Modulating vaccine responses with dendritic cells and Toll-like receptors

Protective immunity against H5N1 influenza virus by a single dose vaccination with virus-like particles

We generated influenza virus-like particles (VLPs) containing the wild type (WT) H5 hemagglutinin (HA) from A/Viet Nam/1203/04 virus or a mutant H5 HA with a deletion of the multibasic cleavage motif. VLPs containing mutant H5 HA were found to be as immunogenic as VLPs containing WT HA. A single intramuscular vaccination with either type of H5 VLPs provided complete protection against lethal challenge. In contrast, the recombinant H5 HA vaccine was less immunogenic and vaccination even with a 5 fold higher dose did not induce protective immunity. VLP vaccines were superior to the recombinant HA in inducing T helper type 1 immune responses, hemagglutination inhibition titers, and antibody secreting cells, which significantly contribute to inducing protective immunity after a single dose vaccination. This study provides insights into the potential mechanisms of improved immunogenicity by H5 VLP vaccines as an approach to improve the protective efficacy against potential pandemic viruses.

Role of host cell factors in flavivirus infection: Implications for pathogenesis and development of antiviral drugs

The genus Flavivirus contains approximately 70 arthropod-borne enveloped RNA viruses many of which cause severe human and in some cases, animal disease. They include dengue virus, yellow fever virus, West Nile virus, Japanese encephalitis virus, and tick-borne encephalitis virus. Hundreds of thousands of deaths due to flavivirus infections occur each year, many of which are unpreventable due to lack of availability of appropriate vaccines and/or antiviral drugs. Flaviviruses exploit the cytoplasmic cellular machinery to facilitate propagation of infectious progeny virions. They engage in dynamic and antagonistic interactions with host cell membranes and biochemical processes. Following infection, the cells initiate various antiviral strategies to counteract viral invasion. In its defense, the virus has alternative strategies to suppress these host responses to infection. The fine balance between these interactions determines the outcome of the viral infection and disease progression. Published studies have revealed specific effects of flaviviruses on cellular processes, but the underlying mechanisms that determine the specific cytopathogenetic changes induced by different flaviviruses have not, as yet, been elucidated. Independently of the suppression of the type I IFN response which has been described in detail elsewhere, this review focuses on recent discoveries relating to alterations of host metabolism following viral infection. Such studies may contribute to new approaches to antiviral drug development. The role of host cellular factors will be examined in the context of protection and/or pathogenesis resulting from flavivirus infection, with particular emphasis on West Nile virus and dengue virus.

Memory CD4+ T cells induce innate responses independently of pathogen

Inflammation induced by recognition of pathogen-associated molecular patterns markedly affects subsequent adaptive responses. We asked whether the adaptive immune system can also affect the character and magnitude of innate inflammatory responses. We found that the response of memory, but not naive, CD4(+) T cells enhances production of multiple innate inflammatory cytokines and chemokines (IICs) in the lung and that, during influenza infection, this leads to early control of virus. Memory CD4(+) T cell-induced IICs and viral control require cognate antigen recognition and are optimal when memory cells are either T helper type 1 (T(H)1) or T(H)17 polarized but are independent of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) production and do not require activation of conserved pathogen recognition pathways. This represents a previously undescribed mechanism by which memory CD4(+) T cells induce an early innate response that enhances immune protection against pathogens.

The protein moiety of Brucella abortus outer membrane protein 16 is a new bacterial pathogen-associated molecular pattern that activates dendritic cells in vivo, induces a Th1 immune response, and is a promising self-adjuvanting vaccine against systemic and oral acquired brucellosis

Knowing the inherent stimulatory properties of the lipid moiety of bacterial lipoproteins, we first hypothesized that Brucella abortus outer membrane protein (Omp)16 lipoprotein would be able to elicit a protective immune response without the need of external adjuvants. In this study, we demonstrate that Omp16 administered by the i.p. route confers significant protection against B. abortus infection and that the protective response evoked is independent of the protein lipidation. To date, Omp16 is the first Brucella protein that without the requirement of external adjuvants is able to induce similar protection levels to the control live vaccine S19. Moreover, the protein portion of Omp16 (unlipidated Omp16 [U-Omp16]) elicits a protective response when administered by the oral route. Either systemic or oral immunization with U-Omp16 elicits a Th1-specific response. These abilities of U-Omp16 indicate that it is endowed with self-adjuvanting properties. The adjuvanticity of U-Omp16 could be explained, at least in part, by its capacity to activate dendritic cells in vivo. U-Omp16 is also able to stimulate dendritic cells and macrophages in vitro. The latter property and its ability to induce a protective Th1 immune response against B. abortus infection have been found to be TLR4 dependent. The facts that U-Omp16 is an oral protective Ag and possesses a mucosal self-adjuvanting property led us to develop a plant-made vaccine expressing U-Omp16. Our results indicate that plant-expressed recombinant U-Omp16 is able to confer protective immunity, when given orally, indicating that a plant-based oral vaccine expressing U-Omp16 could be a valuable approach to controlling this disease.

Profiles of carbohydrate ligands associated with adsorbed proteins on self-assembled monolayers of defined chemistries

Conserved protein-carbohydrate-lipid pathogen-associated molecular patterns (PAMPs) interact with cells of the innate immune system to mediate antigen recognition and internalization and activation of immune cells. We examined if analogous "biomaterial-associated molecular patterns" composed of proteins, specifically their carbohydrate modifications, existed on biomaterials, which can play a role in mediating the innate immune response to biomaterials. To probe for these carbohydrates in the adsorbed protein layer, as directed by the underlying biomaterial chemistry, self-assembled monolayers (SAMs) presenting -CH(3), -OH, -COOH, or -NH(2) were preincubated with serum/plasma, and the presence of carbohydrate ligands of C-type lectin receptors (CLRs) was investigated using lectin probes in an enzyme-linked lectin assay (ELLA). Presentation of CLR ligands was detected on control tissue culture polystyrene (TCPS). Absorbances of mannose or N-acetylglucosamine increased with decreasing incubating serum concentration, whereas absorbances of sialylated epitopes or fucose remained unchanged. Absorbances of alpha-galactose or N-acetylgalactosamine decreased with decreasing incubating serum concentration; beta-galactose was undetectable. Among SAM endgroups, preincubation with 10% serum resulted in differential presentation of CLR ligands: higher alpha-galactose on COOH SAMs than NH(2) or CH(3) SAMs, highest complex mannose on NH(2) SAMs, and higher complex mannose on OH SAMs than CH(3) SAMs. Least sialylated groups were detected on CH(3) SAMs. In summary, biomaterial chemistry may regulate protein adsorption and hence unique presentation of associated carbohydrates. The ultimate goal is to identify the effects of protein glycosylations associated with biomaterials in stimulating innate immune responses.

Advances in the design and delivery of peptide subunit vaccines with a focus on toll-like receptor agonists

Considerable success has been made with many peptide antigen formulations, and peptide-based vaccines are emerging as the next generation of prophylactic and remedial immunotherapy. However, finding an optimal platform balancing all of the requirements for an effective, specific and safe immune response remains a major challenge for many infectious and chronic diseases. This review outlines how peptide immunogenicity is influenced by the way in which peptides are presented to the immune system, underscoring the need for multifunctional delivery systems that couple antigen and adjuvant into a single construct. Particular attention is given to the ability of Toll-like receptor agonists to act as adjuvants. A survey of recent approaches to developing peptide antigen delivery systems is given, many of which incorporate Toll-like receptor agonists into the design.

