Facultative anaerobic bacteria like E. coli can colonize solid tumors often resulting in tumor growth retardation or even clearance. Little mechanistic knowledge is available for this phenomenon which is however crucial for optimization and further implementation in the clinic. Here, we show that intravenous injections with E. coli TOP10 can induce clearance of CT26 tumors in BALB/c mice. Importantly, re-challenging mice which had cleared tumors showed that clearance was due to a specific immune reaction. Accordingly, lymphopenic mice never showed tumor clearance after infection. Depletion experiments revealed that during induction phase, CD8 1 T cells are the sole effectors responsible for tumor clearance while in the memory phase CD8 1 and CD4 1 T cells were involved. This was confirmed by adoptive transfer. CD4 1 and CD8 1 T cells could reject newly set tumors while CD8 1 T cells could even reject established tumors. Detailed analysis of adoptively transferred CD4 1 T cells during tumor challenge revealed expression of granzyme B, FasL, TNF-a and IFN-c in such T cells that might be involved in the anti-tumor activity. Our findings should pave the way for further optimization steps of this promising therapy.

The interferon (IFN) pathway plays an essential role in the innate immune response following viral infections and subsequent shaping of adaptive immunity. Infections with influenza A viruses (IAV) activate the IFN pathway after the recognition of pathogen-specific molecular patterns by respective pattern recognition receptors. The IFN regulatory factors IRF3 and IRF7 are key players in the regulation of type I and III IFN genes. In this study, we analyzed the role of IRF3 and IRF7 for the host response to IAV infections in Irf3^-/-, Irf7^-/-, and Irf3^-/-Irf7^-/- knockout mice. While the absence of IRF3 had only a moderate impact on IFN expression, deletion of IRF7 completely abolished IFNα production after infection. In contrast, lack of both IRF3 and IRF7 resulted in the absence of both IFNα and IFNβ after IAV infection. In addition, IAV infection of double knockout mice resulted in a strong increase of mortality associated with a massive influx of granulocytes in the lung and reduced activation of the adaptive immune response.

The rational design of intranasal vaccines requires an in-depth understanding of the anatomic, physicochemical and barrier properties of the nasal mucosa, as well as the molecular mechanisms governing the activation of the local innate and adaptive immune system. This would provide the critical knowledge to establish effective approaches to deliver vaccine antigens across the mucosal barrier, supporting the stimulation of a long-lasting protective response at both mucosal and systemic levels. Current developments in the area of adjuvants, nanotechnologies and mucosal immunology, together with the identification of surface receptors that can be exploited for cell targeting and manipulating their physiological properties, will become instrumental for developing a new generation of more effective intranasal vaccines.

Innate lymphoid cells (ILCs) represent diversified subsets of effector cells as well as immune regulators of mucosal immunity and are classified into group 1 ILCs, group 2 ILCs, and group 3 ILCs. Group 1 ILCs encompass natural killer (NK) cells and non-NK ILCs (ILC1s) and mediate their functionality via the rapid production of IFN-γ and TNF-α. The current knowledge of ILC1s mainly associates them to inflammatory processes. Much less is known about their regulation during infection and their capacity to interact with cells of the adaptive immune system. The present study dissected the role of ILC1s during early influenza A virus infection, thereby revealing their impact on the antiviral response. Exploiting in vitro and in vivo H1N1 infection systems, a cross-talk of ILC1s with cells of the innate and the adaptive immunity was demonstrated, which contributes to anti-influenza immunity. A novel association of ILC1 functionality and the expression of the glucocorticoid-induced TNFR-related protein (GITR) was observed, which hints toward a so far undescribed role of GITR in regulating ILC1 responsiveness. Overexpression of GITR inhibits IFN-γ production by ILC1s, whereas partial reduction of GITR expression can reverse this effect, thereby regulating ILC1 functionality. These new insights into ILC1 biology define potential intervention targets to modulate the functional properties of ILC1s, thus contributing toward the development of new immune interventions against influenza.

Among innovative adjuvants conferring a Th1-shift, RNAdjuvant is a promising candidate. This adjuvant consists of a 547-nt uncapped noncoding ssRNA containing polyU repeats that is stabilized by a cationic carrier peptide. Whereas vaccination of mice with an influenza subunit vaccine induced moderate virus-specific IgG1, vaccination together with RNAdjuvant significantly enhanced this IgG1 and additionally promoted the formation of IgG2b/c, which is indicative of Th1 responses. Furthermore, such sera neutralized influenza virus, whereas this effect was not detected upon vaccination with the subunit vaccine alone. Similarly, upon vaccination with virus-like particles displaying vesicular stomatitis virus G protein, RNAdjuvant promoted the formation of virus-specific IgG2b/c and enhanced neutralizing IgG responses to an extent that mice were protected against lethal virus infection. RNAdjuvant induced dendritic cells to upregulate activation markers and produce IFN-I. Although these effects were strictly TLR7 dependent, RNAdjuvant-mediated augmentation of vaccine responses needed concurrent TLR and RIG-I-like helicase signaling. This was indicated by the absence of the adjuvant effect in vaccinated MyD88Cardif mice, which are devoid of TLR (with the exception of TLR3) and RIG-I-like helicase signaling, whereas in vaccinated MyD88 mice the adjuvant effect was reduced. Notably, i.m. RNAdjuvant injection induced local IFN-I responses and did not induce systemic effects, implying good tolerability and a favorable safety profile for RNAdjuvant.

