Oxygen Radicals Induce Poly(ADP-Ribose) Polymerase-Dependent Cell Death in Cytotoxic Lymphocytes

Radiotherapy, PARP Inhibition, and Immune-Checkpoint Blockade: A Triad to Overcome the Double-Edged Effects of Each Single Player

Radiotherapy and, more recently, PARP inhibitors (PARPis) and immune-checkpoint inhibitors represent effective tools in cancer therapy. Radiotherapy exerts its effects not only by damaging DNA and inducing tumor cell death, but also stimulating anti-tumor immune responses. PARPis are known to exert their therapeutic effects by inhibiting DNA repair, and they may be used in combination with radiotherapy. Both radiotherapy and PARPis modulate inflammatory signals and stimulate type I IFN (IFN-I)-dependent immune activation. However, they can also support the development of an immunosuppressive tumor environment and upregulate PD-L1 expression on tumor cells. When provided as monotherapy, immune-checkpoint inhibitors (mainly antibodies to CTLA-4 and the PD-1/PD-L1 axis) result particularly effective only in immunogenic tumors. Combinations of immunotherapy with therapies that favor priming of the immune response to tumor-associated antigens are, therefore, suitable strategies. The widely explored association of radiotherapy and immunotherapy has confirmed this benefit for several cancers. Association with PARPis has also been investigated in clinical trials. Immunotherapy counteracts the immunosuppressive effects of radiotherapy and/or PARPis and synergies with their immunological effects, promoting and unleashing immune responses toward primary and metastatic lesions (abscopal effect). Here, we discuss the beneficial and counterproductive effects of each therapy and how they can synergize to overcome single-therapy limitations.

Role of Phosphoinositide 3-Kinase in Regulation of NOX-Derived Reactive Oxygen Species in Cancer

Activation of NADPH oxidases (NOX) and the ensuing formation of reactive oxygen species (ROS) is a vital aspect of antimicrobial defense but may also promote tumorigenesis. Enhanced NOX activity has been associated with aberrant activation of oncogenic cascades such as the phosphoinositide 3-kinase (PI3K) signaling pathway, which is upregulated in several malignancies. In this review, we examine the role of PI3K on the regulation of NOX-induced ROS formation in cancer.

Prognostic significance of programmed death-1 and programmed death ligand-1 proteins in breast cancer

In numerous studies related to tumor prognosis, programmed death-ligand 1 (PD-L1) has been identified as a biomarker. This work aimed to determine the prognostic importance of PD-L1 in breast cancer. We searched electronic databases such as PubMed, Google scholar, home pages of publishing groups, medical, clinical, and pharmaceutical sciences journals, as well as other relevant sources to discover the importance of PD-1 and PD-L1 expression in breast cancer therapies and also recurrence. The keywords used in this search were autoimmunity, programmed cell death, PD-L1 or PD-1, and breast cancer. Our inclusion criteria included studies showing the synergy between the expression of PD-L1 and PD-1 in primary breast cancers as prognostic markers and this research was limited to humans only. We included review articles, original research, letters to the editor, case reports, and short communications in our study, published in English. We focused our work on PD-L1 mRNA expression in breast cancer cell lines. PD-L1 expression has been decisively demonstrated to be a high-risk factor for breast cancer with a bad prognosis.

CD38: An important regulator of T cell function

Cluster of differentiation 38 (CD38) is a multifunctional extracellular enzyme on the cell surface with NADase and cyclase activities. CD38 is not only expressed in human immune cells, such as lymphocytes and plasma cells, but also is abnormally expressed in a variety of tumor cells, which is closely related to the occurrence and development of tumors. T cells are one of the important immune cells in the body. As NAD consuming enzymes, CD38, ART2, SIRT1 and PARP1 are closely related to the number and function of T cells. CD38 may also influence the activity of ART2, SIRT1 and PARP1 through the CD38-NAD⁺ axis to indirectly affect the number and function of T cells. Thus, CD38-NAD⁺ axis has a profound effect on T cell activity. In this paper, we reviewed the role and mechanism of CD38⁺ CD4⁺ T cells / CD38⁺ CD8⁺ T cells in cellular immunity and the effects of the CD38-NAD⁺ axis on T cell activity. We also summarized the relationship between the CD38 expression level on T cell surface and disease prediction and prognosis, the effects of anti-CD38 monoclonal antibodies on T cell activity and function, and the role of anti-CD38 chimeric antigen receptor (CAR) T cell therapy in tumor immunity. This will provide an important theoretical basis for a comprehensive understanding of the relationship between CD38 and T cells.

New strategies to treat AML: novel insights into AML survival pathways and combination therapies

The effective treatment of acute myeloid leukemia (AML) is very challenging. Due to the immense heterogeneity of this disease, treating it using a "one size fits all" approach is ineffective and only benefits a subset of patients. Instead, there is a shift towards more personalized treatment based on the patients' genomic signature. This shift has facilitated the increased revelation of novel insights into pathways that lead to the survival and propagation of AML cells. These AML survival pathways are involved in drug resistance, evasion of the immune system, reprogramming metabolism, and impairing differentiation. In addition, based on the reports of enhanced clinical efficiencies when combining drugs or treatments, deeper investigation into possible pathways, which can be targeted together to increase treatment response in a wider group of patients, is warranted. In this review, not only is a comprehensive summary of targets involved in these pathways provided, but also insights into the potential of targeting these molecules in combination therapy will be discussed.

