Targeting natural killer cells and natural killer T cells in cancer

Low-doses of sequential-kinetic-activated interferon-γ enhance the ex vivo cytotoxicity of peripheral blood natural killer cells from patients with early-stage colorectal cancer. A preliminary study

Natural killer (NK) cells are innate immune-system lymphocytes capable of killing tumor cells. They secrete cytokines, including interferon (IFN)-γ, which participate in shaping the initial inflammatory and downstream adaptive immune responses. Its potent immunoregulatory action means that IFN-γ might be beneficial in cases of tumor rejection, but its severe side-effects limit clinical applications. This pilot study compared low-dose IFN-γ prepared by sequential-kinetic-activation (SKA), with standard-dose recombinant (r) IFN-γ, in terms of ex-vivo cytotoxic activity of peripheral blood (PB)-NK cells from colorectal carcinoma (CRC) patients. This was tested against the NK-sensitive K562 cell line and the less-sensitive human CRC Caco-2 and HT-29 cell lines. Twenty primitive non-metastatic CRC patients, five metastatic CRC patients, and thirteen healthy donors were enrolled. PB lymphocytes (PBL) were exposed to medium alone, SKA-IFN-γ (0.25fg/ml) or rIFN-γ (1ng/ml). NK-cell cytolytic activity was examined via short-term (51)Cr-release. Pretreatment of PBL from non-metastatic patients with SKA-IFN-γ caused a significant increase in NK-cell cytotoxicity, compared to those from normal donors, although less markedly than pretreatment with rIFN-γ against all three cell lines. In contrast, PBL from metastatic CRC patients displayed significantly decreased NK-cell activity and responsiveness to both rIFN-γ and SKA-IFN-γ treatments. These results demonstrate in principle the immunomodulatory capacity of low-dose SKA-IFN-γ, and might open the door to the possibility of generating a novel, safe, and feasible approach to enhancing NK-cell antitumor activity in early-stage CRC patients.

The role of acupoint stimulation as an adjunct therapy for lung cancer: a systematic review and meta-analysis

Background

Lung cancer is the leading cause of death in cancer patients. Clinical studies showed that a variety of acupoint stimulations have been extensively used for lung cancer patients, including needle insertion, injection with herbal extraction, plaster application, and moxibustion. However, the role of acupoint stimulation in lung cancer treatment was not fully reviewed.

Methods

In the present study, we conducted a systematic review and meta-analysis on the role of acupoint stimulation in lung cancer treatment by electronic and manual searching in seven databases, including Ovid (Ovid MEDLINE, AMED, CAB Abstracts, EMBASE), EBSCOhost research databases (Academic Search premier, MEDLINE, CIHAHL Plus), PreQuest (British Nursing Index, ProQuest Medical Library, ProQuest Dissertations & Theses A&I, PsycINFO), and ISI web of knowledge (Web of Science, BIOSIS Citation Index, Biological Abstracts, Chinese Science Citation Database), CNKI, Wanfang Data, and CQVIP.

Results

Our study showed that acupoint stimulation has strong immunomodulatory effect for lung cancer patients as demonstrated by the significant increase of IL-2, T cell subtypes (CD3+ and CD4+, but not CD8+ cells), and natural killer cells. Further analysis revealed that acupoint stimulation remarkably alleviates the conventional therapy-induced bone marrow suppression (hemoglobin, platelet, and WBC reduction) in lung cancer patients, as well as decreases nausea and vomiting. The pooled studies also showed that acupoint stimulation can improve Karnofsky performance status, immediate tumor response, quality of life (EORCT-QLQ-C30), and pain control of cancer patients.

Conclusions

Acupoint stimulation is found to be effective in lung cancer treatment, further confirmatory evaluation via large scale randomized trials is warranted.

Functional Significance of CD57 Expression on Human NK Cells and Relevance to Disease

Historically, human NK cells have been identified as CD3(-)CD56(+)CD16(±) lymphocytes. More recently it has been established that CD57 expression defines functionally discrete sub-populations of NK cells. On T cells, CD57 expression has been regarded as a marker of terminal differentiation and (perhaps wrongly) of anergy and senescence. Similarly, CD57 expression seems to identify the final stages of peripheral NK cell maturation; its expression increases with age and is associated with chronic infections, particularly human cytomegalovirus infection. However, CD57(+) NK cells are highly cytotoxic and their presence seems to be beneficial in a number of non-communicable diseases. The purpose of this article is to review our current understanding of CD57 expression as a marker of NK cell function and disease prognosis, as well as to outline areas for further research.

Cancer immunotherapy: accomplishments to date and future promise

Cancer remains a devastating disease as existing therapies are too often ineffective and toxicities remain unacceptably high. Immunotherapies for cancer offer the promise of the specificity and memory of the immune system against malignant cells to achieve durable cure with minimal toxicity. Beginning with the success of bone marrow transplantation for blood-borne cancers, and the more recent development of monoclonal antibody therapeutics for a variety of tumors, immunotherapies are already among the most successful class of treatments for cancer. Greater understanding of immunoregulatory mechanisms and improved techniques for immune cell manipulation and engineering have led to new immunomodulatory approaches and cell-based therapies for cancer that have generated great excitement within the biomedical community. As these technologies continue to improve, and as new approaches for harnessing the power and specificity of the immune system are developed, immunotherapies will play an increasingly important role in the treatment of cancer. Here, we review the history of immunotherapies for cancer and discuss existing and emerging immunotherapy technologies that hope to translate the promise of immunotherapy into clinical reality.

Commensal microbiota and NKT cells in the control of inflammatory diseases at mucosal surfaces

Natural Killer T (NKT) cells are a phenotypically and functionally diverse subset of T cells, which recognizes self- and microbial lipids in the context of the atypical MHC class I molecule CD1d. NKT cells exhibit potent effector functions and play critical roles in antimicrobial defense, cancer immunosurveillance and the modulation of immune-mediated disorders. Recent evidence has revealed extensive cross-regulation between the mucosal microbiota and CD1d as well as NKT cells. Microbial exposure at mucosal surfaces, particularly during early postnatal development, regulates NKT cell trafficking and function in the intestine and the lung and determines the susceptibility to NKT cell-mediated inflammatory disorders. Conversely, CD1d controls the composition of the intestinal microbiota; perhaps through the regulation of Paneth cell function. Here, we provide an overview of recent findings on the crosstalk between the microbiota and NKT cells and discuss the implication for mucosal homeostasis and its dysregulation in inflammatory disorders.

