Mechanisms of mouse spleen dendritic cell function in the generation of influenza-specific, cytolytic T lymphocytes

Dynamic metabolic reprogramming in dendritic cells: An early response to influenza infection that is essential for effector function

Infection with the influenza virus triggers an innate immune response that initiates the adaptive response to halt viral replication and spread. However, the metabolic response fueling the molecular mechanisms underlying changes in innate immune cell homeostasis remain undefined. Although influenza increases parasitized cell metabolism, it does not productively replicate in dendritic cells. To dissect these mechanisms, we compared the metabolism of dendritic cells to that of those infected with active and inactive influenza A virus and those treated with toll-like receptor agonists. Using quantitative mass spectrometry, pulse chase substrate utilization assays and metabolic flux measurements, we found global metabolic changes in dendritic cells 17 hours post infection, including significant changes in carbon commitment via glycolysis and glutaminolysis, as well as mitochondrial respiration. Influenza infection of dendritic cells led to a metabolic phenotype distinct from that induced by TLR agonists, with significant resilience in terms of metabolic plasticity. We identified c-Myc as one transcription factor modulating this response. Restriction of c-Myc activity or mitochondrial substrates significantly changed the immune functions of dendritic cells, such as reducing motility and T cell activation. Transcriptome analysis of inflammatory dendritic cells isolated following influenza infection showed similar metabolic reprogramming occurs in vivo. Thus, early in the infection process, dendritic cells respond with global metabolic restructuring, that is present in inflammatory lung dendritic cells after infection, and this is important for effector function. These findings suggest metabolic switching in dendritic cells plays a vital role in initiating the immune response to influenza infection.

Dendritic cells are critical in mounting an effective immune response to influenza infection by initiating the immune response to influenza and activating the adaptive response to mediate viral clearance and manifest immune memory for protection against subsequent infections. We found dendritic cells undergo a profound metabolic shift after infection. They alter the concentration and location of hundreds of proteins, including c-Myc, facilitating a shift to a highly glycolytic phenotype that is also flexible in terms of fueling respiration. Nonetheless, we found limiting access to specific metabolic pathways or substrates diminished key immune functions. We previously described an immediate, fixed hypermetabolic state in infected respiratory epithelial cells. Here we present data indicating the metabolic response of dendritic cells is increased yet flexible, distinct from what we previously showed for epithelial cells. Additionally, we demonstrate dendritic cells tailor their metabolic response to the pathogen or TLR stimulus. This metabolic reprogramming occurs rapidly in vitro and is sustained in inflammatory dendritic cells in vivo for at least 9 days following influenza infection. These studies introduce the possibility of modulating the immune response to viral infection using customized metabolic therapy to enhance or diminish the function of specific cells.

Surprisingly Effective Priming of CD8+ T Cells by Heat-Inactivated Vaccinia Virus Virions

Robust priming of CD8+ T cells by viruses is considered to require infection and de novo expression of viral antigens. A corollary of this is that inactivated viruses are thought of as being inevitably poor vaccines for eliciting these responses. In contrast to this dogma, we found that some antigens present in vaccinia virus (VACV) virions prime strong CD8+ T cell responses when the virus was rendered noninfectious by heat. More surprisingly, in some cases these responses were similar in magnitude to those primed by infectious virus administered at an equivalent dose. Next, we tested whether this was a special property of particular antigens and their epitopes and found that foreign epitopes tagged onto three different VACV virion proteins were able to elicit CD8+ T cell responses irrespective of whether the virus was viable or heat killed. Further, the polyfunctionality and cytotoxic ability of the CD8+ T cells primed by these VACVs was equivalent irrespective of whether they were administered to mice as inactivated or live viruses. Finally, we used these VACVs in prime-boost combinations of inactivated and live virus and found that priming with dead virus before a live booster was the most immunogenic regime. We conclude that VACV virions can be efficient vectors for targeting antigens to dendritic cells for effective priming of CD8+ T cells, even when rendered noninfectious and speculate that this might also be the case for other viruses.IMPORTANCE The design of viral vectored vaccines is often considered to require a trade-off between efficacy and safety. This is especially the case for vaccines that aim to induce killer (CD8+) T cells, where there is a well-established dogma that links infection in vaccinated individuals with effective induction of immunity. However, we found that some proteins of vaccinia virus generate strong CD8+ T cell responses even when the virus preparation was inactivated by heat prior to administration as a vaccine. We took advantage of this finding by engineering a new vaccine vector virus that could be used as an inactivated vaccine. These results suggest that vaccinia virus may be a more versatile vaccine vector than previously appreciated and that in some instances safety can be prioritized by the complete elimination of viral replication without a proportional loss of immunogenicity.

Hemagglutinin Stability Regulates H1N1 Influenza Virus Replication and Pathogenicity in Mice by Modulating Type I Interferon Responses in Dendritic Cells

Hemagglutinin (HA) stability, or the pH at which HA is activated to cause membrane fusion, has been associated with the replication, pathogenicity, transmissibility, and interspecies adaptation of influenza A viruses. Here, we investigated the mechanisms by which a destabilizing HA mutation, Y17H (activation pH, 6.0), attenuates virus replication and pathogenicity in DBA/2 mice compared to wild-type (WT) virus (activation pH, 5.5). The extracellular lung pH was measured to be near neutral (pH 6.9 to 7.5). WT and Y17H viruses had similar environmental stability at pH 7.0; thus, extracellular inactivation was unlikely to attenuate the Y17H virus. The Y17H virus had accelerated replication kinetics in MDCK, A549, and RAW 264.7 cells when inoculated at a multiplicity of infection (MOI) of 3 PFU/cell. The destabilizing mutation also increased early infectivity and type I interferon (IFN) responses in mouse bone marrow-derived dendritic cells (DCs). In contrast, the HA-Y17H mutation reduced virus replication in murine airway murine nasal epithelial cell and murine tracheal epithelial cell cultures and attenuated virus replication, virus spread, the severity of infection, and cellular infiltration in the lungs of mice. Normalizing virus infection and weight loss in mice by inoculating them with Y17H virus at a dose 500-fold higher than that of WT virus revealed that the destabilized mutant virus triggered the upregulation of more host genes and increased type I IFN responses and cytokine expression in DBA/2 mouse lungs. Overall, HA destabilization decreased virulence in mice by boosting early infection in DCs, resulting in the greater activation of antiviral responses, including the type I IFN response. These studies reveal that HA stability may regulate pathogenicity by modulating IFN responses.IMPORTANCE Diverse influenza A viruses circulate in wild aquatic birds, occasionally infecting farm animals. Rarely, an avian- or swine-origin influenza virus adapts to humans and starts a pandemic. Seasonal and many universal influenza vaccines target the HA surface protein, which is a key component of pandemic influenza viruses. Understanding the HA properties needed for replication and pathogenicity in mammals may guide response efforts to control influenza. Some antiviral drugs and broadly reactive influenza vaccines that target the HA protein have suffered resistance due to destabilizing HA mutations that do not compromise replicative fitness in cell culture. Here, we show that despite not compromising fitness in standard cell cultures, a destabilizing H1N1 HA stalk mutation greatly diminishes viral replication and pathogenicity in vivo by modulating type I IFN responses. This encourages targeting the HA stalk with antiviral drugs and vaccines as well as reevaluating previous candidates that were susceptible to destabilizing resistance mutations.

