New horizons in adjuvants for vaccine development

Protective T cell immunity in mice following protein-TLR7/8 agonist-conjugate immunization requires aggregation, type I IFN, and multiple DC subsets

The success of a non-live vaccine requires improved formulation and adjuvant selection to generate robust T cell immunity following immunization. Here, using protein linked to a TLR7/8 agonist (conjugate vaccine), we investigated the functional properties of vaccine formulation, the cytokines, and the DC subsets required to induce protective multifunctional T cell immunity in vivo. The conjugate vaccine required aggregation of the protein to elicit potent Th1 CD4+ and CD8+ T cell responses. Remarkably, the conjugate vaccine, through aggregation of the protein and activation of TLR7 in vivo, led to an influx of migratory DCs to the LN and increased antigen uptake by several resident and migratory DC subsets, with the latter effect strongly influenced by vaccine-induced type I IFN. Ex vivo migratory CD8-DEC205+CD103-CD326- langerin-negative dermal DCs were as potent in cross-presenting antigen to naive CD8+ T cells as CD11c+CD8+ DCs. Moreover, these cells also influenced Th1 CD4+ T cell priming. In summary, we propose a model in which broad-based T cell-mediated responses upon vaccination can be maximized by codelivery of aggregated protein and TLR7/8 agonist, which together promote optimal antigen acquisition and presentation by multiple DC subsets in the context of critical proinflammatory cytokines.

A novel non-toxic combined CTA1-DD and ISCOMS adjuvant vector for effective mucosal immunization against influenza virus

Here we demonstrate that by using non-toxic fractions of saponin combined with CTA1-DD we can achieve a safe and above all highly efficacious mucosal adjuvant vector. We optimized the construction, tested the requirements for function and evaluated proof-of-concept in an influenza A virus challenge model. We demonstrated that the CTA1-3M2e-DD/ISCOMS vector provided 100% protection against mortality and greatly reduced morbidity in the mouse model. The immunogenicity of the vector was superior to other vaccine formulations using the ISCOM or CTA1-DD adjuvants alone. The versatility of the vector was best exemplified by the many options to insert, incorporate or admix vaccine antigens with the vector. Furthermore, the CTA1-3M2e-DD/ISCOMS could be kept 1 year at 4°C or as a freeze-dried powder without affecting immunogenicity or adjuvanticity of the vector. Strong serum IgG and mucosal IgA responses were elicited and CD4 T cell responses were greatly enhanced after intranasal administration of the combined vector. Together these findings hold promise for the combined vector as a mucosal vaccine against influenza virus infections including pandemic influenza. The CTA1-DD/ISCOMS technology represents a breakthrough in mucosal vaccine vector design which successfully combines immunomodulation and targeting in a safe and stable particulate formation.

Role of AS04 in human papillomavirus vaccine: mode of action and clinical profile

INTRODUCTION

Understanding the mode of action of adjuvants is important for the interpretation of clinical studies.

AREAS COVERED

This paper discusses how the results of GSK's clinical studies with an AS04-adjuvanted human papillomavirus (HPV) vaccine are supported by the mode of action of AS04. AS04 and antigens must be injected at the same intramuscular site together or within 24 h of each other. AS04 induces local cytokine production leading to increased recruitment of dendritic cells and monocytes and raised numbers of antigen presenting cells in the draining lymph node. The localized and transient nature of the innate immune response supports the acceptable safety profile observed in clinical studies. The readers will gain a comprehensive understanding of the mode of action of AS04 and how it relates to results of clinical studies.

EXPERT OPINION

The AS04-adjuvanted HPV vaccine has an acceptable safety profile and induces an enhanced and sustained immune response and high protection against HPV types 16/18. Cross-protection against oncogenic HPV types 31/33/45 not contained in the vaccine is also observed. The mode of action of AS04 supports the clinical profile of the AS04-adjuvanted HPV vaccine.

Protective immunity to pre-erythrocytic stage malaria

The development of a vaccine against malaria is a major research priority given the burden of disease, death and economic loss inflicted upon the tropical world by this parasite. Despite decades of effort, however, a vaccine remains elusive. The best candidate is a subunit vaccine termed RTS,S but this provides only partial protection against clinical disease. This review examines what is known about protective immunity against pre-erythrocytic stage malaria by considering the humoral and T cell-mediated immune responses that are induced by attenuated sporozoites and by the RTS,S vaccine. On the basis of these observations a set of research priorities are defined that are crucial for the development of a vaccine capable of inducing long-lasting and high-grade protection against malaria.

Liposomes containing glucosyl ceramide specifically bind T4 bacteriophage: a self-assembling nanocarrier formulation

A unique formulation is described comprising liposomes containing glucosyl ceramide (GluCer) in the lipid bilayer to which bacteriophage T4 was attached. Binding of the phage T4 did not occur to glycolipids, such as galactosyl ceramide, containing an aldose in which the C-2 or C-4 conformations were not identical to glucose. These results strongly support previous proposals that glucose is a major receptor moiety for T4 binding to Escherichia coli. By using the binding of T4 to liposomal GluCer, we further describe a formulation that can be used as a self-assembling combined antigen and adjuvant carrier. A peptide antigen derived from C-trimer (Ct) of HIV-1 gp41 was fused to the highly antigenic outer capsid protein (Hoc), a nonessential protein of T4 that spontaneously binds to the T4 capsid. This resulted in display of the Ct-Hoc construct on the T4 capsid, and specific binding of a human monoclonal antibody that recognizes a peptide sequence of Ct was demonstrated. Liposomes containing monophosphoryl lipid A (MPLA) have been demonstrated to have potent adjuvant activities for experimental vaccines both in humans and animals, and because of this, mice were immunized with the Ct-Hoc-T4 construct that was bound to liposomes containing both GluCer and MPLA, resulting in the induction of high titers of Ct-specific antibodies. We conclude that liposomes containing both GluCer and MPLA can spontaneously bind to a construct of T4 that displays antigens that spontaneously binds to the capsid of T4 bacteriophage. This formulation could be utilized as an easily manufactured self-assembling antigen and adjuvant carrier.

