Induction of protective immune responses against Venezuelan equine encephalitis (VEE) virus aerosol challenge with microencapsulated VEE virus vaccine

An inventory of adjuvants used for vaccination in horses: the past, the present and the future

Vaccination is one of the most widely used strategies to protect horses against pathogens. However, available equine vaccines often have limitations, as they do not always provide effective, long-term protection and booster injections are often required. In addition, research efforts are needed to develop effective vaccines against emerging equine pathogens. In this review, we provide an inventory of approved adjuvants for equine vaccines worldwide, and discuss their composition and mode of action when available. A wide range of adjuvants are used in marketed vaccines for horses, the main families being aluminium salts, emulsions, polymers, saponins and ISCOMs. We also present veterinary adjuvants that are already used for vaccination in other species and are currently evaluated in horses to improve equine vaccination and to meet the expected level of protection against pathogens in the equine industry. Finally, we discuss new adjuvants such as liposomes, polylactic acid polymers, inulin, poly-ε-caprolactone nanoparticles and co-polymers that are in development. Our objective is to help professionals in the horse industry understand the composition of marketed equine vaccines in a context of mistrust towards vaccines. Besides, this review provides researchers with a list of adjuvants, either approved or at least evaluated in horses, that could be used either alone or in combination to develop new vaccines.

Recent advances in microencapsulation of drugs for veterinary applications

Microencapsulation is a process where very minute droplets or particles of solid or liquid or gas are trapped with a polymer to isolate the internal core material from external environmental hazards. Microencapsulation is applied mostly for flavor masking, fortification, and sustained and control release. It improves palatability, absorption, and bioavailability of drugs with good conformity. Microencapsulation has been widely studied in numerous drug delivery systems for human health. The application of microcapsules in the veterinary pharmaceutical sciences is increasing day by day. The treatment systems for humans and animals are likely to be similar, but more complex in the veterinary field due to the diversity of the species, breeds, body size, biotransformation rate, and other factors associated with animal physiology. Commercially viable, economically profitable, and therapeutically effective microencapsulated vaccine, anthelmintic, antibacterial, and other therapeutics have a great demand for livestock and poultry production. Nowadays, researchers emphasize the controlled and sustained-release dosage form of drugs in the veterinary field. This paper has highlighted the microencapsulation materials, preparation techniques, characteristics, roles, and the application of microcapsules in veterinary medicine.

Veterinary vaccine nanotechnology: pulmonary and nasal delivery in livestock animals

Veterinary vaccine development has several similarities with human vaccine development to improve the overall health and well-being of species. However, veterinary goals lean more toward feasible large-scale administration methods and low cost to high benefit immunization. Since the respiratory mucosa is easily accessible and most infectious agents begin their infection cycle at the mucosa, immunization through the respiratory route has been a highly attractive vaccine delivery strategy against infectious diseases. Additionally, vaccines administered via the respiratory mucosa could lower costs by removing the need of trained medical personnel, and lowering doses yet achieving similar or increased immune stimulation. The respiratory route often brings challenges in antigen delivery efficiency with enough potency to induce immunity. Nanoparticle (NP) technology has been shown to enhance immune activation by producing higher antibody titers and protection. Although specific mechanisms between NPs and biological membranes are still under investigation, physical parameters such as particle size and shape, as well as biological tissue distribution including mucociliary clearance influence the protection and delivery of antigens to the site of action and uptake by target cells. For respiratory delivery, various biomaterials such as mucoadhesive polymers, lipids, and polysaccharides have shown enhanced antibody production or protection in comparison to antigen alone. This review presents promising NPs administered via the nasal or pulmonary routes for veterinary applications specifically focusing on livestock animals including poultry.