Regulation of CD4 T-cell receptor diversity by vaccine adjuvants

New vaccines based on soluble recombinant antigens (Ags) require adjuvants to elicit long-lasting protective humoral and cellular immunity. Despite the importance of CD4 T helper cells for the generation of long-lived memory B and CD8 T cells, the impact of adjuvants on CD4 T-cell responses is still poorly understood. Adjuvants are known to promote dendritic cell (DC) maturation and migration to secondary lymphoid organs where they present foreign peptides bound to class II major histocompatibility complex molecules (pMHCII) to naïve CD4 T cells. Random and imprecise rearrangements of genetic elements during thymic development ensure that a vast amount of T-cell receptors (TCRs) are present in the naïve CD4 T-cell repertoire. Ag-specific CD4 T cells are selected from this vast pre-immune repertoire based on the affinity of their TCR for pMHCII. Here, we review the evidence demonstrating a link between the adjuvant and the specificity and clonotypic diversity of the CD4 T-cell response, and consider the potential mechanisms at play.

Cytolytic CD4 cells: Direct mediators in infectious disease and malignancy

CD4 T cells have traditionally been regarded as helpers and regulators of adaptive immune responses; however, a novel role for CD4 T cells as direct mediators of protection against viral infections has emerged. CD4 T cells with cytolytic potential have been described for almost 40 years, but their role in host protection against infectious disease is only beginning to be realized. In this review, we describe the current literature identifying these cells in patients with various infections, mouse models of viral infection and our own work investigating the development of cytolytic CD4 cells in vivo and in vitro. CD4 CTL are no longer considered an artefact of cell culture and may play a physiological role in viral infections such as EBV, CMV, HIV and influenza. Therefore, vaccine strategies aimed at targeting CD4 CTL should be developed in conjunction with vaccines incorporating B cell and CD8 CTL epitopes.

Generation of T cell responses targeting the reactive metabolite of halothane in mice

Immune-mediated adverse drug reactions (IADRs) represent a significant problem in clinical practice and drug development. Studies of the underlying mechanisms of IADRs have been hampered by the lack of animal models. Halothane causes severe allergic hepatitis with clinical features consistent with an IADR. Our ultimate goal is to develop a mouse model of halothane hepatitis. Evidence suggests that adaptive immune responses targeting liver protein adducts of the reactive metabolite (trifluoroacetyl (TFA)) play an important role in the pathogenesis. The present study demonstrated that the combination of an anti-CD40 antibody (Ab) and a Toll-like receptor (TLR) agonist served as a potent adjuvant in generating TFA-specific T cell responses in mice. Both CD4(+) and CD8(+) subsets of T cells were activated and the TFA-specific responses were detected not only in the spleen but also in the liver of mice immunized with mouse serum albumin adducts of TFA (TFA-MSA) plus the combined CD40/TLR agonist. Whereas all three TLR agonists examined were effective in eliciting TFA-specific immune responses in BALB/cByJ mice, only polyI:C was effective in DBA/1 mice and none of the TLR agonists could aid the generation of TFA-specific T cells in C57BL/6J mice. This result, combined with our previous finding that BALB/cByJ mice were the most susceptible to halothane-induced acute liver injury, provides the basis for employing this strain in future studies. Collectively, our data demonstrated the successful completion of a crucial first step in the development of a murine model of halothane hepatitis.

Enhanced memory responses to seasonal H1N1 influenza vaccination of the skin with the use of vaccine-coated microneedles

BACKGROUND

Morbidity and mortality due to influenza could be reduced by improved vaccination.

METHODS

To develop a novel skin delivery method that is simple and allows for easy self-administration, we prepared microneedle patches with stabilized influenza vaccine and investigated their protective immune responses.

RESULTS

Mice vaccinated with a single microneedle dose of trehalose-stabilized influenza vaccine developed strong antibody responses that were long-lived. Compared with traditional intramuscular vaccination, stabilized microneedle vaccination was superior in inducing protective immunity, as was evidenced by efficient clearance of virus from the lung and enhanced humoral and antibody-secreting cell immune responses after 100% survival from lethal challenge. Vaccine stabilization was found to be important, because mice vaccinated with an unstabilized microneedle vaccine elicited a weaker immunoglobulin G 2a antibody response, compared with the stabilized microneedle vaccine, and were only partially protected against viral challenge. Improved trafficking of dendritic cells to regional lymph nodes as a result of microneedle delivery to the skin might play a role in contributing to improved protective immunity.

CONCLUSIONS

These findings suggest that vaccination of the skin using a microneedle patch can improve protective efficacy and induce long-term sustained immunogenicity and may also provide a simple method of administration to improve influenza vaccination coverage.

Using 3 TLR ligands as a combination adjuvant induces qualitative changes in T cell responses needed for antiviral protection in mice

TLR ligands are promising candidates for the development of novel vaccine adjuvants that can elicit protective immunity against emerging infectious diseases. Adjuvants have been used most frequently to increase the quantity of an immune response. However, the quality of a T cell response can be more important than its quantity. Stimulating certain pairs of TLRs induces a synergistic response in terms of activating dendritic cells and eliciting/enhancing T cell responses through clonal expansion, which increases the number of responding T cells. Here, we have found that utilizing ligands for 3 TLRs (TLR2/6, TLR3, and TLR9) greatly increased the protective efficacy of vaccination with an HIV envelope peptide in mice when compared with using ligands for only any 2 of these TLRs; surprisingly, increased protection was induced without a marked increase in the number of peptide-specific T cells. Rather, the combination of these 3 TLR ligands augmented the quality of the T cell responses primarily by amplifying their functional avidity for the antigen, which was necessary for clearance of virus. The triple combination increased production of DC IL-15 along with its receptor, IL-15Ralpha, which contributed to high avidity, and decreased expression of programmed death-ligand 1 and induction of Tregs. Therefore, selective TLR ligand combinations can increase protective efficacy by increasing the quality rather than the quantity of T cell responses.

Virally mediated immunotherapy for brain tumors

Brain tumors are a leading cause of mortality and morbidity in the United States. Malignant brain tumors occur in approximately 80,000 adults. Furthermore, the average 5-year survival rate for malignant brain tumors across all ages and races is approximately 30% and has remained relatively static over the past few decades, showing the need for continued research and progress in brain tumor therapy. Improved techniques in molecular biology have expanded understanding of tumor genetics and permitted viral engineering and the anticancer therapeutic use of viruses as directly cytotoxic agents and as gene vectors. Preclinical models have shown promising antitumor effects, and generation of clinical grade vectors is feasible. In parallel to these developments, better understanding of antitumor immunity has been accompanied by progress in cancer immunotherapy, the goal of which is to stimulate host rejection of a growing tumor. This article reviews the intersection between the use of viral therapy and immunotherapy in the treatment of malignant gliomas. Each approach shows great promise on its own and in combined or integrated forms.

Original encounter with antigen determines antigen-presenting cell imprinting of the quality of the immune response in mice

Background

Obtaining a certain multi-functionality of cellular immunity for the control of infectious diseases is a burning question in immunology and in vaccine design. Early events, including antigen shuttling to secondary lymphoid organs and recruitment of innate immune cells for adaptive immune response, determine host responsiveness to antigens. However, the sequence of these events and their impact on the quality of the immune response remain to be elucidated. Here, we chose to study Modified Vaccinia virus Ankara (MVA) which is now replacing live Smallpox vaccines and is proposed as an attenuated vector for vaccination strategies against infectious diseases.

