Conditional Deletion of PGC-1α Results in Energetic and Functional Defects in NK Cells

The ω-3 Polyunsaturated Fatty Acid Docosahexaenoic Acid Enhances NK-Cell Antitumor Effector Functions

ω-3 polyunsaturated fatty acids (PUFA) are known to directly repress tumor development and progression. In this study, we explored whether docosahexaenoic acid (DHA), a type of ω-3 PUFA, had an immunomodulatory role in inhibiting tumor growth in immunocompetent mice. The number of natural killer (NK) cells but not the number of T or B cells was decreased by DHA supplementation in various tissues under physiologic conditions. Although the frequency and number of NK cells were comparable, IFNγ production by NK cells in both the spleen and lung was increased in DHA-supplemented mice in the mouse B16F10 melanoma tumor model. Single-cell RNA sequencing revealed that DHA promoted effector function and oxidative phosphorylation in NK cells but had no obvious effects on other immune cells. Using Rag2-/- mice and NK-cell depletion by PK136 antibody injection, we demonstrated that the suppression of B16F10 melanoma tumor growth in the lung by DHA supplementation was dependent mainly on NK cells. In vitro experiments showed that DHA directly enhanced IFNγ production, CD107a expression, and mitochondrial oxidative phosphorylation (OXPHOS) activity and slightly increased proliferator-activated receptor gamma coactivator-1α (PGC-1α) protein expression in NK cells. The PGC-1α inhibitor SR-18292 in vitro and NK cell-specific knockout of PGC-1α in mice reversed the antitumor effects of DHA. In summary, our findings broaden the current knowledge on how DHA supplementation protects against cancer growth from the perspective of immunomodulation by upregulating PGC-1α signaling-mediated mitochondrial OXPHOS activity in NK cells.

Immunometabolic features of natural killer cells are associated with infection outcomes in critical illness

Immunosuppression increases the risk of nosocomial infection in patients with chronic critical illness. This exploratory study aimed to determine the immunometabolic signature associated with nosocomial infection during chronic critical illness. We prospectively recruited patients who were admitted to the respiratory care center and who had received mechanical ventilator support for more than 10 days in the intensive care unit. The study subjects were followed for the occurrence of nosocomial infection until 6 weeks after admission, hospital discharge, or death. The cytokine levels in the plasma samples were measured. Single-cell immunometabolic regulome profiling by mass cytometry, which analyzed 16 metabolic regulators in 21 immune subsets, was performed to identify immunometabolic features associated with the risk of nosocomial infection. During the study period, 37 patients were enrolled, and 16 patients (43.2%) developed nosocomial infection. Unsupervised immunologic clustering using multidimensional scaling and logistic regression analyses revealed that expression of nuclear respiratory factor 1 (NRF1) and carnitine palmitoyltransferase 1a (CPT1a), key regulators of mitochondrial biogenesis and fatty acid transport, respectively, in natural killer (NK) cells was significantly associated with nosocomial infection. Downregulated NRF1 and upregulated CPT1a were found in all subsets of NK cells from patients who developed a nosocomial infection. The risk of nosocomial infection is significantly correlated with the predictive score developed by selecting NK cell-specific features using an elastic net algorithm. Findings were further examined in an independent cohort of COVID-19-infected patients, and the results confirm that COVID-19-related mortality is significantly associated with mitochondria biogenesis and fatty acid oxidation pathways in NK cells. In conclusion, this study uncovers that NK cell-specific immunometabolic features are significantly associated with the occurrence and fatal outcomes of infection in critically ill population, and provides mechanistic insights into NK cell-specific immunity against microbial invasion in critical illness.

Sufficiently activated mature natural killer cells derived from peripheral blood mononuclear cells substantially enhance antitumor activity

BACKGROUND

Peripheral blood-derived natural killer (NK) cells spontaneously lyse tumor cells without prior sensitization. However, NK cells in peripheral blood (PBNK cells) are in a resting state and exhibit inhibitory phenotypes and impaired cytotoxicity. Thus, strengthening the cytotoxic effector function of PBNK cells and improving NK cell expansion in vitro for a convenient allogeneic therapy are essential.