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.

cROSsing the Line: Between Beneficial and Harmful Effects of Reactive Oxygen Species in B-Cell Malignancies

B-cell malignancies are a heterogeneous group of hematological neoplasms derived from cells at different stages of B-cell development. Recent studies revealed that dysregulated redox metabolism is one of the factors contributing to the pathogenesis and progression of B-cell malignancies. Elevated levels of oxidative stress markers usually correlate with the advanced stage of various B-cell malignancies. In the complex tumor microenvironment, reactive oxygen species affect not only malignant cells but also bystander cells, including immune cells. Importantly, malignant cells, due to genetic dysregulation, are able to adapt to the increased demands for energy and reducing equivalents via metabolic reprogramming and upregulation of antioxidants. The immune cells, however, are more sensitive to oxidative imbalance. This may cause their dysfunction, leading to immune evasion and tumor progression. On the other hand, the already imbalanced redox homeostasis renders malignant B-cells particularly sensitive to further elevation of reactive oxygen species. Indeed, targeting antioxidant systems has already presented anti-leukemic efficacy in preclinical models. Moreover, the prooxidant treatment that triggers immunogenic cell death has been utilized to generate autologous anti-leukemic vaccines. In this article, we review novel research on the dual role of the reactive oxygen species in B-cell malignancies. We highlight the mechanisms of maintaining redox homeostasis by malignant B-cells along with the antioxidant shield provided by the microenvironment. We summarize current findings regarding therapeutic targeting of redox metabolism in B-cell malignancies. We also discuss how the oxidative stress affects antitumor immune response and how excessive reactive oxygens species influence anticancer prooxidant treatments and immunotherapies.

CD38: T Cell Immuno-Metabolic Modulator

Activation and subsequent differentiation of T cells following antigenic stimulation are triggered by highly coordinated signaling events that lead to instilling cells with a discrete metabolic and transcriptional feature. Compelling studies indicate that intracellular nicotinamide adenine dinucleotide (NAD⁺) levels have profound influence on diverse signaling and metabolic pathways of T cells, and hence dictate their functional fate. CD38, a major mammalian NAD⁺ glycohydrolase (NADase), expresses on T cells following activation and appears to be an essential modulator of intracellular NAD⁺ levels. The enzymatic activity of CD38 in the process of generating the second messenger cADPR utilizes intracellular NAD^+, and thus limits its availability to different NAD⁺ consuming enzymes (PARP, ART, and sirtuins) inside the cells. The present review discusses how the CD38-NAD⁺ axis affects T cell activation and differentiation through interfering with their signaling and metabolic processes. We also describe the pivotal role of the CD38-NAD⁺ axis in influencing the chromatin remodeling and rewiring T cell response. Overall, this review emphasizes the crucial contribution of the CD38^-NAD⁺ axis in altering T cell response in various pathophysiological conditions.

Two may be better than one: PD-1/PD-L1 blockade combination approaches in metastatic breast cancer

Antibodies blocking programmed death 1 (anti-PD-1) or its ligand (anti-PD-L1) are associated with modest response rates as monotherapy in metastatic breast cancer, but are generally well tolerated and capable of generating dramatic and durable benefit in a minority of patients. Anti-PD-1/L1 antibodies are also safe when administered in combination with a variety of systemic therapies (chemotherapy, targeted therapies), as well as with radiotherapy. We summarize preclinical, translational, and preliminary clinical data in support of combination approaches with anti-PD-1/L1 in metastatic breast cancer, focusing on potential mechanisms of synergy, and considerations for clinical practice and future investigation.

Combining PARP inhibition, radiation, and immunotherapy: A possible strategy to improve the treatment of cancer?

Immunotherapy has revolutionized the practice of oncology, improving survival in certain groups of patients with cancer. Immunotherapy can synergize with radiation therapy, increase locoregional control, and have abscopal effects. Combining it with other treatments, such as targeted therapies, is a promising means of improving the efficacy of immunotherapy. Because the value of immunotherapy is amplified with the expression of tumor antigens, coupling poly(ADP-ribose) polymerase (PARP) inhibitors and immunotherapy might be a promising treatment for cancer. Further, PARP inhibitors (PARPis) are being combined with radiation therapy to inhibit DNA repair functions, thus enhancing the effects of radiation; this association might interact with the antitumor immune response. Cytotoxic T lymphocytes are central to the antitumor immune response. PARP inhibitors and ionizing radiation can enhance the infiltration of cytotoxic T lymphocytes into the tumor bed, but they can also enhance PD-1/PDL-1 expression. Thus, the addition of immune checkpoint inhibitors with PARP inhibitors and/or ionizing radiation could counterbalance such immunosuppressive effects. With the present review article, we proposed to evaluate some of these associated therapies, and we explored the biological mechanisms and medical benefits of the potential combination of radiation therapy, immunotherapy, and PARP inhibitors.

