The CD16−/CD56brightSubset of NK Cells Is Resistant to Oxidant-Induced Cell Death

Immunotherapy Using Activated Natural Killer Cells Improves Postoperative Neutrophil-to-Lymphocyte Ratio and Long-Term Prognosis of Living Donor Liver Transplant Recipients With Hepatocellular Carcinoma

OBJECTIVE

Preoperative neutrophil-to-lymphocyte ratio (NLR) is a well-known prognostic indicator in various malignancies; however, the impact of postoperative NLR on living donor liver transplant (LDLT) recipients is unknown. Immunotherapy with donor liver-derived activated natural killer (NK) cells may improve postoperative NLR by coactivating immune cells or suppressing activated neutrophils. This study aims to clarify the clinical significance of postoperative NLR in recipients after LDLT with HCC and assess whether immunotherapy improves postoperative NLR.

METHODS

We conducted a retrospective study of LDLT recipients between 2001 and 2022 to evaluate the clinical significance of postoperative NLR. Furthermore, the correlation between postoperative NLR and the activation marker of infused NK cells was also evaluated. The postoperative NLR was examined 4 weeks after LDLT.

RESULTS

The postoperative high NLR group (N = 78) had preoperative lower NLR and higher model for end-stage liver disease and a higher rate of postoperative infection within 30 days after LDLT than the postoperative low NLR group (N = 41). Postoperative high NLR (hazard ratio [HR], 2.62; 95% confidence interval [CI], 1.01-6.79; P = .047) and nontreatment of immunotherapy (HR, 3.10; 95% CI, 1.33-7.22; P < .01) were independent risk factors for poor overall survival in multivariate analysis. Furthermore, the activation marker of infused NK cells is inversely correlated with decreased postoperative NLR.

CONCLUSIONS

The higher level of postoperative NLR was independently associated with poor prognosis in patients after LDLT with HCC. Immunotherapy using activated NK cells may improve postoperative NLR and long-term prognosis.

Clinical application and prospect of immune checkpoint inhibitors for CAR-NK cell in tumor immunotherapy

Chimeric antigen receptor (CAR) engineering of natural killer (NK) cells is an attractive research field in tumor immunotherapy. While CAR is genetically engineered to express certain molecules, it retains the intrinsic ability to recognize tumor cells through its own receptors. Additionally, NK cells do not depend on T cell receptors for cytotoxic killing. CAR-NK cells exhibit some differences to CAR-T cells in terms of more precise killing, numerous cell sources, and increased effectiveness in solid tumors. However, some problems still exist with CAR-NK cell therapy, such as cytotoxicity, low transfection efficiency, and storage issues. Immune checkpoints inhibit immune cells from performing their normal killing function, and the clinical application of immune checkpoint inhibitors for cancer treatment has become a key therapeutic strategy. The application of CAR-T cells and immune checkpoint inhibitors is being evaluated in numerous ongoing basic research and clinical studies. Immune checkpoints may affect the function of CAR-NK cell therapy. In this review, we describe the combination of existing CAR-NK cell technology with immune checkpoint therapy and discuss the research of CAR-NK cell technology and future clinical treatments. We also summarize the progress of clinical trials of CAR-NK cells and immune checkpoint therapy.

PRDX-1 Supports the Survival and Antitumor Activity of Primary and CAR-Modified NK Cells under Oxidative Stress

Oxidative stress, caused by the imbalance between reactive species generation and the dysfunctional capacity of antioxidant defenses, is one of the characteristic features of cancer. Here, we quantified hydrogen peroxide in the tumor microenvironment (TME) and demonstrated that hydrogen peroxide concentrations are elevated in tumor interstitial fluid isolated from murine breast cancers in vivo, when compared with blood or normal subcutaneous fluid. Therefore, we investigated the effects of increased hydrogen peroxide concentration on immune cell functions. NK cells were more susceptible to hydrogen peroxide than T cells or B cells, and by comparing T, B, and NK cells' sensitivities to redox stress and their antioxidant capacities, we identified peroxiredoxin-1 (PRDX1) as a lacking element of NK cells' antioxidative defense. We observed that priming with IL15 protected NK cells' functions in the presence of high hydrogen peroxide and simultaneously upregulated PRDX1 expression. However, the effect of IL15 on PRDX1 expression was transient and strictly dependent on the presence of the cytokine. Therefore, we genetically modified NK cells to stably overexpress PRDX1, which led to increased survival and NK cell activity in redox stress conditions. Finally, we generated PD-L1-CAR NK cells overexpressing PRDX1 that displayed potent antitumor activity against breast cancer cells under oxidative stress. These results demonstrate that hydrogen peroxide, at concentrations detected in the TME, suppresses NK cell function and that genetic modification strategies can improve CAR NK cells' resistance and potency against solid tumors.

Defining the AHR-regulated transcriptome in NK cells reveals gene expression programs relevant to development and function

AHR directly regulates a wide range of genes in NK cells, including those involved in cell signaling, oxidative stress, and metabolism.

Knowing of the repertoire of genes regulated by AHR may help us better understand NK-cell dysfunction mediated by AHR ligands in cancer.

