Mitochondria, the powerhouse organelles responsible for cellular energy production, play a pivotal role in immune cell functionality. Previous studies had demonstrated that T cells accumulating depolarized, dysfunctional mitochondria are prone to losing their effector capabilities and adopt an exhausted phenotype. However, the exact biochemical and molecular pathways connecting mitochondrial impairment to this exhaustion remained elusive. The latest data fills this gap by highlighting how damaged mitochondria lead to increased proteasomal activity within the T cells.

Through meticulous experiments, the researchers observed that accumulations of depolarized mitochondria significantly elevate proteasome activity. The proteasome—a cellular complex responsible for degrading damaged or unneeded proteins—selectively breaks down mitochondrial proteins as part of quality control mechanisms. This proteasome hyperactivity results in the liberation of haem, a critical prosthetic group found in many proteins, through the breakdown of haemoproteins. The presence and accumulation of this regulatory haem within the cell nucleus fundamentally alter transcriptional landscapes relevant to T cell functionality.

A key discovery is that the increased nuclear haem disrupts the function of BACH2, a transcription factor central to maintaining T cell stemness and preventing exhaustion. BACH2 normally acts as a repressive regulator, restraining genes that promote exhaustion. However, when haem levels surge, BACH2-mediated transcription is impaired, effectively exacerbating the exhaustion process. This revelation links mitochondrial health, proteasomal activity, and haem signalling in a previously unappreciated network that dictates T cell fate under chronic stimulation.

Delving deeper, the team demonstrated that inhibiting the nuclear import of regulatory haem preserves BACH2 integrity and its transcriptional control. This intervention notably reverses aspects of the exhaustion phenotype, enhancing T cell stemness and their ability to mount a vigorous immune response. The therapeutic implications are profound, especially concerning adoptive cellular therapies such as chimeric antigen receptor (CAR)-T cells, which often face challenges related to T cell exhaustion during manufacturing and clinical application.

Analyzing clinical data from patients treated with CD19+ CAR-T therapies for B cell acute lymphoblastic leukemia (B-ALL), the study identified a robust negative correlation between proteasome gene signatures in CAR-T cells and treatment efficacy. Essentially, T cells exhibiting elevated proteasome activity post-manufacturing were less effective anti-tumor warriors. This insight provides a direct biomarker that could predict and potentially improve CAR-T cell therapeutic outcomes.

The researchers exploited this mechanistic understanding by incorporating bortezomib, an FDA-approved proteasome inhibitor, into the CAR-T cell manufacturing process. Bortezomib-treated CAR-T cells exhibited decreased hallmarks of exhaustion, maintained superior functional capacity, and demonstrated enhanced anti-tumor efficacy in preclinical models. This repurposing of an established drug offers a promising strategy to optimize CAR-T therapies, potentially extending their benefits to a broader patient population.

Beyond its therapeutic promise, the study illuminates a general principle in immunometabolism and transcriptional regulation. It underscores how mitochondrial integrity is not just a metabolic checkpoint but also a molecular conductor orchestrating intracellular signalling cascades that impact T cell destiny. This foundational concept may have broader application across diverse immune cell types and disease contexts marked by chronic stimulation and cellular fatigue.

Importantly, this research bridges previously disconnected fields—mitochondrial biology, proteostasis, haem signalling, and immunology—into a coherent model that explains T cell exhaustion at a molecular level. The idea that mitochondrial damage triggers proteasome-mediated haem release which in turn sabotages a pivotal transcription factor is a paradigm shift with the potential to recalibrate approaches to immunotherapy.

While the findings shine a bright spotlight on the proteasome-haem-BACH2 axis, they also provoke new questions. How universal is this mechanism in other exhausted or dysfunctional immune cell subsets? Are there additional haem-regulated transcription factors influencing exhaustion? What are the long-term effects of proteasome inhibition during T cell expansion? These questions set the stage for future investigations that could refine and extend this therapeutic strategy.

The study also highlights the importance of intracellular haem as a regulatory molecule beyond its classical role in oxygen transport and electron transport chains. Its emerging role as a modulator of gene expression within immune cells might inspire new lines of research into haem-targeted therapies across autoimmune diseases, infections, and cancer.

In summary, this pioneering work identifies a previously uncharted proteasome-initiated haem signalling axis that fundamentally governs CD8+ T cell exhaustion by modulating transcription factor BACH2. It offers a compelling molecular explanation for how mitochondrial dysfunction translates into functional impairment in T cells. By revealing actionable targets such as proteasome activity and nuclear haem transport, this research paves the way for innovative interventions designed to bolster the immune system’s capacity to fight cancer and chronic diseases.

