Therapy-Induced Tumor Immunosurveillance Involves IFN-Producing Killer Dendritic Cells

Effect of Multiple Vaccinations with Tumor Cell-Based Vaccine with Codon-Modified GM-CSF on Tumor Growth in a Mouse Model

Ectopic expression of codon-modified granulocyte-macrophage colony-stimulating factor (cGM-CSF) in TC-1 cells (TC-1/cGM-CSF), a model cell line for human papillomavirus (HPV)-infected cervical cancer cells, increased the expression level of GM-CSF and improved the efficacy of tumor cell-based vaccines in a cervical cancer mouse model. The number of vaccine doses required to induce a long-term immune response in a cervical cancer mouse model is poorly understood. Here, we investigated one, three, and five doses of the irradiated TC-1/cGM-CSF vaccine to determine which dose was effective in inducing a greater immune response and the suppression of tumors. Our findings showed that three doses of irradiated TC-1/cGM-CSF vaccine elicited slower tumor growth rates and enhanced survival rates compared with one dose or five doses of irradiated TC-1/cGM-CSF vaccine. Consistently, mice vaccinated with three doses of irradiated TC-1/cGM-CSF vaccine exhibited stronger interferon gamma (IFN-γ) production in HPV E7-specific CD8⁺ T cells and CD4⁺ T cells. A higher percentage of natural killer cells and interferon-producing killer dendritic cells (IKDCs) appeared in the splenocytes of the mice vaccinated with three doses of irradiated TC-1/cGM-CSF vaccine compared with those of the mice vaccinated with one dose or five doses of irradiated TC-1/cGM-CSF vaccine. Our findings demonstrate that single or multiple vaccinations, such as five doses, with irradiated TC-1/cGM-CSF vaccine suppressed the immune response, whereas three doses of irradiated TC-1/cGM-CSF vaccine elicited a greater immune response and subsequent tumor suppression.

A novel recombinant protein of ephrinA1-PE38/GM-CSF activate dendritic cells vaccine in rats with glioma

Dendritic cells loaded with tumor-associated antigens can effectively stimulate the antitumor immune response of cytotoxic T lymphocytes in the body, which facilitates the development of novel and effective treatments for cancer. In this study, the adenovirus-mediated ephrinA1-PE38/GM-CSF was successfully constructed using the overlap extension method, and verified with sequencing analysis. HEK293 cells were infected with the adenovirus and the cellular expression of ephrinA1-PE38/GM-CSF was measured with an enzyme-linked immunosorbent assay. The recombinant adenovirus was then delivered into the tumor-bearing rats and the results showed that such treatment significantly reduced the volumes of gliomas and improved the survival of the transplanted rats. The results from immunohistochemistry and flow cytometry suggested that this immunomodulatory agent cause activation of dendritic cells. The findings that ephrinA1-PE38/GM-CSF had a high efficacy in the activation of the dendritic cells would facilitate the development of in vivo dendritic-cell vaccines for the treatment of gliomas in rats. Our new method of DC vaccine production induces not only a specific local antitumor immune response but also a systemic immunotherapeutic effect. In addition, this method completely circumvents the risk of contamination related to the in vitro culture of DCs, thus greatly improving the safety and feasibility of clinical application of the DC vaccines in glioma.

Plk1 inhibition causes post-mitotic DNA damage and senescence in a range of human tumor cell lines

Plk1 is a checkpoint protein whose role spans all of mitosis and includes DNA repair, and is highly conserved in eukaryotes from yeast to man. Consistent with this wide array of functions for Plk1, the cellular consequences of Plk1 disruption are diverse, spanning delays in mitotic entry, mitotic spindle abnormalities, and transient mitotic arrest leading to mitotic slippage and failures in cytokinesis. In this work, we present the in vitro and in vivo consequences of Plk1 inhibition in cancer cells using potent, selective small-molecule Plk1 inhibitors and Plk1 genetic knock-down approaches. We demonstrate for the first time that cellular senescence is the predominant outcome of Plk1 inhibition in some cancer cell lines, whereas in other cancer cell lines the dominant outcome appears to be apoptosis, as has been reported in the literature. We also demonstrate strong induction of DNA double-strand breaks in all six lines examined (as assayed by γH2AX), which occurs either during mitotic arrest or mitotic-exit, and may be linked to the downstream induction of senescence. Taken together, our findings expand the view of Plk1 inhibition, demonstrating the occurrence of a non-apoptotic outcome in some settings. Our findings are also consistent with the possibility that mitotic arrest observed as a result of Plk1 inhibition is at least partially due to the presence of unrepaired double-strand breaks in mitosis. These novel findings may lead to alternative strategies for the development of novel therapeutic agents targeting Plk1, in the selection of biomarkers, patient populations, combination partners and dosing regimens.

