Blockade of natural killer cell-mediated lysis by NCAM140 expressed on tumor cells

Human NK cells responses are enhanced by CD56 engagement

Natural Killer (NK) cells are important innate lymphocytes for effective immune responses against intracellular pathogens and tumors. CD56 is a well-known marker for human NK cells, but there is very limited information about a functional role of this surface receptor. Here we show that engagement of CD56 can induce NK cell activation resulting in degranulation, IFN-γ secretion and morphological changes, making CD56 a potential co-activating receptor in NK cells. Interestingly, this effect was only observed in cytokine pre-activated and not in freshly isolated human NK cells, demonstrating that NK cell reactivity upon CD56 engagement was dependent on cytokine stimulation. Inhibition of Syk, PI3K, Erk and src-family-kinases impaired CD56-mediated NK cell stimulation. Finally, we used CRISPR/Cas9 to delete CD56 from primary human NK cells. While this abolished the stimulatory effect of CD56 on pre-activated NK cells, the cytotoxic activity of NK cells against several tumor target cells was not affected by the absence of CD56. This demonstrates that the stimulating effect of CD56 on pre-activated NK cells does not have a major impact on their cytotoxic activity, but it may contribute to the function of CD56 as a fungal recognition receptor and in the NK cell developmental synapse. This article is protected by copyright. All rights reserved.

Re-Expression of Poly/Oligo-Sialylated Adhesion Molecules on the Surface of Tumor Cells Disrupts Their Interaction with Immune-Effector Cells and Contributes to Pathophysiological Immune Escape

Glycans linked to surface proteins are the most complex biological macromolecules that play an active role in various cellular mechanisms. This diversity is the basis of cell-cell interaction and communication, cell growth, cell migration, as well as co-stimulatory or inhibitory signaling. Our review describes the importance of neuraminic acid and its derivatives as recognition elements, which are located at the outermost positions of carbohydrate chains linked to specific glycoproteins or glycolipids. Tumor cells, especially from solid tumors, mask themselves by re-expression of hypersialylated neural cell adhesion molecule (NCAM), neuropilin-2 (NRP-2), or synaptic cell adhesion molecule 1 (SynCAM 1) in order to protect themselves against the cytotoxic attack of the also highly sialylated immune effector cells. More particularly, we focus on α-2,8-linked polysialic acid chains, which characterize carrier glycoproteins such as NCAM, NRP-2, or SynCam-1. This characteristic property correlates with an aggressive clinical phenotype and endows them with multiple roles in biological processes that underlie all steps of cancer progression, including regulation of cell-cell and/or cell-extracellular matrix interactions, as well as increased proliferation, migration, reduced apoptosis rate of tumor cells, angiogenesis, and metastasis. Specifically, re-expression of poly/oligo-sialylated adhesion molecules on the surface of tumor cells disrupts their interaction with immune-effector cells and contributes to pathophysiological immune escape. Further, sialylated glycoproteins induce immunoregulatory cytokines and growth factors through interactions with sialic acid-binding immunoglobulin-like lectins. We describe the processes, which modulate the interaction between sialylated carrier glycoproteins and their ligands, and illustrate that sialic acids could be targets of novel therapeutic strategies for treatment of cancer and immune diseases.

Sialic Acids and Their Influence on Human NK Cell Function

Sialic acids are sugars with a nine-carbon backbone, present on the surface of all cells in humans, including immune cells and their target cells, with various functions. Natural Killer (NK) cells are cells of the innate immune system, capable of killing virus-infected and tumor cells. Sialic acids can influence the interaction of NK cells with potential targets in several ways. Different NK cell receptors can bind sialic acids, leading to NK cell inhibition or activation. Moreover, NK cells have sialic acids on their surface, which can regulate receptor abundance and activity. This review is focused on how sialic acids on NK cells and their target cells are involved in NK cell function.

CD56 regulates human NK cell cytotoxicity through Pyk2

Human natural killer (NK) cells are defined as CD56+CD3-. Despite its ubiquitous expression on human NK cells the role of CD56 (NCAM) in human NK cell cytotoxic function has not been defined. In non-immune cells, NCAM can induce signaling, mediate adhesion, and promote exocytosis through interactions with focal adhesion kinase (FAK). Here we demonstrate that deletion of CD56 on the NK92 cell line leads to impaired cytotoxic function. CD56-knockout (KO) cells fail to polarize during immunological synapse (IS) formation and have severely impaired exocytosis of lytic granules. Phosphorylation of the FAK family member Pyk2 at tyrosine 402 is decreased in NK92 CD56-KO cells, demonstrating a functional link between CD56 and signaling in human NK cells. Cytotoxicity, lytic granule exocytosis, and the phosphorylation of Pyk2 are rescued by the reintroduction of CD56. These data highlight a novel functional role for CD56 in stimulating exocytosis and promoting cytotoxicity in human NK cells.

