Intranasal immunization of mice with a formalin-inactivated bovine respiratory syncytial virus vaccine co-formulated with CpG oligodeoxynucleotides and polyphosphazenes results in enhanced protection

The protective immunity induced by intranasally inoculated serotype 63 chimpanzee adenovirus vector expressing human respiratory syncytial virus prefusion fusion glycoprotein in BALB/c mice

Human respiratory syncytial virus (RSV) is a ubiquitous pediatric pathogen causing serious lower respiratory tract disease worldwide. No licensed vaccine is currently available. In this work, the coding gene for mDS-Dav1, the full-length and prefusion conformation RSV fusion glycoprotein (F), was designed by introducing the stabilized prefusion F (preF) mutations from DS-Cav1 into the encoding gene of wild-type RSV (wtRSV) F protein. The recombinant adenovirus encoding mDS-Cav1, rChAd63-mDS-Cav1, was constructed based on serotype 63 chimpanzee adenovirus vector and characterized in vitro. After immunizing mice via intranasal route, the rChAd63-mDS-Cav1 induced enhanced neutralizing antibody and F-specific CD8+ T cell responses as well as good immune protection against RSV challenge with the absence of enhanced RSV disease (ERD) in BALB/c mice. The results indicate that rChAd63-mDS-Cav1 is a promising mucosal vaccine candidate against RSV infection and warrants further development.

Polyphosphazenes as Adjuvants for Animal Vaccines and Other Medical Applications

Polyphosphazenes are a class of experimental adjuvants that have shown great versatility as vaccine adjuvants in many animal species ranging from laboratory rodents to large animal species. Their adjuvant activity has shown promising results with numerous viral and bacterial antigens, as well as with crude and purified antigens. Vaccines adjuvanted with polyphosphazenes can be delivered via systemic and mucosal administration including respiratory, oral, rectal, and intravaginal routes. Polyphosphazenes can be used in combination with other adjuvants, further enhancing immune responses to antigens. The mechanisms of action of polyphosphazenes have not fully been defined, but several systematic studies have suggested that they act primarily by activating innate immunity. In the present review, we will highlight progress in the development of polyphosphazenes as adjuvants in animals and their other medical applications.

A novel vaccine adjuvant based on straight polyacrylate potentiates vaccine-induced humoral and cellular immunity in cynomolgus macaques

Adjuvants are central to the efficacy of subunit vaccines. Although several new adjuvants have been approved in human vaccines over the last decade, the panel of adjuvants in licensed human vaccines remains small. There is still a need for novel adjuvants that can be safely used in humans, easy to source and to formulate with a wide range of antigens and would be broadly applicable to a wide range of vaccines. In this article, using the Respiratory Syncytial Virus (RSV) nanoparticulate prefusion F model antigen developed by Sanofi, we demonstrate in the macaque model that the polyacrylate (PAA)-based adjuvant SPA09 is well tolerated and increases vaccine antigen-specific humoral immunity (sustained neutralizing antibodies, memory B cells and mucosal immunity) and elicits strong T_H1-type responses (based on IFNγ and IL-2 ELISpots) in a dose-dependent manner. These data warrant further development of the SPA09 adjuvant for evaluation in clinical trials.

Polyphosphazene immunoadjuvants: Historical perspective and recent advances

The development of successful vaccines has been increasingly reliant on the use of immunoadjuvants - additives, which can enhance and modulate immune responses to vaccine antigens. Immunoadjuvants of the polyphosphazene family encompass synthetic biodegradable macromolecules, which attain in vivo activity via antigen delivery and immunostimulation mechanisms. Over the last decades, the technology has witnessed evolvement of next generation members, expansion to include various antigens and routes of administration, and progression to clinical phase. This was accompanied by gaining important insights into the mechanism of action and the development of a novel class of virus-mimicking nano-assemblies for antigen delivery. The present review evaluates in vitro and in vivo data generated to date in the context of latest advances in understanding the primary function and biophysical behavior of these macromolecules. It also provides an overview of relevant synthetic and characterization methods, macromolecular biodegradation pathways, and polyphosphazene-based multi-component, nanoparticulate, and microfabricated formulations.

Human respiratory syncytial virus F protein expressed in Pichia pastoris or Escherichia coli induces protective immunity without inducing enhanced respiratory disease in mice

Human respiratory syncytial virus (hRSV) is the primary cause of severe respiratory tract disease in children and infants as well as in elderly and immunocompromised adults. The fusion protein (F) of hRSV is the major antigen eliciting a neutralizing antibody response and protective immunity in the host, especially those recognizing the prefusion F protein (pre-F). In this study, we made genetic constructs for expression of a recombinant prefusion F protein in Pichia pastoris GS115, called RGF. Using Escherichia coli BL21, we expressed the pre-F and postfusion F protein (Post-F), called RBF and Post-RBF, respectively. RGF and RBF showed high affinity for 5C4, a highly potent monoclonal antibody specific for pre-F. We studied the immunogenicity of RGF and RBF in mice. Compared to mice immunized with formalin-inactivated RSV (FI-RSV), mice immunized with RGF or RBF exhibited superior protective immunity, which was confirmed by serum neutralizing activity and viral clearance after challenge. As judged from the IgG1/IgG2a ratios and numbers of IFN-γ- and IL-4-secreting cells, RGF or RBF with alum adjuvant induced a balanced Th1-biased immune response and produced no signs of enhanced respiratory disease (ERD) upon hRSV challenge. In addition, the immunogenicity and protective efficacy of RGF were superior to those of RBF in mice. Therefore, RGF represents a potential vaccine candidate for the prevention of human infection with hRSV.