Noncanonical roles of the immune system in eliciting oncogene addiction

Cancer is highly complex. The magnitude of this complexity makes it highly surprising that even the brief suppression of an oncogene can sometimes result in rapid and sustained tumor regression, illustrating that cancers can be 'oncogene addicted' [1-10]. The essential implication is that oncogenes may not only fuel the initiation of tumorigenesis, but in some cases must be excessively activated to maintain a neoplastic state [11]. Oncogene suppression acutely restores normal physiological programs that effectively overrides secondary genetic events and a cancer collapses [12,13]. Oncogene addiction is the description of the dramatic and sustained regression of some cancers upon the specific inactivation of a single oncogene [1-13,14(••),15,16(••)], that can occur through tumor intrinsic [1,2,4,12], but also host immune mechanisms [17-23]. Notably, oncogene inactivation elicits a host immune response that involves specific immune effectors and cytokines that facilitate a remodeling of the tumor microenvironment including the shut down of angiogenesis and the induction of cellular senescence of tumor cells [16(••)]. Hence, immune effectors are not only critically involved in tumor prevention, initiation [17-19], and progression [20], but also appear to be essential to tumor regression upon oncogene inactivation [21,22(••),23(••)]. Understanding how the inactivation of an oncogene elicits a systemic signal in the host that prompts a deconstruction of a tumor could have important implications. The combination of oncogene-targeted therapy together with immunomodulatory therapy may be ideal for the development of both robust tumor intrinsic and immunological responses, effectively leading to sustained tumor regression.

Pattern recognition receptors of innate immunity and their application to tumor immunotherapy

Dendritic cells (DC) begin maturation in response to complex stimuli consisting of antigens and pattern molecules (PAMP) for the activation of the immune system. Immune adjuvant usually contains PAMP. Infection represents one event that is capable of inducing such a complex set of stimuli. Recently, DC were subdivided into a number of subsets with distinct cell-surface markers, with each subset displaying unique differential maturation in response to pattern molecules to induce various types of effector cells. In the present study, we review how pattern recognition molecules and adaptors in each DC subset drive immune effector cells and their effect in the stimulated DC. Although tumor cells harbor tumor-associated antigens, they usually lack PAMP. Hence, we outline the properties of exogenously-added PAMP in the modulation of raising tumor immunity. In addition, we describe the mechanism by which DC-dependent natural killer activation is triggered for the induction of antitumor immunity.

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.

[Immunological evaluation for CML and its possibility for an immunotherapy]

Chronic myelogenous leukemia (CML) is associated with the Ph1 chromosome translocation, which produces a chimeric tyrosine-specific kinase gene, the product of the fusion of the BCR gene and the ABL gene. The immune system has long been implicated in the control of CML. We found oligoclonal T cell responses in treated patients with IFN-alpha or leukemic dendritic cells. Also other groups treated chronic phase CML (CP-CML) patients with various leukemic antigen peptides, resulted in apparent immune response and clinical response. Imatinib mesylate is currently used as the first line therapy for CP-CML patients. Although it selectively targets the ABL portion of BCR-ABL protein as a reversible tyrosine kinase inhibitor, it cannot kill the leukemic stem cells of CML. To find a possibility to enhance the immunity in imatinib-treated CML patients by combining it with immunotherapy, we summarized the immune response of innate and adaptive immunity in CML. Development of such immunotherapeutic strategies would be a promising approach to treat the imatinib-treated CML-CP patients.

