Antipeptide antibody responses following intranasal immunization: effectiveness of mucosal adjuvants

Immunomodulatory consequences of ODN CpG-polycation complexes

Immunostimulatory ODN CpGs have extensively been tested as adjuvants and immunotherapeutics and hold a lot of promise for human use. In our studies we took advantage of their negative charge to study their biological activities after being complexed with carbon nanotubes, a novel vector for vaccine delivery and Tat protein of HIV, a target protein for therapeutic or prophylactic intervention. In the case of carbon nanotubes, ODN CpGs were able to form stable complexes based on charge interaction and exert increased immunostimulatory activity in vitro. With regard to the Tat protein, ODN CpGs were shown to bind effectively through the basic domain of the protein representing residues 44-61. Moreover, using surface Plasmon Resonance Technology and an in vitro cellular system, ODN CpGs were shown to inhibit the interaction of Tat protein with the transactivation responsive element, a bulged RNA hairpin structure. However, when ODN CpGs were complexed with Tat they readily increased the apoptotic properties of this protein as studied in CD3-stimulated Jurkat cells. Overall, our findings together with published data support the view that for harnessing the beneficial effects of ODN CpGs a careful consideration has to be given depending on the target intervention.

Intranasal immunization with a recombinant truncated FimH adhesin adjuvanted with CpG oligodeoxynucleotides protects mice against uropathogenic Escherichia coli challenge

In this work, we assessed the efficacy of an experimental intranasal vaccine against urinary-tract infections. The vaccine contained a recombinant truncated FimH (rFimHt) adhesin plus CpG oligodeoxynucleotides. The efficacy of the vaccine was compared with that of an intramuscular vaccine that was formulated with the same immunogen plus Freund's adjuvant. Our results show that serum immunoglobulin G titers of vaccinated animals were similarly enhanced in both cases. However, the intranasal vaccine elicited higher vaginal-wash-specific immunoglobulin A titers against rFimHt than the intramuscular route. Both vaccines reduced the in vivo colonization of the bladder by uropathogenic Escherichia coli more than 100-fold in a murine cystitis model. Our results indicate that a recombinant truncated FimH adhesin plus CpG oligodeoxynucleotides is a suitable immunogenic combination that can contribute to the development of a highly efficacious urinary tract infection vaccine.

Enhancement of infectious disease vaccines through TLR9-dependent recognition of CpG DNA

The adaptive immune system-with its remarkable ability to generate antigen-specific antibodies and T lymphocytes against pathogens never before "seen" by an organism-is one of the marvels of evolution. However, to generate these responses, the adaptive immune system requires activation by the innate immune system. Toll-like receptors (TLRs) are perhaps the best-understood family of innate immune receptors for detecting infections and stimulating adaptive immune responses. TLR9 appears to have evolved to recognize infections by a subtle structural difference between eukaryotic and prokaryotic/viral DNA; only the former frequently methylates CpG dinucleotides. Used as vaccine adjuvants, synthetic oligodeoxynucleotide (ODN) ligands for TLR9--CpG ODN--greatly enhance the speed and strength of the immune responses to vaccination.

Intranasal immunization using biphasic lipid vesicles as delivery systems for OmlA bacterial protein antigen and CpG oligonucleotides adjuvant in a mouse model

The nasal mucosa is an important arm of the mucosal system since it is often the first point of contact for inhaled antigens. The ineffectiveness of the simple delivery of soluble antigens to mucosal membranes for immunization has stimulated extensive studies in appropriate delivery systems and adjuvants. We have evaluated biphasic lipid vesicles as a novel intranasal (i.n.) delivery system (designated as vaccine targeting adjuvant, VTA) containing bacterial antigens and CpG oligodeoxynucleotides (ODNs). Results show that administration of antigen and CpG ODNs in biphasic lipid vesicles resulted in greater induction of IgA levels in serum (P< 0.05) and mucosal antibody responses such as IgA in nasal secretions and lung (P< 0.01) after immunization with a combined subcutaneous (s.c.)/i.n. as compared to s.c./s.c. approach. Based on antibody responses, VTA formulations were found to be suitable as delivery systems for antigens and CpG ODNs by the intranasal route, resulting in a Th2-type of immune response, characterized by IgG1 and IL-4 production at the systemic level.

