Abstract Natural killer (NK) cells infiltrate many solid tumours, yet the mechanisms that determine their functional heterogeneity across tumour types remain poorly understood. Differences in tumour immunogenicity, inhibitory signalling, and nutrient availability have all been implicated, but unifying explanations are lacking. Here, we compared four syngeneic tumour models implanted at identical anatomical sites to isolate tumour-intrinsic effects on NK-cell fate. Tumour-infiltrating NK cells displayed striking tumour-specific differences in cytokine production, cytotoxic protein expression, and persistence. These differences were not explained by cytokine availability or global features of the tumour metabolic environment. Instead, quantitative proteomics and time-resolved in vivo labelling revealed that NK cells enter tumours in a functionally competent state but rapidly diverge thereafter. In suppressive tumour microenvironments, NK cells undergo early mitochondrial loss, translational repression, and impaired proteostatic responses, accompanied by increased apoptotic priming. These defects result in reduced effector function and failure of intratumoural persistence despite preserved recruitment. In contrast, permissive tumours sustain NK-cell translational capacity, cytokine responsiveness, and long-term residency. Together, these findings identify disruption of translational and mitochondrial homeostasis as a central mechanism limiting NK-cell persistence in solid tumours. This work establishes early tumour-induced defects in protein synthesis and cellular fitness as key constraints on durable NK-cell immunity and provides a framework for restoring effective innate anti-tumour responses.

Abstract Cutaneous melanoma is a highly metastatic cancer which had limited treatment options until the advent of immune checkpoint inhibitors (ICI); however, only around 50% of patients respond. Natural killer (NK) cells are potent cytotoxic and cytokine producing lymphocytes which present a promising avenue for immunotherapy. However, the progressive dysfunction of NK cells during cancer development represents a major barrier to effective autologous therapies. This study investigated the metabolic and functional plasticity of circulating NK cells during melanoma progression from Stage III lymph node positive and Stage IV metastatic melanoma. Stage III patient NK cells displayed reduced mitochondrial mass, fragmented morphology and dysregulated mTORC1 activity, accompanied by impaired cytotoxicity. Stage IV patients showed severe mitochondrial fragmentation, altered mTORC1 activation and markedly reduced cytokine responsiveness. Pharmacologic restoration of mTORC1 activity using MHY1485 rescued IFN-y production in Stage III but not Stage IV patient NK cells, suggesting stage-dependent differences in metabolic responsiveness. Collectively, these findings indicate progressive metabolic and functional impairment of circulating NK cells as melanoma advances and highlight a potential window for therapeutic intervention earlier in disease progression.

Natural Killer (NK) cells are innate lymphocytes that are key to intrinsic cancer immunosurveillance and an important target for cancer immunotherapy. Understanding fundamental human NK cell metabolism provides opportunities for optimizing NK cell therapies. Little is known about how glutamine, an important cell nutrient and carbon source, is utilized by human NK cells. To address this, we performed U13C-glutamine tracing experiments by Liquid Chromatography Mass Spectrometry and Gas Chromatography Mass Spectrometry analysis of human NK cells stimulated with IL-2 for 18 h to provide a global overview of glutamine usage by these cells. Our results show that glutamine is taken up by resting NK cells and that this increases further upon IL-2 stimulation. Metabolite labelling analysis identified that IL-2 stimulation results in greater conversion of glutamine to glutamate, allowing for anaplerotic flux into the TCA cycle. The fate of the glutamine-derived carbons diverged at oxaloacetate allowing both bioenergetic and biosynthetic outcomes - some carbons continued around the TCA cycle while others were exported, converted to aspartate and subsequently used for pyrimidine synthesis. Nucleotide synthesis by IL-2 activated NK cells was found to be essential for expression of the activation marker CD69. The data indicate that glutamine is a key nutrient taken up by human NK cells, and that IL-2 drives glutaminolysis. Subsequent glutamate is used to support the TCA cycle, generating energy and providing intermediates for de novo pyrimidine synthesis.

High-grade serous ovarian cancer (HGSOC) remains an urgent unmet clinical need, with more than 70% of patients presenting with metastatic disease. Many patients develop large volumes of ascites, which promotes metastasis and is associated with poor therapeutic response and survival. Immunotherapy trials have shown limited success, highlighting the need to better understand HGSOC immunology. Here, we analyzed cytotoxic lymphocytes [natural killer (NK), T, and innate T cells] from patients with HGSOC and observed widespread dysfunction across primary and metastatic sites. Although nutrient rich, ascites was immunosuppressive for all lymphocyte subsets. NK cell dysfunction was driven by uptake of polar lipids, with associated dysregulation in lipid storage. Phosphatidylcholine was a key immunosuppressive metabolite, disrupting NK cell membrane order and cytotoxicity. Blocking lipid uptake through SR-B1 protected NK cell antitumor functions in ascites. These findings offer insights into immune suppression in HGSOC and have important implications for the design of future immunotherapies.