Immunosurveillance of lung melanoma metastasis in EBI-3-deficient mice mediated by CD8+ T cells

EBV-induced gene 3 (EBI-3) codes for a soluble type I receptor homologous to the p40 subunit of IL-12 that is expressed by APCs following activation. In this study, we assessed the role of EBI-3 in a model of lung melanoma metastasis. Intravenous injection of the B16-F10 cell line resulted in a significant reduction of lung tumor metastasis in EBI-3(-/-) recipient mice compared with wild-type mice. The immunological finding accompanying this effect was the expansion of a newly described cell subset called IFN-gamma producing killer dendritic cells associated with CD8(+) T cell responses in the lung of EBI-3(-/-) mice including IFN-gamma release and TNF-alpha-induced programmed tumor cell death. Depletion of CD8(+) T cells as well as targeting T-bet abrogated the protective effects of EBI-3 deficiency on lung melanoma metastases. Finally, adoptive transfer of EBI-3(-/-) CD8(+) T cells into tumor bearing wild-type mice inhibited lung metastasis in recipient mice. Taken together, these data demonstrate that targeting EBI-3 leads to a T-bet-mediated antitumor CD8(+) T cell responses in the lung.

Effect of Tα1 on ESCC RNA-transfected human cord blood dendritic cells induced antitumor activity of cytotoxic T lymphocytes

AIM: To investigate effect of human cord blood dendritic cells (DCs) transfected with RNA of esophageal carcinoma cells on the proliferation of T lymphocyte and on the antitumor activity of cytotoxic T lymphocytes (CTL), and immunoa-djuvant effect of Tα1 on human cord blood dendritic cells.

METHODS: The RNA of T.Tn cells were prepared by TRIzol reagent. The cord blood monocytes were cultured to produce DCs with rhSCF, rhGM-CSF and rhlL-4. The DCs were collected and transfected with tumor cell total RNA. Tα1 was added in culture system to enhance the DCs vaccine. MHC-I, MHC-II and co-stimulatory molecules, CD54, CD80 and CD86 on the surface of DCs were analyzed by FCM. The mixed lymphocyte reaction (MLR) and cytotoxicity of CTLs to T.Tn cells was assayed using MTT colorimetry.

RESULTS: Compared with pre-transfection group, expressions of MHC-I, MHC-II, CD54, CD80 and CD86 (MHC-I: 70.36 ± 6.09vs 8.17 ± 1.93; MHC-II: 72.03 ± 5.32 vs 7.64 ± 5.33; CD54: 69.36 ± 7.33 vs 2.05 ± 2.03; CD80: 67.21 ± 6.77 vs 2.33 ± 1.65; CD86: 68.85 ± 7.41 vs 6.73 ± 1.97, P < 0.01) were significantly higher in DCs transfected with RNA of esophageal carcinoma cells; T cell proliferation was markedly enhanced (10 : 1: 4.77 ± 0.79 vs 1.65 ± 0.71; 50 : 1: 3.85 ± 0.57 vs 1.56 ± 0.13; 100 : 1: 2.89 ± 0.59 vs 1.19 ± 0.21, P < 0.05); and tumor cytolytic activities of cytotoxic T lymphocyte were effectively induced (10 : 1: 27.36 ± 8.93 vs 10.35 ± 2.93; 20 : 1: 44.55 ± 2.36 vs 11.77 ± 1.03; 50 : 1: 51.08 ± 4.92 vs 12.75 ± 1.49, P < 0.05). Tα1 enhanced significantly the surface molecule expression (MHC-I: 87.88 ± 9.13 vs 70.36 ± 6.09; MHC-II: 93.16 ± 3.34 vs 72.03 ± 5.32; CD54: 91.75 ± 3.84 vs 69.36 ± 7.33; CD80: 87.27 ± 8.68 vs 67.21 ± 6.77; CD86: 89.09 ± 6.86 vs 68.85 ± 7.41, P < 0.05), stimulation of proliferation (10 : 1: 8.31 ± 1.78 vs 4.77 ± 0.79; 50 : 1: 5.97 ± 0.14 vs 3.85 ± 0.57; 100 : 1: 4.03 ± 0.13vs 2.89 ± 0.59, P < 0.05) and activity of cytotoxic T lymphocytes (10 : 1: 47.66 ± 4.12 vs 27.36 ± 8.93; 20 : 1: 56.72 ± 7.24 vs44.55 ± 2.36; 50 : 1: 76.48 ± 3.47 vs 51.08 ± 4.92, P < 0.05).