CD3(-)CD16(-)CD56(bright) immunoregulatory NK cells are increased in the tumor microenvironment and inversely correlate with advanced stages in patients with papillary thyroid cancer

BACKGROUND

The innate immune system is the first line of defense and plays a key role in thyroid cancer development. The role of the tumor-infiltrating natural killer (NK) cells is becoming increasingly important in research and potential cancer therapies. NK cell subpopulations, CD3(-)CD16(+)CD56(dim) and CD3(-)CD16(-)CD56(bright), demonstrate a significant role in the tumor immuno-surveillance process.

METHODS

We investigated the distribution of CD3(-)CD16(+)CD56(dim) and CD3(-)CD16(-)CD56(bright) NK subpopulations in tissue and blood samples from patients with papillary thyroid cancer (PTC) and nodular goiter (NG). Twenty-eight patients with PTC, 13 patients with NG, and 50 healthy donors were included in the study. Tissue and blood samples from all patients and blood samples from healthy donors were analyzed for CD3(-)CD16(+)CD56(dim) and CD3(-)CD16(-)CD56(bright) NK cells by flow cytometry.

RESULTS

A significant predominance of CD3(-)CD16(+)CD56(dim) cells compared to CD3(-)CD16(-)CD56(bright) NK cells was found in blood samples in all groups (p<0.0001 in PTC, NG, and healthy donors). Increased infiltration by CD3(-)CD16(-)CD56(bright) NK cells was observed in thyroid tissue of patients with PTC, as compared to CD3(-)CD16(+)CD56(dim) NK cells (p=0.046), while CD3(-)CD16(+)CD56(dim) NK cells demonstrated a higher infiltration of NG tissues. CD3(-)CD16(+)CD56(dim) NK cell tissue infiltration positively correlated with advanced stages of PTC. In contrast, the CD3(-)CD16(-)CD56(bright) NK cell population was negatively associated with tumor stage in patients with PTC.

CONCLUSION

CD3(-)CD16(-)CD56(bright) NK cell infiltration seems to be associated with PTC progression. These findings contribute to a better understanding of the immune response in PTC and may lead to novel immunotherapeutic approaches in these patients.

Homo-oligomerization of the activating natural killer cell receptor NKp30 ectodomain increases its binding affinity for cellular ligands

The natural cytotoxicity receptors, comprised of three type I membrane proteins NKp30, NKp44, and NKp46, are a unique set of activating proteins expressed mainly on the surface of natural killer (NK) cells. Among these, NKp30 is a major receptor targeting virus-infected cells, malignantly transformed cells, and immature dendritic cells. To date, only few cellular ligands of NKp30 have been discovered, and the molecular details of ligand recognition by NKp30 are poorly understood. Within the current study, we found that the ectodomain of NKp30 forms functional homo-oligomers that mediate high affinity binding to its corresponding cellular ligand B7-H6. Notably, this homo-oligomerization is strongly promoted by the stalk domain of NKp30. Based on these data, we suggest that homo-oligomerization of NKp30 in the plasma membrane of NK cells, which might be favored by IL-2-dependent up-regulation of NKp30 expression, provides a way to improve recognition and lysis of target cells by NK cells.

T cell regulation of natural killer cells

In light of their role in the immune response against tumors and viruses, natural killer (NK) cells represent a promising target for immunotherapy. Before this target is reached, the various mechanisms that control NK cell activity must first be identified and understood. In the past decades, studies have identified two critical processes that prevent spontaneous NK cell-mediated autoimmune activation while maximizing the efficiency of these cells during an immune response. First is the education process, whereby NK cells adapt to their environment by sensing ligands for inhibitory and activating receptors. Second is the priming phase of NK cell activation, which arms NK cells with appropriate cytotoxic molecules during inflammation. New studies now indicate that NK cell proliferation, accumulation, and activation are also under the control of regulatory T cells that restrict availability of IL-2 released by activated CD4(+) T cells. Together with other recent studies, these data highlight the importance of the adaptive immune system in the regulation of NK cell activity.

JUNB/AP-1 controls IFN-γ during inflammatory liver disease

Understanding the molecular pathogenesis of inflammatory liver disease is essential to design efficient therapeutic approaches. In hepatocytes, the dimeric transcription factor c-JUN/AP-1 is a major mediator of cell survival during hepatitis, although functions for other JUN proteins in liver disease are less defined. Here, we found that JUNB was specifically expressed in human and murine immune cells during acute liver injury. We analyzed the molecular function of JUNB in experimental models of hepatitis, including administration of concanavalin A (ConA) or α-galactosyl-ceramide, which induce liver inflammation and injury. Mice specifically lacking JUNB in hepatocytes displayed a mild increase in ConA-induced liver damage. However, targeted deletion of Junb in immune cells and hepatocytes protected against hepatitis in experimental models that involved NK/NKT cells. The absence of JUNB in immune cells decreased IFN-γ expression and secretion from NK and NKT cells, leading to reduced STAT1 pathway activation. Systemic IFN-γ treatment or adenovirus-based IRF1 delivery to Junb-deficient mice restored hepatotoxicity, and we demonstrate that Ifng is a direct transcriptional target of JUNB. These findings demonstrate that JUNB/AP-1 promotes cell death during acute hepatitis by regulating IFN-γ production in NK and NKT cells and thus functionally antagonizes the hepatoprotective function of c-JUN/AP-1 in hepatocytes.

Interferon-α-secreting mesenchymal stem cells exert potent antitumor effect in vivo

Mesenchymal stem cells (MSCs) are a kind of adult stem cells that can be isolated easily from bone marrow, adipose tissue, umbilical cord and many other tissues. MSCs have been shown to specifically migrate to inflammatory sites, including tumors, and hold great promise as tumor-specific vectors to deliver antitumor agents. Interferon-α (IFNα) has been used in clinic to treat various types of tumors; however, because of its short half-life, significant therapeutic effects require high doses that often results in serious side effects. Here, we tested whether MSCs continuingly secreting IFNα can exert a persistent antitumor effect and eliminate the side effects associated with high clinical doses of recombinant IFNα. We found that even a small number of IFNα-secreting MSCs could potently halt B16 tumor growth in vivo. The antitumor activity of IFNα-secreting MSCs was largely abolished in immunodeficient mice, an effect largely attributed to natural killer cells and CD8(+) T cells. Therefore, IFNα-secreting MSCs provide an innovative strategy for tumor therapy.

