Nasal vaccines

Noninvasive delivery technologies: respiratory delivery of vaccines

This paper reviews the developments in noninvasive methods of drug delivery, with a focus on the delivery of vaccines via the respiratory tract. Recent results indicate that the respiratory system, and the nasal mucosa in particular, provide a valuable target site for immunisation against respiratory and mucosal pathogens. Vaccine delivery via the nasal and pulmonary routes each present distinct sets of performance requirements. Current delivery systems in development for both routes are reviewed herein. The storage and respiratory delivery of drugs and vaccines in powder form has been shown to provide improved stability and extended retention time in the respiratory mucosa. These features, in addition to the noninvasive nature of respiratory delivery, can provide benefits to public health vaccination campaigns, facilitating mass vaccination without the high cost of maintaining cold-chain storage.

Immunogenicity of a malaria parasite antigen displayed by Lactococcus lactis in oral immunisations

A putative protective protein from Plasmodium falciparum merozoites, MSA2, was expressed in two different ways on the cell surface of the Gram-positive food-grade bacterium, Lactococcus lactis. The first display format exploits an LPXTG-type anchoring motif of the lactococcal proteinase PrtP to covalently anchor MSA2 to the genetically modified producer cells. In a second display format, MSA2 was fused to the peptidoglycan-binding domain (Protein Anchor) of the lactococcal cell wall hydrolase AcmA and was non-covalently rebound to the surface of non-genetically modified, non-living high-binder L. lactis cells, termed Gram-positive enhancer matrix (GEM) particles. The L. lactis recombinants carrying covalently bound MSA2 were used to immunise rabbits through nasal and oral routes. The highest levels of IgG antibodies reacting with near-native MSA2 on merozoites was elicited by oral administration. Intestinal antibodies to MSA2 were produced only after oral immunisation. MSA2-specific T(h)-cell activation could be demonstrated. Based on these results, the immunogenicity in oral immunisations of MSA2, bound non-covalently to non-genetically modified L. lactis GEM particles, was compared with MSA2 that was bound covalently to genetically modified L. lactis. These two forms elicited similar titres of serum antibodies. The results illustrate the potential of using non-genetically modified L. lactis as a safe vaccine delivery vehicle to elicit systemic antibodies, thereby avoiding the dissemination of recombinant DNA into the environment.

Preparation and characterization of protein-loaded N-trimethyl chitosan nanoparticles as nasal delivery system

In this study, the potential of N-trimethyl chitosan (TMC) nanoparticles as a carrier system for the nasal delivery of proteins was investigated. TMC nanoparticles were prepared by ionic crosslinking of TMC solution (with or without ovalbumin) with tripolyphosphate, at ambient temperature while stirring. The size, zeta-potential and morphology of the nanoparticles were investigated as a function of the preparation conditions. Protein loading, protein integrity and protein release were studied. The toxicity of the TMC nanoparticles was tested by ciliary beat frequency measurements of chicken embryo trachea and in vitro cytotoxicity assays. The in vivo uptake of FITC-albumin-loaded TMC nanoparticles by nasal epithelia tissue in rats was studied by confocal laser scanning microscopy. The nanoparticles had an average size of about 350 nm and a positive zeta-potential. They showed a loading efficiency up to 95% and a loading capacity up to 50% (w/w). The integrity of the entrapped ovalbumin was preserved. Release studies showed that more than 70% of the protein remained associated with the TMC nanoparticles for at least 3 h on incubation in PBS (pH 7.4) at 37 degrees C. Cytotoxicity tests with Calu-3 cells showed no toxic effects of the nanoparticles, whereas a partially reversible cilio-inhibiting effect on the ciliary beat frequency of chicken trachea was observed. In vivo uptake studies indicated the transport of FITC-albumin-associated TMC nanoparticles across the nasal mucosa. In conclusion, TMC nanoparticles are a potential new delivery system for transport of proteins through the nasal mucosa.

