Tumoricidal potential of native blood dendritic cells: direct tumor cell killing and activation of NK cell-mediated cytotoxicity

Dendritic cell transfer for cancer immunotherapy

Dendritic cells (DCs) play a major role in cancer immunosurveillance as they bridge innate and adaptive immunity by detecting tumor-associated antigens and presenting them to T lymphocytes. The adoptive transfer of antigen loaded DCs has been proposed as an immunotherapeutic approach for the treatment of various types of cancer. Nevertheless, despite promising preclinical data, the therapeutic efficacy of DC transfer is still deceptive in cancer patients. Here we summarize recent findings in DC biology with a special focus on the development of actionable therapeutic strategies and discuss experimental and clinical approaches that aim at improving the efficacy of DC-based immunotherapies, including, but not limited to, optimized DC production and antigen loading, stimulated maturation, the co-treatment with additional immunotherapies, as well as the inhibition of DC checkpoints.

Novel mechanisms of action contributing to Benralizumab's potent anti-eosinophilic activity

Benralizumab is a humanised, anti-IL-5Rα monoclonal antibody with anti-eosinophilic activity. Lack of fucose (afucosylation) increases its affinity to CD16a and significantly enhances antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells. Although benralizumab proved clinically efficacious in clinical trials for patients with severe asthma and hypereosinophilic syndrome, in-depth characterisation of its anti-eosinophilic mechanisms of action remain elusive. Here, we further investigated the mechanisms involved in benralizumab's anti-eosinophilic activities. In the presence of NK cells benralizumab induced potent eosinophil apoptosis as demonstrated by the upstream induction of caspase 3/7 and upregulation of cytochrome C. In addition, we uncovered a previously unrecognised mechanism whereby benralizumab can induce eosinophil phagocytosis/efferocytosis by macrophages, a process called antibody-dependent cell phagocytosis (ADCP). Using live cell imaging we unravel the stepwise processes leading to eosinophil apoptosis and uptake by activated macrophages. Through careful observations of cellular co-culture assays we identified a novel role for macrophage derived TNF to further enhance benralizumab-mediated eosinophil apoptosis through activation of TNF-receptor 1 on eosinophils. TNF-induced eosinophil apoptosis was associated with Cytochrome C upregulation, mitochondrial membrane depolarisation, and increased caspase 3/7 activity. Moreover, activated NK cells were found to amplify this axis through the secretion of IFNγ, subsequently driving TNF expression by macrophages. Our data provide insights into the timely appearance of events leading to benralizumab-induced eosinophil apoptosis and suggest that additional mechanisms may contribute to the potent anti-eosinophilic activity of benralizumab in vivo Importantly, afucosylation of benralizumab strongly enhanced its potency for all mechanisms investigated.

Natural Killer-Dendritic Cell Interactions in Liver Cancer: Implications for Immunotherapy

Simple Summary

The reciprocal crosstalk between dendritic cells (DCs) and natural killer (NK) cells plays a pivotal role in regulating immune defense against viruses and tumors. The Th-cell polarizing ability, cytokine-producing capacity, chemokine expression, and migration of DCs are regulated by activated NK cells. Conversely, the effector functions including lysis and cytokine production, proliferation, and migration of NK cells are influenced by close interactions with activated DCs. In this review, we explore the impact of DC–NK cell crosstalk and its therapeutic potential in immune control of liver malignances.

Abstract

Natural killer (NK) and dendritic cells (DCs) are innate immune cells that play a crucial role in anti-tumor immunity. NK cells kill tumor cells through direct cytotoxicity and cytokine secretion. DCs are needed for the activation of adaptive immune responses against tumor cells. Both NK cells and DCs are subdivided in several subsets endowed with specialized effector functions. Crosstalk between NK cells and DCs leads to the reciprocal control of their activation and polarization of immune responses. In this review, we describe the role of NK cells and DCs in liver cancer, focusing on the mechanisms involved in their reciprocal control and activation. In this context, intrahepatic NK cells and DCs present unique immunological features, due to the constant exposure to non-self-circulating antigens. These interactions might play a fundamental role in the pathology of primary liver cancer, namely hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). Additionally, the implications of these immune changes are relevant from the perspective of improving the cancer immunotherapy strategies in HCC and ICC patients.

Profiles of immune infiltration and its relevance to survival outcome in meningiomas

Tumor-infiltrating immune cells play a decisive part in prognosis and survival. Until now, previous researches have not made clear about the diversity of cell types involved in the immune response. The objective of this work was to confirm the composition of tumor-infiltrating immune cells and their correlation with prognosis in meningiomas based on a metagene approach (known as CIBERSORT) and online databases. A total of 22 tumor-infiltrating immune cells were detected to determine the relationship between the immune infiltration pattern and survival. The proportion of M2 macrophages was more abundant in 68 samples, reaching more than 36%. Univariate Cox regression analysis displayed that the proportion of dendritic cells was obviously related to prognosis. Hierarchical clustering analysis identified two clusters by the method of within sum of squares errors, which exhibited different infiltrating immune cell composition and survival. To summarize, our results indicated that proportions of tumor-infiltrating immune cells as well as cluster patterns were associated with the prognosis, which offered clinical significance for research of meningiomas.

Human innate immune cell crosstalk induces melanoma cell senescence

Mononuclear phagocytes and NK cells constitute the first line of innate immune defense. How these cells interact and join forces against cancer is incompletely understood. Here, we observed an early accumulation of slan⁺ (6-sulfo LacNAc) non-classical monocytes (slanMo) in stage I melanoma, which was followed by an increase in NK cell numbers in stage III. Accordingly, culture supernatants of slanMo induced migration of primary human NK cells in vitro via the chemotactic cytokine IL-8 (CXCL8), suggesting a role for slanMo in NK cell recruitment into cancer tissues. High levels of TNF-α and IFN-γ were produced in co-cultures of TLR-ligand stimulated slanMo and NK cells, whereas much lower levels were contained in cultures of slanMo and NK cells alone. Moreover, TNF-α and IFN-γ concentrations in slanMo/NK cell co-cultures exceeded those in CD14⁺ monocyte/NK cell and slanMo/T cell co-cultures. Importantly, TNF-α and IFN-γ that was produced in TLR-ligand stimulated slanMo/NK cell co-cultures induced senescence in different melanoma cell lines, as indicated by reduced melanoma cell proliferation, increased senescence-associated β-galactosidase expression, p21 upregulation, and induction of a senescence-associated secretory phenotype (SASP). Taken together, we identified a role for slanMo and NK cells in a collaborative innate immune defense against melanoma by generating a tumor senescence-inducing microenvironment. We conclude that enhancing the synergistic innate immune crosstalk of slanMo and NK cells could improve current immunotherapeutic approaches in melanoma.