Intranasal Administration of Whole Inactivated Influenza Virus Vaccine as a Promising Influenza Vaccine Candidate

The effect of the current influenza vaccine, an inactivated virus vaccine administered by subcutaneous/intramuscular injection, is limited to reducing the morbidity and mortality associated with seasonal influenza outbreaks. Intranasal vaccination, by contrast, mimics natural infection and induces not only systemic IgG antibodies but also local secretory IgA (S-IgA) antibodies found on the surface of the mucosal epithelium in the upper respiratory tract. S-IgA antibodies are highly effective at preventing virus infection. Although the live attenuated influenza vaccine (LAIV) administered intranasally can induce local antibodies, this vaccine is restricted to healthy populations aged 2-49 years because of safety concerns associated with using live viruses in a vaccine. Instead of LAIV, an intranasal vaccine made with inactivated virus could be applied to high-risk populations, including infants and elderly adults. Normally, a mucosal adjuvant would be required to enhance the effect of intranasal vaccination with an inactivated influenza vaccine. However, we found that intranasal administration of a concentrated, whole inactivated influenza virus vaccine without any mucosal adjuvant was enough to induce local neutralizing S-IgA antibodies in the nasal epithelium of healthy individuals with some immunological memory for seasonal influenza viruses. This intranasal vaccine is a novel candidate that could improve on the current injectable vaccine or the LAIV for the prevention of seasonal influenza epidemics.

Dendritic Cells in Oncolytic Virus-Based Anti-Cancer Therapy

Dendritic cells (DCs) are specialized antigen-presenting cells that have a notable role in the initiation and regulation of innate and adaptive immune responses. In the context of cancer, appropriately activated DCs can induce anti-tumor immunity by activating innate immune cells and tumor-specific lymphocytes that target cancer cells. However, the tumor microenvironment (TME) imposes different mechanisms that facilitate the impairment of DC functions, such as inefficient antigen presentation or polarization into immunosuppressive DCs. These tumor-associated DCs thus fail to initiate tumor-specific immunity, and indirectly support tumor progression. Hence, there is increasing interest in identifying interventions that can overturn DC impairment within the TME. Many reports thus far have studied oncolytic viruses (OVs), viruses that preferentially target and kill cancer cells, for their capacity to enhance DC-mediated anti-tumor effects. Herein, we describe the general characteristics of DCs, focusing on their role in innate and adaptive immunity in the context of the TME. We also examine how DC-OV interaction affects DC recruitment, OV delivery, and anti-tumor immunity activation. Understanding these roles of DCs in the TME and OV infection is critical in devising strategies to further harness the anti-tumor effects of both DCs and OVs, ultimately enhancing the efficacy of OV-based oncotherapy.

Single-Dose CpG Immunization Protects Against a Heterosubtypic Challenge and Generates Antigen-Specific Memory T Cells

Despite extensive research, influenza A virus (IAV) remains a major cause of morbidity, mortality, and healthcare expenditure. Emerging pandemics from highly pathogenic IAV strains, such as H5N1 and pandemic H1N1, highlight the need for universal, cross-protective vaccines. Current vaccine formulations generate strain-specific neutralizing antibodies primarily against the outer coat proteins, hemagglutinin and neuraminidase. In contrast to these highly mutable proteins, internal proteins of IAV are more conserved and are a favorable target for developing vaccines that induce strong T cell responses in addition to humoral immunity. Here, we found that intranasal administration with a single dose of CpG and inactivated x31 (H3N2) reduced viral titers and partially protected mice from a heterosubtypic challenge with a lethal dose of PR8 (H1N1). Early after immunization, vaccinated mice showed increased innate immune activation with high levels of MHCII and CD86 expression on dendritic cells in both draining lymph nodes and lungs. Three days after immunization, CD4 and CD8 cells in the lung upregulated CD69, suggesting that activated lymphocytes are present at the site of vaccine administration. The ensuing effector Th1 responses were capable of producing multiple cytokines and were present at least 30 days after immunization. Furthermore, functional memory responses were observed, as antigen-specific IFN-γ⁺ and GrB⁺ cells were detected early after lethal infection. Together, this work provides evidence for using pattern recognition receptor agonists as a mucosal vaccine platform for inducing robust T cell responses capable of protecting against heterologous IAV challenges.

Comparative analysis of cytotoxic T lymphocyte response induced by dendritic cells pulsed with recombinant adeno-associated virus carrying α-fetoprotein gene or cancer cell lysate

Hepatocellular carcinoma (HCC) is one of the most common and difficult to treat types of cancer worldwide. Antigen‑targeted immunotherapy has the potential to be a novel and effective adjuvant for use in HCC. In the present study, recombinant adeno‑associated virus carrying the α‑fetoprotein gene (rAAV/AFP) and cancer cell lysates were used to pulse antigen‑presenting dendritic cells (DCs) in order to stimulate a cytotoxic T lymphocyte (CTL) response against HCC. rAAV/AFP‑pulsed and cancer cell lysate‑pulsed DCs resulted in a mature DC phenotype with high expression of major histocompatibility complex (MHC) class I, MHC class II, CD80, CD83 and CD86 molecules. However, rAAV/AFP‑pulsed DCs exhibited superiority over cancer cell lysate‑pulsed DCs in terms of stimulating proliferation of T cells, activating T cells to secret interferon‑γ (IFN‑γ) and inducing an AFP‑specific MHC class I‑restricted CTL response. The current data suggest that pulsing of DCs using rAAV/AFP is more effective than the cancer cell lysate‑pulsing technique, and that this technique may be used for the development of immunotherapy in AFP‑positive HCC.

Dendritic cell-based tumor vaccinations in epithelial ovarian cancer: a systematic review

After decades of extensive research, epithelial ovarian cancer still remains a lethal disease. Multiple new studies have reported that the immune system plays a critical role in the growth and spread of ovarian carcinoma. This review summarizes the development of dendritic cell (DC) vaccinations specific for ovarian cancer. So far, DC-based vaccines have induced effective antitumor responses in animal models, but only limited results from human clinical trials are available. Although DC-based immunotherapy has proven to be clinically safe and efficient at inducing tumor-specific immune responses, its clear role in the therapy of ovarian cancer still needs to be clarified. The relatively disappointing low-response rates in early clinical trials point to the need for the development of more effective and personalized DC-based anticancer vaccines. This article reviews the basic mechanisms, limitations and future directions of DC-based anti-ovarian cancer vaccine development.

