Cancer Metabolism vs Immunotherapy: Friend or Enemy?

By Editorial Team

Introduction: Two Revolutions Converging

Immuno-oncology has transformed cancer treatment. PD-1/PD-L1 checkpoint inhibitors, CTLA-4 blockade, CAR-T cell therapy, and bispecific antibodies have produced durable responses in cancers once considered uniformly fatal. At the same time, the field of cancer metabolism has established that tumours are not passive masses of cells but active metabolic ecosystems that consume, divert, and reprogramme the biochemical environment around them.

These two revolutions — immunotherapy and metabolic oncology — are now converging. And the relationship they reveal is both deeply consequential and considerably more complex than either field anticipated.

The fundamental question is: does the metabolic behaviour of the tumour help or harm immune-mediated killing?

The answer, as of 2026, is that tumour metabolism is one of the primary mechanisms of immune evasion — and that correcting the metabolic environment may be one of the most powerful ways to restore immunotherapy efficacy in patients who currently don't respond.

The Tumour Microenvironment as a Metabolic Battlefield

The tumour microenvironment (TME) is not a passive space around the cancer cells — it is a contested biochemical territory in which tumour cells and immune cells compete for the same limited resources.

Tumour cells demand:

  • Glucose (primary carbon source for glycolysis)
  • Glutamine (nitrogen and carbon for biosynthesis)
  • Oxygen (for OXPHOS-active subpopulations)
  • Amino acids (cysteine, methionine, arginine)

Infiltrating immune cells need:

  • Glucose (T cells are highly glycolytic during activation and effector function)
  • Glutamine (essential for T cell proliferation)
  • Arginine (required for macrophage M1 polarisation and T cell signalling)
  • Oxygen and adequate pH (acidic lactate-rich environments impair T cell function)

When rapidly proliferating tumours consume these substrates and excrete metabolic waste products (lactate, protons, adenosine, kynurenine), they create a metabolically hostile microenvironment that is immunosuppressive by design — not by accident.

Key Mechanisms of Metabolic Immune Suppression

1. Lactate-Mediated T Cell and NK Cell Dysfunction

As described in our biomarker article, Warburg-active tumours export lactate via MCT4 transporters, creating a highly acidic, lactate-saturated microenvironment (intratumoral pH can fall as low as 6.0–6.5).

This lactate-acidic environment impairs immune cells through multiple mechanisms:

T cell effects:

  • Lactate import via MCT1 disrupts the lactate gradient required for T cells' own glycolytic metabolism
  • Acidic pH reduces TCR signalling intensity
  • Lactate reduces IFN-γ production — a critical cytokine for anti-tumour T cell effector function
  • Sustained exposure to high lactate drives T cell exhaustion (upregulation of PD-1, TIM-3, LAG-3)

NK cell effects:

  • NK cells rely heavily on glycolysis for cytotoxic granule release
  • Lactate-enriched environments blunt NK cell cytotoxicity against tumour cells
  • Acidic pH impairs NK cell receptor-ligand interactions

Consequence: Even if checkpoint inhibitors successfully block PD-1/PD-L1 inhibitory signalling, T cells infiltrating a lactate-saturated, acidic tumour may be metabolically incapable of mounting effective cytotoxic function.

Therapeutic implication: MCT1/MCT4 inhibitors (in development, e.g., AZD3965) and sodium bicarbonate buffering of tumour pH have both been investigated as strategies to restore immune cell function in the TME. Early-phase data is promising but not yet practice-changing.

2. Glucose Competition and T Cell Metabolic Starvation

In high-glycolytic tumours, glucose is consumed so rapidly by tumour cells that infiltrating T cells face glucose deprivation. This matters profoundly because:

  • Activated effector T cells are highly glycolytic — glucose is their primary fuel during cytotoxic function
  • Glucose-deprived T cells shift to fatty acid oxidation (FAO), which supports memory T cell survival but impairs effector cytotoxicity
  • Low intratumoral glucose reduces glycolytic metabolites that serve as epigenetic substrates — specifically acetyl-CoA (from pyruvate), which is required for histone acetylation in the IFN-γ gene promoter

This last point is particularly elegant: tumour glucose consumption doesn't just starve T cells of energy — it epigenetically silences their ability to produce cytotoxic cytokines.

A landmark 2021 study (Chang et al., Nature) demonstrated that tumours with higher glycolytic activity suppressed T cell IFN-γ production through exactly this mechanism, and that restoring T cell glucose access (via glycolysis competitor restriction) rescued anti-tumour function.

Therapeutic implication: Strategies that limit tumour glucose consumption — glucose-lowering drugs, dietary carbohydrate restriction, GLUT1 inhibitors — may paradoxically improve T cell metabolic access to glucose within the TME, enhancing immunotherapy efficacy.