Methodology/Principal findings

We analyzed in vivo mechanisms triggered following intradermal (i.d.) and intramuscular (i.m.) Modified Vaccinia virus Ankara (MVA) administration. We demonstrated significant differences in the antigen shuttling to lymphoid organs by macrophages (MΦs), myeloid dendritic cells (DCs), and neutrophils (PMNs). MVA i.d. administration resulted in better antigen distribution and more sustained antigen-presenting cells (APCs) recruitment into draining lymph nodes than with i.m. administration. These APCs, which comprise both DCs and MΦs, were differentially involved in T cell priming and shaped remarkably the quality of cytokine-producing virus-specific T cells according to the entry route of MVA.

Conclusions/Significance

This study improves our understanding of the mechanisms of antigen delivery and their consequences on the quality of immune responses and provides new insights for vaccine development.

Multiple innate signaling pathways cooperate with CD40 to induce potent, CD70-dependent cellular immunity

We have previously shown that Toll-like receptor (TLR) agonists cooperate with CD40 to generate CD8 T cell responses exponentially larger than the responses generated with traditional vaccine formulations. We have also shown that combined TLR agonist/anti-CD40 immunization uniquely induces the upregulation of CD70 on antigen bearing dendritic cells (DCs). In contrast, immunization with either a TLR agonist or a CD40 stimulus alone does not significantly increase CD70 expression on DCs. Furthermore, the CD8(+) T cell response generated by combined TLR agonist/anti-CD40 immunization is dependent on the expression of CD70 by DCs, as CD70 blockade following immunization dramatically decreases the CD8 T cell response. Here we show that other innate pathways, independent of the TLRs, can also cooperate with CD40 to induce potent, CD70 dependent, CD8 T cell responses. These innate stimuli include Type I IFN (IFN) and alpha-galactosylceramide (alphaGalCer) or aC-GalCer, glycolipids that are presented by a nonclassical class I MHC molecule, CD1d, and are able to activate NKT cells. Furthermore, this combined IFN/anti-CD40 immunization generates protective memory against bacterial challenge with Listeria monocytogenes. Together these data indicate the importance of assessing CD70 expression on DCs as a marker for the capacity of a given vaccine formulation to potently activate cellular immunity. Our data indicate that optimal induction of CD70 expression requires a coordinated stimulation of both innate (TLR, IFN, alphaGalCer) and adaptive (CD40) signaling pathways.

Booster vaccinations: can immunologic memory outpace disease pathogenesis?

Almost all current vaccines work by the induction of antibodies in serum or on the mucosa to block adherence of pathogens to epithelial cells or interfere with microbial invasion of the bloodstream. However, antibody levels usually decline after vaccination to undetectable amounts if further vaccination does not occur. Persistence of vaccine-induced antibodies usually goes well beyond the time when they should have decayed to undetectable levels because of ongoing "natural" boosting or other immunologic mechanisms. The production of memory B and T cells is of clear importance, but the likelihood that a memory response will be fast enough in the absence of a protective circulating antibody level likely depends on the pace of pathogenesis of a specific organism. This concept is discussed with regard to Haemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis; hepatitis A and B; diphtheria, tetanus, and pertussis; polio, measles, mumps, rubella, and varicella; rotavirus; and human papilloma virus. With infectious diseases for which the pace of pathogenesis is less rapid, some individuals will contract infection before the memory response is fully activated and implemented. With infectious diseases for which the pace of pathogenesis is slow, immune memory should be sufficient to prevent disease.

Stabilization of influenza vaccine enhances protection by microneedle delivery in the mouse skin

Background

Simple and effective vaccine administration is particularly important for annually recommended influenza vaccination. We hypothesized that vaccine delivery to the skin using a patch containing vaccine-coated microneedles could be an attractive approach to improve influenza vaccination compliance and efficacy.

Methodology/Principal Findings

Solid microneedle arrays coated with inactivated influenza vaccine were prepared for simple vaccine delivery to the skin. However, the stability of the influenza vaccine, as measured by hemagglutination activity, was found to be significantly damaged during microneedle coating. The addition of trehalose to the microneedle coating formulation retained hemagglutination activity, indicating stabilization of the coated influenza vaccine. For both intramuscular and microneedle skin immunization, delivery of un-stabilized vaccine yielded weaker protective immune responses including viral neutralizing antibodies, protective efficacies, and recall immune responses to influenza virus. Immunization using un-stabilized vaccine also shifted the pattern of antibody isotypes compared to the stabilized vaccine. Importantly, a single microneedle-based vaccination using stabilized influenza vaccine was found to be superior to intramuscular immunization in controlling virus replication as well as in inducing rapid recall immune responses post challenge.

Conclusions/Significance

The functional integrity of hemagglutinin is associated with inducing improved protective immunity against influenza. Simple microneedle influenza vaccination in the skin produced superior protection compared to conventional intramuscular immunization. This approach is likely to be applicable to other vaccines too.

Translational Mini-Review Series on Vaccines for HIV: Harnessing innate immunity for HIV vaccine development

Innate immunity is critical for shaping vaccine-elicited adaptive immune responses. Several classes of immune sensors, including Toll-like receptors, retinoic acid-inducible gene-I-like receptors, nucleotide-binding oligomerization domain-like receptors and cytosolic DNA receptors mediate important innate immune pathways and provide potential targets for novel adjuvant development. Understanding how innate immunity modulates adaptive immune responses will probably be important for optimizing vaccine candidates. Here, we review recent advances in innate immunity, focusing upon their potential applications in developing adjuvants and vectors for HIV vaccines.

Salmonella flagellins are potent adjuvants for intranasally administered whole inactivated influenza vaccine

Bacterial flagellins are potent inducers of innate immune responses in the mouse lung because they bind to TLR5 expressed on the apical surfaces of airway epithelial cells. TLR engagement leads to the initiation of a signaling cascade that results in a pro-inflammatory response with subsequent up-regulation of several cytokines and leads to adaptive immune responses. We examined the ability of two soluble flagellins, a monomeric flagellin expressed in Escherichia coli and a highly purified polymeric flagellin directly isolated from Salmonella, to enhance the efficacy of influenza vaccines in mice. Here we demonstrate that both flagellins co-administered intranasally with inactivated A/PR/8/34 (PR8) virus induced robust increases of systemic influenza-specific IgA and IgG titers and resulted in a more comprehensive humoral response as indicated by the increase of IgG2a and IgG2b subclass responses. Groups immunized with the adjuvanted vaccines were fully protected against high dose lethal challenge by homologous virus whereas inactivated PR8 alone conferred only partial protection. Finally we show that shortly after immunization the adjuvanted vaccines induced a dramatic increase in pro-inflammatory cytokines in the lung, resulting in extensive lung infiltration by granulocytes and monocytes/macrophages. Our results reveal a promising perspective for the use of both soluble monomeric and polymeric flagellin as mucosal vaccine adjuvants to improve protection against influenza epidemics as well as a range of other infectious diseases.

Modulation of adaptive immunity with Toll-like receptors

The discovery of Toll-like receptors (TLRs), and their role in sensing infections represents one of the most seminal advances in immunology in recent years. It is now clear that TLRs play a fundamental role in innate recognition of microbes, and stimulate and tune the quality of the adaptive immune response. However, major knowledge gaps remain in our understanding of how TLRs regulate the development and persistence of T- and B-cell memory. Here, we review our current understanding of how TLR-signaling shapes the adaptive immune response, and highlight unanswered questions, the solution of which will be imperative in the rational exploitation of TLRs in vaccine design and immune therapy.

