TLR-based immune adjuvants

Emphasis on the Role of PF4 in the Incidence, Pathophysiology and Treatment of Heparin Induced Thrombocytopenia

Heparin Induced Thrombocytopenia (HIT) is caused by antibodies that recognize platelet factor 4 (PF4) associated with polyanionic glycosaminoglycan drugs or displayed on vascular cell membranes. These antibodies are elicited by multimolecular complexes that can occur when heparin is administered in clinical settings associated with abundant PF4. Heparin binding alters native PF4 and elicits immune recognition and response. While the presence of heparin is integral to immunogenesis, the HIT antibody binding site is within PF4. Thus HIT antibodies develop and function to cause thrombocytopenia and/or thrombosis only in the presence of PF4. Future emphasis on understanding the biology, turnover and regulation of PF4 may lead to insights into the prevention and treatment of HIT.

Combined TLR7/8 and TLR9 ligands potentiate the activity of a Schistosoma japonicum DNA vaccine

Background

Toll-like receptor (TLR) ligands have been explored as vaccine adjuvants for tumor and virus immunotherapy, but few TLR ligands affecting schistosoma vaccines have been characterized. Previously, we developed a partially protective DNA vaccine encoding the 26-kDa glutathione S-transferase of Schistosoma japonicum (pVAX1-Sj26GST).

Methodology/Principal Findings

In this study, we evaluated a TLR7/8 ligand (R848) and a TLR9 ligand (CpG oligodeoxynucleotides, or CpG) as adjuvants for pVAX1-Sj26GST and assessed their effects on the immune system and protection against S. japonicum. We show that combining CpG and R848 with pVAX1-Sj26GST immunization significantly increases splenocyte proliferation and IgG and IgG2a levels, decreases CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Treg) frequency in vivo, and enhances protection against S. japonicum. CpG and R848 inhibited Treg-mediated immunosuppression, upregulated the production of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-4, IL-10, IL-2, and IL-6, and decreased Foxp3 expression in vitro, which may contribute to prevent Treg suppression and conversion during vaccination and allow expansion of antigen-specific T cells against pathogens.

Conclusions

Our data shows that selective TLR ligands can increase the protective efficacy of DNA vaccines against schistosomiasis, potentially through combined antagonism of Treg-mediated immunosuppression and conversion.

There is evidence that TLR activation can block Treg cell responses and thereby break tolerance to self-antigens. It is expected that the use of TLR ligands as vaccine adjuvants will induce potent anti-pathogen immune responses and simultaneously overcome immune inhibition mediated by Tregs. However, the impact of TLR ligands on schistosomiasis vaccines is unclear. Here, we demonstrate that the use of a TLR7/8 ligand (R848) and a TLR9 ligand (CpG) as adjuvants in combination with the S. japonicum vaccine pVAX1-Sj26GST improves disease protection. The combination of CpG and R848 administered after vaccination causes an immune response marked by an upregulation of splenocyte proliferation and IgG and IgG2a levels that also coincides with a decreased proportion of CD4⁺CD25⁺ Tregs in mice. We also show that combined adjuvant use of CpG and R848 may impair Treg development and function by promoting the secretion of proinflammatory cytokines and reducing Foxp3 expression. Our findings suggest that in combination with the vaccine, TLR ligands may protect the effector response from Treg-mediated suppression, thereby eliciting the appropriate immune response to improve vaccine efficacy. Immunization combined with the TLR ligands CpG and R848 thus represents a promising new approach for the design of schistosoma vaccines.

Nanovaccines : nanocarriers for antigen delivery

Vaccination has become one of the most important health interventions of our times, revolutionizing health care, and improving the quality of life and life expectancy of millions all over the world. In spite of this, vaccine research remains a vast field for innovation and improvement. Indeed, the shift towards the use of sub-unit antigens, much safer but less immunogenic, and the recognized need to facilitate the access to vaccines in the global framework is currently stimulating the search for safe and efficient adjuvants and delivery technologies. Within this context, nanocarriers have gained particular attention over the last years and appear as one of the most promising strategies for antigen delivery. A number of biomaterials and technologies can be used to design nanovaccines that fulfill the requirements of new vaccination approaches, such as single-dose and transmucosal immunization, critical for achieving a widespread coverage while reducing the overall costs in relation to traditional forms of vaccination. Here we present an overview of the current state of nanocarriers for antigen delivery, developed with the perspective of contributing to the global vaccination goal.