A new synthetic toll-like receptor 1/2 ligand is an efficient adjuvant for peptide vaccination in a human volunteer

BACKGROUND

We previously showed that the bacterial lipopeptide Pam₃Cys-Ser-Ser, meanwhile established as a toll-like receptor (TLR) 1/2 ligand, acts as a strong adjuvant for the induction of virus specific CD8⁺ T cells in mice, when covalently coupled to a synthetic peptide.

CASE PRESENTATION

We now designed a new water-soluble synthetic Pam₃Cys-derivative, named XS15 and characterized it in vitro by a TLR2 NF-κB luciferase reporter assay. Further, the capacity of XS15 to activate immune cells and stimulate peptide-specific CD8⁺ T and NK cells by 6-sulfo LacNAc⁺ monocytes was assessed by flow cytometry as well as cytokine induction using immunoassays. The induction of a functional immune response after vaccination of a volunteer with viral peptides was assessed by ELISpot assay and flow cytometry in peripheral blood cells and infiltrating cells at the vaccination site, as well as by immunohistochemistry and imaging. XS15 induced strong ex vivo CD8⁺ and T_H1 CD4⁺ responses in a human volunteer upon a single injection of XS15 mixed to uncoupled peptides in a water-in-oil emulsion (Montanide™ ISA51 VG). A granuloma formed locally at the injection site containing highly activated functional CD4⁺ and CD8⁺ effector memory T cells. The total number of vaccine peptide-specific functional T cells was experimentally assessed and estimated to be 3.0 × 10⁵ in the granuloma and 20.5 × 10⁶ in peripheral blood.

CONCLUSION

Thus, in one volunteer we show a granuloma forming by peptides combined with an efficient adjuvant in a water-in-oil-emulsion, inducing antigen specific T cells detectable in circulation and at the vaccination site, after one single vaccination only. The ex vivo T cell responses in peripheral blood were detectable for more than one year and could be strongly boosted by a second vaccination. Hence, XS15 is a promising adjuvant candidate for peptide vaccination, in particular for tumor peptide vaccines in a personalized setting.

Current Concepts on 6-sulfo LacNAc Expressing Monocytes (slanMo)

The human mononuclear phagocytes system consists of dendritic cells (DCs), monocytes, and macrophages having different functions in bridging innate and adaptive immunity. Among the heterogeneous population of monocytes the cell surface marker slan (6-sulfo LacNAc) identifies a specific subset of human CD14^- CD16⁺ non-classical monocytes, called slan⁺ monocytes (slanMo). In this review we discuss the identity and functions of slanMo, their contributions to immune surveillance by pro-inflammatory cytokine production, and cross talk with T cells and NK cells. We also consider the role of slanMo in the regulation of chronic inflammatory diseases and cancer. Finally, we highlight unresolved questions that should be the focus of future research.

Neoadjuvant Radiochemotherapy Significantly Alters the Phenotype of Plasmacytoid Dendritic Cells and 6-Sulfo LacNAc+ Monocytes in Rectal Cancer

Neoadjuvant radiochemotherapy (nRCT) can significantly influence the tumor immune architecture that plays a pivotal role in regulating tumor growth. Whereas, various studies have investigated the effect of nRCT on tumor-infiltrating T cells, little is known about its impact on the frequency and activation status of human dendritic cells (DCs). Plasmacytoid DCs (pDCs) essentially contribute to the regulation of innate and adaptive immunity and may profoundly influence tumor progression. Recent studies have revealed that higher pDC numbers are associated with poor prognosis in cancer patients. 6-sulfo LacNAc-expressing monocytes (slanMo) represent a particular proinflammatory subset of human non-classical blood monocytes that can differentiate into DCs. Recently, we have reported that activated slanMo produce various proinflammatory cytokines and efficiently stimulate natural killer cells and T lymphocytes. slanMo were also shown to accumulate in clear cell renal cell carcinoma (ccRCC) and in metastatic lymph nodes from cancer patients. Here, we investigated the influence of nRCT on the frequency of rectal cancer-infiltrating pDCs and slanMo. When evaluating rectal cancer tissues obtained from patients after nRCT, a significantly higher density of pDCs in comparison to pre-nRCT tissue samples was found. In contrast, the density of slanMo was not significantly altered by nRCT. Further studies revealed that nRCT significantly enhances the proportion of rectal cancer-infiltrating CD8⁺ T cells expressing the cytotoxic effector molecule granzyme B. When exploring the impact of nRCT on the phenotype of rectal cancer-infiltrating pDCs and slanMo, we observed that nRCT markedly enhances the percentage of inducible nitric oxide synthase (iNOS)- or tumor necrosis factor (TNF) alpha-producing slanMo. Furthermore, nRCT significantly increased the percentage of mature CD83⁺ pDCs in rectal cancer tissues. Moreover, the proportion of pDCs locally expressing interferon-alpha, which plays a major role in antitumor immunity, was significantly higher in post-nRCT tissues compared to pre-nRCT tumor specimens. These novel findings indicate that nRCT significantly influences the frequency and/or phenotype of pDCs, slanMo, and CD8⁺ T cells, which may influence the clinical response of rectal cancer patients to nRCT.

