Dynamics of APC recruitment at the site of injection following injection of vaccine adjuvants

Ally, adversary, or arbitrator? The context-dependent role of eosinophils in vaccination for respiratory viruses and subsequent breakthrough infections

Eosinophils are a critical type of immune cell and central players in type 2 immunity. Existing literature suggests that eosinophils also can play a role in host antiviral responses, typically type 1 immune events, against multiple respiratory viruses, both directly through release of antiviral mediators and indirectly through activation of other effector cell types. One way to prime host immune responses toward effective antiviral responses is through vaccination, where typically a type 1-skewed immunity is desirable in the context of intracellular pathogens like respiratory viruses. In the realm of breakthrough respiratory viral infection in vaccinated hosts, an event in which virus can still establish productive infection despite preexisting immunity, eosinophils are most prominently known for their link to vaccine-associated enhanced respiratory disease upon natural respiratory syncytial virus infection. This was observed in a pediatric cohort during the 1960s following vaccination with formalin-inactivated respiratory syncytial virus. More recent research has unveiled additional roles of the eosinophil in respiratory viral infection and breakthrough infection. The specific contribution of eosinophils to the quality of vaccine responses, vaccine efficacy, and antiviral responses to infection in vaccinated hosts remains largely unexplored, especially regarding their potential roles in protection. On the basis of current findings, we will speculate upon the suggested function of eosinophils and consider the many potential ways by which eosinophils may exert protective and pathological effects in breakthrough infections. We will also discuss how to balance vaccine efficacy with eosinophil-related risks, as well as the use of eosinophils and their products as potential biomarkers of vaccine efficacy or adverse events.

Modulating Adjuvant Release Kinetics From Scaffold Vaccines to Tune Adaptive Immune Responses

Increasing the potency, quality, and durability of vaccines represents a major public health challenge. A critical parameter that shapes vaccine immunity is the spatiotemporal context in which immune cells interact with antigen and adjuvant. While various material-based strategies demonstrate that extended antigen release enhances both cellular and humoral immunity, the effect of adjuvant kinetics on vaccine-mediated immunity remains incompletely understood. Here, a previously characterized mesoporous silica rod (MPS) biomaterial vaccine is used to develop a facile, electrostatics-driven approach to tune in vivo kinetics of the TLR9 agonist cytosine phosphoguanosine oligodeoxynucleotide (CpG). It is demonstrated that rapid release of CpG from MPS vaccines, mediated by alterations in MPS chemistry that tune surface charge, generates potent cytotoxic T cell responses and robust, T helper type 1 (Th1)-skewed IgG2a/c antibody titers. Immunophenotyping of lymphoid organs after MPS vaccination with slow or fast CpG release kinetics suggests that differential engagement of migratory dendritic cells and natural killer cells may contribute to the more potent responses observed with rapid adjuvant release. Taken together, these findings suggest that vaccine approaches that pair sustained release of antigen with rapid release of adjuvants with similar characteristics to CpG may drive particularly potent Th1 responses.

Adjuvants influence the immune cell populations present at the injection site granuloma induced by whole-cell inactivated paratuberculosis vaccines in sheep

Vaccination is the most effective tool for paratuberculosis control. Currently, available vaccines prevent the progression of clinical disease in most animals but do not fully protect them against infection and induce the formation of an injection site granuloma. The precise mechanisms that operate in response to vaccination and granuloma development, as well as the effect that adjuvants could trigger, have not been fully investigated. Therefore, this study aimed to investigate the injection site granulomas induced by two inactivated paratuberculosis vaccines, which differ in the adjuvant employed. Two groups of 45-day-old lambs were immunized with two commercially available vaccines-one (n = 4) with Gudair® and the other (n = 4) with Silirum®. A third group (n = 4) was not vaccinated and served as control. The peripheral humoral response was assessed throughout the study by a commercial anti-Mycobacterium avium subspecies paratuberculosis (Map) antibody indirect ELISA, and the cellular immune response was assessed similarly by the IFN-γ release and comparative intradermal tests. The injection site granulomas were measured during the experiment and sampled at 75 days post-vaccination (dpv) when the animals were euthanized. The tissue damage, antigen and adjuvant distribution, and the presence and amount of immune cells were then determined and assessed by immunohistochemical methods. Antibodies against Map antigens; a general macrophage marker (Iba1), M1 (iNOS), and M2 (CD204) macrophages; T (CD3), B (CD20), and γδ T lymphocytes, proteins MHC-II and NRAMP1, and cytokines IL-4, IL-10, TNF, and IFN-γ were employed. Silirum® elicited a stronger peripheral cellular immune response than Gudair®, while the latter induced larger granulomas and more tissue damage at the site of injection. Additionally, adjuvant and Map antigen distribution throughout the granulomatous inflammatory infiltrate, as well as the NRAMP1 cell expression, which is linked to antigen phagocytosis, were highly irregular. In Silirum® induced granulomas, a higher number of MHC-II and TNF-expressing cells and a lower number of M2 macrophages suggested an improved antigen presentation, which could be due to the better antigen distribution and reduced tissue damage induced by this vaccine.