Immune systems in developed and developing countries; implications for the design of vaccines that will work where BCG does not

New vaccine candidates for tuberculosis are beginning to enter clinical trials. In this review we discuss issues surrounding the design of these candidates, and the way they were screened in animal models. First, screening vaccines for their ability to attenuate inevitably fatal tuberculosis in immunologically naïve mice might be leading to the selection of inappropriate candidates. We need to screen vaccines for their ability to stop the development of progressive disease, since this is what they must achieve in man. A solution to this problem is proposed. Secondly, we point out that some mouse models of tuberculosis in laboratories in developing countries, where exposure to environmental mycobacteria is large, mimic neglected aspects of human disease more closely than do low-dose infections in hyper-susceptible immunologically naïve mice in the USA or Europe. We need to think more about geographical differences in immunological experience, and these mouse models can help us. Thirdly, we conclude that in developing countries where BCG fails this is not because there is too little Th1 response, but rather because the Th1 response is rendered ineffective and immunopathological by other subversive mechanisms, including IL-4 responses and inappropriate regulatory T cell function. Therefore, we suggest that vaccines that will work in those countries might need to have immunoregulatory properties that can switch off pre-existing subversive mechanisms, and block their development in the future. The development of such vaccines, that might work where BCG does not, will require a greater understanding of the roles of the many types of regulatory T cell in tuberculosis.

Induction of protective and specific antibodies against cocaine by intranasal immunisation using a glyceride adjuvant

The goal of this study was to investigate an intranasal cocaine vaccine containing the mucosal adjuvant macrogol-6-glycerol capylocaprate (RhinoVax). Cocaine-KLH conjugate was prepared and administered in two formulations. Ten mice were immunised intranasally using RhinoVax as adjuvant and ten subcutaneously using aluminium hydroxide as an adjuvant. A negative control group (n=10) received unconjugated KLH with RhinoVax intranasally. Specific cocaine antibodies in serum were measured following primary and booster immunisation. Relative antibody responses in serum indicated that the immunisation was successful. Animals were then challenged with cocaine either intranasally or intraperitoneally with subsequent measurement of drug distribution into the serum, brain and olfactory bulb. The cocaine-immunised groups revealed significantly lower cocaine levels in the brain compared to the negative control group. The inhibition of cocaine distribution to the brain in the intranasal immunised group was comparable to that of the subcutaneous immunised group. This was unexpected because the cocaine specific antibody levels in serum were fivefold lower in the intranasal immunised group. However, the presence of mucosal cocaine specific antibodies after intranasal immunisation could play an important role in hindering direct access of cocaine into the brain via the olfactory bulb.

Immunization without needles

Most current immunization procedures make use of needles and syringes for vaccine administration. With the increase in the number of immunizations that children around the world routinely receive, health organizations are beginning to look for safer alternatives that reduce the risk of cross-contamination that arises from needle reuse. This article focuses on contemporary developments in needle-free methods of immunization, such as liquid-jet injectors, topical application to the skin, oral pills and nasal sprays.

Modified Pulmonary Surfactant Is a Potent Adjuvant That Stimulates the Mucosal IgA Production in Response to the Influenza Virus Antigen

The intranasal administration of influenza hemagglutinin (HA) vaccine with Surfacten, a modified pulmonary surfactant free of antigenic c-type lectins, as a mucosal adjuvant induced the highest protective mucosal immunity in the airway. The intranasal immunization of mice with HA vaccine (0.2 microg)-Surfacten (0.2 microg) selectively induced the neutralizing anti-HA IgA, but not IgG, and conferred nearly maximal protection in the airway, without inducing a systemic response. In contrast, intranasal inoculation of vaccine with 0.2 microg of the potent mucosal adjuvant cholera toxin B* (CT-B*), prepared by adding 0.2% native CT to the B subunit of CT, induced both anti-HA IgA and IgG in the airway and in the serum. The intranasal administration of HA vaccine alone induced a limited amount of mucosal IgA against influenza virus. Although the s.c. administration of HA vaccine prominently induced serum IgG and IgA, Surfacten and CT-B* did not enhance their induction, and the concentrations of Abs leaking into the airways were insufficient to prevent viral multiplication. The intranasal administration of HA-Surfacten stimulated the expression of MHC class II, CD40, and CD86 molecules in the CD11c-positive cells isolated from the nasal mucosa, but not the expression of cells from the lungs or spleens. Lymphocytes isolated from the airway mucosa after intranasal HA-Surfacten immunization prominently induced TGF-beta1 which, compared with inoculation without Surfacten, promoted an Ag-specific mucosal IgA response. Surfacten alone, however, did not induce TGF-beta1. Our observations suggest that Surfacten, by mimicking the natural surfactant, is an effective mucosal adjuvant in the process of airway immunization.