TLR9 agonist, but not TLR7/8, functions as an adjuvant to diminish FI-RSV vaccine-enhanced disease, while either agonist used as therapy during primary RSV infection increases disease severity

Agonists for TLR7, TLR8, and TLR9 have been shown to enhance vaccine immunogenicity. We evaluated the impact of TLR activation on RSV disease in a murine model by administering TLR7/8 and TLR9 agonists during FI-RSV immunization or RSV infection. CpG administered during immunization reduced disease following challenge as evidenced by decreased lung pathology, illness, and cytokines. In marked contrast, TLR7/8 agonist had little impact. To evaluate potential therapeutic use, TLR agonists were administered during primary infection. Although type 2 cytokine responses decreased and type 1 cytokines and MIP-1-alpha/beta increased, both TLR7/8 and TLR9 agonists increased clinical symptoms and pulmonary inflammation when administered during primary infection. Thus, TLR9-induced signaling during FI-RSV immunization reduced vaccine-enhanced disease whereas immunostimulatory properties of TLR agonists enhanced disease severity when used during RSV infection. Immunomodulation elicited by TLR9 agonist confirms the adjuvant potential of TLR agonists during RSV immunization. However, in contrast to work done with HIV-1 vaccines, the inability of TLR7/8 agonist to boost type 1 vaccine-induced RSV immunity demonstrates pathogen-TLR specificity. These data reveal that the timing of administration of immunomodulatory agents is critical. Furthermore, these data underscore that amplification of anti-viral immune responses may result in immunopathology rather than immune-mediated protection.

Transdermal influenza immunization with vaccine-coated microneedle arrays

Background

Influenza is a contagious disease caused by a pathogenic virus, with outbreaks all over the world and thousands of hospitalizations and deaths every year. Due to virus antigenic drift and short-lived immune responses, annual vaccination is required. However, vaccine coverage is incomplete, and improvement in immunization is needed. The objective of this study is to investigate a novel method for transdermal delivery using metal microneedle arrays (MN) coated with inactivated influenza virus to determine whether this route is a simpler and safer approach than the conventional immunization, capable to induce robust immune responses and confer protection against lethal virus challenge.

Methodology/Principal Findings

Inactivated A/Aichi/2/68 (H3N2) influenza virus was coated on metal microneedle arrays and applied to mice as a vaccine in the caudal dorsal skin area. Substantial antibody titers with hemagglutination inhibition activity were detected in sera collected two and four weeks after a single vaccine dose. Challenge studies in mice with 5×LD₅₀ of mouse adapted Aichi virus demonstrated complete protection. Microneedle vaccination induced a broad spectrum of immune responses including CD4+ and CD8+ responses in the spleen and draining lymph node, a high frequency of antigen-secreting cells in the lung and induction of virus-specific memory B-cells. In addition, the use of MN showed a dose-sparing effect and a strong Th2 bias when compared to an intramuscular (IM) reference immunization.

Conclusions/Significance

The present results show that delivery of inactivated influenza virus through the skin using metal microneedle arrays induced strong humoral and cellular immune responses capable of conferring protection against virus challenge as efficiently as intramuscular immunization, which is the standard vaccination route. In view of the convenience of delivery and the potential for self-administration, vaccine-coated metal microneedles may provide a novel and highly effective immunization method.

Targeting the porcine immune system--particulate vaccines in the 21st century

During the last decade, the propagation of immunological knowledge describing the critical role of dendritic cells (DC) in the induction of efficacious immune responses has promoted research and development of vaccines systematically targeting DC. Based on the promise for the rational design of vaccine platforms, the current review will provide an update on particle-based vaccines of both viral and synthetic origin, giving examples of recombinant virus carriers such as adenoviruses and biodegradable particulate carriers. The viral carriers carry pathogen-associated molecular patterns (PAMP), used by the original virus for targeting DC, and are particularly efficient and versatile gene delivery vectors. Efforts in the field of synthetic vaccine carriers are focussing on decorating the particle surface with ligands for DC receptors such as heparan sulphate glycosaminoglycan structures, integrins, Siglecs, galectins, C-type lectins and toll-like receptors. The emphasis of this review will be placed on targeting the porcine immune system, but reference will be made to advances with murine and human vaccine delivery systems where information on DC targeting is available.

Toll-like receptor 2-dependent induction of vitamin A-metabolizing enzymes in dendritic cells promotes T regulatory responses and inhibits autoimmunity

Immune sensing of a microbe occurs via multiple receptors. How signals from different receptors are coordinated to yield a specific immune response is poorly understood. We show that two pathogen recognition receptors, Toll-like receptor 2 (TLR2) and dectin-1, recognizing the same microbial stimulus, stimulate distinct innate and adaptive responses. TLR2 signaling induced splenic dendritic cells (DCs) to express the retinoic acid metabolizing enzyme retinaldehyde dehydrogenase type 2 and interleukin-10 (IL-10) and to metabolize vitamin A and stimulate Foxp3(+) T regulatory cells (T(reg) cells). Retinoic acid acted on DCs to induce suppressor of cytokine signaling-3 expression, which suppressed activation of p38 mitogen-activated protein kinase and proinflammatory cytokines. Consistent with this finding, TLR2 signaling induced T(reg) cells and suppressed IL-23 and T helper type 17 (T(H)17) and T(H)1-mediated autoimmune responses in vivo. In contrast, dectin-1 signaling mostly induced IL-23 and proinflammatory cytokines and augmented T(H)17 and T(H)1-mediated autoimmune responses in vivo. These data define a new mechanism for the systemic induction of retinoic acid and immune suppression against autoimmunity.

Mucosal adjuvanticity of a Shigella invasin complex with dna-based vaccines

Protection against many infectious diseases may require the induction of cell-mediated and mucosal immunity. Immunization with plasmid DNA-based vaccines has successfully induced cell-mediated immune responses in small animals but is less potent in humans. Therefore, several methods are under investigation to augment DNA vaccine immunogenicity. In the current study, a mucosal adjuvant consisting of an invasin protein-lipopolysaccharide complex (Invaplex) isolated from Shigella spp. was evaluated as an adjuvant for DNA-based vaccines. Coadministration of plasmid DNA encoding the Orientia tsutsugamushi r56Karp protein with Invaplex resulted in enhanced cellular and humoral responses in intranasally immunized mice compared to immunization with DNA without adjuvant. Mucosal immunoglobulin A, directed to plasmid-encoded antigen, was detected in lung and intestinal compartments after Invaplex-DNA immunization followed by a protein booster. Moreover, immunization with Invaplex elicited Shigella-specific immune responses, highlighting its potential use in a combination vaccine strategy. The capacity of Invaplex to enhance the immunogenicity of plasmid-encoded genes suggested that Invaplex promoted the uptake and expression of the delivered genes. To better understand the native biological activities of Invaplex related to its adjuvanticity, interactions between Invaplex and mammalian cells were characterized. Invaplex rapidly bound to and was internalized by nonphagocytic, eukaryotic cells in an endocytic process dependent on actin polymerization and independent of microtubule formation. Invaplex also mediated transfection with several plasmid DNA constructs, which could be inhibited with monoclonal antibodies specific for IpaB and IpaC or Invaplex-specific polyclonal sera. The cellular binding and transport capabilities of Invaplex likely contribute to the adjuvanticity and immunogenicity of Invaplex.

