Interleukin 2 and interleukin 15 differentially predispose natural killer cells to apoptosis mediated by endothelial and tumour cells

Suppression of NK Cell Activation by JAK3 Inhibition: Implication in the Treatment of Autoimmune Diseases

Natural killer (NK) cell is an essential cytotoxic lymphocyte in our innate immunity. Activation of NK cells is of paramount importance in defending against pathogens, suppressing autoantibody production and regulating other immune cells. Common gamma chain (γc) cytokines, including IL-2, IL-15, and IL-21, are defined as essential regulators for NK cell homeostasis and development. However, it is inconclusive whether γc cytokine-driven NK cell activation plays a protective or pathogenic role in the development of autoimmunity. In this study, we investigate and correlate the differential effects of γc cytokines in NK cell expansion and activation. IL-2 and IL-15 are mainly responsible for NK cell activation, while IL-21 preferentially stimulates NK cell proliferation. Blockade of Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway by either JAK inhibitors or antibodies targeting γc receptor subunits reverses the γc cytokine-induced NK cell activation, leading to suppression of its autoimmunity-like phenotype in vitro. These results underline the mechanisms of how γc cytokines trigger autoimmune phenotype in NK cells as a potential target to autoimmune diseases.

Anti-Inflammatory Effects of Nutritionally Relevant Concentrations of Oleuropein and Hydroxytyrosol on Peripheral Blood Mononuclear Cells: An Age-Related Analysis

Immunosenescence and inflammaging facilitate the insurgence of chronic diseases. The Mediterranean diet is a non-invasive intervention to improve the chronic low-grade inflammatory status associated with aging. Olive oil oleuropein (OLE) and hydroxytyrosol (HT) demonstrated a controversial modulatory action on inflammation in vitro when tested at concentrations exceeding those detectable in human plasma. We studied the potential anti-inflammatory effects of OLE and HT at nutritionally relevant concentrations on peripheral blood mononuclear cells (PBMCs) as regards cell viability, frequency of leukocyte subsets, and cytokine release, performing an age-focused analysis on two groups of subjects: Adult (age 18-64 years) and Senior (age ≥ 65 years). OLE and HT were used alone or as a pre-treatment before challenging PBMCs with lipopolysaccharide (LPS). Both polyphenols had no effect on cell viability irrespective of LPS, but 5 µM HT had an LPS-like effect on monocytes, reducing the intermediate subset in Adult subjects. OLE and HT had no effect on LPS-triggered release of TNF-α, IL-6 and IL-8, but 5 µM HT reduced IL-10 secretion by PBMCs from Adult vs. Senior group. In summary, nutritionally relevant concentrations of OLE and HT elicit no anti-inflammatory effect and influence the frequency of immune cell subsets with age-related different outcomes.

Murine models to study human NK cells in human solid tumors

Since the first studies, the mouse models have provided crucial support for the most important discoveries on NK cells, on their development, function, and circulation within normal and tumor tissues. Murine tumor models were initially set to study murine NK cells, then, ever more sophisticated human-in-mice models have been developed to investigate the behavior of human NK cells and minimize the interferences from the murine environment. This review presents an overview of the models that have been used along time to study NK cells, focusing on the most popular NOG and NSG models, which work as recipients for the preparation of human-in-mice tumor models, the study of transferred human NK cells, and the evaluation of various enhancers of human NK cell function, including cytokines and chimeric molecules. Finally, an overview of the next generation humanized mice is also provided along with a discussion on how traditional and innovative in-vivo and in-vitro approaches could be integrated to optimize effective pre-clinical studies.

Phospho-proteomics reveals that RSK signaling is required for proliferation of natural killer cells stimulated with IL-2 or IL-15

Natural killer (NK) cells are cytotoxic lymphocytes that play a critical role in the innate immune system. Although cytokine signaling is crucial for the development, expansion, and cytotoxicity of NK cells, the signaling pathways stimulated by cytokines are not well understood. Here, we sought to compare the early signaling dynamics induced by the cytokines interleukin (IL)-2 and IL-15 using liquid chromatography-mass spectrometry (LC-MS)-based phospho-proteomics. Following stimulation of the immortalized NK cell line NK-92 with IL-2 or IL-15 for 5, 10, 15, or 30 min, we identified 8,692 phospho-peptides from 3,023 proteins. Comparing the kinetic profiles of 3,619 fully quantified phospho-peptides, we found that IL-2 and IL-15 induced highly similar signaling in NK-92 cells. Among the IL-2/IL-15-regulated phospho-peptides were both well-known signaling events like the JAK/STAT pathway and novel signaling events with potential functional significance including LCP1 pSer5, STMN1 pSer25, CHEK1 pSer286, STIM1 pSer608, and VDAC1 pSer104. Using bioinformatic approaches, we sought to identify kinases regulated by IL-2/IL-15 stimulation and found that the p90 ribosomal S6 kinase (p90RSK) family was activated by both cytokines. Using pharmacological inhibitors, we then discovered that RSK signaling is required for IL-2 and IL-15-induced proliferation in NK-92 cells. Taken together, our analysis represents the first phospho-proteomic characterization of cytokine signaling in NK cells and increases our understanding of how cytokine signaling regulates NK cell function.

Infusion reactions in natural killer cell immunotherapy: a retrospective review

BACKGROUND AIMS

The use of natural killer (NK) cells as a cellular immunotherapy has increased over the past decade, specifically in patients with hematologic malignancies. NK cells have been used at the authors' institution for over 15 years. Most patients have a reaction to NK cell infusion. The authors retrospectively analyzed the reactions associated with NK cell infusions to characterize the types of reactions and investigate why some patients have higher-grade reactions than others.