Strong mucosal and systemic immunities induced by nasal immunization with anthrax protective antigen protein incorporated in liposome-protamine-DNA particles

PURPOSE

The very lengthy and complicated dosing schedule of the current anthrax vaccine adsorbed, which was licensed in the USA for the prevention of cutaneous anthrax infection, calls for the development of an efficacious and easily administrable vaccine to prevent against the most lethal form of anthrax infection, the inhalation anthrax. We propose to develop a nasal anthrax vaccine using anthrax protective antigen (PA) protein carried by liposome-protamine-DNA (LPD) particles.

METHODS

PA was incorporated in LPD particles and nasally dosed to mice. The resulting PA-specific immune response and lethal toxin neutralization activity were measured.

RESULTS

Mice nasally immunized with PA incorporated into LPD particles developed both systemic and mucosal anti-PA responses. The anti-PA immunities induced included the production of anti-PA antibodies (IgG and IgM in the serum and IgA in nasal and lung mucosal secretions) and the proliferation of splenocytes after in vitro stimulation. The anti-PA IgG subtype induced was mainly IgG1. Finally, anthrax lethal toxin neutralization activity was detected both in the serum and in the mucosal secretions.

CONCLUSIONS

The anti-PA immune response induced by nasal PA incorporated in LPD was comparable to that induced by nasal PA adjuvanted with cholera toxin or subcutaneously injected PA adjuvanted with aluminum hydroxide.

Lipid microparticles for mucosal immunization against hepatitis B

Parenteral administration of vaccines often does not lead to optimal or long lasting protection against disease causing organisms particularly those that are inhaled, ingested or sexually transmitted. For optimal mucosal protection induction of immune response via mucosal routes is therefore highly desirable. Double emulsion-solvent evaporation (w/o/w) method best suited for water-soluble bioactives was selected for the preparation of hepatitis B surface antigen (HBsAg) loaded lipid microparticles. Intranasal route was considered for mucosal administration and hence to prepare the delivery system biocompatible and least irritable, soyalecithin (phospholipid) was taken instead of polymer because phosphatidylcholine is the major component of endogenous lung surfactant. The studies performed in present work included antigen characterization, development of lipid microparticles, stability studies of the prepared lipid microparticle formulations, percent mucoadhesion, ex vivo cellular uptake studies and in vivo studies. The general order obtained from in vivo studies for mucosal immune response (IgA) followed the sequence: LMST-HBsAg (IN)>LM-HBsAg (IN)>alum-HBsAg (IN)>LMST-HBsAg (IM)>alum-HBsAg (IM)>or=LM-HBsAg (IM)>plain HBsAg (IN)>plain HBsAg (IM).

The influence of gellan gum on the transfer of fluorescein dextran across rat nasal epithelium in vivo

The nasal uptake of a 3000 Da fluorescein dextran (FD3) was investigated in rats, using fluorescence microscopy. The uptake from a formulation containing deacetylated gellan gum, an in situ gelling agent, was compared to that from a mannitol solution. Additionally, the rheological behavior of the gellan gum in water and saline was studied. It was shown that the gellan gum solution was easily administered owing to its low viscosity, and upon contact with the mucosa, a gel was formed. The epithelial uptake and transfer of FD3 appeared to be increased and prolonged using the gellan gum formulation. This increase was not accompanied by qualitative changes of the epithelial FD3 distribution or any visible harmful effects.