CpG-Recoding in Zika Virus Genome Causes Host-Age-Dependent Attenuation of Infection With Protection Against Lethal Heterologous Challenge in Mice

Experimental increase of CpG dinucleotides in an RNA virus genome impairs infection providing a promising approach for vaccine development. While CpG recoding is an emerging and promising vaccine approach, little is known about infection phenotypes caused by recoded viruses in vivo. For example, infection phenotypes, immunogenicity, and protective efficacy induced by CpG-recoded viruses in different age groups were not studied yet. This is important, because attenuation of infection phenotypes caused by recoded viruses may depend on the population-based expression of cellular components targeting viral CpG dinucleotides. In the present study, we generated several Zika virus (ZIKV) variants with the increasing CpG content and compared infection in neonatal and adult mice. Increasing the CpG content caused host-age-dependent attenuation of infection with considerable attenuation in neonates and high attenuation in adults. Expression of the zinc-finger antiviral protein (ZAP)—the host protein targeting viral CpG dinucleotides—was also age-dependent. Similar to the wild-type virus, ZIKV variants with the increased CpG content evoked robust cellular and humoral immune responses and protection against lethal challenge. Collectively, the host age should be accounted for in future studies on mechanisms targeting viral CpG dinucleotides, development of safe dinucleotide recoding strategies, and applications of CpG-recoded vaccines.

Intranasal treatment with CpG-B oligodeoxynucleotides protects CBA mice from lethal equine herpesvirus 1 challenge by an innate immune response

Equine herpesvirus 1 (EHV-1) is the causative agent of a number of equine disease manifestations, including severe disease of the central nervous system, respiratory infections, and abortion storms. Our results showed that intranasal treatment with CpG-B oligodeoxynucleotides (ODN 1826) protected CBA mice from pathogenic EHV-1 RacL11 challenge. The IFN-γ gene and seven interferon-stimulated genes (ISGs) were upregulated 39.4- to 260.3-fold at 8 h postchallenge in the lungs of RacL11-challenged mice that had been treated with CpG-B ODN. Interestingly, IFN-γ gene expression was upregulated by 26-fold upon RacL11 challenge in CpG-B ODN-treated mice lungs as compared to that of CpG-A ODN (ODN 1585)-treated mice lungs; however, the seven ISGs were upregulated by 2.4-5.0-fold, suggesting that IFN-γ is a major factor in the protection of CBA mice from the lethal challenge. Pre-treatment with IFN-γ significantly reduced EHV-1 yield in murine alveolar macrophage MH-S cells, but not in mouse lung epithelial MLE12 cells. These results suggest that CpG-B ODN may be used as a prophylactic agent in horses and provide a basis for more effective treatment of EHV-1 infection.

Recent advances in experimental polyphosphazene adjuvants and their mechanisms of action

Vaccination continues to be a very important public health intervention to control infectious diseases in the world. Subunit vaccines are generally poorly immunogenic and require the addition of adjuvants to induce protective immune responses. Despite their critical role in vaccines, adjuvant mechanism of action remains poorly understood, which is a barrier to the development of new, safe and effective vaccines. In the present review, we focus on recent progress in understanding the mechanisms of action of the experimental adjuvants poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[di(sodiumcarboxylatoethyl-phenoxy)phosphazene] (PCEP) (in this review, adjuvants PCPP and PCEP are collectively referred to as PZ denoting polyphosphazenes). PZs are high molecular weight, water-soluble, synthetic polymers that have been shown to regulate innate immune response genes, induce cytokines and chemokines secretion at the site of injection and, also, induce immune cell recruitment to the site of injection to create a local immune-competent environment. There is an evidence that as well as its role as an immunoadjuvant (that activate innate immune responses), PZ can also act as a vaccine carrier. The mechanism of action that explains how PZ leads to these effects is not known and is a barrier to the development of designer vaccines.

Pasteurella multocida inactivated with ferric chloride and adjuvanted with bacterial DNA is a potent and efficacious vaccine in Balb/c mice

PURPOSE

Pasteurella multocida (P. multocida) is a principal pathogen of domestic animals and an opportunistic pathogen of humans. It is the causative agent of pneumonia and haemorrhagic septicaemia in cattle, sheep and goats, fowl cholera in chickens and progressive atrophic rhinitis in swine. In this study, we investigated the humoral and cellular immune responses and protective immunity conferred by an iron-inactivated vaccine with bacterial DNA (IIV+bDNA) as an adjuvant in mice.

METHODOLOGY

P. multocida was grown in BHI broth, inactivated with formalin and FeCl3 and adjuvanted with alum and bDNA. Mice were immunized with two whole-cell inactivated vaccine doses 2 weeks apart. The animals were challenged 4 weeks after booster immunization. Immunogens (vaccines and bDNA) posed no safety problems when mice were injected subcutaneously (s/c) with these preparations. The serum antibody titres were tested by ELISA. At 28 days post immunization, cell-mediated immunity responses were determined. The responses were measured by assay of IL-6 and IL-12 in lymphocyte spleen culture supernatants.

RESULTS

ELISA results showed that the levels of antibodies in iron inactivated with bDNA adjuvant groups were higher than in the formalin inactivated with alum adjuvant vaccine group. The protection rate of IIV+bDNA adjuvant vaccine was superior to that of the other vaccines and it protected 100 % of the challenge group mice. Following immunization, bDNA promoted increased production of interleukins compared to the control groups.

CONCLUSION

These studies indicate that bDNA is effective as an immune adjuvant, and along with stimulatory bDNA represent promising new humoral and cellular immune enhancers for vaccination applications. In addition, this vaccine is able to provide long-term protection against infection.