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.

Decreased Poly(ADP-Ribose) Polymerase 1 Expression Attenuates Glucose Oxidase-Induced Damage in Rat Cochlear Marginal Strial Cells

Oxidative damage to the inner ear is responsible for several types of sensorineural deafness. Cochlear stria marginal cells (MCs) are thought to be vulnerable to such oxidative stress. Activated poly(ADP-ribose) polymerase 1 (PARP1) has been implicated in several diseases, but the effect of PARP1 on MCs subjected to oxidative stress remains elusive. In this study, we established an in vitro cellular oxidative stress model using glucose oxidase (GO) and attempted to explore the role that PARP1 plays in the oxidative damage of MCs. In this study, PARP1 and poly-ADP-ribose (PAR) were highly expressed in GO-treated MCs, and this was accompanied by loss of MC viability, excessive generation of reactive oxygen species (ROS), collapse of mitochondria membrane potential (ΔΨm), and redistribution of the mitochondrial downstream pathway-related molecules Bax and cytochrome c, eventually causing MC death. These effects were almost completely counteracted by suppressing PARP1 expression with small interfering RNA (siRNA). We also found that caspase-3 activation was a downstream event of PARP activation and that apoptosis of MCs was suppressed, although not completely, by pretreatment with the pan-caspase inhibitor z-VAD-fmk. The suppression was less than that when PARP1 expression was inhibited. We conclude that GO treatment induces activation of PARP1, which causes MC damage via mitochondrial mediation. PARP1 plays a pivotal role in GO-induced MC death, at least in part, via the caspase-3 cascade. Our study might provide a new cellular and molecular approach for the treatment of oxidative stress-related sensorineural deafness.

TLR-Stimulated Neutrophils Instruct NK Cells To Trigger Dendritic Cell Maturation and Promote Adaptive T Cell Responses

Polymorphonuclear neutrophils (PMNs) are innate effector cells with pivotal roles in pathogen recognition, phagocytosis, and eradication. However, their role in the development of subsequent immune responses is incompletely understood. This study aimed to identify mechanisms of relevance to the cross talk between human neutrophils and NK cells and its potential role in promoting adaptive immunity. TLR-stimulated PMNs were found to release soluble mediators to attract and activate NK cells in vitro. PMN-conditioned NK cells displayed enhanced cytotoxicity and cytokine production, and responded vigorously to ensuing stimulation with exogenous and endogenous IL-12. The neutrophil-induced activation of NK cells was prevented by caspase-1 inhibitors and by natural antagonists to IL-1 and IL-18, suggesting a role for the NOD-like receptor family pyrin domain containing-3 inflammasome. In addition, PMN-conditioned NK cells triggered the maturation of monocyte-derived dendritic cells, which promoted T cell proliferation and IFN-γ production. These data imply that neutrophils attract NK cells to sites of infection to convert these cells into an active state, which drives adaptive immune responses via maturation of dendritic cells. Our results add to a growing body of evidence that suggests a sophisticated role for neutrophils in orchestrating the immune response to pathogens.

Histamine dihydrochloride for maintaining remission in acute myeloid leukemia

SUMMARY 

Maintaining complete remission in patients with acute myeloid leukemia (AML) is a great challenge. Targeting the remaining malignant clones, using different regimens of chemotherapeutic agents did not prove to be fruitful. Host residual leukemia stem cells may be eradicated by donor immune cells in case of allogeneic stem cell transplantation. However, only a minority of AML patients may benefit from this procedure. IL-2 is very well known in its ability to enhance activation and proliferation of natural killer and T cells, albeit in the clinical setting this effect is suppressed by myeloid cells derived oxygen species. Histamine dihydrochloride can inhibit myeloid cells activity, therefore reaugment antileukemic natural killer/T-cell cytotoxic activity. This review summarizes different strategies to maintain complete remission in AML patients focusing on the use of histamine dihydrochloride/IL-2 treatment.

Role of the ERK pathway for oxidant-induced parthanatos in human lymphocytes

Reactive oxygen species (ROS) are formed by myeloid cells as a defense strategy against microorganisms. ROS however also trigger poly(ADP-ribose) polymerase 1- (PARP-1) dependent cell death (parthanatos) in adjacent lymphocytes, which has been forwarded as a mechanism of immune escape in several forms of cancer. The present study assessed the role of mitogen-activated protein kinases (MAPKs), in particular the extracellular signal-regulated kinase (ERK), in ROS-induced signal transduction leading to lymphocyte parthanatos. We report that inhibitors of ERK1/2 phosphorylation upheld natural killer (NK) cell-mediated cytotoxicity under conditions of oxidative stress and rescued NK cells and CD8⁺ T lymphocytes from cell death induced by ROS-producing monocytes. ERK1/2 phosphorylation inhibition also protected lymphocytes from cell death induced by exogenous hydrogen peroxide (H₂O₂) and from ROS generated by xanthine oxidase or glucose oxidase. Phosphorylation of ERK1/2 was observed in lymphocytes shortly after exposure to ROS. ROS-generating myeloid cells and exogenous H₂O₂ triggered PARP 1-dependent accumulation of poly ADP-ribose (PAR), which was prevented by ERK pathway inhibitors. ERK1/2 phosphorylation was induced by ROS independently of PARP-1. Our findings are suggestive of a role for ERK1/2 in ROS-induced lymphocyte parthanatos, and that the ERK axis may provide a therapeutic target for the protection of lymphocytes against oxidative stress.