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates cellular processes in cancer and immunity, including innate immune cell development and effector function. However, the transcriptional repertoire through which AHR mediates these effects remains largely unexplored. To elucidate the transcriptional elements directly regulated by AHR in natural killer (NK) cells, we performed RNA and chromatin immunoprecipitation sequencing on NK cells exposed to AHR agonist or antagonist. We show that mature peripheral blood NK cells lack AHR, but its expression is induced by Stat3 during interleukin-21–driven activation and proliferation, coincident with increased NCAM1 (CD56) expression resulting in a CD56^bright phenotype. Compared with control conditions, NK cells expanded in the presence of the AHR antagonist, StemRegenin-1, were unaffected in proliferation or cytotoxicity, had no increase in NCAM1 transcription, and maintained the CD56^dim phenotype. However, it showed altered expression of 1004 genes including those strongly associated with signaling pathways. In contrast, NK cells expanded in the presence of the AHR agonist, kynurenine, showed decreased cytotoxicity and altered expression of 97 genes including those strongly associated with oxidative stress and cellular metabolism. By overlaying these differentially expressed genes with AHR chromatin binding, we identified 160 genes directly regulated by AHR, including hallmark AHR targets AHRR and CYP1B1 and known regulators of phenotype, development, metabolism, and function such as NCAM1, KIT, NQO1, and TXN. In summary, we define the AHR transcriptome in NK cells, propose a model of AHR and Stat3 coregulation, and identify potential pathways that may be targeted to overcome AHR-mediated immune suppression.

The immune potential of decidua-resident CD16+CD56+ NK cells in human pregnancy

Human CD56⁺CD3^- NK cells can be subdivided into two different subsets according to the expression pattern of CD56 and CD16. CD56^+/brightCD16^- (CD16^-) NK cells are prominently cytokine producers with little cytotoxicity whereas CD56^+/dimCD16⁺ (CD16⁺) NK cells are efficient killers with poorer cytokine production potential. In human pregnancy, CD56⁺ decidual (d)NK cells accumulate in the maternal fetal interface to regulate placental immunity and development. Unlike peripheral blood (pb)NK cells, the majority of dNK cells are CD56 positive with limited CD16 reactivity. Our results demonstrated that in normal and pathological pregnancies, CD16⁺ dNK cells are a unique population in comparison to CD16^- dNK subset. The expression of NK activation receptors CD335, CD336, CD244 and CD314 on CD16⁺ dNK subpopulation was lower than that on CD16^- dNK cells. Upon cytokine stimulation with rhIL-12/15/18 or TGFβ blockade, the CD16⁺ dNK subset exhibited more robust response on the expression of IFNG, IL-8 and CD107a, compared to that of the CD16^- dNK subpopulation. Functions of the CD16⁺ dNK subset were shown to be independent of cellular interaction with trophoblast cells. Studies of preeclamptic patients revealed lower proportions of CD16⁺ dNK cells, suggesting potential protective roles of these cells during normal gestations.. Therefore, we suggest that the CD16⁺ dNK subset, through compensating CD16^- dNK cell function, is an indispensable componentto regulate decidual immune response and to support placentation.

Docosahexaenoic Acid Modulates NK Cell Effects on Neutrophils and Their Crosstalk

Natural killer (NK) cells and neutrophils engage in crosstalk that is important in inflammation and likely also for resolution of inflammation. NK cells activate neutrophils and induce their infiltration to the inflamed sites but may also influence their apoptosis and their subsequent efferocytosis by macrophages. Several studies indicate that docosahexaenoic acid (DHA) can inhibit NK cell cytotoxicity but the effects of DHA on the ability of NK cells to engage in crosstalk with neutrophils and affect their functions have not been described. This study explored the kinetics of the effects of NK cells and NK cells pre-treated with DHA on neutrophil surface molecule expression and apoptosis, as well as the ability of NK cells to affect other neutrophil functions. In addition, the study explored the effects of neutrophils on NK cell phenotype and function. Primary NK cells were pre-incubated with or without DHA, then stimulated and co-cultured with freshly isolated neutrophils. When co-cultured with NK cells, neutrophils had higher expression levels of CD11b and CD47; secreted more IL-8, IL-1ra, and CXCL10; had increased phagocytic ability; and their apoptosis was increased early after initiation of the co-culture while dampened at a later time-point. Pre-incubation of NK cells with DHA attenuated NK cell-induced upregulation of CD11b and CD47 on neutrophils, had minor effects on NK cell induction of cytokine/chemokine secretion or their phagocytic ability. Neutrophils also affected the function of NK cells, lowering the frequency of NKp46⁺ and CXCR3⁺ NK cells and increasing the concentrations of IFN-γ, TNF-α, and GM-CSF in the co-cultures. Pre-incubation of NK cells with DHA further decreased the frequency of NKp46⁺ NK cells in the co-culture with neutrophils and decreased the concentrations of IFN-γ, CCL3 and GM-CSF. These findings indicate that NK cells have mostly pro-inflammatory effects on neutrophils and that DHA can attenuate some of these pro-inflammatory effects. Neutrophils had both anti- and pro-inflammatory effects on NK cells. When NK cells had been pre-treated with DHA, the anti-inflammatory effects were increased and some of the pro-inflammatory effects attenuated. Overall, the results suggest that DHA may lead to a more anti-inflammatory microenvironment for NK cell and neutrophil crosstalk.