METHODS

A retrospective chart review of NK cell infusions was performed at the authors' institution under nine clinical protocols from 2008 to 2016. An infusion reaction was defined as any symptom from the time of NK cell infusion up to 4 h after infusion completion. The severity of infusion reactions was graded based on Common Terminology Criteria for Adverse Events, version 4. Two major endpoints of interest were (i) infusion reaction with any symptom and (ii) grade ≥3 infusion reaction. Multivariable logistic regression models were used to investigate the association between variables of interest and outcomes. Odds ratios (ORs) and 95% confidence intervals (CIs) were obtained for each variable.

RESULTS

A total of 130 patients were receiving NK cell infusions at the authors' institution. The most common reported symptom was chills (n = 110, 85%), which were mostly grade 1 and 2, with only half of patients requiring intervention. There were 118 (91%) patients with infusion reactions, and only 36 (28%) were grade 3. There was one life-threatening grade 4 reaction, and no death was reported due to infusion reaction. Among grade ≥3 reactions, cardiovascular reactions (mainly hypertension) were the most common, and less than half of those with hypertension required intervention. NK cell dose was not associated with any of the grade 3 infusion reactions, whereas monocyte dose was associated with headache (grade ≤3, OR, 2.17, 95% CI, 1.19-3.97) and cardiovascular reaction (grade ≥3, OR, 2.13, 95% CI, 1.13-3.99). Cardiovascular reaction (grade ≥3) was also associated with in vitro IL-2 incubation and storage time. Additionally, there was no association between grade ≥3 infusion reactions and overall response rate (OR, 0.75, 95% CI, 0.29-1.95).

CONCLUSIONS

The majority of patients who receive NK cell therapy experience grade 1 or 2 infusion reactions. Some patients experience grade 3 reactions, which are mainly cardiovascular, suggesting that close monitoring within the first 4 h is beneficial. The association of monocytes with NK cell infusion reaction relates to toxicities seen in adoptive T-cell therapy and needs further exploration.

Autophagy-Mediated Exosomes as Immunomodulators of Natural Killer Cells in Pancreatic Cancer Microenvironment

Pancreas ductal adenocarcinoma is a highly aggressive cancer with an incredible poor lifespan. Different chemotherapeutic agents' schemes have been tested along the years without significant success. Furthermore, immunotherapy also fails to cope with the disease, even in combination with other standard approaches. Autophagy stands out as a chemoresistance mechanism and is also becoming relevant as responsible for the inefficacy of immunotherapy. In this complex scenario, exosomes have emerged as a new key player in tumor environment. Exosomes act as messengers among tumor cells, including tumor microenvironment immune cells. For instance, tumor-derived exosomes are capable of generating a tolerogenic microenvironment, which in turns conditions the immune system behavior. But also, immune cells-derived exosomes, under non-tolerogenic conditions, induce tumor suppression, although they are able to promote chemoresistance. In that way, NK cells are well known key regulators of carcinogenesis and the inhibition of their function is detrimental for tumor suppression. Additionally, increasing evidence suggests a crosstalk between exosome biogenesis and the autophagy pathway. This mini review has the intention to summarize the available data in the complex relationships between the autophagy pathway and the broad spectrum of exosomes subpopulations in pancreatic cancer, with focus on the NK cells response.

NK cells: A double edge sword against SARS-CoV-2

Natural killer (NK) cells are pivotal effectors of the innate immunity protecting an individual from microbes. They are the first line of defense against invading viruses, given their substantial ability to directly target infected cells without the need for specific antigen presentation. By establishing cellular networks with a variety of cell types such as dendritic cells, NK cells can also amplify and modulate antiviral adaptive immune responses. In this review, we will examine the role of NK cells in SARS-COV2 infections causing the ongoing COVID19 pandemic, keeping in mind the controversial role of NK cells specifically in viral respiratory infections and in inflammatory-driven lung damage. We discuss lessons learnt from previous coronavirus outbreaks in humans (caused by SARS-CoV-1 and MERS-COV).

Understanding the Synergy of NKp46 and Co-Activating Signals in Various NK Cell Subpopulations: Paving the Way for More Successful NK-Cell-Based Immunotherapy

The NK cell population is characterized by distinct NK cell subsets that respond differently to the various activating stimuli. For this reason, the determination of the optimal cytotoxic activation of the different NK cell subsets can be a crucial aspect to be exploited to counter cancer cells in oncologic patients. To evaluate how the triggering of different combination of activating receptors can affect the cytotoxic responses of different NK cell subsets, we developed a microbead-based degranulation assay. By using this new assay, we were able to detect CD107a⁺ degranulating NK cells even within the less cytotoxic subsets (i.e., resting CD56^bright and unlicensed CD56^dim NK cells), thus demonstrating its high sensitivity. Interestingly, signals delivered by the co-engagement of NKp46 with 2B4, but not with CD2 or DNAM-1, strongly cooperate to enhance degranulation on both licensed and unlicensed CD56^dim NK cells. Of note, 2B4 is known to bind CD48 hematopoietic antigen, therefore this observation may provide the rationale why CD56^dim subset expansion correlates with successful hematopoietic stem cell transplantation mediated by alloreactive NK cells against host T, DC and leukemic cells, while sparing host non-hematopoietic tissues and graft versus host disease. The assay further confirms that activation of LFA-1 on NK cells leads to their granule polarization, even if, in some cases, this also takes to an inhibition of NK cell degranulation, suggesting that LFA-1 engagement by ICAMs on target cells may differently affect NK cell response. Finally, we observed that NK cells undergo a time-dependent spontaneous (cytokine-independent) activation after blood withdrawal, an aspect that may strongly bias the evaluation of the resting NK cell response. Altogether our data may pave the way to develop new NK cell activation and expansion strategies that target the highly cytotoxic CD56^dim NK cells and can be feasible and useful for cancer and viral infection treatment.