Actinidia eriantha polysaccharide exerts adjuvant activity by targeting linc-AAM

Actinidia eriantha polysaccharide (AEPS) is a potent adjuvant with dual Th1 and Th2 potentiating activity. linc-AAM has been previously proved to facilitate the expression of immune response genes (IRGs) in AEPS-activated RAW264.7 macrophages. However, its role in mediating adjuvant activity of AEPS remains to be elucidated. In this study, bone marrow-derived macrophages (BMDMs) from wide-type (WT) and linc-AAM knockout C57BL/6J mice treated with AEPS were subjected to transcriptome sequencing and bioinformatic analysis. linc-AAM deficiency inhibited M1 and M2 immune responses in BMDMs induced by AEPS. In mechanisms, AEPS facilitated the expression of IRGs and activated BMDMs through NF-κB-linc-AAM-JAK/STAT axis. Furthermore, linc-AAM knockout inhibited cytokine and chemokine production, immune cell recruitment as well as immune cell migration to draining lymph nodes at peritoneal cavity in mice induced by AEPS. More importantly, linc-AAM deletion reduced the adjuvant activity of APES on antigen-specific cellular and humoral immune responses to ovalbumin in mice. This study has for the first time demonstrated the role of lncRNAs in regulating the adjuvant activity of polysaccharides and its mechanisms. These findings expanded current knowledge on the mechanism of action of adjuvant and provide a new target for the design and development of vaccine adjuvants.

Identification of a linear B-cell epitope on the African swine fever virus CD2v protein

African swine fever virus (ASFV) poses a serious threat to domestic pigs and wild boars, which is responsible for substantial production and economic losses. A dominant ASFV specific linear B cell epitope that reacted with the convalescent serum was explored and identified with the help of immune informatics techniques. It is essential in understanding the host immunity and in developing diagnostic technical guidelines and vaccine design. The confirmation of dominant epitopes with a positive serological matrix is feasible. To improve the immunogenicity of the epitope, we designed the dominant epitope of CD2v in the form of 2 branch Multiple-Antigen peptide (MAPs-2), CD2v-MAPs-2. Notably, CD2v peptide can be taken up by dendritic cells (DCs) to activate T lymphocytes and induce highly effective valence antibodies in BALB/c mice. The specific CD8+ T cell response were observed. The dominant epitope peptide identified in this study was able to effectively activate humoral and cellular immunity in mice model.

Emergence of SARS-CoV-2 spike protein at the vaccination site

BACKGROUND

The anti-coronavirus disease 2019 (COVID-19) vaccines are of paramount importance in the fight against the COVID-19 pandemic. Both viral vector- and nucleic acid-based vaccines are known to effectively induce protection against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus by generating high antibody titers and effective T-cell responses to the spike protein they encode. Although these vaccines are being applied worldwide and have been extensively investigated, the immunomorphological events at the vaccination site with respect to SARS-CoV-2 spike protein expression have not yet been described.

METHODS

We had the opportunity to examine the deltoid muscles of three men who died shortly after vaccination for unrelated reasons. We examined the vaccination sites histologically and immunohistochemically with various antibodies. Furthermore we incubated two different cell lines with one vaccine and examined the expression of the spike protein.