3. Adenosine and the Immunosuppressive Purine Axis

When cancer cells and stressed stromal cells die or experience hypoxia, they release ATP, which is rapidly catabolised in the TME to adenosine by the ectoenzymes CD39 and CD73. Adenosine binds to A2A receptors on T cells and NK cells, triggering a potent immunosuppressive programme:

  • Elevated cAMP → PKA activation → suppression of TCR signalling
  • Reduced effector cytokine production (IL-2, IFN-γ, TNF-α)
  • Promotion of regulatory T cell (Treg) expansion
  • Suppression of DC maturation and antigen presentation

The adenosine axis is intimately connected to tumour metabolism: hypoxia-inducible CD39 and CD73 upregulation is driven by HIF-1α — directly linking Warburg hypoxic physiology to immunosuppression.

Therapeutic implication: CD39 and CD73 inhibitors are in clinical trials (oleclumab, mupadolimab), aiming to reduce adenosine accumulation in the TME. These represent a direct metabolic-immune interface therapeutic target. Dietary purines (found in red meat, organ meats, shellfish) and their systemic metabolism may also modulate this axis — a hypothesis not yet rigorously tested.

4. Indoleamine 2,3-Dioxygenase (IDO) and Kynurenine

IDO1 and IDO2 are metabolic enzymes expressed by tumour cells and immunosuppressive macrophages that catabolise tryptophan into kynurenine and downstream metabolites.

The consequences are twofold:

  1. Tryptophan depletion: T cells require tryptophan for protein synthesis; depletion in the local microenvironment activates the GCN2 eIF2α kinase stress pathway, halting T cell proliferation
  2. Kynurenine accumulation: Kynurenine activates the aryl hydrocarbon receptor (AhR) in T cells, driving differentiation toward immunosuppressive regulatory T cells (Tregs) and suppressing effector function

IDO1 expression is upregulated by IFN-γ — meaning that successful early immunotherapy responses can paradoxically induce IDO-mediated immune suppression, creating an adaptive resistance loop.

Dietary connection: Tryptophan intake (from protein-rich foods) influences systemic tryptophan availability. Targeted reduction of tryptophan precursors is being explored in this context. More practically, IDO inhibitors (epacadostat, BMS-986205) were a major area of clinical development — early results were disappointing in combination with pembrolizumab, but the biology remains relevant and refinement continues.

5. Hypoxia and PD-L1 Upregulation

Hypoxia — a near-universal feature of solid tumours — drives expression of PD-L1 (programmed death-ligand 1) on tumour cells and myeloid cells via HIF-1α. This creates a metabolic-immune feedback loop:

  • Tumour glycolysis → oxygen consumption → hypoxia → HIF-1α activation → PD-L1 upregulation → T cell exhaustion → impaired tumour killing → tumour progression

This means that the very act of consuming glucose aerobically is, in part, a mechanism of immune evasion. Tumour glycolysis and immune checkpoint expression are not independent phenomena — they are mechanistically linked.

Implication: Reducing tumour glucose consumption (via caloric restriction, glucose-lowering interventions) may reduce hypoxia, HIF-1α activation, and PD-L1 expression — potentially sensitising tumours to checkpoint inhibition.

This hypothesis is now being tested in clinical trials pairing dietary or pharmacological glucose restriction with anti-PD-1/PD-L1 therapy.

The Other Side: Metabolism as an Ally of Immunotherapy

Despite the immunosuppressive mechanisms above, tumour metabolism is not uniformly hostile to immune function. Several metabolic scenarios support rather than suppress anti-tumour immunity:

Caloric Restriction and Fasting Enhance Anti-Tumour Immunity

Short-term fasting and caloric restriction produce a systemic hormonal shift (low insulin, low IGF-1, elevated corticosteroids) that paradoxically enhances some aspects of immune function:

  • Fasting promotes hematopoietic stem cell regeneration
  • Reduced systemic IGF-1 decreases Treg number and function
  • Ketone bodies (BHB) have direct anti-inflammatory effects via NLRP3 inflammasome inhibition
  • Autophagy upregulation during fasting may enhance antigen presentation by dendritic cells

Animal studies have consistently shown that fasting-mimicking diets (FMD) improve response to multiple immunotherapy modalities, including checkpoint inhibitors and CAR-T cells. Clinical translation of these findings is ongoing.

Fatty Acid Oxidation Supports CD8+ Memory T Cells

Memory T cells — the long-lived immune cells that provide durable protection after successful tumour clearance — rely preferentially on fatty acid oxidation (FAO) rather than glycolysis for energy. This is why:

  • Metformin, which promotes AMPK activation and FAO, may enhance memory T cell persistence after immunotherapy
  • Ketogenic diets, which increase fatty acid and ketone availability, may support memory T cell maintenance in the post-treatment setting

This is a genuinely positive intersection: metabolic interventions that support FAO may not only impair tumour glycolysis but concurrently enhance the metabolic substrate availability for the immune cells we most want to preserve.