Measuring the activity of cytolytic lymphocytes

The protocols in this unit describe how to measure the activity of the two most common types of lymphocytes that have cytolytic activity: cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. Measurement of CTL activity requires priming of cells, which can be performed either in vivo or in vitro. Priming leads to a population of differentiated, antigen-specific CTL. Protocols in which CTL are primed in vivo and in vitro are included in this unit. In contrast to CTL, the cytolytic activity of NK cells can be measured in the absence of antigen priming. In all of these protocols, single-cell suspensions of effector and target cells are prepared separately. The target cells are labeled with (51)Cr, and then the effector and target cells are co-cultured for several hours. The amount of target cell lysis is determined by measuring the amount of (51)Cr released into the culture medium. For all of the protocols, the effector cells are derived from mouse spleen. The target cells are either spleen cells from mice of a different MHC haplotype, virus-infected cells, tumor cells, or cultured cell lines. These protocols provide a methodological framework that can be adapted for measuring the activity of cytolytic lymphocytes in a variety of experimental paradigms.

Dendritic cells and influenza A virus infection

Influenza A virus (IAV) is a dangerous virus equipped with the potential to evoke widespread pandemic disease. The 2009 H1N1 pandemic highlights the urgency for developing effective therapeutics against IAV infection. Vaccination is a major weapon to combat IAV and efforts to improve current regimes are critically important. Here, we will review the role of dendritic cells (DCs), a pivotal cell type in the initiation of robust IAV immunity. The complexity of DC subset heterogeneity in the respiratory tract and lymph node that drains the IAV infected lung will be discussed, together with the varied and in some cases, conflicting contributions of individual DC populations to presenting IAV associated antigen to T cells.

Abortive replication of influenza virus in mouse dendritic cells

The interaction between influenza virus and dendritic cells (DCs) remains poorly defined and controversial. Here we show that influenza virus replication in mouse bone marrow-derived DCs is abortive, despite viral genome transcription and replication occurring for each gene segment and viral hemagglutinin and nucleoprotein, at least, being produced. Electron microscopy reveals that virus assembly, rather than release of virus from the cell surface, is defective.

Enforced viral replication activates adaptive immunity and is essential for the control of a cytopathic virus

The innate immune system limits viral replication via type I interferon and also induces the presentation of viral antigens to cells of the adaptive immune response. Using infection of mice with vesicular stomatitis virus, we analyzed how the innate immune system inhibits viral propagation but still allows the presentation of antigen to cells of the adaptive immune response. We found that expression of the gene encoding the inhibitory protein Usp18 in metallophilic macrophages led to lower type I interferon responsiveness, thereby allowing locally restricted replication of virus. This was essential for the induction of adaptive antiviral immune responses and, therefore, for preventing the fatal outcome of infection. In conclusion, we found that enforced viral replication in marginal zone macrophages was an immunological mechanism that ensured the production of sufficient antigen for effective activation of the adaptive immune response.

Innate immunity in allergic disease

The innate immune system consists of multiple cell types that express germline-encoded pattern recognition receptors that recognize pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs). Allergens are frequently found in forms and mixtures that contain PAMPs and DAMPs. The innate immune system is interposed between the external environment and the internal acquired immune system. It is also an integral part of the airways, gut, and skin. These tissues face continuous exposure to allergens, PAMPs, and DAMPs. Interaction of allergens with the innate immune system normally results in immune tolerance but, in the case of allergic disease, this interaction induces recurring and/or chronic inflammation as well as the loss of immunologic tolerance. Upon activation by allergens, the innate immune response commits the acquired immune response to a variety of outcomes mediated by distinct T-cell subsets, such as T-helper 2, regulatory T, or T-helper 17 cells. New studies highlighted in this review underscore the close relationship between allergens, the innate immune system, and the acquired immune system that promotes homeostasis versus allergic disease.

Major histocompatibility complex class II expression and hemagglutinin subtype influence the infectivity of type A influenza virus for respiratory dendritic cells

Dendritic cells (DC) play a key role in antiviral immunity, functioning both as innate effector cells in early phases of the immune response and subsequently as antigen-presenting cells that activate the adaptive immune response. In the murine respiratory tract, there are several respiratory dendritic cell (RDC) subsets, including CD103(+) DC, CD11b(hi) DC, monocyte/macrophage DC, and plasmacytoid DC. However, little is known about the interaction between these tissue-resident RDC and viruses that are encountered during natural infection in the respiratory tract. Here, we show both in vitro and in vivo that the susceptibility of murine RDC to infection with type A influenza virus varies with the level of MHC class II expression by RDC and with the virus strain. Both CD103(+) and CD11b(hi) RDC, which express the highest basal level of major histocompatibility complex (MHC) class II, are highly susceptible to infection by type A influenza virus. However, efficient infection is restricted to type A influenza virus strains of the H2N2 subtype. Furthermore, enhanced infectivity by viruses of the H2N2 subtype is linked to expression of the I-E MHC class II locus product. These results suggest a potential novel role for MHC class II molecules in influenza virus infection and pathogenesis in the respiratory tract.

Dendritic Cells in Innate and Adaptive Immune Responses against Influenza Virus

Dendritic cells (DC) are major players in both innate and adaptive immune responses against influenza virus. These immune responses, as well as the important interface between the innate and adaptive systems, are orchestrated by specialized subsets of DC, including conventional steady-state DC, migratory DC and plasmacytoid DC. The characteristics and efficacy of the responses are dependent on the relative activity of these DC subsets, rendering DC crucial for the development of both naïve and memory immune responses. However, due to their critical role, DC also contribute to the immunopathological processes observed during acute influenza, such as that caused by the pathogenic H5N1 viruses. Therein, the role of different DC subsets in the induction of interferon type I, pro-inflammatory cytokine and chemokine responses is important for the outcome of interaction between the virus and host immune defences. The present review will present current knowledge on this area, relating to the importance of DC activity for the induction of efficacious humoral and cell-mediated immune responses. This will include the main viral elements associated with the triggering or inhibition of DC activation. Finally, the current knowledge on understanding how differences in various vaccines influence the manner of immune defence induction will be presented.

Innate immune control and regulation of influenza virus infections

Adaptive immune responses are critical for the control and clearance of influenza A virus (IAV) infection. However, in recent years, it has become increasingly apparent that innate immune cells, including natural killer cells, alveolar macrophages (aMphi), and dendritic cells (DC) are essential following IAV infection in the direct control of viral replication or in the induction and regulation of virus-specific adaptive immune responses. This review will discuss the role of these innate immune cells following IAV infection, with a particular focus on DC and their ability to induce and regulate the adaptive IAV-specific immune response.