RESULTS

The vaccination sites show a dense lymphohistiocytic interstitial infiltrate which surrounds the small vessels and extends into the perimysium. The spike protein is expressed by histiocytic cells with a dendritic shape that are CD68-positive and CD207-negative, fibrocytes, and very rare S100-positive cells. Interestingly, the skeletal muscle, being constitutively human leukocyte antigen (HLA)-A,B,C-negative, is induced at different levels in each specimen. In a cell culture experiment, we confirmed the ability of fibroblasts and interdigitating dendritic sarcoma cells to express spike protein in vitro after incubation with the Comirnaty vaccine.

CONCLUSIONS

Histiocytic cells and fibrocytes are the heralds of spike protein synthesis at the vaccination site. The underlying cause of this apparent cell specifity is unknown. This needs to be investigated in future experiments, for example in an animal model.

Advances on the early cellular events occurring upon exposure of human macrophages to aluminum oxyhydroxide adjuvant

Aluminum compounds are the most widely used adjuvants in veterinary and human vaccines. Despite almost a century of use and substantial advances made in recent decades about their fate and biological effects, the exact mechanism of their action has been continuously debated, from the initial "depot-theory" to the direct immune system stimulation, and remains elusive. Here we investigated the early in vitro response of primary human PBMCs obtained from healthy individuals to aluminum oxyhydroxide (the most commonly used adjuvant) and a whole vaccine, in terms of internalization, conventional and non-conventional autophagy pathways, inflammation, ROS production, and mitochondrial metabolism. During the first four hours of contact, aluminum oxyhydroxide particles, with or without adsorbed vaccine antigen, (1) were quickly recognized and internalized by immune cells; (2) increased and balanced two cellular clearance mechanisms, i.e. canonical autophagy and LC3-associated phagocytosis; (3) induced an inflammatory response with TNF-α production as an early event; (4) and altered mitochondrial metabolism as assessed by both decreased maximal oxygen consumption and reduced mitochondrial reserve, thus potentially limiting further adaptation to other energetic requests. Further studies should consider a multisystemic approach of the cellular adjuvant mechanism involving interconnections between clearance mechanism, inflammatory response and mitochondrial respiration.

Adjuvant activity of tubeimosides by mediating the local immune microenvironment

Rhizoma Bolbostemmatis, the dry tuber of Bolbostemma paniculatum, has being used for the treatment of acute mastitis and tumors in traditional Chinese medicine. In this study, tubeimoside (TBM) I, II, and III from this drug were investigated for the adjuvant activities, structure-activity relationships (SAR), and mechanisms of action. Three TBMs significantly boosted the antigen-specific humoral and cellular immune responses and elicited both Th1/Th2 and Tc1/Tc2 responses towards ovalbumin (OVA) in mice. TBM I also remarkably facilitated mRNA and protein expression of various chemokines and cytokines in the local muscle tissues. Flow cytometry revealed that TBM I promoted the recruitment and antigen uptake of immune cells in the injected muscles, and augmented the migration and antigen transport of immune cells to the draining lymph nodes. Gene expression microarray analysis manifested that TBM I modulated immune, chemotaxis, and inflammation-related genes. The integrated analysis of network pharmacology, transcriptomics, and molecular docking predicted that TBM I exerted adjuvant activity by interaction with SYK and LYN. Further investigation verified that SYK-STAT3 signaling axis was involved in the TBM I-induced inflammatory response in the C2C12 cells. Our results for the first time demonstrated that TBMs might be promising vaccine adjuvant candidates and exert the adjuvant activity through mediating the local immune microenvironment. SAR information contributes to developing the semisynthetic saponin derivatives with adjuvant activities.

LigA formulated in AS04 or Montanide ISA720VG induced superior immune response compared to alum, which correlated to protective efficacy in a hamster model of leptospirosis