Phase I safety and immunogenicity trial of Plasmodium vivax CS derived long synthetic peptides adjuvanted with montanide ISA 720 or montanide ISA 51

We assessed the safety, tolerability, and immunogenicity of a mixture of three synthetic peptides derived from the Plasmodium vivax circumsporozoite protein formulated in Montanide ISA 720 or Montanide ISA 51. Forty healthy malaria-naive volunteers were allocated to five experimental groups (A-E): four groups (A-D) were immunized intramuscularly with 50 and 100 μg/dose injections of a mixture of N, R, and C peptides formulated in the two different adjuvants at 0, 2, and 4 months and one group was administered placebo. Vaccines were immunogenic, safe, well tolerated, and no serious adverse events related to the vaccine occurred. Seroconversion occurred in > 90% of the vaccines and antibodies recognized the sporozoite protein on immunofluorescent antibody test. Vaccines in Montanide ISA 51 showed a higher sporozoite protein recognition and interferon production. Results encourage further testing of the vaccine protective efficacy.

Interbilayer-crosslinked multilamellar vesicles as synthetic vaccines for potent humoral and cellular immune responses

Vaccines based on recombinant proteins avoid the toxicity and antivector immunity associated with live vaccine (for example, viral) vectors, but their immunogenicity is poor, particularly for CD8(+) T-cell responses. Synthetic particles carrying antigens and adjuvant molecules have been developed to enhance subunit vaccines, but in general these materials have failed to elicit CD8(+) T-cell responses comparable to those for live vectors in preclinical animal models. Here, we describe interbilayer-crosslinked multilamellar vesicles formed by crosslinking headgroups of adjacent lipid bilayers within multilamellar vesicles. Interbilayer-crosslinked vesicles stably entrapped protein antigens in the vesicle core and lipid-based immunostimulatory molecules in the vesicle walls under extracellular conditions, but exhibited rapid release in the presence of endolysosomal lipases. We found that these antigen/adjuvant-carrying vesicles form an extremely potent whole-protein vaccine, eliciting endogenous T-cell and antibody responses comparable to those for the strongest vaccine vectors. These materials should enable a range of subunit vaccines and provide new possibilities for therapeutic protein delivery.

Development and characterization of synthetic glucopyranosyl lipid adjuvant system as a vaccine adjuvant

Innate immune responses to vaccine adjuvants based on lipopolysaccharide (LPS), a component of gram-negative bacterial cell walls, are driven by Toll-like receptor (TLR) 4 and adaptor proteins including MyD88 and TRIF, leading to the production of inflammatory cytokines, type I interferons, and chemokines. We report here on the characterization of a synthetic hexaacylated lipid A derivative, denoted as glucopyranosyl lipid adjuvant (GLA). We assessed the effects of GLA on murine and human dendritic cells (DC) by combining microarray, mRNA and protein multiplex assays and flow cytometry analyses. We demonstrate that GLA has multifunctional immunomodulatory activity similar to naturally-derived monophosphory lipid A (MPL) on murine DC, including the production of inflammatory cytokines, chemokines, DC maturation and antigen-presenting functions. In contrast, hexaacylated GLA was overall more potent on a molar basis than heterogeneous MPL when tested on human DC and peripheral blood mononuclear cells (PBMC). When administered in vivo, GLA enhanced the immunogenicity of co-administered recombinant antigens, producing strong cell-mediated immunity and a qualitative T(H)1 response. We conclude that the GLA adjuvant stimulates and directs innate and adaptive immune responses by inducing DC maturation and the concomitant release of pro-inflammatory cytokines and chemokines associated with immune cell trafficking, activities which have important implications for the development of future vaccine adjuvants.

Role of adjuvants in modeling the immune response

PURPOSE OF REVIEW

Recent clinical trial results have indicated that it may be possible for vaccines to induce protection against HIV. To build on this result, strategies should be designed to enhance duration, breadth, and magnitude of antibody production. Strategic formulation of agonists of the innate immune system and carriers that selectively present the target antigen yields a class of pharmaceuticals, named 'adjuvants', that greatly influence immunity resulting from vaccination. As researchers begin to focus not only on creating an immune response to an antigen, but also on the quality of that response, the role of adjuvants is becoming increasingly significant. This review is intended to give an overview of recent findings on how adjuvants model the immune response to antigens with a focus on the field of vaccines for HIV.

RECENT FINDINGS

It is clear that innate and adaptive immunity are linked by communication channels that allow innate signals to influence the quality of adaptive responses as well as adaptive signals that temper innate responses. Adjuvants take advantage of this bridge to shape the immune response to antigens. In this review, we will discuss the different classes of adjuvants currently available; recent findings on the relationship between adjuvants and the type of immune profile generated; and the breadth of neutralizing antibodies as influenced by adjuvants.

SUMMARY

Because adjuvants influence the breadth of antibodies generated and the type of cells that proliferate in response to a vaccine this review is relevant for scientists clinicians involved in creating a new HIV vaccine.

Construction of an Escherichia coli mutant producing monophosphoryl lipid A

Lipid A is a major component in the outer membrane of most gram-negative bacteria. Monophosphoryl lipid A contains no phosphate group at 1-position and can be used as an adjuvant. We constructed an Escherichia coli mutant CW001 by integrating a gene lpxE into the chromosome of E. coli W3110. The gene lpxE encodes an enzyme LpxE which removes the 1-phosphate group of lipid A. CW001 predominantly produces 1-dephosphorylated lipid A in vivo, as adjudged by thin layer chromatography and electro-spray ionization mass spectrometry. This study not only is important for the development of lipid A adjuvants but also provides a novel method for integration of heterologous genes into the chromosome of E. coli.