Poly(I:C)/alum mixed adjuvant priming enhances HBV subunit vaccine-induced immunity in mice when combined with recombinant adenoviral-based HBV vaccine boosting

Background

Virus-specific cellular immune responses play a critical role in virus clearance during acute or chronic HBV infection. Currently, the commercially available HBV vaccine is combined with alum adjuvant, which stimulates mainly Th2 immune responses. Therefore, development of new therapeutic HBV vaccine adjuvants and immune strategies that also promote Th1 and CTL responses is urgently needed.

Methodology/Principal findings

To improve the immunity induced by the novel HBSS1 HBV vaccine, we evaluated the ability of adjuvants, including alum, CpG and polyriboinosinic polyribocytidylic acid [poly(I:C)], to enhance the response when boosted with the recombinant adenoviral vector vaccine rAdSS1. The immune responses to different adjuvant combinations were assessed in C57BL/6 mice by enzyme-linked immunosorbent assay (ELISA), ELISpot and cytokine release assays. Among the combinations tested, a HBV protein particle vaccine with CpG/alum and poly(I:C)/alum priming combinations accelerated specific seroconversion and produced high antibody (anti-PreS1, anti-S antibody) titres with a Th1 bias. After boosting with recombinant adenoviral vector vaccine rAdSS1, both groups produced a strong multi-antigen (S and PreS1)-specific cellular immune response. HBSS1 immunisation with poly(I:C)/alum priming also generated high-level CD4⁺ and CD8⁺ T cell responses in terms of Th1 cytokines (IFN-γand IL-2).

Conclusions

The protein-vaccine HBSS1 with mixed poly(I:C)/alum adjuvant priming, followed by a rAdSS1 vaccine boost, maximises specific antibody and Th1-biased cellular immune responses. This regime might prove useful in the development of HBV therapeutic vaccines. Furthermore, this promising strategy might be applied to vaccines against other persistent infections, such as human immunodeficiency virus and tuberculosis.

Implication of double-stranded RNA signaling in the etiology of autoimmune myasthenia gravis

OBJECTIVE

Myasthenia gravis (MG) is an autoimmune disease mediated mainly by anti-acetylcholine receptor (AChR) antibodies. The thymus plays a primary role in MG pathogenesis. As we recently showed an inflammatory and antiviral signature in MG thymuses, we investigated whether pathogen-sensing molecules could contribute to an anti-AChR response.

METHODS

We studied the effects of toll-like receptor agonists on the expression of α-AChR and various tissue-specific antigens (TSAs) in human thymic epithelial cell (TEC) cultures. As polyinosinic-polycytidylic acid (poly[I:C]), which mimics double-stranded RNA (dsRNA), stimulated specifically α-AChR expression, the signaling pathways involved were investigated. In parallel, we analyzed the expression of dsRNA-signaling components in the thymus of MG patients, and the relevance of our data was investigated in vivo in poly(I:C)-injected mice.

RESULTS

We demonstrate that dsRNA signaling induced by poly(I:C) specifically triggers the overexpression of α-AChR in TECs and not of other TSAs. A poly(I:C) effect was also observed on MG TECs. This induction is mediated through toll-like receptor 3 (TLR3) and protein kinase R (PKR), and by the release of interferon (IFN)-β. In parallel, human MG thymuses also display an overexpression of TLR3, PKR, and IFN-β. In addition, poly(I:C) injections specifically increase thymic expression of α-AChR in wild-type mice, but not in IFN-I receptor knockout mice. These injections also lead to an anti-AChR autoimmune response characterized by a significant production of serum anti-AChR antibodies and a specific proliferation of B cells.

INTERPRETATION

Because anti-AChR antibodies are highly specific for MG and are pathogenic, dsRNA-signaling activation could contribute to the etiology of MG.