Host responses from innate to adaptive immunity after vaccination: molecular and cellular events

The availability of effective vaccines has had the most profound positive effect on improving the quality of public health by preventing infectious diseases. Despite many successful vaccines, there are still old and new emerging pathogens against which there is no vaccine available. A better understanding of how vaccines work for providing protection will help to improve current vaccines as well as to develop effective vaccines against pathogens for which we do not have a proper means to control. Recent studies have focused on innate immunity as the first line of host defense and its role in inducing adaptive immunity; such studies have been an intense area of research, which will reveal the immunological mechanisms how vaccines work for protection. Toll-like receptors (TLRs), a family of receptors for pathogen-associated molecular patterns on cells of the innate immune system, play a critical role in detecting and responding to microbial infections. Importantly, the innate immune system modulates the quantity and quality of longterm T and B cell memory and protective immune responses to pathogens. Limited studies suggest that vaccines which mimic natural infection and/or the structure of pathogens seem to be effective in inducing long-term protective immunity. A better understanding of the similarities and differences of the molecular and cellular events in host responses to vaccination and pathogen infection would enable the rationale for design of novel preventive measures against many challenging pathogens.

Highly efficient transduction of human plasmacytoid dendritic cells without phenotypic and functional maturation

BACKGROUND

Gene modified dendritic cells (DC) are able to modulate DC functions and induce therapeutic immunity or tolerance in an antigen-specific manner. Among the different DC subsets, plasmacytoid DC (pDC) are well known for their ability to recognize and respond to a variety of viruses by secreting high levels of type I interferon.

METHODS

We analyzed here, the transduction efficiency of a pDC cell line, GEN2.2, and of pDC derived from CD34+ progenitors, using lentiviral vectors (LV) pseudotyped with different envelope glycoproteins such as the vesicular stomatitis virus envelope (VSVG), the gibbon ape leukaemia virus envelope (GaLV) or the feline endogenous virus envelope (RD114). At the same time, we evaluated transgene expression (E-GFP reporter gene) under the control of different promoters.

RESULTS

We found that efficient gene transfer into pDC can be achieved with VSVG-pseudotyped lentiviral vectors (LV) under the control of phoshoglycerate kinase (PGK) and elongation factor-1 (EF1alpha) promoters (28% to 90% of E-GFP+ cells, respectively) in the absence of phenotypic and functional maturation. Surprisingly, promoters (desmin or synthetic C5-12) described as muscle-specific and which drive gene expression in single strand AAV vectors in gene therapy protocols were very highly active in pDC using VSVG-LV.

CONCLUSION

Taken together, our results indicate that LV vectors can serve to design pDC-based vaccines in humans, and they are also useful in vitro to evaluate the immunogenicity of the vector preparations, and the specificity and safety of given promoters used in gene therapy protocols.

The stimulation of CD8+ T cells by dendritic cells pulsed with polyketal microparticles containing ion-paired protein antigen and poly(inosinic acid)-poly(cytidylic acid)

New adjuvants and delivery strategies are needed to optimize the ability of protein-based vaccines to elicit CD8(+) T cell responses. We have developed a model vaccine formulation containing ovalbumin (OVA) and the double-stranded RNA analog poly(inosinic acid)-poly(cytidylic acid) (poly(I:C)), a TLR3 agonist. OVA and poly(I:C) were each ion-paired to cetyltrimethylammonium bromide (CTAB) to produce hydrophobic complexes, which were co-encapsulated in pH-sensitive polyketal (PK3) microparticles (1-3 microm) using a single emulsion method. Loading levels ranged from 13.6 to 18.8 microg/mg OVA and 4.8 to 10.3 microg/mg poly(I:C). Murine splenic dendritic cells (DCs) pulsed with PK3-OVA-poly(I:C) microparticles, at antigen doses of 0.01 and 0.1 microg/mL, induced a higher percentage of IFNgamma-producing CD8(+) T cells than DCs treated with PK3-OVA particles or soluble OVA/poly(I:C). A higher antigen dose (1 microg/mL) was less effective, which can be attributed to CTAB toxicity. At the lowest antigen dose (0.01 microg/mL), PK3-OVA-poly(I:C) microparticles also enhanced TNF-alpha and IL-2 production in CD8(+) T cells. These data demonstrate the potential of polyketal microparticles in formulating effective CD8(+) T cell-inducing vaccines comprising protein antigens and dsRNA adjuvants.

Heat-shock proteins in cancer vaccines: agents of antigen cross-presentation

Heat-shock proteins (HSPs) derived from tumors are capable of eliciting an anticancer immune response by facilitating antigen cross-presentation in antigen-presenting cells (APCs). This process involves the ability of such chaperones to bind tumor antigens and facilitate their uptake by APCs. Recent evidence reveals that HSP-tumor antigen complexes bind cell surface proteins on APCs that mediate complex internalization and antigen-processing events, as well as inducing an innate immune response. Binding of HSPs to surface receptors is, thus, an imposing gateway to the induction of tumor-specific immune responses. Extensive studies in animals have indicated the usefulness of such HSP-based immunotherapy in killing established tumors and causing tumor regression. Currently, one HSP, the endoplasmic reticulum stress-response protein Gp96 is undergoing clinical trials for cancer treatment and has yielded promising results, including the induction of anti-tumor immunity and some benefit for patients when administered as part of a multidose regimen. Future advances in HSP-based immunotherapy will be aided by an understanding of the mechanisms by which HSP-peptide complexes induce innate and adaptive immunity to tumor cells and target the killing of primary and metastatic cancer cells.

Dendritic cells--at the front-line of pathogen attack

Efficient immune defence function is dependent on the role played by dendritic cells (DCs), particularly the interaction between conventional DC (cDC) and plasmacytoid DC (pDC), together with other monocytic cells. This functionality of immune defences is open to manipulation by viral pathogens infecting DC, a situation further complicated by the diversity of mechanisms employed by different viruses and the subset of DC involved. The present review uses two virus examples--classical swine fever virus (CSFV) and porcine circovirus type 2 (PCV2)--to demonstrate the complexity of this host-pathogen scenario. CSFV is a monocytotropic RNA virus infecting and replicating in both cDC and pDC. This virus employs its non-structural Npro protein for antagonizing the Type I interferon (IFN) induction pathway. The Npro protein promotes proteasomal degradation of interferon regulatory factor (IRF)3, particularly notable in cDC. In contrast, CSFV infection induces IFNalpha production by pDC, probably due to a lack of interference by the Npro protein with the IRF7 more prominent in pDC. Such ability of the virus to inhibit cDC while augmenting IFNalpha production by pDC might lead to an exaggerated pDC response, relating to the immunopathological characteristics of the disease. PCV2 is an ssDNA containing virus, which in contrast to CSFV is inefficient in its capacity to replicate in DC. Recent evidence suggests that virus replication occurs in endothelial cells, with the DC being more involved through their particularly elevated endocytosis of the virus. PCV2 can accumulate to high levels both in vitro and in vivo, a phenomenon dependent on the virus capsid protein, inferring that the viral capsid or genome impedes DC endocytic degradation of the virus. Nevertheless, the presence of PCV2 in cDC does not interfere with processing of other antigens. The immunoregulatory characteristics of PCV2 are manifest as impairment of "danger" recognition by cells of the innate defences. This varies dependent on the "danger" signal and the cells responding, especially when one compares cDC and pDC. Overall, the PCV2-induced immunomodulation contrasts with that of CSFV in being a property dependent on the viral genome, particularly the dsDNA replicative form, and with immunoregulatory capacity for both cDC and pDC. Moreover, PCV2 compromises immune defence development against other pathogens rather than itself. In conclusion, the DC family represents a critical immune defence element open to modulation by virus infection, with serious consequences for host resistance to disease. The characteristics of the immune modulation depend on the virus and the DC subsets involved. Overall, the roles played by the pDC can be decisive in shaping the outcome of the infection and the characteristics of the virus-induced immunocompromisation.