As immunotherapy continues to revolutionize medicine, understanding and manipulating T cell exhaustion will be crucial to maximize therapeutic potential. This study provides vital mechanistic insights and actionable strategies, potentially transforming current CAR-T cell manufacturing processes and improving patient outcomes. The integration of metabolic, proteolytic, and transcriptional pathways into a holistic model marks a significant advance in immunology and cellular therapy research.

With proteasome inhibitors already clinically approved, rapid translation of these insights into trials is feasible, heralding a new era in adoptive cell therapy optimization. This work not only enhances our understanding of T cell biology but also underscores the immense complexity and interconnectivity of cellular regulation mechanisms. The future of cancer immunotherapy may well hinge on modulating these intricate molecular circuits unveiled by this landmark study.

Subject of Research: CD8+ T cell exhaustion mechanisms and their impact on immunotherapy efficacy.

Article Title: Proteasome-guided haem signalling axis contributes to T cell exhaustion.

Article References:
Xu, Y., Shangguan, Y., Chuang, YM. et al. Proteasome-guided haem signalling axis contributes to T cell exhaustion. Nature (2026). https://doi.org/10.1038/s41586-026-10250-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-026-10250-y

At the core of this discovery lies the behavior of mitochondria under stress. Upon depolarization—a condition indicating a loss of mitochondrial membrane potential—CD8⁺ T cells ramp up proteasome activity, the cellular machinery responsible for degrading proteins. Intriguingly, this process selectively targets mitochondrial hemoproteins. Their breakdown results in the liberation of regulatory heme, a molecule traditionally considered merely as a metabolic byproduct rather than a signaling entity. This reframing of regulatory heme heralds a paradigm shift in our understanding of intracellular communication pathways governing immune cell fate.

Rather than lingering inertly within the cytoplasm, the freed regulatory heme embarks on a journey to the nucleus of the T cell, where it executes a critical role. Here, heme binds to the transcription factor Bach2, inducing its destabilization. Bach2 normally acts as a repressor of Blimp1, a master regulator of terminal exhaustion in T cells. The degradation of Bach2 effectively lifts this repression, triggering the upregulation of Blimp1. This shift decisively locks T cells into an exhausted, dysfunctional state and erodes their stem-like properties critical for sustained immune responses.

Deciphering this cellular circuitry required delving deep into the molecular players orchestrating these changes. The researchers identified the E3 ubiquitin ligase CBLB as a pivotal driver in tagging mitochondrial proteins for proteasomal degradation. This selective ubiquitination marks hemoproteins for breakdown, fueling the excess heme pool. Meanwhile, PGRMC2 was characterized as the chaperone responsible for escorting regulatory heme into the nucleus, facilitating its interaction with Bach2. Together, these molecules form an elegant metabolic signaling switch bridging mitochondrial status to transcriptional fate decisions.

Professor Ho emphasizes the significance of this discovery: “We uncovered a metabolic signaling switch that converts mitochondrial stress into a permanent transcriptional decision. This pathway explains how energy failure becomes immune failure.” His team has further demonstrated that this molecular axis is not merely descriptive but clinically actionable. Through transient, low-dose administration of the proteasome inhibitor bortezomib during CAR-T cell manufacture, proteasome-driven heme signaling can be attenuated. This intervention downregulates exhaustion-associated gene programs, promoting durable epigenetic reprogramming toward a stem-like, memory phenotype that correlates with enhanced T cell persistence.

The clinical relevance of these findings is underscored by patient data from individuals with B-cell acute lymphoblastic leukemia (B-ALL). CAR-T cells exhibiting elevated proteasome activity were associated with poorer therapeutic outcomes, highlighting the prognostic and potentially therapeutic value of targeting this heme signaling pathway. As first author Y. Xu notes, “Our previous work identified mitochondrial damage as the cause of T cell failure, and this study reveals the molecular switch behind it and how to turn exhaustion off. Identifying regulatory heme as a signaling mediator was unexpected and provides a tangible avenue for intervention.”

Collectively, these discoveries redefine T cell exhaustion not simply as a consequence of chronic antigen exposure but as an active outcome of dysregulated metabolic signaling cascades. The integration of proteostasis, mitochondrial health, and nuclear transcription factor modulation represents a sophisticated cellular strategy regulating immune cell fate under stress conditions. Such insights into fundamental T cell biology are poised to reshape approaches to adoptive cell therapies, including CAR-T cells, where durability and functional persistence remain major clinical challenges.

