Krebs cycle’s citraconate revives immune cell function boosting cancer response

Study identifies citraconate as a metabolic regulator that reverses T cell exhaustion, suppresses lipid-driven toxicity and improves immunotherapy response in cancer models

A metabolite known as citraconate has demonstrated the capacity to prevent T cell exhaustion and enhance antitumour immunity within the tumour microenvironment, according to a study that has integrated mouse models with analyses of human patient samples. The findings have identified a metabolically regulated checkpoint that governs cytotoxic T lymphocyte performance and have linked this pathway to improved clinical outcomes in patients who receive immunotherapy.

The work has built on prior understanding of immunometabolism, particularly the role of metabolites derived from the tricarboxylic acid cycle – the ‘Krebs Cycle’ – was led by a team researchers at the Chinese Academy of Medical Sciences Suzhou Institute of Systems Medicine alongside collaborators from Soochow University, Xi'an Jiaotong University School of Basic Medical Sciences, Zhengzhou University, Xuzhou Medical University all in China, McMaster University, Ontario, Canada and the Universite de Lausanne in France.

The related metabolite itaconate has been well characterised as an immunomodulatory molecule that can suppress CD8-positive T cell proliferation and effector function. Citraconate – a structural isomer of itaconate – had now emerged as a functionally distinct molecule with the capacity to promote stem-like differentiation programmes in T cells. Until now, its role in tumour immunity had remained underdefined.

The investigators reported that citraconate levels had been depleted in exhausted or hypoxic CD8-positive T cells isolated from tumour-bearing mice and from human tumour tissues. This observation has suggested that loss of this metabolite may contribute directly to T cell dysfunction within the hostile metabolic environment of solid tumours, where nutrient limitation and hypoxia impose sustained stress on infiltrating immune cells.

Experimental exposure to citraconate in vitro restored T cell functionality. In cultured CD8-positive T cells derived from human tumours, treatment increased activation, reinforced stem-like characteristics and reduced phenotypic markers of exhaustion. These effects have pointed to a mechanism through which metabolic supplementation may reverse the progressive loss of T cell fitness that undermines durable antitumour responses.

Mechanistic analysis has revealed that citraconate can elevate intracellular levels of cyclic adenosine monophosphate, a second messenger that regulates diverse signalling cascades. This increase has activated the protein kinase A – cAMP response element-binding protein pathway, a central axis in cellular transcriptional control. Activation of this pathway has suppressed expression of arachidonate 5-lipoxygenase, an enzyme that participates in fatty acid metabolism and inflammatory signalling.

Arachidonate 5-lipoxygenase has been identified as a driver of T cell exhaustion, in part through its role in the accumulation of lipid-derived intermediates that can exert cytotoxic stress. By suppressing this pathway, citraconate has limited the build-up of harmful fatty acid byproducts and protected T cells against ferroptosis, a form of iron-dependent cell death associated with lipid peroxidation.

Localised intratumoural delivery of citraconate in mouse models has enhanced T cell cytotoxicity and improved antitumour activity. These findings have suggested that spatially targeted metabolic modulation within the tumour microenvironment may represent a viable strategy to augment immune-mediated tumour clearance.

Analysis of single-cell RNA sequencing datasets from human tumours has reinforced the translational relevance of the pathway. Lower expression of arachidonate 5-lipoxygenase has correlated with reduced T cell exhaustion and improved response rates to immune checkpoint blockade therapies. This association has indicated that the citraconate – protein kinase A signalling axis may serve both as a therapeutic target and as a biomarker to identify whether patients are likely benefit from immunotherapy.

“These findings reveal a metabolic checkpoint governing T cell fitness and offer a potentially clinically actionable approach to enhance CD8 T cell antitumour immunity and immune checkpoint blockade efficacy,” Dr. Wenhui Li and colleagues wrote.

Taken together, the study has positioned citraconate as a promising candidate in the emerging field of metabolic immunotherapy. By directly addressing the biochemical constraints that limit T cell persistence and function in tumours, this strategy may complement existing checkpoint inhibitors and help to overcome resistance mechanisms that continue to restrict their effectiveness in many patients.

For further reading please visit: 10.1126/sciimmunol.adz0348