Intranasal immunization with a single dose of the fusion protein formulated with a combination adjuvant induces long-term protective immunity against respiratory syncytial virus

Respiratory syncytial virus (RSV) is the most common cause of respiratory tract infections in both children and elderly people. In this study we evaluated the short- and long-term protective efficacy of a single intranasal (IN) immunization with a RSV vaccine formulation consisting of a codon-optimized fusion (F) protein formulated with poly(I:C), an innate defense regulator peptide and a polyphosphazene (ΔF/TriAdj). This vaccine induced strong systemic and local immune responses, including RSV F-specific IgG1 and IgG2a, SIgA and virus neutralizing antibodies in mice. Furthermore, ΔF/TriAdj promoted production of IFN-γ-secreting T cells and RSV F85-93-specific CD8+ effector T cells. After RSV challenge, no virus was recovered from the lungs of the vaccinated mice. To evaluate the duration of immunity induced by a single IN vaccination, mice were again immunized once with ΔF/TriAdj and challenged with RSV five months later. High levels of IgG1, IgG2a and virus neutralizing antibodies were detected in the ΔF/TriAdj-vaccinated animals. Moreover, this vaccine formulation induced robust local SIgA production and IgA-secreting memory B cell development, and conferred complete protection against subsequent RSV challenge. In conclusion, a single IN vaccination with RSV ΔF protein formulated with TriAdj induced robust, long-term protective immune responses against RSV infection.

Vaccination with a human parainfluenza virus type 3 chimeric FHN glycoprotein formulated with a combination adjuvant induces protective immunity

Human parainfluenza virus type 3 (PIV3) is a major cause of lower respiratory disease i.e. bronchitis, bronchiolitis or pneumonia, in infants and young children. Presently there is no licensed vaccine against PIV3. To produce an effective subunit vaccine, a chimeric FHN glycoprotein consisting of the N-terminal ectodomain of the fusion (F) protein linked to the haemagglutinin-neuraminidase (HN) protein without transmembrane domain, and secreted forms of the individual F and HN glycoproteins, were expressed in mammalian cells and purified. Mice and cotton rats were immunized intramuscularly (IM) with FHN or both F and HN proteins (F + HN), formulated with poly(I:C) and an innate defense regulator peptide in polyphosphazene (TriAdj). Significantly higher levels of systemic virus-neutralizing antibodies were observed in mice and cotton rats immunized with FHN/TriAdj when compared to animals immunized with the combination of F and HN proteins (F + HN/TriAdj). As PIV3 is a pneumotropic virus, another goal is to produce an effective mucosal subunit vaccine. Intranasal (IN) administration with FHN/TriAdj resulted in mucosal IgA production in the lung and virus neutralizing antibodies in the sera. After PIV3 challenge no virus was detected in cotton rats immunized with FHN/TriAdj regardless of the route of delivery. Protective immunity against PIV3 was also induced by FHN/TriAdj in hamsters. In conclusion, the FHN protein formulated with TriAdj has potential for development of a safe and effective vaccine against PIV3.

PCPP-Adjuvanted Respiratory Syncytial Virus (RSV) sF Subunit Vaccine: Self-Assembled Supramolecular Complexes Enable Enhanced Immunogenicity and Protection

PCPP, a well-defined polyphosphazene macromolecule, has been studied as an immunoadjuvant for a soluble form of the postfusion glycoprotein of respiratory syncytial virus (RSV sF), which is an attractive vaccine candidate for inducing RSV-specific immunity in mice and humans. We demonstrate that RSV sF-PCPP formulations induce high neutralization titers to RSV comparable to alum formulations even at a low PCPP dose and protect animals against viral challenge both in the lung and in the upper respiratory tract. PCPP formulations were also characterized by Th1-biased responses, compared to Th2-biased responses that are more typical for RSV sF alone or RSV sF-alum formulations, suggesting an inherent immunostimulating activity of the polyphosphazene adjuvant. We defined these immunologically active RSV sF-PCPP formulations as self-assembled water-soluble protein-polymer complexes with distinct physicochemical parameters. The secondary structure and antigenicity of the protein in the complex were fully preserved during the spontaneous aqueous self-assembly process. These findings further advance the concept of polyphosphazene immunoadjuvants as unique dual-functionality adjuvants integrating delivery and immunostimulating modalities in one water-soluble molecule.

Formulation of the respiratory syncytial virus fusion protein with a polymer-based combination adjuvant promotes transient and local innate immune responses and leads to improved adaptive immunity

Respiratory syncytial virus (RSV) causes serious upper and lower respiratory tract infections in newborns and infants. Presently, there is no licensed vaccine against RSV. We previously reported the safety and efficacy of a novel vaccine candidate (ΔF/TriAdj) in rodent and lamb models following intranasal immunization. However, the effects of the vaccine on the innate immune system in the upper and lower respiratory tracts, when delivered intranasally, have not been characterized. In the present study, we found that ΔF/TriAdj triggered transient production of chemokines, cytokines and interferons in the nasal tissues and lungs of BALB/c mice. The types of chemokines produced were consistent with the populations of immune cells recruited, i.e. dendritic cells, macrophages and neutrophils, in the nose-associated lymphoid tissue (NALT), lung and their draining lymph nodes of the ΔF/TriAdj-immunized group. In addition, ΔF/TriAdj stimulated cellular activation with generation of mucosal and systemic antibody responses, and conferred complete protection from viral infection in the lungs upon RSV challenge. The effect of ΔF/TriAdj was short-lived in the nasal tissues and more prolonged in the lungs. In addition, both innate and adaptive immune responses were lower when mice were immunized with ΔF alone. These results suggest that ΔF/TriAdj modulates the innate mucosal environment in both upper and lower respiratory tracts, which contributes to robust adaptive immune responses and long-term protective efficacy of this novel vaccine formulation.