Therapeutic Potential of Natural Killer Cells in Gastric Cancer

Gastric cancer (GC) is one of the most common cancers, with a high incidence of cancer death. Despite various therapeutic approaches, the cures and prognosis of advanced GC remain poor. Natural killer (NK) cells, which are known as important lymphocytes in innate immunity, play vital roles in suppressing GC initiation, progression, and metastases. A wide range of clinical settings shows that increasing the number of NK cells or improving NK cell antitumor activity is promising in GC patients. NK cell adoptive therapy (especially expanded NK cells) is a safe and well-tolerated method, which can enhance NK cell cytotoxicity against GC. Meanwhile, cytokines, immunomodulatory drugs, immune checkpoint blockades, antibodies, vaccines, and gene therapy have been found to directly or indirectly activate NK cells to improve their killing activity toward GC. In this review, we summarize recent advancements in the relationship between NK cells and GC and point out all the innovative strategies that can enhance NK cells' function to inhibit the growth of GC.

slan+ Monocytes and Macrophages Mediate CD20-Dependent B-cell Lymphoma Elimination via ADCC and ADCP

Terminal tissue differentiation and function of slan⁺ monocytes in cancer is largely unexplored. Our recent studies demonstrated that slan⁺ monocytes differentiate into a distinct subset of dendritic cells (DC) in human tonsils and that slan⁺ cells colonize metastatic carcinoma-draining lymph nodes. Herein, we report by retrospective analysis of multi-institutional cohorts that slan⁺ cells infiltrate various types of non-Hodgkin lymphomas (NHL), particularly the diffuse large B-cell lymphoma (DLBCL) group, including the most aggressive, nodal and extranodal, forms. Nodal slan⁺ cells displayed features of either immature DC or macrophages, in the latter case ingesting tumor cells and apoptotic bodies. We also found in patients with DLBCL that peripheral blood slan⁺ monocytes, but not CD14⁺ monocytes, increased in number and displayed highly efficient rituximab-mediated antibody-dependent cellular cytotoxicity, almost equivalent to that exerted by NK cells. Notably, slan⁺ monocytes cultured in conditioned medium from nodal DLBCL (DCM) acquired a macrophage-like phenotype, retained CD16 expression, and became very efficient in rituximab-mediated antibody-dependent cellular phagocytosis (ADCP). Macrophages derived from DCM-treated CD14⁺ monocytes performed very efficient rituximab-mediated ADCP, however, using different FcγRs from those used by slan⁺ macrophages. Our observations shed new light on the complexity of the immune microenvironment of DLBCL and demonstrate plasticity of slan⁺ monocytes homing to cancer tissues. Altogether, data identify slan⁺ monocytes and macrophages as prominent effectors of antibody-mediated tumor cell targeting in patients with DLBCL.Significance: slan⁺ monocytes differentiate into macrophages that function as prominent effectors of antibody-mediated tumor cell targeting in lymphoma.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/13/3544/F1.large.jpg Cancer Res; 78(13); 3544-59. ©2018 AACR.

Transcriptional profiling reveals functional dichotomy between human slan+ non-classical monocytes and myeloid dendritic cells

Human 6-sulfo LacNac-positive (slan⁺) cells have been subject to a paradigm debate. They have previously been classified as a distinct dendritic cell (DC) subset. However, evidence has emerged that they may be more related to monocytes than to DCs. To gain deeper insight into the functional specialization of slan⁺ cells, we have compared them with both conventional myeloid DC subsets (CD1c⁺ and CD141⁺) in human peripheral blood (PB). With the use of genome-wide transcriptional profiling, as well as functional tests, we clearly show that slan⁺ cells form a distinct, non-DC-like population. They cluster away from both DC subsets, and their gene-expression profile evidently suggests involvement in distinct inflammatory processes. An extensive transcriptional meta-analysis confirmed the relationship of slan⁺ cells with the monocytic compartment rather than with DCs. From a functional perspective, their ability to prime CD4⁺ and CD8⁺ T cells is relatively low. Combined with the finding that "antigen presentation by MHC class II" is at the top of under-represented pathways in slan⁺ cells, this points to a minimal role in directing adaptive T cell immunity. Rather, the higher expression levels of complement receptors on their cell surface, together with their high secretion of IL-1β and IL-6, imply a specific role in innate inflammatory processes, which is consistent with their recent identification as non-classical monocytes. This study extends our knowledge on DC/monocyte subset biology under steady-state conditions and contributes to our understanding of their role in immune-mediated diseases and their potential use in immunotherapeutic strategies.

slanDCs/M-DC8+ cells constitute a distinct subset of dendritic cells in human tonsils [corrected]

Human blood dendritic cells (DCs) include three main distinct subsets, namely the CD1c⁺ and CD141⁺ myeloid DCs (mDCs) and the CD303⁺ plasmacytoid DCs (pDCs). More recently, a population of slan/M-DC8⁺ cells, also known as “slanDCs”, has been described in blood and detected even in inflamed secondary lymphoid organs and non-lymphoid tissues. Nevertheless, hallmarks of slan/M-DC8⁺ cells in tissues are poorly defined. Herein, we report a detailed characterization of the phenotype and function of slan/M-DC8⁺ cells present in human tonsils. We found that tonsil slan/M-DC8⁺ cells represent a unique DC cell population, distinct from their circulating counterpart and also from all other tonsil DC and monocyte/macrophage subsets. Phenotypically, slan/M-DC8⁺ cells in tonsils display a CD11c⁺HLA-DR⁺CD14⁺CD11b^dim/negCD16^dim/negCX3CR1^dim/neg marker repertoire, while functionally they exhibit an efficient antigen presentation capacity and a constitutive secretion of TNFα. Notably, such DC phenotype and functions are substantially reproduced by culturing blood slan/M-DC8⁺ cells in tonsil-derived conditioned medium (TDCM), further supporting the hypothesis of a full DC-like differentiation program occurring within the tonsil microenvironment. Taken together, our data suggest that blood slan/M-DC8⁺ cells are immediate precursors of a previously unrecognizedcompetent DC subset in tonsils, and pave the way for further characterization of slan/M-DC8⁺ cells in other tissues.

IL-1β limits the extent of human 6-sulfo LacNAc dendritic cell (slanDC)-mediated NK cell activation and regulates CD95-induced apoptosis

To function optimally, human blood natural killer (NK) cells need to communicate with other immune cells. Previously, it has been shown that NK cells communicate with 6-sulfo LacNAc dendritic cells (slanDCs), which are able to stimulate NK cells in vitro. In this study, we investigated how slanDCs regulate the level of NK cell activation. The secretion of interleukin (IL)-1β by slanDCs during coculture with NK cells increased as a result of signaling via intercellular adhesion molecule-1 on slanDCs following its interaction with lymphocyte function-associated antigen-1 on NK cells. IL-1β induced the expression of Fas receptor (CD95) on NK cells. The binding of Fas ligand (CD178) to CD95 induced the apoptosis of activated NK cells. Moreover, IL-1β also induced increased cyclooxygenase-2 expression in slanDCs, which in turn enabled the cells to secrete prostaglandin (PG)-E2. Consequently, PGE2 acted as a suppressing agent, tuning down the activation level of NK cells. In summary, IL-1β limits the level of NK cell activation by inducing apoptosis and suppression as a homeostatic regulatory function.