Understanding the Synergy of NKp46 and Co-Activating Signals in Various NK Cell Subpopulations: Paving the Way for More Successful NK-Cell-Based Immunotherapy

The NK cell population is characterized by distinct NK cell subsets that respond differently to the various activating stimuli. For this reason, the determination of the optimal cytotoxic activation of the different NK cell subsets can be a crucial aspect to be exploited to counter cancer cells in oncologic patients. To evaluate how the triggering of different combination of activating receptors can affect the cytotoxic responses of different NK cell subsets, we developed a microbead-based degranulation assay. By using this new assay, we were able to detect CD107a⁺ degranulating NK cells even within the less cytotoxic subsets (i.e., resting CD56^bright and unlicensed CD56^dim NK cells), thus demonstrating its high sensitivity. Interestingly, signals delivered by the co-engagement of NKp46 with 2B4, but not with CD2 or DNAM-1, strongly cooperate to enhance degranulation on both licensed and unlicensed CD56^dim NK cells. Of note, 2B4 is known to bind CD48 hematopoietic antigen, therefore this observation may provide the rationale why CD56^dim subset expansion correlates with successful hematopoietic stem cell transplantation mediated by alloreactive NK cells against host T, DC and leukemic cells, while sparing host non-hematopoietic tissues and graft versus host disease. The assay further confirms that activation of LFA-1 on NK cells leads to their granule polarization, even if, in some cases, this also takes to an inhibition of NK cell degranulation, suggesting that LFA-1 engagement by ICAMs on target cells may differently affect NK cell response. Finally, we observed that NK cells undergo a time-dependent spontaneous (cytokine-independent) activation after blood withdrawal, an aspect that may strongly bias the evaluation of the resting NK cell response. Altogether our data may pave the way to develop new NK cell activation and expansion strategies that target the highly cytotoxic CD56^dim NK cells and can be feasible and useful for cancer and viral infection treatment.

Innate and adaptive immune responses against human Puumala virus infection: immunopathogenesis and suggestions for novel treatment strategies for severe hantavirus-associated syndromes

Two related hyperinflammatory syndromes are distinguished following infection of humans with hantaviruses: haemorrhagic fever with renal syndrome (HFRS) seen in Eurasia and hantavirus pulmonary syndrome (HPS) seen in the Americas. Fatality rates are high, up to 10% for HFRS and around 35%-40% for HPS. Puumala virus (PUUV) is the most common HFRS-causing hantavirus in Europe. Here, we describe recent insights into the generation of innate and adaptive cell-mediated immune responses following clinical infection with PUUV. First described are studies demonstrating a marked redistribution of peripheral blood mononuclear phagocytes (MNP) to the airways, a process that may underlie local immune activation at the site of primary infection. We then describe observations of an excessive natural killer (NK) cell activation and the persistence of highly elevated numbers of NK cells in peripheral blood following PUUV infection. A similar vigorous CD8 Tcell response is also described, though Tcell responses decline with viraemia. Like MNPs, many NK cells and CD8 T cells also localize to the lung upon acute PUUV infection. Following this, findings demonstrating the ability of hantaviruses, including PUUV, to cause apoptosis resistance in infected target cells, are described. These observations, and associated inflammatory cytokine responses, may provide new insights into HFRS and HPS disease pathogenesis. Based on similarities between inflammatory responses in severe hantavirus infections and other hyperinflammatory disease syndromes, we speculate whether some therapeutic interventions that have been successful in the latter conditions may also be applicable in severe hantavirus infections.

Overcoming Resistance to Natural Killer Cell Based Immunotherapies for Solid Tumors

Despite advances in the diagnostic and therapeutic modalities, the prognosis of several solid tumor malignancies remains poor. Different factors associated with solid tumors including a varied genetic signature, complex molecular signaling pathways, defective cross talk between the tumor cells and immune cells, hypoxic and immunosuppressive effects of tumor microenvironment result in a treatment resistant and metastatic phenotype. Over the past several years, immunotherapy has emerged as an attractive therapeutic option against multiple malignancies. The unique ability of natural killer (NK) cells to target cancer cells without antigen specificity makes them an ideal candidate for use against solid tumors. However, the outcomes of adoptive NK cell infusions into patients with solid tumors have been disappointing. Extensive studies have been done to investigate different strategies to improve the NK cell function, trafficking and tumor targeting. Use of cytokines and cytokine analogs has been well described and utilized to enhance the proliferation, stimulation and persistence of NK cells. Other techniques like blocking the human leukocyte antigen-killer cell receptors (KIR) interactions with anti-KIR monoclonal antibodies, preventing CD16 receptor shedding, increasing the expression of activating NK cell receptors like NKG2D, and use of immunocytokines and immune checkpoint inhibitors can enhance NK cell mediated cytotoxicity. Using genetically modified NK cells with chimeric antigen receptors and bispecific and trispecific NK cell engagers, NK cells can be effectively redirected to the tumor cells improving their cytotoxic potential. In this review, we have described these strategies and highlighted the need to further optimize these strategies to improve the clinical outcome of NK cell based immunotherapy against solid tumors.