Reduction of the CD16(-)CD56bright NK cell subset precedes NK cell dysfunction in prostate cancer

Background

Natural cytotoxicity, mediated by natural killer (NK) cells plays an important role in the inhibition and elimination of malignant tumor cells. To investigate the immunoregulatory role of NK cells and their potential as diagnostic markers, NK cell activity (NKA) was analyzed in prostate cancer (PCa) patients with particular focus on NK cell subset distribution.

Methods

Prospective data of NKA and NK cell subset distribution patterns were measured from 51 patients initially diagnosed with PCa and 54 healthy controls. NKA was represented by IFN-γ levels after stimulation of the peripheral blood with Promoca®. To determine the distribution of NK cell subsets, PBMCs were stained with fluorochrome-conjugated monoclonal antibodies. Then, CD16⁺CD56^dim and CD16⁻CD56^bright cells gated on CD56⁺CD3⁻ cells were analyzed using a flow-cytometer.

Results

NKA and the proportion of CD56^bright cells were significantly lower in PCa patients compared to controls (430.9 pg/ml vs. 975.2 pg/ml and 2.3% vs. 3.8%, respectively; p<0.001). Both tended to gradually decrease according to cancer stage progression (p for trend = 0.001). A significantly higher CD56^dim-to-CD56^bright cell ratio was observed in PCa patients (41.8 vs. 30.3; p<0.001) along with a gradual increase according to cancer stage progression (p for trend = 0.001), implying a significant reduction of CD56^bright cells in relation to the alteration of CD56^dim cells. The sensitivity and the specificity of NKA regarding PCa detection were 72% and 74%, respectively (best cut-off value at 530.9 pg/ml, AUC = 0.786).

Conclusions

Reduction of CD56^bright cells may precede NK cell dysfunction, leading to impaired cytotoxicity against PCa cells. These observations may explain one of the mechanisms behind NK cell dysfunction observed in PCa microenvironment and lend support to the development of future cancer immunotherapeutic strategies.

Recipient leukocyte infusion enhances the local and systemic graft-versus-neuroblastoma effect of allogeneic bone marrow transplantation in mice

Allogeneic hematopoietic stem cell transplantation and donor leukocyte infusion (DLI) may hold potential as a novel form of immunotherapy for high-risk neuroblastoma. DLI, however, carries the risk of graft-versus-host disease (GvHD). Recipient leukocyte infusion (RLI) induces graft-versus-leukemia responses without GvHD in mice and is currently being explored clinically. Here, we demonstrate that both DLI and RLI, when given to mixed C57BL/6→A/J radiation chimeras carrying subcutaneous Neuro2A neuroblastoma implants, can slow the local growth of such tumors. DLI provoked full donor chimerism and GvHD; RLI produced graft rejection but left mice healthy. Flow cytometric studies showed that the chimerism of intratumoral leukocytes paralleled the systemic chimerism. This was associated with increased CD8/CD4 ratios, CD8+ T-cell IFN-γ expression and NK-cell Granzyme B expression within the tumor, following both DLI and RLI. The clinically safe anti-tumor effect of RLI was further enhanced by adoptively transferred naïve recipient-type NK cells. In models of intravenous Neuro2A tumor challenge, allogeneic chimeras showed superior overall survival over syngeneic chimeras. Bioluminescence imaging in allogeneic chimeras challenged with luciferase-transduced Neuro2A cells showed both DLI and RLI to prolong metastasis-free survival. This is the first experimental evidence that RLI can safely produce a local and systemic anti-tumor effect against a solid tumor. Our data indicate that RLI may provide combined T-cell and NK-cell reactivity effectively targeting Neuro2A neuroblastoma.

In-vivo stimulation of macaque natural killer T cells with α-galactosylceramide

Natural killer T cells are a potent mediator of anti-viral immunity in mice, but little is known about the effects of manipulating NKT cells in non-human primates. We evaluated the delivery of the NKT cell ligand, α-galactosylceramide (α-GalCer), in 27 macaques by studying the effects of different dosing (1-100 μg), and delivery modes [directly intravenously (i.v.) or pulsed onto blood or peripheral blood mononuclear cells]. We found that peripheral NKT cells were depleted transiently from the periphery following α-GalCer administration across all delivery modes, particularly in doses of ≥10 μg. Furthermore, NKT cell numbers frequently remained depressed at i.v. α-GalCer doses of >10 μg. Levels of cytokine expression were also not enhanced after α-GalCer delivery to macaques. To evaluate the effects of α-GalCer administration on anti-viral immunity, we administered α-GalCer either together with live attenuated influenza virus infection or prior to simian immunodeficiency virus (SIV) infection of two macaques. There was no clear enhancement of influenza-specific T or B cell immunity following α-GalCer delivery. Further, there was no modulation of pathogenic SIVmac251 infection following α-GalCer delivery to a further two macaques in a pilot study. Accordingly, although macaque peripheral NKT cells are modulated by α-GalCer in vivo, at least for the dosing regimens tested in this study, this does not appear to have a significant impact on anti-viral immunity in macaque models.

Research on stress-induced apoptosis of natural killer cells and the alteration of their killing activity in mouse liver

AIM: To investigate the stress-induced apoptosis of natural killer (NK) cells and the changes in their killing activity in mouse livers.

METHODS: A restraint stress model was established in mice. Flow cytometry was employed to measure the percentage of NK cells and the changes in their absolute number in mouse liver. The cytotoxicity of hepatic and splenic NK cells was assessed against YAC-1 target cells via a 4 h 51Cr-release assay.