Evaluation of TLR agonists as potential mucosal adjuvants for HIV gp140 and tetanus toxoid in mice

In the present study we investigate the impact of a range of TLR ligands and chitosan as potential adjuvants for different routes of mucosal immunisation (sublingual (SL), intranasal (IN), intravaginal (IVag) and a parenteral route (subcutaneous (SC)) in the murine model. We assess their ability to enhance antibody responses to HIV-1 CN54gp140 (gp140) and Tetanus toxoid (TT) in systemic and vaginal compartments. A number of trends were observed by route of administration. For non-adjuvanted antigen, SC>SL>IN immunisation with respect to systemic IgG responses, where endpoint titres were greater for TT than for gp140. In general, co-administration with adjuvants increased specific IgG responses where IN = SC>SL, while in the vaginal compartment IN>SL>SC for specific IgA. In contrast, for systemic and mucosal IgA responses to antigen alone SL>IN = SC. A number of adjuvants increased specific systemic IgA responses where in general IN>SL>SC immunisation, while for mucosal responses IN = SL>SC. In contrast, direct intravaginal immunisation failed to induce any detectable systemic or mucosal responses to gp140 even in the presence of adjuvant. However, significant systemic IgG responses to TT were induced by intravaginal immunisation with or without adjuvant, and detectable mucosal responses IgG and IgA were observed when TT was administered with FSL-1 or Poly I∶C. Interestingly some TLRs displayed differential activity dependent upon the route of administration. MPLA (TLR4) suppressed systemic responses to SL immunisation while enhancing responses to IN or SC immunisation. CpG B enhanced SL and IN responses, while having little or no impact on SC immunisation. These data demonstrate important route, antigen and adjuvant effects that need to be considered in the design of mucosal vaccine strategies.

TLR agonists are highly effective at eliciting functional memory CTLs of effector memory phenotype in peptide immunization

Given the importance of memory cytotoxic T lymphocytes (CTLs) in eliminating altered self-cells, including virus-infected and tumor cells, devising effective vaccination strategies for generating memory CTLs is a priority in the field of immunology. Herein, we elaborate upon a novel boosting approach that utilizes synthetic peptides and Toll-like receptor (TLR) agonists as adjuvants to generate sufficient numbers of memory CTLs to protect against infection in mice. Peptide boosting with lipopolysaccharide (LPS), a TLR4-ligand, has been shown to progressively enhance memory CTLs. Whether this result is strictly dependent on activation of TLR4 or can be similarly achieved by signaling through other TLRs is of practical interest in vaccine development but is yet unknown. In this report, we present evidence that intravenous peptide boosting together with TLR3 and TLR9 agonists (Poly IC and CpG, respectively) is highly effective and induces large quantities of memory CTLs of effector memory phenotype after three boosts. Compared to LPS, CpG and Poly IC generate more robust immune responses after the first and second boosts, indicating that a protective level of CTLs might be achieved with fewer boosts when CpG or Poly IC is used. Lastly, the resultant memory CTLs from boosting with different TLR agonists as adjuvant are equally protective against pathogen challenge and are not immune senescent. Therefore, TLR agonists are effective adjuvants in intravenous peptide boosting for the generation of functional memory CTLs.

Cancer and innate immune system interactions: translational potentials for cancer immunotherapy

Passive immunotherapy, including adoptive T-cell therapy and antibody therapy, has shown encouraging results in cancer treatment lately. However, active immunotherapy of solid cancers remains an elusive goal. It is now known that the human innate immune system recognizes pathogen-associated molecular patterns conserved among microbes or damage-associated molecular patterns released from tissue injuries to initiate adaptive immune responses during infection and tissue inflammation, respectively. In contrast, how the innate immune system recognizes endogenously arising cancer remains poorly understood at the molecular level, which poses a significant roadblock to the development of active cancer immunotherapy. We hereby review the current knowledge of how solid cancers directly and indirectly interact with cells of the human innate immune system, with a focus on the potential effect of such interactions to the resultant adaptive immune responses against cancer. We believe that understanding cancer and innate immune system interactions may allow us to better manipulate the adaptive immune system at the molecular level to develop effective active immunotherapy against cancer. Current and future perspectives in clinical development that exploits these molecular interactions are discussed.