Natural Killer Cell-Based Cancer Immunotherapy: A Review on 10 Years Completed Clinical Trials

NK cell cancer immunotherapy is an emerging anti-tumour therapeutic strategy that explores NK cell stimulation. In this review, we address strategies developed to circumvent limitations to clinical application of NK cell-based therapies, and comprehensively review the design and results of clinical trials conducted in the past 10 years (2008-2018) to test their therapeutic potential. NK cell-based immunotherapy of solid cancers remains controversial, but merit further detailed investigation.

IL15 induces a potent antitumor activity in NK cells isolated from malignant pleural effusions and overcomes the inhibitory effect of pleural fluid

Natural Killer (NK) cells are capable of recognizing and killing cancer cells and play an important role in tumor immunosurveillance. However, tumor-infiltrating NK cells are frequently impaired in their functional capability. A remarkable exception is represented by NK cells isolated from malignant pleural effusions (PE) that are not anergic and, upon IL2-induced activation, efficiently kill tumor cells. Although IL2 is used in various clinical trials, severe side effects may occur in treated patients. In this study, we investigated whether also other clinical-grade cytokines could induce strong cytotoxicity in NK cells isolated from pleural fluid of patients with primary or metastatic tumors of different origins. We show that PE-NK cells, cultured for short-time intervals with IL15, maintain the CD56^bright phenotype, a high expression of the main activating receptors, produce cytokines and kill tumor cells in vitro similarly to those treated with IL2. Moreover, IL15-activated PE-NK cells could greatly reduce the growth of established tumors in mice. This in vivo antitumor effect correlated with the ability of IL15-activated PE-NK cells to traffic from periphery to the tumor site. Finally, we show that IL15 can counteract the inhibitory effect of the tumor pleural microenvironment. Our study suggests that IL15-activated NK cells isolated from pleural fluid (otherwise discarded after thoracentesis) may represent a suitable source of effector cells to be used in adoptive immunotherapy of cancer.

Natural killer cells stimulated with PM21 particles expand and biodistribute in vivo: Clinical implications for cancer treatment

BACKGROUND AIMS

Natural killer (NK) cell immunotherapy for treatment of cancer is promising, but requires methods that expand cytotoxic NK cells that persist in circulation and home to disease site.

METHODS

We developed a particle-based method that is simple, effective and specifically expands cytotoxic NK cells from peripheral blood mononuclear cells (PBMCs) both ex vivo and in vivo. This method uses particles prepared from plasma membranes of K562-mb21-41BBL cells, expressing 41BBL and membrane bound interleukin-21 (PM21 particles).

RESULTS

Ex vivo, PM21 particles caused specific NK-cell expansion from PBMCs from healthy donors (mean 825-fold, range 163-2216, n = 13 in 14 days) and acute myeloid leukemia patients. The PM21 particles also stimulated in vivo NK cell expansion in NSG mice. Ex vivo pre-activation of PBMCs with PM21 particles (PM21-PBMC) before intraperitoneal (i.p.) injection resulted in 66-fold higher amounts of hNK cells in peripheral blood (PB) of mice compared with unactivated PBMCs on day 12 after injection. In vivo administration of PM21 particles resulted in a dose-dependent increase of PB hNK cells in mice injected i.p. with 2.0 × 10(6) PM21-PBMCs (11% NK cells). Optimal dose of 800 µg/injection of PM21 particles (twice weekly) with low-dose interleukin 2 (1000 U/thrice weekly) resulted in 470 ± 40 hNK/µL and 95 ± 2% of total hCD45(+) cells by day 12 in PB. Furthermore, hNK cells were found in marrow, spleen, lung, liver and brain (day 16 after i.p. PM21/PBMC injection), and mice injected with PM21 particles had higher amounts.

CONCLUSIONS

The extent of NK cells observed in PB, their persistence and the biodistribution would be relevant for cancer treatment.

Manufacturing Natural Killer Cells as Medicinal Products

Natural Killer (NK) cells are innate lymphoid cells (ILC) with cytotoxic and regulatory properties. Their functions are tightly regulated by an array of inhibitory and activating receptors, and their mechanisms of activation strongly differ from antigen recognition in the context of human leukocyte antigen presentation as needed for T-cell activation. NK cells thus offer unique opportunities for new and improved therapeutic manipulation, either in vivo or in vitro, in a variety of human diseases, including cancers. NK cell activity can possibly be modulated in vivo through direct or indirect actions exerted by small molecules or monoclonal antibodies. NK cells can also be adoptively transferred following more or less substantial modifications through cell and gene manufacturing, in order to empower them with new or improved functions and ensure their controlled persistence and activity in the recipient. In the present review, we will focus on the technological and regulatory challenges of NK cell manufacturing and discuss conditions in which these innovative cellular therapies can be brought to the clinic.

Natural Killer Cell Adoptive Transfer Therapy: Exploiting the First Line of Defense Against Cancer

Natural killer (NK) cells constitute an important component of the initial immunological response against transformed cells. However, chronic exposure to the tumor microenvironment can fundamentally alter the ability of NK cells to sufficiently control tumor progression. Thus, the adoptive transfer of healthy, functional NK cells as an interventional therapy has been an area of great interest for improving patient outcomes. Recent developments in the field have provided a better understanding of what makes the NK compartment effective against malignant cells. Moreover, there are now multiple potential sources of NK cell products for infusion as well as techniques to manipulate these cells to enhance their antitumor functions. This review explores the advantages and disadvantages of various sources of NK cells as well as prospective therapeutic enhancements to adoptively transferred NK cells.