RESULTS: The restraint stress stimulation induced the apoptosis of NK cells in the liver and the spleen, which decreased the cell number. The number and percentage of NK cells in the spleen decreased. However, the number of NK cells in the liver decreased, whereas the percentage of NK cells was significantly increased. The apoptosis of NK cells increased gradually with prolonged stress time, and the macrophage-1 (Mac-1)⁺ NK cells were more susceptible to apoptosis than Mac-1^- NK cells. Large numbers of Mac-1^- NK cells in the liver, which are more resistant to stress-induced apoptosis, were observed than the Mac-1^- NK cells in the spleen. The stress stimulation diminished the killing activity of NK cells in the spleen was significantly decreased, but the retention of numerous Mac-1^- NK cells in the liver maintained the killing ability.

CONCLUSION: Significant stress-induced apoptosis was observed among Mac-1⁺ NK cells, but not Mac-1^- NK cells in the mouse liver. Stress stimulation markedly decreased the killing activity of NK cells in the spleen but remained unchanged in the liver.

Colon Macrophages Polarized by Commensal Bacteria Cause Colitis and Cancer through the Bystander Effect

Intestinal commensal bacteria have recently been shown to trigger macrophages to produce diffusible clastogens (or chromosome-breaking factors) through a bystander effect (BSE) that mediates DNA damage and induces chromosomal instability in neighboring cells. Colon macrophages appear central to colon carcinogenesis and BSE through the expression of tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2). The former induces netrin-1, a regulator of intestinal epithelial cell apoptosis, and the latter generates trans-4-hydroxy-2-nonenal (4-HNE), an endogenous mutagen. To test whether colon macrophages are key effectors for BSE, we depleted these cells in interleukin-10 knockout mice colonized with Enterococcus faecalis using encapsulated liposomal clodronate (ELC), a bisphosphonate that causes macrophage apoptosis. We observed that E. faecalis polarizes colon macrophages to an M1 phenotype. In addition, depleting these cells suppressed COX-2 and TNF-α, blocked the formation of 4-HNE protein adducts, and inhibited up-regulation of netrin-1-all markers for BSE. Finally, treatment with ELC prevented colitis, β-catenin activation, and cancer formation. These results show that selected human commensals can polarize colon macrophages to the M1 phenotype and, when activated, serve as the key effector for bacterial-induced BSE. Our findings suggest that depleting M1-polarized macro-phages is a mechanism for the chemopreventive activity of bisphosphonates and that it represents a new strategy for preventing colon cancer induced by intestinal commensals.

The emerging role of immunosurveillance in dictating metastatic spread in breast cancer

It is now well known that the immune system can recognize transformed cells and control the initiation and growth of some cancers, a process termed tumor immunosurveillance. Key regulators of this process have been described in the primary tumor setting, where the balance of protumor and antitumor responses dictates tumor initiation and progression. Accumulating evidence suggests that immunosurveillance may also be critical for regulating metastatic spread, the most fatal aspect of cancer, and that mechanisms of overcoming immune control may be quite different from those at the primary site. Our recent findings support loss of type I interferon (IFN) signaling as a tumor-cell intrinsic mechanism of evading metastasis-specific immune responses in breast cancer. We revealed that type I IFN-induced innate (natural killer) and adaptive (CD8(+) T cell) responses suppressed bone metastatic growth and this was associated with decreased accumulation of immune suppressor cells (myeloid-derived suppressor cells). This review summarizes recent findings that are in support of tumor-induced immunosurveillance in regulating metastatic spread, including evidence that immune regulation of primary tumors may be distinct from those dictating metastasis.

Perturbation of NK cell peripheral homeostasis accelerates prostate carcinoma metastasis

The activating receptor NK cell group 2 member D (NKG2D) mediates antitumor immunity in experimental animal models. However, whether NKG2D ligands contribute to tumor suppression or progression clinically remains controversial. Here, we have described 2 novel lines of "humanized" bi-transgenic (bi-Tg) mice in which native human NKG2D ligand MHC class I polypeptide-related sequence B (MICB) or the engineered membrane-restricted MICB (MICB.A2) was expressed in the prostate of the transgenic adenocarcinoma of the mouse prostate (TRAMP) model of spontaneous carcinogenesis. Bi-Tg TRAMP/MICB mice exhibited a markedly increased incidence of progressed carcinomas and metastasis, whereas TRAMP/MICB.A2 mice enjoyed long-term tumor-free survival conferred by sustained NKG2D-mediated antitumor immunity. Mechanistically, we found that cancer progression in TRAMP/MICB mice was associated with loss of the peripheral NK cell pool owing to high serum levels of tumor-derived soluble MICB (sMICB). Prostate cancer patients also displayed reduction of peripheral NK cells and high sMIC levels. Our study has not only provided direct evidence in "humanized" mouse models that soluble and membrane-restricted NKG2D ligands pose opposite impacts on cancer progression, but also uncovered a mechanism of sMIC-induced impairment of NK cell antitumor immunity. Our findings suggest that the impact of soluble NKG2D ligands should be considered in NK cell-based cancer immunotherapy and that our unique mouse models should be valuable for therapy optimization.

Purinergic signaling in inflammatory cells: P2 receptor expression, functional effects, and modulation of inflammatory responses

Extracellular ATP and related nucleotides promote a wide range of pathophysiological responses via activation of cell surface purinergic P2 receptors. Almost every cell type expresses P2 receptors and/or exhibit regulated release of ATP. In this review, we focus on the purinergic receptor distribution in inflammatory cells and their implication in diverse immune responses by providing an overview of the current knowledge in the literature related to purinergic signaling in neutrophils, macrophages, dendritic cells, lymphocytes, eosinophils, and mast cells. The pathophysiological role of purinergic signaling in these cells include among others calcium mobilization, actin polymerization, chemotaxis, release of mediators, cell maturation, cytotoxicity, and cell death. We finally discuss the therapeutic potential of P2 receptor subtype selective drugs in inflammatory conditions.