Idelalisib Rescues Natural Killer Cells from Monocyte-Induced Immunosuppression by Inhibiting NOX2-Derived Reactive Oxygen Species

The phosphatidylinositol-4,5-bisphosphate-3 kinase-δ (PI3Kδ) inhibitor idelalisib, used alone or in combination with anti-CD20, is clinically efficacious in B-cell lymphoma and chronic lymphocytic leukemia (CLL) by promoting apoptosis of malignant B cells. PI3K regulates the formation of reactive oxygen species (ROS) by the myeloid NADPH oxidase NOX2, but the role of PI3Kδ in myeloid cell-induced immunosuppression is unexplored. We assessed the effects of idelalisib on the spontaneous and IgG antibody-induced ROS production by human monocytes, on ROS-induced cell death of human natural killer (NK) cells, and on tumor cell clearance in an NK cell-dependent mouse model of metastasis. Idelalisib potently and efficiently inhibited the formation of NOX2-derived ROS from monocytes and rescued NK cells from ROS-induced cell death. Idelalisib also promoted NK cell cytotoxicity against anti-CD20-coated primary human CLL cells and cultured malignant B cells. Experiments using multiple PI3K inhibitors implicated the PI3Kδ isoform in regulating NOX2-induced ROS formation and immunosuppression. In B6 mice, systemic treatment with idelalisib significantly reduced the formation of lung metastases from intravenously injected melanoma cells but did not affect metastasis in B6.129S6-Cybbtm1Din (Nox2 ^-/-) mice or in NK cell-deficient mice. Our results imply that idelalisib rescues NK cells from NOX2/ROS-dependent immunosuppression and thus exerts antineoplastic efficacy beyond B-cell inhibition.

Association of T and NK Cell Phenotype With the Diagnosis of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a pathological condition characterized by incapacitating fatigue and a combination of neurologic, immunologic, and endocrine symptoms. At present its diagnosis is based exclusively on clinical criteria. Several studies have described altered immunologic profiles; therefore, we proposed to further examine the more significant differences, particularly T and NK cell subpopulations that could be conditioned by viral infections, to discern their utility in improving the diagnosis and characterization of the patients. The study included 76 patients that fulfilled the revised Canadian Consensus Criteria (CCC 2010) for ME/CFS and 73 healthy controls, matched for age and gender. Immunophenotyping of different T cell and natural killer cell subpopulations in peripheral blood was determined by flow cytometry. ME/CFS patients showed significantly lower values of T regulatory cells (CD4⁺CD25^++(high)FOXP3⁺) and higher NKT-like cells (CD3⁺CD16^+/-CD56⁺) than the healthy individuals. Regarding NK phenotypes, NKG2C was significantly lower and NKCD69 and NKCD56 bright were significantly higher in the patients group. A classification model was generated using the more relevant cell phenotype differences (NKG2C and T regulatory cells) that was able to classify the individuals as ME/CFS patients or healthy in a 70% of cases. The observed differences in some of the subpopulations of T and NK cells between patients and healthy controls could define a distinct immunological profile that can help in the diagnostic process of ME/CFS patients, contribute to the recognition of the disease and to the search of more specific treatments. However, more studies are needed to corroborate these findings and to contribute to establish a consensus in diagnosis.

Reactive oxygen species induced by therapeutic CD20 antibodies inhibit natural killer cell-mediated antibody-dependent cellular cytotoxicity against primary CLL cells

The antibody-dependent cellular cytotoxicity (ADCC) of natural killer (NK) cells is assumed to contribute to the clinical efficacy of monoclonal antibodies (mAbs) in chronic lymphocytic leukemia (CLL) and other hematopoietic malignancies of B cell origin. We sought to determine whether reactive oxygen species (ROS)-producing monocytes regulate the ADCC of NK cells against primary CLL cells using anti-CD20 as the linking antibody. The monoclonal CD20 antibodies rituximab and ofatumumab were found to trigger substantial release of ROS from monocytes. Antibody-exposed monocytes induced NK cell apoptosis and restricted NK cell-mediated ADCC against autologous CLL cells. The presence of inhibitors of ROS formation and scavengers of ROS preserved NK cell viability and restored NK cell-mediated ADCC against primary CLL cells. We propose that limiting the antibody-induced induction of immunosuppressive ROS may improve the anti-leukemic efficacy of anti-CD20 therapy in CLL.

Potential roles of neutrophils in regulating intestinal mucosal inflammation of inflammatory bowel disease

Inflammatory bowel diseases (IBD), comprising of ulcerative colitis and Crohn's disease, are inflammatory disorders of the gastrointestinal tract characterized by chronically relapsing mucosal inflammation. Neutrophils, as the effector cells of acute inflammation, have long been reported to play a role in the maintenance of intestinal homeostasis and pathogenesis of IBD. At the early stage of mucosal inflammation in patients with IBD, neutrophils flood into intestinal mucosa, phagocytose pathogenic microbes, and promote mucosal healing and resolution of inflammation. However, large numbers of neutrophils infiltrating in the inflamed mucosa and accumulating in the epithelia cause damage of mucosal architecture, compromised epithelial barrier and production of inflammatory mediators. In this review we discuss the critical roles of neutrophils in modulating innate and adaptive immune responses in intestinal mucosa, and, importantly, clarify the potential roles of neutrophils related to their production of inflammatory mediators, transenthothelial and transepithelial migration into intestinal mucosa, and the underlying mechanisms in regulating mucosal inflammation of IBD. Moreover, we also describe a new subset of neutrophils (i.e., CD177⁺ neutrophils) and illustrate its protective role in modulating intestinal mucosal immune responses in IBD.

Combination Cancer Therapy Using Chimeric Antigen Receptor-Engineered Natural Killer Cells as Drug Carriers

The therapeutic limitations of conventional chemotherapeutic drugs include chemo-resistance, tumor recurrence, and metastasis. Numerous nanoparticle-based active targeting approaches have emerged to enhance the intracellular concentration of drugs in tumor cells; however, efficient delivery of these systems to the tumor site while sparing healthy tissue remains elusive. Recently, much attention has been given to human immune-cell-directed nanoparticle drug delivery, because immune cells can traffic to the tumor and inflammatory sites. Natural killer cells are a subset of cytotoxic lymphocytes that play critical roles in cancer immunosurveillance. Engineering of the human natural killer cell line, NK92, to express chimeric antigen receptors to redirect their antitumor specificity has shown significant promise. We demonstrate that the efficacy of chemotherapy can be enhanced in vitro and in vivo while reducing off-target toxicity by using chimeric antigen receptor-engineered NK92 cells as carriers to direct drug-loaded nanoparticles to the target site.