Role of NK cells in immunotherapy and virotherapy of solid tumors

Although natural killer (NK) cells are endowed with powerful cytolytic activity against cancer cells, their role in different therapies against solid tumors has not yet been fully elucidated. Their interactions with various elements of the tumor microenvironment as well as their possible effects in contributing to and/or limiting oncolytic virotherapy render this potential immunotherapeutic tool still difficult to exploit at the bedside. Here, we will review the current literature with the aim of providing new hints to manage this powerful cell type in future innovative therapies, such as the use of NK cells in combination with new cytokines, specific mAbs (inducing ADCC), Tyr-Kinase inhibitors, immunomodulatory drugs and/or the design of oncolytic viruses aimed at optimizing the effect of NK cells in virotherapy.

Clinical utility of natural killer cells in cancer therapy and transplantation

Natural killer (NK) cells recognize deranged cells that display stress receptors or loss of major histocompatibility complex (MHC) class I. During development, NK cells become "licensed" only after they encounter cognate human leukocyte antigen (HLA) class I, leading to the acquisition of effector function. NK cells can be exploited for cancer therapy in several ways. These include targeting with monoclonal antibodies alone or combined with ex vivo and in vivo NK cell activation to facilitate adoptive immunotherapy using donor-derived NK cell products to induce graft-vs-tumor effects. In the adoptive transfer setting, persistence and in vivo expansion requires lymphodepleting chemotherapy to prevent rejection and provide homeostatic cytokines (such as IL-15) that activate NK cells. IL-15 has the advantage of avoiding regulatory T-cell expansion. Clinical applications are currently being tested. To enhance in vivo expansion, IL-2 has been used at low doses. However, low dose administration also leads to the stimulation of regulatory T cells. Monoclonal antibodies and bispecific killer engagers (BiKEs) may enhance specificity by targeting CD16 on NK cells to tumor antigens. Inhibition of CD16 shedding may also promote enhanced cytotoxicity. Future strategies include exploiting favorable donor immunogenetics or ex vivo expansion of NK cells from blood, progenitors, or pluripotent cells. Comparative clinical trials are needed to test these approaches.

NK cell-based immunotherapy for malignant diseases

Natural killer (NK) cells play critical roles in host immunity against cancer. In response, cancers develop mechanisms to escape NK cell attack or induce defective NK cells. Current NK cell-based cancer immunotherapy aims to overcome NK cell paralysis using several approaches. One approach uses expanded allogeneic NK cells, which are not inhibited by self histocompatibility antigens like autologous NK cells, for adoptive cellular immunotherapy. Another adoptive transfer approach uses stable allogeneic NK cell lines, which is more practical for quality control and large-scale production. A third approach is genetic modification of fresh NK cells or NK cell lines to highly express cytokines, Fc receptors and/or chimeric tumor-antigen receptors. Therapeutic NK cells can be derived from various sources, including peripheral or cord blood cells, stem cells or even induced pluripotent stem cells (iPSCs), and a variety of stimulators can be used for large-scale production in laboratories or good manufacturing practice (GMP) facilities, including soluble growth factors, immobilized molecules or antibodies, and other cellular activators. A list of NK cell therapies to treat several types of cancer in clinical trials is reviewed here. Several different approaches to NK-based immunotherapy, such as tissue-specific NK cells, killer receptor-oriented NK cells and chemically treated NK cells, are discussed. A few new techniques or strategies to monitor NK cell therapy by non-invasive imaging, predetermine the efficiency of NK cell therapy by in vivo experiments and evaluate NK cell therapy approaches in clinical trials are also introduced.

Natural killer cell lines in tumor immunotherapy

Natural killer (NK) cells are considered to be critical players in anticancer immunity. However, cancers are able to develop mechanisms to escape NK cell attack or to induce defective NK cells. Current NK cell-based cancer immunotherapy is aimed at overcoming NK cell paralysis through several potential approaches, including activating autologous NK cells, expanding allogeneic NK cells, usage of stable allogeneic NK cell lines and genetically modifying fresh NK cells or NK cell lines. The stable allogeneic NK cell line approach is more practical for quality-control and large-scale production. Additionally, genetically modifying NK cell lines by increasing their expression of cytokines and engineering chimeric tumor antigen receptors could improve their specificity and cytotoxicity. In this review, NK cells in tumor immunotherapy are discussed, and a list of therapeutic NK cell lines currently undergoing preclinical and clinical trials of several kinds of tumors are reviewed.

Interleukin-15 supports generation of highly potent clinical-grade natural killer cells in long-term cultures for targeting hematological malignancies

OBJECTIVE

Interleukin (IL)-15 is a promising novel cytokine for natural killer (NK) cell activation and survival. We studied the effects of IL-15 compared to IL-2 on NK cells in long-term cultures for clinical translation.

MATERIALS AND METHODS

CD56(+)CD3(-) NK cells were expanded with IL-2 or IL-15 for 2 to 4 weeks within lymphokine-activated killer (LAK) cell cultures (LAK-NK) in serum-enriched AIM V or CellGro Stem Cell Growth Medium (SCGM). Cell growth, viability, and NK cell content were monitored and cytotoxicity assessed in a flow cytometric cytotoxicity assay.

RESULTS

IL-15 (100-1000 U/mL) could replace IL-2 (1000 U/mL) in AIM V cultures to achieve efficient LAK cell expansion. However, IL-15-stimulated LAK cells exceeded cytotoxicity of IL-2-stimulated LAK cells against K562, notably at later culture points. In the powerful CellGro SCGM, LAK cells expanded over 28 days an average of 905-fold ± 320-fold standard error of the mean (SEM) for IL-2 (500 U/mL) and 484-fold ± 98-fold SEM for IL-15 (500 U/mL), and NK cells within such LAK cultures expanded an average of 2320-fold ± 975-fold SEM for IL-2 and 1084-fold ± 309-fold SEM for IL-15. Importantly, such IL-15-activated LAK-NK cells retained enhanced cytotoxicity at later culture points against K562 as well. IL-15-stimulated effectors were also highly cytotoxic against hematological targets MOLT-4 and KU812 and nontoxic against autologous nonmalignant cells. Interestingly, IL-15-LAK-NK cells showed overall significant upregulation of the main activating and inhibitory NK cell receptors after long-term cytokine stimulation.