CD56 Homodimerization and Participation in Anti-Tumor Immune Effector Cell Functioning: A Role for Interleukin-15

A particularly interesting marker to identify anti-tumor immune cells is the neural cell adhesion molecule (NCAM), also known as cluster of differentiation (CD)56. Namely, hematopoietic expression of CD56 seems to be confined to powerful effector immune cells. Here, we sought to elucidate its role on various killer immune cells. First, we identified the high motility NCAM-120 molecule to be the main isoform expressed by immune cells. Next, through neutralization of surface CD56, we were able to (1) demonstrate the direct involvement of CD56 in tumor cell lysis exerted by CD56-expressing killer cells, such as natural killer cells, gamma delta (γδ) T cells, and interleukin (IL)-15-cultured dendritic cells (DCs), and (2) reveal a putative crosstalk mechanism between IL-15 DCs and CD8 T cells, suggesting CD56 as a co-stimulatory molecule in their cell-to-cell contact. Moreover, by means of a proximity ligation assay, we visualized the CD56 homophilic interaction among cancer cells and between immune cells and cancer cells. Finally, by blocking the mitogen-activated protein kinase (MAPK) pathway and the phosphoinositide 3-kinase (PI3K)-Akt pathway, we showed that IL-15 stimulation directly led to CD56 upregulation. In conclusion, these results underscore the previously neglected importance of CD56 expression on immune cells, benefiting current and future immune therapeutic options.

A Mechanism of Resistance to Antibody-Targeted Immune Attack

Targeted monoclonal antibody therapy is a promising therapeutic strategy for cancer, and antibody-dependent cell-mediated cytotoxicity (ADCC) represents a crucial mechanism underlying these approaches. The majority of patients have limited responses to monoclonal antibody therapy due to the development of resistance. Models of ADCC provide a system for uncovering immune-resistance mechanisms. We continuously exposed epidermal growth factor receptor (EGFR+) A431 cells to KIR-deficient NK92-CD16V effector cells and the anti-EGFR cetuximab. Persistent ADCC exposure yielded ADCC-resistant cells (ADCCR1) that, compared with control ADCC-sensitive cells (ADCCS1), exhibited reduced EGFR expression, overexpression of histone- and interferon-related genes, and a failure to activate NK cells, without evidence of epithelial-to-mesenchymal transition. These properties gradually reversed following withdrawal of ADCC selection pressure. The development of resistance was associated with lower expression of multiple cell-surface molecules that contribute to cell-cell interactions and immune synapse formation. Classic immune checkpoints did not modulate ADCC in this unique model system of immune resistance. We showed that the induction of ADCC resistance involves genetic and epigenetic changes that lead to a general loss of target cell adhesion properties that are required for the establishment of an immune synapse, killer cell activation, and target cell cytotoxicity.

One-Step Method for Instant Generation of Advanced Allogeneic NK Cells

Conventional combinatorial anticancer therapy has shown promising outcomes; still, a significant interest in developing new methods to reinforce and possibly merge chemotherapy and immunotherapy persists. Here, a new one-step method that immediately modifies immune cells into a targeted form of chemoimmunotherapy through spontaneous and rapid incorporation of hydrophobized antibody-drug conjugates (ADCs) on the surface of immune cells is presented. Therapeutic objectives of this approach include targeted delivery of a potent chemotherapeutic agent to avoid adverse effects, enhancing the mobilization of infused immune cells toward tumor sites, and preserving the intense cytotoxic activities of immune cells against tumor cells. The embedding of hydrophobized ADCs on the immune cell membrane using the strategy in this study provides noninvasive, nontoxic, and homogenous modifications that transiently arm immune cells with highly potent cytotoxic drugs targeted toward cancer cells. The resulting surface-engineered immune cells with ADCs significantly suppress the tumor growth and drive the eradication of target cancer cells through combinatorial anticancer effects. This novel strategy allows convenient and timely preparation of advanced chemoimmunotherapy on a single immune cell to treat various types of cancer.

Production and characterization of monoclonal antibody against a triple negative breast cancer cell line

Breast cancer is the most prevalent malignancy among women around the world such that more than 1,400,000 new cases are being diagnosed each year. Despite immense studies over many years on diagnosis and treatment of breast cancer, about 30% of treated patients will relapse and require subsequent therapy. By development of hybridoma technology, murine monoclonal antibodies (MAbs) against several human tumor-associated antigens have been produced and characterized in many laboratories. The purpose of these studies is to generate effective monoclonal antibodies that could be useful in tumor diagnosis and therapy. In this study, splenic lymphocytes of immunized BALB/c mouse with a new established breast cancer cell line (Pari-ICR cell line, established in Shiraz Institute for Cancer Research) were fused with the mouse myeloma cell line SP2/0 in the presence of polyethylene glycol. We generated a panel of monoclonal antibodies against the newly established cell line. The hybrid cultures were screened by flow cytometry. Hybridomas that produced antibody to surface antigens of immunizing cell line but not to Human Gingival Fibroblasts, adipose stem cells, and leucocytes isolated from peripheral blood were selected and cloned by limiting dilution method. The 1E3 clone (IgG2a type) that displayed clonal stability was further analyzed for specificity by flow cytometry. MAb 1E3 showed weak to strong reactivity to other cell lines compared with Pari-ICR cell line. Antigen identification was performed by a workflow consisting of immunoaffinity purification, SDS-PAGE, Western blotting, and mass spectrometry analysis. The target of 1E3 mAb was identified as NCAM1. In conclusion, using the antibody-based strategy we identified NCAM1 as a potential therapeutic target and biomarker for breast cancer.