CD83 increases MHC II and CD86 on dendritic cells by opposing IL-10-driven MARCH1-mediated ubiquitination and degradation

Effective vaccine adjuvants must induce expression of major histocompatibility (MHC) class II proteins and the costimulatory molecule CD86 on dendritic cells (DCs). However, some adjuvants elicit production of cytokines resulting in adverse inflammatory consequences. Development of agents that selectively increase MHC class II and CD86 expression without triggering unwanted cytokine production requires a better understanding of the molecular mechanisms influencing the production and degradation of MHC class II and CD86 in DCs. Here, we investigate how CD83, an immunoglobulin protein expressed on the surface of mature DCs, promotes MHC class II and CD86 expression. Using mice with an N-ethyl-N-nitrosourea-induced mutation eliminating the transmembrane (TM) region of CD83, we found that the TM domain of CD83 enhances MHC class II and CD86 expression by blocking MHC class II association with the ubiquitin ligase MARCH1. The TM region of CD83 blocks interleukin 10-driven, MARCH1-dependent ubiquitination and degradation of MHC class II and CD86 in DCs. Exploiting this posttranslational pathway for boosting MHC class II and CD86 expression on DCs may provide an opportunity to enhance the immunogenicity of vaccines.

An oral vaccine based on U-Omp19 induces protection against B. abortus mucosal challenge by inducing an adaptive IL-17 immune response in mice

As Brucella infections occur mainly through mucosal surfaces, the development of mucosal administered vaccines could be radical for the control of brucellosis. In this work we evaluated the potential of Brucella abortus 19 kDa outer membrane protein (U-Omp19) as an edible subunit vaccine against brucellosis. We investigated the protective immune response elicited against oral B. abortus infection after vaccination of mice with leaves from transgenic plants expressing U-Omp19; or with plant-made or E. coli-made purified U-Omp19. All tested U-Omp19 formulations induced protection against Brucella when orally administered without the need of adjuvants. U-Omp19 also induced protection against a systemic challenge when parenterally administered. This built-in adjuvant ability of U-Omp19 was independent of TLR4 and could be explained at least in part by its capability to activate dendritic cells in vivo. While unadjuvanted U-Omp19 intraperitoneally administered induced a specific Th1 response, following U-Omp19 oral delivery a mixed specific Th1-Th17 response was induced. Depletion of CD4(+) T cells in mice orally vaccinated with U-Omp19 resulted in a loss of the elicited protection, indicating that this cell type mediates immune protection. The role of IL-17 against Brucella infection has never been explored. In this study, we determined that if IL-17A was neutralized in vivo during the challenge period, the mucosal U-Omp19 vaccine did not confer mucosal protection. On the contrary, IL-17A neutralization during the infection did not influence at all the subsistence and growth of this bacterium in PBS-immunized mice. All together, our results indicate that an oral unadjuvanted vaccine based on U-Omp19 induces protection against a mucosal challenge with Brucella abortus by inducing an adaptive IL-17 immune response. They also indicate different and important new aspects i) IL-17 does not contribute to reduce the bacterial burden in non vaccinated mice and ii) IL-17 plays a central role in vaccine mediated anti-Brucella mucosal immunity.

Nano-microparticles as immune adjuvants: correlating particle sizes and the resultant immune responses

The development of novel immune adjuvants is emerging as a significant area of vaccine delivery based on the continued necessity to amplify immune responses to a wide array of new antigens that are poorly immunogenic. This article specifically focuses on the application of nanoparticles and microparticles as vaccine adjuvants. Many investigators are in agreement that the size of the particles is crucial to their adjuvant activities. However, reports on correlating the size of particle-based adjuvants and the resultant immune responses have been conflicting, with investigators on both sides of the fence with impressive data in support of the effectiveness of particles with small sizes (submicron) over those with larger sizes (micron) and vice versa, while other investigators reported data that showed submicron- and micron-sized particles are effective to the same degree as immune adjuvants. We have generated a list of biological, immunological and, more importantly, vaccine formulation parameters that may have contributed to the inconsistency from different studies and made recommendations on future studies attempting to correlate the size of particulate adjuvants and the immune responses induced. The information gathered could lead to strategies to optimize the performance of nano-microparticles as immune adjuvants.

Carnauba wax nanoparticles enhance strong systemic and mucosal cellular and humoral immune responses to HIV-gp140 antigen

Induction of humoral responses to HIV at mucosal compartments without inflammation is important for vaccine design. We developed charged wax nanoparticles that efficiently adsorb protein antigens and are internalized by DC in the absence of inflammation. HIV-gp140-adsorbed nanoparticles induced stronger in vitro T-cell proliferation responses than antigen alone. Such responses were greatly enhanced when antigen was co-adsorbed with TLR ligands. Immunogenicity studies in mice showed that intradermal vaccination with HIV-gp140 antigen-adsorbed nanoparticles induced high levels of specific IgG. Importantly, intranasal immunization with HIV-gp140-adsorbed nanoparticles greatly enhanced serum and vaginal IgG and IgA responses. Our results show that HIV-gp140-carrying wax nanoparticles can induce strong cellular/humoral immune responses without inflammation and may be of potential use as effective mucosal adjuvants for HIV vaccine candidates.

New approaches in the diagnosis and treatment of latent tuberculosis infection

With nearly 9 million new active disease cases and 2 million deaths occurring worldwide every year, tuberculosis continues to remain a major public health problem. Exposure to Mycobacterium tuberculosis leads to active disease in only ~10% people. An effective immune response in remaining individuals stops M. tuberculosis multiplication. However, the pathogen is completely eradicated in ~10% people while others only succeed in containment of infection as some bacilli escape killing and remain in non-replicating (dormant) state (latent tuberculosis infection) in old lesions. The dormant bacilli can resuscitate and cause active disease if a disruption of immune response occurs. Nearly one-third of world population is latently infected with M. tuberculosis and 5%-10% of infected individuals will develop active disease during their life time. However, the risk of developing active disease is greatly increased (5%-15% every year and ~50% over lifetime) by human immunodeficiency virus-coinfection. While active transmission is a significant contributor of active disease cases in high tuberculosis burden countries, most active disease cases in low tuberculosis incidence countries arise from this pool of latently infected individuals. A positive tuberculin skin test or a more recent and specific interferon-gamma release assay in a person without overt signs of active disease indicates latent tuberculosis infection. Two commercial interferon-gamma release assays, QFT-G-IT and T-SPOT.TB have been developed. The standard treatment for latent tuberculosis infection is daily therapy with isoniazid for nine months. Other options include therapy with rifampicin for 4 months or isoniazid + rifampicin for 3 months or rifampicin + pyrazinamide for 2 months or isoniazid + rifapentine for 3 months. Identification of latently infected individuals and their treatment has lowered tuberculosis incidence in rich, advanced countries. Similar approaches also hold great promise for other countries with low-intermediate rates of tuberculosis incidence.