Generation of a dual-functioning antitumor immune response in the peritoneal cavity

Tumor cell metastasis to the peritoneal cavity is observed in patients with tumors of peritoneal organs, particularly colon and ovarian tumors. Following release into the peritoneal cavity, tumor cells rapidly attach to the omentum, a tissue consisting of immune aggregates embedded in adipose tissue. Despite their proximity to potential immune effector cells, tumor cells grow aggressively on these immune aggregates. We hypothesized that activation of the immune aggregates would generate a productive antitumor immune response in the peritoneal cavity. We immunized mice i.p. with lethally irradiated cells of the colon adenocarcinoma line Colon38. Immunization resulted in temporary enlargement of immune aggregates, and after challenge with viable Colon38 cells, we did not detect tumor growth on the omentum. When Colon38-immunized mice were challenged with cells from the unrelated breast adenocarcinoma line E0771 or the melanoma line B16, these tumors also did not grow. The nonspecific response was long-lived and not present systemically, highlighting the uniqueness of the peritoneal cavity. Cellular depletions of immune subsets revealed that NK1.1(+) cells were essential in preventing growth of unrelated tumors, whereas NK1.1(+) cells and T cells were essential in preventing Colon38 tumor growth. Collectively, these data demonstrate that the peritoneal cavity has a unique environment capable of eliciting potent specific and nonspecific antitumor immune responses.

DOCK8 is critical for the survival and function of NKT cells

Patients with the dedicator of cytokinesis 8 (DOCK8) immunodeficiency syndrome suffer from recurrent viral and bacterial infections, hyper-immunoglobulin E levels, eczema, and greater susceptibility to cancer. Because natural killer T (NKT) cells have been implicated in these diseases, we asked if these cells were affected by DOCK8 deficiency. Using a mouse model, we found that DOCK8 deficiency resulted in impaired NKT cell development, principally affecting the formation and survival of long-lived, differentiated NKT cells. In the thymus, DOCK8-deficient mice lack a terminally differentiated subset of NK1.1(+) NKT cells expressing the integrin CD103, whereas in the liver, DOCK8-deficient NKT cells express reduced levels of the prosurvival factor B-cell lymphoma 2 and the integrin lymphocyte function-associated antigen 1. Although the initial NKT cell response to antigen is intact in the absence of DOCK8, their ongoing proliferative and cytokine responses are impaired. Importantly, a similar defect in NKT cell numbers was detected in DOCK8-deficient humans, highlighting the relevance of the mouse model. In conclusion, our data demonstrate that DOCK8 is required for the development and survival of mature NKT cells, consistent with the idea that DOCK8 mediates survival signals within a specialized niche. Accordingly, impaired NKT cell numbers and function are likely to contribute to the susceptibility of DOCK8-deficient patients to recurrent infections and malignant disease.

Tumor microenvironmental conversion of natural killer cells into myeloid-derived suppressor cells

How myeloid-derived suppressor cells (MDSC) emerge in the tumor environment remains unclear. Here, we report that GM-CSF can convert natural killer (NK) cells into MDSCs. When transferred into tumor-bearing mice, adoptively transferred NK cells lost their NK phenotype and were converted into Ly6C(high)Ly6G(high) MDSC. This conversion was abolished by exposure to IL-2 either in vitro or in vivo. Notably, we found that of the 4 maturation stages based on CD11b/CD27 expression levels, only the CD11b(high)CD27(high) NK cells could be converted into CD11b(+)Gr1(+) MDSC ex vivo. Transfer of CD27(high) NK cells from tumor-bearing mice into tumor-bearing recipients was associated with conversion to MDSC in a manner associated with reduced numbers of CD11b(high)CD27(high) and CD11b(high)CD27(low) NK cell populations in the recipients. Our results identify a pathway of MDSC development from immature NK cells in tumor-bearing hosts, providing new insights into how tumor cells modulate their host immune microenvironment to escape immune surveillance.

An acidic microenvironment increases NK cell killing of Cryptococcus neoformans and Cryptococcus gattii by enhancing perforin degranulation

Cryptococcus gattii and Cryptococcus neoformans are encapsulated yeasts that can produce a solid tumor-like mass or cryptococcoma. Analogous to malignant tumors, the microenvironment deep within a cryptococcoma is acidic, which presents unique challenges to host defense. Analogous to malignant cells, NK cells kill Cryptococcus. Thus, as in tumor defense, NK cells must kill yeast cells across a gradient from physiologic pH to less than 6 in the center of the cryptococcoma. As acidic pH inhibits anti-tumor activities of NK cells, we sought to determine if there was a similar reduction in the anticryptococcal activity of NK cells. Surprisingly, we found that both primary human NK cells and the human NK cell line, YT, have preserved or even enhanced killing of Cryptococcus in acidic, compared to physiological, pH. Studies to explore the mechanism of enhanced killing revealed that acidic pH does not increase the effector to target ratio, binding of cytolytic cells to Cryptococcus, or the active perforin content in effector cells. By contrast, perforin degranulation was greater at acidic pH, and increased degranulation was preceded by enhanced ERK1/2 phosphorylation, which is essential for killing. Moreover, using a replication defective ras1 knockout strain of Cryptococcus increased degranulation occurred during more rapid replication of the organisms. Finally, NK cells were found intimately associated with C. gattii within the cryptococcoma of a fatal infection. These results suggest that NK cells have amplified signaling, degranulation, and greater killing at low pH and when the organisms are replicating quickly, which would help maintain microbicidal host defense despite an acidic microenvironment.

Immune responses that protect from infection must occur in a variety of unique and potentially hostile environments. Within these environments, acidosis causes profound affects on protective responses. Low pH can occur in focal tumor-like infections, such as in a cryptococcoma produced by the fungal pathogen Cryptococcus. Similarly, low pH occurs in focal malignant tumors. It follows that Cryptococcus and malignant cells can both be killed by NK cells, which provide an important mechanism of host defense. Thus, we asked whether low pH, which impairs tumor killing, might also affect NK cell killing of Cryptococcus. Surprisingly, despite impaired tumor killing, NK cells possess enhanced killing of Cryptococcus at low pH. The mechanism involved a gain in intracellular signal transduction that led to enhanced perforin degranulation. This led us to examine NK cells in persistent cryptococcoma of a fatal brain infection and lung. We found that NK cells associate with Cryptococcus within the cryptococcoma, but perforin is reduced. These studies suggest NK cell cytotoxicity need not be impaired at low pH, and that enhanced signal transduction and degranulation at low pH might be used to enhance host defense.

Immunosuppressive microenvironment in neuroblastoma

According to the cancer immunoediting model, the interplay between tumor cells and the host immune system is crucial for the control of tumor growth. NB is a pediatric tumor that presents with metastatic disease at diagnosis in about 50% of the cases, the majority of which have poor prognosis. In this Review article, immune escape pathways adopted by human neuroblastoma (NB) cells are reviewed. These include intrinsic defects of tumor cells such impaired expression of the HLA class I related antigen processing machinery and functional alterations of the tumor microenvironment (TM) induced by NB cell-derived immunosuppressive molecules as MICA and HLA-G. Finally, examples of therapeutic interventions targeting the TM are discussed to emphasize the concept that successful cancer treatment may be achieved using this strategy.

