Markus P. Radsak

Sorafenib, but not sunitinib, affects function of dendritic cells and induction of primary immune responses

The tyrosine kinase inhibitors sorafenib and sunitinib are approved for the treatment of patients with malignant diseases. To analyze the possible use of these compounds in combination with immunotherapeutic approaches, we analyzed the effects of both inhibitors on the immunostimulatory capacity of human dendritic cells (DCs) and the induction of primary immune responses in vivo. Sorafenib, but not sunitinib, inhibits function of DCs, characterized by reduced secretion of cytokines and expression of CD1a, major histocompatibility complex, and costimulatory molecules in response to TLR ligands as well as by their impaired ability to migrate and stimulate T-cell responses. These inhibitory effects are mediated by inhibition of PI3 and MAP kinases and NFkappaB signaling. In contrast, sorafenib had no influence on the phenotype and proliferation of T cells. To analyze the effects of both TKIs on cytotoxic T-cell induction in vivo, C57BL/6 mice were pretreated with sorafenib or sunitinib and immunized with OVA(257-264) peptide. Sorafenib, but not sunitinib, application significantly reduced the induction of antigen-specific T cells. Numbers of regulatory T cells were reduced in peripheral blood mononuclear cells from mice treated with sunitinib. These results indicate that sunitinib, but not sorafenib, is suitable for combination with immunotherapeutic approaches for treatment of cancer patients.

Neutrophils: Between host defence, immune modulation, and tissue injury.

Neutrophils, the most abundant human immune cells, are rapidly recruited to sites of infection, where they fulfill their life-saving antimicrobial functions. While traditionally regarded as short-lived phagocytes, recent findings on long-term survival, neutrophil extracellular trap (NET) formation, heterogeneity and plasticity, suppressive functions, and tissue injury have expanded our understanding of their diverse role in infection and inflammation. This review summarises our current understanding of neutrophils in host-pathogen interactions and disease involvement, illustrating the versatility and plasticity of the neutrophil, moving between host defence, immune modulation, and tissue damage.

Aspergillus fumigatus antigens activate innate immune cells via toll-like receptors 2 and 4

Invasive aspergillosis (IA) is a leading cause of mortality in haematological patients. Appropriate activation of the innate immune system is crucial for the successful clearance of IA. Therefore, we studied the Aspergillus fumigatus‐mediated activation of human granulocytes and monocyte‐derived immature dendritic cells (DCs), as well as murine bone marrow‐derived DCs (BMDCs) from wild type, toll‐like receptor (TLR)4‐deficient, TLR2 knockout, and TLR2/TLR4 double deficient mice. Aspergillus fumigatus antigens induced the activation and maturation of immature DCs as characterized by CD83 expression, upregulation of major histocompatibility complex and co‐stimulatory molecules. Moreover, fungal antigens enhanced the phagocytosis and production of interleukin (IL)‐8 in granulocytes. The release of IL‐12 by BMDCs in response to A. fumigatus antigens was dependent on the expression of TLR2, whereas the release of IL‐6 was dependent on the expression of functional TLR4 molecules. The protein precipitate of A. fumigatus supernatant provided strong stimulation of DCs and granulocytes, indicating that a factor secreted by A. fumigatus might activate innate immune cells. In conclusion, A. fumigatus antigens induced the activation of DCs and granulocytes. Our results indicated that this activation was mediated via TLR2 and TLR4. Future studies are needed to assess the clinical impact of these findings in patients at high risk for IA.

Triggering Receptor Expressed on Myeloid Cells-1 in Neutrophil Inflammatory Responses: Differential Regulation of Activation and Survival

Polymorphonuclear neutrophils (PMN) are crucial in the innate host defense by their ability to rapidly accumulate in inflamed tissues and clear a site of infection from microbial pathogens by their potent effector mechanisms. The triggering receptor expressed on myeloid cells (TREM)-1 is a recently described activating receptor on PMN with an important role in inflammation. However, the effects of TREM-1 stimulation on a cellular level remain to be further defined. To characterize TREM-1-mediated activation of human PMN, we evaluated the effect of receptor ligation on PMN effector functions. Activation via TREM-1 induces immediate degranulation of neutrophilic granules resulting in the release of IL-8, respiratory burst, and phagocytosis. TREM-1 ligation synergizes with the activation by the Toll-like receptors (TLR) ligands LPS, Pam3Cys, and R-848. In contrast, no synergy between TREM-1- and TLR-mediated stimulation was observed concerning PMN survival, whereas TLR-mediated stimuli protect PMN from apoptosis, concurrent TREM-1 activation neutralizes these anti-apoptotic effects. These results give a new perspective for the regulation of neutrophil inflammatory responses emphasizing the importance of TREM-1 in innate immunity.