Vaccines for the elderly

Vaccination is the most efficient strategy to prevent infectious disease. The increased vulnerability to infection of the elderly makes them a particularly important target population for vaccination. However, most vaccines are less immunogenic and efficient in the elderly because of age-related changes in the immune system. Vaccination against influenza, Streptococcus pneumoniae and varicella zoster virus is recommended for the elderly in many countries. Various strategies such as the use of adjuvants and novel administration routes are pursued to improve influenza vaccination for the elderly and recent developments in the field of pneumococcal vaccination led to the licensure of protein-conjugated polysaccharide vaccines containing up to 13 serotypes. As antibody titres are generally lower in the elderly and-particularly for inactivated vaccines-decline fast in the elderly, regular booster immunizations, for example against tetanus, diphtheria and, in endemic areas, tick-borne encephalitis, are essential during adulthood to ensure protection of the elderly. With increasing health and travel opportunities in old age the importance of travel vaccines for persons over the age of 60 is growing. However, little is known about immunogenicity and efficacy of travel vaccines in this age group. Despite major advances in the field of vaccinology over the last decades, there are still possibilities for improvement concerning vaccines for the elderly. Novel approaches, such as viral vectors for antigen delivery, DNA-based vaccines and innovative adjuvants, particularly toll-like receptor agonists, will help to achieve optimal protection against infectious diseases in old age.

Repetitive peptide boosting progressively enhances functional memory CTLs

Cytotoxic T lymphocytes (CTLs) play a critical role in controlling intracellular pathogens and cancer cells, and induction of memory CTLs holds promise for developing effective vaccines against critical virus infections. However, generating memory CTLs remains a major challenge for conventional vector-based, prime-boost vaccinations. Thus, it is imperative that we explore nonconventional alternatives, such as boosting without vectors. We show here that repetitive intravenous boosting with peptide and adjuvant generates memory CD8 T cells of sufficient quality and quantity to protect against infection in mice. The resulting memory CTLs possess a unique and long-lasting effector memory phenotype, characterized by decreased interferon-γ but increased granzyme B production. These results are observed in both transgenic and endogenous models. Overall, our findings have important implications for future vaccine development, as they suggest that intravenous peptide boosting with adjuvant following priming can induce long-term functional memory CTLs.

B cell TLRs and induction of immunoglobulin class-switch DNA recombination

Toll-like receptors (TLRs) are a family of conserved pattern recognition receptors (PRRs). Engagement of B cell TLRs by microbe-associated molecular patterns (MAMPs) induces T-independent (TI) antibody responses and plays an important role in the early stages of T-dependent (TD) antibody responses before specific T cell help becomes available. The role of B cell TLRs in the antibody response is magnified by the synergy of B cell receptor (BCR) crosslinking and TLR engagement in inducing immunoglobulin (Ig) class switch DNA recombination (CSR), which crucially diversifies the antibody biological effector functions. Dual BCR/TLR engagement induces CSR to all Ig isotypes, as directed by cytokines, while TLR engagement alone induces marginal CSR. Integration of BCR and TLR signaling results in activation of the canonical and non-canonical NF-κB pathways, induction of activation-induced cytidine deaminase (AID) and germline transcription of IgH switch (S) regions. A critical role of B cell TLRs in CSR and the antibody response is emphasized by the emergence of several TLR ligands as integral components of vaccines that greatly boost humoral immunity in a B cell-intrinsic fashion.

MF59 formulated with CpG ODN as a potent adjuvant of recombinant HSP65-MUC1 for inducing anti-MUC1+ tumor immunity in mice

MF59 is an oil-in-water emulsion adjuvant approved for influenza vaccines for human use in Europe. Due to its Th2 inducing properties, MF59 is seldom tested for cancer vaccines. In this study, MF59 formulated with a C-type CpG oligodeoxynucleotide (YW002) was tested for its Th1 adjuvant activity to induce immune responses to HSP65-MUC1, a recombinant fusion protein incorporating a mycobacterial heat shock protein (HSP65) and mucin 1, cell surface associated (MUC1) derived peptide. Combination of YW002 with MF59 (MF59-YW002) could confer a potent Th1 biasing property to the adjuvant, which enhanced the immunogenicity of HSP65-MUC1 to induce significantly higher levels of specific IgG2c, increased IFN-γ mRNA expression in splenocytes and the generation of antigen-specific cytotoxic T lymphocytes in mice. When prophylactically applied, MF59-YW002 adjuvant containing HSP65-MUC1 inhibited the growth of MUC1⁺ B16 melanoma and prolonged the survival of tumor-bearing mice. In contrast, adjuvant containing MF59 with HSP65-MUC1 in the absence of YW002, promoted the growth of MUC1⁺ B16 melanoma in mice. These results suggest that MF59 plus CpG oligodeoxynucleotide might be developed as an efficient adjuvant for tumor vaccines against melanoma, and possibly other tumors.