CONCLUSION: DCs from human cord blood monocytes exhibit high expression of MHC and co-stimulatory molecules and enhances T lymphocyte capability after transfection with RNA of esophageal carcinoma. The vaccine of cord blood DCs with adjuvant of Tα1 may provide an effective and specific way for immunotherapy of esophageal carcinoma.

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

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

Trans-presentation of IL-15 dictates IFN-producing killer dendritic cells effector functions

IFN-producing killer dendritic cells (IKDC) were initially described as B220(+)CD11c(+)CD3(-)NK1.1(+) tumor-infiltrating cells that mediated part of the antitumor effects of the combination therapy with imatinib mesylate and IL-2. In this study, we show their functional dependency on IL-15 during homeostasis and inflammatory processes. Trans-presentation of IL-15 by IL-15Ralpha allows dramatic expansion of IKDC in vitro and in vivo, licenses IKDC for TRAIL-dependent killing and endows IKDC with immunizing potential, all three biological attributes not shared by B220(-)NK cells. However, IL-15 down-regulates the capacity of IKDC to induce MHC class I- or II-restricted T cell activation in vitro. Trans-presentation of IL-15 by IL-15Ralpha allows IKDC to respond to TLR3 and TLR4 ligands for the production of CCL2, a chemokine that is critical for IKDC trafficking into tumor beds (as described recently). We conclude that IKDC represent a unique subset of innate effectors functionally distinguishable from conventional NK cells in their ability to promptly respond to IL-15-driven inflammatory processes.

A novel cell subset: interferon-producing killer dendritic cells

Recent reports introduce a novel cell subset of DCs with antigenic phenotypes shared by both NK cells and B cells, but without surface markers of pDCs and T cells, appearing to be a chimera of NK cells and DCs, namely interferon-producing killer dendritic cells (IKDCs). IKDCs not only secret type I and type II interferons to recognize and kill tumor cells effectively, but also express MHC-II molecules to present antigens. Thus, IKDCs are considered as important immunosurveilance cells for tumors, providing a link between innate and adaptive immunity.

T-cell-mediated and antigen-dependent differentiation of human monocyte into different dendritic cell subsets: a feedback control of Th1/Th2 responses

It is well established that human monocytes differentiate into dendritic cells (DCs) when cultured with certain cytokine cocktails, such as granulocyte-macrophage colony-stimulating factor and interleukin-4. Conversely, it is not completely established which cell population synthesizes the cytokines required for monocyte differentiation and how their secretion is regulated. We show that on specific activation T cells induce the differentiation into DCs of antigen-presenting and bystander monocytes. Monocytes exposed to cytokines released by Th1 and Th0 lymphocytes differentiate into DCs with a reduced antigen uptake and antigen presentation capacity. Moreover, these DCs show a limited capacity to induce Th1 polarization of naive T cells but are capable of priming interleukin-10-secreting T cells. Conversely, DCs derived from monocytes sensing cytokines released by Th2 lymphocytes are antigen-presenting-cell (APC) endowed with a marked Th1 polarization capacity. Monocytes are corecruited with lymphocytes in chronic inflammation sites; thus our results suggest that functionally different DCs can be generated in environments characterized by the prevalent release of Th1-, Th0-, or Th2-associated cytokines. Because the APC capacities of these DCs have opposite functional consequences, a contribution in the regulation of the ongoing immune response by monocyte-derived inflammatory DCs is envisaged.