CONCLUSIONS

Our results demonstrate the potential for IL-15 to support large-scale expansion of clinical-grade LAK-NK effectors, which could retain enhanced longer-term potency and preserve activation receptors in therapy of hematological malignancies. Protocols are readily clinically translatable.

Rapid expansion and long-term persistence of elevated NK cell numbers in humans infected with hantavirus

Acute hantavirus infection in humans triggers a rapid expansion and long-term persistence of NK cells.

Natural killer (NK) cells are known to mount a rapid response to several virus infections. In experimental models of acute viral infection, this response has been characterized by prompt NK cell activation and expansion followed by rapid contraction. In contrast to experimental model systems, much less is known about NK cell responses to acute viral infections in humans. We demonstrate that NK cells can rapidly expand and persist at highly elevated levels for >60 d after human hantavirus infection. A large part of the expanding NK cells expressed the activating receptor NKG2C and were functional in terms of expressing a licensing inhibitory killer cell immunoglobulin-like receptor (KIR) and ability to respond to target cell stimulation. These results demonstrate that NK cells can expand and remain elevated in numbers for a prolonged period of time in humans after a virus infection. In time, this response extends far beyond what is considered normal for an innate immune response.

Immunotherapy in the context of hematopoietic stem cell transplantation: the emerging role of natural killer cells and mesenchymal stromal cells

Immunotherapy in the context of hematopoietic stem cell transplantation has been dominated for many years by T-cell- and dendritic-cell-based treatment modalities. During the last decade, insight into the biology of natural killer (NK) cells and mesenchymal stromal cells (MSC) has rapidly increased and resulted in NK- and MSC-based therapeutic strategies in clinical practice. This article reviews current knowledge of the biology and clinical aspects of NK cells and MSC.

The human ortholog of granulocyte macrophage colony-stimulating factor and interleukin-2 fusion protein induces potent ex vivo natural killer cell activation and maturation

Natural killer (NK) cells are appealing cellular pharmaceuticals for cancer therapy because of their innate ability to recognize and kill tumor cells. Therefore, the development of methods that can enhance the potency in their anticancer effect would be desirable. We have previously shown that a murine granulocyte macrophage colony-stimulating factor (GM-CSF)/interleukin 2 (IL-2) fusion protein displays novel antitumor properties in vivo compared with both cytokines in combination due to recruitment of NK cells. In the present work, we have found that human ortholog of the GM-CSF/IL-2 fusion protein (a.k.a. hGIFT2) induces robust NK cell activation ex vivo with significant secretion of RANTES and a 37-fold increase in IFNgamma production when compared with either IL-2 or GM-CSF single cytokine treatment or their combination. Moreover, hGIFT2 upregulates the expression of NK cell activating receptors NKp44, NKp46, and DNAM-1 (CD226), as well as CD69, CD107a, and IL-2Rbeta expression. In addition, hGIFT2 promotes NK cell maturation, based on the downregulation of CD117 expression and upregulation of CD11b. This phenotype correlates with significantly greater cytotoxicity against tumor cells. At the molecular level, hGIFT2 leads to a potent activation of Janus-activated kinases (JAK) downstream of both IL-2 and GM-CSF receptors (JAK1 and JAK2, respectively) and consequently leads to a hyperphosphorylation of signal transducers and activators of transcription (STAT)1, STAT3, and STAT5. In conclusion, hGIFT2 fusokine possesses unique biochemical properties distinct from IL-2 and GM-CSF, constitutes a novel and potent tool for ex vivo NK cell activation and maturation, and may be of use for cancer cell immunotherapy.

NK cell-mediated targeting of human cancer and possibilities for new means of immunotherapy

Insights into the molecular basis for natural killer (NK) cell recognition of human cancer have been obtained in recent years. Here, we review current knowledge on the molecular specificity and function of human NK cells. Evidence for NK cell targeting of human tumors is provided and new strategies for NK cell-based immunotherapy against human cancer are discussed. Based on current knowledge, we foresee a development where more cancers may be subject to treatment with drugs or other immunomodulatory agents affecting NK cells, either directly or indirectly. We also envisage a possibility that certain forms of cancers may be subject to treatment with adoptively transferred NK cells, either alone or in combination with other therapeutic interventions.

Angiostatic activity of the antitumor cytokine interleukin-21

Interleukin-21 (IL-21) is a recently described immunoregulatory cytokine. It has been identified as a very potent immunotherapeutic agent in several cancer types in animal models, and clinical studies are ongoing. IL-21 belongs to the type I cytokine family of which other members, ie, IL-2, IL-15, and IL-4, have been shown to exert activities on vascular endothelial cells (ECs). We hypothesized that IL-21, in addition to inducing the antitumor immune response, also inhibits tumor angiogenesis. In vitro experiments showed a decrease of proliferation and sprouting of activated ECs after IL-21 treatment. We found that the IL-21 receptor is expressed on vascular ECs. Furthermore, in vivo studies in the chorioallantoic membrane of the chick embryo and in mouse tumors demonstrated that IL-21 treatment disturbs vessel architecture and negatively affects vessel outgrowth. Our results also confirm the earlier suggested angiostatic potential of IL-2 in vitro and in vivo. The angiostatic effect of IL-21 is confirmed by the decrease in expression of angiogenesis-related genes. Interestingly, IL-21 treatment of ECs leads to a decrease of Stat3 phosphorylation. Our research shows that IL-21 is a very powerful antitumor compound that combines the induction of an effective antitumor immune response with inhibition of tumor angiogenesis.

