NK dendritic cells expanded in IL-15 exhibit antitumor responses in vivo

Immunity from NK Cell Subsets Is Important for Vaccine-Mediated Protection in HPV+ Cancers

High-risk human papillomaviruses (HPVs) are associated with genital and oral cancers, and the incidence of HPV+ head and neck squamous cell cancers is fast increasing in the USA and worldwide. Survival rates for patients with locally advanced disease are poor after standard-of-care chemoradiation treatment. Identifying the antitumor host immune mediators important for treatment response and designing strategies to promote them are essential. We reported earlier that in a syngeneic immunocompetent preclinical HPV tumor mouse model, intranasal immunization with an HPV peptide therapeutic vaccine containing the combination of aGalCer and CpG-ODN adjuvants (TVAC) promoted clearance of HPV vaginal tumors via induction of a strong cytotoxic T cell response. However, TVAC was insufficient in the clearance of HPV oral tumors. To overcome this deficiency, we tested substituting aGalCer with a clinically relevant adjuvant QS21 (TVQC) and observed sustained, complete regression of over 70% of oral and 80% of vaginal HPV tumors. The TVQC-mediated protection in the oral tumor model correlated with not only strong total and HPV-antigen-specific CD8 T cells, but also natural killer dendritic cells (NKDCs), a novel subset of NK cells expressing the DC marker CD11c. Notably, we observed induction of significantly higher overall innate NK effector responses by TVQC relative to TVAC. Furthermore, in mice treated with TVQC, the frequencies of total and functional CD11c+ NK cell populations were significantly higher than the CD11c- subset, highlighting the importance of the contributions of NKDCs to the vaccine response. These results emphasize the importance of NK-mediated innate immune effector responses in total antitumor immunity to treat HPV+ cancers.

Early Differentiation of Human CD11c+NK Cells with γδ T Cell Activation Properties Is Promoted by Dialyzable Leukocyte Extracts

Reconstitution of the hematopoietic system during immune responses and immunological and neoplastic diseases or upon transplantation depends on the emergent differentiation of hematopoietic stem/progenitor cells within the bone marrow. Although in the last decade the use of dialyzable leukocyte extracts (DLE) as supportive therapy in both infectious and malignant settings has increased, its activity on the earliest stages of human hematopoietic development remains poorly understood. Here, we have examined the ability of DLE to promote replenishment of functional lymphoid lineages from CD34⁺ cells. Our findings suggest that DLE increases their differentiation toward a conspicuous CD56⁺CD16⁺CD11c⁺ NK-like cell population endowed with properties such as IFNy production, tumor cell cytotoxicity, and the capability of inducing γδ T lymphocyte proliferation. Of note, long-term coculture controlled systems showed the bystander effect of DLE-stromal cells by providing NK progenitors with signals to overproduce this cell subset. Thus, by direct effect on progenitor cells and through activation and remodeling of the supporting hematopoietic microenvironment, DLE may contribute a robust innate immune response by promoting the emerging lymphopoiesis of functional CD11c⁺ NK cells in a partially TLR-related manner. Unraveling the identity and mechanisms of the involved DLE components may be fundamental to advance the NK cell-based therapy field.

Deficient Natural Killer Dendritic Cell Responses Underlay the Induction of Theiler's Virus-Induced Autoimmunity

The initiating events in autoimmune disease remain to be completely understood, but it is thought that genetic predisposition synergizes with “environmental” factors, including viral infection, leading to disease. One elegant animal model used to study the pathogenesis of multiple sclerosis that perfectly blends genetics and environmental components in the context of virus-induced autoimmunity is Theiler’s murine encephalitis virus-induced demyelinating disease (TMEV-IDD). TMEV-infected disease-susceptible SJL/J mice develop a persistent central nervous system (CNS) infection and later develop autoimmune demyelination, while disease-resistant C57BL/6 (B6) mice rapidly clear the infection and develop no autoimmune pathology. Mice of the (B6 × SJL/J)F₁ cross between these two mouse strains are classified as intermediately susceptible. We employed this model to investigate if rapid virus clearance in B6 versus SJL/J mice was perhaps related to differences in the innate immune response in the CNS of the two strains in the first few days following intracerebral virus inoculation. Here we show that SJL/J mice lack, in addition to NK cells, a novel innate immune subset known as natural killer dendritic cells (NKDCs), which express phenotypic markers (CD11c^int NK1.1⁺) and functional activity of both NK cells and DCs. These NKDCs are activated in the periphery and migrate into the infected CNS in a very late antigen 4 (VLA-4)-dependent fashion. Most significantly, NKDCs are critical for CNS clearance of TMEV, as transfer of NKDCs purified from B6 mice into TMEV-IDD-susceptible (B6 × SJL/J)F₁ mice promotes viral clearance. Together the findings of this work show for the first time a link between NKDCs, viral infection, and CNS autoimmunity.