Leptospirosis is a zoonotic disease of global importance. The current vaccine provides serovar-specific and short-term immunity and does not prevent bacterial shedding in infected animals. Subunit vaccines based on surface proteins have shown to induce protection in an animal model. However, these proteins were tested with non-clinical adjuvants and induced low to moderate protective efficacy. We formulated a variable region of Leptospira immunoglobulin-like protein A (LAV) in clinical adjuvants, AS04 and Montanide ISA720VG, and then evaluated the immune response in mice and protective efficacy in a hamster model. Our results show that animals immunized with LAV-AS04 and LAV-Montanide ISA720VG (LAV-M) induced significantly higher levels of LAV-specific antibodies than LAV-Alum. While LAV-Alum induced Th2 response with the induction of IgG1 and IL-4, AS04 and LAV-M induced a mixed Th1/Th2 response with significant levels of both IgG1/IL-4 and IgG2c/IFN-γ. Both LAV-AS04 and LAV-M induced the generation of a significantly higher number of cytotoxic T cells (CTLs). The immune response in LAV-AS04- and LAV-M-immunized animals was maintained for a long period (>180 days) with the generation of a significant level of B- and T-cell memory. The strong immune response by both vaccines correlated to enhanced recruitment and activation of innate immune cells particularly DCs at draining lymph nodes and the formation of germinal centers (GCs). Furthermore, the immune response generated in mice correlated to protective efficacy in the hamster model of leptospirosis. These results indicate that LAV-AS04 and LAV-M are promising vaccines and can be further evaluated in clinical trials.

Hollow Aluminum Hydroxide Modified Silica Nanoadjuvants with Amplified Immunotherapy Effects through Immunogenic Cell Death Induction and Antigen Release

In spite of the widespread application of vaccine adjuvants in various preventive vaccines at present, the existing adjuvants are still hindered by weak cellular immunity responses in therapeutic cancer vaccines. Herein, a hollow silica nanoadjuvant containing aluminum hydroxide spikes on the surface (SiAl) is synthesized for the co-loading of chemotherapeutic drug doxorubicin (Dox) and tumor fragment (TF) as tumor antigens (SiAl@Dox@TF). The obtained nanovaccines show significantly elevated anti-tumor immunity responses thanks to silica and aluminum-based composite nanoadjuvant-mediated tumor antigen release and Dox-induced immunogenic cell death (ICD). In addition, the highest frequencies of dendritic cells (DCs), CD4⁺ T cells, CD8⁺ T cells, and memory T cells as well as the best mice breast cancer (4T1) tumor growth inhibitory are also observed in SiAl@Dox@TF group, indicating favorable potential of SiAl nanoadjuvants for further applications. This work is believed to provide inspiration for the design of new-style nanoadjuvants and adjuvant-based cancer vaccines.

Designing spatial and temporal control of vaccine responses

Vaccines are the key technology to combat existing and emerging infectious diseases. However, increasing the potency, quality and durability of the vaccine response remains a challenge. As our knowledge of the immune system deepens, it becomes clear that vaccine components must be in the right place at the right time to orchestrate a potent and durable response. Material platforms, such as nanoparticles, hydrogels and microneedles, can be engineered to spatially and temporally control the interactions of vaccine components with immune cells. Materials-based vaccination strategies can augment the immune response by improving innate immune cell activation, creating local inflammatory niches, targeting lymph node delivery and controlling the time frame of vaccine delivery, with the goal of inducing enhanced memory immunity to protect against future infections. In this Review, we highlight the biological mechanisms underlying strong humoral and cell-mediated immune responses and explore materials design strategies to manipulate and control these mechanisms.

Respiratory Syncytial Virus F Subunit Vaccine With AS02 Adjuvant Elicits Balanced, Robust Humoral and Cellular Immunity in BALB/c Mice

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory illness, particularly in infants, the elderly, and immunocompromised adults. There is no licensed commercial vaccine against RSV. Importantly, formalin-inactivated RSV vaccines mediate enhanced respiratory disease. RSV fusion (F) protein with pre-fusion conformation is a promising candidate subunit vaccine. However, some problems remain to be solved, such as low immunogenicity and humoral immunity bias. Adjuvants can effectively enhance and adjust vaccine immune responses. In this study, we formulated pre-fusion RSV-F protein with the adjuvants, Alhydrogel, MF59, AS03, AS02, and glycol chitosan (GCS). We then conducted head-to-head comparisons of vaccine-induced immune responses in BALB/c mice. All adjuvanted vaccines enhanced antigen-specific and neutralizing antibody titers and viral clearance and gave an order of adjuvant activity: AS02 > AS03, MF59 > GCS, and Alhydrogel. Among them, AS02 elicited the highest antibody expression, which persisted until week 18. Moreover, AS02 significantly enhanced Th1 type immune response in immunized mice. Mice in the AS02 group also showed faster recovery from viral attacks in challenge tests. Further transcriptome analysis revealed that AS02 regulates immune balance by activating TLR-4 and promotes Th1-type immune responses. These results suggest that AS02 may be an excellent candidate adjuvant for RSV-F subunit vaccines. This study also provides valuable information regarding the effect of other adjuvants on immune responses of RSV-F subunit vaccines.