Administration of Poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and Avian Beta Defensin as Adjuvants in Inactivated Inclusion Body Hepatitis Virus and its Hexon Protein-Based Experimental Vaccine Formulations in Chickens

Inclusion body hepatitis (IBH) is one of the major infectious diseases adversely affecting the poultry industry of the United States and Canada. Currently, no effective and safe vaccine is available for the control of IBH virus (IBHV) infection in chickens. However, based on the excellent safety and immunogenic profiles of experimental veterinary vaccines developed with the use of new generation adjuvants, we hypothesized that characterization of vaccine formulations containing inactivated IBHV or its capsid protein hexon as antigens, along with poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and avian beta defensin 2 (ABD2) as vaccine adjuvants, will be helpful in development of an effective and safe vaccine formulation for IBH. Our data demonstrated that experimental administration of vaccine formulations containing inactivated IBHV and a mixture of PCEP with or without ABD2 as an adjuvant induced significantly higher antibody responses compared with other vaccine formulations, while hexon protein-based vaccine formulations showed relatively lower levels of antibody responses. Thus, a vaccine formulation containing inactivated IBHV with PCEP or a mixture of PCEP and ABD2 (with a reduced dosage of PCEP) as an adjuvant may serve as a potential vaccine candidate. However, in order to overcome the risks associated with whole virus inactivated vaccines, characterization of additional viral capsid proteins, including fiber protein and penton of IBHV along with hexon protein in combination with more new generation adjuvants, will be helpful in further improvements of vaccines against IBHV infection.

Immunogenicity of a bovine herpesvirus 1 glycoprotein D DNA vaccine complexed with bovine neutrophil beta-defensin 3

Protective efficacy against bovine herpesvirus 1 (BoHV-1) has been demonstrated to be induced by a plasmid encoding bovine neutrophil beta-defensin 3 (BNBD3) as a fusion construct with truncated glycoprotein D (tgD). However, in spite of the increased cell-mediated immune responses induced by this DNA vaccine, the clinical responses of BoHV-1-challenged cattle were not reduced over those observed in animals vaccinated with the plasmid encoding tgD alone; this might have been because the vaccine failed to improve humoral responses. We hypothesized that an alternative vaccine design strategy that utilized the DNA vaccine pMASIA-tgD as a complex with BNBD3 might improve humoral responses while maintaining robust Th1-type cell-mediated responses. C57BL/6 mice were vaccinated with pMASIA-tgD complexed with 0, 0.01875, 0.1875, or 1.875 nmol of a stable synthesized analog of BNBD3 (aBNBD3). The best results were seen in mice immunized with the vaccine composed of pMASIA-tgD complexed to 0.1875 nmol aBNBD3. In this group, humoral responses were improved, as evidenced by increased virus neutralization, tgD-specific early IgG1, and later IgG2a titers, while the strong cell-mediated immune responses, measured based on specific gamma interferon (IFN-γ)-secreting cells, were maintained relative to pMASIA-tgD. Modulation of the immune response might have been due in part to the effect of BNBD3 on dendritic cells (DCs). In vitro studies showed that murine bone marrow-derived DCs (BMDCs) pretreated with aBNBD3 were activated, as evidenced by CD11c downregulation, and were functionally mature, as shown by increased allostimulatory ability. Native, synthetic, and analog forms of BNBD3 were equally capable of inducing functional maturation of BMDCs.

A single, low dose oral antigen exposure in newborn piglets primes mucosal immunity if administered with CpG oligodeoxynucleotides and polyphosphazene adjuvants

By definition, soluble antigens ingested orally trigger mucosal tolerance such that any subsequent re-exposure by a systemic route results in suppression of immunity. We propose that antigens introduced in extreme early life can readily traverse the gut wall and therefore circumvent induction of mucosal tolerance and instead induce immunity. Piglets were drenched with low-doses of ovalbumin (OVA; 5mg or 0.05 mg) alone, OVA plus adjuvants (CpG oligodeoxynucleotides and PCEP polyphosphazene) or saline within 6h of birth. At 28 days of age, they were administered 10mg OVA plus 1:1 Montanide adjuvant (or saline) via the intraperitoneal (i.p.) route or via the oral route. Serum was obtained on day 28 and day 49 to measure OVA-specific antibodies titres. All piglets boosted orally with OVA plus Montanide, regardless of prior OVA exposure, failed to induce immunity. As expected, piglets drenched with saline but boosted via the i.p. route with OVA plus Montanide showed significant induction of anti-OVA IgA, IgG, IgG1 and IgG2 relative to saline control piglets. Newborn animals drenched with 5mg or 0.05 mg OVA failed to induce oral immunity. A second intramuscular injection in adulthood triggered immunity in the piglets that were drenched with 0.05 mg OVA and boosted initially by the i.p. route suggesting that some systemic lymphocytes were primed despite initial lack of induction of humoral immunity. In contrast, piglets orally immunized with 5mg or 0.05 mg OVA plus adjuvants resulted in significant induction of anti-OVA IgA (5mg only), IgM, IgG, IgG1 and IgG2 in serum relative to saline control piglets as well as significant induction of anti-OVA IgA, IgM (5mg only) IgG, IgG1 (5mg only) or IgG2 relative to piglets drenched with OVA alone. These data clearly show that the response was sensitive to the oral vaccine components and was not simply a response to the i.p. immunization at day 28. This work demonstrates that newborn piglets respond to oral antigens with immunity if re-exposure to the antigen occurs via a systemic route and if adjuvants are included with the oral vaccine administered at birth. These results should be further explored to establish whether early life oral vaccination can be exploited to protect this susceptible population against infectious diseases.