Viral infection is an important cofactor, along with genetic susceptibility, in the initiation of a variety of organ-specific autoimmune diseases. Thus, in-depth understanding of how virus infections trigger autoimmunity may lead to novel ways to prevent or treat these diseases. Theiler’s murine encephalitis virus-induced demyelinating disease (TMEV-IDD) serves as an important model for the human T cell-mediated autoimmune demyelinating disease multiple sclerosis. Induction of TMEV-IDD is genetically controlled as SJL/J mice develop persistent central nervous system (CNS) infection leading to chronic autoimmune demyelination, while C57BL/6 mice rapidly clear virus and are disease resistant. We determined that, as opposed to resistant B6 mice, disease-susceptible SJL/J mice lacked a unique innate immune population, the natural killer dendritic cell (NKDC), which was shown to play a critical role in early CNS virus clearance via its ability to both present virus antigen to T cells and to lyse target cells.

Cutting Edge: Induction of Inflammatory Disease by Adoptive Transfer of an Atypical NK Cell Subset

Several mouse models of systemic lupus erythematosus, including FcγRIIB-KO and TLR7tg mice, develop an expansion of an atypical NK cell subset with functional similarity to cells referred as IFN-producing killer DCs or pre-mature NKs in other systems. In this study, we show that atypical NKs purified from spleens of systemic lupus erythematosus-prone mice, and identified as NK1.1(+)CD11c(+)CD122(+)MHC-II(+), induce persistent autoimmune disease in an IFN-I- and CD40L-dependent manner when transferred to wild-type mice. A single transfer of 4 × 10(6) NK1.1(+) cells from TLR7tg into wild-type induces a 2-wk-long wave of inflammatory cytokines in the serum; a sustained increase in T cell activation and follicular helper cells for the following months; and a progressive expansion of dendritic cells, monocytes, and granulocytes. Furthermore, IL-15 deficiency, which impedes development of NK cells, ameliorates the autoimmune pathology of TLR7tg mice. These results suggest that cells of the NK lineage can develop into cytokine-producing/APCs that affect the priming and progression of systemic autoimmune disease.

IL-15 activated human peripheral blood dendritic cell kill allogeneic and xenogeneic endothelial cells via apoptosis

IL-15 is a pleotropic cytokine, which plays an important role in natural killer (NK) cell activity, T cell proliferation, and T cell cytotoxic activity. Dendritic cells (DCs) are the major antigen presenting cells in the immune system and presumed to play an important role in immune recognition of allo and xenotransplantation. We showed that IL-15 activated human peripheral blood DC is cytotoxic to human and porcine aortic endothelial cells. Unlike DCs, CD14+ monocytes show no cytotoxicity against the endothelial cells. This cytotoxic potential of IL-15 activated DC against endothelial cells is dose dependent and increases significantly upon treatment of endothelial cells with inflammatory cytokines like TNF-α or IFN-γ. The cytotoxic potential of IL-15 activated DC is associated with apoptosis of endothelial cells, as indicated by the increased Annexin V staining, caspase activation and loss of mitochondrial membrane potential. Further it was observed that DC mediated cytotoxicity against endothelial cell is mediated via granzyme B possibly secreted by the activated DCs.

Efficient xenoengraftment in severe immunodeficient NOD/Shi-scid IL2rγnull mice is attributed to a lack of CD11c+B220+CD122+ cells

Xenograft animal models using immunodeficient mice have been widely applied in medical research on various human diseases. NOD/Shi-scid-IL2rγ(null) (NOG) mice are known to show an extremely high engraftment rate of xenotransplants compared with conventional immunodeficient mice. This high engraftment rate of xenotransplants in NOG mice was substantially suppressed by the transfer of spleen cells from NOD-scid mice that were devoid of NK cells. These results indicate that cell types other than splenic NK cells present in NOD-scid mice but not in NOG mice may be involved in this suppression. To identify the cell types responsible for this effect, we transferred subpopulations of spleen cells from NOD-scid mice into NOG mice and assessed the levels of human cell engraftment after human PBMC (hPBMC) transplantation. These experiments revealed that CD11c(+)B220(+) plasmacytoid dendritic cells (pDCs) from NOD-scid mice markedly inhibited engraftment of human cells. The CD11c(+)B220(+)CD122(+) cells further fractionated from the pDCs based on the expression of CD122, which is an NK cell marker strongly inhibited during hPBMC engraftment in NOG mice. Moreover, the CD122(+) cells in the pDC fraction were morphologically distinguishable from conventional CD122(+) NK cells and showed a higher rejection efficiency. The current results suggest that CD11c(+)B220(+)CD122(+) cells play an important role in xenograft rejection, and their absence in NOG mice may be critical in supporting the successful engraftment of xenotransplants.