Cytomegalovirus (CMV) is a ubiquitous beta-herpesvirus whose reactivation from latency is a major cause of morbidity and mortality in immunocompromised hosts. Mouse CMV (MCMV) is a well-established model virus to study virus-host interactions. We showed in this study that the CD8-independent antiviral function of myeloid dendritic cells (mDC) is biologically relevant for the inhibition of MCMV replication in vivo and in vitro. In vivo ablation of CD11c ؉ DC resulted in higher viral titers and increased susceptibility to MCMV infection in the first 3 days postinfection. We developed in vitro coculture systems in which we cocultivated MCMV-infected endothelial cells or fibroblasts with T cell subsets and/or dendritic cells. H uman cytomegalovirus (HCMV) is a betaherpesvirus which establishes a lifelong latent infection in immunocompetenthosts. Latent HCMV is present in the majority of people worldwide, but the primary infection is usually asymptomatic. The primary infection is well contained by the immune cells, such as natural killer (NK) cells and T cells, which also prevent viral reactivation from latency (1, 2).Their activation depends on cross talk with dendritic cells (DC) (3, 4), and this interaction plays an important role in CMV control (5-7). The direct effect of DC on viral replication remains, however, unclear.In immunocompromised hosts, like AIDS patients or people undergoing transplantation, the virus cannot be contained, and its reactivation from latency has been associated with severe disease (8). Therefore, to develop new therapeutic approaches against CMV disease, it is exceedingly important to understand the immune mechanisms that drive the virus into latency.Murine cytomegalovirus (MCMV) is a natural pathogen of the mouse. It shows numerous analogies in latency and reactivation to the human virus, and its genome displays substantial similarity to the HCMV one (9). Therefore, MCMV is a widely used model for CMV infection and immunity (10)(11)(12).During primary infection, MCMV infects various different cell types, such as macrophages and DC but also nonhematopoietic cells, including endothelial and epithelial cells (13). On the other hand, the establishment of latency appears to be restricted to certain cell types. Latent HCMV was found in blood monocytes and in progenitor cells of the myeloid lineage (14-19), whereas liver sinusoidal endothelial cells (LSEC) were shown to be a site of MCMV latency and reactivation (20, 21), although myeloid cells might also present a latent reservoir in the mouse (22, 23).

NK cells represent a vital component of the innate immune system. The recent discoveries demonstrating that the functionality of NK cells depends on their differentiation and education status underscore their potential as targets for immune intervention.However, to exploit their full potential, a detailed understanding of the cellular interactions involved in these processes is required. In this regard, the cross-talk between NKT cells and NK cells needs to be better understood. Our results provide strong evidence for NKT cell-induced effects on key biological features of NK cells. NKT-cell activation results in the generation of highly active CD27 high NK cells with improved functionality. In this context, degranulation activity and IFNγ production were mainly detected in the educated subset. In a mCMV infection model, we also demonstrated that NKT-cell stimulation induced the generation of highly functional educated and uneducated NK cells, crucial players in viral control. Thus, our findings reveal new fundamental aspects of the NKT-NK cell axis that provide important hints for the manipulation of NK cells in clinical settings.Keywords: αGalCerMPEG r mCMV r NK-cell differentiation r NK-cell education r NKT cells Additional supporting information may be found in the online version of this article at the publisher's web-site Introduction NK cells represent a first line of defence against transformed or viral-infected cells by exerting immune regulatory and cytotoxic functions [1]. It was long believed that NK cells are a homogenous and short-lived innate lymphocyte population that retains their fixed phenotypic and functional characteristics. However, findings of a continuous NK-cell differentiation process at steadyCorrespondence: Dr. Peggy Riese e-mail: Peggy.Riese@helmholtz-hzi.de state conditions underscore their, up to now underestimated, multifunctional properties [2][3][4]. Several groups demonstrated that human and mouse NK cells represent a heterogeneous population that can be divided into different subsets with distinct functional properties [5][6][7][8]. In this context, CD27 and Mac-1 have been identified as key markers to dissect murine NK cells. CD27 high Mac-1 high NK cells display enhanced responsiveness, whereas the CD27 low Mac-1 high subset represents NK cells with a higher activation * These authors contributed equally to this work.C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2015. 45: 1794-1807 Innate immunity 1795 threshold [9,10]. The similarities between CD27 and Mac-1 expressing murine NK cells and human CD56 bright and CD56 dim NK-cell subsets enables a phenotypic and functional characterization comparable to the human system [11,12]. To ensure self-tolerance, NK-cell functionality is controlled by a process termed "education." Educated NK cells expressing inhibitory receptors binding to self-MHC molecules are more responsive to stimulation, whereas uneducated NK cells lacking self-MHC class I receptors are considered to be hypo-responsive [13][...

Cyclic di-nucleotides (CDN) are potent stimulators of innate and adaptive immune responses. Cyclic di-AMP (CDA) is a promising adjuvant that generates humoral and cellular immunity. The strong STING-dependent stimulation of type I IFN represents a key feature of CDA. However, recent studies suggested that this is dispensable for adjuvanticity. Here we demonstrate that stimulation of IFN-γ-secreting CD8+ cytotoxic T lymphocytes (CTL) is significantly decreased after vaccination in the absence of type I IFN signaling. The biological significance of this CTL response was confirmed by the stimulation of MHC class I-restricted protection against influenza virus challenge. We show here that type I IFN (and not TNF-α) is essential for CDA-mediated cross-presentation by a cathepsin independent, TAP and proteosome dependent cytosolic antigen processing pathway, which promotes effective cross-priming and further CTL induction. Our data clearly demonstrate that type I IFN signaling is critical for CDN-mediated cross-presentation.