This study bridges metabolic biology and immuno-oncology, presenting a seamless mechanism whereby proteasome-guided heme signaling irrevocably imprints exhaustion programs onto T cells. Therapeutic modulation of this axis opens new frontiers in optimizing CAR-T cell manufacturing protocols and designing combination therapies to circumvent immune failure. By targeting early molecular events linking energy deprivation to transcriptional reprogramming, future interventions could dramatically enhance the longevity and efficacy of engineered immune cells deployed against cancer.

The international collaborative effort spearheaded by Professor Ho and Y. Xu involved researchers from institutions spanning Switzerland, China, Taiwan, the United Kingdom, and the United States, underscoring the global commitment to unraveling immune dysfunction in cancer. Their work received robust support from prestigious funding agencies including the Swiss National Science Foundation and the Cancer Research Institute. Such multidisciplinary and multinational endeavors exemplify the power of converging expertise to solve complex biomedical puzzles.

In summary, the revelation of regulatory heme as a pivotal signaling molecule in T cell exhaustion heralds a new chapter in understanding how metabolic stress translates into irreversible immune cell fate decisions. This metabolic-transcriptional crosstalk mediated by proteasome activity, CBLB, and PGRMC2 not only elucidates fundamental mechanisms of immune dysfunction but also offers a promising therapeutic switch. Attenuating this pathway could revolutionize adoptive immunotherapies and pave the way toward more durable cancer treatments, finally turning the tide in the battle against T cell exhaustion.

Subject of Research:
T cell exhaustion and metabolic signaling pathways in cancer immunotherapy

Article Title:
Proteasome-guided haem signalling axis contributes to T cell exhaustion

News Publication Date:
18-Mar-2026

Web References:
http://dx.doi.org/10.1038/s41586-026-10250-y

Image Credits:
Ho Lab, 2025

Keywords:
Cancer, T lymphocytes, Mitochondria, Proteasomes, Transcription factors, Immunotherapy, Hemoproteins, Regulatory heme, CAR-T cells, Proteasome activity, Immune exhaustion, Metabolic signaling

The immune system is an exquisitely dynamic network requiring constant energy input to sustain its myriad components, from rapidly proliferating lymphocytes to long-lived tissue-resident immune cells. Metabolic pathways provide not only the fuel but also crucial signaling intermediates that influence immune cell fate, activation, and function. However, as organisms transition beyond reproductive age, this metabolic-immune axis undergoes profound alterations. Mitochondrial dysfunction, impaired nutrient sensing, and altered metabolite flux within immune cells collectively contribute to declining immunocompetence. Paramount among the consequences is the insidious rise of unresolved chronic inflammation—a biological state often referred to as “inflammaging”—which underpins many age-related diseases.

A central hallmark of immunological aging is the progressive erosion of the naive T cell pool, a process intricately linked to thymic involution. The thymus, the primary organ responsible for producing naive T cells, dramatically shrinks with age, reducing both the quantity and diversity of emerging T cells. This diminishment restricts the T cell receptor (TCR) repertoire, severely compromising the adaptive immune system’s ability to recognize and respond to novel pathogens and malignancies. Underlying this phenomenon is a confluence of metabolic and molecular perturbations within thymic epithelial cells and hematopoietic progenitors, emphasizing how metabolism governs not only immune cell functionality but also developmental niches.

Innate immune cells, such as macrophages, neutrophils, and dendritic cells, also display age-associated functional declines, many of which are metabolically driven. As these cells age, a shift in their metabolic programming impairs their phagocytic capacity and cytokine production, thereby perpetuating a low-grade inflammatory milieu. The chronic activation of innate immunity exacerbates tissue damage and immune dysregulation, further accelerating systemic aging processes. Understanding the metabolic rewiring that enforces this hyperactive yet dysfunctional innate immune state remains a critical challenge with profound therapeutic implications.

Beyond individual immune cell dysfunction, the systemic metabolic environment plays a determinative role in shaping immune aging. Age-related alterations in nutrient availability, hormonal signaling, and adipose tissue metabolism create an unfavorable backdrop for immune cells. Elevated levels of circulating pro-inflammatory metabolites and altered glucose and lipid metabolism collectively contribute to immune senescence. Moreover, the crosstalk between metabolic organs—such as liver, adipose tissue, and muscle—and the immune system governs the systemic inflammatory tone, influencing susceptibility to infections, autoimmunity, and chronic diseases like cardiovascular pathology and neurodegeneration.

Several converging lines of evidence highlight the potential of modulating metabolism to restore immune competence and extend healthspan. Pharmacological agents targeting key metabolic regulators, such as mTOR inhibitors, AMPK activators, and NAD+ boosters, have demonstrated promising results in rejuvenating immune function in preclinical models. These interventions appear to recalibrate immune cell metabolism, enhance the generation of naive T cells, reduce chronic inflammation, and improve pathogen defense. Crucially, these metabolic interventions could retard immunological aging without compromising immune vigilance or provoking autoimmunity, which historically has complicated immune-targeted therapies.