Impedance-based analysis of Natural Killer cell stimulation

The use of impedance-based label free cell analysis is increasingly popular and has many different applications. Here, we report that a real-time cell analyzer (RTCA) can be used to study the stimulation of Natural Killer (NK) cells. Engagement of NK cells via plate-bound antibodies directed against different activating surface receptors could be measured in real time using the label-free detection of impedance. The change in impedance was dependent on early signal transduction events in the NK cells as it was blocked by inhibitors of Src-family kinases and by inhibiting actin polymerization. While CD16 was the only receptor that could induce a strong change in impedance in primary NK cells, several activating receptors induced changes in impedance in expanded NK cells. Using PBMCs we could detect T cell receptor-mediated T cell activation and CD16-mediated NK cell activation in the same sample. Performing a dose-response analysis for the Src-family kinases inhibitor PP1 we show that T cells are more sensitive to inhibition compared to NK cells. Our data demonstrate that the RTCA can be used to detect physiological activation events in NK cells in a label-free and real-time fashion.

Infections in Hospitalised Patients with Multiple Myeloma: Main Characteristics and Risk Factors

OBJECTIVE

Multiple myeloma is a common haematological malignancy and immune dysfunction is the hallmark of the disease. It leads to an increased infection risk, which is still a major cause of mortality. The infection spectrum and characteristics have evolved with the introduction of novel agents. An understanding of risk factors that increase susceptibility to infections is critical in fighting them. This retrospective investigation aimed to establish the incidence and main characteristics of infections in non-transplanted hospitalised myeloma patients in our department over a 3-year period, as well as factors associated with infections.

MATERIALS AND METHODS

A total of 240 hospitalised patients with multiple myeloma (120 males and 120 females; average age: 69 years, range: 41-89 years) who were diagnosed or treated in our department from January 2008 to December 2010 were included in this study and their data were retrospectively analysed.

RESULTS

Infections were identified in 17.9% of hospitalised patients. The most common pathogen found was Pseudomonas aeruginosa. The frequency of gram-positive and gram-negative pathogens was similar. In 37.2% of cases, the agent was not isolated. The most common sites of infections were the urinary system and the blood (septicemia). The frequency of infection increased with duration of disease and the rate of reinfection was 41.9%. The patients treated with bortezomib had the highest infection occurrence. Fatal outcome occurred in 9.3% of cases.

CONCLUSION

The factors associated with infections in this investigation were female sex, 3B clinical stage of disease, increased serum creatinine and ferritin levels, neutropenia, poor general condition, and presence of catheters. Myeloma patients with one or more of these mentioned risk factors should be monitored with particular care in order to decrease the incidence and severity of infective complications.

Failure recovery of circulating NKG2D+CD56dimNK cells in HBV-associated hepatocellular carcinoma after hepatectomy predicts early recurrence

Dysfunction of natural killer (NK) cells has been implicated in the failure of antitumor immune responses in hepatocellular carcinoma (HCC) patients. However, the changes of NK profile in peripheral blood after surgery and tumor tissues of HCC patients, as well as the underlying reason and the significance are vague. Here, we observed that the frequencies of circulating NKG2D⁺CD56^dimNK cells decreased significantly in HBV-related HCC and were negatively correlated with the levels of serum TGF-β and soluble MICA (sMICA). In vitro experiments confirmed that the TGF-β and sMICA in tumor tissue homogenates, as well as sMICA in HCC cells culture supernatants could reduce the frequency of NKG2D⁺CD56^dimNK cells. In addition, in HCC patients the lower frequency of circulating NKG2D⁺CD56^dimNK cells was associated with larger tumor size and/or higher serum GGT. Noticeably, the frequency of NKG2D⁺CD56^dimNK cells at one month after surgery usually failed to restore in early recurrent patients, and that frequency was negatively associated with early recurrence and shorter overall survival. These results suggest that declined frequency of NKG2D⁺CD56^dimNK cells in HCC was associated with higher TGF-β and sMICA production, and low frequency of circulating NKG2D⁺CD56^dimNK cells at one month after surgery may predict poor prognosis of HBV-related HCC patients accepting hepatectomy.