Upregulation of thioredoxin-1 in activated human NK cells confers increased tolerance to oxidative stress

Adoptive transfer of immune cells, such as T lymphocytes and NK cells, has potential to control cancer growth. However, this can be counteracted by immune escape mechanisms within the tumor microenvironment, including those mediated by reactive oxygen species (ROS). Here, we determined the levels of anti-oxidant molecules in NK cells and their capacity to overcome ROS-induced immune suppression. We investigated the effect of H2O2 on resting NK cells, IL-2-activated NK cells and NK cells expanded by coculture with the K562 leukemia cell line genetically modified to express membrane-bound IL-15 and 4-1BB ligand (K562-mb15-41BBL). Expression of anti-oxidant and anti-apoptotic genes was evaluated by expression array, and protein levels of anti-oxidant molecules by Western blot. Activated NK cells, IL-2-activated NK cells and NK cells expanded by K562-mb15-41BBL were significantly more resistant to H2O2-induced cell death than resting NK. Thioredoxin-1 (TXN1) and peroxiredoxin-1 (PRDX1) were also up-regulated in activated NK cells. Moreover, H2O2-induced cell death after IL-2 activation was significantly induced in the presence of an anti-TXN1-neutralising antibody. Collectively, these data document that activated NK cells can resist to H2O2-induced cell death by up-regulation of TXN1.

Bystander cells enhance NK cytotoxic efficiency by reducing search time

Natural killer (NK) cells play a central role during innate immune responses by eliminating pathogen-infected or tumorigenic cells. In the microenvironment, NK cells encounter not only target cells but also other cell types including non-target bystander cells. The impact of bystander cells on NK killing efficiency is, however, still elusive. In this study we show that the presence of bystander cells, such as P815, monocytes or HUVEC, enhances NK killing efficiency. With bystander cells present, the velocity and persistence of NK cells were increased, whereas the degranulation of lytic granules remained unchanged. Bystander cell-derived H2O2 was found to mediate the acceleration of NK cell migration. Using mathematical diffusion models, we confirm that local acceleration of NK cells in the vicinity of bystander cells reduces their search time to locate target cells. In addition, we found that integrin β chains (β1, β2 and β7) on NK cells are required for bystander-enhanced NK migration persistence. In conclusion, we show that acceleration of NK cell migration in the vicinity of H2O2-producing bystander cells reduces target cell search time and enhances NK killing efficiency.

Balance between activating NKG2D, DNAM-1, NKp44 and NKp46 and inhibitory CD94/NKG2A receptors determine natural killer degranulation towards rheumatoid arthritis synovial fibroblasts

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and synovial hyperplasia leading to progressive joint destruction. Fibroblast-like synoviocytes (FLS) are central components of the aggressive, tumour-like synovial structure termed pannus, which invades the joint space and cartilage. A distinct natural killer (NK) cell subset expressing the inhibitory CD94/NKG2A receptor is present in RA synovial fluid. Little is known about possible cellular interactions between RA-FLS and NK cells. We used cultured RA-FLS and the human NK cell line Nishi, of which the latter expresses an NK receptor repertoire similar to that of NK cells in RA synovial fluid, as an in vitro model system of RA-FLS/NK cell cross-talk. We show that RA-FLS express numerous ligands for both activating and inhibitory NK cell receptors, and stimulate degranulation of Nishi cells. We found that NKG2D, DNAM-1, NKp46 and NKp44 are the key activating receptors involved in Nishi cell degranulation towards RA-FLS. Moreover, blockade of the interaction between CD94/NKG2A and its ligand HLA-E expressed on RA-FLS further enhanced Nishi cell degranulation in co-culture with RA-FLS. Using cultured RA-FLS and the human NK cell line Nishi as an in vitro model system of RA-FLS/NK cell cross-talk, our results suggest that cell-mediated cytotoxicity of RA-FLS may be one mechanism by which NK cells influence local joint inflammation in RA.

Natural killer cells in patients with severe chronic fatigue syndrome

Maintenance of health and physiological homeostasis is a synergistic process involving tight regulation of proteins, transcription factors and other molecular processes. The immune system consists of innate and adaptive immune cells that are required to sustain immunity. The presence of pathogens and tumour cells activates innate immune cells, in particular Natural Killer (NK) cells. Stochastic expression of NK receptors activates either inhibitory or activating signals and results in cytokine production and activation of pathways that result in apoptosis of target cells. Thus, NK cells are a necessary component of the immunological process and aberrations in their functional processes, including equivocal levels of NK cells and cytotoxic activity pre-empts recurrent viral infections, autoimmune diseases and altered inflammatory responses. NK cells are implicated in a number of diseases including chronic fatigue syndrome (CFS). The purpose of this review is to highlight the different profiles of NK cells reported in CFS patients and to determine the extent of NK immune dysfunction in subtypes of CFS patients based on severity in symptoms.

