Mucosal delivery of vaccines.

Oral delivery represents one of the most pursued approaches for large-scale human vaccination. Due to the different characteristics of mucosal immune response, as compared with systemic response, oral immunization requires particular methods of antigen preparation and selective strategies of adjuvanticity. In this paper, we describe the preparation and use of genetically detoxified bacterial toxins as mucosal adjuvants and envisage the possibility of their future exploitation for human oral vaccines.     

Particulate delivery systems for animal vaccines

The requirements for veterinary vaccines are different to those of human vaccines. Indeed, while more side effects can be tolerated in animals than in humans; there are stricter requirements in terms of cost, ease of delivery (including to wildlife), and a need to develop vaccines in species for which relatively little is known in terms of molecular immunology. By their nature particulate vaccine delivery systems are well suited to address these challenges. Here, we review particulate vaccine delivery systems, ranging from cm-sized long-distance ballistic devices to nano-bead technology for veterinary species and wildlife.     

Adjuvant formulations and delivery systems for DNA vaccines

DNA vaccines have become a reliable and major means to elicit immune responses in the past decade. We and others have attempted to obtain stronger, more long lasting, and optimized immune responses, subsequent to the pioneering works demonstrating the ability of plasmid DNA to raise specific immune responses. Advances in molecular biology and biotechnology allow the application of various adjuvants, immunologic agents that increase the antigenic response, in DNA vaccines. Adjuvants can be broadly separated into two classes based on their origin-genetic and conventional. Genetic adjuvants are expression vectors of cytokines or other molecules that can modulate immune responses when administered with a vaccine antigen. Conventional adjuvants are chemical compounds that enhance, prolong, or modulate antigen-specific immune responses. The use of an appropriate adjuvant is pivotal in optimizing the response to DNA vaccines. Moreover, DNA vaccines themselves possess their own adjuvant activity because of the presence of unmethylated CpG motifs in particular base contents. The route of inoculation is also a critical factor in determining the outcome of vaccination. It is well known that intramuscular injection preferentially induces Th1-type immunity, whereas particle bombardment by gene gun predominantly induces Th2-type response. This article focuses on providing the detailed procedure to construct genetic adjuvant plasmids and prepare DNA vaccines formulated with conventional adjuvants. We also offer a practical guide for the procedure of intramuscular DNA injection.     

Mucosal delivery of native and recombinant protein vaccines against Trichostrongylus colubriformis

This paper describes a series of five pilot trials to test the feasibility of inducing a protective mucosal immune response against a non-blood-feeding intestinal nematode by delivery of antigens across the mucosal epithelium. A number of antigen preparations from Trichostrongylus colubriformis (viable larvae, larval homogenate and recombinant 17 kDa excretory-secretory protein) were delivered to the luminal surface of the mucosal epithelium overlying jejunal or rectal lymphoid tissue in cellulose or chitosan formulations. Significant protection was induced following delivery of viable larvae, larval homogenate or recombinant protein to the epithelium overlying rectal Peyer’s patches, and recombinant protein to the epithelium overlying jejunal Peyer’s patches. Viable larvae were associated with a jejunal IgE/IgG1 response, while the 17 kDa antigen was associated with a jejunal IgA response. The results demonstrate that delivery of Trichostrongylus native and recombinant antigens across the epithelium overlying rectal lymphoid patches can result in significant protective immunity even in the absence of adjuvant. They warrant the further investigation of appropriate mucosal delivery methods and adjuvants for induction of protective mucosal responses to stages and species of gastrointestinal helminths which do not ingest serum antibodies.     

用于疫苗的免疫增强剂和递送系统

疫苗是抵抗传染病的最重要的预防性手段。在开发有效疫苗的过程中,人们面临的挑战一方面是要鉴定最为相关的免疫原及有效的免疫接种程序,另一方面则是免疫原用不同的能够影响抗体应答亲和性成熟和细胞介导的免疫应答的佐剂配成制剂。因此,有必要开发既能激发天然免疫应答,又能激发适应性免疫应答的有效佐剂和递送系统。主要阐述了不同免疫增强剂以及可利用于新一代疫苗的递送系统的研制进展情况。     

Archaeosomes as adjuvants for combination vaccines

The present study evaluated the potential of archaesomes, prepared from the total polar lipids extracted from Methanobrevibacter smithii, as adjuvants for combination (multivalent) vaccines. Groups of Balb/c mice were immunized subcutaneously at day 0 and 21 with one of the following vaccines: trivalent vaccine formulated by the simultaneous co-encapsulation of bovine serum albumine (BSA), ovalbumin (OVA) and hen egg lysozyme (HEL) into archaeosomes (CEC vaccine); an univalent archaeosome vaccine (UVE vaccine) containing either BSA, OVA or HEL; or an admixture vaccine (AMC vaccine) consisting of the three UVE vaccines. Serum specific antibody (IgG + M) responses were determined at day 32, 112 and 203, and specific IgG1 and IgG2a responses were determined at day 112. Mice immunized with the CEC of AMC vaccine developed strong and sustained specific antibody responses to all three antigens at a magnitude similar to those seen in control mice immunized with UVE vaccines. Moreover, the serum BSA-, OVA-, and HEL-specific IgG1 and IgG2a levels in the CEC and AMC immunized mice were overall comparable to those of the UVE immunized control mice. Boosting CEC and AMC vaccinated mice with antigens alone at day 203 elicited strong antibody memory responses, comparable to those in the UVE vaccinated groups. These results show that archaeosomes could be used as adjuvants in developing combination vaccines.     