Biodegradable nanoparticle delivery of inactivated swine influenza virus vaccine provides heterologous cell-mediated immune response in pigs

Swine influenza virus (SwIV) is one of the important zoonotic pathogens. Current flu vaccines have failed to provide cross-protection against evolving viruses in the field. Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable FDA approved polymer and widely used in drug and vaccine delivery. In this study, inactivated SwIV H1N2 antigens (KAg) encapsulated in PLGA nanoparticles (PLGA-KAg) were prepared, which were spherical in shape with 200 to 300nm diameter, and induced maturation of antigen presenting cells in vitro. Pigs vaccinated twice with PLGA-KAg via intranasal route showed increased antigen specific lymphocyte proliferation and enhanced the frequency of T-helper/memory and cytotoxic T cells (CTLs) in peripheral blood mononuclear cells (PBMCs). In PLGA-KAg vaccinated and heterologous SwIV H1N1 challenged pigs, clinical flu symptoms were absent, while the control pigs had fever for four days. Grossly and microscopically, reduced lung pathology and viral antigenic mass in the lung sections with clearance of infectious challenge virus in most of the PLGA-KAg vaccinated pig lung airways were observed. Immunologically, PLGA-KAg vaccine irrespective of not significantly boosting the mucosal antibody response, it augmented the frequency of IFN-γ secreting total T cells, T-helper and CTLs against both H1N2 and H1N1 SwIV. In summary, inactivated influenza virus delivered through PLGA-NPs reduced the clinical disease and induced cross-protective cell-mediated immune response in a pig model. Our data confirmed the utility of a pig model for intranasal particulate flu vaccine delivery platform to control flu in humans.

Particulate delivery systems for vaccination against bioterrorism agents and emerging infectious pathogens

Bioterrorism agents that can be easily transmitted with high mortality rates and cause debilitating diseases pose major threats to national security and public health. The recent Ebola virus outbreak in West Africa and ongoing Zika virus outbreak in Brazil, now spreading throughout Latin America, are case examples of emerging infectious pathogens that have incited widespread fear and economic and social disruption on a global scale. Prophylactic vaccines would provide effective countermeasures against infectious pathogens and biological warfare agents. However, traditional approaches relying on attenuated or inactivated vaccines have been hampered by their unacceptable levels of reactogenicity and safety issues, whereas subunit antigen-based vaccines suffer from suboptimal immunogenicity and efficacy. In contrast, particulate vaccine delivery systems offer key advantages, including efficient and stable delivery of subunit antigens, co-delivery of adjuvant molecules to bolster immune responses, low reactogenicity due to the use of biocompatible biomaterials, and robust efficiency to elicit humoral and cellular immunity in systemic and mucosal tissues. Thus, vaccine nanoparticles and microparticles are promising platforms for clinical development of biodefense vaccines. In this review, we summarize the current status of research efforts to develop particulate vaccine delivery systems against bioterrorism agents and emerging infectious pathogens. WIREs Nanomed Nanobiotechnol 2017, 9:e1403. doi: 10.1002/wnan.1403 For further resources related to this article, please visit the WIREs website.

Pulmonary vaccine delivery

This review will discuss developments in the field of pulmonary vaccine delivery. The possibilities of adopting aerosol-generation technology and specific pharmaceutical formulations for the purpose of pulmonary immunization are described. Aerosol-generation systems might offer advantages with respect to vaccine stability and antigenicity. Adjuvants and their inclusion in vaccine-delivery systems are described. Other formulation components, such as surfactants, particulate systems and dispersion of the aerosols are detailed in this paper. The noninvasive, relatively safe and low-cost nature of pulmonary delivery may provide great benefits to the public health vaccination campaign.