Natural killer cells require monocytic Gr-1(+)/CD11b(+) myeloid cells to eradicate orthotopically engrafted glioma cells

Malignant gliomas are resistant to natural killer (NK) cell immune surveillance. However, the mechanisms used by these cancers to suppress antitumor NK cell activity remain poorly understood. We have recently reported on a novel mechanism of innate immune evasion characterized by the overexpression of the carbohydrate-binding protein galectin-1 by both mouse and rat malignant glioma. Here, we investigate the cytokine profile of galectin-1-deficient GL26 cells and describe the process by which these tumors are targeted by the early innate immune system in RAG1(-/-) and C57BL/6J mice. Our data reveal that galectin-1 knockdown in GL26 cells heightens their inflammatory status leading to the rapid recruitment of Gr-1(+)/CD11b(+) myeloid cells and NK1.1(+) NK cells into the brain tumor microenvironment, culminating in tumor clearance. We show that immunodepletion of Gr-1(+) myeloid cells in RAG1(-/-) mice permits the growth of galectin-1-deficient glioma despite the presence of NK cells, thus demonstrating an essential role for myeloid cells in the clearance of galectin-1-deficient glioma. Further characterization of tumor-infiltrating Gr-1(+)/CD11b(+) cells reveals that these cells also express CCR2 and Ly-6C, markers consistent with inflammatory monocytes. Our results demonstrate that Gr-1(+)/CD11b(+) myeloid cells, often referred to as myeloid-derived suppressor cells (MDSCs), are required for antitumor NK cell activity against galectin-1-deficient GL26 glioma. We conclude that glioma-derived galectin-1 represents an important factor in dictating the phenotypic behavior of monocytic Gr-1(+)/CD11b(+) myeloid cells. Galectin-1 suppression may be a valuable treatment approach for clinical glioma by promoting their innate immune-mediated recognition and clearance through the concerted effort of innate myeloid and lymphoid cell lineages.

slanDCs selectively accumulate in carcinoma-draining lymph nodes and marginate metastatic cells

Dendritic cells (DCs) initiate adaptive immune responses to cancer cells by activating naive T lymphocytes. 6-sulfo LacNAc(+) DCs (slanDCs) represent a distinct population of circulating and tissue proinflammatory DCs, whose role in cancer immune surveillance is unknown. Herein, by screening a large set of clinical samples, we demonstrate accumulation of slanDCs in metastatic tumour-draining lymph nodes (M-TDLN) from carcinoma patients. Remarkably, slanDCs are absent at the primary carcinoma site, while their selective nodal recruitment follows the arrival of cancer cells to M-TDLN. slanDCs surround metastatic carcinoma deposits in close proximity to dead cells and efficiently phagocytose tumour cells. In colon carcinoma patients, the contingent of circulating slanDCs remains intact and competent in terms of IL-12p70 and tumour necrosis factor alpha production, induction of T-cell proliferation and migratory capacity to a set of chemokines produced in M-TDLN. We conclude that activated slanDCs represent previously unrecognized players of nodal immune responses to cancer cells.

[The role of human 6-sulfo LacNAc dendritic cells (slanDCs) in autoimmunity and tumor diseases]

Dendritic cells play a central role in the regulation of immunological reactivity. The existence of functionally specialized populations of skin dendritic cells is a consequence of qualitatively different attacks on our organism. slanDCs are human inflammatory dendritic cells that are characterized by the specific expression of the carbohydrate 6-sulfo LacNAc (slan). After phenotypic maturation slanDCs are capable of producing very high amounts of proinflammatory mediators like IL-12, TNF-α, IL-1β â and IL-23. Recent data describe a potential role of slanDCs in a number of different diseases like psoriasis, lupus erythematosus but also tumor diseases and therefore open up new areas of research on their respective pathogenesis. Furthermore, as a basis of a directed therapeutic manipulation,a slanDC-specific targeting system has been developed. Future challenges of slanDC research include the elaboration of a deeper understanding of the significance of slanDCs for the regulation of adaptive and innate immune responses as well as a translation of this knowledge into therapeutic options.

Accumulation of tolerogenic human 6-sulfo LacNAc dendritic cells in renal cell carcinoma is associated with poor prognosis

Dendritic cells (DCs) essentially contribute to the induction and regulation of innate and adaptive immunity. Based on these important properties, DCs may profoundly influence tumor progression in patients. However, little is known about the role of distinct human DC subsets in primary tumors and their impact on clinical outcome. In the present study, we investigated the characteristics of human 6-sulfo LacNAc (slan) DCs in clear cell renal cell carcinoma (ccRCC). slanDCs have been shown to display various tumor-directed properties and to accumulate in tumor-draining lymph nodes from patients. When evaluating 263 ccRCC and 227 tumor-free tissue samples, we found increased frequencies of slanDCs in ccRCC tissues compared to tumor-free tissues. slanDCs were also detectable in the majority of 24 metastatic lymph nodes and 67 distant metastases from ccRCC patients. Remarkably, a higher density of slanDCs was significantly associated with a reduced progression-free, tumor-specific or overall survival of ccRCC patients. Tumor-infiltrating slanDCs displayed an immature phenotype expressing interleukin-10. ccRCC cells efficiently impaired slanDC-induced T-cell proliferation and programming as well as natural killer (NK) cell activation. In conclusion, these findings indicate that higher slanDC numbers in ccRCC tissues are associated with poor prognosis. The induction of a tolerogenic phenotype in slanDCs leading to an insufficient activation of innate and adaptive antitumor immunity may represent a novel immune escape mechanism of ccRCC. These observations may have implications for the design of therapeutic strategies that harness tumor-directed functional properties of DCs against ccRCC.