Vaccination with the RSV fusion protein formulated with a combination adjuvant induces long-lasting protective immunity

Respiratory syncytial virus (RSV) is one of the primary causative agents of upper and lower respiratory tract infections in young children, in particular infants. Recently, we reported the protective efficacy of a RSV vaccine formulation consisting of a truncated version of the fusion (F) protein formulated with a Toll-like receptor (TLR) agonist and an immunostimulatory peptide in a carrier system (ΔF/TriAdj). To evaluate the duration of immunity induced by this vaccine candidate, we carried out long-term trials. The ΔF was formulated with triple adjuvant (TriAdj) containing either polyinosinic : polycytidylic acid (polyI : C) or cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODNs) and administered intranasally to mice. One year after the second vaccination all mice were challenged with RSV. Both ΔF/TriAdj formulations mediated the induction of high levels of IgG1, IgG2a and virus-neutralizing antibodies, and IgA in the lungs. Based on the numbers of IFN-γ- and IL-5-secreting cells in the spleen, the immune response was slightly T-helper cell type 1 (Th1)-biased. This was confirmed by the presence of F85-93-specific CD8(+) effector T cells in the lungs of both ΔF/TriAdj(polyI : C)- and ΔF/TriAdj(CpG)-immunized mice. Both ΔF/TriAdj formulations induced RSV-specific CD8(+) T cells. However, ΔF/TriAdj(polyI : C) generated significantly higher IgG affinity maturation and higher numbers of RSV-specific CD8(+) effector memory T cells in lungs and CD8(+) central memory T cells in spleen and lymph nodes than ΔF/TriAdj(CpG). After RSV challenge, no virus replication and no evidence of vaccine-induced pathology were detected in mice immunized with either of the ΔF/TriAdj formulations, demonstrating that the duration of immunity induced with these vaccines is at least one year.

Inclusion of the bovine neutrophil beta-defensin 3 with glycoprotein D of bovine herpesvirus 1 in a DNA vaccine modulates immune responses of mice and cattle

Bovine herpesvirus 1 (BoHV-1) causes recurrent respiratory and genital infections in cattle and predisposes them to lethal secondary infections. While modified live and killed BoHV-1 vaccines exist, these are not without problems. Development of an effective DNA vaccine for BoHV-1 has the potential to address these issues. As a strategy to enhance DNA vaccine immunity, a plasmid encoding the bovine neutrophil beta-defensin 3 (BNBD3) as a fusion with truncated glycoprotein D (tgD) and a mix of two plasmids encoding BNBD3 and tgD were tested in mice and cattle. In mice, coadministration of BNBD3 on the separate plasmid enhanced the tgD-induced gamma interferon (IFN-γ) response but not the antibody response. BNBD3 fused to tgD did not affect the antibody levels or the number of IFN-γ-secreting cells but increased the induction of tgD-specific cytotoxic T lymphocytes (CTLs). In cattle, the addition of BNBD3 as a fusion construct also modified the immune response. While the IgG and virus-neutralizing antibody levels were not affected, the number of IFN-γ-secreting cells was increased after BoHV-1 challenge, specifically the CD8(+) IFN-γ(+) T cells, including CD8(+) IFN-γ(+) CD25(+) CTLs. While reduced virus shedding, rectal temperature, and weight loss were observed, the level of protection was comparable to that observed in pMASIA-tgD-vaccinated animals. These data show that coadministration of BNBD3 with a protective antigen as a fusion in a DNA vaccine strengthened the Th1 bias and increased cell-mediated immune responses but did not enhance protection from BoHV-1 infection.

The role of dendritic cells in innate and adaptive immunity to respiratory syncytial virus, and implications for vaccine development

Respiratory syncytial virus (RSV) is a common human pathogen that causes cold-like symptoms in most healthy adults and children. However, RSV often moves into the lower respiratory tract in infants and young children predisposed to respiratory illness, making it the most common cause of pediatric broncheolitis and pneumonia. The development of an appropriate balanced immune response is critical for recovery from RSV, while an unbalanced and/or excessively vigorous response may lead to immunopathogenesis. Different dendritic cell (DC) subsets influence the magnitude and quality of the host response to RSV infection, with myeloid DCs mediating and plasmacytoid DCs modulating immunopathology. Furthermore, stimulation of DCs through Toll-like receptors is essential for induction of protective immunity to RSV. These characteristics have implications for the rational design of a RSV vaccine.

Low dose antigen exposure for a finite period in newborn rats prevents induction of mucosal tolerance

Background

In adult rats, initial exposure to antigens by a mucosal route triggers tolerance such that any subsequent re-exposure, even by a systemic route, results in suppression of immunity. The newborn’s gut is semi-permeable for a finite period to allow maternal antibodies to enter the newborn’s circulation. We propose that antigens introduced in extreme early life can readily traverse the gut wall and therefore circumvent induction of mucosal tolerance.

Methodology/Principle Findings

Rat pups were gavaged with low-doses of ovalbumin (OVA; oral exposure group) or saline (parenteral control group) every second day for several weeks followed by an intraperitoneal (i.p.) injection at 1 month of age. When gavage was initiated the day after birth, newborn oral exposure pups responded with significantly higher anti-OVA IgA, IgM, IgG2a, and IgG1 titres in their serum and anti-OVA IgA, IgG2a and IgG1 titres in their lungs compared to negative control pups. Oral exposure alone failed to induce immunity. Pups exposed to the same treatment regimen starting at 14 days of age showed induction of mucosal tolerance after i.p. immunization. Newborn oral exposure groups subjected to secondary i.p. immunization responded with significantly increased humoral immunity in lung and sera suggesting that once antigen-specific mucosal tolerance if circumvented, it persists. Lymphocytes derived from mesenteric lymph node cells re-simulated with OVA ex vivo, from newborn oral exposure pups exposed to secondary immunization produced significantly higher IFN-γ expression and lymphocyte proliferation relative to control pups indicating prevention of tolerance in the cell-mediated immune system.