Biodegradable nanoparticle-entrapped vaccine induces cross-protective immune response against a virulent heterologous respiratory viral infection in pigs

Biodegradable nanoparticle-based vaccine development research is unexplored in large animals and humans. In this study, we illustrated the efficacy of nanoparticle-entrapped UV-killed virus vaccine against an economically important respiratory viral disease of pigs called porcine reproductive and respiratory syndrome virus (PRRSV). We entrapped PLGA [poly (lactide-co-glycolides)] nanoparticles with killed PRRSV antigens (Nano-KAg) and detected its phagocytosis by pig alveolar macrophages. Single doses of Nano-KAg vaccine administered intranasally to pigs upregulated innate and PRRSV specific adaptive responses. In a virulent heterologous PRRSV challenge study, Nano-KAg vaccine significantly reduced the lung pathology and viremia, and the viral load in the lungs. Immunologically, enhanced innate and adaptive immune cell population and associated cytokines with decreased secretion of immunosuppressive mediators were observed at both mucosal sites and blood. In summary, we demonstrated the benefits of intranasal delivery of nanoparticle-based viral vaccine in eliciting cross-protective immune response in pigs, a potential large animal model.

Evaluation of formalin inactivated V3526 virus with adjuvant as a next generation vaccine candidate for Venezuelan equine encephalitis virus

V3526, a genetically modified strain of Venezuelan equine encephalitis virus (VEEV), was formalin inactivated for evaluation as a next generation vaccine candidate for VEEV. In this study, we tested formalin-inactivated V3526 (fV3526) with and without adjuvant for immunogenicity and efficacy in BALB/c mice and results were compared to the existing inactivated VEEV vaccine, C84. Mice were vaccinated intramuscularly (IM) or subcutaneously (SC) with fV3526 formulations and challenged with VEEV IAB Trinidad donkey (VEEV TrD) strain by SC or aerosol exposure. Efficacy following SC or aerosol challenge was not significantly different between the fV3526 formulations or compared to C84 despite C84 being administered in more doses and higher concentration of viral protein per dose. These data support further evaluation of fV3526 formulations as a next generation VEEV vaccine.

Acute infection with venezuelan equine encephalitis virus replicon particles catalyzes a systemic antiviral state and protects from lethal virus challenge

The host innate immune response provides a critical first line of defense against invading pathogens, inducing an antiviral state to impede the spread of infection. While numerous studies have documented antiviral responses within actively infected tissues, few have described the earliest innate response induced systemically by infection. Here, utilizing Venezuelan equine encephalitis virus (VEE) replicon particles (VRP) to limit infection to the initially infected cells in vivo, a rapid activation of the antiviral response was demonstrated not only within the murine draining lymph node, where replication was confined, but also within distal tissues. In the liver and brain, expression of interferon-stimulated genes was detected by 1 to 3 h following VRP footpad inoculation, reaching peak expression of >100-fold over that in mock-infected animals. Moreover, mice receiving a VRP footpad inoculation 6, 12, or 24 h prior to an otherwise lethal VEE footpad challenge were completely protected from death, including a drastic reduction in challenge virus titers. VRP pretreatment also provided protection from intranasal VEE challenge and extended the average survival time following intracranial challenge. Signaling through the interferon receptor was necessary for antiviral gene induction and protection from VEE challenge. However, VRP pretreatment failed to protect mice from a heterologous, lethal challenge with vesicular stomatitis virus, yet conferred protection following challenge with influenza virus. Collectively, these results document a rapid modulation of the host innate response within hours of infection, capable of rapidly alerting the entire animal to pathogen invasion and leading to protection from viral disease.

Alpha interferon as an adenovirus-vectored vaccine adjuvant and antiviral in Venezuelan equine encephalitis virus infection

There are no widely available vaccines or antiviral drugs capable of protecting against infection with Venezuelan equine encephalitis virus (VEEV), although an adenovirus vector expressing VEEV structural proteins protects mice from challenge with VEEV and is potentially a vaccine suitable for human use. This work examines whether alpha interferon (IFN-α) could act as an adjuvant for the adenovirus-based vaccine. IFN-α was either expressed by a plasmid linked to the adenovirus vaccine or encoded by a separate adenovirus vector administered as a mixture with the vaccine. In contrast to previous reports with other vaccines, the presence of IFN-α reduced the antibody response to VEEV. When IFN-α was encoded by adenovirus, the lack of a VEEV-specific response was accompanied by an increase in the immune response to the adenovirus vector. IFN-α also plays a direct role in defence against virus infection, inducing the expression of a large number of antiviral proteins. Adenovirus-delivered IFN-α protected mice from VEEV disease when administered 24 h prior to challenge, but not when administered 6 h post-challenge, suggesting that up to 24 h is required for the development of the IFN-mediated antiviral response.