A Canine-Directed Chimeric Multi-Epitope Vaccine Induced Protective Immune Responses in BALB/c Mice Infected with Leishmania infantum

Leishmaniases are complex vector-borne diseases caused by intracellular parasites of the genus Leishmania. The visceral form of the disease affects both humans and canids in tropical, subtropical, and Mediterranean regions. One health approach has suggested that controlling zoonotic visceral leishmaniasis (ZVL) could have an impact on the reduction of the human incidence of visceral leishmaniasis (VL). Despite the fact that a preventive vaccination could help with leishmaniasis elimination, effective vaccines that are able to elicit protective immune responses are currently lacking. In the present study, we designed a chimeric multi-epitope protein composed of multiple CD8⁺ and CD4⁺ T cell epitopes which were obtained from six highly immunogenic proteins previously identified by an immunoproteomics approach, and the N-termini of the heparin-binding hemagglutinin (HBHA) of Mycobacterium tuberculosis served as an adjuvant. A preclinical evaluation of the candidate vaccine in BALB/c mice showed that when it was given along with the adjuvant Addavax it was able to induce strong immune responses. Cellular responses were dominated by the presence of central and effector multifunctional CD4⁺ and CD8⁺ T memory cells. Importantly, the vaccination reduced the parasite burden in both short-term and long-term vaccinated mice challenged with Leishmania infantum. Protection was characterized by the continuing presence of IFN-γ⁺TNFα⁺-producing CD8⁺ and CD4⁺ T cells and increased NO levels. The depletion of CD8⁺ T cells in short-term vaccinated mice conferred a significant loss of protection in both target organs of the parasite, indicating a significant involvement of this population in the protection against L. infantum challenge. Thus, the overall data could be considered to be a proof-of-concept that the design of efficacious T cell vaccines with the help of reverse vaccinology approaches is possible.

Integrating context of tumor biology and vaccine design to shape multidimensional immunotherapies

Advances in cancer therapy have offered great promise but only modest clinical benefits as monotherapies to date. Patients usually respond well to therapies targeted at specific mutations, but only for a short time. Conversely, immunotherapies help fewer patients, but increase survival. Combination therapies, which could offer the best of both worlds, are currently limited by substantial toxicity. While recent advances in genomics and proteomics have yielded an unprecedented depth of enabling datasets, it has also shifted the focus toward  in silico predictions. Designing the next wave of multidimensional immunotherapies will require leveraging this knowledge while providing a renewed emphasis on tumor biology and vaccine design. This includes careful selection of tumor clinical stage in the context of pre-existing tumor microenvironments, target antigen and technology platform selections to maximize their effect, and treatment staging. Here, we review strategies on how to approach an increasingly complex landscape of immunotherapeutic agents for use in combination therapies.

Characterization of potential biomarkers of reactogenicity of licensed antiviral vaccines: randomized controlled clinical trials conducted by the BIOVACSAFE consortium

Biomarkers predictive of inflammatory events post-vaccination could accelerate vaccine development. Within the BIOVACSAFE framework, we conducted three identically designed, placebo-controlled inpatient/outpatient clinical studies (NCT01765413/NCT01771354/NCT01771367). Six antiviral vaccination strategies were evaluated to generate training data-sets of pre-/post-vaccination vital signs, blood changes and whole-blood gene transcripts, and to identify putative biomarkers of early inflammation/reactogenicity that could guide the design of subsequent focused confirmatory studies. Healthy adults (N = 123; 20-21/group) received one immunization at Day (D)0. Alum-adjuvanted hepatitis B vaccine elicited vital signs and inflammatory (CRP/innate cells) responses that were similar between primed/naive vaccinees, and low-level gene responses. MF59-adjuvanted trivalent influenza vaccine (ATIV) induced distinct physiological (temperature/heart rate/reactogenicity) response-patterns not seen with non-adjuvanted TIV or with the other vaccines. ATIV also elicited robust early (D1) activation of IFN-related genes (associated with serum IP-10 levels) and innate-cell-related genes, and changes in monocyte/neutrophil/lymphocyte counts, while TIV elicited similar but lower responses. Due to viral replication kinetics, innate gene activation by live yellow-fever or varicella-zoster virus (YFV/VZV) vaccines was more suspended, with early IFN-associated responses in naïve YFV-vaccine recipients but not in primed VZV-vaccine recipients. Inflammatory responses (physiological/serum markers, innate-signaling transcripts) are therefore a function of the vaccine type/composition and presence/absence of immune memory. The data reported here have guided the design of confirmatory Phase IV trials using ATIV to provide tools to identify inflammatory or reactogenicity biomarkers.