The chromatin-remodeling enzyme BRG1 coordinates CIITA induction through many interdependent distal enhancers

The chromatin-remodeling enzyme BRG1 is critical for interferon-gamma (IFN-gamma)-mediated gene induction. Promoter-proximal elements are sufficient to mediate BRG1 dependency at some IFN-gamma targets. In contrast, we show here that at CIITA, which encodes the 'master regulator' of induction of major histocompatibility complex class II, distal elements conferred BRG1 dependency. At the uninduced locus, many sites formed BRG1-independent loops. One loop juxtaposed a far downstream element adjacent to a far upstream site. Notably, BRG1 was recruited to the latter site, which triggered the appearance of a histone 'mark' linked to activation. This subtle change was crucial, as subsequent IFN-gamma-induced recruitment of the transcription factors STAT1, IRF1 and p300, as well as histone modifications, accessibility and additional loops, showed BRG1 dependency. Like BRG1, each remote element was critical for the induction of CIITA expression. Thus, BRG1 regulates CIITA through many interdependent remote enhancers, not through the promoter alone.

The critical role of IL-15 in the antitumor effects mediated by the combination therapy imatinib and IL-2

The synergistic antitumor effects of the combination therapy imatinib mesylate (IM) and IL-2 depended upon NK1.1- expressing cells and were associated with the accumulation of CD11c(int)B220(+)NK1.1(+) IFN-producing killer dendritic cells (IKDC) into tumor beds. In this study, we show that the antitumor efficacy of the combination therapy was compromised in IL-15 and IFN-type 1R loss-of-function mice. IL-15Ralpha was required for the proliferation of IKDC during IM plus IL-2 therapy. Trans-presentation of IL-15/IL-15Ralpha activated IKDC to express CCR2 and to respond to type 1 IFN by producing CCL2. Moreover, the antitumor effects of the combination therapy correlated with a CCL2-dependent recruitment of IKDC, but not B220(-) NK cells, into tumor beds. Altogether, the IL-15-driven peripheral expansion and the CCL-2-dependent intratumoral chemoattraction of IKDC are two critical parameters dictating the antitumor efficacy of IM plus IL-2 in mice.

Interleukin-15 liver gene transfer increases the number and function of IKDCs and NK cells

The surface phenotype CD3-NK1.1+DX5+CD11c(int)B220+GR1- has been recently ascribed to a novel subset of mouse leukocytes termed interferon (IFN)-producing killer dendritic cells (IKDCs) that shares functions with natural killer (NK) cells and DCs. Interleukin-15 (IL-15) is critical for NK cells but its relationship with IKDC remained unexplored. An expression cassette encoding human IL-15 (hIL-15) has been transferred by hydrodynamic injection into the liver of mice, resulting in transient expression of the cytokine that is detectable during the first 48 h. hIL-15 hydrodynamic gene transfer resulted in an expansion of NK cells and IKDCs. Relative expansions of IKDCs were more dramatic in the IL-15 gene-transferred hepatic tissue than in the spleen. Adoptively transferred DX5+ cells comprising both NK cells and IKDCs proliferated in response to hydrodynamic injection of hIL-15, indicating that quantitative increases are at least in part the result of proliferation from already differentiated cells. Expansion is accompanied by enhanced cytolytic activity and increased expression of TRAIL and CD137 (4-1BB), without augmenting interferon-gamma production. The effects of a single hydrodynamic injection surpassed those of two intraperitoneal doses of the recombinant protein. The novel functional link between circulating IL-15 and IKDCs opens new possibilities to study the biology and applications of this minority cell subset.

The interaction between HMGB1 and TLR4 dictates the outcome of anticancer chemotherapy and radiotherapy

For the last four decades, the treatment of cancer has relied on four treatment modalities, namely surgery, radiotherapy, cytotoxic chemotherapy, and hormonotherapy. Most of these therapies are believed to directly attack and eradicate tumor cells. The emerging concept that cancer is not just a disease of a tissue or an organ but also a host disease relies on evidence of tumor-induced immunosuppression and polymorphisms in genes involved in host protection against tumors. This theory is now gaining new impetus, based on our recent data showing that optimal therapeutic effects require the immunoadjuvant effect of tumor cell death induced by cytotoxic anticancer agents. Here, we show that the release of the high mobility group box 1 protein (HMGB1) by dying tumor cells is mandatory to license host dendritic cells (DCs) to process and present tumor antigens. HMGB1 interacts with Toll-like receptor 4 (TLR4) on DCs, which are selectively involved in the cross-priming of anti-tumor T lymphocytes in vivo. A TLR4 polymorphism that affects the binding of HMGB1 to TLR4 predicts early relapse after anthracycline-based chemotherapy in breast cancer patients. This knowledge may be clinically exploited to predict the immunogenicity and hence the efficacy of chemotherapeutic regimens.