Complete inactivation of Venezuelan equine encephalitis virus by 1,5-iodonaphthylazide

Hydrophobic alkylating compounds like 1,5-iodonaphthylazide (INA) partitions into biological membranes and accumulates selectively into the hydrophobic domain of the lipid bilayer. Upon irradiation with far UV light, INA binds selectively to transmembrane proteins in the viral envelope and renders them inactive. Such inactivation does not alter the ectodomains of the membrane proteins thus preserving the structural and conformational integrity of immunogens on the surface of the virus. In this study, we have used INA to inactivate Venezuelan equine encephalitis virus (VEEV). Treatment of VEEV with INA followed by irradiation with UV light resulted in complete inactivation of the virus. Immuno-fluorescence for VEEV and virus titration showed no virus replication in-vitro. Complete loss of infectivity was also achieved in mice infected with INA treated plus irradiated preparations of VEEV. No change in the structural integrity of VEEV particles were observed after treatment with INA plus irradiation as assessed by electron microscopy. This data suggest that such inactivation strategies can be used for developing vaccine candidates for VEEV and other enveloped viruses.

Inhibition of multiple strains of Venezuelan equine encephalitis virus by a pool of four short interfering RNAs

RNA interference, mediated by short interfering RNAs (siRNAs), has been shown to have activity against a wide range of viruses and is a promising new antiviral therapy. Using multiple siRNAs that target conserved areas of the genome allows for increased chances of antiviral activity against different viral strains and also helps to prevent the emergence of escape mutants. In this study, four siRNAs were designed to target areas of conserved sequence between divergent strains of Venezuelan equine encephalitis virus (VEEV). A pool of these siRNAs inhibited the replication of all six strains of VEEV tested. A single nucleotide mismatch at the extreme 3′ end of one of the siRNA sense strands did not affect antiviral activity but other mutations were not tolerated. Two strains of VEEV were tested for their abilities to overcome the inhibitory effects of RNA interference following 10 consecutive incubations in the presence of siRNAs. One strain remained susceptible throughout the course of the experiment but the other strain became resistant to the activity of siRNAs. Sequence analysis of the siRNA target sites in this strain showed that no mutations had been generated, indicating that the virus may had become resistant in some other manner. In the absence of effective antiviral drugs and vaccines to combat VEEV infection, these siRNAs offer a potential new therapeutic approach but, as with all antimicrobial agents, caution needs to be exercised with respect to the generation of resistance.

Bioregulators as prototypic nontraditional threat agents

Bioregulators are naturally occurring organic compounds that regulate a multitude of biologic processes. Under natural circumstances, bioregulators are synthesized in minute quantities in a variety of living organisms and are essential for physiologic homeostasis. In the wrong hands, these compounds have the capability to be used as nontraditional threat agents that are covered by the prohibitions of the Chemical Weapons Convention and the Biological and Toxin Weapons Convention. Unlike traditional biowarfare/bioterrorism agents that have a latency period of hours to days,the onset of action of bioregulators may occur within minutes after host exposure. Concerns regarding the potential misuse of bioregulators for nefarious purposes relate to the ability of these nontraditional agents to induce profound physiologic effects.