Vaccination of multiple myeloma: Current strategies and future prospects

Tumor immunotherapy holds great promise in controlling multiple myeloma (MM) and may provide an alternative treatment modality to conventional chemotherapy for MM patients. For this reason, a major area of investigation is the development of cancer vaccines to generate myeloma-specific immunity. Several antigens that are able to induce specific T-cell responses are involved in different critical mechanisms for cell differentiation, inhibition of apoptosis, demethylation and proliferation. Strategies under development include infusion of vaccine-primed and ex vivo expanded/costimulated autologous T cells after high-dose melphalan, genetic engineering of autologous T cells with receptors for myeloma-specific epitopes, administration of dendritic cell/plasma cell fusions and administration expanded marrow-infiltrating lymphocytes. In addition, novel immunomodulatory drugs may synergize with immunotherapies. The task ahead is to evaluate these approaches in appropriate clinical settings, and to couple them with strategies to overcome mechanisms of immunoparesis as a means to induce more robust clinically significant immune responses.

Genome-wide siRNA screen reveals a new cellular partner of NK cell receptor KIR2DL4: heparan sulfate directly modulates KIR2DL4-mediated responses

KIR2DL4 (CD158d) is a distinct member of the killer cell Ig-like receptor (KIR) family in human NK cells that can induce cytokine production and cytolytic activity in resting NK cells. Soluble HLA-G, normally expressed only by fetal-derived trophoblast cells, was reported to be a ligand for KIR2DL4; however, KIR2DL4 expression is not restricted to the placenta and can be found in CD56(high) subset of peripheral blood NK cells. We demonstrated that KIR2DL4 can interact with alternative ligand(s), expressed by cells of epithelial or fibroblast origin. A genome-wide high-throughput siRNA screen revealed that KIR2DL4 recognition of cell-surface ligand(s) is directly regulated by heparan sulfate (HS) glucosamine 3-O-sulfotransferase 3B1 (HS3ST3B1). KIR2DL4 was found to directly interact with HS/heparin, and the D0 domain of KIR2DL4 was essential for this interaction. Accordingly, exogenous HS/heparin can regulate cytokine production by KIR2DL4-expressing NK cells and HEK293T cells (HEK293T-2DL4), and induces differential localization of KIR2DL4 to rab5(+) and rab7(+) endosomes, thus leading to downregulation of cytokine production and degradation of the receptor. Furthermore, we showed that intimate interaction of syndecan-4 (SDC4) HS proteoglycan (HSPG) and KIR2DL4 directly affects receptor endocytosis and membrane trafficking.

Serum markers in small cell lung cancer: opportunities for improvement

Lung cancer is one of the leading causes of death from malignancy worldwide. In particular small cell lung cancers, which comprise about 15-20% of all lung cancers, are extremely aggressive and cure rates are extremely low. Therefore, new treatment modalities are needed and detection at an early stage of disease, as well as adequate monitoring of treatment response is essential in order to improve outcome. In this respect, the use of non-invasive tools for screening and monitoring has gained increasing interest and the clinical applicability of reliable, tumor-related substances that can be detected as tumor markers in easily accessible body fluids is subject of intense investigation. Some of these indicators, such as high LDH levels in serum as a reflection of the disease, have been in use for a long time as a general tumor marker. To allow for improved monitoring of the efficacy of new therapeutic modalities and for accurate subtyping, there is a strong need for specific and sensitive markers that are more directly related to the biology and behavior of small cell lung cancer. In this review the current status of these potential markers, like CEA, NSE, ProGRP, CK-BB, SCC, CgA, NCAM and several cytokeratins will be critically analyzed with respect to their performance in blood based assays. Based on known cleavage sites for cytoplasmic and extracellular proteases, a prediction of stable fragments can be obtained and used for optimal test design. Furthermore, insight into the synthesis of specific splice variants and neo-epitopes resulting from protein modification and cleavage, offers further opportunities for improvement of tumor assays. Finally, we discuss the possibility that detection of SCLC related autoantibodies in paraneoplastic disease can be used as a very early indicator of SCLC.

Immune dysfunction in multiple myeloma

SUMMARY Although there have been advances in the field, multiple myeloma, the second most common hematological malignancy, remains an incurable disease characterized by ever-shortening cycles of treatment and relapse. Myriad experimental and observational studies over the last few decades have comprehensively documented a state of profound immune dysfunction, which is progressive and correlated with disease stage. Nonetheless, immune responses against the tumor have demonstrated efficacy ex vivo, in animal models and in human disease. In this review we examine the immune defects in multiple myeloma and consider current and future approaches toward correction and manipulation of immune responses to affect clinically useful antitumor effects.

Enhancement of natural killer cell effector functions against selected lymphoma and leukemia cell lines by dasatinib