Tumor-treating fields (TTFs) are a non-invasive treatment for glioblastoma (GBM) that applies low-intensity, intermediate-frequency, alternating electric fields. Given a 5-year survival of less than 7% for GBM patients, multi-modal treatments are required to improve survival. Natural killer (NK) cells are innate lymphocytes that kill cancer cells and are thus a major target for new immunotherapy approaches. There is potential to combine TTFs with an NK cell-based therapy for GBM treatment. Here, we investigate the impact of TTFs on NK cell viability and functions. Exposure to TTFs does not affect NK cell viability or interferon (IFN)-γ production, a key NK cell function. Of significance, exposure to TTFs increases NK cell degranulation, a proxy of cell killing. These data suggest that the combination of TTFs and NK cell-based therapy may boost tumor cell killing. This provides a basis to further explore this combination, with the end goal of enhancing NK cell immunotherapy potential for patients with GBM.

The recent pandemic was caused by the emergence of a new human pathogen, SARS-CoV-2. While the rapid development of many vaccines provided an end to the immediate crisis, there remains an urgent need to understand more about this new virus and what constitutes a beneficial immune response in terms of successful resolution of infection. Indeed, this is key for development of vaccines that provide long lasting protective immunity. The interferon lambda (IFNL) family of cytokines are produced early in response to infection and are generally considered anti-viral and beneficial. However, data regarding production of IFNL cytokines in coronavirus disease 2019 (COVID-19) patients is highly variable, and generally from underpowered studies. In this study, we measured all three IFNL1, IFNL2, and IFNL3 cytokines in plasma from a well characterized, large COVID-19 cohort (n = 399) that included good representation from patients with a more indolent disease progression, and hence a beneficial immune response. While all three cytokines were produced, they differed in both the frequency of expression in patients, and the levels produced. IFNL3 was produced in almost all patients but neither protein level nor IFNL3/IFNL4 single nucleotide polymorphisms were associated with clinical outcome. In contrast, both IFNL1 and IFNL2 levels were significantly lower, or absent, in plasma of patients that had a more severe disease outcome. These data are consistent with the concept that early IFNL1 and IFNL2 cytokine production is protective against SARS-CoV-2 infection.

High risk neuroblastoma is responsible for 15% of deaths in pediatric cancer patients. The introduction of anti-GD2 immunotherapy has significantly improved outcomes but there is still only approximately a 50% 5 year event-free-survival for these children and improvements in treatments are urgently required. Anti-GD2 immunotherapy uses the patients’ own immune system to kill cancer cells. In particular, Natural Killer (NK) cells kill antibody coated tumor cells by a process called antibody dependent cellular cytotoxicity (ADCC). However, our previous work has highlighted metabolic exhaustion of NK cells in circulating blood of adult cancer patients, identifying this as a potential therapeutic target. In this study, we investigated circulating NK cells in patients newly diagnosed with neuroblastoma. We found evidence of activation of NK cells in vivo by the cancer itself. While some evidence of NK cell dysfunction was observed in terms of IFNγ production, most results indicated that the NK cell compartment remained relatively intact. In fact, some aspects of metabolic and functional activities were actually increased in patients compared to controls. Glycolytic responses, which we show are crucial for ADCC, were actually enhanced in patients and CD16, the NK cell receptor that mediates ADCC, was also expressed at high levels in some patients. Overall, the data suggest that patient NK cells could be harvested at diagnosis for subsequent beneficial autologous use during immunotherapy. Enhancing glycolytic capacity of cell therapies could also be a strategic goal of future cell therapies for patients with neuroblastoma and indeed other cancers.

Effective vaccines for human immunodeficiency virus-1 (HIV-1) and hepatitis C virus (HCV) remain a significant challenge for these infectious diseases. Given that the innate immune response is key to controlling the scale and nature of developing adaptive immune responses, targeting natural killer (NK) cells that can promote a T-helper type 1 (Th1)-type immune response through the production of interferon-γ (IFNγ) remains an untapped strategic target for improved vaccination approaches. Here, we investigate metabolic and functional responses of NK cells to simian adenovirus prime and MVA boost vaccination in a cohort of healthy volunteers receiving a dual HCV-HIV-1 vaccine. Early and late timepoints demonstrated metabolic changes that contributed to the sustained proliferation of all NK cells. However, a strong impact of human cytomegalovirus (HCMV) on some metabolic and functional responses in NK cells was observed in HCMV seropositive participants. These changes were not restricted to molecularly defined adaptive NK cells; indeed, canonical NK cells that produced most IFNγ in response to vaccination were equally impacted in individuals with latent HCMV. In summary, NK cells undergo metabolic changes in response to vaccination, and understanding these in the context of HCMV is an important step towards rational vaccine design against a range of human viral pathogens.