Conclusions/Significance

This work demonstrates that newborns may be uniquely qualified to prevent induction of mucosal tolerance to oral antigens. These results should be further explored to establish whether prevention of tolerance by early life oral vaccination can be exploited to prime for mucosal as well as systemic immunity and thus protect this susceptible population against infectious diseases.

Enhanced immune responses and protection by vaccination with respiratory syncytial virus fusion protein formulated with CpG oligodeoxynucleotide and innate defense regulator peptide in polyphosphazene microparticles

Although respiratory syncytial virus (RSV) is the leading cause of serious respiratory tract disease in children, to date no RSV vaccine is available. To produce an effective subunit vaccine, a truncated secreted version of the F protein (ΔF) was expressed in mammalian cells, purified and shown to form trimers. The ΔF protein was then formulated with a CpG oligodeoxynucleotide (ODN) and an innate defense regulator (IDR) peptide in polyphosphazene microparticles (ΔF-MP). Mice immunized either intramuscularly (IM) or intranasally (IN) with ΔF-MP developed significantly higher levels of virus-neutralizing antibodies in the sera and lungs, as well as higher numbers of IFN-γ secreting cells than mice immunized with the ΔF protein alone. In contrast, the IM delivered ΔF induced high production of IL-5 while the IN delivered ΔF did not elicit a measurable immune response. After RSV challenge, essentially no virus and no evidence of immunopathology were detected in mice immunized with ΔF-MP regardless of the route of delivery. While the mice immunized IM with ΔF alone also showed reduced virus replication, they developed enhanced levels of pulmonary IgE, IL-4, IL-5, IL-13 and eotaxin, as well as eosinophilia after challenge. The level of protection induced by the ΔF-MP formulation was equivalent after IM and IN delivery. The efficacy and safety of the ΔF-MP formulation was confirmed in cotton rats, which also developed enhanced immune responses and were fully protected from RSV challenge after vaccination with ΔF-MP. In conclusion, formulation of recombinant ΔF with CpG ODN and IDR peptide in polyphosphazene microparticles should be considered for further evaluation as a safe and effective vaccine against RSV.

Activation of adjuvant core response genes by the novel adjuvant PCEP

Adjuvants are critical components of many vaccines but their mechanisms of action are often poorly understood. Understanding the mechanisms of adjuvant activity is critical in defining how innate immunity influenced adaptive immunity. We investigated the capacity of a novel adjuvant, poly[di(sodiumcarboxylatoethylphenoxy)phosphazene] (PCEP), to induce innate immune responses at the site of injection. PCEP induced time-dependent changes in the gene expression of many "adjuvant core response genes" including cytokines, chemokines, innate immune receptors, interferon-induced genes, adhesion molecules and antigen-presentation genes. In addition, PCEP triggered local production of cytokines and the chemokine CCL-2 as indicated by ELISA. Interestingly, PCEP up-regulated the gene expression of the inflammasome receptor, Nlrp3, and induced the production of pro-inflammatory cytokines IL-1β, and IL-18 at the site of injection. Secretion of these cytokines is predominantly a result of activation of the inflammasome, a multi-protein complex that activates caspase-1, leading to the processing and secretion of proinflammatory cytokines. These results suggest that PCEP may modulate antigen-specific immune responses by strongly activating early innate immune responses and promoting a strong immuno-stimulatory environment at the site of injection.

Interferon-gamma and B-cell Activating Factor (BAFF) promote bovine B cell activation independent of TLR9 and T-cell signaling

We previously reported that CD21(+) B cells purified from bovine blood do not respond to CpG-ODN stimulation unless either CD14(+) monocytes or B-cell Activating Factor (BAFF), a cytokine produced by activated monocytes, are present. In this report, we present evidence that CD14(+) monocytes are critical for CpG-specific lymphocyte proliferation within the peripheral blood mononuclear cell (PBMC) population but that this response is not mediated by soluble factors produced by CpG-activated monocytes. We further determine that bovine monocytes stimulated with IFN-γ induce expression of the BAFF gene and that recombinant IFN-γ and BAFF induced robust B cell activation when cultured in the absence of CpG ODN. These data suggest that CpG-stimulated monocytes may indirectly promote B cell activation by promoting release of cytokines and/or other soluble factors from accessory cells which in turn act on CpG-stimulated B cells to promote antigen-independent and T cell independent B cell activation. Understanding the T cell independent signals that induce B cell activation has important implications for understanding B cell development in locations where T cells are limited and in understanding polyclonal B cell activation that may contribute to autoimmune diseases.

B-cell activating factor (BAFF) promotes CpG ODN-induced B cell activation and proliferation

It is controversial whether naïve B cells are directly activated in response to TLR9 ligand, CpG ODN. Although bovine blood-derived CD21(+) B cells express TLR9 and proliferate in response to CpG in mixed-cell populations, purified bovine B cells do not proliferate significantly in response to CpG ODN, even when the B cell receptor is engaged. When co-cultured with CD14(+) myeloid cells and/or B-cell activating factor (BAFF), a cytokine produced by activated myeloid cells, there was a significant increase in CpG-specific B cell proliferation, and the number of large B cells in general or positive for CD25, all of which are markers for B cell activation. These data suggest that activated myeloid cells and BAFF prime B cells for significant CpG-specific activation. Understanding the signals required to mediate efficient CpG-induced, antigen-independent and T-cell independent activation of B cells has implications for polyclonal B cell activation and the development of autoimmune diseases.