Synergistic anti-cancer effect of phenformin and oxamate

Phenformin (phenethylbiguanide; an anti-diabetic agent) plus oxamate [lactate dehydrogenase (LDH) inhibitor] was tested as a potential anti-cancer therapeutic combination. In in vitro studies, phenformin was more potent than metformin, another biguanide, recently recognized to have anti-cancer effects, in promoting cancer cell death in the range of 25 times to 15 million times in various cancer cell lines. The anti-cancer effect of phenformin was related to complex I inhibition in the mitochondria and subsequent overproduction of reactive oxygen species (ROS). Addition of oxamate inhibited LDH activity and lactate production by cells, which is a major side effect of biguanides, and induced more rapid cancer cell death by decreasing ATP production and accelerating ROS production. Phenformin plus oxamate was more effective than phenformin combined with LDH knockdown. In a syngeneic mouse model, phenformin with oxamate increased tumor apoptosis, reduced tumor size and (18)F-fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography compared to control. We conclude that phenformin is more cytotoxic towards cancer cells than metformin. Furthermore, phenformin and oxamate have synergistic anti-cancer effects through simultaneous inhibition of complex I in the mitochondria and LDH in the cytosol, respectively.

Natural killer cells modulation in hematological malignancies

Hematological malignancies (HM) treatment improved over the last years resulting in increased achievement of complete or partial remission, but unfortunately high relapse rates are still observed, due to remaining minimal residual disease. Therefore, sustainment of long-term remission is crucial, using either drug maintenance treatment or by boosting or prolonging an immune response. Immune system has a key role in tumor surveillance. Nonetheless, tumor-cells evade the specific T-lymphocyte mediated immune surveillance using many mechanisms but especially by the down-regulation of the expression of HLA class I antigens. In theory, these tumor-cells lacking normal expression of HLA class I molecules should be destroyed by natural killer (NK) cells, according to the missing-self hypothesis. NK cells, at the frontier of innate and adaptive immune system, have a central role in tumor-cells surveillance as demonstrated in the setting of allogenic stem cell transplantation. Nevertheless, tumors develop various mechanisms to escape from NK innate immune pressure. Abnormal NK cytolytic functions have been described in many HM. We present here various mechanisms involved in the escape of HM from NK-cell surveillance, i.e., NK-cells quantitative and qualitative abnormalities.

Beyond DNA repair, the immunological role of PARP-1 and its siblings

ADP-ribosylation is the addition of one or more (up to some hundreds) ADP-ribose moieties to acceptor proteins. There are two major families of enzymes that catalyse this reaction: extracellular ADP-ribosyl-transferases (ARTs), which are bound to the cell membrane by a glycosylphosphatidylinositol anchor or are secreted, and poly(ADP-ribose)-polymerases (PARPs), which are present in the cell nucleus and/or cytoplasm. Recent findings revealed a wide immunological role for ADP-ribosylating enzymes. ARTs, by sensing extracellular NAD concentration, can act as danger detectors. PARP-1, the prototypical representative of the PARP family, known to protect cells from genomic instability, is involved in the development of inflammatory responses and several forms of cell death. PARP-1 also plays a role in adaptive immunity by modulating the ability of dendritic cells to stimulate T cells or by directly affecting the differentiation and functions of T and B cells. Both PARP-1 and PARP-14 (CoaSt6) knockout mice were described to display reduced T helper type 2 cell differentiation and allergic responses. Our recent findings showed that PARP-1 is involved in the differentiation of Foxp3+ regulatory T (Treg) cells, suggesting a role for PARP-1 in tolerance induction. Also ARTs regulate Treg cell homeostasis by promoting Treg cell apoptosis during inflammatory responses. PARP inhibitors ameliorate immune-mediated diseases in several experimental models, including rheumatoid arthritis, colitis, experimental autoimmune encephalomyelitis and allergy. Together these findings show that ADP-ribosylating enzymes, in particular PARP-1, play a pivotal role in the regulation of immune responses and may represent a good target for new therapeutic approaches in immune-mediated diseases.