Differential induction of MyD88- and TRIF-dependent pathways in equine monocytes by Toll-like receptor agonists

Our understanding of the innate immune response in the horse has been limited by a lack of definitive data concerning cell signaling in response to microbial products. Toll-like receptors (TLRs) recognize conserved molecular motifs of microbes and elicit immune responses through their coupling with intracellular adaptor molecules, particularly MyD88 and TRIF. To provide a more definitive characterization of TLR signaling in the horse, the objectives of this study were to: (1) characterize the responses of equine monocytes to TLR ligands that signal through MyD88, TRIF or both in other species, and (2) determine the profiles of gene expression initiated utilizing these adaptor molecules. Monocytes were used to establish concentration response curves for Escherichia coli lipopolysaccharide (LPS; TLR4 ligand) and N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-[R]-cysteinyl-[S]-seryl-[S]-lysyl-[S]-lysyl-[S]-lysyl-[S]-lysine x 3 HCl (Pam(3)CSK(4); TLR2 ligand) based on expression of procoagulant activity (PCA) and production of tumor necrosis factor-alpha (TNF-alpha); effects of polyinosine-polycytidylic acid (Poly I:C; TLR3 ligand) were determined by quantifying expression of mRNA for interferon-beta (IFN-ss). Expression of genes associated with the MyD88- (TNF-alpha, IL-1ss, IL-6 and IL-10) and TRIF-dependent pathways (IFN-ss, IP-10, RANTES and TRAF1) were measured at intervals spanning 20 h. LPS and Pam(3)CSK(4) induced significantly higher expression of TNF-alpha, IL-1ss, and IL-10 than did Poly I:C. Poly I:C induced significantly higher expression of IFN-ss, IP-10 and RANTES than did either the TLR2 or TLR4 ligands. High concentrations of E. coli LPS did not significantly increase expression of genes associated with the TRIF-dependent pathway. The results of this study suggest that equine monocytes utilize a common intracellular pathway in response to TLR2 and TLR4 ligands, but a distinct pathway in response to TLR3 ligands.

Retinoic acid-dependent regulation of immune responses by dendritic cells and macrophages

Dendritic cells (DCs) control the strength and quality of antigen-specific T and B cell responses. Recent advances point to a novel mechanism, in which metabolism of vitamin A into retinoic acid (RA) in DCs, regulate critical parameters of lymphocyte differentiation. First, RA enhances the induction of Foxp3(+) T regulatory cells by DCs. Thus, specific subsets of intestinal DCs and macrophages constitutively express RA synthesizing enzymes, and induce T regulatory cells. In addition, RA programs DCs to imprint mucosal homing properties on activated T and B cells, and enhanced induction of immunoglobulin-A (IgA) by B cells. Here, we review these recent advances, in the context of the pleiotropic effects of RA in regulating diverse biological processes.

Activated plasmacytoid dendritic cells act synergistically with hepatitis B core antigen-pulsed monocyte-derived dendritic cells in the induction of hepatitis B virus-specific CD8 T-cell response

It is important to further improve the efficiency of hepatitis B core antigen-pulsed monocyte-derived dendritic cell (core-DC) vaccine in clinical immunotherapy for chronic hepatitis B virus (HBV) infection in humans. Our study shows that CpG-treated plasmacytoid dendritic cells (pDCs) can efficiently promote core-DC terminal maturation and increase interleukin-12 production. These CpG-activated pDCs can act synergistically in vitro with core-DCs in inducing autologous HBV-specific CD8 T-cell proliferation and interferon (IFN)-gamma production. This promotion was mainly dependent on pDC-derived IFN-alpha, because blockade of IFN-alpha nearly completely aborted the effects of pDCs on core-DCs. In addition, the supernatants derived from CpG-treated peripheral blood mononuclear cells can also effectively improve the aforementioned maturation and function of core-DCs. These findings will facilitate a better understanding of how the pDCs regulate myeloid dendritic cell-mediated immune responses, and highlight the notion that manipulating pDCs might have implications in DC vaccine therapy for patients with chronic hepatitis B.

Brucella lipoproteins mimic dendritic cell maturation induced by Brucella abortus

Infection with Brucella abortus induces a pro-inflammatory response that drives T cell responses toward a Th1 profile. The mechanism by which this bacterium triggers this response is unknown. Dendritic cells (DC) are crucial mediators at the host-pathogen interface and are potent Th1-inducing antigen-presenting cells. Thus, we examined the mechanism whereby B. abortus stimulate human DC maturation. B. abortus-infected DC increased the expression of CD86, CD80, CCR7, CD83, MHCII, MHCI and CD40 and induced the production of TNF-alpha, IL-6, IL-10 and IL-12. Both phenomena were not dependent on bacterial viability since they were also induced by heat-killed B. abortus (HKBA). B. abortus LPS was unable to induce markers up-regulation or cytokine production. We next investigated the capacity of the outer membrane protein 19 (Omp19) as a B. abortus lipoprotein model to induce DC maturation. Lipidated Omp19 (L-Omp19), but not its unlipidated form, increased the expression of cell surface markers and the secretion of cytokines. L-Omp19-matured DC also have decreased endocytic activity and displayed enhanced T cell stimulatory activity in a MLR. Pre-incubation of DC with anti-TLR2 mAb blocked L-Omp19-mediated cytokine production. These results demonstrate that B. abortus lipoproteins can stimulate DC maturation providing a mechanism by which these bacteria generate a Th1-type immune response.

Clinical investigations of Toll-like receptor agonists

BACKGROUND

Toll-like receptors (TLR) represent a family of surface molecules that function as primary sensors of the innate immune system to recognize microbial pathogens. Ligand binding to TLR results in activation of cellular signaling pathways that regulate expression of genes involved in inflammation and immunity.

OBJECTIVE

Use of synthetic TLR ligands (agonists) for treatment and prevention of infectious and neoplastic diseases.

METHODS

Review of literature about clinical investigations of agonists of TLR 4, 7, 8, and 9.

RESULTS/CONCLUSIONS

Imiquimod was the first TLR agonist approved for treatment of anogenital warts, actinic keratosis and superficial basal cell carcinoma in humans. Several other agonists of TLRs 4, 7, 8 and 9 were also shown to be effective for treatment of infections and cancers and, furthermore, were used as adjuvants for vaccination. Based on safety and efficacy of the TLR agonists used to date, applications are likely to increase in the future.

Host-directed drug targeting of factors hijacked by pathogens

The current paradigm for managing infectious diseases has targeted unique processes or enzymes within pathogens. A serious disadvantage of this pathogen-directed drug targeting strategy has been the development of microbial drug resistance and consequent resurgence of once-contained infectious diseases. A new drug discovery paradigm has therefore emerged focusing on identifying and targeting host factors essential for pathogen entry, survival, and replication. Innovative strategies combining genome-wide computational biology, genomics, proteomics, and traditional forward and reverse genetics have identified host-pathogen interactions and host functions critical for the establishment of infection. Chemogenomics and chemical genetics have allowed rapid identification of new and existing licensed drugs with antimicrobial activity. Although most host-directed drug targeting studies have focused on viral infections, they have provided a proof of concept for similar approaches to bacterial and parasite infections. Future therapies may combine conventional targeting of microbial virulence factors, together with host-directed drug therapy and augmentation of protective host factors, to efficiently eliminate the invading pathogen.