PCPP (poly[di(carboxylatophenoxy)-phosphazene]) microparticles co-encapsulating ovalbumin and CpG oligo-deoxynucleotides are potent enhancers of antigen specific Th1 immune responses in mice

We generated poly[di(carboxylatophenoxy)-phosphazene] (PCPP) microparticles encapsulating ovalbumin (OVA) and CpG of 0.5-2.5 μm in diameter with an encapsulation efficiency of approximately 63% and 95% respectively. In mice the microparticles generated high antigen-specific IgG, IgG1 and IgG2a titers with higher IgG2a/IgG1 ratios. Whole body in vivo imaging of mice subcutaneously injected with MPs showed several fold increase of OVA and CpG in draining inguinal lymph nodes compared to soluble formulations. We conclude that PCPP MPs are more effective in enhancing immune responses compared to soluble formulations, due to co-delivery of OVA and CpG resulting in a Th1 type of immune response.

A novel triple adjuvant formulation promotes strong, Th1-biased immune responses and significant antigen retention at the site of injection

Ovalbumin (OVA) was labeled with a near infra-red dye (*OVA) and formulated with the host defense peptide indolicidin (Indol), CpG oligodeoxynucleotide (ODN) 1826 (CpG) and/or poly(p-dicarboxylatophenoxy)-phosphazene (PP4). The immunogenicity of these *OVA formulations was evaluated in mice. All double and triple adjuvant combinations elicited strong antibody responses. *OVA formulated with CpG ODN in combination with indolicidin, PP4 or both induced only IFN-γ, while formulations with indolicidin and/or PP4 promoted predominantly IL-5 production. Overall, both IgG and IFN-γ production was superior when *OVA was combined with CpG/Indol/PP4. Furthermore, mice injected with *OVA formulated with CpG/Indol/PP4 contained detectable *OVA in the injection site two months post immunization. These results indicate that the CpG/Indol/PP4 combination promotes prolonged antigen retention and strong, antigen-specific Th1-biased immune responses.

PCEP enhances IgA mucosal immune responses in mice following different immunization routes with influenza virus antigens

Background

We previously demonstrated that polyphosphazenes, particularly PCEP, enhance immune responses in mice immunized subcutaneously and intranasally. The objective of the present study was to investigate the efficacy of polyphosphazenes as adjuvants when delivered through different routes of vaccine administration.

Methods

BALB/c mice were immunized through intranasal, subcutaneous, oral and intrarectal delivery with vaccine formulations containing either influenza X:31 antigen alone or formulated in PCEP. Serum and mucosal washes were collected and assayed for antigen-specific antibody responses by ELISA, while splenocytes were assayed for antigen-specific cytokine production by ELISPOT.

Results

Intranasal immunization with PCEP+X:31 induced significantly higher IgA titers in all mucosal secretions (lung, nasal, and vaginal) compared to the other routes. Serum analysis showed that all mice given the PCEP+X:31 combination showed evidence of enhanced IgG2a titers in all administered routes, indicating that PCEP can be effective as an adjuvant in enhancing systemic immune responses when delivered via different routes of administration.

Conclusions

We conclude that PCEP is a potent and versatile mucosal adjuvant that can be administered in a variety of routes and effectively enhances systemic and local immune responses. Furthermore, intranasal immunization was found to be the best administration route for enhancing IgA titers, providing further evidence for the potential of PCEP as a mucosal adjuvant.

Intranasal immunization of mice with a bovine respiratory syncytial virus vaccine induces superior immunity and protection compared to those by subcutaneous delivery or combinations of intranasal and subcutaneous prime-boost strategies

Bovine respiratory syncytial virus (BRSV) infects cells of the respiratory mucosa, so it is desirable to develop a vaccination strategy that induces mucosal immunity. To achieve this, various delivery routes were compared for formalin-inactivated (FI) BRSV formulated with CpG oligodeoxynucleotide (ODN) and polyphosphazene (PP). Intranasal delivery of the FI-BRSV formulation was superior to subcutaneous delivery in terms of antibody, cell-mediated, and mucosal immune responses, as well as reduction in virus replication after BRSV challenge. Although intranasal delivery of FI-BRSV also induced higher serum and lung antibody titers and gamma interferon (IFN-gamma) production in the lungs than intranasal-subcutaneous and/or subcutaneous-intranasal prime-boost strategies, no significant differences were observed in cell-mediated immune responses or virus replication in the lungs of challenged mice. Interleukin 5 (IL-5), eotaxin, and eosinophilia were enhanced after BRSV challenge in the lungs of subcutaneously immunized mice compared to unvaccinated mice, but not in the lungs of mice immunized intranasally or through combinations of the intranasal and subcutaneous routes. These results suggest that two intranasal immunizations with FI-BRSV formulated with CpG ODN and PP are effective and safe as an approach to induce systemic and mucosal responses, as well to reduce virus replication after BRSV challenge. Furthermore, intranasal-subcutaneous and subcutaneous-intranasal prime-boost strategies were also safe and almost as efficacious. In addition to the implications for the development of a protective BRSV vaccine for cattle, formulation with CpG ODN and PP could also prove important in the development of a mucosal vaccine that induces protective immunity against human RSV.