Intranasal immunisation with defective adenovirus serotype 5 expressing the Venezuelan equine encephalitis virus E2 glycoprotein protects against airborne challenge with virulent virus

There is no vaccine licensed for human use to protect laboratory or field workers against infection with Venezuelan equine encephalitis virus (VEEV). Infection of these groups is most likely to occur via the airborne route and there is evidence to suggest that protection against airborne infection may require high antibody levels and the presence of antibody on the mucosal surface of the respiratory tract. Recombinant defective type 5 adenoviruses, expressing the E3E26K structural genes of VEEV were examined for their ability to protect mice against airborne challenge with virulent virus. After intranasal administration, good protection was achieved against the homologous serogroup 1A/B challenge virus (strain Trinidad donkey). There was less protection against enzootic serogroup II and III viruses, indicating that inclusion of more than one E3E26K sequence in a putative vaccine may be necessary. These studies confirm the potential of recombinant adenoviruses as vaccine vectors for VEEV and will inform the development of a live replicating adenovirus-based VEEV vaccine, deliverable by a mucosal route and suitable for use in humans.

Biotechnology: impact on biological warfare and biodefense

Advances in biological research likely will permit development of a new class of advanced biological warfare (ABW) agents engineered to elicit novel effects. In addition, biotechnology will have applications supporting ABW weaponization, dissemination, and delivery. Such new agents and delivery systems would provide a variety of new use options, expanding the BW paradigm. Although ABW agents will not replace threats posed by traditional biological agents such as Bacillus anthracis (anthrax) and Variola (smallpox), they will necessitate novel approaches to counterproliferation, detection, medical countermeasures, and attribution.

The immune response of rats to vaccination with the cDNA or protein forms of the cysteine proteinase of Fasciola hepatica

Our previous experiments have shown that intramuscular injection of Sprague-Dawley rats with a pcDNA 3.1 vector carrying cDNA encoding for a cysteine proteinase (CP) of F. hepatica may induce a high level of protection against subsequent infection with F. hepatica metacercariae (mc). The aim of the present study is to compare the immune response of Sprague-Dawley rats vaccinated intranasally with plasmid containing cDNA of CP of the fluke and intramuscularly or intraperitoneally with the recombinated enzyme protein to challenge with fluke metacercariae. In addition, protection following intranasal DNA vaccination was evaluated. Two experiments were carried out. In the first experiment rats were vaccinated twice with 50microg of cDNA containing plasmid or with 100microg protein of recombinated CP. Three weeks after the second vaccination rats were challenged orally with 25 mc. On days 0, 21, 42 and 63 after the challenge blood samples were collected for the evaluation of white blood cell, eosinophil and specific antibody responses. During the second experiment groups of five male and female rats were vaccinated twice intranasally with CPcDNA then challenged with 30 mc and dissected 5 weeks later. Results obtained in the experiments suggested that intranasal immunisation of rats with CPcDNA seems to favour a Th2 regulated antibody response. Intramuscular or intraperitoneal injections of CP protein stimulate both Th1 and Th2-dependent antibodies. Mean worm burdens found in rats vaccinated intranasally 5 or 10 weeks after the challenge were reduced by 61-75% in comparison with the challenge controls which suggests that intranasal vaccination with CPcDNA may protect hosts against F. hepatica infection.

Cytotoxic T-cell activity is not detectable in Venezuelan equine encephalitis virus-infected mice

Previously published research has established that the immune response to the Venezuelan equine encephalitis virus (VEEV) vaccine strain TC-83 is Th 1-mediated, with local activation of both CD4+ and CD8+ T cells. This suggests that cytotoxic lymphocytes CTL may play a role in protection against virulent VEEV. Studies involving a variety of immunisation schedules with either TC-83 or strain CAAR 508 (serogroup 5) of VEEV, and six different haplotypes of mice, failed to reveal functional CTL activity against VEEV-infected targets in secondary antigen-stimulated lymphocyte cultures from either the draining lymph nodes (LN) or spleen. Nor were VEEV-specific CTL detected after immunisation of mice (three haplotypes) with recombinant vaccinia viruses (VV) expressing either the non-structural (nsP1-4) or the structural (C-E3-E2-6K-E1) genes of TC-83. Reciprocal experiments in which mice were immunised with TC-83, and their lymphocytes tested against VV recombinant-infected targets also failed to detect CTL activity. These data suggest that VEEV infection of mice does not elicit detectable CTL activity, and that CTL are unlikely to play a role in protection against virulent VEEV.