Peripheral blood NK cells from breast cancer patients are tumor-induced composite subsets

Human NK lymphocytes are involved in antitumor immunity. The therapeutic potential of this population against cancers has stimulated their study and led to the discovery of several NK cell subsets, each of which is endowed with different immunoregulatory functions. We have previously reported that NK cell functions are profoundly altered in advanced breast cancer patients. In this study, we show that these tumor-mediated alterations also variably affect NK cell subsets. We found that in addition to the known human CD56(dim)CD16(+), CD56(bright)CD16(-), and CD56(-)CD16(+) NK cell subsets, two additional subsets, namely the CD56(bright)CD16(+) and CD56(dim)CD16(-) subsets, were increased in the peripheral blood of patients with advanced invasive breast cancers. These subsets corresponded to the main two subsets found at the tumor site. The extensive phenotype of these subsets revealed an "à la carte" pattern of expression for the various NK receptors, functional molecules, adhesion molecules, and chemokine receptors, depending on the subset. We next compared these subsets to known NK cell populations endowed with specific phenotypic characteristics, but also with functional properties. Our data show that advanced breast cancer patients have an increased proportion of more immature and noncytotoxic NK cell subsets in their peripheral blood, which might account for at least part of the low cytotoxic functions observed in these patients. They reveal a major heterogeneity and plasticity of the NK cell compartment, which are both tightly linked to the microenvironment. The identification of NK cell subsets endowed with particular functional capabilities might help monitor residual antitumor NK cell-mediated responses in breast cancer patients.

Monocytic AML cells inactivate antileukemic lymphocytes: role of NADPH oxidase/gp91(phox) expression and the PARP-1/PAR pathway of apoptosis

Dysfunction of T cells and natural killer (NK) cells has been proposed to determine the course of disease in acute myeloid leukemia (AML), but only limited information is available on the mechanisms of lymphocyte inhibition. We aimed to evaluate to what extent human malignant AML cells use NADPH oxidase-derived reactive oxygen species (ROS) as an immune evasion strategy. We report that a subset of malignant myelomonocytic and monocytic AML cells (French-American-British [FAB] classes M4 and M5, respectively), recovered from blood or BM of untreated AML patients at diagnosis, expressed the NADPH oxidase component gp91(phox). Highly purified FAB M4/M5 AML cells produced large amounts of ROS on activation and triggered poly-[ADP-ribose] polymerase-1-dependent apoptosis in adjacent NK cells, CD4(+) T cells, and CD8(+) T cells. In contrast, immature (FAB class M1) and myeloblastic (FAB class M2) AML cells rarely expressed gp91(phox), did not produce ROS, and did not trigger NK or T-cell apoptosis. Microarray data from 207 AML patients confirmed a greater expression of gp91(phox) mRNA by FAB-M4/M5 AML cells than FAB-M1 cells (P < 10(-11)) or FAB-M2 cells (P < 10(-9)). Our data are suggestive of a novel mechanism by which monocytic AML cells evade cell-mediated immunity.

Receptor-dependent and -independent immunomodulatory effects of phenol-soluble modulin peptides from Staphylococcus aureus on human neutrophils are abrogated through peptide inactivation by reactive oxygen species

The virulence and pathogenesis mechanisms of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains depend on a newly described group of phenol-soluble modulin (PSM) peptides (the PSMα peptides) with cytolytic activity. These toxins are α-helical peptides with a formyl group at the N terminus, and they activate neutrophils through formyl peptide receptor 2 (FPR2), a function closely correlated to the capacity of staphylococcal species to cause invasive infections. The effects of two synthetic PSMα peptides were investigated, and we show that they utilize FPR2 and promote neutrophils to produce reactive oxygen species (ROS) which in turn trigger inactivation of the peptides. Independently of FPR2, the PSMα peptides also downregulate the neutrophil response to other stimuli and exert a cytolytic effect to which apoptotic neutrophils are more sensitive than viable cells. The novel immunomodulatory functions of the PSMα peptides were sensitive to ROS generated by the neutrophil myeloperoxidase (MPO)-H(2)O(2) system, suggesting a role for this enzyme system in counteracting bacterial virulence.

Camouflage and sabotage: tumor escape from the immune system

The field of tumor immunology has made great progress in understanding tumor immune interactions. As a consequence a number of immuno-therapeutic approaches have been successfully introduced into the clinic and a large number of promising therapeutic strategies are investigated in ongoing clinical trials. Evaluation of anti-tumor immunity in such trials as well as in animal models has shown that tumor escape from immune recognition and tumor-mediated suppression of anti-tumor immunity can pose a significant obstacle to successful cancer therapy. Here, we review mechanisms of tumor immune escape and immune-subversion with a focus on the research interests in our laboratory: loss of MHC class I on tumor cells, increased oxidative stress, recruitment of myeloid-derived suppressor cells, and regulatory T cells.

Enhancing Cell therapies from the Outside In: Cell Surface Engineering Using Synthetic Nanomaterials

Therapeutic treatments based on the injection of living cells are in clinical use and preclinical development for diseases ranging from cancer to cardiovascular disease to diabetes. To enhance the function of therapeutic cells, a variety of chemical and materials science strategies are being developed that engineer the surface of therapeutic cells with new molecules, artificial receptors, and multifunctional nanomaterials, synthetically endowing donor cells with new properties and functions. These approaches offer a powerful complement to traditional genetic engineering strategies for enhancing the function of living cells.