Exploiting the Lymph-Node-Amplifying Effect for Potent Systemic and Gastrointestinal Immune Responses via Polymer/Lipid Nanoparticles

Parenteral vaccinations are not able to elicit effective systemic and gastrointestinal immune protection simultaneously because the lymphocytes are typically restricted to primed tissues. Although all-trans retinoic acid (atRA) was reported to trigger the gut-homing of immunocytes, the bioavailability and systemic immune responses remain limited for use in robust enteric vaccinations. Here, we show that co-delivery of atRA, CpG oligodeoxynucleotides (CpG), and antigens via engineered polymer/lipid nanoparticles (PLNPs) could exploit the amplifying function of draining lymph nodes (DLNs) for potent gut tropism and immune activations. After intramuscular injection, forming an immune-potentiated environment at the injection site, the PLNPs induced the designated transfer of primed dendritic cells (DCs) to the DLNs instead of the gastrointestinal tissues. Within the DLNs, the immune-potentiated environment markedly amplified the antigen presentation and homing receptor switch among immunocytes, which simultaneously stimulated the preferential dissipation of activated lymphocytes in the peripheral and gastrointestinal tissues, that is, exerted a DLN-amplifying effect. Compared with current atRA-containing formulations, the PLNPs not only boosted potent IgG secretions and T cell activations in the peripheral tissue but also provoked robust T cell homing and antigen-specific IgA levels in the gastrointestinal tracts in both ovalbumin and EV71 vaccinations. These data indicate that exploiting DLN amplification can stimulate potent systemic and gastrointestinal responses for more efficient enteric vaccinations.

Combining activatable nanodelivery with immunotherapy in a murine breast cancer model

A successful chemotherapy-immunotherapy solid-tumor protocol should accomplish the following goals: debulk large tumors, release tumor antigen for cross-presentation and cross-priming, release cancer-suppressive cytokines and enhance anti-tumor immune cell populations. Thermally-activated drug delivery particles have the potential to synergize with immunotherapeutics to accomplish these goals; activation can release chemotherapy within bulky solid tumors and can enhance response when combined with immunotherapy. We set out to determine whether a single protocol, combining locally-activated chemotherapy and agonist immunotherapy, could accomplish these goals and yield a potentially translational therapy. For effective delivery of free doxorubicin to tumors with minimal toxicity, we stabilized doxorubicin with copper in temperature-sensitive liposomes that rapidly release free drug in the vasculature of cancer lesions upon exposure to ultrasound-mediated hyperthermia. We found that in vitro exposure of tumor cells to hyperthermia and doxorubicin resulted in immunogenic cell death and the local release of type I interferons across murine cancer cell lines. Following intravenous injection, local activation of the liposomes within a single tumor released doxorubicin and enhanced cross-presentation of a model antigen at distant tumor sites. While a variety of protocols achieved a complete response in >50% of treated mice, the complete response rate was greatest (90%) when 1 week of immunotherapy priming preceded a single activatable chemotherapeutic administration. While repeated chemotherapeutic delivery reduced local viable tumor, the complete response rate and a subset of tumor immune cells were also reduced. Taken together, the results suggest that activatable chemotherapy can enhance adjuvant immunotherapy; however, in a murine model the systemic adaptive immune response was greatest with a single administration of chemotherapy.

Subunit-based mucosal vaccine delivery systems for pulmonary delivery - Are they feasible?