As NK cell immunotherapy is still poorly successful, combinations with drugs enhancing NK cell activity are of major interest. NK large granular lymphocyte expansions associated with improved survival have been described under monotherapy with the Bcr-Abl/Src inhibitor dasatinib, which inhibits NK cell functions in vitro. As Src kinases play a major role in inhibitory and activating signaling pathways of NK cells, both outcomes appear plausible. To clarify these contradictory observations and potentially enable the use of dasatinib as adjuvant, we analyzed how clinically relevant doses promote NK cell effector functions. Polyclonal human NK cells were studied ex vivo. Functional outcomes assessed included conjugate formation, calcium flux, receptor regulation, cytokine production, degranulation, cytotoxicity, apoptosis induction and signal transduction. While dasatinib inhibits NK cell effector functions during functional assays, 24 hr pretreatment of NK cells followed by washout of dasatinib, led to dose-dependent enhancement of cytokine production, degranulation marker expression and cytotoxicity against selected lymphoma and leukemia cell lines. Mechanistically, this was neither due to an altered viability of NK cells nor increased NKG2D, LFA-1 or conjugate formation with target cells. Receptor proximal signaling events were inhibited. However, a slight time dependent enhancement of Vav phosphorylation was observed under certain circumstances. The shift in Vav phosphorylation level may be one major mechanism for NK cell activity enhancement induced by dasatinib. Our findings argue for a careful timing and dosing of dasatinib application during leukemia/lymphoma treatment to enhance NK cell immunotherapeutic efforts.

Biological activity of lenalidomide and its underlying therapeutic effects in multiple myeloma

Lenalidomide is a synthetic compound derived by modifying the chemical structure of thalidomide. It belongs to the second generation of immunomodulatory drugs (IMiDs) and possesses pleiotropic properties. Even if lenalidomide has been shown to be active in the treatment of several hematologic malignancies, this review article is mostly focalized on its mode of action in multiple myeloma. The present paper is about the direct and indirect antitumor effects of lenalidomide on malignant plasmacells, bone marrow microenvironment, bone resorption and host's immune response. The molecular mechanisms and targets of lenalidomide remain largely unknown, but recent evidence shows cereblon (CRBN) as a possible mediator of its therapeutical effects.

Novel strategies for immunotherapy in multiple myeloma: previous experience and future directions

Multiple myeloma (MM) is a life-threatening haematological malignancy for which standard therapy is inadequate. Autologous stem cell transplantation is a relatively effective treatment, but residual malignant sites may cause relapse. Allogeneic transplantation may result in durable responses due to antitumour immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. Cellular immunotherapy using specific antigen-presenting cells (APCs), to overcome aspects of immune incompetence in MM patients, has received great attention, and numerous clinical trials have evaluated the potential for dendritic cell (DC) vaccines as a novel immunotherapeutic approach. This paper will summarize the data investigating aspects of immunity concerning MM, immunotherapy for patients with MM, and strategies, on the way, to target the plasma cell more selectively. We also include the MM antigens and their specific antibodies that are of potential use for MM humoral immunotherapy, because they have demonstrated the most promising preclinical results.

Cellular immunotherapy using dendritic cells against multiple myeloma

Cellular therapy with dendritic cells (DCs) is emerging as a useful immunotherapeutic tool to treat multiple myeloma (MM). DC-based idiotype vaccination was recently suggested to induce idiotype-specific immune responses in MM patients. However, the clinical results so far have been largely disappointing, and the clinical effectiveness of such vaccinations in MM still needs to be demonstrated. DC-based therapies against MM may need to be boosted with other sources of tumor-associated antigens, and potent DCs should be recruited to increase the effectiveness of treatment. DCs with both high migratory capacity and high cytokine production are very important for effective DC-based cancer vaccination in order to induce high numbers of Th1-type CD4⁺ T cells and CD8⁺ cytotoxic T lymphocytes. The tumor microenvironment is also important in the regulation of tumor cell growth, proliferation, and the development of therapeutic resistance after treatment. In this review, we discuss how the efficacy of DC vaccination in MM can be improved. In addition, novel treatment strategies that target not only myeloma cells but also the tumor microenvironment are urgently needed to improve treatment outcomes.

Tumor-primed natural killer cells from patients with multiple myeloma lyse autologous, NK-resistant, bone marrow-derived malignant plasma cells

Natural killer (NK) cells are cytotoxic lymphocytes able to kill tumor cells and virus-infected cells. Human-resting NK cells can be activated by co-culture with NK-resistant CTV-1a cells. These tumor-activated cells (TaNKs) are cytotoxic to a range of NK-resistant tumor cells in vitro. This potential, however, has not been explored in multiple myeloma (MM). In this study, we demonstrate that TaNK cells from 21 MM patients lyse a variety of myeloma targets, including primary isolates of autologous and allogeneic CD138+ myeloma cells whilst sparing CD138-ve bone marrow cells. Myeloma patients' TaNK-induced lysis of the U266 cell line was significantly higher compared to normal controls (median-specific lysis 79.1% vs. 69.5%) (P = 0.003). In addition, TaNKs induced substantial lysis of autologous and allogeneic CD138+ myeloma cells (median-specific lysis 52.5% and 37.4%, respectively). The percentage of specific lysis did not correlate with important disease characteristics (ISS, age, and high-risk molecular abnormalities) or with the disease status and antimyeloma treatment, including novel agents and dexamethasone. In conclusion, tumor-primed NK cells are able to induce substantial lysis of myeloma targets including autologous and allogeneic CD138+ myeloma plasma cells and could be an additional therapeutic approach in MM, particularly in the era of novel agents.