A novel dry powder influenza vaccine and intranasal delivery technology: induction of systemic and mucosal immune responses in rats

Intranasal (i.n.) vaccination represents an attractive non-invasive alternative to needle-based injection and provides superior protection at mucosal surfaces. However, new formulations are needed to improve efficacy and reduce the refrigerated storage and distribution requirements associated with standard liquid vaccines. Here, we describe a powder formulation of whole inactivated influenza virus and a novel i.n. delivery platform. The powder-formulated vaccine elicited a significant serum antibody response in rats that was at least as strong as that provided by the liquid vaccine administered i.n. or via intramuscular (i.m.) injection. Significant nasal IgA responses were also observed solely after i.n. delivery. This study demonstrates for the first time the generation of potent nasal mucosal and systemic immune responses using an i.n. delivered influenza vaccine powder and suggests an alternative approach to vaccination against influenza and other infectious diseases.

Comparative evaluation of intranasal and subcutaneous route of immunization for development of mucosal vaccine against experimental tuberculosis

Activation of mucosal immunity in the respiratory tract is crucial for protection against respiratory infections. Whether the intranasal route of vaccination imparts better protection against pulmonary tuberculosis than that of subcutaneous vaccination remains a debatable issue. In this study, we have investigated the effect of the routes of immunization on the induction of immunoprotection against experimental tuberculosis employing mycobacterial culture filtrate proteins complexed with dimethyldioctadecylammonium bromide. Vaccination via intranasal and subcutaneous routes triggered immune activation in the spleen and cervical lymph node, while the former route of vaccination lead to higher antigen-specific lymphocyte proliferation, interferon-gamma, interleukin-12 and interleukin-4 responses in cervical lymph node and induction of antigen-specific IgA responses at mucosal level of the respiratory tract. Mice vaccinated via the intranasal route were found to be better protected against experimental tuberculosis particularly in lung compared to subcutaneous-immunized mice. These results emphasize the importance of the intranasal route vaccination in tuberculosis.

Preparation of chitosan-plasmid DNA nanoparticles encoding zona pellucida glycoprotein-3alpha and its expression in mouse

In the present study, the porcine zona pellucida (ZP)-3alpha eukaryotic expression vector pVAX1-pZP3alpha was constructed by genetic recombinant technology, then the recombinant plasmid was encapsulated in nanoparticles with chitosan, and the imaging of chitosan/pVAX1-pZP3alpha nanoparticles by Atomic Force Microscope (AFM) was processed. Feeding mouse with those microencapsulation by gastric larvae, and after 5 days, detecting its expression in mouse intestine by RT-PCR and indirect immunofluorescence (IIF). Results show that the porcine ZP-3alpha eukaryotic expression vector pVAX1-pZP3alpha had been constructed correctly, and the chitosan-DNA expressing ZP microencapsulation was prepared successfully. After 5 days of feeding mouse, the transcription and expression of those DNA vaccines were found in mouse alvine chorion. The preparation of chitosan/pVAX1-pZP3alpha plasmid DNA nanoparticles and its expression in mice will help to investigate the feasibility of ZP DNA vaccine to induce oviduct local mucosal immunity against ZP to block the fertilization without causing ovarian dysfunction, which will provide new ideas and ways for research and exploiting more effective, more convenient oral contraceptive vaccines.

Bi-Directional Nasal Delivery of Aerosols Can Prevent Lung Deposition

Nasal delivery of drugs and vaccines has important advantages compared to injection and oral administration, and is being considered for a widening range of vaccines and substances with topical and systemic action. Traditional nasal delivery technologies are, however, trapped in the dilemma between achieving improved nasal distribution and limiting deposition in the lower airways. The novel bi-directional nasal delivery concept takes advantage of the posterior connection between the nasal passages persisting when the soft palate automatically closes during oral exhalation. Exhalation into the delivery device triggers release of liquid or powder particles into an airflow, which enters one nostril via a sealing nozzle and exits through the other nostril. In a study of 16 healthy subjects using 99mTc labeled nebulized particles with a mean particle size of 3.5 microm, delivery with this novel concept showed no or minimal lung deposition (0.8 +/- 2.0% (range -4.1% to 5.6%) for bi-directional delivery, whereas significant fractions were deposited in the lungs in all 16 subjects (mean 22.3 +/- 8.1%, range 12.2-39.3%) following conventional nasal inhalation (p < 0.0005). In the latter case, the fraction deposited in the lungs correlated significantly (r2 = 0.47, p < 0.004) with the volume of the nasal passages. The bi-directional nasal delivery concept minimizes the risks and problems related to lung deposition occurring during conventional nasal inhalation from a nebulizer and opens up a new range of opportunities for nasal delivery of drugs and vaccines.