Human immunome, bioinformatic analyses using HLA supermotifs and the parasite genome, binding assays, studies of human T cell responses, and immunization of HLA-A*1101 transgenic mice including novel adjuvants provide a foundation for HLA-A03 restricted CD8+T cell epitope based, adjuvanted vaccine protective against Toxoplasma gondii

Background

Toxoplasmosis causes loss of life, cognitive and motor function, and sight. A vaccine is greatly needed to prevent this disease. The purpose of this study was to use an immmunosense approach to develop a foundation for development of vaccines to protect humans with the HLA-A03 supertype. Three peptides had been identified with high binding scores for HLA-A03 supertypes using bioinformatic algorhythms, high measured binding affinity for HLA-A03 supertype molecules, and ability to elicit IFN-γ production by human HLA-A03 supertype peripheral blood CD8⁺ T cells from seropositive but not seronegative persons.

Results

Herein, when these peptides were administered with the universal CD4⁺T cell epitope PADRE (AKFVAAWTLKAAA) and formulated as lipopeptides, or administered with GLA-SE either alone, or with Pam₂Cys added, we found we successfully created preparations that induced IFN-γ and reduced parasite burden in HLA-A*1101(an HLA-A03 supertype allele) transgenic mice. GLA-SE is a novel emulsified synthetic TLR4 ligand that is known to facilitate development of T Helper 1 cell (TH1) responses. Then, so our peptides would include those expressed in tachyzoites, bradyzoites and sporozoites from both Type I and II parasites, we used our approaches which had identified the initial peptides. We identified additional peptides using bioinformatics, binding affinity assays, and study of responses of HLA-A03 human cells. Lastly, we found that immunization of HLA-A*1101 transgenic mice with all the pooled peptides administered with PADRE, GLA-SE, and Pam₂Cys is an effective way to elicit IFN-γ producing CD8⁺ splenic T cells and protection. Immunizations included the following peptides together: KSFKDILPK (SAG1_224-232); AMLTAFFLR (GRA6_164-172); RSFKDLLKK (GRA7_134-142); STFWPCLLR (SAG2C_13-21); SSAYVFSVK(_SPA250-258); and AVVSLLRLLK(SPA_89-98). This immunization elicited robust protection, measured as reduced parasite burden using a luciferase transfected parasite, luciferin, this novel, HLA transgenic mouse model, and imaging with a Xenogen camera.

Conclusions

Toxoplasma gondii peptides elicit HLA-A03 restricted, IFN-γ producing, CD8⁺ T cells in humans and mice. These peptides administered with adjuvants reduce parasite burden in HLA-A*1101 transgenic mice. This work provides a foundation for immunosense based vaccines. It also defines novel adjuvants for newly identified peptides for vaccines to prevent toxoplasmosis in those with HLA-A03 supertype alleles.

Highly effective generic adjuvant systems for orphan or poverty-related vaccines

Safe and effective adjuvants are needed for many vaccines with limited commercial appeal, such as vaccines to infrequent (orphan) diseases or to neglected and poverty-related diseases. Here we found that three nonproprietary liposome formulations containing monophosphoryl lipid A each induced 3-fold to 5-fold increased titers of binding and neutralizing antibodies to anthrax protective antigen compared to aluminum hydroxide-adsorbed antigen in monkeys. All vaccinated monkeys were protected against lethal challenge with aerosolized Ames strain spores.

Future vaccination strategies against tuberculosis: thinking outside the box

With almost a dozen vaccine candidates in clinical trials, tuberculosis (TB) research and development is finally reaping the first fruits of its labors. Vaccine candidates in clinical trials may prevent TB disease reactivation by efficiently containing the pathogen Mycobacterium tuberculosis (Mtb). Future research should target vaccines that achieve sterile eradication of Mtb or even prevent stable infection. These are ambitious goals that can be reached only by highly cooperative engagement of basic immunologists, vaccinologists, and clinical researchers--or in other words, by translation from basic immunology to vaccine research and development, as well as reverse translation of insights from clinical trials back to hypothesis-driven research in the basic laboratory. Here, we review current and future strategies toward the rational design of novel vaccines against TB, as well as the progress made thus far, and the hurdles that need to be overcome in the near and distant future.

Malaria vaccine design: immunological considerations

The concept of a malaria vaccine has sparked great interest for decades; however, the challenge is proving to be a difficult one. Immune dysregulation by Plasmodium and the ability of the parasite to mutate critical epitopes in surface antigens have proved to be strong defense weapons. This has led to reconsideration of polyvalent and whole parasite strategies and ways to enhance cellular immunity to malaria that may be more likely to target conserved antigens and an expanded repertoire of antigens. These and other concepts will be discussed in this review.

Unmet needs in modern vaccinology: adjuvants to improve the immune response

The key objective of vaccination is the induction of an effective pathogen-specific immune response that leads to protection against infection and/or disease caused by that pathogen, and that may ultimately result in its eradication from humanity. The concept that the immune response to pathogen antigens can be improved by the addition of certain compounds into the vaccine formulation was demonstrated about one hundred years ago when aluminium salts were introduced. New vaccine technology has led to vaccines containing highly purified antigens with improved tolerability and safety profiles, but the immune response they induce is suboptimal without the help of adjuvants. In parallel, the development of effective vaccines has been facing more and more important challenges linked to complicated pathogens (e.g. malaria, TB, HIV, etc.) and/or to subjects with conditions that jeopardize the induction or persistence of a protective immune response. A greater understanding of innate and adaptive immunity and their close interaction at the molecular level is yielding insights into the possibility of selectively stimulating immunological pathways to obtain the desired immune response. The better understanding of the mechanism of 'immunogenicity' and 'adjuvanticity' has prompted the research of new vaccine design based on new technologies, such as naked DNA or live vector vaccines and the new adjuvant approaches. Adjuvants can be used to enhance the magnitude and affect the type of the antigen-specific immune response, and the combination of antigens with more than one adjuvant, the so called adjuvant system approach, has been shown to allow the development of vaccines with the ability to generate effective immune responses adapted to both the pathogen and the target population. This review focuses on the adjuvants and adjuvant systems currently in use in vaccines, future applications, and the remaining challenges the field is facing.