ISCOMATRIX: a novel adjuvant for use in prophylactic and therapeutic vaccines against infectious diseases

The ISCOMATRIX adjuvant has antigen delivery and presentation properties as well as immunomodulatory capabilities, which combine to provide enhanced and accelerated immune responses. The responses are broad, including a range of subclasses of antibodies as well as CD4(+) and CD8(+) T-cells. A range of ISCOMATRIX vaccines (ISCOMATRIX adjuvant combined with antigen) have now been tested in clinical trials and have been shown to be generally safe and well tolerated as well as immunogenic, generating both antibody (Ab) and T-cell responses. The mechanisms by which ISCOMATRIX adjuvant facilitates its immune effects are the scope of significant study and indicate that ISCOMATRIX adjuvant (i) rapidly traffics antigen into the cytosol of multiple dendritic cell subsets, (ii) induces the induction of an array of cytokines and chemokines and (iii) links the innate and adaptive immune responses in vivo in a Toll-like-receptor-independent but MyD88-dependent manner. These data highlight the clinical utility of ISCOMATRIX adjuvant in the development of prophylactic and therapeutic vaccines for infectious disease.

An engineered mutant of HIV-1 gp120 formulated with adjuvant Quil A promotes elicitation of antibody responses overlapping the CD4-binding site

A major priority in HIV vaccine research is the development of an immunogen to elicit broadly neutralizing antibodies (NAbs). Monoclonal antibody (mAb) b12 is one of now several broadly neutralizing mAbs that bind epitopes overlapping the CD4-binding site (CD4bs) on HIV-1 gp120 and that serve as templates to engineer effective immunogens. We are exploring a strategy whereby extra glycans are incorporated onto gp120 to occlude the epitopes of non-neutralizing mAbs while maintaining exposure of the b12 site. Immunizing with these so-called hyperglycosylated gp120s is hypothesized to preferentially elicit b12-like NAbs. Here, the effects of two adjuvants, monophosphoryl lipid A (MPL) and Quil A, on eliciting b12-like responses when formulated with a new hyperglycosylated mutant, ΔN2mCHO(Q105N), is presented. Sera from ΔN2mCHO(Q105N)_MPL immunized animals bound the homologous antigen ΔN2mCHO(Q105N) with greater preference than sera from ΔN2mCHO(Q105N)_QuilA immunized animals, demonstrating the modulation of antibody fine specificity by these two adjuvants. We also found that sera from ΔN2mCHO(Q105N)_QuilA immunized animals bound best to a resurfaced HIV gp120 core protein on which non-CD4bs epitopes are substituted with non-HIV residues, suggesting that these sera contain a relatively larger fraction of CD4bs-specific antibodies. Consistent with these data, inhibition assays revealed epitope overlap with the binding sites of the CD4bs-specific antibodies b12, b13 and VRC03. Unexpectedly, these sera did not exhibit significant neutralizing activity against a set of HIV-1 primary strains. Our results show that although formulating mutant ΔN2mCHO(Q105N) with Quil A promotes the elicitation of CD4bs-directed antibodies relative to wild-type gp120, tweaking of the immunization regimen is needed to yield robust, CD4bs-focused NAbs.