Natural killer cell-directed therapies: moving from unexpected results to successful strategies

Natural killer (NK) cells influence innate and adaptive immune host defenses. Existing data indicate that manipulating the balance between inhibitory and activating NK receptor signals, the sensitivity of target cells to NK cell-mediated apoptosis, and NK cell cross-talk with dendritic cells might hold therapeutic promise. Efforts to modulate NK cell trafficking into inflamed tissues and/or lymph nodes, and to counteract NK cell suppressors, might also prove fruitful in the clinic. However, deeper investigation into the benefits of combination therapy, greater understanding of the functional distinctions between NK cell subsets, and design of new tools to monitor NK cell activity are needed to strengthen our ability to harness the power of NK cells for therapeutic aims.

Blockade of hyaluronan inhibits IL-2-induced vascular leak syndrome and maintains effectiveness of IL-2 treatment for metastatic melanoma

Vascular leak syndrome (VLS) is a life-threatening toxicity induced during IL-2 treatment of cancer patients. The mechanism of IL-2-induced VLS is still poorly understood. At present, there is no specific therapy for VLS. Previous studies from our laboratory demonstrated that hyaluronan (HA), a large glycosaminoglycan, abundant in the extracellular matrix and on the cell surface, caused a marked increase of IL-2-induced VLS in the lungs and liver of C57BL/6 mice. Conversely, blockade or knockout of its major receptor, CD44, resulted in a marked decrease of VLS, thereby suggesting a role for HA in VLS. In this study, we report a novel means to prevent IL-2-induced VLS by blocking endogenous HA with HA-specific binding peptide, Pep-1, a newly isolated peptide which specifically binds to soluble, cell-associated, and immobilized forms of HA. Our results demonstrated that blocking HA with Pep-1 dramatically inhibited IL-2-induced VLS in both normal mice as well as in mice bearing melanoma. Moreover, Pep-1 treatment maintained the effectiveness of IL-2 and prevented the metastasis of melanoma. IL-2-induced emigration of lymphocytes across the endothelium and cytotoxicity against tumor by lymphokine-activated killer cells were not affected by Pep-1. Instead, use of Pep-1 maintained endothelial integrity and reduced their apoptosis during IL-2-induced VLS. These data suggested that HA plays a critical role in regulating endothelial cell damage and induction of IL-2-mediated VLS. Also, blockade of HA using Pep-1 could constitute a novel therapeutic modality to prevent IL-2-mediated toxicity, thereby facilitating the effectiveness of high-dose IL-2 in the treatment of metastatic melanomas.

NK Cells and Cancer

In this review, we overview the main features and functions of NK cells, focusing on their role in cell-mediated immune response to tumor cells. In parallel, we discuss the information available in the field of NK cell receptors and offer a wide general overview of functional aspects of cell targeting and killing, focusing on the recent acknowledgments on the efficacy of NK cells after cytokine and mAb administration in cancer therapy. Since efficacy of NK cell-based immunotherapy has been proven in KIR-mismatch regimens or in TRAIL-dependent apoptosis, the ability to manipulate the balance of activating and inhibitory receptors on NK cells and of their cognate ligands, as well as the sensitivity of tumor cells to apoptosis, opens new perspectives for NK cell-based immunotherapy.

Microparticulate formulations for the controlled release of interleukin-2

Interleukin 2 (IL-2) is a pleotropic growth factor essential to immune system function. Current methods of administration are limited by the necessity of hospitalization as well as dose-limiting toxicities and side effects. There is also the issue of low therapeutic concentrations at the desired site of action; for instance, in the case of solid tumor treatment. Here we describe the design of controlled-release vehicles for the local administration of IL-2 based on single (SE) and double emulsion (DE) poly(lactic-co-glycolic acid) (PLGA) systems and a newly developed class of spray-dried lipid-protein-sugar systems composed of L-alpha-dipalmitoylphosphatidylcholine (DPPC) and 0.2% Eudragit E 100. All three systems demonstrated the release of therapeutic drug quantities. Totals of 2.0, 0.5, and 2.8 microg of IL-2 (per mg of solid) were encapsulated in the SE, DE, and spray-dried formulations, respectively. The SE and DE released of 30 and 15% of the encapsulated protein, respectively, with delivery of biologically active IL-2 during the first 5 to 10 days. The lipid-protein-sugar-based system demonstrated extended sustained release of biologically active IL-2 for a period of 4 months. These systems provide a potential framework for long-term loco-regional immunotherapeutic treatment regimens.