Development of oral microencapsulated forms for delivering viral vaccines

Rapid development in biotechnology during the last decade has allowed novel ideas in the development of antiviral vaccines to be considered and provides interesting technological approaches to their realization. Designing of microencapsulated forms for delivering bacterial and viral antigens or antigenic complexes using biodegradable biopolymers is an important novel direction. This approach involves the production of polymeric spherical particles with a diameter of 1 microm to 3 mm, containing isolated viral antigens or whole viral particles. Microencapsulated antigens administered orally are protected from low pH values of the gastric juice, bile acids, their salts and proteolytic enzymes of the gastrointestinal tract. The ability to drastically potentiate the immune response to encapsulated antigens, together with the ability to penetrate into the intestinal and respiratory mucosae upon oral and tracheal administrations, respectively, with induction of local and systemic immune reactions are the special merits of such polymers. However, the majority of data on microencapsulated viral vaccines has so far been obtained in animal models, as well as a limited number of studies on the protective effect they elicit. Certain success in the development of vaccines against a number of human viral infections, such as hepatitis B, cytomegalovirus and rotavirus, gives hope to successful completion of this research. Presumably, such vaccines will be safe and innocuous, simple in administration and capable of inducing both the systemic and local immune responses at the primary portal of viral infection.

Role for mucosal immune responses and cell-mediated immune functions in protection from airborne challenge with Venezuelan equine encephalitis virus

Venezuelan equine encephalitis virus (VEEV) replicates in lymphoid tissues following peripheral inoculation and a high titre viraemia develops. Encephalitis develops after the virus enters the central nervous system from the blood, with the earliest neuronal involvement being via the olfactory nerve. Following aerosol challenge with virulent VEEV, the virus is thought to replicate in the nasal mucosa and there could be direct entry into the olfactory nerve via infected neuroepithelial cells. Protection from VEEV infection is believed to be primarily mediated by virus specific antibody. The correlation between protection and neutralising serum antibody titres is, however, inconsistent when the virulent virus is administered by the airborne route. This study demonstrates a link between antibody in serum and the nasal mucosa and protection by means of passive immunisation studies. Intra-nasal administration of antibody increased protection against airborne virus in Balb/c mice. Vaccination of mu MT strain mice that do not have functional B cells and cannot produce antibody revealed normal proliferation of spleen cells in vitro and robust cytokine production. Aerosol challenge of mu MT mice demonstrated that complete protection was only achieved when passive immunisation with antibody was supplemented with active immunisation with the TC-83 vaccine strain of the virus. This implies that cell-mediated immune functions are required for protection against airborne challenge with virulent VEEV.

Monoclonal antibody protects mice against infection and disease when given either before or up to 24 h after airborne challenge with virulent Venezuelan equine encephalitis virus

Airborne infection with Venezuelan equine encephalitis virus (VEEV) is a significant hazard for laboratory workers, who may not be immunised against VEEV infection as there is no vaccine currently available suitable for human use. We describe a potential alternative strategy that could protect workers exposed to VEEV or similar viruses. VEEV-specific murine monoclonal antibodies (MAB), given by intraperitoneal (i.p.) injection to mice as a single dose of 100 microg, have a half-life of 6-10 days in serum and spread by transudation to respiratory secretions. Administration of MAB (approximately 4 mg/kg) to mice 24h before challenge with approximately 100LD50 of virulent VEEV protected up to 100% animals. The same dose of MAB delivered up to 24h after challenge protected approximately 50%. Two MAB that were synergistic in vitro in plaque reduction neutralisation tests were not synergistic in vivo in protection assays. An examination of virus multiplication, in the blood and internal organs (brain, spleen, lung) of MAB-treated mice infected by the airborne route with VEEV, suggested that therapeutic activity depended both upon the prevention of virus infection of the brain, and the rapid clearance of virus from the periphery. Antiviral therapy with VEEV-specific human or "humanised" MAB, providing that they are administered early, may offer an alternative means of specific medical intervention for those with a known exposure to VEEV.