A new synthetic TLR4 agonist, GLA, allows dendritic cells targeted with antigen to elicit Th1 T-cell immunity in vivo

Protein-based vaccines offer safety and cost advantages but require adjuvants to induce immunity. Here we examined the adjuvant capacity of glucopyranosyl lipid A (GLA), a new synthetic non-toxic analogue of lipopolysaccharide. In mice, in comparison with non-formulated LPS and monophosphoryl lipid A, formulated GLA induced higher antibody titers and generated Type 1 T-cell responses to HIV gag-p24 protein in spleen and lymph nodes, which was dependent on TLR4 expression. Immunization was greatly improved by targeting HIV gag p24 to DCs with an antibody to DEC-205, a DC receptor for antigen uptake and processing. Subcutaneous immunization induced antigen-specific T-cell responses in the intestinal lamina propria. Immunity did not develop in mice transiently depleted of DCs. To understand how GLA works, we studied DCs directly from vaccinated mice. Within 4 h, GLA caused DCs to upregulate CD86 and CD40 and produce cytokines including IL-12p70 in vivo. Importantly, DCs removed from mice 4 h after vaccination became immunogenic, capable of inducing T-cell immunity upon injection into naïve mice. These data indicate that a synthetic and clinically feasible TLR4 agonist rapidly stimulates full maturation of DCs in vivo, allowing for adaptive immunity to develop many weeks to months later.

Modulation of the humoral response to Dermatophagoides pteronyssinus allergens in BALB/c mice by extract modification and adjuvant use

BACKGROUND

Currently, several strategies are being used in order to improve the safety and efficacy of allergen-specific immunotherapy; these strategies include the use of modified hypoallergenic extracts as well as different adjuvants with immunomodulatory properties in combination with native or modified extracts. The objectives of this study were to investigate the humoral response generated in mice to modified Dermatophagoides pteronyssinus extracts in the presence or absence of two different adjuvants.

METHODS

BALB/c mice were inoculated either with native, depigmented or depigmented-polymerised D. pteronyssinus without adjuvants or combined with aluminium hydroxide or oligodeoxinucleotides containing CpG motifs. IgE concentration, specific total IgG, IgG1 and IgG2a titres were measured in mice sera and cross-reactivity inhibition experiments were performed. IgG antigenic profiles were obtained by immunoblotting for all formulations.

RESULTS

Inoculation of depigmented-polymerised extract induced statistically significant lower IgE levels than the native extract even when adsorbed onto aluminium hydroxide. When this extract was inoculated in the presence of oligodeoxinucleotides containing CpG motifs, it elicited high IgG levels, a high IgG2a/lgG1 ratio and low IgE production. Furthermore, the antigenic profiles observed after extract inoculation showed punctual differences between the depigmented-polymerised extract and the native or depigmented extracts.

CONCLUSIONS

Our results suggest that the depigmentation and polymerisation process modifies the native extract's antigenic and immunogenic properties and converts the depigmented-polymerised extract into a better choice for allergen-specific immunotherapy.

Vaccines for the twenty-first century society

The childhood vaccination campaigns of the twentieth century represent one of the great success stories of modern medicine. But are we yet to realize the full potential of vaccines? This article discusses the medical needs of the twenty-first century society and proposes that new vaccines will play a major part in addressing these needs.

Vaccines have been one of the major revolutions in the history of mankind and, during the twentieth century, they eliminated most of the childhood diseases that used to cause millions of deaths. In the twenty-first century, vaccines will also play a major part in safeguarding people's health. Supported by the innovations derived from new technologies, vaccines will address the new needs of a twenty-first century society characterized by increased life expectancy, emerging infections and poverty in low-income countries.

Intranasal administration of a flagellin-adjuvanted inactivated influenza vaccine enhances mucosal immune responses to protect mice against lethal infection