Differential response of respiratory dendritic cell subsets to influenza virus infection

Dendritic cells (DC) are believed to play an important role in the initiation of innate and adaptive immune responses to infection, including respiratory tract infections, where respiratory DC (RDC) perform this role. In this report, we examined the susceptibilities of isolated murine RDC to influenza virus infection in vitro and the effect of the multiplicity of infection (MOI) on costimulatory ligand upregulation and inflammatory cytokine/chemokine production after infection. We found that the efficiency of influenza virus infection of RDC increased with increasing MOIs. Furthermore, distinct subpopulations of RDC differed in their susceptibilities to influenza virus infection and in the magnitude/tempo of costimulatory ligand expression. Additional characterization of the CD11c-positive (CD11c(+)) RDC revealed that the identifiable subsets of RDC differed in susceptibility to infection, with CD11c(+) CD103(+) DC exhibiting the greatest susceptibility, CD11c(+) CD11b(hi) DC exhibiting intermediate susceptibility, and CD11c(+) B220(+) plasmacytoid DC (pDC) exhibiting the least susceptibility to infection. A companion analysis of the in vivo susceptibilities of these RDC subsets to influenza virus revealed a corresponding infection pattern. The three RDC subsets displayed different patterns of cytokine/chemokine production in response to influenza virus infection in vitro: pDC were the predominant producers of most cytokines examined, while CD103(+) DC and CD11b(hi) DC produced elevated levels of the murine chemokine CXCL1 (KC), interleukin 12p40, and RANTES in response to influenza virus infection. Our results indicate that RDC are targets of influenza virus infection and that distinct RDC subsets differ in their susceptibilities and responses to infection.

Respiratory dendritic cells: mediators of tolerance and immunity

The respiratory tract is under constant bombardment from both innocuous and pathogenic material. The decision of how to respond to these challenges is mediated by a specialized set of antigen presenting cells within the lungs called dendritic cells (DC). Proper respiratory homeostasis requires that these respiratory DC (rDC) utilize both the local lung inflammatory environment as well as recognition of pathogen-specific patterns to determine whether to maintain homeostasis by either driving tolerance or immunity to the inhaled material. This review will focus on rDC and highlight how rDC regulate tolerance and immunity.

The threat of avian influenza A (H5N1). Part IV: Development of vaccines

Among emerging and re-emerging infectious diseases, influenza constitutes one of the major threats to mankind. In this review series epidemiologic, virologic and pathologic concerns raised by infections of humans with avian influenza virus A/H5N1 are discussed. This fourth part focuses on vaccine development. Several phase I clinical studies with vaccines against H5 viruses have demonstrated limited efficacy compared to seasonal influenza vaccines. To induce protective immunity two immunisations with increased amounts of H5N1 vaccine were required. Novel vaccination strategies that are egg- and adjuvant-independent, broadly cross-reactive and long-lasting are highly desirable.

Tregs and rethinking cancer immunotherapy

Tumors express antigens that should induce immune-mediated rejection, but spontaneous rejection of established tumors is rare. Recent work demonstrates that one reason for the lack of tumor rejection is that tumors actively defeat host immunity. This concept forces us to rethink current approaches to harnessing potent, specific host immunity to battle cancer, most of which are based on the paradigm that inducing more antitumor immune cells alone is therapeutic. However, as I discuss in this Personal Perspective, a newer paradigm predicts that reducing tumor-driven immune suppression will be clinically beneficial. CD4+CD25+ Tregs are one mechanism of tumor-driven immune evasion that provide prototypical targets for testing novel anticancer treatment strategies within the newer paradigm.

Indirect regulation of CD4 T-cell responses by tumor necrosis factor receptors in an acute viral infection

Despite the well-recognized importance of CD4 T-cell help in the induction of antibody production and cytotoxic-T-lymphocyte responses, the regulation of CD4 T-cell responses is not well understood. Using mice deficient for TNF receptor I (TNFR I) and/or TNFR II, we show that TNFR I and TNFR II play redundant roles in down regulating the expansion of CD4 T cells during an acute infection of mice with lymphocytic choriomeningitis virus (LCMV). Adoptive transfer experiments using T-cell-receptor transgenic CD4 T cells and studies with mixed bone marrow chimeras indicated that indirect effects and not direct effects on T cells mediated the suppressive function of TNF on CD4 T-cell expansion during the primary response. Further studies to characterize the indirect effects of TNF suggested a role for TNFRs in LCMV-induced deletion of CD11c(hi) dendritic cells in the spleen, which might be a mechanism to limit the duration of antigenic stimulation and CD4 T-cell expansion. Consequent to enhanced primary expansion, there was a substantial increase in the number of LCMV-specific memory CD4 T cells in the spleens of mice deficient for both TNFR I and TNFR II. In summary, our findings suggest that TNFRs down regulate CD4 T-cell responses during an acute LCMV infection by a non-T-cell autonomous mechanism.

Intradermal Vaccination of Dendritic Cell–Derived Exosomes Is Superior to a Subcutaneous One in the Induction of Antitumor Immunity

Because dendritic cell (DC)-derived exosomes (EXO) harbor many important DC molecules involved in inducing immune responses, EXO-based vaccines have been extensively used to induce antitumor immunity in different animal tumor models. However, it is not clear which route of EXO administration can induce more efficient antitumor immune responses. In this study, we compared the antitumor immunity derived from EXO vaccine by way of the two common administration routes, the subcutaneous (s.c.) and the intradermal (i.d.) administrations. Our data showed that the i.d. EXO administration resulted in more EXO-absorbed DC migrating into the T-cell areas of draining lymph nodes than the s.c. administration. Interestingly, the i.d. EXO administration also resulted in an enhanced ovalbumin (OVA)-specific CD8(+) T-cell proliferation and CD8(+) CTL effector responses in vivo, compared to the s.c. administration. Similarly, compared to the s.c. vaccination, the i.d. vaccination induced stronger antitumor immunity in the animal tumor model. Therefore, the i.d. EXO vaccination is superior to the s.c. one and should be considered when EXO-based vaccine is designed.

Immunologic roles of hyaluronan

Hyaluronan (HA), a large glycosaminoglycan composed of D-N-acetylglucosamine and D-glucuronic acid, is expressed in virtually all tissues and has long been considered to serve as a structural component or filling material in the tissue interstitium (Filler Theory). This idea was revised with the discovery of HA-binding proteins that introduced the concept that HA may also serve as an adhesive substrate for cellular trafficking (Adhesion Theory). Most recently, it has been shown that HA fragments can deliver maturational signals to dendritic cells (DCs) and high molecular weight HA polymers can deliver costimulatory signals to T-cells (Signaling Theory). Thus, HA may represent an important component of the immune system. Recently, we have evaluated the impact of HA on Langerhans cell (LC) maturation and migration using a novel peptide inhibitor of HA function, termed Pep-1 (GAHWQFNALTVR). As skin-specific members of the DC family, LCs are crucial for the initiation of cutaneous immune responses. Local injections of Pep-1 prevented hapten-induced LC migration from the epidermis, providing the first experimental evidence that HA facilitates their emigration. Moreover, Pep-1 also significantly inhibited the hapten-induced maturation of LCs in vivo as assessed by cell morphology, costimulatory molecule expression, and their ability to induce proliferation of allogeneic T-cells. HA therefore has dual functionality to facilitate LC migration and maturation, the two critical events for the initiation of adaptive immune responses. Finally, we have observed that DC-dependent, antigen-specific T-cell proliferation and cytokine secretion is blocked by Pep-1. These results have revealed a previously unrecognized role for HA in antigen presentation. Thus, far from an inert structural biopolymer, HA represents a multifunctional carbohydrate mediator of immune processes.