Modulation of NKp30- and NKp46-mediated natural killer cell responses by poxviral hemagglutinin

Natural killer (NK) cells are an important element in the immune defense against the orthopox family members vaccinia virus (VV) and ectromelia virus (ECTV). NK cells are regulated through inhibitory and activating signaling receptors, the latter involving NKG2D and the natural cytotoxicity receptors (NCR), NKp46, NKp44 and NKp30. Here we report that VV infection results in an upregulation of ligand structures for NKp30 and NKp46 on infected cells, whereas the binding of NKp44 and NKG2D was not significantly affected. Likewise, infection with ectromelia virus (ECTV), the mousepox agent, enhanced binding of NKp30 and, to a lesser extent, NKp46. The hemagglutinin (HA) molecules from VV and ECTV, which are known virulence factors, were identified as novel ligands for NKp30 and NKp46. Using NK cells with selectively silenced NCR expression and NCR-CD3ζ reporter cells, we observed that HA present on the surface of VV-infected cells, or in the form of recombinant soluble protein, was able to block NKp30-triggered activation, whereas it stimulated the activation through NKp46. The net effect of this complex influence on NK cell activity resulted in a decreased NK lysis susceptibility of infected cells at late time points of VV infection when HA was expression was pronounced. We conclude that poxviral HA represents a conserved ligand of NCR, exerting a novel immune escape mechanism through its blocking effect on NKp30-mediated activation at a late stage of infection.

Immune alterations in untreated and treated multiple myeloma

The incidence of second malignancies was shown to be increased in patients with multiple myeloma. Although a shared genetic predisposition or common environmental carcinogens may account for the occurrence of both myeloma and additional cancers, multiple immune defects encountered in myeloma might play an important role in this regard. This review explores the impairments in both cellular and humoral mediated immunity in multiple myeloma, linking them with increased susceptibility to infections and additional cancers. In addition, the recent therapeutic advances transformed myeloma into a chronic entity, with multiple relapses and salvage therapies, which may result in cumulative immunosuppression. Although recent reports have suggested an increased rate of second cancers in myeloma patients treated with lenalidomide, the true impact of this agent and other novel anti-myeloma therapies on the incidence of additional malignancies remains to be clarified.

Immune recovery after cyclophosphamide treatment in multiple myeloma: implication for maintenance immunotherapy

Multiple myeloma (MM) is a progressive B-lineage neoplasia characterized by clonal proliferation of malignant plasma cells. Increased numbers of regulatory T cells (Tregs) were determined in mouse models and in patients with MM, which correlated with disease burden. Thus, it became rational to target Tregs for treating MM. The effects of common chemotherapeutic drugs on Tregs are reviewed with a focus on cyclophosphamide (CYC). Studies indicated that selective depletion of Tregs may be accomplished following the administration of a low-dose CYC. We report that continuous nonfrequent administrations of CYC at low doses block the renewal of Tregs in MM-affected mice and enable the restoration of an efficient immune response against the tumor cells, thereby leading to prolonged survival and prevention of disease recurrence. Hence, distinctive time-schedule injections of low-dose CYC are beneficial for breaking immune tolerance against MM tumor cells.

Natural killer cells and malignant haemopathies: a model for the interaction of cancer with innate immunity

Despite recent progress in the therapeutic approach of malignant haemopathies, their prognoses remain frequently poor. Immunotherapy offers an alternative of great interest in this context but defect or abnormal expression of human leukocyte antigens (HLA), frequently observed in cancer cells, limits its efficiency. Natural killer (NK) cells, which are able to kill target cells in a HLA-independent way, represent a novel tool in the treatment of haematological malignancies. Abnormal NK cytolytic function is observed in all the haematological malignancies studied, such as acute leukaemia, myelodysplastic syndromes or chronic myeloid/lymphoid leukaemia. Several mechanisms are involved in the alterations of NK cytotoxicity: decreased expression of activating receptors, increased expression of inhibitory receptors or defective expression of NK ligands on target cells. Further studies are needed to identify how each type of haematological malignancy escapes from the innate immune response. Attempts to increase the expression of activating receptors, to counteract inhibitory receptors expression, or to increase NK cell cytotoxic capacities could overcome tumour escape from innate immunity. These therapies are based on monoclonal antibodies or culture of NK cells in presence of cytokines or dendritic cells. Moreover, many novel drugs used in haematological malignancies [tyrosine kinase inhibitors, IMIDs(®), proteasome inhibitors, demethylating agents, histone deacetylase inhibitors (HDACis), histamine dihydrochloride] display interesting immunomodulatory properties that affect NK cells. These data suggest that combined modalities associating cytotoxic drugs with innate immunity modulators may represent a major breakthrough in tumour eradication.