Rapid reconstitution of functionally active 6-sulfoLacNAc(+) dendritic cells (slanDCs) of donor origin following allogeneic haematopoietic stem cell transplant

The role of dendritic cells (DCs) and macrophages in allogeneic haematopoietic stem cell transplant (HSCT) is critical in determining the extent of graft-versus-host response. The goal of this study was to analyse slanDCs, a subset of human proinflammatory DCs, in haematopoietic stem cell (HSC) sources, as well as to evaluate their 1-year kinetics of reconstitution, origin and functional capacities in peripheral blood (PB) and bone marrow (BM) of patients who have undergone HSCT, and their presence in graft-versus-host disease (GVHD) tissue specimens. slanDCs were also compared to myeloid (m)DCs, plasmacytoid (p)DCs and monocytes in HSC sources and in patients' PB and BM throughout reconstitution. slanDCs accounted for all HSC sources. In patients' PB and BM, slanDCs were identified from day +21, showing median frequencies comparable to healthy donors, donor origin and kinetics of recovery similar to mDCs, pDCs, and monocytes. Under cyclosporin treatment, slanDCs displayed a normal pattern of maturation, and maintained an efficient chemotactic activity and capacity of releasing tumour necrosis factor (TNF)-α upon lipopolysaccharide (LPS) stimulation. None the less, they were almost undetectable in GVHD tissue specimens, being present only in intestinal acute GVHD samples. slanDCs reconstitute early, being donor-derived and functionally competent. The absence of slanDCs from most of the GVHD-targeted tissue specimens seems to rule out the direct participation of these cells in the majority of the local reactions characterizing GVHD.

TNFR2 and IL-12 coactivation enables slanDCs to support NK-cell function via membrane-bound TNF-α

Human blood NK cells exert strong cytotoxicity against transformed cells and produce different cytokines and chemokines with an important role in modulating immune responses. However, the nature of NK-cell function depends on NK-cell interaction with other immune cells. One type of immune cells that communicate with NK cells are 6-sulfo LacNAc DCs (slanDCs), which comprise a major subpopulation of proinflammatory human blood DCs. In this study, we investigated the molecular mechanisms by which slanDCs interact with NK cells. Our in vitro studies demonstrate that LPS-stimulated slanDCs enhance activation and function of NK cells essentially via membrane-bound TNF-α (mTNF-α). LPS stimulation upregulates expression of mTNF-α in slanDCs, and surface TNF receptor 2 (TNFR2) is upregulated on NK cells after coincubation with slanDCs. IL-12 secreted by slanDCs increases surface expression of TNFR2 in NK cells. TNFR2 signaling in NK cells leads to activation of NF-kB, a transcription factor for cytokines such as GM-CSF. GM-CSF provided by NK cells is responsible for enhancing IL-12 secretion in slanDCs. In conclusion, TNFR2 and IL-12 signaling, which support one another, enables slanDCs to enhance NK-cell function through mTNF-α, thereby regulating immune responses.

Accumulation and therapeutic modulation of 6-sulfo LacNAc(+) dendritic cells in multiple sclerosis

Objective:

To examine the potential role of 6-sulfo LacNAc⁺ (slan) dendritic cells (DCs) displaying pronounced proinflammatory properties in the pathogenesis of multiple sclerosis (MS).

Methods:

We determined the presence of slanDCs in demyelinated brain lesions and CSF samples of patients with MS. In addition, we explored the impact of methylprednisolone, interferon-β, glatiramer acetate, or natalizumab on the frequency of blood-circulating slanDCs in patients with MS. We also evaluated whether interferon-β modulates important proinflammatory capabilities of slanDCs.

Results:

SlanDCs accumulate in highly inflammatory brain lesions and are present in the majority of CSF samples of patients with MS. Short-term methylprednisolone administration reduces the percentage of slanDCs in blood of patients with MS and the proportion of tumor necrosis factor-α– or CD150-expressing slanDCs. Long-term interferon-β treatment decreases the percentage of blood-circulating slanDCs in contrast to glatiramer acetate or natalizumab. Furthermore, interferon-β inhibits the secretion of proinflammatory cytokines by slanDCs and their capacity to promote proliferation and differentiation of T cells.

Conclusion:

Accumulation of slanDCs in highly inflammatory brain lesions and their presence in CSF indicate that slanDCs may play an important role in the immunopathogenesis of MS. The reduction of blood-circulating slanDCs and the inhibition of their proinflammatory properties by methylprednisolone and interferon-β may contribute to the therapeutic efficiency of these drugs in patients with MS.

Tumoricidal activity of human dendritic cells

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Human DC subsets can exert tumoricidal activity.

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Killer DCs exploit several mechanisms for direct killing of target cells, including TRAIL and granzyme B.

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Antigen presentation and/or IFN production are important additional effector functions.

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Killer DCs are promising targets for immunotherapeutic strategies.

Dendritic cells (DCs) are a family of professional antigen-presenting cells (APCs) that are able to initiate innate and adaptive immune responses against pathogens and tumor cells. The DC family is heterogeneous and is classically divided into two main subsets, each with its unique phenotypic and functional characteristics: myeloid DCs (mDCs) and plasmacytoid DCs (pDCs). Recent results have provided intriguing evidence that both DC subsets can also function as direct cytotoxic effector cells; in particular, against cancer cells. In this review, we delve into this understudied function of human DCs and discuss why these so-called killer DCs might become important tools in future cancer immunotherapies.

TLR7/8 agonists trigger immunostimulatory properties of human 6-sulfo LacNAc dendritic cells

Imiquimod and resiquimod represent Toll-like receptor (TLR) 7 and 8 agonists, which emerged as attractive candidates for tumor therapy. To elucidate immune cells, which mainly contribute to TLR7/8-mediated antitumoral activity, we investigated the impact of imiquimod and resiquimod on native human 6-sulfo LacNAc (slan) dendritic cells (DCs). We found that both TLR7/8 agonists significantly improve the release of various proinflammatory cytokines by slanDCs and promote their tumor-directed cytotoxic activity. Furthermore, resiquimod efficiently augmented the ability of slanDCs to stimulate T cells and natural killer cells. These results indicate that imiquimod and resiquimod trigger various immunostimulatory properties of slanDCs, which may contribute to their antitumor effects.

Dendritic cells in myelodysplastic syndromes: from pathogenesis to immunotherapy

Myelodysplastic syndromes (MDS) are clonal disorders of the hematopoietic stem cell characterized by ineffective hematopoiesis leading to peripheral cytopenias. Different processes are involved in its pathogenesis, such as (epi)genetic alterations and immunological dysfunctions. The nature of immune dysregulation is markedly different between various MDS risk groups. In low-risk MDS, the immune system is in a proinflammatory state, whereas in high-risk disease, immunosuppressive features facilitate expansion of the dysplastic clone and can eventually lead to disease progression to acute myeloid leukemia. Various cell types contribute to dysregulation of immune responses in MDS. Dendritic cells (DCs) are important regulators of immunity. However, the role of DCs in MDS has yet to be elucidated. It has been suggested that impaired DC function can hamper adequate immune responses. This review focuses on the involvement of DCs in immune dysregulation in low- and high-risk MDS and the implications for DC-targeted therapies.