Cytokines as adjuvants for avian vaccines

The worldwide trend towards a reduced reliance on in-feed antibiotics has increased the pressure to develop alternative strategies to manage infectious diseases in poultry. With this in mind, there is a great emphasis on vaccine use and the enhancement of existing vaccines to provide long-term protection. Currently existing adjuvants for poultry can have deleterious side-effects, such as inflammation, resulting in the down-grading of meat quality and a subsequent reduction in profits. Therefore, to enhance the use of vaccination, alternative adjuvants must be developed. The use of recombinant cytokines as adjuvants in poultry is attracting considerable attention, and their potential role as such has been addressed by several studies. The recent identification of a number of chicken cytokine genes has provided the possibility to study their effectiveness in enhancing the immune response during infection and vaccination. This review focuses on the recent studies involving the assessment of cytokines as vaccine adjuvants.     

Thermosensitive and mucoadhesive delivery systems of mucosal vaccines

Mucosal vaccination is emerging as a potential administration route for eliciting antigen-specific mucosal and systemic immunogenicity. Most mucosal vaccines have been administered in a phosphate-buffered saline vehicle that may limit the exposure of antigens to the mucosal surfaces and result in poor immunogenicity. To improve the potency of the mucosal vaccines, we have developed mucosal vaccine delivery systems that might prevent leakage and increase retention of vaccines on mucosal surfaces. Thermosensitive polymers have been used to reduce the leakage problems of nasal or vaginal vaccines, while mucoadhesive polymers have been employed to increase the mucosal contact of the vaccines. Here, we describe the formulation and delivery methods of mucosal vaccines using thermosensitive and mucoadhesive polymers.     

A comparison of DNA- and RNA-based clone libraries from the same marine bacterioplankton community

Clones from the same marine bacterioplankton community were sequenced, 100 clones based on DNA (16S rRNA genes) and 100 clones based on RNA (16S rRNA). This bacterioplankton community was dominated by alpha-Proteobacteria in terms of repetitive DNA clones (52%), but gamma-Proteobacteria dominated in terms of repetitive RNA clones (44%). The combined analysis led to a characterization of phylotypes otherwise uncharacterized if only the DNA or RNA libraries would have been analyzed alone. Of the DNA clones, 25.5% were found only in this library and no close relatives were detected in the RNA library. For clones from the RNA library, 21.5% of RNA clones did not indicate close relatives in the DNA library. Based on the comparisons between DNA and RNA libraries, our data indicate that the characterization of the bacterial community based on RNA has the potential to characterize distinct phylotypes from the marine environment, which remain undetected on the DNA level.     

Poly (DL-lactide-co-glycolide) based delivery systems for vaccines and drugs

Current vaccination and drug delivery strategies emphasize on the development of controlled release techniques for persistent and sustained effects. In the recent years, polymer based systems for the delivery of bioactive agents have gained considerable attention due to their marked adjuvanticity, established biodegradability and biocompatibility, excellent mechanical strength and controlled release profiles. This review deals with the potential applications of synthetic polymers mainly PLG polymers in delivery of vaccines and drugs.     

Recent developments in adjuvants for vaccines against infectious diseases

New generation vaccines, particularly those based on recombinant proteins and DNA, are likely to be less reactogenic than traditional vaccines, but are also less immunogenic. Therefore, there is an urgent need for the development of new and improved vaccine adjuvants. Adjuvants can be broadly separated into two classes, based on their principal mechanisms of action; vaccine delivery systems and 'immunostimulatory adjuvants'. Vaccine delivery systems are generally particulate e.g. emulsions, microparticles, iscoms and liposomes, and mainly function to target associated antigens into antigen presenting cells (APC). In contrast, immunostimulatory adjuvants are predominantly derived from pathogens and often represent pathogen associated molecular patterns (PAMP) e.g. LPS, MPL, CpG DNA, which activate cells of the innate immune system. Once activated, cells of innate immunity drive and focus the acquired immune response. In some studies, delivery systems and immunostimulatory agents have been combined to prepare adjuvant delivery systems, which are designed for more effective delivery of the immunostimulatory adjuvant into APC. Recent progress in innate immunity is beginning to yield insight into the initiation of immune responses and the ways in which immunostimulatory adjuvants may enhance this process. However, a rational approach to the development of new and more effective vaccine adjuvants will require much further work to better define the mechanisms of action of existing adjuvants. The discovery of more potent adjuvants may allow the development of vaccines against infectious agents such as HIV which do not naturally elicit protective immunity. New adjuvants may also allow vaccines to be delivered mucosally.     