T cells expanded in presence of IL-15 exhibit increased antioxidant capacity and innate effector molecules

Persistence of effector cytotoxic T lymphocytes (CTLs) during an immunological response is critical for successfully controlling a viral infection or tumor growth. Various cytokines are known to play an important part in regulating the immune response. The IL-2 family of cytokines that includes IL-2 and IL-15 are known to function as growth and survival factors for antigen-experienced T cells. IL-2 and IL-15 possess similar properties, including the ability to induce T cell proliferation. Whereas long-term IL-2 exposure has been shown to promote apoptosis and limit CD8(+) memory T cell survival and proliferation, it is widely believed that IL-15 can inhibit apoptosis and helps maintain a memory CD8(+) T-cell population. However, mechanisms for superior outcomes for IL-15 as compared to IL-2 are still under investigation. Our data shows that human T cells cultured in the presence of IL-15 exhibit increased expression of anti-oxidant molecules glutathione reductase (GSR), thioredoxin reductase 1 (TXNDR1), peroxiredoxin (PRDX) and superoxide dismutase (SOD). An increased expression of cell-surface thiols, intracellular glutathione, and thioredoxins was also noted in IL-15 cultured T cells. Additionally, IL-15 cultured T cells showed an increase in cytolytic effector molecules. Apart from increased level of Granzyme A and Granzyme B, IL-15 cultured T cells exhibited increased accumulation of reactive oxygen (ROS) and reactive nitrogen species (RNS) as compared to IL-2 cultured T cells. Overall, this study suggests that T cells cultured in IL-15 show increased persistence not only due to levels of anti-apoptotic proteins, but also due to increased anti-oxidant levels, which is complimented by increased cytolytic effector functions.

Over-expression of aldehyde dehydrogenase-2 protects against H₂O₂-induced oxidative damage and apoptosis in peripheral blood mononuclear cells

AIM

To construct an eukaryotic expression vector containing the aldehyde dehydrogenase-2 (ALDH2) gene, and determine whether transfection with the ALDH2 gene can provide protection against hydrogen peroxide-induced oxidative damage, as well as attenuate apoptosis or cell death in human peripheral blood mononuclear cells (PBMCs).

METHODS

The ALDH2 gene was cloned from human hepatocytes by RT-PCR. The eukaryotic expression vector containing the gene was constructed and then transfected into PBMCs via liposomes. RT-PCR, indirect immunofluorescence assay, and Western blot were used to evaluate the expression of the transgene in target cells. MTT assay and flow cytometry were used to detect the effects of ALDH2 on PBMCs damaged by hydrogen peroxide (H₂O₂). The level of intracellular reactive oxygen species (ROS) was determined by fluorescence spectrophotometry.

RESULTS

The eukaryotic expression vector pcDNA3.1/myc-His-ALDH2 was successfully constructed and transfected into PBMCs. RT-PCR results showed higher mRNA expression of ALDH2 in the gene-transfected group than in the two control groups (empty vector-transfected group and negative control). Indirect immunofluorescence assay and Western blot indicated distinct higher protein expression of ALDH2 in the gene-transfected group. The cell survival rate against H₂O₂-induced oxidative damage was higher in the ALDH2 gene-transfected group. Moreover, apoptosis rates in gene-transfected PBMCs incubated with 50 and 75 μmol/L H₂O₂ decreased by 7% and 6%, respectively. The generation of intracellular ROS was also markedly downregulated.

CONCLUSION

ALDH2 gene transfection can protect PBMCs against H₂O₂-induced damage and attenuate apoptosis, accompanied with a downregulation of intracellular ROS. ALDH2 functions as a protector against oxidative stress.

Human neutrophils interact with both 6-sulfo LacNAc+ DC and NK cells to amplify NK-derived IFN{gamma}: role of CD18, ICAM-1, and ICAM-3

The role of neutrophils as key players in the regulation of innate and adaptive immune responses is increasingly being recognized. We report that human neutrophils establish a network with both natural killer (NK) cells and 6-sulfo LacNAc(+) dendritic cells (slanDCs), which ultimately serves to up-regulate NK-derived interferonγ (IFNγ). This network involves direct reciprocal interactions and positive amplification loops mediated by cell-derived cytokines. Accordingly, we show that after lipopolysaccharide + interleukin-2 (IL-2) or IL-15/IL-18 stimulation, neutrophils directly interact with and potentiate the activity of both slanDCs and NK cells. On the one hand, neutrophils augment the release of IL-12p70 by slanDCs via a CD18/ intercellular adhesion molecule-1 (ICAM-1) interaction that stimulates activated NK cells to produce IFNγ. IFNγ further potentiates the interaction between neutrophils and slanDCs and the release of slanDC-derived IL-12p70, thus creating a positive feedback loop. On the other hand, neutrophils directly co-stimulate NK cells via CD18/ICAM-3, leading to the production of IFNγ. Colocalization of neutrophils, NK cells, and slanDCs, as well as of IL-12p70 and IFNγ, in inflamed tissues of Crohn disease and psoriasis provides strong evidence for a novel cellular and cytokine cooperation within the innate immune system in which neutrophils act as amplifiers of NK cell/slanDC-mediated responses.

The CD14(+/low)CD16(+) monocyte subset is more susceptible to spontaneous and oxidant-induced apoptosis than the CD14(+)CD16(-) subset

Human monocytes can be classified into two subsets with distinctive characteristics. In this study, we report a difference in apoptotic potential between these two subsets with CD14^+/lowCD16⁺ monocytes being more susceptible than CD14⁺CD16⁻ monocytes to undergo spontaneous apoptosis and apoptosis induced by reactive oxygen species (ROS). By global transcriptomic and proteomic approaches, we observed that CD14^+/lowCD16⁺ monocytes expressed higher levels of pro-apoptotic genes and proteins such as TNFα, caspase 3, Bax and cytochrome c and showed more caspases 3 and 7 activities. They also exhibited greater aerobic respiration resulting in a higher production of ROS from the mitochondria. CD14⁺CD16⁻ monocytes, in contrast, showed higher expression of glutathione (GSH)-metabolizing genes such as GSH peroxidase and microsomal GSH S-transferase and were more resistant to oxidative stress than CD14^+/lowCD16⁺ monocytes. The apoptosis of CD14^+/lowCD16⁺ monocytes was ROS dependent as reducing ROS levels significantly reduced cell death. This is the first report of a differential apoptotic propensity of human monocyte subsets, and gaining a better understanding of this process may help to provide a better understanding of the roles of these subsets during homeostasis and under pathological conditions, particularly in situations in which high levels of oxidants are present.