Reconstitution of 6-sulfo LacNAc dendritic cells after allogeneic stem-cell transplantation

BACKGROUND

Infections and acute graft-versus-host disease (GvHD) represent major complications of allogeneic stem-cell transplantation (SCT). Dendritic cells (DCs) display an extraordinary capacity to induce innate and adaptive immune responses. Therefore, they play a crucial role in the elimination of pathogens and in the pathogenesis of acute GvHD. 6-Sulfo LacNAc DCs (slanDCs) are a major subpopulation of human blood DCs with a high proinflammatory capacity. We investigated for the first time the reconstitution of slanDCs in the blood of patients after SCT and the modulation of their frequency by bacterial infection, cytomegalovirus (CMV) reactivation, and acute GvHD.

METHODS

The frequency of slanDCs, CD1c myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) in the peripheral blood was quantified by flow cytometry in 80 patients after SCT. To assess individual DC subsets, we used pregating of the HLADRLin subset and antibodies against slanDCs, blood DC antigen 1 (CD1c mDCs), and blood DC antigen 2 (pDCs).

RESULTS

SlanDCs showed the slowest reconstitution in the first month after SCT compared with CD1c mDCs and pDCs. Interestingly, in the second and third months after SCT, their percentage steadily increased, and slanDCs were the most abundant DC subset. In addition, we observed a markedly reduced frequency of slanDCs in the blood of patients with bacterial infection, CMV reactivation, or severe acute GvHD. Furthermore, slanDCs showed the most prominent reduction after steroid treatment of acute GvHD.

CONCLUSIONS

These results indicate that SCT-associated complications such as bacterial infection, CMV reactivation, and acute GvHD can significantly modulate the frequency of slanDCs.

Interleukin-15-induced CD56(+) myeloid dendritic cells combine potent tumor antigen presentation with direct tumoricidal potential

Dendritic cells (DCs) are the quintessential antigen-presenting cells of the human immune system and play a prime role in coordinating innate and adaptive immune responses, explaining the strong and still growing interest in their application for cancer immunotherapy. Much current research in the field of DC-based immunotherapy focuses on optimizing the culture conditions for in vitro DC generation in order to assure that DCs with the best possible immunogenic qualities are being used for immunotherapy. In this context, monocyte-derived DCs that are alternatively induced by interleukin-15 (IL-15 DCs) have attracted recent attention due to their superior immunostimulatory characteristics. In this study, we show that IL-15 DCs, in addition to potent tumor antigen-presenting function, possess tumoricidal potential and thus qualify for the designation of killer DCs. Notwithstanding marked expression of the natural killer (NK) cell marker CD56 on a subset of IL-15 DCs, we found no evidence of a further phenotypic overlap between IL-15 DCs and NK cells. Allostimulation and antigen presentation assays confirmed that IL-15 DCs should be regarded as bona fide myeloid DCs not only from the phenotypic but also from the functional point of view. Concerning their cytotoxic activity, we demonstrate that IL-15 DCs are able to induce apoptotic cell death of the human K562 tumor cell line, while sparing tumor antigen-specific T cells. The cytotoxicity of IL-15 DCs is predominantly mediated by granzyme B and, to a small extent, by tumor necrosis factor-α (TNF-α)-related apoptosis-inducing ligand (TRAIL) but is independent of perforin, Fas ligand and TNF-α. In conclusion, our data provide evidence of a previously unappreciated role for IL-15 in the differentiation of human monocytes towards killer DCs. The observation that IL-15 DCs have killer DC capacity lends further support to their implementation in DC-based immunotherapy protocols.

Cellular-based immunotherapies for patients with glioblastoma multiforme

Treatment of patients with glioblastoma multiforme (GBM) remains to be a challenge with a median survival of 14.6 months following diagnosis. Standard treatment options include surgery, radiation therapy, and systemic chemotherapy with temozolomide. Despite the fact that the brain constitutes an immunoprivileged site, recent observations after immunotherapies with lysate from autologous tumor cells pulsed on dendritic cells (DCs), peptides, protein, messenger RNA, and cytokines suggest an immunological and even clinical response from immunotherapies. Given this plethora of immunomodulatory therapies, this paper gives a structure overview of the state-of-the art in the field. Particular emphasis was also put on immunogenic antigens as potential targets for a more specific stimulation of the immune system against GBM.

Th-1 lymphocytes induce dendritic cell tumor killing activity by an IFN-γ-dependent mechanism

Dendritic cells (DCs) encompass a heterogeneous population of cells capable of orchestrating innate and adaptive immune responses. The ability of DCs to act as professional APCs has been the foundation for the development and use of these cells as vaccines in cancer immunotherapy. DCs are also endowed with the nonconventional property of directly killing tumor cells. The current study investigates the regulation of murine DC cytotoxic function by T lymphocytes. We provide evidence that CD4(+) Th-1, but not Th-2, Th-17 cells, or regulatory T cells, are capable of inducing DC cytotoxic function. IFN-γ was identified as the major factor responsible for Th-1-induced DC tumoricidal activity. Tumor cell killing mediated by Th-1-activated killer DCs was dependent on inducible NO synthase expression and NO production. Importantly, Th-1-activated killer DCs were capable of presenting the acquired Ags from the killed tumor cells to T lymphocytes in vitro or in vivo. These observations offer new possibilities for the application of killer DCs in cancer immunotherapy.

Cytotoxic dendritic cells generated from cancer patients

Known for years as professional APCs, dendritic cells (DCs) are also endowed with tumoricidal activity. This dual role of DC as killers and messengers may have important implications for tumor immunotherapy. However, the tumoricidal activity of DCs has mainly been investigated in animal models. Cancer cells inhibit antitumor immune responses using numerous mechanisms, including the induction of immunosuppressive/ tolerogenic DCs that have lost their ability to present Ags in an immunogenic manner. In this study, we evaluated the possibility of generating tumor killer DCs from patients with advanced-stage cancers. We demonstrate that human monocyte-derived DCs are endowed with significant cytotoxic activity against tumor cells following activation with LPS. The mechanism of DC-mediated tumor cell killing primarily involves peroxynitrites. This observed cytotoxic activity is restricted to immature DCs. Additionally, after killing, these cytotoxic DCs are able to activate tumor Ag-specific T cells. These observations may open important new perspectives for the use of autologous cytotoxic DCs in cancer immunotherapy strategies.