Infection of mature dendritic cells with herpes simplex virus type 1 dramatically reduces lymphoid chemokine-mediated migration

Herpes simplex virus type 1 (HSV-1) is able to establish latency in infected individuals. In order to characterize potential new immune-escape mechanisms, mature dendritic cells (DCs) were infected with HSV-1 and total cellular RNA was isolated from infected and mock-infected populations at different time points. RNA profiling on Affymetrix Human Genome U133A arrays demonstrated a dramatic downregulation of the migration-mediating surface molecules CCR7 and CXCR4, an observation that was further confirmed by RT-PCR and fluorescence-activated cell sorting analyses. Furthermore, migration assays revealed that, upon infection of mature DCs, CCR7- and CXCR4-mediated migration towards the corresponding CCL19 and CXCL12 chemokine gradients was strongly reduced. It is noteworthy that the infection of immature DCs with HSV-1 prior to maturation led to a failure of CCR7 and CXCR4 upregulation during DC maturation and, as a consequence, also induced a block in their migratory capacity. Additional migration assays with a Δvhs mutant virus lacking the virion host shutoff (vhs) gene, which is known to degrade cellular mRNAs, suggested a vhs-independent mechanism. These results indicate that HSV-1-infected mature DCs are limited in their capacity to migrate to secondary lymphoid organs, the areas of antigen presentation and T-cell stimulation, thus inhibiting an antiviral immune response. This represents a novel, previously unrecognized mechanism for HSV-1 to escape the human immune system.

Dendritic cells might be one of key factors for eliciting antitumor effect by chemoimmunotherapy in vivo

In this study, we demonstrated that chemoimmunotherapy using S-1, a novel oral fluoropyrimidine anticancer drug, combined with lentinan (LNT), a beta (1 --> 3) glucan, was effective in vivo, and we clarified the augmentation of the function of dendritic cells (DCs) in vivo and in vitro. The survival period of Colon-26-bearing mice treated with S-1 + LNT was significantly more prolonged than that of mice treated with S-1 alone (P < 0.05). On the other hand, LNT did not prolong the survival period when combined with S-1 in Colon-26-bearing athymic mice. The frequency of CD86+ DCs infiltrated into Colon-26 was increased in mice treated with S-1 + LNT, and splenic DCs harvested from mice treated with S-1 + LNT showed more potent T-cell proliferation activity than that of DCs from mice treated with S-1 alone (P < 0.05). Furthermore, the activity of cytotoxic T lymphocytes (CTLs) in splenocytes of S-1 + LNT-treated mice was specific and more potent than that of CTLs from mice treated with S-1 alone (P < 0.05). These results suggest that modulation of specific immunity with LNT has a significant role in enhanced antitumor effects through the modification of DC function. We demonstrated that DCs might play an important role in chemotherapy, and the combination therapy of S-1 and LNT presents a promising chemoimmunotherapy, which might lead to better survival for cancer patients.

Expression of tissue-specific autoantigens in the hematopoietic cells leads to activation-induced cell death of autoreactive T cells in the secondary lymphoid organs

Many tissue-specific antigens are expressed in specialized cells called peripheral antigen-expressing cells (PAE) in the thymus and can induce central tolerance. While thymic medullary epithelial cells are the prototypic PAE that express peripheral antigens via an aire-dependent mechanism, some studies also describe bone marrow (BM)-derived dendritic cells (DC) and macrophages as PAE in both the thymus and secondary lymphoid organs. However, the role of these cells in development of tolerance to tissue-specific antigens has not been elucidated. Here we use BM radiation chimeric mice to study the existence of hematopoietic PAE and their contribution to tolerance to tissue-specific antigens. Our results reveal that BM-derived PAE exist in both central and secondary lymphoid organs and that the expression of peripheral antigens in the BM-derived cells does not correlate with aire expression. Using double-transgenic mice expressing TCR specific for a model antigen expressed under the control of a prostate-specific promoter, we show that expression of self antigen in PAE of non-hematopoietic origin is both necessary and sufficient to induce clonal deletion. Surprisingly, while BM-derived PAE fail to induce clonal deletion, they do cause the activation-induced cell death of autoreactive cells in the secondary lymphoid organs. Thus, BM-derived PAE have a distinct function in the maintenance of tolerance to tissue-specific antigens.

Fewer CTL, not enhanced NK cells, are sufficient for viral clearance from the lungs of immunocompromised mice

Activation of the aryl hydrocarbon receptor (AhR) causes numerous defects in anti-viral immunity, including suppressed CTL generation and impaired host resistance. However, despite a reduced CTL response, mice that survive infection clear the virus. Therefore, we examined the contribution of NK cells and pro-inflammatory cytokines to viral clearance in influenza virus-infected mice exposed to TCDD, the most potent AhR agonist. Infection caused transient increases in pulmonary TNFalpha, IL-1, and IFNalpha/beta levels, but neither the kinetics nor magnitude of this response was affected by AhR activation. No IL-18 was detected at any time point examined. Exposure to TCDD enhanced NK cell numbers in the lung but did not affect their IFNgamma production. Furthermore, depletion of NK cells did not alter anti-viral cytolytic activity. In contrast, removal of CD8+ T cells ablated virus-specific cytolytic activity. These results demonstrate that the pulmonary CTL response to influenza virus is robust and few CTL are necessary for viral clearance.

Differential requirements for CTL generation by novel immunostimulants: APC tropism, use of the TAP-independent processing pathway, and dependency on CD80/CD86 costimulation

A major drawback of subunit vaccines is their inability to generate cytolytic T lymphocytes (CTL), a deficit attributed to segregation of the class I and class II antigen-processing pathways. We sought to understand processes involved in CTL induction by three proprietary adjuvants: Tomatine, PROVAX, and a synthesized glycolipid (Glc-N-(8/16), Glycolipid). We used in vivo models to investigate antigen uptake, macrophage involvement, TAP-independent processing, and costimulatory molecule dependencies. Glycolipid required splenic and lymph node macrophages, whereas Tomatine generated CTL independently of either macrophage population. In contrast, PROVAX showed partial macrophage requirements. Immunized TAP knockout mice revealed that ovalbumin (OVA)-Tomatine and OVA-PROVAX, but not OVA-Glycolipid, generate class I-peptide complexes. All three immunostimulants also elicited CD86-dependent TH1 cytokine responses.

Dendritic cell vaccination and viral infection--animal models

Dendritic cells (DCs) play a pivotal role in the initiation and maintenance of immune responses against viruses and other microbial pathogens. Adoptively transferred, in vitro manipulated DCs presenting antigen derived from different viruses have been shown to elicit cytotoxic T cell (CTL) and T helper (Th) cell responses and to induce protective antiviral immunity. Furthermore, DC-based adoptive immunotherapies have the potential to specifically (re)activate antiviral immunity in chronic viral diseases such as HIV or hepatitis virus infections. Cellular dendritic cell vaccines, however, are not suitable for large-scale prophylactic immunization. Strategies for vaccine development should therefore aim at the specific delivery of microbial antigens to DCs in situ. Furthermore, appropriate mobilization and activation of DCs by the vaccine is important for the generation of optimal antimicrobial immune responses. Here, we discuss recent data on induction of antiviral immunity with various DC-vaccination approaches and outline future directions for the development of specific antigen targeting to DCs.