Pulmonary infections are the most common cause of death globally. However, the development of mucosal vaccines that provide protective immunity against respiratory pathogens are limited. In contrast to needle-based vaccines, efficient vaccines that are delivered via noninvasive mucosal routes (such as via the lungs and nasal passage) produce both antigen-specific local mucosal IgA and systemic IgG protective antibodies. One major challenge in the development of pulmonary vaccines using subunit antigens however, is the production of optimal immune responses. Subunit vaccines therefore rely upon use of adjuvants to potentiate immune responses. While the lack of suitable mucosal adjuvants has hindered progress in the development of efficient pulmonary vaccines, particle-based systems can provide an alternative approach for the safe and efficient delivery of subunit vaccines. In particular, the rational engineering of particulate vaccines with optimal physicochemical characteristics can produce long-term protective immunity. These protect antigens against enzymatic degradation, target antigen presenting cells and initiate optimal humoral and cellular immunity. This review will discuss our current understanding of pulmonary immunology and developments in fabricating particle characteristics that may evoke potent and durable pulmonary immunity.

Biomaterials for vaccine-based cancer immunotherapy

The development of therapeutic cancer vaccines as a means to generate immune reactivity against tumors has been explored since the early discovery of tumor-specific antigens by Georg Klein in the 1960s. However, challenges including weak immunogenicity, systemic toxicity, and off-target effects of cancer vaccines remain as barriers to their broad clinical translation. Advances in the design and implementation of biomaterials are now enabling enhanced efficacy and reduced toxicity of cancer vaccines by controlling the presentation and release of vaccine components to immune cells and their microenvironment. Here, we discuss the rational design and clinical status of several classes of cancer vaccines (including DNA, mRNA, peptide/protein, and cell-based vaccines) along with novel biomaterial-based delivery technologies that improve their safety and efficacy. Further, strategies for designing new platforms for personalized cancer vaccines are also considered.

The parasite-derived rOv-ASP-1 is an effective antigen-sparing CD4+ T cell-dependent adjuvant for the trivalent inactivated influenza vaccine, and functions in the absence of MyD88 pathway

Vaccination remains the most cost-effective biomedical approach for controlling influenza disease. In times of pandemics, however, these vaccines cannot be produced in sufficient quantities for worldwide use by the current manufacturing capacities and practices. What is needed is the development of adjuvanted vaccines capable of inducing an adequate or better immune response at a decreased antigen dose. Previously we showed that the protein adjuvant rOv-ASP-1 augments influenza-specific antibody titers and survival after virus challenge in both young adult and old-age mice when administered with the trivalent inactivated influenza vaccine (IIV3). In this study we show that a reduced amount of rOv-ASP-1, with 40-times less IIV3 can also induce protection. Apparently the potency of the rOv-ASP-1 adjuvanted IIV3 vaccine is independent of the IIV3-specific Th1/Th2 associated antibody responses, and independent of the presence of HAI antibodies. However, CD4⁺ T helper cells were indispensable for the protection. Further, rOv-ASP-1 with or without IIV3 elicited the increased level of various chemokines, which are known chemoattractant for immune cells, into the muscle 4 h after immunization, and significantly induced the recruitment of monocytes, macrophages and neutrophils into the muscles. The recruited monocytes had higher expression of the activation marker MHCII on their surface as well as CXCR3 and CCR2; receptors for IP-10 and MCP-1, respectively. These results show that the rOv-ASP-1 adjuvant allows substantial antigen sparing of IIV3 by stimulating at the site of injection the accumulation of chemokines and the recruitment of immune cells that can augment the activation of CD4⁺ T cell immune responses, essential for the production of antibody responses. Protection elicited by the rOv-ASP-1 adjuvanted IIV3 vaccine also appears to function in the absence of MyD88-signaling. Future studies will attempt to delineate the precise mechanisms by which the rOv-ASP-1 adjuvanted IIV3 vaccine works.