Directing dendritic cell immunotherapy towards successful cancer treatment

The use of dendritic cells (DCs) for tumor immunotherapy represents a powerful approach for harnessing the patient's own immune system to eliminate tumor cells. However, suboptimal conditions for generating potent immunostimulatory DCs, as well as the induction of tolerance and suppression mediated by the tumors and its microenvironment have contributed to limited success. Combining DC vaccines with new approaches that enhance immunogenicity and overcome the regulatory mechanisms underlying peripheral tolerance may be the key to achieving effective and durable anti-tumor immune responses that translate to better clinical outcomes.

A novel laser vaccine adjuvant increases the motility of antigen presenting cells

Background

Development of a potent vaccine adjuvant without introduction of any side effects remains an unmet challenge in the field of the vaccine research.

Methodology/Principal Findings

We found that laser at a specific setting increased the motility of antigen presenting cells (APCs) and immune responses, with few local or systemic side effects. This laser vaccine adjuvant (LVA) effect was induced by brief illumination of a small area of the skin or muscle with a nondestructive, 532 nm green laser prior to intradermal (i.d.) or intramuscular (i.m.) administration of vaccines at the site of laser illumination. The pre-illumination accelerated the motility of APCs as shown by intravital confocal microscopy, leading to sufficient antigen (Ag)-uptake at the site of vaccine injection and transportation of the Ag-captured APCs to the draining lymph nodes. As a result, the number of Ag⁺ dendritic cells (DCs) in draining lymph nodes was significantly higher in both the 1° and 2° draining lymph nodes in the presence than in the absence of LVA. Laser-mediated increases in the motility and lymphatic transportation of APCs augmented significantly humoral immune responses directed against a model vaccine ovalbumin (OVA) or influenza vaccine i.d. injected in both primary and booster vaccinations as compared to the vaccine itself. Strikingly, when the laser was delivered by a hair-like diffusing optical fiber into muscle, laser illumination greatly boosted not only humoral but also cell-mediated immune responses provoked by i.m. immunization with OVA relative to OVA alone.

Conclusion/Significance

The results demonstrate the ability of this safe LVA to augment both humoral and cell-mediated immune responses. In comparison with all current vaccine adjuvants that are either chemical compounds or biological agents, LVA is novel in both its form and mechanism; it is risk-free and has distinct advantages over traditional vaccine adjuvants.

Application of the immunological disease continuum to study autoimmune and other inflammatory events after vaccination

In vaccine safety monitoring, the evaluation of possible autoimmune events is challenging. Developing grouping systems based on pathophysiology, instead of organ systems, may enhance our ability to identify or verify associations between vaccines and adverse immunologically mediated events in clinical trials and post-licensure surveillance. Emerging data suggest that self-directed tissue inflammation occurs along a continuum from innate immune-driven diseases to adaptive immune-driven diseases. Herein, we develop this proposed classification for the vaccination setting in which inflammatory diseases are placed along a continuum according to the two major arms of the immune system, the innate immune arm (mediated by cells including neutrophils, macrophages and complement) and the adaptive immune arm (cell-mediated and humoral response). We incorporate hypersensitivity reactions and molecular mimicry vaccine-related reactions into this mechanistic scheme. We show how this could have important implications to assess mechanisms of potential immune-mediated adverse events following vaccination.

Naloxone and alum synergistically augment adjuvant activities of each other in a mouse vaccine model of Salmonella typhimurium infection

Alum is the most commonly used adjuvant for human vaccination but is a poor inducer of cell mediated immunity and T helper 1 (Th1) responses. We have previously shown that naloxone (NLX), which is a general opioid antagonist, acts as an effective adjuvant in enhancing vaccine-induced cellular immunity and Th1 immune responses. Here, we tested the efficacy of an alum-NLX mixture, as a new adjuvant, in the induction of humoral and cellular immunity in response to endotoxin-removed lysate (ERL) of Salmonella typhimurium (S. typhimurium) as a model vaccine. BALB/c mice were divided into five vaccination groups. Mice in the experimental groups received either the ERL vaccine alone or in combination with the adjuvant alum, NLX or the alum-NLX mixture. Mice in the negative control group received phosphate-buffered saline. All mice were immunized on days 0 and 7. Two weeks after the last immunization, immune responses to S. typhimurium were assessed. Our results indicate that including the alum-NLX mixture as an adjuvant during vaccination increased the ability of the ERL vaccine to enhance lymphocyte proliferation, shifted the immune response toward a Th1 profile and increased S. typhimurium-specific IgG, IgG2a and the ratio of IgG2a to IgG1. This resulted in improved protective immunity against S. typhimurium. In conclusion, administering an alum-NLX mixture adjuvant in combination with the ERL vaccine enhances both humoral and cellular immunity, and shifts the immune response to a Th1 pattern.

In vivo efficacy of a chitosan/IL-12 adjuvant system for protein-based vaccines

Vaccines based on recombinant proteins require adjuvant systems in order to generate Th1-type immune responses. We have developed a vaccine adjuvant system using a viscous chitosan solution and interleukin (IL)-12, a Th1-inducing cytokine. The chitosan solution is designed to create a depot of antigen and IL-12 at a subcutaneous injection site. We measured the in vivo immune response of a vaccine containing 0.25, 1, or 4 μg murine IL-12 and 75 μg ovalbumin (OVA), formulated in a 1.5% chitosan glutamate solution. The chitosan/IL-12/OVA vaccine, in comparison to chitosan/OVA, IL-12/OVA, or OVA alone, elicited greater antigen-specific CD4(+) and CD8(+) T-cell responses, as determined by CD4(+) splenocyte proliferation, Th1 cytokine release, CD8(+) T-cell interferon-γ release, and MHC class I peptide pentamer staining. The combination of chitosan and IL-12 also enhanced IgG2a and IgG2b antibody responses to OVA. Co-formulation of chitosan and IL-12 thus promoted the generation of a Th1 immune response to a model protein vaccine.

