Molecular mechanisms controlling the survival and differentiation of human yσ thymocytes

Tese de doutoramento, Ciências Biomédicas (Imunologia), Universidade de Lisboa, Faculdade de Medicina, 2017Among the various leukocyte populations that build up the immune defense against infections and tumors, γδ T lymphocytes constitute an enigmatic lineage whose molecular mechanisms of differentiation and activation are still poorly understood. The key roles played by γδ T cells in immunity critically depend on their survival, activation and differentiation into effectors capable of secreting cytokines and killing infected or transformed cells. These processes are controlled, at the molecular level, by surface receptors that capture key extracellular cues and convey downstream intracellular signals that regulate both lymphocyte physiology and pathology. In this PhD thesis we evaluated the contribution of cell receptor signaling pathways to human γδ T cell differentiation and activation. Firstly, we showed that human γδ thymocytes are functionally immature and their differentiation program requires additional IL-2 or IL-15 signals to drive their differentiation into IFN-γ and TNF-α producers endowed with potent cytotoxicity against leukemia targets. We further elucidated the signals involved in normal/ healthy γδ T cell maintenance as well as in γδ T cell tumorigenesis. We identified that the protein kinase CK2 (Casein Kinase 2) is overactivated in the γδ T cell lineage compared to αβ counterparts. We further showed that the clinical grade-inhibitor of CK2, CX- 4945, impairs γδ T cell survival by inhibiting the CK2/AKT/mTOR/GSK3β signaling pathway. Moreover, we showed that CK2 is hyperactivated in γδ T acute lymphoblastic leukemia (T-ALL) samples, compared to both normal γδ T cells and αβ T-ALL. Importantly, we demonstrated a high sensitivity of γδ T-ALL cells to CX- 4945 treatment in vitro and in vivo, thus supporting the use of CK2 inhibitors as a putative therapy for γδ T-ALL. Overall, the data presented in this thesis provided new evidences indicating that: (i) human γδ thymocytes are functionally immature and require IL-2 or IL-15 to differentiate into type 1 cytotoxic effector lymphocytes; (ii) the protein kinase CK2 is a novel determinant of both healthy and leukemic γδ T cell survival; and (iii) the CX-4945 chemical inhibitor is a promising therapeutic approach for γδ T-ALL.European Research Council (ERC); Excellence in Life Sciences (EMBO); Foundation Arc Pour Sur Le Cancer; Sociedade Portuguesa de Imunologia; European Federation of Immunological Societies (EFIS); Gabinete de Apoio à Investigação Científica Tecnológica e Inovação (GAPIC