Role of natural killer dendritic cells in host resistance against Pseudomonas aeruginosa infection after thermal injury in mice

The contributions of dendritic cells (DCs) and natural killer dendritic cells (NKDCs) on host antibacterial innate immunities have been described. We have previously reported that mice with partial-thickness burn injuries (PT-burn mice) are resistant to burn wound infections, whereas mice with full-thickness burn injuries (FT-burn mice) are susceptible. In this study, the effect of burn stress on the appearance and properties of DCs and NKDCs was investigated in two different murine models of thermal injury. Dendritic cells isolated from PT-burn mice produced CCL3 and IL-12, whereas these soluble factors were not produced by DCs from FT-burn mice. As compared with unburned mouse controls, a large number of NKDCs were isolated from the DC preparations from PT-burn mice, whereas fewer NKDCs were detected in the DC preparations from FT-burn mice. Nonobese diabetic severe combined immunodeficiency mice inoculated with NKDCs were shown to be resistant against a lethal s.c. Pseudomonas aeruginosa infection. These results strongly suggest that NKDCs influenced by partial-thickness burn injury play a role on the resistance of PT-burn mice to P. aeruginosa s.c. infection.

Activation of porcine natural killer cells and lysis of foot-and-mouth disease virus infected cells

Natural killer (NK) cells play a vital role in innate response against viral infections and cellular transformation. In vivo modulation of their response may enhance their antiviral function. Here we describe the phenotype of porcine NK cells, test potential proinflammatory cytokines for activation of these cells and assess the capability of porcine NK cells to kill virus-infected or tumor cells in vitro. The CD2+/CD8+/CD3(-) cell compartment contained porcine NK cells, which at the resting stage were minimally cytotoxic toward foot-and-mouth disease virus (FMDV)-infected porcine cells or tumor cell lines. Direct stimulation of NK cells with proinflammatory cytokines induced efficient lysis of FMDV-infected cells with interleukin (IL)-2 or IL-15 showing the highest stimulatory capacity. Lower levels of NK cell activation were induced by IL-12, IL-18, or interferon (IFN)-alpha, however, IL-12 and IL-18 synergistically activated NK cells. Combinations of IL-15 and IL-12 or IL-15 and IL-18 did not further increase the porcine NK cell lytic capability over IL-15 alone. Natural killer cells expressed IFN-gamma regardless of the cytokine used for stimulation while expression of perforin increased modestly. The enhancement of porcine NK cell activity by proinflammatory cytokines offers a promising tool for development of antiviral approaches against virus infection.

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.

Dendritic cells as danger-recognizing biosensors

Dendritic cells (DCs) are antigen presenting cells that are characterized by a potent capacity to initiate immune responses. DCs comprise several subsets with distinct phenotypes. After sensing any danger(s) to the host via their innate immune receptors such as Toll-like receptors, DCs become mature and subsequently present antigens to CD4⁺ T cells. Since DCs possess the intrinsic capacity to polarize CD4⁺ helper cells, it is critical to understand the immunological roles of DCs for clinical applications. Here, we review the different DC subsets, their danger-sensing receptors and immunological functions. Furthermore, the cytokine reporter mouse model for studying DC activation is introduced.

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.

IFN-producing killer dendritic cells contribute to the inhibitory effect of poly I:C on the progression of murine melanoma

Toll-like receptor 3 agonist polyinosinic-polycytidilic acid (poly I:C) has been widely used as a potent adjuvant in tumor immunotherapy. In the present study, it was demonstrated that intraperitoneal injection of poly I:C could inhibit lung and liver metastasis of B16 melanoma cells in C57BL/6 mice in natural killer (NK) cells and interferon (IFN)-gamma dependent manner, leading to prolonged survival of the mice. B220 CD11c NK1.1 cells, recently defined as IFN-producing killer dendritic cells (IKDCs) were markedly increased in the spleen, lung, and liver of poly I:C-treated tumor bearing mice, compared with the control group. IFN-gamma induction by poly I:C in this unique NK cell subset indicated its critical contribution in tumor suppression in this model. Meanwhile, results of in vitro culture assay showed that poly I:C synergized with B16 cells could significantly promote IKDCs expansion in lymphocytes from different organs along with IFN-gamma production. Moreover, these ex vivo expanded IKDCs also exerted cytolytic activities against B16 cells and YAC-1 cells as conventional NK cells did. In conclusion, the findings of this study provide new insights into the role of IFN-gamma and IKDCs in the antitumor effect of poly I:C, and will possibly be helpful to explain why poly I:C may work as an adjucant to improve the antitumor effects of innate cells.

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.