PD-1 Blockade Restores T Cell Glycolytic Capacity

PD-1 signalling directly suppresses T cell metabolism by inhibiting the PI3K/AKT/mTOR axis — suppressing glycolysis and reducing mitochondrial fitness. When PD-1 is blocked with checkpoint inhibitors, T cells regain metabolic fitness:

  • Restored glucose uptake (GLUT1 surface expression recovers)
  • Enhanced mitochondrial biogenesis
  • Improved effector cytokine production

This creates a virtuous cycle: checkpoint inhibition restores T cell metabolism, enabling effector function. Metabolic interventions that pre-condition T cells to be metabolically fit may amplify this effect.

Combination Strategies: Metabolic Oncology Meets Immuno-Oncology

The convergence of these fields has generated multiple active areas of combination research:

1. Ketogenic Diet + Checkpoint Inhibitors

Preclinical data shows that ketogenic diets reduce tumour glycolysis, lower intratumoral lactate, improve T cell infiltration, and enhance anti-PD-1 efficacy in mouse models. Several human pilot studies are underway.

Key question: Does KD-induced BHB have direct immunostimulatory effects beyond its metabolic role? Early evidence suggests BHB may inhibit HDAC enzymes and promote specific immune gene expression — a potentially synergistic mechanism.

2. Metformin + Anti-PD-1/PD-L1

Metformin is perhaps the most extensively studied metabolic-immune combination partner. Proposed mechanisms:

  • Reduces tumour glycolysis and lactate production
  • Lowers systemic insulin and IGF-1
  • Activates AMPK in both tumour and immune cells → differential effects favouring immune activation
  • May reduce MDSCs (myeloid-derived suppressor cells) in the TME
  • Directly promotes CD8+ T cell memory phenotype

Retrospective studies show improved anti-PD-1 response rates in diabetic cancer patients on metformin. Prospective trials (e.g., EXTRA trial in NSCLC, MK-3475 combinations) are generating Phase II data.

3. MCT Inhibitors + Immunotherapy

If lactate is a primary immunosuppressive metabolite, then blocking its export should sensitise tumours to immune attack. AZD3965 (MCT1 inhibitor) has completed Phase I with demonstrated target engagement. Combination strategies with checkpoint inhibitors are in development.

4. IDO Inhibitors + PD-1 Blockade

Despite disappointing Phase III data with epacadostat + pembrolizumab (ECHO-301, 2018), the IDO pathway remains a legitimate metabolic-immune target. The failure may have been patient selection rather than mechanism. Next-generation IDO inhibitors with better selectivity are in development.

5. Fasting-Mimicking Diets (FMD) + Standard Immunotherapy

FMD protocols — cycling 5-day very-low-calorie fasting periods monthly — are being tested alongside pembrolizumab, atezolizumab, and other checkpoint inhibitors. The DIRECT-FMD trial (Italy) is generating prospective data. The CALERIE-CANCER trial extension is investigating FMD effects on circulating immune cell phenotype.

Patient Selection: Who Benefits from Metabolic-Immune Combinations?

Not all patients receiving immunotherapy will benefit from metabolic co-interventions. Likely responders to metabolic-immune combination strategies include patients with:

  • High tumour glycolytic activity (FDG-PET SUVmax >8) — greatest metabolic immunosuppression, most to gain from metabolic correction
  • Low or absent TILs at baseline — if T cell exclusion is metabolically mediated, correcting metabolism may allow infiltration
  • High systemic insulin/HOMA-IR — systemic metabolic improvement may dually reduce tumour driver signalling and improve immune surveillance
  • Adequate nutritional status — cachexic patients cannot tolerate restriction strategies; immune function in cachexia is already compromised

Patients who are less likely to benefit or who may be harmed include those with:

  • Active autoimmune disease (metabolic manipulation may unpredictably affect autoimmune flares)
  • Severe cachexia (further restriction may worsen outcomes)
  • Low tumour metabolic activity (less metabolic immunosuppression to correct)

Conclusion: From Competition to Collaboration

The relationship between cancer metabolism and immunotherapy is not adversarial in a simple sense — it is bidirectional, context-dependent, and ultimately reconcilable. Tumour metabolism creates immunosuppressive conditions that impair the efficacy of checkpoint inhibitors and cellular therapies. But the same metabolic mechanisms that impair tumour immunity can be modulated — through diet, pharmacology, and lifestyle — to restore the conditions that allow immunotherapy to work.

In 2026, the integration of metabolic oncology and immuno-oncology is no longer a speculative frontier. It is an active clinical research priority, with multiple combination trials underway and a growing body of mechanistic evidence supporting the hypothesis that correcting tumour metabolism is one of the most actionable ways to enhance immune-mediated cancer control.

For patients currently receiving checkpoint inhibitors without response, the metabolic microenvironment should be considered alongside conventional resistance mechanisms (tumour mutational burden, antigen loss, mismatch repair status) as a modifiable contributor to treatment failure.

The future of oncology is not immunotherapy alone or metabolic therapy alone — it is the intelligent, biomarker-guided integration of both.

This article is for educational purposes for clinicians, researchers, and informed patients. It does not constitute medical advice. Always discuss treatment decisions with a qualified oncologist.

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