Structure of NKp65 bound to its keratinocyte ligand reveals basis for genetically linked recognition in natural killer gene complex

The natural killer (NK) gene complex (NKC) encodes numerous C-type lectin-like receptors that govern the activity of NK cells. Although some of these receptors (Ly49s, NKG2D, CD94/NKG2A) recognize MHC or MHC-like molecules, others (Nkrp1, NKRP1A, NKp80, NKp65) instead bind C-type lectin-like ligands to which they are genetically linked in the NKC. To understand the basis for this recognition, we determined the structure of human NKp65, an activating receptor implicated in the immunosurveillance of skin, bound to its NKC-encoded ligand keratinocyte-associated C-type lectin (KACL). Whereas KACL forms a homodimer resembling other C-type lectin-like dimers, NKp65 is monomeric. The binding mode in the NKp65-KACL complex, in which a monomeric receptor engages a dimeric ligand, is completely distinct from those used by Ly49s, NKG2D, or CD94/NKG2A. The structure explains the exceptionally high affinity of the NKp65-KACL interaction compared with other cell-cell interaction pairs (KD = 6.7 × 10(-10) M), which may compensate for the monomeric nature of NKp65 to achieve cell activation. This previously unreported structure of an NKC-encoded receptor-ligand complex, coupled with mutational analysis of the interface, establishes a docking template that is directly applicable to other genetically linked pairs in the NKC, including Nkrp1-Clr, NKRP1A-LLT1, and NKp80-AICL.

Invariant natural killer T (iNKT) cell exhaustion in sarcoidosis

Invariant natural killer T (iNKT) cells are integral components of immune responses during many chronic diseases, yet their surface phenotypes, subset distribution, and polyfunctional capacity in this environment are largely unknown. Therefore, using flow cytometry, we determined iNKT cell phenotypic and functional characteristics in subjects with chronic inflammatory disease sarcoidosis and matched controls. We found that sarcoidosis subjects displayed lower iNKT-cell frequencies, which correlated with lung fibrosis, C-reactive protein levels, and other measures of clinical disease. The CD4(-) CD8(-) (double negative, DN) iNKT-cell population was selectively lower in diseased individuals and the remaining DN iNKT cells exhibited higher frequencies of the activation markers CD69 and CD56. Functionally, both total IFN-γ(+) and the dual-functional IFN-γ(+) TNF-α(+) iNKT cells were decreased in sarcoidosis subjects and these functional defects correlated with total iNKT-cell circulating frequencies. As the loss of polyfunctionality can reflect functional exhaustion, we measured the surface antigens programmed death-1 receptor and CD57 and found that levels inversely correlated with dual-functional iNKT-cell percentages. These findings reveal that, similar to traditional T cells, iNKT cells may also undergo functional exhaustion, and that circulating iNKT-cell frequencies reflect these defects. Programmed death-1 receptor antagonists may therefore be attractive therapeutic candidates for sarcoidosis and other iNKT-cell-mediated chronic diseases.

Molecular signatures mostly associated with NK cells are predictive of relapse free survival in breast cancer patients

Background

Recent observations suggest that immune-mediated tissue destruction is dependent upon coordinate activation of immune genes expressed by cells of the innate and adaptive immune systems.

Methods

Here, we performed a retrospective pilot study to investigate whether the coordinate expression of molecular signature mostly associated with NK cells could be used to segregate breast cancer patients into relapse and relapse-free outcomes.

Results

By analyzing primary breast cancer specimens derived from patients who experienced either 58–116 months (~5-9 years) relapse-free survival or developed tumor relapse within 9–76 months (~1-6 years) we found that the expression of molecules involved in activating signaling of NK cells and in NK cells: target interaction is increased in patients with favorable prognosis.

Conclusions

The parameters identified in this study, together with the prognostic signature previously reported by our group, highlight the cooperation between the innate and adaptive immune components within the tumor microenvironment.

Arming NK cells with enhanced antitumor activity: CARs and beyond

Natural killer (NK) cells hold great promise for adoptive cancer immunotherapy. The antitumor activity of NK cells can be enhanced by the transgene driven expression of chimeric antigen receptors that facilitate the selective recognition and killing of malignant cells. Recent data from our laboratory suggest that NK cells may similarly be “armed” against neoplastic cells by the expression of cancer-specific granzyme B-containing fusion proteins that are released as soluble factors upon NK-cell activation.

Neuroblastoma: developmental biology, cancer genomics and immunotherapy

Neuroblastoma is a solid tumour that arises from the developing sympathetic nervous system. Over the past decade, our understanding of this disease has advanced tremendously. The future challenge is to apply the knowledge gained to developing risk-based therapies and, ultimately, improving outcome. In this Review we discuss the key discoveries in the developmental biology, molecular genetics and immunology of neuroblastoma, as well as new translational tools for bringing these promising scientific advances into the clinic.

Clinical grade purification and expansion of NK cell products for an optimized manufacturing protocol

Allogeneic natural killer (NK) cells are used for adoptive immunotherapy after stem cell transplantation. In order to overcome technical limitations in NK cell purification and activation, the following study investigates the impact of different variables on NK cell recovery, cytotoxicity, and T-cell depletion during good manufacturing practice (GMP)-grade NK cell selection. Forty NK cell products were derived from 54 unstimulated donor leukaphereses using immunomagnetic CD3 T-cell depletion, followed by a CD56 cell enrichment step. For T-cell depletion, either the depletion 2.1 program in single or double procedure (D2.1_1depl, n = 18; D2.1_2depl, n = 13) or the faster depletion 3.1 (D3.1, n = 9) was used on the CliniMACS instrument. Seventeen purified NK cell products were activated in vitro by IL-2 for 12 days. The whole process resulted in a median number of 7.59 × 10⁸ CD56⁺CD3⁻ cells with both purity and viability of 94%, respectively. The T-cell depletion was significantly better using D2.1_1depl/2depl compared to D3.1 (log 4.6/log 4.9 vs. log 3.7; p < 0.01) and double procedure in two stages led always to residual T cells below 0.1%. In contrast D3.1 was superior to D2.1_1depl/2depl with regard to recovery of CD56⁺CD3⁻ NK cells (68% vs. 41%/38%). Concomitant monocytes and especially IL-2 activation led to increased NK cell activity against malignant target cells compared to unstimulated NK cells, which correlated with both up-regulation of natural cytotoxicity receptors and intracellular signaling. Overall, wide variations in the NK cell expansion rate and the distribution of NK cell subpopulations were found. In conclusion, our results indicate that GMP-grade purification of NK cells might be improved by a sequential processing of T-cell depletion program D2.1 and D3.1. In addition NK cell expansion protocols need to be further optimized.