The influenza virus, a mucosal pathogen that infects the respiratory tract, is a major global health issue. There have been attempts to mucosally administer inactivated influenza vaccines to induce both mucosal and systemic immune responses. However, mucosally administered inactivated influenza vaccine has low immunogenicity, which is partially due to the lack of an effective mucosal adjuvant. The development of a safe and effective mucosal adjuvant is a prerequisite to the practical use of a mucosal inactivated influenza vaccine. We have previously demonstrated that a bacterial flagellin, Vibrio vulnificus FlaB, when mixed with antigen and administered intranasally, exerts a strong mucosal adjuvant activity by stimulating the Toll-like receptor 5 (TLR5). In this study, we tested whether the FlaB protein could serve as an effective mucosal adjuvant for an inactivated trivalent influenza vaccine (TIV) manufactured for humans; in a murine vaccination model, this vaccine consists of A/Brisbane/59/07 (H1N1 subtype), A/Uruguay/716/07 (H3N2 subtype), and B/Florida/4/06 (B type). Intranasal co-administration of the TIV with FlaB induced prominent humoral responses as demonstrated by high influenza-specific IgA levels in both the mucosal secretions and serum and significant specific IgG induction in the systemic compartment. The FlaB protein significantly potentiated influenza-specific cytokine production by draining lymph node cells and splenocytes. The FlaB mucosal adjuvant conferred excellent protection against a lethal challenge with a live virulent virus with high hemagglutination inhibition (HAI) antibody (Ab) titers. The FlaB did not accumulate in the olfactory nerve and epithelium, guaranteeing against a retrograde uptake into the central nervous system. These results suggest that FlaB can be used as a promising mucosal adjuvant for nasal inactivated influenza vaccine development.

Vaccines for the future: learning from human immunology

Conventional vaccines have been extremely successful in preventing infections by pathogens expressing relatively conserved antigens through antibody‐mediated effector mechanisms. Thanks to vaccination some diseases have been eradicated and mortality due to infectious diseases has been significantly reduced. However, there are still many infections that are not preventable with vaccination, which represent a major cause of mortality worldwide. Some of these infections are caused by pathogens with a high degree of antigen variability that cannot be controlled only by antibodies, but require a mix of humoral and cellular immune responses. Novel technologies for antigen discovery, expression and formulation allow now for the development of vaccines that can better cope with pathogen diversity and trigger multifunctional immune responses. In addition, the application of new genomic assays and systems biology approaches in human immunology can help to better identify vaccine correlates of protection. The availability of novel vaccine technologies, together with the knowledge of the distinct human immune responses that are required to prevent different types of infection, should help to rationally design effective vaccines where conventional approaches have failed.

CpG DNA as a vaccine adjuvant

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs trigger cells that express Toll-like receptor 9 (including human plasmacytoid dendritic cells and B cells) to mount an innate immune response characterized by the production of Th1 and proinflammatory cytokines. When used as vaccine adjuvants, CpG ODNs improve the function of professional antigen-presenting cells and boost the generation of humoral and cellular vaccine-specific immune responses. These effects are optimized by maintaining ODNs and vaccine in close proximity. The adjuvant properties of CpG ODNs are observed when administered either systemically or mucosally, and persist in immunocompromised hosts. Preclinical studies indicate that CpG ODNs improve the activity of vaccines targeting infectious diseases and cancer. Clinical trials demonstrate that CpG ODNs have a good safety profile and increase the immunogenicity of coadministered vaccines.

In vivo evidence of oral vaccination with PLGA nanoparticles containing the immunostimulant monophosphoryl lipid A

Although oral vaccination has numerous advantages over the commonly used parenteral route, degradation of vaccine and its low uptake in the lymphoid tissue of the gastrointestinal (GI) tract still impede their development. In this study, the model antigen ovalbumin (OVA) and the immunostimulant monophosphoryl lipid A (MPLA) were incorporated in polymeric nanoparticles based on poly(D,L-lactide-co-glycolide) (PLGA). These polymeric carriers were orally administered to BALB/c mice (Bagg albino, inbred strain of mouse) and the resulting time-dependent systemic and mucosal immune responses towards OVA were assessed by measuring the OVA-specific IgG and IgA titers using an enzyme-linked immunosorbent assay (ELISA). PLGA nanoparticles were spherical in shape, around 320 nm in size, negatively charged (around -20 mV) and had an OVA and MPLA payload of 9.6% and 0.86%, respectively. A single immunization with formulation containing (OVA + MPLA) incorporated in PLGA nanoparticles induced a stronger IgG immune response than that induced by OVA in PBS solution or OVA incorporated into PLGA nanoparticles. Moreover, significantly higher IgA titers were generated by administration of (OVA + MPLA)/PLGA nanoparticles compared to IgA stimulated by control formulations, proving the capability of inducing a mucosal immunity. These findings demonstrate that co-delivery of OVA and MPLA in PLGA nanoparticles promotes both systemic and mucosal immune responses and represents therefore a suitable strategy for oral vaccination.