The M cell-targeting ligand promotes antigen delivery and induces antigen-specific immune responses in mucosal vaccination

Oral mucosal immunization can induce protective immunity in both systemic compartments and the mucosa. Successful mucosal immunization depends on Ag delivery to the mucosal immune induction site. The high transcytotic activity of M cells within the mucosa makes these cells attractive targets for mucosal Ag delivery, although it remains unclear whether delivery of Ag to M cells only can guarantee the induction of effective immune responses. In this study, we evaluated the ability of an M cell-targeting ligand with adjuvant activity to induce immunity against ligand-fused Ag. We selected M cell-targeting ligands through biopanning of a phage display library against differentiated in vitro M-like cells and produced the recombinant Ags fused to the selected ligands using the model Ag. One of the selected peptide ligands, Co1, promoted the binding of ligand-fused Ag to mouse Peyer's patch M cells and human M-like cells that had been defined by binding with the M cell-specific and anti-GP2 Abs. In addition, Co1 ligand enhanced the uptake of fused Ag by immunogenic tissue in an ex vivo loop assay and in vivo oral administration experiments. After oral administration, the ligand-fused Ag enhanced immune responses against the fused Ag compared with those of the control Ag without ligand. In addition, this use of the ligand supported a skewed Th2-type immune response against the fused Ag. Collectively, these results suggest that the ligand selected through biopanning against cultured M-like cells could be used as an adjuvant for targeted Ag delivery into the mucosal immune system to enhance immune induction.

Immunomodulators as adjuvants for vaccines and antimicrobial therapy

A highly effective strategy for combating infectious diseases is to enhance host defenses using immunomodulators, either preventatively, through vaccination, or therapeutically. The effectiveness of many vaccines currently in use is due in part to adjuvants, molecules that have little immunogenicity by themselves but which help enhance and appropriately skew the immune response to an antigen. The development of new vaccines necessitates the development of new types of adjuvants to ensure an appropriate immune response. Herein, we review commonly used vaccine adjuvants and discuss promising adjuvant candidates. We also discuss various other immunomodulators (namely cytokines, Toll-like receptor agonists, and host defense peptides) that are, or have potential to be, useful for antimicrobial therapies that exert their effects by boosting host immune responses rather than targeting pathogens directly.

Interleukin-1 family cytokines as mucosal vaccine adjuvants for induction of protective immunity against influenza virus

A safe and potent adjuvant is needed for development of mucosal vaccines against etiological agents, such as influenza virus, that enter the host at mucosal surfaces. Cytokines are potential adjuvants for mucosal vaccines because they can enhance primary and memory immune responses enough to protect against some infectious agents. For this study, we tested 26 interleukin (IL) cytokines as mucosal vaccine adjuvants and compared their abilities to induce antigen (Ag)-specific immune responses against influenza virus. In mice intranasally immunized with recombinant influenza virus hemagglutinin (rHA) plus one of the IL cytokines, IL-1 family cytokines (i.e., IL-1α, IL-1β, IL-18, and IL-33) were found to increase Ag-specific immunoglobulin G (IgG) in plasma and IgA in mucosal secretions compared to those after immunization with rHA alone. In addition, high levels of both Th1- and Th2-type cytokines were observed in mice immunized with rHA plus an IL-1 family cytokine. Furthermore, mice intranasally immunized with rHA plus an IL-1 family cytokine had significant protection against a lethal influenza virus infection. Interestingly, the adjuvant effects of IL-18 and IL-33 were significantly decreased in mast cell-deficient W/W(v) mice, indicating that mast cells have an important role in induction of Ag-specific mucosal immune responses induced by IL-1 family cytokines. In summary, our results demonstrate that IL-1 family cytokines are potential mucosal vaccine adjuvants and can induce Ag-specific immune responses for protection against pathogens like influenza virus.

Pediatric vaccines on the horizon

Vaccines have saved the lives of millions of children and continue to be essential interventions to control infectious diseases among people of all ages. The list of recommended vaccines for children has expanded in recent years; however, many viral, bacterial and parasitic infections remain a major cause of morbidity and mortality in children. Improved vaccines to prevent Streptococcus pneumoniae and Neisseria meningitidis infections in children will soon be available. Recent scientific advances are being applied to design new childhood vaccines affording enhanced efficacy, safety and tolerability. Financial barriers and other obstacles to adequate vaccine access need to be eliminated to assure coverage for all children and adolescents.

Blood-stage malaria vaccines - recent progress and future challenges

Plasmodium falciparum malaria is a major global health problem, responsible for up to 1 million deaths each year. Major efforts have been made to develop an effective vaccine against this disease, to reduce the associated morbidity and mortality. There has already been considerable progress, with the first vaccine against the pre-erythrocytic stages of P. falciparum now en route to licensure. There remains, however, a strong scientific rationale for the development of a highly effective additional vaccine component against the blood stages of the parasite, which could be deployed in conjunction with partially effective control measures against the pre-erythrocytic stages. Here, recent progress in the clinical development of blood-stage vaccines is reviewed, including methods of antigen selection, the limitations of in-vitro assays for selecting vaccines for clinical development, and the results of recently published clinical trials. This review seeks to summarize recent developments in our understanding of immunity to blood-stage parasites, as well as the relevant key advances made in vaccine technologies over the last decade. The future challenges that face this field of vaccine research are also described.