Intranasal immunization with a colloid-formulated bacterial extract induces an acute inflammatory response in the lungs and elicits specific immune responses

Nonspecific stimulation of lung defenses by repeated oral administration of immunomodulators, such as bacterial extracts, has shown potential for the prevention of respiratory tract infections. Here, we show that intranasal (i.n.) immunization with a bacterial extract formulated as a colloid induces an acute inflammatory response in the lungs characterized by increased production of CCL and CXCL chemokines and a major influx of dendritic cells (DCs) and neutrophils, with a higher proportion of DCs showing an activated phenotype (high CD80/CD86 expression). Cytokine levels measured in bronchoalveolar-lavage samples showed a small increase in the production of tumor necrosis factor alpha and similar levels of the other cytokines measured (interleukin 10 [IL-10], IL-12, and gamma interferon [IFN-gamma]) in immunized mice compared with control mice. However, the recall response of primed animals after antigenic challenge induced increased expression of IL-12 and IFN-gamma mRNAs in lung homogenates. Overall, all these effects were not due to the lipopolysaccharide content in the bacterial extract. Furthermore, we found that three i.n. doses administered 2 to 3 weeks apart were enough to elicit long-lasting specific serum immunoglobulin G (IgG) and secretory IgA antibody responses. Assessment of IgG subclasses showed a balanced pattern of IgG1-IgG2a responses. The serum total IgE concentrations were also elevated in immunized mice 2 weeks after the third dose, but they significantly decreased soon afterwards. Our results suggest that simple formulations of bacterial extracts administered i.n. are highly immunogenic, eliciting local and systemic immune responses, and may serve as the basis for cost-effective immunotherapies for the prevention and treatment of respiratory infections.

Absorption enhancers for nasal drug delivery

This paper describes the basic concepts for the transmucosal delivery of drugs, and in particular the use of the nasal route for delivery of challenging drugs such as polar low-molecular-weight drugs and peptides and proteins. Strategies for the exploitation of absorption enhancers for the improvement of nasal delivery are discussed, including consideration of mechanisms of action and the correlation between toxic effect and absorption enhancement. Selected enhancer systems, such as cyclodextrins, phospholipids, bioadhesive powder systems and chitosan, are discussed in detail. Examples of the use of these enhancers in preclinical and clinical studies are given. Methods for assessing irritancy and damage to the nasal membrane from the use of absorption enhancers are also described. Finally, the mucosal use of absorption enhancers (chitosan) for the improved nasal delivery of vaccines is reported with reference to recent phase I/II clinical studies.

Single intranasal mucosal Mycobacterium bovis BCG vaccination confers improved protection compared to subcutaneous vaccination against pulmonary tuberculosis

Whether the intranasal (i.n.) route of Mycobacterium bovis BCG vaccination provides better protection against pulmonary tuberculosis than subcutaneous (s.c.) vaccination remains an incompletely solved issue. In the present study, we compared both immune responses and protection elicited by single BCG vaccinations via the i.n. or s.c. route in BALB/c mice. While both i.n. and s.c. vaccination triggered comparable levels of primary immune activation in the spleen and draining lymph nodes, i.n. vaccination led to a greater antigen-specific gamma interferon recall response in splenocytes than s.c. vaccination upon secondary respiratory mycobacterial challenge, accompanied by an increased frequency of antigen-specific lymphocytes. There was also a quicker cellular response in the lungs of i.n. vaccinated mice upon mycobacterial challenge. Mice vaccinated i.n. were found to be much better protected, particularly in the lung, than s.c. vaccinated counterparts against pulmonary tuberculosis at both 3 and 6 months postvaccination. These results suggest that the i.n. route of vaccination improves the protective effect of the current BCG vaccine.