Tumor stroma: a complexity dictated by the hypoxic tumor microenvironment

A lot of effort has been done to study how cancer cells react to low-oxygen tension, a condition known as hypoxia. Indeed, abnormal and dysfunctional blood vessels in the tumor are incapable to restore oxygenation, therefore perpetuating hypoxia, which, in turn, will fuel tumor progression, metastasis and resistance to antitumor therapies. Nevertheless, how stromal components including blood and lymphatic endothelial cells, pericytes and fibroblasts, as well as hematopoietic cells, respond to low-oxygen tension in comparison with their normoxic counterparts has been a matter of investigation in the last few years only and, to date, this field of research remains poorly understood. In general, opposing phenotypes can arise from the same stromal component when embedded in different tumor microenvironments, and, vice versa, different stromal components can have opposite reaction to the same tumor microenvironment. In this article, we will discuss the emerging link between tumor stroma and hypoxia, and how this complexity is translated at the molecular level.

Invariant natural killer T cells are phenotypically and functionally altered in Fabry disease

Fabry disease is a lysosomal storage disease belonging to the group of sphingolipidoses. In Fabry disease there is accumulation of mainly globotriaosylceramide due to deficiency of the lysosomal enzyme α-galactosidase A. The lysosome is an important compartment for the activity of invariant natural killer T (iNKT) cells. iNKT cells are lipid-specific T cells that were shown to be important in infection, autoimmunity and tumor surveillance. In several mouse models of lysosomal storage disorders there is a decrease in iNKT cell numbers. Furthermore, alterations on iNKT cell subsets have been recently described in the Fabry disease mouse model. Herein, we analyzed iNKT cells and their subsets in Fabry disease patients. Although there were no differences in the percentage of iNKT cells between Fabry disease patients and control subjects, Fabry disease patients presented a reduction in the iNKT CD4(+) cells accompanied by an increase in the iNKT DN cells. Since iNKT cell subsets produce different quantities of pro-inflammatory and anti-inflammatory cytokines, we analyzed IFN-γ and IL-4 production by iNKT cells of Fabry disease patients and mice. We found a significant reduction in the production of IL-4 by mice splenic iNKT cells and human iNKT cell subsets, but no significant alterations in the production of IFN-γ. Altogether, our results suggest a bias towards a pro-inflammatory phenotype in Fabry disease iNKT cells.

Protein Kinase Inhibitors CK59 and CID755673 Alter Primary Human NK Cell Effector Functions

Natural killer (NK) cells are part of the innate immune response and play a crucial role in the defense against tumors and virus-infected cells. Their effector functions include the specific killing of target cells, as well as the modulation of other immune cells by cytokine release. Kinases constitute a relevant part in signaling, are prime targets in drug research and the protein kinase inhibitor Dasatinib is already used for immune-modulatory therapies. In this study, we tested the effects of the kinase inhibitors CK59 and CID755673. These inhibitors are directed against calmodulin kinase II (CaMKII; CK59) and PKD family kinases (CID755673) that were previously suggested as novel components of NK activation pathways. Here, we use a multi-parameter, FACS-based assay to validate the influence of CK59 and CID755673 on the effector functions of primary NK cells. Treatment with CK59 and CID755673 indeed resulted in a significant dose-dependent reduction of NK cell degranulation markers and cytokine release in freshly isolated Peripheral blood mononuclear cell populations from healthy blood donors. These results underline the importance of CaMKII for NK cell signaling and suggest protein kinase D2 as a novel signaling component in NK cell activation. Notably, kinase inhibition studies on pure NK cell populations indicate significant donor variations.

The immunosuppressive tumour network: myeloid-derived suppressor cells, regulatory T cells and natural killer T cells

Myeloid-derived suppressor cells (MDSC) and regulatory T (Treg) cells are major components of the immune suppressive tumour microenvironment (TME). Both cell types expand systematically in preclinical tumour models and promote T-cell dysfunction that in turn favours tumour progression. Clinical reports show a positive correlation between elevated levels of both suppressors and tumour burden. Recent studies further revealed that MDSCs can modulate the de novo development and induction of Treg cells. The overlapping target cell population of Treg cells and MDSCs is indicative for the importance and flexibility of immune suppression under pathological conditions. It also suggests the existence of common pathways that can be used for clinical interventions aiming to manipulate the TME. Elimination or reprogramming of the immune suppressive TME is one of the major current challenges in immunotherapy of cancer. Interestingly, recent findings suggest that natural killer T (NKT) cells can acquire the ability to convert immunosuppressive MDSCs into immunity-promoting antigen-presenting cells. Here we will review the cross-talk between MDSCs and other immune cells, focusing on Treg cells and NKT cells. We will consider its impact on basic and applied cancer research and discuss how targeting MDSCs may pave the way for future immunocombination therapies.