Routing dependent immune responses after experimental R848-adjuvated vaccination

Most traditional vaccines are administered via the intramuscular route. Other routes of administration however, can induce equal or improved protective memory responses and might provide practical advantages such as needle-free immunization, dose sparing and induction of tissue-specific (mucosal) immunity. Here we explored the differences in immunological outcome after immunization with model antigens via two promising immunization routes (intradermal and intranasal) with or without the experimental adjuvant and TLR7/8-agonist R848. Because the adaptive immune response is largely determined by the local innate cells at the site of immunization, the effect of R848-adjuvation on local cellular recruitment, antigenic uptake by antigen-presenting cells and the initiation of the adaptive response were analyzed for the two routes of administration. We show a general immune-stimulating effect of R848 irrespective of the route of administration. This includes influx of neutrophils, macrophages and dendritic cells to the respective draining lymph nodes and an increase in antigen-positive antigen-presenting cells which leads for both intradermal and intranasal immunization to a mainly T_H1 response. Furthermore, both intranasal and intradermal R848-adjuvated immunization induces a local shift in DC subsets; frequencies of CD11b⁺DC increase whereas CD103⁺DC decrease in relative abundance in the draining lymph node. In spite of these similarities, the outcome of immune responses differs for the respective immunization routes in both magnitude and cytokine profile. Via the intradermal route, the induced T-cell response is higher compared to that after intranasal immunization, which corresponds with the local higher uptake of antigen by antigen-presenting cells after intradermal immunization. Furthermore, R848-adjuvation enhances ex vivo IL-10 and IL-17 production after intranasal, but not intradermal, T-cell activation. Quite the opposite, intradermal immunization leads to a decrease in IL-10 production by the vaccine induced T-cells. This knowledge may lead to a more rational development of novel adjuvanted vaccines administered via non-traditional routes.

Virus-derived immunostimulatory RNA induces type I IFN-dependent antibodies and T-cell responses during vaccination

Adjuvants potentiate and direct the type of immunity elicited during vaccination. However, there is a shortage of adjuvants that elicit robust type-1 immunity required for the control of intracellular pathogens, including viruses. RNA derived from Sendai virus defective viral genomes (DVGs) stimulates RIG-I-like receptor signaling leading to type-1 immunity during infection. Here, we investigated whether a 268nt DVG-derived oligonucleotide (DDO) functions as a strong type-1 immunity-inducing adjuvant during vaccination against influenza virus. We show that DDO induces robust IgG2c antibody production when used in an inactivated influenza A virus (IAV) vaccine. Additionally, DDO induces Th1 and CD8+ T-cell responses able to protect against heterosubtypic IAV challenge. Interestingly, DDO synergized with AddaVax and skewed the immune response towards type-1 immunity. The adjuvancy of DDO alone and in synergy with AddaVax was heavily dependent on type I interferon signaling. Our data support a critical role for type I interferon in the induction of type-1 immune responses during vaccination and demonstrate that DDO is a type-1 immunity orienting vaccine adjuvant that can be used alone or in synergy with other adjuvants.

Bystander activation of irrelevant CD4+ T cells following antigen-specific vaccination occurs in the presence and absence of adjuvant

Autoimmune and other chronic inflammatory diseases (AID) are prevalent diseases which can severely impact the quality of life of those that suffer from the disease. In most cases, the etiology of these conditions have remained unclear. Immune responses that take place e.g. during natural infection or after vaccination are often linked with the development or exacerbation of AID. It is highly debated if vaccines induce or aggravate AID and in particular adjuvants are mentioned as potential cause. Since vaccines are given on a large scale to healthy individuals but also to elderly and immunocompromised individuals, more research is warranted. Non-specific induction of naïve or memory autoreactive T cells via bystander activation is one of the proposed mechanisms of how vaccination might be involved in AID. During bystander activation, T cells unrelated to the antigen presented can be activated without (strong) T cell receptor (TCR) ligation, but via signals derived from the ongoing response directed against the vaccine-antigen or adjuvant at hand. In this study we have set up a TCR transgenic T cell transfer mouse model by which we were able to measure local bystander activation of transferred and labeled CD4+ T cells. Intramuscular injection with the highly immunogenic Complete Freund's Adjuvant (CFA) led to local in vivo proliferation and activation of intravenously transferred CD4+ T cells in the iliac lymph node. This local bystander activation was also observed after CFA prime and Incomplete Freund's Adjuvant (IFA) boost injection. Furthermore, we showed that an antigen specific response is sufficient for the induction of a bystander activation response and the general, immune stimulating effect of CFA or IFA does not appear to increase this effect. In other words, no evidence was obtained that adjuvation of antigen specific responses is essential for bystander activation.