Immunotherapeutic strategies for relapse control in acute myeloid leukemia

Despite that the initial phases of chemotherapy induce disappearance of leukemic cells in many patients with acute myeloid leukemia (AML), the prevention of life-threatening relapses in the post-remission phase remains a significant clinical challenge. Allogeneic bone marrow transplantation, which is available for a minority of patients, efficiently prevents recurrences of leukemia by inducing immune-mediated elimination of leukemic cells, and over the past decades, numerous immunotherapeutic protocols have been developed aiming to mimic the graft-versus-leukemia reaction for the prevention of relapse. Here we review past and present strategies for relapse control with focus on overcoming leukemia-related immunosuppression in AML. We envisage future treatment protocols, in which systemic immune activators, such as vaccines, dendritic cell-based therapies, engineered variants of IL-2, or IL-15, are combined with agents that counter immunosuppression mediated by, e.g., the PD/PDL interaction, CTLA-4, CD200, reactive oxygen species, IDO expression, CXCR4, or the KIR/class I interaction, based on characteristics of the prevailing malignant clone. This combinatorial approach may pave the way for individualized immunotherapy in AML.

Chronic myeloid leukemic cells trigger poly(ADP-ribose) polymerase-dependent inactivation and cell death in lymphocytes

NK cells and T cells are commonly dysfunctional in CML, and their status may determine the course of disease. We aimed to define the molecular mechanisms of leukemia-induced immunosuppression with focus on the role of ROS and the PARP-1 pathway of cell death. Malignant granulocytes from patients with BCR-ABL-positive CML expressed the oxygen radical-producing enzyme NOX, produced large amounts of ROS, and triggered extensive cell death in NK cells. Inhibition of PARP-1 maintained NK cell viability in cocultures with suppressive leukemic cells. Under conditions of oxidative stress, PARP-1 inhibition upheld the capacity of NK cells to kill myeloid leukemic cells, in addition to restoring the proliferation and cytokine production of NK cells and cytotoxic T cells. Our findings are suggestive of a novel pathway of relevance to immunosuppression in CML.

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.

Antitumor activity of a novel STAT3 inhibitor and redox modulator in non-small cell lung cancer cells

NSC-743380 is a novel STAT3 inhibitor that suppresses the growth of several NCI-60 cancer cell lines derived from different tissues and induces regression of xenograft tumors in vivo at various doses. To evaluate the antitumor activity of NSC-743380 in lung cancer cells, we analyzed the susceptibility of 50 NSCLC cell lines to this compound using cell viability assay. About 32% (16 of 50) of these cell lines were highly susceptible to this compound, with a 50% inhibitory concentration (IC₅₀) of < 1 μM. In mechanistic studies, the increased numbers of apoptotic cells as well as increased PARP cleavage showed that cytotoxic effects correlate with apoptosis induction. Treatment with NSC-743380 inhibited transcription factor STAT3 activation and induced ROS production in sensitive human lung cancer cell lines but not in resistant cells. Blocking ROS generation with the antioxidant NDGA dramatically abolished NSC-743380-induced growth suppression and apoptosis, but had minimal effect on NSC-743380-induced STAT3 inhibition, suggesting that STAT3 inhibition is not caused by ROS production. Interestingly, knockdown of STAT3 with use of shSTAT3 induced ROS generation and suppressed tumor cell growth. Moreover, scavenging ROS induced by STAT3 inhibition also diminished antitumor activity of STAT3 inhibition. In vivo administration of NSC-743380 suppressed tumor growth and p-STAT3 in lung tumors. Our results indicate that NSC-743380 is a potent anticancer agent for lung cancer and that its apoptotic effects in lung cancer cells are mediated by induction of ROS through STAT3 inhibition.

Analyzing cell death events in cultured leukocytes

Cell death is of utmost importance in immunity, in part as a way to control the development and activity of leukocytes, but also as a strategy employed by leukocytes to rid the body of unwanted cells. Apoptosis is the classic type of programmed cell death involving an ordered sequence of cellular events, resulting in morphological changes that include cleavage/fragmentation of DNA, condensation of nuclei, cell shrinkage, and alterations of the plasma membrane. The apoptotic cell is a nonfunctional, but structurally intact, entity with preserved membrane integrity that is engulfed by surrounding cells (a process known as clearance) in an immunologically silent manner. In contrast, necrotic cells, i.e., nonfunctional cells that have lost membrane integrity, are freely permeable and leak intracellular constituents that may shift immunological homeostasis. Thus, membrane integrity of dead leukocytes is very important from an immunological point of view. For the analysis of leukocyte cell death, a wide variety of assays are available to monitor different events along the cell death pathway; a combination of different methods is advantageous in order to gain a more complete understanding of this dynamic process. In this chapter, we describe several in vitro methods for evaluating leukocyte cell death, mainly focusing on apoptosis in human neutrophils and lymphocytes. Special emphasis is given to assessment of membrane integrity of the cultured cells. Furthermore, a protocol for monitoring clearance of apoptotic neutrophils by monocyte-derived macrophages is provided.

Characterization of the metabolic phenotype of rapamycin-treated CD8+ T cells with augmented ability to generate long-lasting memory cells

Background

Cellular metabolism plays a critical role in regulating T cell responses and the development of memory T cells with long-term protections. However, the metabolic phenotype of antigen-activated T cells that are responsible for the generation of long-lived memory cells has not been characterized.