Increased thioredoxin-1 production in human naturally occurring regulatory T cells confers enhanced tolerance to oxidative stress

Levels of regulatory T cells (Tregs) are increased in different cancer types as well as in inflammatory diseases, such as rheumatoid arthritis. Treg accumulation may result from aberrant proliferation and trafficking as well as greater resilience to oxidative stress compared with conventional T cells. This enhanced antioxidative capacity of Tregs possibly serves as feedback inhibition during inflammation and prevents uncontrolled immune reactions by favoring survival of suppressor rather than effector cells. In this study, we demonstrate that human Tregs express and secrete higher levels of thioredoxin-1, a major antioxidative molecule. Thioredoxin-1 has an essential role in maintaining their surface thiol density as the first line of antioxidative defense mechanisms and is sensitive to proinflammatory stimuli, mainly tumor necrosis factor-α, in a nuclear factor-κB-dependent fashion. The antiapoptotic and oncogenic potential of (secreted) Trx-1 suggests that it may exert effects in Tregs beyond redox regulation.

The defensive alliance between neutrophils and NK cells as a novel arm of innate immunity

The immune system is equipped with a plethora of mechanisms that protect the host from the harmful effects of environmental insults. However, the traditional "hierarchical" view of the immune response, in which innate, "nonspecific" cells are first recruited to the site of damage, before the highly "specific", adaptive immune response develops, has been questioned recently. First, the innate response is much more specific than recognized previously: indeed, each cell of the innate system is not only endowed with an ever-expanding array of germ-line-encoded receptors, which differentiate between distinct insults, but also is modulated continuously by other leukocytes that concomitantly interact with and respond to that particular insult. The other reason is that the cells of the innate system are instrumental for the adaptive system to accomplish its function, as they can also modulate the activity of lymphocytes reciprocally during the entire course of the immune response. This complex pattern of interactions is illustrated by recent advances on the functions of PMNs, clearly showing that unexpectedly, these cells also contribute to the regulation of the host immune response by crosstalk with innate and adaptive leukocytes, including NK cells. Herein, given the peculiar role of neutrophils and NK cells in inflammation, clearance of pathogens/viral-infected cells, and cancer immunosurveillance, we summarize the current knowledge about the mechanisms whereby neutrophils and NK cells interact and regulate the activities of one another, as well as discuss their potential implications involved in the pathogenesis of chronic, inflammatory pathologies, infections, and tumors.

Histamine dihydrochloride and low-dose interleukin-2 as post-consolidation immunotherapy in acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. Although most patients achieve complete remission (CR) after chemotherapy, the majority suffer from subsequent leukemic relapse, which is associated with poor long-term survival. Thus, new therapies to maintain CR are highly warranted. After the completion of chemotherapy, AML patients have a minimal burden of leukemic cells, which are reportedly susceptible to cytotoxic lymphocytes such as NK cells and T cells. A therapy that boosts the function of these effector cells therefore has the potential to eradicate the malignant clone in AML and prevent relapse, Here, we briefly review the literature on the role of the immune system in AML and introduce the rationale for the use of histamine dihydrochloride (HDC) in conjuction with low-dose IL-2 as relapse-preventive immunotherapy for this disease.

Oxidative stress mediates a reduced expression of the activating receptor NKG2D in NK cells from end-stage renal disease patients

To characterize the immune defect of patients with end-stage renal disease (ESRD), we performed NK cell subset analysis in 66 patients with ESRD treated by hemodialysis (n = 59) or peritoneal dialysis (n = 7). Compared with healthy blood donors, patients undergoing chronic dialysis showed a profound decrease in NKG2D(+) cells within both the CD8(+) T cell (58% vs 67%, p = 0.03) and NK cell (39% vs 56%, p = 0.002) populations. CD56(dim) cells, which comprise the majority of NK cells in the periphery, were more affected in this regard than were CD56(bright) cells. Uremic serum could decrease NKG2D expression on NK cells from healthy donors. Among factors that could contribute to the decrease in NKG2D expression in ESRD patients, reactive oxygen species (ROS) play a major role. We found that catalase could reverse the effects of uremic serum on NKG2D expression (p < 0.001) and that ROS down-regulated NKG2D at the mRNA level and at the NK cell surface. Additionally, ESRD patients had both increased membrane-bound MHC class I-related chain A (MICA) on monocytes (p = 0.04) and increased soluble MICA (203 pg/ml vs 110 pg/ml; p < 0.001). Both ROS and uremic serum could significantly increase in vitro the expression of the NKG2D ligand MICA on the renal epithelial cell line HK-2. Taken together, these studies suggest for the first time that both low NKG2D expression and up-regulation of its ligand MICA are related to ROS production and may be involved in the immune deficiency of ESRD patients.