Ex vivo activation of CD56(+) immune cells that eradicate neuroblastoma

Despite the use of intensive contemporary multimodal therapy, the overall survival of patients with high-risk neuroblastoma is still less than 50%. Therefore, immunotherapy without cross-resistance and overlapping toxicity has been proposed. In this study, we report the development of a novel strategy to specifically activate and expand human CD56(+) (NCAM1) natural killer (NK) immune cells from normal donors and patients with neuroblastoma. Enriched CD56(+) cells from peripheral blood were mixed with CD56(-) fraction at 1:1 ratio and cultured in the presence of OKT3, interleukin (IL)-2, and -15 for five days and then without OKT3 for 16 more days. The final products contained more than 90% CD56(+) cells and could kill neuroblastoma cells effectively that were originally highly resistant to nonprocessed NK cells. Mechanistically, cytolysis of neuroblastoma was mediated through natural cytotoxicity receptor (NCR), DNAX accessory molecule-1 (DNAM-1; CD226), perforin, and granzyme B. Successful clinical scale-up in a good manufacturing practices (GMP)-compliant bioreactor yielded effector cells that in a neuroblastoma xenograft model slowed tumor growth and extended survival without GVHD. Investigation of CD56(+) cells from patients with neuroblastoma revealed a similar postactivation phenotype and lytic activity. Our findings establish a novel and clinically expedient strategy to generate allogeneic or autologous CD56(+) cells that are highly cytotoxic against neuroblastoma with minimal risk of GVHD.

Activating natural cytotoxicity receptors of natural killer cells in cancer and infection

Natural killer (NK) cells are central players in the vertebrate immune system that rapidly eliminate malignantly transformed or infected cells. The natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46 are important mediators of NK cell cytotoxicity, which trigger an immune response on recognition of cognate cellular and viral ligands. Tumour and viral immune escape strategies targeting these receptor-ligand systems impair NK cell cytotoxicity and promote disease. Therefore, a molecular understanding of the function of the NCRs in immunosurveillance is instrumental to discovering novel access points to combat infections and cancer.

Efficient tumor targeting by anaerobic butyrate-producing bacteria

Butyrate as an important short chain fatty acid has been shown to affect different kinds of cancer cells. Butyrate exerts its anti-cancerous effects by several mechanisms and has lead to successful outcomes in phase I and II clinical trials. Moreover, since solid tumors grow rapidly, multiple regions of hypoxia and anoxia forms within them that provide good niches for the growth of anaerobic bacteria. It has been shown that bacterial tumor targeting is an applicable strategy for tumor-selective therapy. Therefore, we propose that nonpathogenic anaerobic butyrate-producing bacteria may be a versatile tool in tumor therapy as they can grow in anoxic and hypoxic regions of tumors and influence tumor cells by producing butyric acid. Moreover, this approach may overcome the existing problems of butyrate delivery to the sites of tumor and enhance its bioavailability. Also reversion of cancer drug resistance by butyrate will be plausible. Tumor targeting with nonpathogenic anaerobic bacteria with a higher capacity to produce butyrate could be the focus of future research.

Lung tumor microenvironment induces specific gene expression signature in intratumoral NK cells

Natural killer (NK) cells are able to recognize and kill tumor cells, however whether they contribute to tumor immunosurveillance is still debated. Our previous studies demonstrated the presence of NK cells in human lung tumors. Their comparison with NK cells from non-tumoral lung tissues and with blood NK cells from the same individuals revealed a decreased expression of some NK receptors and impaired ex vivo cytotoxic functions occurring specifically in NK cells isolated from the tumor microenvironment. The aim of the present study was to characterize the transcriptional profile of such intratumoral NK cells, by comparative microarray analysis of sorted NK cells isolated from non-tumoral (Non-Tum-NK) and tumoral (Tum-NK) lung tissues of 12 Non-Small Cell Lung Cancer patients. Our results reveal a specific gene expression signature of Tum-NK cells particularly in activation processes and cytotoxicity, confirming that tumor environment induces modifications in NK cells biology. Indeed, intratumoral NK cells display higher expression levels of NKp44, NKG2A, Granzymes A and K, and Fas mRNA. A particular pattern of receptors involved in chemotaxis was also observed, with an overexpression of CXCR5 and CXCR6, and a lower expression of CX3CR1 and S1PR1 genes in Tum-NK as compared to Non-Tum-NK cells. The precise identification of the molecular pathways modulated in the tumor environment will help to decipher the role of NK cells in tumor immunosurveillance and will open future investigations to manipulate their antitumoral functions.

Invariant natural killer T cells: an innate activation scheme linked to diverse effector functions

Invariant natural killer T (iNKT) cells exist in a 'poised effector' state, which enables them to rapidly produce cytokines following activation. Using a nearly monospecific T cell receptor, they recognize self and foreign lipid antigens presented by CD1d in a conserved manner, but their activation can catalyse a spectrum of polarized immune responses. In this Review, we discuss recent advances in our understanding of the innate-like mechanisms underlying iNKT cell activation and describe how lipid antigens, the inflammatory milieu and interactions with other immune cell subsets regulate the functions of iNKT cells in health and disease.

Human hemato-lymphoid system mice: current use and future potential for medicine

To directly study complex human hemato-lymphoid system physiology and respective system-associated diseases in vivo, human-to-mouse xenotransplantation models for human blood and blood-forming cells and organs have been developed over the past three decades. We here review the fundamental requirements and the remarkable progress made over the past few years in improving these systems, the current major achievements reached by use of these models, and the future challenges to more closely model and study human health and disease and to achieve predictive preclinical testing of both prevention measures and potential new therapies.

Impact of brief exercise on peripheral blood NK cell gene and microRNA expression in young adults

Natural killers (NK) cells are unique innate immune cells that increase up to fivefold in the circulating blood with brief exercise and are known to play a key role in first-response defense against pathogens and cancer immunosurveillance. Whether exercise alters NK cell gene and microRNA (miRNA) expression is not known. Thirteen healthy men (20-29 yr old) performed ten 2-min bouts of cycle ergometer exercise at a constant work equivalent to an average of 77% of maximum O2 consumption interspersed with 1-min rest. Blood was drawn before and immediately after the exercise challenge. NK cells were isolated from peripheral blood mononuclear cells using a negative magnetic cell separation method. We used Affymetrix U133+2.0 arrays for gene expression and Agilent Human miRNA V2 Microarray for miRNAs. A stringent statistical approach (false discovery rate < 0.05) was used to determine that exercise significantly altered the expression of 986 genes and 23 miRNAs. Using in silico analysis, we found exercise-related gene pathways where there was a high likelihood of gene-miRNA interactions. These pathways were predominantly associated with cancer and cell communication, including p53 signaling pathway, melanoma, glioma, prostate cancer, adherens junction, and focal adhesion. These data support the hypothesis that exercise affects the gene and miRNA expression pattern in the population of NK cells in the circulation and suggest mechanisms through which physical activity could alter health through the innate immune system.