Tumor stress, cell death and the ensuing immune response

A cornucopia of physiological and pathological circumstances including anticancer chemotherapy and radiotherapy can induce cell death. However, the immunological consequences of tumor cell demise have remained largely elusive. The paradigm opposing 'apoptosis versus necrosis' as to their respective immunogenicity does not currently hold to predict long-term immunity. Moreover, the notion that tumor cells may be 'stressed' before death to be recognized by immune cells deserves to be underlined. 'Eat-me', 'danger' and 'killing' signals released by stressed tumor under the pressure of cytotoxic compounds may serve as links between the chemotherapy-elicited response of tumor cells and subsequent immune responses. This review will summarize the state-of-the-art of cancer immunity and describe how tumor cell death dictates the links between innate and acquired immunity.

CD11cloB220+ interferon-producing killer dendritic cells are activated natural killer cells

Interferon-producing killer dendritic cells (IKDCs) are a recently described subset of CD11c^loB220⁺ cells that share phenotypic and functional properties of DCs and natural killer (NK) cells (Chan, C.W., E. Crafton, H.N. Fan, J. Flook, K. Yoshimura, M. Skarica, D. Brockstedt, T.W. Dubensky, M.F. Stins, L.L. Lanier, et al. 2006. Nat. Med. 12:207–213; Taieb, J., N. Chaput, C. Menard, L. Apetoh, E. Ullrich, M. Bonmort, M. Pequignot, N. Casares, M. Terme, C. Flament, et al. 2006. Nat. Med. 12:214–219). IKDC development appears unusual in that cytokines using the interleukin (IL)-2 receptor β (IL-2Rβ) chain but not those using the common γ chain (γ_c) are necessary for their generation. By directly comparing Rag2^−/−γ_c^−/y, Rag2^−/−IL-2Rβ^−/−, Rag2^−/−IL-15^−/−, and Rag2^−/−IL-2^−/− mice, we demonstrate that IKDC development parallels NK cell development in its strict IL-15 dependence. Moreover, IKDCs uniformly express NK-specific Ncr-1 transcripts (encoding NKp46), whereas NKp46⁺ cells are absent in Ncr1^gfp/+γ_c^−/y mice. Distinguishing features of IKDCs (CD11c^loB220⁺MHC-II⁺) were carefully examined on developing NK cells in the bone marrow and on peripheral NK cells. As B220 expression was heterogeneous, defining B220^lo versus B220^hi NK1.1⁺ NK cells could be considered as arbitrary, and few phenotypic differences were noted between NK1.1⁺ NK cells bearing different levels of B220. CD11c expression did not correlate with B220 or major histocompatibility complex (MHC) class II (MHC-II) expression, and most MHC-II⁺ NK1.1⁺ cells did not express B220 and were thus not IKDCs. Finally, CD11c, MHC-II, and B220 levels were up-regulated on NK1.1⁺ cells upon activation in vitro or in vivo in a proliferation-dependent fashion. Our data suggest that the majority of CD11c^loB220⁺ “IKDC-like” cells represent activated NK cells.

Interferon-γ is produced by another player of innate immune responses: The interferon-producing killer dendritic cell (IKDC)

Interferon-gamma is a key cytokine in tumor immunosurveillance. The recently described interferon-producing killer dendritic cell (IKDC), can be distinguished from other innate effectors by its ability to kill a large variety of tumor cells and to produce high amounts of interferon-gamma after encountering tumors in the absence of exogenous cytokines. The cytotoxic activity of IKDC was unraveled during an efficient immunotherapy combining c-kit tyrosine kinase inhibitors and interleukin-2, and is mediated through tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and interferon type IIR.