Upper Respiratory Tract Immunity

Most viral infections occur via mucosal surfaces like the respiratory, gastrointestinal, or genital epithelium. The mucosal immune system is an important component of the body's defense against such infections and consequently induction of mucosal, in addition to systemic immunity, might improve vaccine efficacy. Several orally administered vaccines, for example, against poliovirus and gastrointestinal bacterial infections, have been developed and are widely used. In contrast, to date most vaccines against respiratory pathogens are applied parenterally and thus do not induce significant mucosal immunity. For the development of effective mucosal vaccines a more profound understanding of the immune mechanisms operative at mucosal surfaces and of the interplay between different mucosal compartments is needed. Moreover, factors like the dose, form of application, and type of mucosal adjuvants are critical to the induction of effective mucosal immunity. This brief review will focus mainly on the nasal route and will summarize some recent findings concerning the function of the mucosal immune system of the upper respiratory tract. Furthermore, routes of cross-immunization between distinct mucosal compartments and how they might be relevant to vaccine development will be addressed. Finally, I will outline critical factors for the rational design of nasal vaccines and in this context highlight some recent preclinical and clinical developments in the field.

Correlation of SEC/MALLS with ultracentrifuge and viscometric data for chitosans

Attempts have been made to correlate estimates of molecular weight for a group of cationic polysaccharides known as chitosans between the highly popular technique of size-exclusion chromatography coupled to multi-angle laser light scattering, "SEC-MALLS", and the less convenient but more established technique of sedimentation equilibrium in the analytical ultracentrifuge. Four pharmaceutical grade chitosans of various molecular weights and degrees of acetylation (4-30%) were chosen. Better correlation than previous was achieved, although some batch variability was observed. Despite the broad spectrum in degree of acetylation, a log s degrees(20,w) versus log Mw scaling plot appeared to fit a straight line with power-law exponent b=0.25 +/- 0.04, i.e. between the limits of rod (0.15) and coil (0.4-0.5), although this may be the average of a lower b value at low Mw and higher b at high Mw. With regard to viscosity, a logeta versus logMw scaling plot appeared to also fit a straight line with power-law exponent a=0.96 +/- 0.10, again between the coil (0.5-0.7) and rod (1.8) limits.

Nasal delivery of chitosan-DNA plasmid expressing epitopes of respiratory syncytial virus (RSV) induces protective CTL responses in BALB/c mice

Respiratory syncytial virus (RSV), an important pathogen of the lower respiratory tract, is responsible for severe illness both in new born and young children and in elderly people. Due to complications associated with the use of the early developed vaccines, there is still a need for an effective vaccine against RSV. Most pathogens enter the body via mucosal surfaces and therefore vaccine delivery via routes such as the nasal, may well prove to be superior in inducing protective immune responses against respiratory viruses, since both local and systemic immunity can be induced by nasal immunisation. Previously we have shown that intradermal immunisation of a plasmid DNA encoding the CTL epitope from the M2 protein of RSV induced protective CTL responses. In the present study, the mucosal delivery of plasmid DNA formulated with chitosan has been investigated. Chitosan is a polysachharide consisting of copolymers of N-acetylglucosamine and glucosamine that is derived from chitin, a material found in the shells of crustacea. Intranasal immunisation with plasmid DNA formulated with chitosan induced peptide- and virus-specific CTL responses in BALB/c mice that were comparable to those induced via intradermal immunisation. Following RSV challenge of chitosan/DNA immunised mice, a significant reduction (P<0.001) in the virus load was observed in the lungs of immunised mice compared to that in the control group. These results indicate the potential of immunisation with chitosan-formulated epitope-based vaccines via the intranasal route.

A non-toxic lectin for antigen delivery of plant-based mucosal vaccines

RicinB, the non-toxic galactose/N-acetylgalactosamine-binding subunit of ricin, was fused to a model antigen, green fluorescent protein (GFP), and expressed in tobacco plants and hairy root cultures to test for utility in mucosal vaccine delivery/adjuvancy. The fusion protein retained both GFP fluorescence and galactose/galactosamine-binding activity. Intranasal immunization of mice with galactosamine-affinity purified ricinB:GFP recovered from tobacco root cultures triggered significant increases in GFP-specific serum IgGs. This strong humoral response was comparable to that observed following GFP immunization with cholera toxin adjuvant. GFP at the same concentrations but without an adjuvant was non-immunogenic. Induction of higher levels of IgG(1) than IgG(2a) following ricinB:GFP immunization suggested the presence of a Th2 response. Serum and fecal anti-GFP IgA were also induced by immunization with ricinB:GFP. Our data suggest that ricinB can be used as an adjuvant and antigen carrier to the mucosa and is efficient in eliciting systemic and mucosal immune responses.