Dietary interventions stand out as one of the most accessible and impactful strategies to modulate immunometabolism. Caloric restriction and intermittent fasting have long been linked to lifespan extension, and their beneficial effects on the immune system are now coming into focus. Such regimens reduce systemic inflammation, improve mitochondrial function, and reinvigorate thymic output, collectively counteracting immune exhaustion. Additionally, manipulating macronutrient composition to favor metabolic flexibility and bolster mitochondrial health could further optimize immune resilience. Research into how specific dietary components influence metabolic pathways in various immune subsets is rapidly expanding, promising tailored nutritional strategies for healthy aging.

Beyond metabolism and diet, genetic factors substantially influence the pace of immunological aging. Variants in genes regulating mitochondrial biogenesis, antioxidant capacity, and metabolic sensing pathways can predispose individuals to accelerated immune decline or, conversely, confer resilience. Dissecting these genetic determinants in human populations, alongside mechanistic studies in animal models, will allow the identification of biomarkers predictive of immune aging and targets for individualized therapy. This personalization of immunometabolic interventions represents an exciting frontier, blending genomics with metabolic medicine.

Intriguingly, the concept of “organ-resident immunity” has gained traction, revealing a nuanced picture of how local tissue environments shape immune cell metabolism and function. Unlike circulating immune cells, tissue-resident populations such as macrophages and memory T cells exhibit unique metabolic profiles adapted to their niches. Aging alters these microenvironments through fibrosis, altered extracellular matrix, and shifts in local metabolite concentrations, which in turn disrupt resident immune cell behavior. Understanding the metabolic dialogue between these cells and their surrounding tissue may unlock novel strategies to restore immune surveillance in aged organs.

The interplay between cellular senescence and immunometabolism is also a burgeoning area of interest. Senescent cells accumulate with age, secreting pro-inflammatory factors that exacerbate immunological decline. Metabolically, senescent cells exhibit enhanced glycolysis and mitochondrial dysfunction, which could influence neighboring immune cells and systemic inflammation. Therapies aimed at eliminating senescent cells or modulating their metabolic output—termed senolytics and senomorphics—are actively being explored for their capacity to rejuvenate immune functions and extend organismal healthspan.

A key challenge in this field remains the precise dissection of cause and effect within the metabolism-immunity-aging triangle. While metabolic dysregulation clearly drives immune decline, immune dysfunction itself feeds back to disrupt metabolism, creating a vicious cycle. Advanced technologies, such as single-cell metabolomics and high-dimensional immunophenotyping, are empowering researchers to unravel these complex interactions at unprecedented resolution. Integrative computational modeling further aids in predicting system-wide impacts of metabolic interventions on immune aging, paving the way for rational design of clinical trials.

Translation of these insights from bench to bedside holds transformative potential for medicine. Strategies to metabolically rejuvenate the immune system could profoundly impact vaccine efficacy, infection outcomes, cancer immunotherapy, and management of chronic inflammatory diseases in older adults. As the immune-metabolic landscape becomes better charted, clinical interventions can be tailored to individual metabolic profiles and immune status, ushering in an era of precision geroscience.

Moreover, the recognition that metabolic regulation governs immune aging prompts a re-evaluation of aging as a modifiable disease process rather than an inevitable decline. By targeting the metabolic underpinnings of immune dysfunction, it becomes conceivable to not only extend lifespan but also meaningfully enhance quality of life during aging. This paradigm shift aligns with growing societal demands to reduce the burden of age-associated diseases, thereby minimizing healthcare costs and societal impacts.

In conclusion, the metabolic regulation of immunological aging represents a critical nexus for understanding and intervening in the aging process. The intertwined decline of metabolic homeostasis and immune competence dictates susceptibility to disease and lifespan outcomes. Unveiling the precise molecular mechanisms through which metabolism shapes immune aging opens an exciting therapeutic horizon. Interventions spanning genetic, pharmacological, and dietary realms demonstrate that immune rejuvenation through metabolic modulation is within reach. Harnessing this knowledge promises not only to extend healthspan but also to revolutionize how aging is managed in the clinic, offering hope for healthier, more resilient older populations in the near future.

Subject of Research: Metabolic regulation of immunological aging and its impact on healthspan and lifespan.

Article Title: Metabolic regulation of immunological aging.

Article References:
Kim, HH., Dixit, V.D. Metabolic regulation of immunological aging. Nat Aging 5, 1425–1440 (2025). https://doi.org/10.1038/s43587-025-00921-2

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s43587-025-00921-2