Drug-mediated and cellular immunotherapy in multiple myeloma

Multiple myeloma is an immunologically relevant disease, which subverts and suppresses immunity, but that may also be amenable to immunological control. Novel drug and cell-based therapies provide an opportunity for the design of antimyeloma immunotherapy. Reversing the immunosuppression associated myeloma remains a substantial challenge. The minimal residual disease setting achieved by autologous stem cell transplant or highly efficacious induction therapy may reverse this immunoparesis and provide a setting for induction of antimyeloma T-cell responses. Adoptive cytotoxic T-lymphocyte/NK therapy and comprehensive treatment with immunomodulatory drug therapy represent means by which antimyeloma immune responses may be promoted. In addition, apoptosis-inducing therapies may prime endogenous antigen presentation via immunogenic cell death, which again may be enhanced by the addition of immunomodulatory drug therapy.

Breaking tolerance in a mouse model of multiple myeloma by chemoimmunotherapy

A unique mouse model of multiple myeloma (MM), namely 5T2MM-bearing mouse, was useful for elucidating the pathophysiological mechanisms underlying the disease. Increased accumulation of suppressive CD4(+)CD25(High)Foxp3(+) regulatory T cells (Tregs) was observed in the thymus and lymphoid peripheral organs during disease progression. Adoptive transfer of Tregs, but not other thymocytes, from 5T2MM-bearing mice led to increased progression of disease manifestations in young syngeneic mice. Depletion of Tregs, a proposed strategy in cancer immunotherapy, was tested using cyclophosphamide (CYC), an alkylating agent with selective cytotoxicity. Both low- and high-dose CYC, administered to sick mice with hind limb paralysis, caused the paralysis to disappear, the plasma tumor cells in the bone marrow (BM) cavity to be replaced by normal cell populations, and the survival of the mice to be significantly prolonged. Low-dose CYC, which selectively depletes Tregs, decreased MM incidence, in contrast to high-dose CYC, which was generally cytotoxic, and did not reduce MM incidence. In contrast, low-dose CYC induced Tregs to become susceptible to apoptosis by downregulating Bcl-xL and CTLA-4 in these cells, and by decreasing the production of IL-2 by effector CD4 cells. This treatment consequently triggered the recovery of IFN-gamma-producing natural killer T cells and the maturation of dendritic cells. Transient gradual depletion of Tregs in low-dose CYC-treated 5T2MM mice was maintained beyond 45 days. Thus, less frequent injections of low-dose CYC enabled us to recruit compatible immune-derived cells that would reduce tumor load and delay or prevent tumor recurrence, hence breaking immune tolerance toward MM tumor cells.

Mechanism of action of immunomodulatory drugs (IMiDS) in multiple myeloma

Immunomodulatory drugs (IMiDs) are thalidomide analogues, which possess pleiotropic anti-myeloma properties including immune-modulation, anti-angiogenic, anti-inflammatory and anti-proliferative effects. Their development was facilitated by an improved understanding in myeloma (MM) biology and initiated a profound shift in the therapeutic approach towards MM. Despite the diverse effects of IMiDs in vitro, the relative contribution of each effect towards their ultimate anti-MM activity is still unclear. Based on in vitro data, it appears that anti-proliferative effects and downregulation of crucial cytokines are their most important anti-MM attributes. Although the co-stimulatory effects on T and NK cells have been heralded as a unique and important property of IMiDs towards enhancing anti-MM immune activity, these in vitro effects have yet to be firmly corroborated in vivo. Much is yet to be elucidated regarding the complex interplay of immunomodulatory cytokines that occurs in vivo, which ultimately dictates the net effects of IMiDs in MM-the understanding of which is necessary to facilitate optimal manipulation of these drugs in future MM management.

Expression of adhesion molecules and ligands for activating and costimulatory receptors involved in cell-mediated cytotoxicity in a large panel of human melanoma cell lines

Knowledge of the interactions between MHC-unrestricted cytotoxic effector cells and solid tumour cells is essential for introducing more effective NK cell-based immunotherapy protocols into clinical practise. Here, to begin to obtain an overview of the possible universe of molecules that could be involved in the interactions between immune effector cells and melanoma, we analyse the surface expression of adhesion and costimulatory molecules and of ligands for NK-activating receptors on a large panel of cell lines from the "European Searchable Tumour Cell Line and Data Bank" (ESTDAB, http://www.ebi.ac.uk/ipd/estdab/ ) and discuss their potential role in the immune response against this tumour. We show that most melanoma cell lines express not only adhesion molecules that are likely to favour their interaction with cells of the immune system, but also their interaction with endothelial cells potentially increasing their invasiveness and metastatic capacity. A high percentage of melanoma cell lines also express ligands for the NK-activating receptor NKG2D; whereas, the majority express MICA/B molecules, ULBP expression, however, was rarely found. In addition to these molecules, we also found that CD155 (poliovirus receptor, PVR) is expressed by the majority of melanoma cell lines, whereas CD112 (Nectin-2) expression was rare. These molecules are DNAM-1 ligands, a costimulatory molecule involved in NK cell-mediated cytotoxicity and cytokine production that also mediates costimulatory signals for triggering naïve T cell differentiation. The phenotypical characterisation of adhesion molecules and ligands for receptors involved in cell cytotoxicity on a large series of melanoma cell lines will contribute to the identification of markers useful for the development of new immunotherapy strategies.