In vitro assessment of human endothelial cell permeability: effects of inflammatory cytokines and dengue virus infection

Electrical resistance across human umbilical vein endothelial cells (HUVECs) was measured using an electrical cell sensor system. The transendothelial electrical resistance (TEER) value was used to estimate the permeability through endothelial cells in vitro. Decrease in the TEER value was associated with increase in the passage of albumin through endothelial cells in the albumin permeability assay. The effects of cytokines and dengue virus infection on the permeability of HUVECs were examined by measuring the TEER value. Tumor necrosis factor alpha (TNF-alpha) at 1 and 0.1 microg/ml decreased the TEER value, but TNF-alpha at lower dose did not. Interferon-gamma (IFN-gamma) at 1 microg/ml also decreased the TEER value. In contrast, interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10) or interferon-beta (IFN-beta) did not decrease the TEER value. The decrease in the TEER value was associated with the morphological changes of HUVECs. Dengue virus infection at a multiplicities of infection (m.o.i.) of 5 pfu/cell decreased the TEER value. Infection at an m.o.i. of 0.5 pfu/cell did not decrease the TEER value; however, addition of 0.01 microg/ml of TNF-alpha to these infected endothelial cells decreased the TEER value. The results suggest that TNF-alpha and dengue virus infection decrease synergistically the TEER value of endothelial cells. The TEER method is easy, reliable and can be applicable to further analysis of the increase in the permeability of endothelial cells in vitro induced by inflammatory cytokines and dengue virus infection.

Use of interleukin-15 for preparation of adherent NK cells from human peripheral blood: comparison with interleukin-2

To search the possibility of utilizing interleukin-15 (IL-15) in preparation of adherent human natural killer (A-NK) cells, recombinant human IL-15 (rhIL-15) or rhIL-2 (500 u/ml of each cytokine) were added to purified human NK cell culture in 24-well plastic plate. The cytokine-induced adherent ratio was calculated by percentage of A-NK cell in whole NK cells. The cytotoxicity of NK cells (NA- or A-NK cells) was examined by 4-h 51Chromium release assay, the surface markers of NK cells were checked by flow cytometry, and the cytokines were analyzed by reverse transcript (RT)-PCR and ELISA method. RhIL-15-induced adherence of human NK cells into plastic was higher than IL-2 when harvesting the A-NK cells at each hour point from hr 1 to hr 12. IL-15- and IL-2-induced adherent ratio peaked to 36.67% and 27.73% at hr 1, and the IL-15-induced adherent ratio was around two folds higher than IL-2-induced group at hrs 2, 3, 4, 5, 6, 7, and 8. The IL-15 group expanded more rapidly than IL-2 during 2 weeks' culture. IL-15- and IL-2-A-NK cells exerted similar levels of higher cytotoxic potentials. A-NK cells were characterized with phenotypes of CD3(-)CD16(+)CD56(+) (more than 93%) in the presence of IL-2 or IL-15 stimulation. CD54, an intracellular adhesion molecule (ICAM), was also continuously expressed in A-NK cells (more than 85%) induced by each cytokine. Interestingly, IL-15 stimulated relatively low level of expression of CD18, a beta2 integrin molecule related to lymphocyte apoptosis in A-NK cells (11.45%), whereas IL-2 exerted a strong effect on CD18 expression (87.54%). IL-11b was only expressed at A-NK cell induced by IL-2 (49.56%), IL-15 did not exert any stimulating effect on CD11b expression. All A-NK cells expressed high levels of interferon gamma (IFNgamma) after stimulation with IL-2 or IL-15. In contrast to IL-2, IL-15 did not stimulate gene expressions of type 2 cytokines (e.g. IL-4, IL-6, IL-10 and IL-13) in A-NK cells. The results indicate that rhIL15 is possibly a stronger stimulator for A-NK cell preparation by improving adherence and proliferation through inhibiting apoptosis by down-regulating the expression of CD18 and type 2 cytokines.

Signaling through MHC in transgenic mice generates a population of memory phenotype cytolytic cells that lack TCR

We constructed a chimeric molecule, composed of the T-cell receptor (TCR)-zeta chain fused to the extracellular domains of a prototypical allogeneic major histocompatibility complex (MHC) class I molecule, Dd, to assess whether such a construct could affect Dd allospecific responses in vitro and in vivo. To generate cytotoxic T lymphocytes (CTLs) expressing the construct, Dd-zeta was targeted to lymphocyte populations in transgenic mice by placing its expression under control of the CD2 promoter. In response to ligation of Dd, lymphocytes from transgenic mice expressing high levels of Dd-zeta are activated to proliferate and kill cells binding to Dd, despite the near total loss of CD8+ T cells in these mice. Thus, the Dd-zeta cytolytic cell was found not to be a conventional CD8+ CTL, but rather an unusual T lineage cell (CD3-CD5+Thy1.1+) that lacked alphabeta or gammadelta TCRs, as well as CD4 and CD8 coreceptors, but expressed surface markers strikingly similar to memory CTLs, including CD44, Ly-6C, and CD122. These cells originate in the thymus and potently veto responses to Dd in vitro. Lacking TCRs, these veto cells are unlikely to mediate graft-versus-host disease (GVHD) and thus may be useful as a cellular therapy for therapeutic deletion of alloreactive T cells in the settings of graft rejection and GVHD.

HIV-1 matrix protein p17 enhances the proliferative activity of natural killer cells and increases their ability to secrete proinflammatory cytokines

We investigated the effects of human immunodeficiency type-1 virus (HIV-1) matrix protein p17 on freshly isolated and purified human natural killer (NK) cells. HIV-1 p17 increased the cytokines interleukin (IL) 2, IL-12 and IL-15, and induced natural killer cell proliferation, but not cytotoxicity. This effect was specific because it was abrogated by anti-p17 monoclonal antibody. Moreover, HIV-1 p17 enhanced the cytokine-induced production of tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma by NK cells. IL-4 downregulated IFN-gamma and TNF-alpha secretion in IL-2- and IL-15-treated NK cells. HIV-1 p17 restored the ability of NK cells to produce both cytokines when added to the cultures simultaneously with IL-4. The property of p17 to increase the production of TNF-alpha and IFN-gamma might be a mechanism used by HIV-1 to modulate the immune system to support its replication and spreading.