Intravital microscopy imaging of macrophage localization to immunogenic particles and co-localized tissue oxygen saturation

Well-designed biomaterial polymer particle-based vaccines will optimally promote immune cell antigen-presenting behavior while minimizing adverse inflammatory responses to the particles and encapsulated drugs or adjuvants. It is important in the design of particle-based vaccines to consider possible harmful effects of immune response on tissue at the vaccination site. Intravital microscopy with rodent dorsal skin window chambers enables in vivo serial observations in the same animal, and such models which have been used to study angiogenesis and macrophage response to implanted biomaterials may also be useful for the development of particle-based vaccines. To our knowledge there have been no reports where intravital microscopy has documented real-time immune cell localization and potentially harmful co-localized tissue effects. In this proof-of-principle study we used fluorescence and spectral imaging intravital microscopy of mouse window chambers to measure macrophage localization and co-localized tissue microvessel hemoglobin saturation changes in response to an immunogenic stimulus from polymer particles loaded with lipopolysaccharide (LPS) serving as a model vaccine/adjuvant system. We observed greater and faster macrophage localization to stronger inflammatory stimuli from LPS-loaded particle doses, a trend of decreased microvessel oxygenation with increased macrophage accumulation and, in an extreme case, complete microvessel collapse accompanied by tissue necrosis. Our technique may be useful for optimizing design of particle-based vaccines and may give insight into the use of hemoglobin saturation as a biomarker of tissue inflammation for clinical investigations of particle-based vaccines.

Mode of action of adjuvants: implications for vaccine safety and design

For decades, the search for new vaccine adjuvants has been largely empirical. A series of new adjuvants and related formulations are now emerging that are acting through identified immunological mechanisms. Understanding adjuvant mechanism of action is crucial for vaccine design, since this allows for directing immune responses towards efficacious disease-specific effector mechanisms and appropriate memory. It is also of great importance to build new paradigms for assessing adjuvant safety at development stages and at regulatory level. This report reflects the conclusions of a group of scientists from academia, regulatory agencies and industry who attended a conference, organized by the International Association for Biologicals (IABS), on the mode of action of adjuvants on 29-30 April 2010 in Bethesda, Maryland, USA, particularly focusing on how understanding adjuvants mode of action can impact on the assessment of vaccine safety and help to develop target-specific vaccines. More information on the conference output can be found on the IABS website, http://www.iabs.org/.

Comparison of BCG, MPL and cationic liposome adjuvant systems in leishmanial antigen vaccine formulations against murine visceral leishmaniasis

Background

The development of an effective vaccine against visceral leishmaniasis (VL) caused by Leishmania donovani is an essential aim for controlling the disease. Use of the right adjuvant is of fundamental importance in vaccine formulations for generation of effective cell-mediated immune response. Earlier we reported the protective efficacy of cationic liposome-associated L. donovani promastigote antigens (LAg) against experimental VL. The aim of the present study was to compare the effectiveness of two very promising adjuvants, Bacille Calmette-Guerin (BCG) and Monophosphoryl lipid A (MPL) plus trehalose dicorynomycolate (TDM) with cationic liposomes, in combination with LAg, to confer protection against murine VL.

Results

All the three formulations afforded significant protection against L. donovani in both the visceral organs, liver and spleen. Although comparable level of protection was observed in BCG+LAg and MPL-TDM+LAg immunized mice, highest level of protection was exhibited by the liposomal LAg immunized group. Significant increase in anti-LAg IgG levels were detected in both MPL-TDM+LAg and liposomal LAg immunized animals with higher levels of IgG2a than IgG1. But BCG+LAg failed to induce any antibody response. As an index of cell-mediated immunity DTH responses were measured and significant response was observed in mice vaccinated with all the three different formulations. However, highest responses were observed with liposomal vaccine immunization. Comparative evaluation of IFN-γ and IL-4 responses in immunized mice revealed that MPL-TDM+LAg group produced the highest level of IFN-γ but lowest IL-4 level, while BCG+LAg demonstrated generation of suboptimum levels of both IFN-γ and IL-4 response. Elicitation of moderate levels of prechallenge IFN-γ along with optimum IL-4 corresponds with successful vaccination with liposomal LAg.

Conclusion

This comparative study reveals greater effectiveness of the liposomal vaccine for protection against progressive VL in BALB/c. Again, evaluation of the immune responses by vaccination emphasizes the need of stimulation of potent cellular immunity based on both Th1 and Th2 cell responses to confer protection against VL.

Combination of pneumococcal surface protein A (PspA) with whole cell pertussis vaccine increases protection against pneumococcal challenge in mice

Streptococcus pneumoniae is the leading cause of respiratory acute infections around the world. In Latin America, approximately 20,000 children under 5 years of age die of pneumococcal diseases annually. Pneumococcal surface protein A (PspA) is among the best-characterized pneumococcal antigens that confer protection in animal models of pneumococcal infections and, as such, is a good alternative for the currently available conjugated vaccines. Efficient immune responses directed to PspA in animal models have already been described. Nevertheless, few low cost adjuvants for a subunit pneumococcal vaccine have been proposed to date. Here, we have tested the adjuvant properties of the whole cell Bordetella pertussis vaccine (wP) that is currently part of the DTP (diphtheria-tetanus-pertussis) vaccine administrated to children in several countries, as an adjuvant to PspA. Nasal immunization of BALB/c mice with a combination of PspA5 and wP or wP(low)--a new generation vaccine that contains low levels of B. pertussis LPS--conferred protection against a respiratory lethal challenge with S. pneumoniae. Both PspA5-wP and PspA5-wP(low) vaccines induced high levels of systemic and mucosal antibodies against PspA5, with similar profile, indicating no essential requirement for B. pertussis LPS in the adjuvant properties of wP. Accordingly, nasal immunization of C3H/HeJ mice with PspA5-wP conferred protection against the pneumococcal challenge, thus ruling out a role for TLR4 responses in the adjuvant activity and the protection mechanisms triggered by the vaccines. The high levels of anti-PspA5 antibodies correlated with increased cross-reactivity against PspAs from different clades and also reflected in cross-protection. In addition, passive immunization experiments indicated that antibodies played an important role in protection in this model. Finally, subcutaneous immunization with a combination of PspA5 with DTP(low) protected mice against challenge with two different pneumococcal strains, opening the possibility for the development of a combined infant vaccine composed of DTP and PspA.