Examining the relationship between impaired host resistance and altered immune function in mice treated with TCDD

Exposure to TCDD suppresses the immune response to numerous antigens, including bacterial and viral pathogens. Although we administer a non-lethal infection with influenza A virus, we often observe significant mortality in TCDD-treated animals. With the goal of identifying which TCDD-induced defects impair host resistance, we conducted a dose response study to examine whether alteration of particular immunological endpoints could be correlated with mortality. C57Bl/6 mice were treated with vehicle control, or 1, 2.5, 5, 7.5 or 10 microg/kg TCDD 1 day prior to intranasal (i.n.) infection with influenza virus. Survival was monitored for 9 days, when remaining mice were sacrificed and multiple endpoints evaluated. Lymphocyte migration to the lung and the production of virus-specific IgG2a, IgG1, and IgG2b antibodies were significantly diminished, even at the lower doses. IgA was enhanced in all groups treated with TCDD. In contrast, T cell expansion in the lymph node, and the production of IFNgamma and IL-12 were relatively resistant to suppression. Treatment with TCDD also enhanced pulmonary neutrophilia in infected mice. These results suggest that decreased antibody production and hyperinflammation may contribute to the death of TCDD-treated mice, and underscore the importance of evaluating numerous endpoints before concluding that a chemical is or is not immunotoxic.

Accelerated migration of respiratory dendritic cells to the regional lymph nodes is limited to the early phase of pulmonary infection

Respiratory dendritic cells (RDC) are believed to play a central role in the induction of adaptive immune responses to pulmonary infection. Herein we examine the basal migration of RDC from the lungs to secondary lymphoid tissues and their enhanced maturation/migration after pulmonary infection/inflammation. We demonstrate that the accelerated migration of RDC to the draining peribronchial lymph nodes occurs only during the first 24 hr after pulmonary virus infection. RDC are refractory to further migration thereafter in spite of ongoing virus replication and pulmonary inflammation. We further demonstrate that induction of this RDC refractory state suppresses additional RDC mobilization to subsequent pulmonary virus infection and results in concomitant suppression of an antiviral pulmonary CD8(+) T cell response.

NOD/SCID/gamma(c)(null) mouse: an excellent recipient mouse model for engraftment of human cells

To establish a more appropriate animal recipient for xenotransplantation, NOD/SCID/gamma(c)(null) mice double homozygous for the severe combined immunodeficiency (SCID) mutation and interleukin-2Rgamma (IL-2Rgamma) allelic mutation (gamma(c)(null)) were generated by 8 backcross matings of C57BL/6J-gamma(c)(null) mice and NOD/Shi-scid mice. When human CD34+ cells from umbilical cord blood were transplanted into this strain, the engraftment rate in the peripheral circulation, spleen, and bone marrow were significantly higher than that in NOD/Shi-scid mice treated with anti-asialo GM1 antibody or in the beta2-microglobulin-deficient NOD/LtSz-scid (NOD/SCID/beta2m(null)) mice, which were as completely defective in NK cell activity as NOD/SCID/gamma(c)(null) mice. The same high engraftment rate of human mature cells was observed in ascites when peripheral blood mononuclear cells were intraperitoneally transferred. In addition to the high engraftment rate, multilineage cell differentiation was also observed. Further, even 1 x 10(2) CD34+ cells could grow and differentiate in this strain. These results suggest that NOD/SCID/gamma(c)(null) mice were superior animal recipients for xenotransplantation and were especially valuable for human stem cell assay. To elucidate the mechanisms involved in the superior engraftment rate in NOD/SCID/gamma(c)(null) mice, cytokine production of spleen cells stimulated with Listeria monocytogenes antigens was compared among these 3 strains of mice. The interferon-gamma production from dendritic cells from the NOD/SCID/gamma(c)(null) mouse spleen was significantly suppressed in comparison with findings in 2 other strains of mice. It is suggested that multiple immunological dysfunctions, including cytokine production capability, in addition to functional incompetence of T, B, and NK cells, may lead to the high engraftment levels of xenograft in NOD/SCID/gamma(c)(null) mice.

Antigens derived from melanocyte differentiation proteins: self-tolerance, autoimmunity, and use for cancer immunotherapy

A large set of peptide antigens presented by class I major histocompatibility complex (MHC) molecules on human and murine melanomas and recognized by CD8+ T cells have been defined. These peptides represent attractive candidates for the development of therapeutic and/or prophylactic approaches to treat this cancer. However, the majority of the peptides that are presented by multiple tumors and recognized by T cells from multiple patients arise from proteins that are also expressed in normal melanocytes. It is expected that immune responses to such peptides will be compromised by self-tolerance or, alternatively, that stimulation of effective immune responses will be accompanied by autoimmune vitiligo. In this review, we describe a preclinical model to evaluate these issues and recent data to suggest that tolerance can be overcome to generate effective antitumor responses. This model also allows the rapid and systematic examination of parameters for the effective use of synthetic peptide vaccines.

Uncoupling of virus-induced inflammation and anti-viral immunity in the brain parenchyma

Non-neuroadapted influenza virus confined to the brain parenchyma does not induce antigen-specific immunity. Nevertheless, infection in this site upregulated major histocompatibility complex (MHC) class I and MHC class II expression and recruited lymphocytes to a perivascular compartment. T cells recovered from the brain had an activated/memory phenotype but did not respond to viral antigens. In contrast, T cells recovered from the brain after infection in a lateral cerebral ventricle, which is immunogenic, showed virus-specific responses. As with infectious virus, influenza virus-infected dendritic cells elicited virus-specific immunity when inoculated into the cerebrospinal fluid but not when inoculated into the brain parenchyma. Thus, inflammation and dendritic cell function were both uncoupled from immune priming in the microenvironment of the brain parenchyma and neither was sufficient to overcome immunological privilege.

Cancer/testis antigens: structural and immunobiological properties

Characterization of tumor-associated antigens recognized by cytotoxic T lymphocytes which has evolved during recent years opens new possibilities for specific anti-cancer immunotherapy. Among different groups of tumor-associated antigens, cancer/testis (CT) antigens (expressed in many tumors and among normal tissues only in testes) represent the most perspective antigens for immunotherapy because of their broad tumor-specific expression. More than 50 CT antigens have been described so far and, for many of them, epitopes recognized by T lymphocytes have been identified. The most studied group of CT antigens is the MAGE proteins, which form the so-called MAGE superfamily, together with some MAGE-like proteins that have a different distribution than classical CT antigens. The MAGE superfamily includes five families: MAGE-A, MAGE-B, MAGE-C, MAGE-D, and necdin. Comparison of the structure of members of MAGE superfamily points to the existence of a domain organization of these proteins. The central, core domain (second domain) is highly conservative. The first domain is homologous among MAGE family members with a CT expression, but unique for each member of the MAGE-D and necdin families. In addition to the homology of the central domain, the third domain is also homologous among all members of MAGE superfamily, but to a much lesser extent. The MAGE-D proteins contain an additional, fourth domain, which in the case of MAGE-D3 coincides with trophinin, a separate molecule described previously as an adhesion molecule that participates in embryo implantation. The structural classification of the members of MAGE superfamily might help in the future to understand the biological function of MAGE proteins. One important property of the CT antigens is the up-regulation of their expression by DNA demethylating agents, indicating a possible mechanism for their re-expression in tumors. One of the implications of this particular property could be that a combination of immunotherapy targeting CT antigens with chemotherapy inducing up-regulation of CT antigens might result in more efficient tumor eradication.

