Use this URL to cite or link to this record in EThOS:
Title: Modulating the immune system by amino acid depletion : IDO and beyond
Author: Vallius, Laura I.
ISNI:       0000 0004 2725 7105
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2011
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
Amino acid availability plays an important role in modulating the activity of T-cells. One of the pathways employed by T-cells to sense nutrient levels is the “mammalian target of rapamycin” (mTOR) pathway that is inhibited in response to nutrient depletion. Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme along the tryptophan catabolising kynurenine pathway. T-cells are very sensitive to lack of this essential amino acid in their microenvironment and this confers strong immunomodulatory properties to cells expressing active IDO. It therefore has a significant physiological role as a homeostatic mechanism used in mammalian organisms to dampen excessive activation of the immune system but is also used as an immune evasion mechanism by many cancers. In this study, we investigated the IDO inhibitory properties and mechanism of action of the tryptophan metabolite 3-hydroxyanthranilic acid (3-HAA) that potentially forms a negative feedback loop in the kynurenine pathway. We studied the molecule in enzymatic assays, in live cells and discovered that it inhibits IDO in an indirect way via the formation of hydrogen peroxide. Secondly, we looked at the effects of tryptophan and its metabolites on T-cell proliferation and mTOR activity, and discovered a metabolite that inhibits T-cell proliferation. Lastly we examined mechanisms of T-cell suppression employed by myeloid derived suppressor cells (MDSCs), focusing on their ability to deplete amino acids from their microenvironment. We were able to exclude tryptophan consumption as a suppressive mechanism and established that by manipulating extracellular concentrations of several amino acids other than arginine and cysteine – that are known to be utilised by MDSCs - we were able to reduce their inhibitory properties. In summary, we have described in detail how 3-HAA inhibits IDO in in vitro assays, outlined how some tryptophan metabolites can inhibit T-cell proliferation, and clarified aspects of suppressive mechanism employed by MDSCs.
Supervisor: Cerundolo, Vincenzo Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Medical Sciences ; Immunology ; Oncology ; Tumours ; Indoleamine 2 ; 3-dioxygenase ; kynurenine ; tumour escape ; amino acid metabolism ; myeloid derived suppressor cells ; tryptophan