Neisseria meningitidis PorB, a Toll-like receptor 2 ligand, improves the capacity of Francisella tularensis lipopolysaccharide to protect mice against experimental tularemia

Francisella tularensis causes severe pneumonia that can be fatal if it is left untreated. Due to its potential use as a biological weapon, research is being conducted to develop an effective vaccine and to select and study adjuvant molecules able to generate a better and long-lasting protective effect. PorB, a porin from Neisseria meningitidis, is a well-established Toll-like receptor 2 ligand and has been shown to be a promising vaccine adjuvant candidate due to its ability to enhance the T-cell costimulatory activity of antigen-presenting cells both in vitro and in vivo. BALB/c mice were immunized with lipopolysaccharide (LPS) isolated from the F. tularensis subsp. holarctica live vaccine strain (LVS), with or without PorB from N. meningitidis, and the antibody levels induced during the vaccination regimen and the level of protection against intranasal challenge with LVS were determined. Antigen administered alone induced a specific F. tularensis LPS immunoglobulin M (IgM) response that was not maintained over the weeks and that conferred protection to only 25% of the mice. In contrast, F. tularensis LPS given in combination with neisserial PorB induced consistent levels of specific IgM throughout the immunization and increased the proportion of surviving mice to 70%. Postchallenge cytokine analysis showed that interleukin-6 (IL-6), monocyte chemoattractant protein 1, and gamma interferon were markers of mortality and that IL-1beta was a correlate of survival, independent of the presence of PorB as an adjuvant. These data indicate that neisserial PorB might be an optimal candidate adjuvant for improving the protective effect of F. tularensis LPS and other subunit vaccines against tularemia, but there is still a need to test its efficacy against virulent type A and type B F. tularensis strains.

Toll-like receptors: lessons to learn from normal and malignant human B cells

The humoral immune system senses microbes via recognition of specific microbial molecular motifs by Toll-like receptors (TLRs). These encounters promote plasma cell differentiation and antibody production. Recent studies have demonstrated the importance of the TLR system in enhancing antibody-mediated defense against infections and maintaining memory B cells. These results have led the way to the design of vaccines that target B cells by engaging TLRs. In hematologic malignancies, cells often retain B cell-specific receptors and associated functions. Among these, TLRs are currently exploited to target different subclasses of B-cell leukemia, and TLR agonists are currently being evaluated in clinical trials. However, accumulating evidence suggests that endogenous TLR ligands or chronic infections promote tumor growth, thus providing a need for further investigations to decipher the exact function of TLRs in the B-cell lineage and in neoplastic B cells. The aim of this review is to present and discuss the latest advances with regard to the expression and function of TLRs in both healthy and malignant B cells. Special attention will be focused on the growth-promoting effects of TLR ligands on leukemic B cells and their potential clinical impact.

Choreography of cell motility and interaction dynamics imaged by two-photon microscopy in lymphoid organs

The immune system is the most diffuse cellular system in the body. Accordingly, long-range migration of cells and short-range communication by local chemical signaling and by cell-cell contacts are vital to the control of an immune response. Cellular homing and migration within lymphoid organs, antigen recognition, and cell signaling and activation are clearly vital during an immune response, but these events had not been directly observed in vivo until recently. Introduced to the field of immunology in 2002, two-photon microscopy is the method of choice for visualizing living cells deep within native tissue environments, and it is now revealing an elegant cellular choreography that underlies the adaptive immune response to antigen challenge. We review cellular dynamics and molecular factors that contribute to basal motility of lymphocytes in the lymph node and cellular interactions leading to antigen capture and recognition, T cell activation, B cell activation, cytolytic effector function, and antibody production.

Expression and function of Toll-like receptors on dendritic cells and other antigen presenting cells from non-human primates

Antigen presenting cells (APCs), especially dendritic cells (DCs), play a crucial role in immune responses against infections by sensing microbial invasion through Toll-like receptors (TLRs). In this regard, TLR ligands are attractive candidates for use in humans and animal models as vaccine adjuvants. So far, no studies have been performed on TLR expression in non-human primates such as rhesus macaques. Therefore, we studied the TLR expression patterns in different subsets of APC in rhesus macaques and compared them to similar APC subsets in human. Also, expression was compared with corresponding DC subsets from different organs from mice. Here we show by semi-quantitative RT-PCR, that blood DC subsets of rhesus macaque expressed the same sets of TLRs as those of human but substantially differed from mouse DC subsets. Macaque myeloid DCs (MDCs) expressed TLR3, 4, 7 and 8 whereas macaque plasmacytoid DCs (PDCs) expressed only TLR7 and 9. Additionally, TLR expression patterns in macaque monocyte-derived dendritic cells (mo-DCs) (i.e., TLR3, 4, 8 and 9), monocytes (i.e., TLR4, 7, and 8) and B cells (i.e., TLR4, 7, 8, and 9) were also similar to their human counterparts. However, the responsiveness of macaque APCs to certain TLR ligands partially differed from that of human in terms of phenotype differentiation and cytokine production. Strikingly, in contrast to human mo-DCs, no IL-12p70 production was observed when macaque mo-DCs were stimulated with TLR ligands. In addition, CD40 and CD86 phenotypic responses to TLR8 ligand (poly U) in mo-DCs of macaque were higher than that of human. Despite these functional differences, our results provide important information for a rational design of animal models in evaluating TLR ligands as adjuvant in vivo.

Human TLR1 deficiency is associated with impaired mycobacterial signaling and protection from leprosy reversal reaction

Toll-like receptors (TLRs) are important regulators of the innate immune response to pathogens, including Mycobacterium leprae, which is recognized by TLR1/2 heterodimers. We previously identified a transmembrane domain polymorphism, TLR1_T1805G, that encodes an isoleucine to serine substitution and is associated with impaired signaling. We hypothesized that this TLR1 SNP regulates the innate immune response and susceptibility to leprosy. In HEK293 cells transfected with the 1805T or 1805G variant and stimulated with extracts of M. leprae, NF-kappaB activity was impaired in cells with the 1805G polymorphism. We next stimulated PBMCs from individuals with different genotypes for this SNP and found that 1805GG individuals had significantly reduced cytokine responses to both whole irradiated M. leprae and cell wall extracts. To investigate whether TLR1 variation is associated with clinical presentations of leprosy or leprosy immune reactions, we examined 933 Nepalese leprosy patients, including 238 with reversal reaction (RR), an immune reaction characterized by a Th1 T cell cytokine response. We found that the 1805G allele was associated with protection from RR with an odds ratio (OR) of 0.51 (95% CI 0.29-0.87, p = 0.01). Individuals with 1805 genotypes GG or TG also had a reduced risk of RR in comparison to genotype TT with an OR of 0.55 (95% CI 0.31-0.97, p = 0.04). To our knowledge, this is the first association of TLR1 with a Th1-mediated immune response. Our findings suggest that TLR1 deficiency influences adaptive immunity during leprosy infection to affect clinical manifestations such as nerve damage and disability.

