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Title: The role of tryptophan and the mTOR pathway in T cell fate determination
Author: Karydis, Ioannis
ISNI:       0000 0004 5361 8285
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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The adaptive immune response forms an essential part of the cancer immuno-editing process, whereby nascent malignant cells are detected and destroyed prior to forming tumours. The process is tightly controlled to minimise collateral damage to healthy tissue. One of the mechanisms evolved for this purpose and frequently co-opted by malignant cells is the creation of a microenvironment scarce in essential amino-acids through the use of catabolic enzymes such as Indoleamine 2,3-dioxygenase (IDO) , responsible for the rate-limiting step in tryptophan catabolism. The evolutionary conserved GCN2 and mTORC1 pathways respond to amino-acid starvation by triggering emergency homeostatic response programmes that aim to conserve nutrients by shutting down biosynthetic pathways, slowing cell cycle progression and facilitating autophagy. This research project focuses on elucidating the interaction between IDO activity and these pathways and its implications for the immune-editing process. The role of the mTOR kinase as a regulator of T cell fate following exposure to cognate antigen has recently become apparent. Experiments described herein confirm that in murine and human models of T cell activation exposure to tryptophan starvation results in significant mTORC1 inhibition and a modified phenotype with reduced Tbet expression, altered cytokine secretion profile, greatly impaired proliferative capability and expanded CD4+ FoxP3+ CD25high subpopulations. Additional results confirmed that the action of IDO is sufficient to deplete tryptophan from the microenvironment to levels sufficient to depress the mTORC1 axis and trigger GCN2 activity even in tumour cell lines. Lower extracellular tryptophan levels were necessary to perturb these pathways In IDO expressing cell lines, suggesting that compensatory mechanisms allow continued proliferation of malignant cells in the face of conditions that severely impede an anti-cancer immune response. In conclusion, manipulation of the mTORC1 axis via IDO-induced tryptophan depletion is an important tumour immune-escape mechanism that can be a target for cancer immunotherapies.
Supervisor: Cerundolo, Vincenzo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Immunology ; Tumours ; T cell biology ; tumour immunology ; immune escape