the generation of antigen-specific Treg, an ideal candidate in autoimmune diseases (AID) setting. The overall objective of this work was to provide new insights into the principles dictating human thymic and peripheral Treg development and homeostasis, thus facilitating the progress of Treg-based immunotherapy. First, we proposed to investigate the capacity of human non-regulatory memory CD4+ T cells to differentiate in vitro into bona-fide FOXP3-expressing cells and to assess the role of the Notch signaling pathway in modulating this conversion. We showed that stable and functional bona-fide Treg can be generated from memory CD4+ T cells and that Delta like (DL)1-mediated Notch signaling activation enhanced this conversion. We additionally showed that DL1 increased Treg proliferation, reinforcing the possible role of Notch in the homeostasis of the human peripheral Treg compartment. Importantly, we also demonstrated that DL1 enhanced the expression of function-related molecules within these cells, contributing to the maintenance of their regulatory phenotype. In order to better clarify the principles governing Treg development in the human thymus, we investigated the role of common gamma-chain (c) cytokines in human tTreg differentiation. We identified interleukin (IL)-2 and IL-15 as key molecular determinants in this process and excluded a major function for IL-4, IL-7 and IL-21. Moreover, we revealed that IL-2 and IL-15 are expressed in a non-overlapping pattern in the human thymus, with the former produced mainly by mature αβ and γδ thymocytes and the latter by monocyte/macrophages and B lymphocytes. Overall, this work has provided a better understading of the core mechanisms governing human Treg differentiation and homeostasis that should facilitate the further establishment of Treg-based therapies. As Células T Reguladoras (T Regs), expressando constitutivamente o factor de transcrição Foxp3/ FOXP3, desempenham um papel crucial na… Advisors/Committee Members: Caramalho, Íris Maria Ferreira, Victorino, Rui M. M., 1949-.