Mucosal delivery of a respiratory syncytial virus CTL peptide with enterotoxin-based adjuvants elicits protective, immunopathogenic, and immunoregulatory antiviral CD8+ T cell responses

In an effort to develop a safe and effective vaccine against respiratory syncytial virus (RSV), we used Escherichia coli heat-labile toxin (LT), and LTK63 (an LT mutant devoid of ADP-ribosyltransferase activity) to elicit murine CD8(+) CTL responses to an intranasally codelivered CTL peptide from the second matrix protein (M2) of RSV. M2(82-90)-specific CD8(+) T cells were detected by IFN-gamma enzyme-linked immunospot and (51)Cr release assay in local and systemic lymph nodes, and their induction was dependent on the use of a mucosal adjuvant. CTL elicited by peptide immunization afforded protection against RSV challenge, but also enhanced weight loss. CTL-mediated viral clearance was not dependent on IFN-gamma since depletion using specific mAb during RSV challenge did not affect cellular recruitment or viral clearance. Depletion of IFN-gamma did, however, reduce the concentration of TNF detected in lung homogenates of challenged mice and largely prevented the weight loss associated with CTL-mediated viral clearance. Mice primed with the attachment glycoprotein (G) develop lung eosinophilia after intranasal RSV challenge. Mucosal peptide vaccination reduced pulmonary eosinophilia in mice subsequently immunized with G and challenged with RSV. These studies emphasize that protective and immunoregulatory CD8(+) CTL responses can be mucosally elicited using enterotoxin-based mucosal adjuvants but that resistance against viral infection may be accompanied by enhanced disease.     

Plants for delivery of edible vaccines

Over the past decade, scientific advances in molecular biology and immunology have improved understanding of many diseases and led to the development of novel strategies for vaccination. The development of plants expressing vaccine antigens is a particularly promising approach. Plant-derived antigenic proteins have delayed or prevented the onset of disease in animals and have proven to be safe and functional in human clinical trials. Future areas of research should further characterize the induction of the mucosal immune system and appropriate crop species for delivery of animal and human vaccines.     

Mucosal vaccines: the promise and the challenge

Most infectious agents enter the body at mucosal surfaces and therefore mucosal immune responses function as a first line of defence. Protective mucosal immune responses are most effectively induced by mucosal immunization through oral, nasal, rectal or vaginal routes, but the vast majority of vaccines in use today are administered by injection. As discussed in this Review, current research is providing new insights into the function of mucosal tissues and the interplay of innate and adaptive immune responses that results in immune protection at mucosal surfaces. These advances promise to accelerate the development and testing of new mucosal vaccines against many human diseases including HIV/AIDS.     

The use of new polymethylmethacrylate adjuvants for split influenza vaccines.

Split influenza virus vaccines with varying antigen content were adjuvated with polymethylmethacrylate particles, produced by polymerizing monomeric methylmethacrylate in the presence of the subunits, or by addition of the subunits to previously polymerized methacrylate particles. Both adjuvants yielded higher antibody titers than aluminum hydroxide or fluid vaccines. The character of the antigen-adjuvant conjugate of both types of polymer adjuvants is discussed.     

基因工程疫苗的病毒载体

病毒基因工程疫苗是以活病毒为载体将一段外源基因导入机体细胞内,并使外源基因维持较高水平的表达。通过使用复制型或复制缺陷型载体能使表达的抗原诱生机体产生相应的体液抗体,并能引起机体产生细胞介导的免疫反应及粘膜免疫反应。本文主要介绍有可能用于基因工程疫苗的DNA及RNA病毒载体构建及其应用。     

The potency and durability of DNA- and protein-based vaccines against Leishmania major evaluated using low-dose, intradermal challenge

DNA- and protein- based vaccines against cutaneous leishmaniasis due to Leishmania major were evaluated using a challenge model that more closely reproduces the pathology and immunity associated with sand fly-transmitted infection. C57BL/6 mice were vaccinated s.c. with a mixture of plasmid DNAs encoding the Leishmania Ags LACK, LmSTI1, and TSA (AgDNA), or with autoclaved L. major promastigotes (ALM) plus rIL-12, and the mice were challenged by inoculation of 100 metacyclic promastigotes in the ear dermis. When challenged at 2 wk postvaccination, mice receiving AgDNA or ALM/rIL-12 were completely protected against the development of dermal lesions, and both groups had a 100-fold reduction in peak dermal parasite loads compared with controls. When challenged at 12 wk, mice vaccinated with ALM/rIL-12 maintained partial protection against dermal lesions and their parasite loads were no longer significantly reduced, whereas the mice vaccinated with AgDNA remained completely protected and had a 1000-fold reduction in dermal parasite loads. Mice vaccinated with AgDNA also harbored few, if any, parasites in the skin during the chronic phase, and their ability to transmit L. major to vector sand flies was completely abrogated. The durable protection in mice vaccinated with AgDNA was associated with the recruitment of both CD8(+) and CD4(+) T cells to the site of intradermal challenge and with IFN-gamma production by CD8(+) T cells in lymph nodes draining the challenge site. These data suggest that under conditions of natural challenge, DNA vaccination has the capacity to confer complete protection against cutaneous leishmaniasis and to prevent the establishment of infection reservoirs.