Comparison of DNA- and mRNA-Transfected Mouse Dendritic Cells as Potential Vaccines against the Human Papillomavirus Type 16 associated Oncoprotein E7

Background

Dendritic cells (DCs) mediate the generation of strong cytotoxic T-lymphocyte (CTL) responses by functioning in antigen presentation and exerting adjuvant properties. We compared several activation markers and parameters of biological activity of DNA- and mRNA-transfected DCs in vitro and in vivo.

Methods

CpG-matured, bone marrow derived C57BL/6 mouse DCs were electroporated either with enhanced green fluorescence protein (EGFP) or human papillomavirus type 16 (HPV16) E7 expression plasmids or in vitro transcribed mRNAs encoding for the codon-optimized E7 or a shuffled version thereof. Activation marker expression and antigen presentation was analysed by fluorescence-activated cell sorting. The migratory behaviour of transfected DCs were investigated by in vitro chemotaxis experiments and cytokine expression by ELISA. CTL-priming capacity of transfected DCs were determined by vaccination of mice.

Results

mRNA transfection produced a two- to fourfold increase of the activation markers CD40, CD80, CD86 and MHC I and MHC II molecules. Predominately antigen-expressing DCs migrated after mRNA transfection. Furthermore, mRNA-transfected DCs were capable of inducing a chemokine gradient. After maturation, electroporation and activation with soluble CD40 ligand and interferon-γ, DCs displayed a T-helper cell type 2 cytokine expression pattern. Nevertheless, E7-transfected DCs were able to prime E7-specific CTL responses in vivo. The highest E7-specific CTL frequencies were found in mice immunized with mRNA-transfected DCs. The in vitro expanded CTLs exerted functional E7-specific cytotoxic activity.

Conclusions

Genetically modified DCs are suitable vehicles for the induction of E7-specific CTL responses in mice and hence could help to eradicate HPV-associated lesions in humans.

Influencing the fates of CD4 T cells on the path to memory: lessons from influenza

In the face of emerging infectious diseases caused by rapidly evolving and highly virulent pathogens, such as influenza, we are challenged to develop innovative vaccine strategies that can induce lasting protection. Since CD4 T cells are needed to generate and maintain protective B-cell and CD8 T-cell immunity, and can also mediate additional protective mechanisms, vaccines should ideally elicit efficient CD4 T cell, in addition to CD8 T and B-cell responses. We outline here the process of CD4 T-cell differentiation from naïve to effector and from effector to memory with an emphasis on how exposure to microbial products and variables in antigen presentation can impact the functional quality and heterogeneity of activation-based CD4 T-cell subsets in vitro and in vivo. We discuss the impact of different phases of antigen recognition, the inflammatory milieu, acute versus chronic antigen presentation, and the contribution of residual antigen depots on CD4 T-cell effector differentiation and the formation and maintenance of CD4 T-cell memory. We propose that novel vaccine strategies, which incorporate both microbial products and antigen targeting, may provide a flexible and long-lived memory CD4 T-cell pool.

Use of dendritic cells in drug selection, development and therapy

BACKGROUND

Dendritic cells (DC) have the unique ability to induce immunity against tumors and various pathogens or to promote tolerance in autoimmunity and transplantation. Hence, they are central to the regulation of immune responses.

OBJECTIVE/METHODS

Due to the unique tolerogenic ability of DC, understanding some of the key molecules that regulate DC function may help with targeting the relevant signals in DC as therapeutic options for many disease conditions. DC are also targets of drugs, and many of the anti-inflammatory and pharmaceutical agents used to prevent autoimmunity or inhibit graft rejection interfere with DC function.

RESULTS/CONCLUSION

The drug-induced changes in DC may provide information for the selection of drugs and further drug discovery along with the use of DC as adjuvant in the treatment of autoimmunity and prevention of graft rejection in transplantation.

HIV-1 gp120 mannoses induce immunosuppressive responses from dendritic cells

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is a vaccine immunogen that can signal via several cell surface receptors. To investigate whether receptor biology could influence immune responses to gp120, we studied its interaction with human, monocyte-derived dendritic cells (MDDCs) in vitro. Gp120 from the HIV-1 strain JR-FL induced IL-10 expression in MDDCs from 62% of donors, via a mannose C-type lectin receptor(s) (MCLR). Gp120 from the strain LAI was also an IL-10 inducer, but gp120 from the strain KNH1144 was not. The mannose-binding protein cyanovirin-N, the 2G12 mAb to a mannose-dependent gp120 epitope, and MCLR-specific mAbs inhibited IL-10 expression, as did enzymatic removal of gp120 mannose moieties, whereas inhibitors of signaling via CD4, CCR5, or CXCR4 were ineffective. Gp120-stimulated IL-10 production correlated with DC-SIGN expression on the cells, and involved the ERK signaling pathway. Gp120-treated MDDCs also responded poorly to maturation stimuli by up-regulating activation markers inefficiently and stimulating allogeneic T cell proliferation only weakly. These adverse reactions to gp120 were MCLR-dependent but independent of IL-10 production. Since such mechanisms might suppress immune responses to Env-containing vaccines, demannosylation may be a way to improve the immunogenicity of gp120 or gp140 proteins.

Dendritic cells (DCs) initiate immune responses to pathogens or vaccine antigens. The HIV-1 gp120 envelope glycoprotein is an antigen that is a focus of vaccine design strategies. We have studied how gp120 proteins interact with DCs in cell culture. Certain gp120s stimulate DCs from some, but not all, human donors to produce IL-10, a cytokine that is generally immunosuppressive. In addition, whether or not the DCs produce IL-10, their ability to mature properly when activated is impaired by gp120—the gp120-treated DCs have a reduced ability to stimulate T cell growth when the two cell types are cultured together. These various effects of gp120 are caused by its binding to cell surface receptors of the mannose C-type lectin receptor family, including (but probably not exclusively) one called DC-SIGN. Gp120 binds to these receptors via mannose residues that are present on some of the glycan structures that overlay much of its protein surface. Removing the mannoses by digesting gp120 with a suitable enzyme prevents IL-10 induction and impairment of DC maturation, as does the use of inhibitors of the binding of gp120 to DC-SIGN and similar receptors. This work could help with the design of better HIV-1 vaccines.

The PorB porin from commensal Neisseria lactamica induces Th1 and Th2 immune responses to ovalbumin in mice and is a potential immune adjuvant

Porins from pathogenic Neisseriae are among several bacterial products with immune adjuvant activity. Neisseria meningitidis (Nme) PorB, has been shown to induce immune cells activation in a TLR2-dependent manner and acts as a vaccine immune adjuvant. The PorB porin from Neisseria lactamica (Nlac), a common nasopharyngeal commensal, shares significant structural and functional similarities with Nme PorB. In this work we ask whether the immune adjuvant ability of porins from pathogenic Neisserial strains is a characteristic shared with porins from non-pathogenic Neisserial species or whether it is unique for bacterial products derived from microorganisms capable of inducing inflammation and disease. We evaluated the potential immune adjuvant effect of Nlac PorB in mice using ovalbumin (OVA) as a prototype antigen. Immunization with Nlac PorB/OVA induced high OVA-specific IgG and IgM titers compared to OVA alone, similar to other adjuvants such as Nme PorB and alum. High titers of IgG1 and IgG2b were detected as well as production of IL-4, IL-10, IL-12 and INF-gamma in response to Nlac PorB, consistent with induction of both a Th1-type and a Th2-type immune response. OVA-specific proliferation was also determined in splenocytes from Nlac PorB/OVA-immunized mice. In addition, B cell activation in vitro and cytokine production in response to Nlac PorB was found to be mediated by TLR2, in a similar manner to Nme PorB.