Microparticle vaccine approaches to stimulate mucosal immunisation

Entrapment of antigens in biodegradable particles for mucosal immunisation has given successful outcomes in animals, but not as yet in man. Formulations using genuinely stable biocompatible nanoparticles with co-entrapped mucosal adjuvants and/or with surface-conjugated human M-cell-targeting ligands may lead to better uptake of intact antigen by Peyer's patch M cells and delivery to antigen-presenting cells.

An immunological profile of Balb/c mice protected from airborne challenge following vaccination with a live attenuated Venezuelan equine encephalitis virus vaccine

The live attenuated vaccine strain of Venezuelan equine encephalitis virus (VEEV), TC-83, protects mice against challenge (subcutaneous and aerosol) with virulent VEEV but is not suitable for widescale human use. Elucidation of the immune response profile of protected mice should assist in the development of an improved vaccine. We determined the optimum dose of TC-83 required to consistently protect Balb/c mice from airborne challenge with the virulent Trinidad Donkey strain of VEEV and studied the development of humoral and cellular immune responses in protected mice between 6 h and 21 days post-vaccination. The most dramatic immune responses occurred in draining lymph nodes 24 h following vaccination with increased levels of activated B cells and T cells of both CD4(+) and CD8(+) subtypes. Activated monocyte/macrophages and natural killer cells were also seen between 6 h and 7 days post-vaccination. Serum contained detectable VEEV-specific IgG on day 5 post-vaccination with titres continuing to rise on days 7, 14 and 21. Isotypes of IgG measured on days 7 and 21 were predominantly of the IgG2a subclass, indicating that the immune response was Th1-mediated. Cytokine mRNA was quantified by RT-PCR and revealed production of the Th1 cytokine IFN-gamma and the inflammatory cytokine TNF-alpha, whereas the Th2 cytokine IL4 was not detected above control levels at any of the time points studied. This data describes key cellular immune responses at early times post-vaccination and is consistent with previous data demonstrating protection against aerosol challenge with VEEV in the absence of detectable levels of specific IgG or IgA antibody.

Protection studies following bronchopulmonary and intramuscular immunisation with yersinia pestis F1 and V subunit vaccines coencapsulated in biodegradable microspheres: a comparison of efficacy

We have compared the ability of intramuscularly and intratracheally administered recombinant F1 and V subunit antigens to safeguard mice from a lethal systemic challenge with plague. The combined subunits (1 microg V plus 5 microg F1) were inoculated either in the 'free' state as a solution, or entrapped within microspheres composed of a biodegradable polyester (Poly-L-lactide), on day 1 and 60 of the experiment. In comparison to the other regimens, introduction of microsphere suspensions into the respiratory tract resulted in statistically elevated levels of specific immunoglobulins in day 82 lung wash samples. A subcutaneous challenge with virulent Yersinia pestis bacteria on day 137, equivalent to more than 10(5) mouse LD(50)s, was comparatively well tolerated by all subunit treatment groups (with survival rates between 66 and 90%). In contrast, 80% of the mice injected intramuscularly with soluble F1 and V were defeated by a 10(7) MLD(50) subcutaneous challenge, whereas the group immunised intramuscularly with microparticles were significantly better protected (p<0.1) with 50% survival. Similarly, mice immunised intratracheally with microparticles were significantly better safeguarded (56% survival) compared with the group immunised with soluble subunits intramuscularly (p<0.01). Soluble sub-units delivered intratracheally afforded 33% protection against 10(7) MLD(50)s. These data indicate that bronchopulmonary administration of microsphere co-encapsulated recombinant F1 and V antigens elicits a similar level of protective immunity against systemic plague infection as that evoked by injecting co-encapsulated subunits into the muscle. Such findings corroborate the thesis that introduction of appropriately formulated F1 and V subunits into the respiratory tract may be an alternative to parenteral immunisation schedules for protecting individuals from plague.