Cutting Edge: Priming of CTL by Transcutaneous Peptide Immunization with Imiquimod

CTL are important in combating cancer and viruses. Therefore, triggering the complete potential of CTL effector functions by new vaccination strategies will not only improve prophylaxis of tumor or virus-related diseases, but also open opportunities for effective therapeutic immunizations. Using transcutaneous immunization, we show that epicutaneous (e.c.)4 application of an ointment containing a CTL epitope and the TLR7 ligand imiquimod is highly effective in activating T cells in mice using TCR-transgenic CTL or in wild-type mice. Transcutaneous immunization-activated CTL mount a full-blown immune response against the target epitope characterized by proliferation, cytolytic activity, and the production of IFN-γ that is completely restricted to the epitope used for vaccination. Our results obtained by simple e.c. application of an ointment, without further skin irritating procedures, provide the basis for the development of new, easy to use vaccines against cancer or virus-associated diseases.

Toll-like receptor-dependent activation of several human blood cell types by protamine-condensed mRNA

We reported that RNA condensed on protamine is protected from RNase‐mediated degradation and can be used for vaccination. Here, we show that such complexes are also danger signals that activate mouse cells through a MyD88‐dependent pathway. Moreover, mRNA‐protamine complexes stimulate human blood cells. They strongly activate DC and monocytes, leading to TNF‐α and IFN‐α secretion. In addition, protamine‐RNA complexes directly activate B cells, NK cells and granulocytes. The detailed analysis of the activated cell types, the study of the cytokines released from PBMC cultured with protamine‐RNA complexes and recently published results suggest that TLR‐7 and TLR‐8 may be involved in the recognition of protamine‐stabilized RNA. Our data indicate that protamine‐stabilized RNA, which may be similar to RNA condensed in the nucleocapsids of RNA viruses, is a strong danger signal. Thus, similarly to plasmid DNA, protamine‐RNA combines antigen production and non‐specific immunostimulation. The studies presented here explain the capacity of protamine‐RNA to act as a vaccine, and pave the way towards the development of safe and efficient mRNA‐based immunotherapies.

Polymorphonuclear neutrophils as accessory cells for T-cell activation: major histocompatibility complex class II restricted antigen-dependent induction of T-cell proliferation

Polymophonuclear cells (PMN) of healthy donors do not express major histocompatibility complex (MHC) class II antigens or the T‐cell costimulatory molecules CD80 or CD86. Expression of these receptors, however, is seen in patients with chronic inflammatory diseases. We now report that, by culturing PMN of healthy donors with autologous serum, interferon‐γ (IFN‐γ) and granulocyte–macrophage colony‐stimulating factor (GM‐CSF), de novo synthesis of MHC class II, CD80 and CD86 could be induced. MHC class II‐positive PMN acquired the capacity to present staphylococcus enterotoxin to peripheral T cells, apparent as induction of interleukin‐2 (IL‐2) synthesis and proliferation of the T cells. Moreover, the PMN also processed tetanus toxoid (TT) and induced proliferation of TT‐specific T cells in a MHC class II‐restricted manner. Taken together, these data indicate that PMN can be activated to function as accessory cells for T‐cell activation.

Interaction of TLR2 and TLR4 Ligands with the N-terminal Domain of Gp96 Amplifies Innate and Adaptive Immune Responses

Activation of dendritic cells by ligands for Toll-like receptors (TLR) is a crucial event in the initiation of innate and adaptive immune responses. Several classes of TLR ligands have been identified that interact with distinct members of the TLR-family. TLR4 ligands include lipopolysaccharide derived from different Gram-negative bacteria and viral proteins. Recent reports have demonstrated the TLR-mediated activation of dendritic cells by heat shock proteins (HSPs). However, doubts were raised as to what extent this effect was due to lipopolysaccharide contaminations of the HSP preparations. We re-examined this phenomenon using Gp96 or its N-terminal domain, nominally endotoxin-free (<0.5 enzyme units/mg). As described previously, innate immune cells are activated by Gp96 at high concentrations (≥50 μg/ml) but not at lower concentrations. However, preincubation of low amounts of Gp96 with TLR2 and TLR4 ligands at concentrations unable to activate dendritic cells by themselves results in the production of high levels of proinflammatory cytokines, up-regulation of activation markers, and amplification of T cell activation. Our results provide significant new insights into the mechanism of HSP-mediated dendritic cell activation and present a new function of HSPs in the amplification of dendritic cell activation by bacterial products and induction of adaptive immune responses.