Immunotherapy of brain cancers: the past, the present, and future directions

Treatment of brain cancers, especially high grade gliomas (WHO stage III and IV) is slowly making progress, but not as fast as medical researchers and the patients would like. Immunotherapy offers the opportunity to allow the patient's own immune system a chance to help eliminate the cancer. Immunotherapy's strength is that it efficiently treats relatively small tumors in experimental animal models. For some patients, immunotherapy has worked for them while not showing long-term toxicity. In this paper, we will trace the history of immunotherapy for brain cancers. We will also highlight some of the possible directions that this field may be taking in the immediate future for improving this therapeutic option.

A novel modular antigen delivery system for immuno targeting of human 6-sulfo LacNAc-positive blood dendritic cells (SlanDCs)

BACKGROUND

Previously, we identified a major myeloid-derived proinflammatory subpopulation of human blood dendritic cells which we termed slanDCs (e.g. Schäkel et al. (2006) Immunity 24, 767-777). The slan epitope is an O-linked sugar modification (6-sulfo LacNAc, slan) of P-selectin glycoprotein ligand-1 (PSGL-1). As slanDCs can induce neoantigen-specific CD4+ T cells and tumor-reactive CD8+ cytotoxic T cells, they appear as promising targets for an in vivo delivery of antigens for vaccination. However, tools for delivery of antigens to slanDCs were not available until now. Moreover, it is unknown whether or not antigens delivered via the slan epitope can be taken up, properly processed and presented by slanDCs to T cells.

METHODOLOGY/PRINCIPAL FINDINGS

Single chain fragment variables were prepared from presently available decavalent monoclonal anti-slan IgM antibodies but failed to bind to slanDCs. Therefore, a novel multivalent anti-slanDC scaffold was developed which consists of two components: (i) a single chain bispecific recombinant diabody (scBsDb) that is directed on the one hand to the slan epitope and on the other hand to a novel peptide epitope tag, and (ii) modular (antigen-containing) linker peptides that are flanked at both their termini with at least one peptide epitope tag. Delivery of a Tetanus Toxin-derived antigen to slanDCs via such a scBsDb/antigen scaffold allowed us to recall autologous Tetanus-specific memory T cells.

CONCLUSIONS/SIGNIFICANCE

In summary our data show that (i) the slan epitope can be used for delivery of antigens to this class of human-specific DCs, and (ii) antigens bound to the slan epitope can be taken up by slanDCs, processed and presented to T cells. Consequently, our novel modular scaffold system may be useful for the development of human vaccines.

Dendritic cell-based immunotherapy for prostate cancer

Dendritic cells (DCs) are professional antigen-presenting cells (APCs), which display an extraordinary capacity to induce, sustain, and regulate T-cell responses providing the opportunity of DC-based cancer vaccination strategies. Thus, clinical trials enrolling prostate cancer patients were conducted, which were based on the administration of DCs loaded with tumor-associated antigens. These clinical trials revealed that DC-based immunotherapeutic strategies represent safe and feasible concepts for the induction of immunological and clinical responses in prostate cancer patients. In this context, the administration of the vaccine sipuleucel-T consisting of autologous peripheral blood mononuclear cells including APCs, which were pre-exposed in vitro to the fusion protein PA2024, resulted in a prolonged overall survival among patients with metastatic castration-resistent prostate cancer. In April 2010, sipuleucel-T was approved by the United States Food and Drug Administration for prostate cancer therapy.

Peroxynitrite-dependent killing of cancer cells and presentation of released tumor antigens by activated dendritic cells

Dendritic cells (DCs), essential for the initiation and regulation of adaptive immune responses, have been used as anticancer vaccines. DCs may also directly trigger tumor cell death. In the current study, we have investigated the tumoricidal and immunostimulatory activities of mouse bone marrow-derived DCs. Our results indicate that these cells acquire killing capabilities toward tumor cells only when activated with LPS or Pam3Cys-SK4. Using different transgenic mouse models including inducible NO synthase or GP91 knockout mice, we have further established that LPS- or Pam3Cys-SK4-activated DC killing activity involves peroxynitrites. Importantly, after killing of cancer cells, DCs are capable of engulfing dead tumor cell fragments and of presenting tumor Ags to specific T lymphocytes. Thus, upon specific stimulation, mouse bone marrow-derived DCs can directly kill tumor cells through a novel peroxynitrite-dependent mechanism and participate at virtually all levels of antitumor immune responses, which reinforces their interest in immunotherapy.

Killer dendritic cells and their potential for cancer immunotherapy

Known for years as the principal messengers of the immune system, dendritic cells (DC) represent a heterogeneous population of antigen presenting cells critically located at the nexus between innate and adaptive immunity. DC play a central role in the initiation of tumor-specific immune responses as they are endowed with the unique ability to take up, process and present tumor antigens to naïve CD4(+) or CD8(+) effector T lymphocytes. By virtue of the cytokines they produce, DC also regulate the type, strength and duration of T cell immune responses. In addition, they can participate in anti-tumoral NK and NKT cell activation and in the orchestration of humoral immunity. More recent studies have documented that besides their primary role in the induction and regulation of adaptive anti-tumoral immune responses, DC are also endowed with the capacity to directly kill cancer cells. This dual role of DC as killers and messengers may have important implications for tumor immunotherapy. First, the direct killing of malignant cells by DC may foster the release and thereby the immediate availability of specific tumor antigens for presentation to cytotoxic or helper T lymphocytes. Second, DC may participate in the effector phase of the immune response, potentially augmenting the diversity of the killing mechanisms leading to tumor elimination. This review focuses on this non-conventional cytotoxic function of DC as it relates to the promotion of cancer immunity and discusses the potential application of killer DC (KDC) in tumor immunotherapy.