Pegylated alpha interferon is an effective treatment for virulent venezuelan equine encephalitis virus and has profound effects on the host immune response to infection

Venezuelan equine encephalitis virus (VEEV) is a highly infectious alphavirus endemic in parts of Central and South America. The disease is transmitted by mosquitoes, and the natural reservoir is the small rodent population, with epidemics occurring in horses and occasionally humans. Following infection, VEEV replicates in lymphoid tissues prior to invasion of the central nervous system. Treatment of VEEV-infected BALB/c mice with polyethylene glycol-conjugated alpha interferon (PEG IFN-alpha) results in a greatly enhanced survival from either a subcutaneous or an aerosol infection. Virus is undetectable within PEG IFN-alpha-treated individuals by day 30 postinfection (p.i.). Treatment results in a number of changes to the immune response characteristics normally associated with VEEV infection. Increased macrophage activation occurs in PEG IFN-alpha-treated BALB/c mice infected with VEEV. The rapid activation of splenic CD4, CD8, and B cells by day 2 p.i. normally associated with VEEV infection is absent in PEG IFN-alpha-treated mice. The high tumor necrosis factor alpha production by macrophages from untreated mice is greatly diminished in PEG IFN-alpha-treated mice. These results suggest key immunological mechanisms targeted by this lethal alphavirus that can be modulated by prolonged exposure to IFN-alpha.

Immunity to airborne challenge with Venezuelan equine encephalitis virus develops rapidly after immunization with the attenuated vaccine strain TC-83

Mice vaccinated subcutaneously with the attenuated vaccine strain of Venezuelan equine encephalitis virus (VEEV) rapidly develop immunity to subcutaneous or airborne challenge with virulent VEEV. The specificity of this immune response was demonstrated by challenge with a heterologous virus (St. Louis encephalitis virus). Examination of the levels of VEEV-specific antibody classes in serum and respiratory secretions suggested that the rapid development of immunity was coincident with the appearance of specific IgM and IgG (but not IgA) in the respiratory tract. In order to confirm the role of respiratory tract antibody, mice were passively immunised either intraperitoneally or intranasally with polyclonal VEEV-specific IgG. Intranasal administration of specific IgG significantly enhanced protection against airborne challenge. These results confirm the need to emphasise local antibody production in the development of improved VEEV vaccines.

Expression, processing, and immunogenicity of the structural proteins of Venezuelan equine encephalitis virus from recombinant baculovirus vectors

Recombinant baculoviruses expressing the structural proteins of Venezuelan equine encephalitis virus (VEE) have been constructed and the intracellular processing, antigenicity, and immunogenicity of the expression products have been assessed. Baculoviruses expressing the entire structural protein region (C-E3-E2-6K-E1), or the complete glycoprotein region (E3-E2-6K-E1), generated products in Sf9 cells that were accurately and completely processed, and resulted in mature proteins that were antigenically and electrophoretically indistinguishable from authentic viral proteins. These products were highly immunogenic in BALB/c mice, induced efficient VEE neutralizing responses, and protected these animals against challenge with virulent VEE. Expression of individual glycoprotein regions (E3-E2 and 6K-E1) generated products that were accurately but incompletely processed, and induced non-neutralizing antibodies that reacted more efficiently with denatured than native VEE proteins. Nonetheless, immunization with the 6K-E1 expression product provided complete protection against VEE challenge.