Preferential infection of immature dendritic cells and B cells by mouse mammary tumor virus

Until now it was thought that the retrovirus mouse mammary tumor virus preferentially infects B cells, which thereafter proliferate and differentiate due to superantigen-mediated T cell help. We describe in this study that dendritic cells are infectable at levels comparable to B cells in the first days after virus injection. Moreover, IgM knockout mice have chronically deleted superantigen-reactive T cells after MMTV injection, indicating that superantigen presentation by dendritic cells is sufficient for T cell deletion. In both subsets initially only few cells were infected, but there was an exponential increase in numbers of infected B cells due to superantigen-mediated T cell help, explaining that at the peak of the response infection is almost exclusively found in B cells. The level of infection in vivo was below 1 in 1000 dendritic cells or B cells. Infection levels in freshly isolated dendritic cells from spleen, Langerhans cells from skin, or bone marrow-derived dendritic cells were compared in an in vitro infection assay. Immature dendritic cells such as Langerhans cells or bone marrow-derived dendritic cells were infected 10- to 30-fold more efficiently than mature splenic dendritic cells. Bone marrow-derived dendritic cells carrying an endogenous mouse mammary tumor virus superantigen were highly efficient at inducing a superantigen response in vivo. These results highlight the importance of professional APC and efficient T cell priming for the establishment of a persistent infection by mouse mammary tumor virus.

Efficient generation of cytotoxic T lymphocytes against cervical cancer cells by adeno-associated virus/human papillomavirus type 16 E7 antigen gene transduction into dendritic cells

Adeno-associated virus (AAV) is able to efficiently deliver a cytokine gene into dendritic cells (DC). Improvements in T cell priming by DC might be effected by the delivery of antigen genes into DC, resulting in continuous protein expression, as most proteins have short half-lives. In this study, a recombinant AAV vector containing the human papillomavirus (HPV)-16 E7 gene was used to pulse/infect DC and compared to the pulsing of DC by the lipofection of bacterially produced E7 protein. Pulsing of DC with AAV/antigen (Ag) gene was found to be superior to pulsing with protein in six different assay systems: (1) the level of antigen transfer into DC as determined by intracellular staining; (2) the level of MHC class I-restricted killing in cytotoxic T lymphocyte (CTL) assays; (3) the level of IFN-gamma expression; (4) the level of DC-T cell priming clusters generated; (5) the level of CD80 and CD83 expression on DC; and (6) in the resulting CD8:CD4 ratio. Finally, AAV/Ag gene pulsing resulted in strong CTL activity after only 7 days of priming. These data suggest that AAV vectors may offer advantages over the commonly used protein-pulsing technique and that AAV vectors may be useful for the stimulation of CTL activity and adoptive immunotherapy protocols.

Rapid induction of cytotoxic T-cell response against cervical cancer cells by human papillomavirus type 16 E6 antigen gene delivery into human dendritic cells by an adeno-associated virus vector

We have shown that the pulsing of dendritic cells (DCs) with human papillomavirus type 16 (HPV-16) antigen proteins by lipofection stimulates class I-restricted cytotoxic T lymphocyte (CTL) response against primary cervical cancer cells. Also, we have shown that adeno-associated virus (AAV) was able to effectively deliver a cytokine gene into DCs. It has been our hypothesis that the delivery of antigen genes into DCs, resulting in endogenous and continuous antigen protein expression, may result in an improvement in T-cell priming by DCs. Here, DCs are pulsed (infected) with an AAV vector containing the HPV-16 E6 gene. After infection, transduced E6 gene mRNA expression and vector chromosomal integration could be identified in infected DCs. Furthermore, priming rosettes formed at early times when the AAV/E6 vector was used. Most importantly, AAV/E6 vector pulsing of DCs induced, after only 7 days of priming, a strong CTL response against primary cervical cancer cell lines, compared to bacterial E6 protein lipofection. Killing was significantly blocked by the addition of anti-MHC class I antibodies. Fluorescence-activated cell sorter (FACS) analysis of resulting primed cell populations revealed higher levels of CD8+ T cells by AAV-based pulsing, with little evidence of CD56 (NK). FACS analysis of the DC populations revealed that AAV/E6 vector-pulsed DCs had higher levels of CD80 and lower levels of CD86 than protein-pulsed DCs. These data suggest that rAAV may be appropriate for antigen pulsing of DCs for immunotherapy protocols. Finally, our protocol represents an advance in regards to the time needed for generating a CTL response compared to other techniques.

Development of a Langerhans cell-targeted gene therapy format using a dendritic cell-specific promoter

Langerhans cells (LC), which are a skin-specific member of the dendritic cell (DC) family of antigen presenting cells, play critical roles in the initiation of cellular immune responses in the skin. We developed a LC-targeted gene therapy format in this study, aimed at the establishment of in situ protocols for genetic manipulation of LC function. Dectin-2 is a unique C-type lectin that is expressed selectively by DC, including epidermal LC. A 3.2 kb 5' flanking fragment isolated from the mouse dectin-2 gene, termed the dectin-2 promoter (pDec2), exhibited significant transcriptional activities in epidermal-derived DC lines of the XS series, but not in any of the tested non-DC lines. When pDec2-driven luciferase gene (pDec2-Luc) or enhanced green fluorescence protein gene (pDec2-EGFP) was delivered to mouse skin using the gene gun, expression of the corresponding gene product was observed in the epidermal compartment almost exclusively by the IA+ population (ie LC). LC in the gene gun-treated sites showed features of mature DC and they migrated to the draining lymph node, suggesting that LC-targeted gene expression may lead to the development of immune responses. In fact, EGFP-specific cellular immune responses became detectable after gene gun-mediated delivery of pDec2-EGFP plasmid. These results introduce a new concept that LC function can be genetically manipulated in situ by the combination of gene gun-mediated DNA delivery and a DC-specific promoter.

Dendritic cells and viral immunity: friends or foes?

Dendritic cells (DC) residing in epithelial tissues of various mucosae and the skin are characterized by the unique ability to capture antigens and migrate to draining lymph nodes, where they can activate naive and memory T cells. Although DC play a pivotal role in inducing protective immunity to viral infection, they can also be exploited by viruses to evade the host immune response, induce immune suppression, or serve as latent viral reservoirs. Thus, virus interactions with DC may lead to an immune response that can be protective, but does not necessarily lead to complete virus elimination, resulting in immunopathology.