Design and Methods

Using lymphocytic choriomeningitis virus (LCMV) peptide gp33-specific CD8⁺ T cells derived from T cell receptor transgenic mice, we characterized the metabolic phenotype of proliferating T cells that were activated and expanded in vitro in the presence or absence of rapamycin, and determined the capability of these rapamycin-treated T cells to generate long-lived memory cells in vivo.

Results

Antigen-activated CD8⁺ T cells treated with rapamycin gave rise to 5-fold more long-lived memory T cells in vivo than untreated control T cells. In contrast to that control T cells only increased glycolysis, rapamycin-treated T cells upregulated both glycolysis and oxidative phosphorylation (OXPHOS). These rapamycin-treated T cells had greater ability than control T cells to survive withdrawal of either glucose or growth factors. Inhibition of OXPHOS by oligomycin significantly reduced the ability of rapamycin-treated T cells to survive growth factor withdrawal. This effect of OXPHOS inhibition was accompanied with mitochondrial hyperpolarization and elevation of reactive oxygen species that are known to be toxic to cells.

Conclusions

Our findings indicate that these rapamycin-treated T cells may represent a unique cell model for identifying nutrients and signals critical to regulating metabolism in both effector and memory T cells, and for the development of new methods to improve the efficacy of adoptive T cell cancer therapy.

L-kynurenine-induced apoptosis in human NK cells is mediated by reactive oxygen species

Recent studies have shown that indoleamine 2,3-dioxygenase (IDO) plays a pivotal role in the modulation of immune response against tumor and virus infection. Here we demonstrate the pro-apoptotic effect of L-kynurenine, a tryptophan catabolite of IDO, on human NK cell line, NK92 MI. Treatment with L-kynurenine dose-dependently induced growth inhibition and apoptosis in NK92 MI cells. Treatment with the antioxidant NAC completely protected cells from L-kynurenine-induced apoptosis. Moreover, we found that treatment with Z-VAD-fmk and ZB4 slightly inhibited L-kynurenine-induced apoptosis, suggesting that L-kynurenine-induced apoptosis in NK cells occurs primarily through an ROS mediated pathway. We observed that the presence of NAC blocks cytochrome c release and activation of caspase-3 during L-kynurenine-induced apoptosis. Overall, we conclude that L-kynurenine resulting from IDO can cause cell death via ROS pathway in NK cells. Our findings provide a new insight into the interaction between NK cells and IDO positive cancer cells in regulating immune responses.

Mitochondrial translocation of oxidized cofilin induces caspase-independent necrotic-like programmed cell death of T cells

Oxidative stress leads to T-cell hyporesponsiveness or death. The actin-binding protein cofilin is oxidized during oxidative stress, which provokes a stiff actin cytoskeleton and T-cell hyporesponsiveness. Here, we show that long-term oxidative stress leads to translocation of cofilin into the mitochondria and necrotic-like programmed cell death (PCD) in human T cells. Notably, cofilin mutants that functionally mimic oxidation by a single mutation at oxidation-sensitive cysteins (Cys-39 or Cys-80) predominately localize within the mitochondria. The expression of these mutants alone ultimately leads to necrotic-like PCD in T cells. Accordingly, cofilin knockdown partially protects T cells from the fatal effects of long-term oxidative stress. Thus, we introduce the oxidation and mitochondrial localization of cofilin as the checkpoint for necrotic-like PCD upon oxidative stress as it occurs, for example, in tumor environments.

Signals of apoptotic pathways in several types of meningioma

Meningiomas are intracranial tumour derived from meningothelial cells, which aggressive behaviour has been frequently associated to cell apoptosis. In this paper activation of several factors involved in apoptosis has been investigated on biopsies of primary, non recurrent meningiomas. Benign (meningotheliomatous, transitional, fibrous, angiomatous), atypical and anaplastic meningiomas were analysed by immunohistochemistry and western blot, to visualize the occurring of different apoptotic pathways and their association with clinical grading. Apoptotic cell have been detected by a double colorimetric staining for TUNEL and caspase-3 active form. Apoptotic signal positive cells have been detected in all type of meningiomas analysed, with exception of meningotheliomatous meningiomas. Differences have been found in the activation of apoptotic pathways between several types of grade I meningiomas and among benign, anaplastic and atypical meningiomas. An intense expression of several apoptotic inhibitor occurred in grade I meningiomas. The correlation among expression of apoptotic and inhibitory factors and cell proliferation index may suggest that in grade I meningiomas apoptosis may be related to mechanisms involved into tumor cells surviving. Instead in grade II and III meningiomas the same correlation seems indicate an high turnover of tumor cells that might be useful as index of cell proliferation and tumor mass growth.

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.