Natural killer (NK) cells are a population of innate immune cells that can rapidly kill cancer cells and produce cytokines such as interferon-γ. A key feature of NK cells is their ability to respond without prior sensitization; however, it is now well established that NK cells can possess memory-like features. After activation with cytokines, NK cells demonstrate enhanced effector functions upon restimulation days or weeks later. This demonstrates that NK cells may be trained to be more effective killers and harnessed as more potent cancer immunotherapy agents. We have previously demonstrated that cellular metabolism is essential for NK cell responses, with NK cells upregulating both glycolysis and oxidative phosphorylation upon cytokine stimulation. Limiting NK cell metabolism results in reduced cytotoxicity and cytokine production. We have also demonstrated that defective NK cell responses in obesity are linked to defective cellular metabolism. In the current study, we investigated if cellular metabolism is required during the initial period of NK cell cytokine training and if NK cells from people with obesity (PWO) can be effectively trained. We show that increased flux through glycolysis and oxidative phosphorylation during the initial cytokine activation period is essential for NK cell training, as is the metabolic signaling factor Srebp. We show that NK cells from PWO, which are metabolically defective, display impaired NK cell training, which may have implications for immunotherapy in this particularly vulnerable group.

BackgroundNatural killer (NK) cells provide important immune protection from cancer and are a key requirement for particular immunotherapies. There is accumulating evidence that NK cells become dysfunctional during cancer. Overcoming NK cell exhaustion would be an important step to allow them to function optimally in a range of NK cell therapies, including those that depend on autologos circulating NK cells. We have previously demonstrated that NK cells undergo a normal metabolic reprogramming in response to cytokine activation and that this is required for optimal function. The objective of this work was to investigate if cellular metabolism of circulating NK cells is dysregulated in patients with metastatic breast cancer and if so, to gain insights into potential mechanisms underpinning this. Such discoveries would provide important insights into how to unleash the full activity of NK cells for maximum immunotherapy output.MethodsSingle-cell analysis, metabolic flux and confocal analysis of NK cells from patients with metastatic breast cancer and healthy controlsResultsIn addition to reduced interferon-γ production and cytotoxicity, peripheral blood NK cells from patients had clear metabolic deficits including reduced glycolysis and oxidative phosphorylation. There were also distinct morphologically alterations in the mitochondria with increased mitochondrial fragmentation observed. Transforminggrowth factor-β (TGFβ) was identified as a key driver of this phenotype as blocking its activity reversed many metabolic and functional readouts. Expression of glycoprotein-A repetitions predominant (GARP) and latency associated peptide (LAP), which are involved with a novel TGFβ processing pathway, was increased on NK cells from some patients. Blocking the GARP–TGFβ axis recapitulated the effects of TGFβ neutralization, highlighting GARP as a novel NK cell immunotherapy target for the first time.ConclusionsTGFβ contributes to metabolic dysfunction of circulating NK cells in patients with metastatic breast cancer. Blocking TGFβ and/or GARP can restore NK cell metabolism and function and is an important target for improving NK cell-based immunotherapies.

Natural Killer (NK) cells have an important role in immune responses to viruses and tumours. Integrating changes in signal transduction pathways and cellular metabolism is essential for effective NK cells responses. The glycolytic enzyme Pyruvate Kinase Muscle 2 (PKM2) has described roles in regulating glycolytic flux and signal transduction, particularly gene transcription. While PKM2 expression is robustly induced in activated NK cells, mice lacking PKM2 in NK cells showed no defect in NK cell metabolism, transcription or antiviral responses to MCMV infection. NK cell metabolism was maintained due to compensatory PKM1 expression in PKM2-null NK cells. To further investigate the role of PKM2, we used TEPP-46, which increases PKM2 catalytic activity while inhibiting any PKM2 signalling functions. NK cells activated with TEPP-46 had reduced effector function due to TEPP-46-induced increases in oxidative stress. Overall, PKM2-regulated glycolytic metabolism and redox status, not transcriptional control, facilitate optimal NK cells responses.

Cellular metabolism is dynamically regulated in NK cells and strongly influences their responses. Metabolic dysfunction is linked to defective NK cell responses in diseases such as obesity and cancer. The transcription factors, sterol regulatory element binding protein (SREBP) and cMyc, are crucial for controlling NK cell metabolic and functional responses, though the mechanisms involved are not fully understood. This study reveals a new role for SREBP in NK cells in supporting de novo polyamine synthesis through facilitating elevated cMyc expression. Polyamines have diverse roles and their de novo synthesis is required for NK cell glycolytic and oxidative metabolism and to support optimal NK cell effector functions. When NK cells with impaired SREBP activity were supplemented with exogenous polyamines, NK cell metabolic defects were not rescued but these NK cells displayed significant improvement in some effector functions. One role for polyamines is in the control of protein translation where spermidine supports the posttranslational hypusination of translation factor eIF5a. Pharmacological inhibition of hypusination also impacts upon NK cell metabolism and effector function. Considering recent evidence that cholesterol-rich tumor microenvironments inhibit SREBP activation and drive lymphocyte dysfunction, this study provides key mechanistic insight into this tumor-evasion strategy.