MATERIALS AND METHODS

Pure cytokine activation and expansion of NK cells (super NK [SNK]) from peripheral blood mononuclear cells were studied. Markers of activated and inhibited NK cells and cytokine secretion by NK cells were examined using flow cytometry. NK cell antitumor activity in vitro was assessed using lactate dehydrogenase (LDH) cytotoxicity assay and an Incucyte real-time imaging system. Additionally, the function of SNK cells against ascites caused by ovarian cancer in NOD-Prkdc(em26Cd52)il2rg(em26Cd22)/Nju (NCG) mice was determined. In a further investigation of the differences between PBNK and SNK, the mRNA of both cells was sequenced and analyzed.

RESULTS

Human peripheral blood mononuclear cells showed selective NK cell expansion upon cytokine activation and culture. Both SNK and PBNK cells expressed activation markers, but at different levels, and SNK cells secreted more cytokines related to cytotoxicity than PBNK cells did. Accordingly, SNK cells exhibited strong antitumor activity ex vivo and improved NCG mice survival after intraperitoneal ovarian cancer transplantation. Mechanistically, SNK cells expressed more genes associated with nucleotide metabolism, fatty acid, and ATP metabolism than PBNK cells.

CONCLUSION

SNK cells derived from peripheral blood mononuclear cells have sufficiently activated mature characteristics and high antitumor activity, rendering them a highly promising and essential therapeutic approach for cancer treatment.

Vaccine-boosted CAR T crosstalk with host immunity to reject tumors with antigen heterogeneity

Chimeric antigen receptor (CAR) T cell therapy effectively treats human cancer, but the loss of the antigen recognized by the CAR poses a major obstacle. We found that in vivo vaccine boosting of CAR T cells triggers the engagement of the endogenous immune system to circumvent antigen-negative tumor escape. Vaccine-boosted CAR T promoted dendritic cell (DC) recruitment to tumors, increased tumor antigen uptake by DCs, and elicited the priming of endogenous anti-tumor T cells. This process was accompanied by shifts in CAR T metabolism toward oxidative phosphorylation (OXPHOS) and was critically dependent on CAR-T-derived IFN-γ. Antigen spreading (AS) induced by vaccine-boosted CAR T enabled a proportion of complete responses even when the initial tumor was 50% CAR antigen negative, and heterogeneous tumor control was further enhanced by the genetic amplification of CAR T IFN-γ expression. Thus, CAR-T-cell-derived IFN-γ plays a critical role in promoting AS, and vaccine boosting provides a clinically translatable strategy to drive such responses against solid tumors.

Enhancement of the Anticancer Ability of Natural Killer Cells through Allogeneic Mitochondrial Transfer

An in vitro culture period of at least 2 weeks is required to produce sufficient natural killer (NK) cells for immunotherapy, which are the key effectors in hematological malignancy treatment. Mitochondrial damage and fragmentation reduce the NK cell immune surveillance capacity. Thus, we hypothesized that the transfer of healthy mitochondria to NK cells could enhance their anticancer effects. Allogeneic healthy mitochondria isolated from WRL-68 cells were transferred to NK cells. We evaluated NK cells' proliferative capacity, cell cycle, and cytotoxic capacity against various cancer cell types by analyzing specific lysis and the cytotoxic granules released. The relationship between the transferred allogenic mitochondrial residues and NK cell function was determined. After mitochondrial transfer, the NK cell proliferation rate was 1.2-fold higher than that of control cells. The mitochondria-treated NK cells secreted a 2.7-, 4.1-, and 5-fold higher amount of granzyme B, perforin, and IFN-γ, respectively, when co-cultured with K562 cells. The specific lysis of various solid cancer cells increased 1.3-1.6-fold. However, once allogeneic mitochondria were eliminated, the NK cell activity returned to the pre-mitochondrial transfer level. Mitochondria-enriched NK cells have the potential to be used as a novel solid cancer treatment agent, without the need for in vitro cytokine-induced culture.