Post-consolidation immunotherapy with histamine dihydrochloride and interleukin-2 in AML

The initial chemotherapy in acute myeloid leukaemia (AML) comprises a first phase of induction and a second phase of consolidation. In the majority of patients, the induction treatment leads to complete remission (CR), defined as microscopic disappearance of leukaemic disease along with the return of normal haematopoiesis. However, despite the introduction of more efficacious consolidation regimens, a worryingly large proportion of AML patients in CR will subsequently experience relapses with poor prospects of long-term survival. A relapse is assumed to be the result of expansion of residual leukaemic cells that have escaped the initial chemotherapy. The anti-leukaemic functions of T cells and natural killer (NK) cells has formed the background to the use of interleukin-2 (IL-2), a T- and NK cell-activating cytokine, with the aim to eliminate residual leukaemia and hence reduce the relapse rate in AML, but the clinical trials using IL-2 monotherapy have yielded disappointment. A recent phase III study has demonstrated that post-consolidation treatment with the combination of histamine dihydrochloride (HDC) and IL-2 significantly prevents relapse in AML patients. Here we account for the preclinical background to the use of HDC/IL-2 in AML along with a review of clinical results.

Transduction with the antioxidant enzyme catalase protects human T cells against oxidative stress

Patients with diseases characterized by chronic inflammation, caused by infection or cancer, have T cells and NK cells with impaired function. The underlying molecular mechanisms are diverse, but one of the major mediators in this immune suppression is oxidative stress caused by activated monocytes, granulocytes, or myeloid-derived suppressor cells. Reactive oxygen species can seriously hamper the efficacy of active immunotherapy and adoptive transfer of T and NK cells into patients. In this study, we have evaluated whether enhanced expression of the antioxidant enzyme catalase in human T cells can protect them against reactive oxygen species. Human CD4(+) and CD8(+) T cells retrovirally transduced with the catalase gene had increased intracellular expression and activity of catalase. Catalase transduction made CD4(+) T cells less sensitive to H(2)O(2)-induced loss-of-function, measured by their cytokine production and ability to expand in vitro following anti-CD3 stimulation. It also enhanced the resistance to oxidative stress-induced cell death after coculture with activated granulocytes, exposure to the oxidized lipid 4-hydroxynonenal, or H(2)O(2). Expression of catalase by CMV-specific CD8(+) T cells saved cells from cell death and improved their capacity to recognize CMV peptide-loaded target cells when exposed to H(2)O(2). These findings indicate that catalase-transduced T cells potentially are more efficacious for the immunotherapy of patients with advanced cancer or chronic viral infections.

The host defense peptide LL-37 selectively permeabilizes apoptotic leukocytes

LL-37 is a cationic host defense peptide that is highly expressed during acute inflammation and that kills bacteria by poorly defined mechanisms, resulting in permeabilization of microbial membranes. High concentrations of LL-37 have also been reported to have cytotoxic effects against eukaryotic cells, but the peptide is clearly capable of differentiating between membranes with different compositions (eukaryotic versus bacterial membranes). Eukaryotic cells such as leukocytes change their membrane composition during apoptotic cell death, when they are turned into nonfunctional but structurally intact entities. We tested whether LL-37 exerted specific activity on apoptotic cells and found that the peptide selectively permeabilized the membranes of apoptotic human leukocytes, leaving viable cells unaffected. This activity was seemingly analogous to the direct microbicidal effect of LL-37, in that it was rapid, independent of known surface receptors and/or active cell signaling, and inhibitable by serum components such as high-density lipoprotein. A similar selective permeabilization of apoptotic cells was recorded for both NK cells and neutrophils. In the latter cell type, LL-37 permeabilized both the plasma and granule membranes, resulting in the release of both lactate dehydrogenase and myeloperoxidase. Apoptosis is a way for inflammatory cells to die silently and minimize collateral tissue damage by retaining tissue-damaging and proinflammatory substances within intact membranes. Permeabilization of apoptotic leukocytes by LL-37, accompanied by the leakage of cytoplasmic as well as intragranular molecules, may thus shift the balance between pro- and anti-inflammatory signals and in this way be of importance for the termination of acute inflammation.

Inhibition of the activity of poly (ADP-ribose) polymerase reduces heart ischaemia/reperfusion injury via suppressing JNK-mediated AIF translocation

Poly (ADP-ribose) polymerase (PARP) has been proposed to play an important role in the pathogenesis of heart ischaemia/reperfusion (I/R) injury. However, the mechanisms of PARP-mediated heart I/R injury in vivo are still not thoroughly understood. Therefore, in this study, we investigate the effect of PARP inhibition on heart I/R injury and try to elucidate the underlying mechanisms. Studies were performed with I/R rats' hearts in vivo. Ischaemia followed by reperfusion caused a significant increase in Poly (ADP-ribose) (PAR), c-Jun NH2-terminal kinase (JNK) and apoptosis-inducing factor (AIF) activity. Administration of 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone (DPQ), an inhibitor of PARP, decreased myocardial infarction size from 61.11+/-7.46%[0] to 38.83+/-5.67% (P<0.05) and cells apoptosis from 35+/-5.3% to 20+/-4.1% (P<0.05) and simultaneously improved the cardiac function. Western blot analysis showed that administration of DPQ reduced the activation of JNK and attenuated mitochondrial-nuclear translocation of AIF. Additionally, administration of SP600125, an inhibitor of JNK, attenuated mitochondrial-nuclear translocation of AIF. The results of the present study demonstrated that the inhibition of PARP was able to reduce heart I/R injury in vivo. Our results also suggested that JNK may be downstream of PARP activation and be required for PARP-mediated AIF translocation. Inhibition of the activity of PARP may reduce heart I/R injury via suppressing AIF translocation mediated by JNK.