Memory T cells and vaccines

T lymphocytes play a central role in the generation of a protective immune response in many microbial infections. After immunization, dendritic cells take up microbial antigens and traffic to draining lymph nodes where they present processed antigens to naïve T cells. These naïve T cells are stimulated to proliferate and differentiate into effector and memory T cells. Activated, effector and memory T cells provide B cell help in the lymph nodes and traffic to sites of infection where they secrete anti-microbial cytokines and kill infected cells. At least two types of memory cells have been defined in humans based on their functional and migratory properties. T central-memory (T(CM)) cells are found predominantly in lymphoid organs and can not be immediately activated, whereas T effector-memory (T(EM)) cells are found predominantly in peripheral tissue and sites of inflammation and exhibit rapid effector function. Most currently licensed vaccines induce antibody responses capable of mediating long-term protection against lytic viruses such as influenza and small pox. In contrast, vaccines against chronic pathogens that require cell-mediated immune responses to control, such as malaria, Mycobacterium tuberculosis (TB), human immunodeficiency virus (HIV) and hepatitis C virus (HCV), are currently not available or are ineffective. Understanding the mechanisms by which long-lived cellular immune responses are generated following vaccination should facilitate the development of safe and effective vaccines against these emerging diseases. Here, we review the current literature with respect to memory T cells and their implications to vaccine development.

Animal models paving the way for clinical trials of attenuated Salmonella enterica serovar Typhi live oral vaccines and live vectors

Attenuated Salmonella enterica serovar Typhi (S. Typhi) strains can serve as safe and effective oral vaccines to prevent typhoid fever and as live vectors to deliver foreign antigens to the immune system, either by the bacteria expressing antigens through prokaryotic expression plasmids or by delivering foreign genes carried on eukaryotic expression systems (DNA vaccines). The practical utility of such live vector vaccines relies on achieving a proper balance between minimizing the vaccine's reactogenicity and maximizing its immunogenicity. To advance to clinical trials, vaccine candidates need to be pre-clinically evaluated in relevant animal models that attempt to predict what their safety and immunogenicity profile will be when administered to humans. Since S. Typhi is a human-restricted pathogen, a major obstacle that has impeded the progress of vaccine development has been the shortcomings of the animal models available to assess vaccine candidates. In this review, we summarize the usefulness of animal models in the assessment of the degree of attenuation and immunogenicity of novel attenuated S. Typhi strains as vaccine candidates for the prevention of typhoid fever and as live vectors in humans.

Uptake of ovalbumin-conjugated starch microparticles by pig respiratory nasal mucosa in vitro

The uptake of ovalbumin-conjugated starch microparticles (OVA-MP) was studied after application to porcine respiratory nasal mucosa in vitro. Nasal mucosa from freshly slaughtered pigs was mounted in horizontal Ussing chambers, which permit monitoring of the viability of the tissue exposed to microparticles and ensure that the microparticles are deposited on the mucosa. The antigen-conjugated starch microparticles have previously been shown to produce strong mucosal, cellular and systemic immune responses to conjugated model antigens following oral administration. Intranasal administration of vaccines for mucosal immunisation is an interesting alternative to oral administration, since nasal delivery systems generally require lower doses of antigen and the site of application is better suited for protection against air-borne antigens. Most of a nasally administered dose is deposited on the surface of the respiratory area of the nasal mucosa. It is therefore important to examine whether the microparticles are taken up in this area and, if so, by which cell type. Confocal laser scanning microscopy and transmission electron microscopy (TEM) of the nasal tissue both showed intracellular OVA-MP in non-ciliated epithelial cells after 45 min' incubation. The morphology of the cells in the TEM preparations did not support the presence of either M cells (specialised antigen sampling cells) or adjacent lymphocytes. Anticytokeratin-18 (Ac18) was used as a potential M cell marker. However, there was no indication of Ac18 binding to M cells, but it did bind to mucus-producing cells in the respiratory nasal mucosa. In conclusion, OVA-MP were taken up intracellularly by non-ciliated epithelial cells in the nasal respiratory mucosa of pigs, in vitro.