Metabolism of NK cells during viral infections

Cellular metabolism is essential for the correct function of immune system cells, including Natural Killer cells (NK). These cells depend on energy to carry out their effector functions, especially in the early stages of viral infection. NK cells participate in the innate immune response against viruses and tumors. Their main functions are cytotoxicity and cytokine production. Metabolic changes can impact intracellular signals, molecule production, secretion, and cell activation which is essential as the first line of immune defense. Metabolic variations in different immune cells in response to a tumor or pathogen infection have been described; however, little is known about NK cell metabolism in the context of viral infection. This review summarizes the activation-specific metabolic changes in NK cells, the immunometabolism of NK cells during early, late, and chronic antiviral responses, and the metabolic alterations in NK cells in SARS-CoV2 infection. The modulation points of these metabolic routes are also discussed to explore potential new immunotherapies against viral infections.

Mechanisms of mitochondrial respiratory adaptation

Mitochondrial energetic adaptations encompass a plethora of conserved processes that maintain cell and organismal fitness and survival in the changing environment by adjusting the respiratory capacity of mitochondria. These mitochondrial responses are governed by general principles of regulatory biology exemplified by changes in gene expression, protein translation, protein complex formation, transmembrane transport, enzymatic activities and metabolite levels. These changes can promote mitochondrial biogenesis and membrane dynamics that in turn support mitochondrial respiration. The main regulatory components of mitochondrial energetic adaptation include: the transcription coactivator peroxisome proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC1α) and associated transcription factors; mTOR and endoplasmic reticulum stress signalling; TOM70-dependent mitochondrial protein import; the cristae remodelling factors, including mitochondrial contact site and cristae organizing system (MICOS) and OPA1; lipid remodelling; and the assembly and metabolite-dependent regulation of respiratory complexes. These adaptive molecular and structural mechanisms increase respiration to maintain basic processes specific to cell types and tissues. Failure to execute these regulatory responses causes cell damage and inflammation or senescence, compromising cell survival and the ability to adapt to energetically demanding conditions. Thus, mitochondrial adaptive cellular processes are important for physiological responses, including to nutrient availability, temperature and physical activity, and their failure leads to diseases associated with mitochondrial dysfunction such as metabolic and age-associated diseases and cancer.

Metabolic Rewiring in the Tumor Microenvironment to Support Immunotherapy: A Focus on Neutrophils, Polymorphonuclear Myeloid-Derived Suppressor Cells and Natural Killer Cells

Leukocytes often undergo rapid changes in cell phenotype, for example, from a resting to an activated state, which places significant metabolic demands on the cell. These rapid changes in metabolic demand need to be tightly regulated to support immune cell effector functions during the initiation and downregulation of an immune response. Prospects for implementing cancer immunotherapy also rest on the idea of optimizing the metabolic profile of immune cell effectors. Here, we examine this issue by focusing on neutrophils and NK cells as cells of increasing interest in cancer immunology and tumor immunometabolism, because they can be targeted or, in the case of NK, used as effectors in immunotherapy. In addition, neutrophils and NK cells have been shown to functionally interact. In the case of neutrophils, we also extended our interest to polymorphonuclear MDSC (PMN-MDSCs), since the granulocytic subset of MDSCs share many phenotypes and are functionally similar to pro-tumor neutrophils. Finally, we reviewed relevant strategies to target tumor metabolism, focusing on neutrophils and NK cells.

PGC1s and Beyond: Disentangling the Complex Regulation of Mitochondrial and Cellular Metabolism

Metabolism is the central engine of living organisms as it provides energy and building blocks for many essential components of each cell, which are required for specific functions in different tissues. Mitochondria are the main site for energy production in living organisms and they also provide intermediate metabolites required for the synthesis of other biologically relevant molecules. Such cellular processes are finely tuned at different levels, including allosteric regulation, posttranslational modifications, and transcription of genes encoding key proteins in metabolic pathways. Peroxisome proliferator activated receptor γ coactivator 1 (PGC1) proteins are transcriptional coactivators involved in the regulation of many cellular processes, mostly ascribable to metabolic pathways. Here, we will discuss some aspects of the cellular processes regulated by PGC1s, bringing up some examples of their role in mitochondrial and cellular metabolism, and how metabolic regulation in mitochondria by members of the PGC1 family affects the immune system. We will analyze how PGC1 proteins are regulated at the transcriptional and posttranslational level and will also examine other regulators of mitochondrial metabolism and the related cellular functions, considering approaches to identify novel mitochondrial regulators and their role in physiology and disease. Finally, we will analyze possible therapeutical perspectives currently under assessment that are applicable to different disease states.