Dendritic cells injected via different routes induce immunity in cancer patients

Dendritic cells (DC) represent potent APCs that are capable of generating tumor-specific immunity. We performed a pilot clinical trial using Ag-pulsed DC as a tumor vaccine. Twenty-one patients with metastatic prostate cancer received two monthly injections of DC enriched and activated from their PBMC. DC were cocultured ex vivo with recombinant mouse prostatic acid phosphatase as the target neoantigen. Following enrichment, DC developed an activated phenotype with up-regulation of CD80, CD86, and CD83 expression. During culture, the DC maintained their levels of various adhesion molecules, including CD44, LFA-1, cutaneous lymphocyte-associated Ag, and CD49d, up-regulated CCR7, but lost CD62 ligand and CCR5. In the absence of CD62 ligand, such cells would not be expected to prime T cells efficiently if administered i.v. due to their inability to access lymphoid tissue via high endothelial venules. To assess this possibility, three patient cohorts were immunized with Ag-pulsed DC by i.v., intradermal (i.d.), or intralymphatic (i.l.) injection. All patients developed Ag-specific T cell immune responses following immunization, regardless of route. Induction of IFN-gamma production, however, was seen only with i.d. and i.l. routes of administration, and no IL-4 responses were seen regardless of route, consistent with the induction of Th1-type immunity. Five of nine patients who were immunized by the i.v. route developed Ag-specific Abs compared with one of six for i.d. and two of six for i.l. routes. These results suggest that while activated DC can prime T cell immunity regardless of route, the quality of this response and induction of Ag-specific Abs may be affected by the route of administration.

Immunosuppression and resultant viral persistence by specific viral targeting of dendritic cells

Among cells of the immune system, CD11c(+) and DEC-205(+) splenic dendritic cells primarily express the cellular receptor (alpha-dystroglycan [alpha-DG]) for lymphocytic choriomeningitis virus (LCMV). By selection, strains and variants of LCMV that bind alpha-DG with high affinity are associated with virus replication in the white pulp, show preferential replication in a majority of CD11c(+) and DEC-205(+) cells, cause immunosuppression, and establish a persistent infection. In contrast, viral strains and variants that bind with low affinity to alpha-DG are associated with viral replication in the red pulp, display minimal replication in CD11c(+) and DEC-205(+) cells, and generate a robust anti-LCMV cytotoxic T lymphocyte response that clears the virus infection. Differences in binding affinities can be mapped to a single amino acid change in the viral glycoprotein 1 ligand that binds to alpha-DG. These findings indicate that receptor-virus interaction on dendritic cells in vivo can be an essential step in the initiation of virus-induced immunosuppression and viral persistence.

Mature dendritic cells infected with herpes simplex virus type 1 exhibit inhibited T-cell stimulatory capacity

Mature dendritic cells (DC) are the most potent antigen-presenting cells within the entire immune system. Interference with the function of these cells therefore constitutes a very powerful mechanism for viruses to escape immune responses. Several members of the Herpesviridae family have provided examples of such escape strategies, including interference with antigen presentation and production of homologous cytokines. In this study we investigated the infection of mature DC with herpes simplex virus type 1 (HSV-1) and the way in which infection alters the phenotype and function of mature DC. Interestingly, the T-cell-stimulatory capacity of these DC was strongly impaired. Furthermore, we demonstrated that HSV-1 leads to the specific degradation of CD83, a cell surface molecule which is specifically upregulated during DC maturation. These data indicate that HSV-1 has developed yet another novel mechanism to escape immune responses.

Dendritic cells in cancer immunotherapy

The potential to harness the potency and specificity of the immune system underlies the growing interest in cancer immunotherapy. One such approach uses bone marrow-derived dendritic cells, phenotypically distinct and extremely potent antigen-presenting cells, to present tumor-associated antigens and thereby generate tumor-specific immunity. Support for this strategy comes from animal studies that have demonstrated that dendritic cells, when loaded ex vivo with tumor antigens and administered to tumor-bearing hosts, can elicit T cell-mediated tumor destruction. These observations have led to clinical trials designed to investigate the immunologic and clinical effects of antigen-loaded dendritic cells administered as a therapeutic vaccine to patients with cancer. In the design and conduct of such trials, important considerations include antigen selection, methods for introducing the antigen into MHC class I and II processing pathways, methods for isolating and activating dendritic cells, and route of administration. Although current dendritic cell-based vaccination methods are cumbersome, promising results from clinical trials in patients with malignant lymphoma, melanoma, and prostate cancer suggest that immunotherapeutic strategies that take advantage of the antigen presenting properties of dendritic cells may ultimately prove both efficacious and widely applicable to human tumors.

Regulation of immunologic homeostasis in peripheral tissues by dendritic cells: the respiratory tract as a paradigm

Dendritic cells are now recognized as the gatekeepers of the immune response, possessing a unique potential for acquisition of antigens at extremely low exposure levels and for efficient presentation of these in an immunogenic form to the naive T-cell system. Dendritic cell populations throughout the body exhibit a wide range of features in common that are associated with their primary functions, and these are considered in the initial section of this review. In addition, it is becoming evident that the properties and functions of these cells are refined by microenvironmental factors unique to their tissues of residence, a prime example being mucosal microenvironments such as those in respiratory tract tissues, and the latter represents the focus of the second section of this review.

Human T lymphocyte priming in vitro by haptenated autologous dendritic cells

Dendritic cells (DC), generated from adherent peripheral blood mononuclear cells (PBMC) by culturing with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4, were used to study in vitro sensitization of naive, hapten-specific T cells and to analyse cross-reactivities to related compounds. DC were hapten-derivatized with nickel sulphate (Ni) or 2-hydroxyethyl-methacrylate (HEMA), followed by tumour necrosis factor-alpha (TNF-alpha)-induced maturation, before autologous T cells and a cytokine cocktail of IL-1beta, IL-2 and IL-7 were added. After T cell priming for 7 days, wells were split and challenged for another 7 days with Ni or HEMA, and potentially cross-reactive haptens. Hapten-specificity of in vitro priming was demonstrated by proliferative responses to the haptens used for priming but not to the unrelated haptens. Highest priming efficiencies were obtained when both IL-4 and IL-12 were added to the cytokine supplement. Marked interferon-gamma (IFN-gamma) release (up to 4 ng/ml) was found when IL-12 was included in the cultures, whereas IL-5 release (up to 500 pg/ml) was observed after addition of IL-4 alone, or in combination with IL-12. Nickel-primed T cells showed frequent cross-reactivities with other metals closely positioned in the periodic table, i.e. palladium and copper, whereas HEMA-primed T cells showed distinct cross-reactivities with selected methacrylate congeners. Similar cross-reactivities are known to occur in allergic patients. Thus, in vitro T cell priming provides a promising tool for studying factors regulating cytokine synthesis, and cross-reactivity patterns of hapten-specific T cells.