Adjuvants for cancer vaccines

The recent FDA approval of sipuleucel-T (Provenge), a patient-specific immunotherapy for androgen-independent prostate cancer developed by Dendreon Corporation, has provided support for the concept of cellular immunotherapy as an approach to cancer treatment. Adjuvants are compounds that enhance the potency of the antigen-specific immune response and can be an essential component of an efficacious vaccine. Cervarix is a prophylactic vaccine against human papilloma virus (HPV) types 16 and 18, which can cause cervical cancer, and recently received approval from the FDA, due in part to the protective immunity it conferred against not only HPV types contained in the vaccine but in addition to oncogenic HPV strains that were not contained in the vaccine. Cervarix is formulated with MPL (monophosphoryl lipid A), a TLR-4 targeted adjuvant shown to promote immune response broadening. The recent FDA approvals of these pioneering vaccines are landmark events, and will likely usher in renewed interest and investment in the development of new therapeutic cancer vaccine candidates. In this review, we examine new molecularly defined adjuvants and formulations and its application to cancer vaccines under development.

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.

Adjuvant activity on murine and human macrophages

Activation of cells of the innate immunity such as macrophages and dendritic cells is critical to mount an adaptive immune response. Recent advances on the understanding of innate immune receptors such as the Toll-like receptors (TLR) and NOD-like receptors (NLR) and the demonstration that microbial products activate specific receptors. This discovery represented a major advance and provided tools to test novel adjuvants in vitro to investigate activation on innate immune cells. Here the isolation and culture of murine macrophages is described, and the use of macrophages derived from gene-deficient mice is proposed to define receptor usage. Novel adjuvants may be tested for their capacity to induce cytokines, chemokines and the expression of costimulatory molecules. The basic methods to assess macrophage activation are given, which may predict an in vivo activity of a novel adjuvant.

CD14-independent responses induced by a synthetic lipid A mimetic

CRX-527 belongs to a new family of synthetic lipid A mimetics, the aminoalkyl glucosaminide 4-phosphates, which are considered as potential vaccine adjuvants or stand-alone immunotherapeutics to harness innate immune defenses. Since natural lipid A from bacterial LPS depends on membrane-bound (mCD14) or soluble CD14 for its TLR4 ligand activity, we investigated the involvement of both forms of CD14 in the responses elicited by CRX-527. First, we found that CRX-527 induces NF-kappaB and interferon regulatory factor-3 (IRF-3) activation in human embryonic kidney cells transfected with TLR4 and MD-2 genes alone, whereas the responses to LPS require either co-transfection of the gene encoding mCD14 or addition of soluble CD14. We then observed that monocyte-derived DC, which are devoid of mCD14 respond to CRX-527 but not to LPS in serum-free medium. Furthermore, we found that, in contrast to LPS, CRX-527 induces the production of cytokines in whole blood of a patient with paroxysmal nocturnal hemoglobinuria, a disease in which mCD14-dependent responses are defective. Finally, we demonstrated that splenocytes from CD14-deficient mice produce cytokines in response to CRX-527 but not to LPS. We conclude that the lipid A mimetic CRX-527 does not require the CD14 co-receptor to elicit TLR4-mediated responses.

Inflammatory and autoimmune reactions in atherosclerosis and vaccine design informatics

Atherosclerosis is the leading pathological contributor to cardiovascular morbidity and mortality worldwide. As its complex pathogenesis has been gradually unwoven, the regime of treatments and therapies has increased with still much ground to cover. Active research in the past decade has attempted to develop antiatherosclerosis vaccines with some positive results. Nevertheless, it remains to develop a vaccine against atherosclerosis with high affinity, specificity, efficiency, and minimal undesirable pathology. In this review, we explore vaccine development against atherosclerosis by interpolating a number of novel findings in the fields of vascular biology, immunology, and bioinformatics. With recent technological breakthroughs, vaccine development affords precision in specifying the nature of the desired immune response—useful when addressing a disease as complex as atherosclerosis with a manifold of inflammatory and autoimmune components. Moreover, our exploration of available bioinformatic tools for epitope-based vaccine design provides a method to avoid expenditure of excess time or resources.

Identification of T. gondii epitopes, adjuvants, and host genetic factors that influence protection of mice and humans

Toxoplasma gondii is an intracellular parasite that causes severe neurologic and ocular disease in immune-compromised and congenitally infected individuals. There is no vaccine protective against human toxoplasmosis. Herein, immunization of L(d) mice with HF10 (HPGSVNEFDF) with palmitic acid moieties or a monophosphoryl lipid A derivative elicited potent IFN-gamma production from L(d)-restricted CD8(+) T cells in vitro and protected mice. CD8(+) T cell peptide epitopes from T. gondii dense granule proteins GRA 3, 6, 7, and Sag 1, immunogenic in humans for HLA-A02(+), HLA-A03(+), and HLA-B07(+) cells were identified. Since peptide repertoire presented by MHC class I molecules to CD8(+) T cells is shaped by endoplasmic reticulum-associated aminopeptidase (ERAAP), polymorphisms in the human ERAAP gene ERAP1 were studied and associate with susceptibility to human congenital toxoplasmosis (p<0.05). These results have important implications for vaccine development.

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.

Novel adjuvants for B cell immune responses

PURPOSE OF REVIEW

To summarize recent progress in the development of adjuvants with a special focus on adjuvants that enhance B-cell responses to protein-based vaccines. Both established and new experimental approaches are described and also briefly we discuss how adjuvants and virus-based vaccines interact with the immune system.

RECENT FINDINGS

Two new adjuvants were recently approved for human applications and many others are in preclinical or clinical testing. Significant advances were made to describe the mechanism of action of adjuvants. For example, aluminum hydroxide salts were shown to engage Nalp3, a member of the cytosolic NOD-like receptors and activation of B cells via invariant natural killer cell presentation of alpha-galactosylceramide was described. The effects of Toll-like receptor ligands on B-cell differentiation were further characterized and a peptide derived from IPS-1, a cytosolic signaling molecule, was shown to provide adjuvant effect. Stimulation of protective antibodies against HIV-1 may require extensive antibody affinity maturation, thus long-term exposure or repeated administration of antigen may be needed to induce effective B-cell responses.

SUMMARY

Advances in our understanding of how specific signaling pathways link innate and adaptive immunity provides a basis for the design of improved adjuvants to promote broad and potent B-cell responses.