Periodic Reporting for period 1 - Tracer-T (Analysis of the effect of the tumour microenvironment on T cell functional phenotype)
Reporting period: 2018-09-01 to 2020-08-31
A successful adaptive immune response requires T cells to be able to adopt a specific metabolic phenotype. However, in diseases such as cancer or those associated with chronic inflammation, the metabolic microenvironment in which a T cell functions is likely to subvert this metabolic phenotype, thereby disrupting function. A better understanding of how the microenvironment affects T cell metabolism and function would permit the development of metabolic 'normalising' treatments that could restore function and permit disease resolution.
The overall aim of Tracer-T was to identify how metabolites that build up in hypoxic tumour microenvironments impair T cell function, and whether this could be reversed to aid tumour cell killing. We planned to use parallel immunological and metabolic analyses, including stable isotope-based tracing approaches, to identify the the precise pathways involved. Subsequently, by inhibiting the metabolic pathway implicated, genetically, pharmacologically, or using physiologically relevant stimuli we would unequivocally link specific immunomodulatory metabolites with T cell function.
The specific research objectives (ROs) of this project were:
RO1: Identify novel hypoxia-induced metabolites that alter T cell function
RO2: Determine the mechanism by which some of these metabolites impair T cell function
RO3: Identify routes by which normal T cell function can be retained in hypoxic conditions
The overall aim of Tracer-T was to identify how metabolites that build up in hypoxic tumour microenvironments impair T cell function, and whether this could be reversed to aid tumour cell killing. We planned to use parallel immunological and metabolic analyses, including stable isotope-based tracing approaches, to identify the the precise pathways involved. Subsequently, by inhibiting the metabolic pathway implicated, genetically, pharmacologically, or using physiologically relevant stimuli we would unequivocally link specific immunomodulatory metabolites with T cell function.
The specific research objectives (ROs) of this project were:
RO1: Identify novel hypoxia-induced metabolites that alter T cell function
RO2: Determine the mechanism by which some of these metabolites impair T cell function
RO3: Identify routes by which normal T cell function can be retained in hypoxic conditions
RO1 was met by completion of work package (WP)1. Briefly, the fellow consulted with the supervisor to identify a number of hypoxia-induced metabolites to screen for potential effects on T cell function. All three screened metabolites (lactate, succinate and urea) were found to alter T cell function, with succinate and lactate found to suppress expression of the anti-tumour T cell cytokine, interferon-gamma and lactate found to have opposing stimulatory vs suppressive effects under normixa vs hypoxia respectively. The fellow decided to further interrogate the effects of succinate on T cell function, since this was the most novel finding and has substantial therapeutic potential in certain tumours (e.g. Succinate Dehydrogenase (SDH)-deficient tumours). Comprehensive immunological assays identified which precisely which aspects of T cell function were impacted by succinate. Alongside this, analysis of patient transcriptional data identified evidence of this suppressive axis in vivo. RO2 was met by completion of WP2. Briefly, in-depth metabolic tracing analyses, combined with assays of key protein expression and activity (e.g. SUCNR1, HIF1-α) identified the mechanism by which succinate impairs T cell function. This appeared not to involve the succinate receptor, SUCNR1 or modulation of HIF1-α expression. Rather, we observed significantly altered glucose metabolism in T cells exposed to succinate, associated with impaired activity of a specific enzyme. RO3 was met by completion of WP3. In brief, having identified that succinate impairs T cell function via inhibition of glucose metabolism, we tested whether reversing this metabolic defect could rescue T cell function, which indeed proved to be the case. These results thereby prove that T cell function can be rescued and normalised in succinate-rich tumour envionments. These primary research data are now being prepared for publication. In addition the fellow has written several review articles during the fellowship.
This project has advanced the current understanding of how T cell immune function is impacted by their metabolic environment and identified novel targets for potential therapeutic application in certain cancer types.