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.

The CD16- CD56(bright) NK cell subset is resistant to reactive oxygen species produced by activated granulocytes and has higher antioxidative capacity than the CD16+ CD56(dim) subset

Human NK cells can be divided into CD56(dim) and CD56(bright) subsets. These two types of NK cells respond to different types of stimuli, with CD56(dim) NK cells having direct cytotoxic ability and CD56(bright) NK cells having mainly an immunoregulatory function. We show that the CD16+ CD56(dim) NK subset is characterized by sensitivity to cell death induced by activated granulocytes. We identified hydrogen peroxide (H2O2) as the major effector molecule responsible for the cytotoxic effect of granulocytes on CD56(dim) NK cells, because the ability of granulocytes to kill CD56(dim) NK cells was completely abrogated in the presence of the hydrogen peroxide scavenger catalase. When exposing NK cells to H2O2, CD56(dim) cells showed rapid mitochondrial depolarization and down-regulation of activating NKRs, eventually resulting in cell death, whereas CD56(bright) cells remained unaffected. The difference in sensitivity to H2O2 was mirrored by a difference in intracellular oxidation levels between CD56(dim) and CD56(bright) NK cells, and cell lysates from the latter subset possessed a greater ability to block H2O2-mediated oxidation. Our data may explain the preferential accumulation of CD56(bright) NK cells often seen in environments rich in reactive oxygen species, such as at sites of chronic inflammation and in tumors.

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

Phagocyte-derived reactive oxygen species ("oxygen radicals") have been ascribed a suppressive role in immunoregulation by inducing dysfunction and apoptotic cell death in lymphocytes. Earlier studies show that human NK cells are exceptionally sensitive to oxygen radical-induced apoptosis and functional inhibition. Two subsets of human CD56(+) NK cells have been identified: the highly cytotoxic CD56(dim) cells which constitute >90% of NK cells in peripheral blood, and the less cytotoxic but efficiently cytokine-producing CD56(bright) cells. In this study, we demonstrate that the CD56(bright) subset of NK cells, in contrast to CD56(dim) cells, remains viable and functionally intact after exposure to phagocyte-derived or exogenously added oxygen radicals. The resistance of CD56(bright) cells to oxidative stress was accompanied by a high capacity of neutralizing exogenous hydrogen peroxide, and by a high cell-surface expression of antioxidative thiols. Our results imply that CD56(bright) NK cells are endowed with an efficient antioxidative defense system that protects them from oxygen radical-induced inactivation.

Cutting Edge: Antioxidative Properties of Myeloid Dendritic Cells: Protection of T Cells and NK Cells from Oxygen Radical-Induced Inactivation and Apoptosis

Dendritic cells (DCs) communicate with nonadaptive and adaptive lymphocytes on multiple levels. Efficient DC-lymphocyte interactions require that lymphocytes remain viable and functional also under conditions of oxidative stress, such as in microbial infection or in the malignant microenvironment. For this study, we exposed human T and NK cells to oxidants delivered either by autologous phagocytes or in the form of exogenous hydrogen peroxide. In accordance with earlier studies, these lymphocytes became dysfunctional and subsequently apoptotic. The presence of myeloid DCs efficiently rescued T cells (CD4+ and CD8+) and NK cells from oxidant-induced inactivation and apoptosis. The mechanism of the myeloid DC-mediated lymphocyte protection was, at least in part, explained by the capacity of the myeloid DCs to neutralize extracellular oxygen radicals, which, in turn, was reversible upon coincubation with a catalase inhibitor. Our results are suggestive of a novel aspect of DC-lymphocyte interaction that may have implications for lymphocyte function in inflamed tissue.

Activation-induced cell death of human melanoma specific cytotoxic T lymphocytes is mediated by apoptosis-inducing factor

Activation-induced cell death (AICD) of T cells can be an impediment towards achieving a robust and long-lived cytolytic T lymphocyte (CTL) response from active specific immunization or after adoptive cell transfer in cancer immunotherapy. The mechanism of AICD in primary CTL, however, remains poorly understood. It is widely believed that AICD is driven by signals from death receptors (DR) and that the cell death takes place in a caspase-dependent manner, although it has been shown that AICD of T cells can be induced by internal triggers and that death takes place in a caspase-independent manner. We show here that AICD in human melanoma epitope-specific primary CTL involves selective mitochondrio-nuclear translocation of the apoptosis inducing factor (AIF) without cytochrome c release, caspase-3 and caspase-8 activation, and results from large-scale DNA fragmentation. The c-jun-N terminal kinase (JNK) inhibitor, SP600125, blocks the mitochondrio-nuclear translocation of AIF and prevents AICD in these CTL. These findings suggest that the AICD in human melanoma epitope specific primary CTL is mediated by mitochondrial AIF release and JNK is involved in regulation of this death process.