Cancer immunoediting by GITR (glucocorticoid-induced TNF-related protein) ligand in humans: NK cell/tumor cell interactions

Glucocorticoid‐induced TNF‐related protein (GITR) has been shown to stimulate T cell‐mediated antitumor immunity in mice. However, the functional relevance of GITR and its ligand (GITRL) for non‐T cells has yet to be fully explored. In addition, recent evidence suggests that GITR plays different roles in mice and humans. We studied the role of GITR‐GITRL interaction in human tumor immunology and report for the first time that primary gastrointestinal cancers and tumor cell lines of different histological origin express substantial levels of GITRL. Signaling through GITRL down‐regulated the expression of the immunostimulatory molecules CD40 and CD54 and the adhesion molecule EpCAM, and induced production of the immunosuppressive cytokine TGF‐β by tumor cells. On NK cells, GITR is constitutively expressed and up‐regulated following activation. Blocking GITR‐GITRL interaction in cocultures of tumor cells and NK cells substantially increased cytotoxicity and IFN‐γ production of NK cells demonstrating that constitutive expression of GITRL by tumor cells diminishes NK cell antitumor immunity. GITRL‐Ig fusion protein or cell surface‐expressed GITRL did not induce apoptosis in NK cells, but diminished nuclear localized c‐Rel and RelB, indicating that GITR might negatively modulate NK cell NF‐κB activity. Taken together, our data indicate that tumor‐expressed GITRL mediates immunosubversion in humans.—Baltz, K. M., Krusch, M., Bringmann, A., Brossart, P., Mayer, F., Kloss, M., Baessler, T., Kumbier, I., Peterfi, A., Kupka, S., Kroeber, S., Menzel, D., Radsak, M. P., Rammensee, H.‐G., Salih, H. R. Cancer immu‐noediting by GITR (glucocorticoid‐induced TNF‐related protein) ligand in humans: NK cell/tumor cell interactions. FASEB J. 21, 2442–2454 (2007)

Interleukin 17 Drives Vascular Inflammation, Endothelial Dysfunction, and Arterial Hypertension in Psoriasis-Like Skin Disease

Objective— Interleukin (IL)-17A is regarded as an important cytokine to drive psoriasis, an inflammatory skin disease marked by increased cardiovascular mortality. We aimed to test the hypothesis that overproduction of IL-17A in the skin leading to dermal inflammation may systemically cause vascular dysfunction in psoriasis-like skin disease. Approach and Results— Conditional overexpression of IL-17A in keratinocytes caused severe psoriasis-like skin inflammation in mice (K14-IL-17Aind/+ mice), associated with increased reactive oxygen species formation and circulating CD11b+ inflammatory leukocytes in blood, with endothelial dysfunction, increased systolic blood pressure, left ventricular hypertrophy, and reduced survival compared with controls. In K14-IL-17Aind/+ mice, immunohistochemistry and flow cytometry revealed increased vascular production of the nitric oxide/superoxide reaction product peroxynitrite and infiltration of the vasculature with myeloperoxidase+CD11b+GR1+F4/80− cells accompanied by increased expression of the inducible nitric oxide synthase and the nicotinamide dinucleotide phosphate (NADPH) oxidase, nox2. Neutrophil depletion by anti-GR-1 antibody injections reduced oxidative stress in blood and vessels. Neutralization of tumor necrosis factor-&agr; and IL-6 (both downstream of IL-17A) reduced skin lesions, attenuated oxidative stress in heart and blood, and partially improved endothelial dysfunction in K14-IL-17Aind/+ mice. Conclusions— Dermal overexpression of IL-17A induces systemic endothelial dysfunction, vascular oxidative stress, arterial hypertension, and increases mortality mainly driven by myeloperoxidase+CD11b+GR1+F4/80− inflammatory cells. Depletion of the GR-1+ immune cells or neutralization of IL-17A downstream cytokines by biologicals attenuates the vascular phenotype in K14-IL-17Aind/+ mice.