Formulation of bovine respiratory syncytial virus fusion protein with CpG oligodeoxynucleotide, cationic host defence peptide and polyphosphazene enhances humoral and cellular responses and induces a protective type 1 immune response in mice

Respiratory syncytial virus (RSV) is the leading cause of serious respiratory tract disease in children and calves; however, RSV vaccine development has been slow due to early observations that formalin-inactivated vaccines induced Th2-type immune responses and led to disease enhancement upon subsequent exposure. Hence, there is a need for novel adjuvants that will promote a protective Th1-type or balanced immune response against RSV. CpG oligodeoxynucleotides (ODNs), indolicidin, and polyphosphazene were examined for their ability to enhance antigen-specific immune responses and influence the Th-bias when co-formulated with a recombinant truncated bovine RSV (BRSV) fusion protein (DeltaF). Mice immunized with DeltaF co-formulated with CpG ODN, indolicidin, and polyphosphazene (DeltaF/CpG/indol/PP) developed higher levels of DeltaF-specific serum IgG, IgG1 and IgG2a antibodies when compared with DeltaF alone, and displayed an increase in the frequency of gamma interferon-secreting cells and decreased interleukin (IL)-5 production by in vitro restimulated splenocytes, characteristic of a Th1 immune response. These results were observed in both C57BL/6 and BALB/c strains of mice. When evaluated in a BRSV challenge model, mice immunized with DeltaF/CpG/indol/PP developed significantly higher levels of BRSV-neutralizing serum antibodies than mice immunized with the DeltaF protein alone, and displayed significantly less pulmonary IL-4, IL-5, IL-13 and eotaxin and reduced eosinophilia after challenge. These results suggest that co-formulation of DeltaF with CpG ODN, host defence peptide and polyphosphazene may result in a safe and effective vaccine for the prevention of BRSV and may have implications for the development of novel human RSV vaccines.

Approaches to enhancing immune responses stimulated by CpG oligodeoxynucleotides

CpG oligodeoxynucleotides (ODN) activate the immune system and are promising immunotherapeutic agents against infectious diseases, allergy/asthma and cancer. It has become apparent that while CpG ODN are potent immune activators in mice, their immune stimulatory effects are often less dramatic in humans and large animals. This disparity between rodents and mammals has been attributed to the differences in TLR9 expression in different species. This along with the sometimes transient activity of ODN may limit its potential immunotherapeutic applications. Several approaches to enhance the activity of CpG ODN have been explored including formulation of ODN in depot-forming adjuvants, and more recently, coadministration with polyphosphazenes, inhibitors of cytokines that downregulate TLR9 activation, and simultaneous activation with multiple TLR agonists. We will discuss these approaches and the mechanisms involved, with emphasis on what we have learned from large animal models.

CpG oligonucleotide, host defense peptide and polyphosphazene act synergistically, inducing long-lasting, balanced immune responses in cattle

Vaccines consisting of subunit or protein antigens are less immunogenic than traditional vaccines, and therefore require formulation with an adjuvant. Conventional adjuvants, however, often cause undesirable injection site reactions and Th2-biased immune responses. Therefore, novel vaccine adjuvants which can safely enhance and selectively bias the resulting immune response are required. Here the adjuvant combination of CpG ODN, indolicidin and polyphosphazene (CpG+indol+PP) was evaluated for its ability to enhance and modulate the immune response when formulated with the antigen hen egg lysozyme (HEL). Cattle immunized with HEL co-adjuvanted with CpG+indol+PP developed higher antigen-specific humoral responses, and long-lasting cell-mediated immune responses, as evidenced by elevated levels of IFN-gamma secretion by re-stimulated PBMCs, that were superior even to EMULSIGEN((R)), an oil-in-water based adjuvant that was used as positive control. Physical characterization of the vaccines indicated that formulation of HEL with CpG+indol+PP resulted in the formation of antigen-adjuvant complexes, which may have contributed to their enhanced immunogenicity. Furthermore, the addition of polyphosphazene to CpG ODN and indolicidin dose-dependently enhanced the secretion of the cytokines IFN-alpha, TNF-alpha and IFN-gammain vitro, indicating that polyphosphazene can also synergize with CpG ODN and indolicidin to stimulate innate immune responses.

The novel adjuvant combination of CpG ODN, indolicidin and polyphosphazene induces potent antibody- and cell-mediated immune responses in mice

The need to enhance the immunogenicity of purified subunit antigens and modulate resulting immune responses has prompted the development of new adjuvants. Here, the ability of CpG oligodeoxynucleotides (ODN), a bovine host defence peptide indolicidin, and polyphosphazene to synergistically combine and enhance innate and adaptive immune responses was examined in mice. In vitro, the adjuvant combination of CpG ODN, indolicidin and polyphosphazene (CpG/indol/PP) enhanced the secretion of TNF-alpha, IL-12p40, and IL-6 by bone marrow-derived DCs (BMDCs) when compared to the individual components. When co-formulated with ovalbumin (OVA), CpG/indol/PP formed antigen-adjuvant complexes, and enhanced antibody and cell-mediated responses in mice, via both MHC I and II pathways, promoting a more balanced antibody-mediated and type 1-biased cell-mediated immune response. Furthermore, substitution of the proline residues of indolicidin with arginine increased the synergistic adjuvant effect of the peptide, and induced significantly higher IgG1 and IgG2a titers and IFN-gamma secretion, as well as increased uptake by antigen presenting cells. These results clearly demonstrate that the use of a combination of CpG ODN, indolicidin, and polyphosphazene as adjuvant can significantly enhance an antigen-specific immune response.

Lack of antibody affinity maturation due to poor Toll-like receptor stimulation leads to enhanced respiratory syncytial virus disease

Respiratory syncytial virus (RSV) is a leading cause of hospitalization in infants. A formalin-inactivated RSV vaccine was used to immunize children in 1966 and elicited non-protective, pathogenic antibody. Two immunized infants died and 80% were hospitalized after subsequent RSV exposure. No vaccine was licensed since.

A widely accepted hypothesis attributed vaccine failure to formalin disruption of protective antigens. Instead, we show that lack of protection was not due to alterations caused by formalin, but to low antibody avidity for protective epitopes. Lack of antibody affinity maturation followed poor Toll-like receptor stimulation. This study explains why the inactivated RSV vaccine failed to protect and consequently led to severe disease, hampering vaccine development for forty-two years. Also, it suggests that inactivated RSV vaccines may be rendered safe and effective by inclusion of TLR-agonists in their formulation. In addition, it identifies affinity maturation as a critical factor for the safe immunization of infants.