Naturally occurring regulatory T cells show reduced sensitivity toward oxidative stress-induced cell death

Although the authors of several studies report elevated numbers of immunosuppressive regulatory T cells (Tregs) in hematologic and solid malignancies, the underlying mechanism is not fully clarified. Cancer is associated with oxidative stress mediated through reactive oxygen species produced by malignant cells, granulocytes, tumor-associated macrophages, and myeloid-derived suppressor cells. Oxidative stress is known to have detrimental effects on natural killer (NK) and T cells during chronic inflammatory conditions and cancer. Paradoxically, greater numbers of Tregs can be detected at tumor sites, indicating that Tregs can persist in this environment of increased oxidative stress. We demonstrate that Tregs, especially naive CD45RA(+), exhibit reduced sensitivity to oxidative stress-induced cell death and maintain their suppressive function, a phenomenon that may be attributed to their observed high antioxidative capacity. This newly described characteristic could explain their enrichment in malignancies associated with increased levels of oxidative stress.

The beta-galactoside binding immunomodulatory lectin galectin-3 reverses the desensitized state induced in neutrophils by the chemotactic peptide f-Met-Leu-Phe: role of reactive oxygen species generated by the NADPH-oxidase and inactivation of the agonist

Neutrophils interacting with a chemoattractant gradually become nonresponsive to further stimulation by the same agonist, a process known as desensitization. Receptor desensitization is a highly regulated process that involves different mechanisms depending on which receptor-ligand pair that is studied. Galectin-3, a member of a large family of beta-galactoside-binding lectins, has been suggested to be a regulator of the inflammatory process, augmenting or directly triggering the neutrophil functional repertoire. We show here that the desensitized state of neutrophils interacting with the chemotactic peptide fMLF is broken by galectin-3 and that this is achieved through an oxygen radical-mediated inactivation of the chemoattractant. The effect was inhibited by the competitor lactose and required the affinity of galectin-3 for N-acetyllactosamine, a saccharide typically found on cell surface glycoproteins. The latter was shown using a galectin-3 mutant that lacked N-acetyllactosamine binding activity, and this protein was not active. The mechanism behind the inactivation of the chemoattractant was found to depend on the ability of galectin-3 to induce a neutrophil generation/secretion of reactive oxygen species which in combined action with myeloperoxidase inactivated the peptides.

Increased proportion of CD56bright natural killer cells in active and inactive systemic lupus erythematosus

Natural killer (NK) cells belong to the innate immune system but can also affect adaptive immune reactions. This immune regulatory function is often ascribed to the CD56(bright) subpopulation of NK cells that is prevalent in secondary lymphoid tissues and has potent cytokine-producing ability. The NK cells have been described as affecting autoimmune disease and stimulating B-cell production of antibodies, but their role in systemic lupus erythematosus (SLE) pathology has not been extensively studied. We have studied NK cells in SLE, a B-cell-driven systemic autoimmune disease, and phenotypically characterized peripheral blood NK cells in comparison to NK cells from patients with immunoglobulin A nephritis, rheumatoid arthritis and healthy individuals. We have found an increased proportion of CD56(bright) NK cells in SLE, regardless of disease activity. We detected a somewhat increased expression of the activating receptor NKp46/CD335 on NK cells from SLE patients, although neither the percentage of NK cells of all lymphocytes nor the expression of other NK receptors analysed (LIR-1/CD85j, CD94, NKG2C/CD159c, NKG2D/CD314, NKp30/CD337, NKp44/CD336, CD69) differed between patient groups. We show that type I interferon, a proinflammatory cytokine known to be abundant in SLE, can cause increases of CD56(bright) NK cells in vitro. We confirmed that serum levels of interferon-alpha were increased in active, but not in inactive, disease in the SLE patient group. In conclusion, we found an increased proportion of CD56(bright) NK cells in the blood of SLE patients, although it remains to be examined whether and how this relates to the disease process.

Natural killer cell subpopulations in putative resistant individuals and patients with active Mycobacterium tuberculosis infection

Herein, we intended to perform flow-cytometric analyses of peripheral blood NK-cell subsets in patients with active tuberculosis (TB) and those putative resistant subjects displaying positive tuberculin skin test (TST+) and compared with TST- healthy controls. Our findings demonstrated distinct phenotypic features in TST+ as compared with TB. While lower values of NK-cells with increased frequency of CD3-CD16+ CD56- and CD3-CD16-CD56+ subsets besides lower frequency of CD3-CD16+ CD56+ NK-cells was observed in TST+, unaltered levels of NK-cells with increased levels of CD3-CD16+ CD56- NK-cells with lower frequency of CD3-CD16+ CD56+ NK-cells was found in TB. Additional analysis highlighted a shift towards increased levels of CD3-CD16-/+CD56bright NK-cells as the hallmark of TST+, whereas unaltered frequency was observed in TB. Increased levels of CD3+CD56+ cells were observed in both TST+ and TB. Further focusing on the monocyte/NK-cell network, we have reported that enhanced frequency of CD14+ CD16+ monocytes particularly observed in TST+. Outstanding were the distinct correlation profiles observed between CD3-CD16-CD56+ NK-cells and CD3+ CD56+ cells CD14+ CD16+ monocytes for TST+ and TB. These data suggested that high levels of CD3-CD16-CD56+ NK-cells aside CD14+ CD16+ monocytes as well as non-concurrent increment of CD3+ CD56+ cells, may be involved in protective mechanisms in putative tuberculosis-resistant individuals. On the other hand, the basal levels of macrophage-like monocytes despite its positive correlation with increased levels of CD3+ CD56+ cells may count for the lack of the protective immunity in patients with active tuberculosis. Further studies focusing on the cytokine profiling of peripheral blood innate immunity cells before and after chemotherapeutic treatment are currently under evaluation.