Activation of natural killer cells by newcastle disease virus hemagglutinin-neuraminidase

The avian paramyxovirus Newcastle disease virus (NDV) selectively replicates in tumor cells and is known to stimulate T-cell-, macrophage-, and NK cell-mediated responses. The mechanisms of NK cell activation by NDV are poorly understood so far. We studied the expression of ligand structures for activating NK cell receptors on NDV-infected tumor cells. Upon infection with the nonlytic NDV strain Ulster and the lytic strain MTH-68/H, human carcinoma and melanoma cells showed enhanced expression of ligands for the natural cytotoxicity receptors NKp44 and NKp46, but not NKp30. Ligands for the activating receptor NKG2D were partially downregulated. Soluble NKp44-Fc and NKp46-Fc, but not NKp30-Fc, chimeric proteins bound specifically to NDV-infected tumor cells and to NDV particle-coated plates. Hemagglutinin-neuraminidase (HN) of the virus serves as a ligand structure for NKp44 and NKp46, as indicated by the blockade of binding to NDV-infected cells and viral particles in the presence of anti-HN antibodies and by binding to cells transfected with HN cDNA. Consistent with the recognition of sialic acid moieties by the viral lectin HN, the binding of NKp44-Fc and NKp46-Fc was lost after desialylation. NKp44- and NKp46-CD3zeta lacZ-inducible reporter cells were activated by NDV-infected cells. NDV-infected tumor cells stimulated NK cells to produce increased amounts of the effector lymphokines gamma interferon and tumor necrosis factor alpha. Primary NK cells and the NK line NK-92 lysed NDV-infected tumor cells with enhanced efficiency, an effect that was eliminated by the treatment of target cells with the neuraminidase inhibitor Neu5Ac2en. These results suggest that direct activation of NK cells contributes to the antitumor effects of NDV.

Functional impairment in circulating and intrahepatic NK cells and relative mechanism in hepatocellular carcinoma patients

Functional defects in natural killer (NK) cells have been proposed to be responsible for the failure of anti-tumor immune responses. Whether and how NK cells are impaired in hepatocellular carcinoma (HCC) patients remain unknown. In this study, we found that HCC patients displayed a dramatic reduction in peripheral CD56(dim)CD16(pos) NK subsets compared with healthy subjects. A significant reduction of CD56(dim)CD16(pos) NK subsets was also found in tumor regions compared with non-tumor regions in the livers of these HCC patients. Both these peripheral and tumor-infiltrating NK cells exhibited poorer capacity to produce IFN-gamma and kill K562 targets, which was further found to be associated with increased CD4(+)CD25(+) T regulatory cells as we previously-described in HCC patients. Addition of Tregs from HCC patients efficiently inhibited the anti-tumor ability of autologous NK cells in vitro. These findings are helpful for understanding the mechanism of NK cell-mediated anti-tumor immune responses in HCC patients.

Expression analysis of the ligands for the Natural Killer cell receptors NKp30 and NKp44

Background

The natural cytotoxicity receptors (NCR) are important to stimulate the activity of Natural Killer (NK) cells against transformed cells. Identification of NCR ligands and their level of expression on normal and neoplastic cells has important implications for the rational design of immunotherapy strategies for cancer.

Methodology/Principal Findings

Here we analyze the expression of NKp30 ligand and NKp44 ligand on 30 transformed or non-transformed cell lines of different origin. We find intracellular and surface expression of these two ligands on almost all cell lines tested. Expression of NKp30 and NKp44 ligands was variable and did not correlate with the origin of the cell line. Expression of NKp30 and NKp44 ligand correlated with NKp30 and NKp44-mediated NK cell lysis of tumor cells, respectively. The surface expression of NKp30 ligand and NKp44 ligand was sensitive to trypsin treatment and was reduced in cells arrested in G₂/M phase.

Conclusion/Significance

These data demonstrate the ubiquitous expression of the ligands for NKp30 and NKp44 and give an important insight into the regulation of these ligands.

Immunodeficiency and immunotherapy in multiple myeloma

Multiple myeloma is a malignant tumour of plasma cells that remains incurable for the vast majority of patients, with a median survival of 2-3 years. It is characterized by the patchy accumulation of tumour cells within bone marrow leading to variable anaemia, bone destruction, hypercalcaemia, renal failure and infections. Immune dysfunction is an important feature of the disease and leads to infections that are both a major cause of morbidity and mortality and may promote tumour growth and resistance to chemotherapy. Numerous defects of the immune system have been described in multiple myeloma although the relative clinical importance of these remains elusive. There has been considerable interest in the identification of an autologous response against myeloma. Although T cells and humoral responses directed against myeloma-associated antigens have been described, it is uncertain if the immune system plays a role in preventing or controlling myeloma cell growth. There is increasing interest in the potential role of immunotherapy but the success of these interventions is likely to be modified by the immunologically hostile environment associated with multiple myeloma. This review attempts to summarize the current knowledge relating to the immune defects found in multiple myeloma.