Nasal drug delivery: new developments and strategies

The use of the nasal route for the delivery of challenging drugs has created much interest in recent years in the pharmaceutical industry. Consequently, drug delivery companies are actively pursuing the development of novel nasal drug-delivery systems and the exploitation of these for administration of conventional generic drugs and peptides, both in-house and with partners in the pharmaceutical industry. This review sets out to discuss some new developments and strategies in nasal drug delivery. An exiting discovery that drugs can be transported directly from nose to brain via the olfactory pathway is discussed and examples of proof-of-concept in man are given.

Intranasal administration of plasmid DNA-coated nanoparticles results in enhanced immune responses

Intranasal immunization offers potential forthe elicitation of effective mucosal and systemic immune responses. In this study, a previously reported novel cationic nanoparticle engineered from a microemulsion precursor was further modified, optimized and applied intranasally to mice to explore its potential as a plasmid DNA (pDNA) vaccine delivery system. To this end, more uniform nanoparticles (around 100 nm) containing less cationic surfactant were developed. The pDNA-coated nanoparticles significantly enhanced the specific serum IgG and IgA titres to an expressed model antigen, beta-galactosidase, by 18-28 and 25-30 fold, respectively, when compared with naked pDNA alone. An enhanced splenocyte proliferative response was also observed after immunization with the pDNA-coated nanoparticles. It was concluded that these plasmid DNA-coated nanoparticles may have potential for immunization via the nasal route.

Influence of dose and immunization route on the serum Ig G antibody response to BSA loaded PLGA microspheres

BSA was entrapped into PLGA 50:50 microspheres and the in vitro release study was performed. Then 1 microg of microencapsulated antigen was subcutaneously administered to Balb/c mice and the serum Ig G response was compared to that obtained after the subcutaneous administration of the same amount of only free antigen or of free antigen emulsified 1:1 with Freund's complete adjuvant (FCA). The specific serum Ig G responses obtained from the microencapsulated antigen were higher than those obtained from the free antigen and similar to those obtained from the antigen emulsified with FCA. Therefore, the immune response obtained with the subcutaneous administration of 1 microg of microencapsulated antigen was used as a positive control to compare the immune response elicited by the administration of the spheres either by the oral or the intranasal route. There is a dose/response relationship in the serum Ig G response elicited after three consecutive oral administrations of microencapsulated antigen at a dosing range from 200 to 50 microg. However, this relationship does not seem to be clear for the intranasal administration of the spheres at the same dosing range. When comparing the serum Ig G responses at each dosing level for the different routes of administration, it can be observed that the intranasal route is a more powerful inducer of the production of specific Ig G antibody than the oral, which could be due to a greater permeability of the nasal epithelium and to qualitative differences between the mechanisms of induction of the immune response by each route. The serum Ig G2a versus Ig G1 ratio is not significantly different among all the groups that received antigen in microspheres.

Development of vaccines against common colds

Respiratory tract viruses are particularly significant causes of illness and death in children and in the elderly. Vaccines offer the possibility of decreasing the severity and complications of viral respiratory disease, but development has been delayed by numerous factors. First, there are more than 200 serologically distinct RNA and DNA virus species and strains which cause an essentially similar spectrum of disease. Some re-infect at high efficiency despite little antigenic variation, while others exhibit extensive coat protein variability. Vaccine candidates show variable efficacy in partially immune adults, the immunocompromised and the elderly, and may be ineffective or pathogenic in neonates or in the presence of maternal antibodies. However, effective childhood vaccines are essential to prevent severe disease due to respiratory syncytial virus (RSV) and parainfluenza and to reduce virus transmission to adults. A number of promising vaccines are in clinical trial, and it is likely that vaccines against RSV and parainfluenza will be licensed within the next 5-10 years. Mucosal delivery and the use of novel adjuvants offers the prospect of better vaccines against influenza. The ultimate goal is to develop multivalent mucosal vaccines offering protection against a spectrum of respiratory infections.