Aglycosylated IgG variants expressed in bacteria that selectively bind FcgammaRI potentiate tumor cell killing by monocyte-dendritic cells

The N-linked glycan of immunoglobulin G (IgG) is indispensable for the interaction of the Fc domain with Fcgamma receptors on effector cells and the clearance of target cells via antibody dependent cell-mediated cytotoxicity (ADCC). Escherichia coli expressed, aglycosylated Fc domains bind effector FcgammaRs poorly and cannot elicit ADCC. Using a novel bacterial display/flow cytometric library screening system we isolated Fc variants that bind to FcgammaRI (CD64) with nanomolar affinity. Binding was critically dependent on amino acid substitutions (E382V, and to a lesser extent, M428I) distal to the putative FcgammaRI binding epitope within the CH3 domain. These mutations did not adversely affect its pH-dependent interaction with FcRn in vitro nor its serum persistence in vivo. Remarkably, the anti-Her2 IgG trastuzumab containing the E382V, M428I substitutions and expressed in E. coli exhibited highly selective binding to FcgammaRI but not to the other activating receptors (FcgammaRIIa, FcgammaRIIIa) nor to the inhibitory receptor, FcgammaRIIb. In contrast, the glycosylated version of trastuzumab (E382V, M428I) purified from HEK293T cells bound to all Fcgamma receptors in a manner similar to that of clinical grade trastuzumab. E. coli-purified trastuzumab (E382V, M428I), but not glycosylated trastuzumab (E382V, M428I) or clinical grade trastuzumab, was capable of potentiating the killing of Her2 overexpressing tumor cells with dendritic cells (DCs) as effectors. These results indicate that aglycosylated IgGs can be engineered to display unique FcgammaR selectivity profiles that, in turn, mediate ADCC via mechanisms that are not normally displayed by glycosylated monoclonal antibodies.

The dendritic cell-like functions of IFN-producing killer dendritic cells reside in the CD11b+ subset and are licensed by tumor cells

IFN producing killer dendritic cells (IKDC) were originally defined as CD11c(int) B220(+)NK1.1(+) (or CD49b(+)) cells that exert a potent tumoricidal activity in animals lacking B, T, and conventional natural killer effectors. MHC class II expression on tumor infiltrating IKDC prompted us to investigate their putative antigen presenting function. Here, we show that tumor cells license IKDC to acquire the properties of antigen presenting cells, i.e., expression of MHC class II and costimulatory CD86 molecules. We show that the CD11b(+) subset of IKDC are able to prime naïve CD4(+) T cells and cross-prime naïve CD8(+) T lymphocytes. Licensing of IKDC by tumor cells was mandatory for the full differentiation of T cells into polarized effectors. IKDC could engulf and process soluble Ova protein in a CD206-dependent manner. Finally, we show that CD11b(+)IKDC is selectively endowed with CTLA4Ig-inhibitable antigen presenting capacities and that targeting this subset with the detoxified adenylate cyclase toxin of Bordetella pertussis fused to antigen resulted in efficient cross-presentation of antigen by IKDC to specific TCR transgenic CD8(+)T cells in vivo. Collectively, our data indicate that upon exposure to tumor cells, IKDC subserve DC-like functions.

Dendritic cells--why can they help and hurt us

Dendritic cells (DCs) show a Janus-like functional behavior. They help us by their orchestration of numerous immune responses to defend our body against invading pathogenic micro-organisms and also induce regulatory T cells to inhibit immune reactions against autoantigens as well as diverse harmless environmental antigens. However, DCs can also be of harm to us when misguided by their microenvironment as in allergic and autoimmune diseases or when DCs are targeted and exploited by microbes and cancer cells to evade the immune defense. This huge and diverse functional repertoire of DCs requires complex decision-making processes and the integration of multiple stimulatory and inhibitory signals. Although a given DC type has an extensive functionally plasticity, DCs are heterogeneous and individual DC subtypes are differentially distributed in tissues, express distinct sets of pattern recognition receptors and differ in their capacity to program naive T cells. With the help of transgenic mouse models and selective ablation of individual DC subtypes, we are just at the beginning of understanding the DC system in its complexity. Obtaining a more detailed knowledge of the DC system in mice and men holds strong promise for the successful induction of immunity and tolerance in therapeutic trials. This review presents the recent advances in the understanding of DC biology and discusses why and how DC can help and hurt us.

CD11c identifies a subset of murine liver natural killer cells that responds to adenoviral hepatitis

The liver contains a unique repertoire of immune cells and a particular abundance of NK cells. We have found that CD11c defines a distinct subset of NK cells (NK1.1(+)CD3(-)) in the murine liver whose function was currently unknown. In naïve animals, CD11c(+) liver NK cells displayed an activated phenotype and possessed enhanced effector functions when compared with CD11c(-) liver NK cells. During the innate response to adenovirus infection, CD11c(+) NK cells were the more common IFN-gamma-producing NK cells in the liver, demonstrated enhanced lytic capability, and gained a modest degree of APC function. The mechanism of IFN-gamma production in vivo depended on TLR9 ligation as well as IL-12 and -18. Taken together, our findings demonstrate that CD11c(+) NK cells are a unique subset of NK cells in the murine liver that contribute to the defense against adenoviral hepatitis.

Dendritic cells as killers: mechanistic aspects and potential roles

Dendritic cells (DC) are professional APC endowed with the unique capacity to activate naive T cells. DC also have important effector functions during the innate immune response, such as pathogen recognition and cytokine production. In fact, DC represent the crucial link between innate and adaptive immune responses. However, DC are quite heterogeneous and various subsets endowed with specific pathogen recognition mechanisms, locations, phenotypes, and functions have been described both in rodents and in humans. A series of studies indicated that rodent as well as human DC could also mediate another important innate function, i.e., cell-mediated cytotoxicity, mostly toward tumor cells. In this article, we will review the phenotypes of these so-called killer DC, their killing mechanism, and putative implication in the immune response.

Circulating HLA-DR(+) natural killer cells have potent lytic ability and weak antigen-presenting cell function

Whether a freshly isolated immune cell can be equipped with both natural killing and antigen-presenting cell (APC) function has recently become controversial in mice. We sought to probe the existence of a candidate human cell with these properties by searching for cells in healthy subjects that co-express APC surface molecules and NK cell receptors. We have found that CD3(-)CD14(-)CD19(-) mononuclear cells of human blood, spleen, liver, and lymph nodes contain two distinct populations of cells that co-express HLA-DR (DR) and CD56. Circulating CD56(+) cells expressing high levels of DR were phenotypically and functionally similar to conventional CD56(-)dendritic cells (DC). Furthermore, we demonstrate here that a separate cohort of CD56(+) cells that express low levels of DR are NK cells that possess dual function as potent killers endowed with weak APC function.