Mucosal immunity induced by pneumococcal glycoconjugate

Host defenses against Streptococcus pneumoniae involve opsonophagocytosis mediated by antibodies and complement. Because the pneumococcus is a respiratory pathogen, mucosal immunity may play an important role in the defense against infection. The mechanism for protection in mucosal immunity consists of induction of immunity by the activation of lymphocytes within the mucosal-associated lymphoid tissues, transport of antigen-specific B and T cells from inductive sites through bloodstream and distribute to distant mucosal effector sites. Secretory IgA is primarily involved in protection of mucosal surfaces. Mucosal immunization is an effective way of inducing immune responses at mucosal surfaces. Several mucosal vaccines are in various stages of development. A number of mucosal adjuvants have been proposed. CpG oligodeoxynucleotide (ODN) has been shown to be an effective mucosal adjuvant for various antigens. Mucosal immunity induced by intranasal immunization was studied with a pneumococcal glycoconjugate, using CpG ODN as adjuvant. Mice immunized with type 9V polysaccharide (PS) conjugated to inactivated pneumolysin (Ply) plus CpG produced high levels of 9V PS IgG and IgA antibodies compared to the group that received the conjugate alone. High levels of subclasses of IgGI, IgG2 and IgG3 antibodies were also observed in sera of mice immunized with 9V PS-Ply plus CpG. In addition, high IgG and IgA antibody responses were observed in sera of young mice immunized with 9V PS-Ply plus CpG or the conjugate plus non-CpG compared with the group received the conjugate alone. These results reveal that mucosal immunization with pneumococcal glycoconjugate using CpG as adjuvant can confer protective immunity against pneumococcal infection.

Mucosal delivery of bacterial antigens and CpG oligonucleotides formulated in biphasic lipid vesicles in pigs

The ineffectiveness of simple delivery of soluble antigens to mucosal membranes for immunization has stimulated extensive studies of strategies for appropriate delivery systems and adjuvants. Biphasic lipid vesicles are formulations suitable for the delivery of proteins, peptides, and oligo/polynucleotides. The purpose of these studies was to investigate the ability of biphasic lipid vesicles (as vaccine-targeting adjuvants) containing a bacterial antigen and unmethylated oligonucleotides containing CGdinucleotides - CpG motifs (CpG ODNs) to induce systemic and mucosal immune responses in pigs. Results showed that while the protein, either alone or with CpG ODNs, did not induce mucosal immune responses, administration of antigen and CpG ODNs in biphasic lipid vesicles resulted in induction of both systemic and local antibody responses after immunization using a combined mucosal/systemic approach.

Peptide dendrimers

Dendrimers are branched structures and represent a fast growing field covering many areas of chemistry. Various types of dendrimers differing in composition and structure are mentioned, together with their practical use spanning from catalysis, transport vehicles to synthetic vaccines. The main stress is given to peptide dendrimers, namely, multiple antigenic peptides (MAPs). Their synthesis, physicochemical properties, biological activities, etc. have been described with many examples. MAPs can be used as diagnostics, mimetics, for complexation of different cations, as vaccines against parasites, bacteria, viruses, etc.

Anatomy of the nasal cavity in the chinchilla

There is currently great interest worldwide in developing noninvasive methods for the delivery of vaccines for upper respiratory tract diseases, including middle ear infection (otitis media, OM). One such noninvasive approach believed to have great potential for the prevention of diseases of the airway is to deliver vaccines by the intranasal (i.n.) route. Induction of a local, mucosal immune response in the upper respiratory tract, and particularly in the nasopharynx, would be a highly efficacious approach to prevention of OM. The chinchilla is the preferred rodent host for studying OM. However, although the anatomy of the chinchilla vomeronasal organ, inner ear, middle ear and Eustachian tube have been well-studied, to date there have been no reports in the literature of a similar complete analysis of the nasopharynx and nasal cavities of the chinchilla. In order to develop a relevant animal model of i.n. delivery as a potential immunization approach for the prevention of OM and to use these models for preclinical assessments of various vaccine candidates, it was important that we better understand the anatomy of the chinchilla nasal cavities and nasopharynx. Our anatomical studies revealed that the naso- and maxilloturbinates of the chinchilla nasal cavity more closely resemble the simple turbinates found in other rodents rather than the branched or complex turbinates seen in dogs, cats, and rabbits thus facilitating the i.n. delivery of vaccine candidates. The chinchilla nasal mucosa also contains numerous lymphoid aggregates like that of other rodents. Our findings thus suggest that we will be able to deliver i.n. vaccines effectively to chinchillas and that these vaccines will likely be able to induce specific immune responses.

Antibodies to malaria peptide mimics inhibit Plasmodium falciparum invasion of erythrocytes

Apical membrane antigen 1 (AMA1) is expressed on the surfaces of Plasmodium falciparum merozoites and is thought to play an important role in the invasion of erythrocytes by malaria parasites. To select for peptides that mimic conformational B-cell epitopes on AMA1, we screened a phage display library of >10(8) individual peptides for peptides bound by a monoclonal anti-AMA1 antibody, 4G2dc1, known to inhibit P. falciparum invasion of erythrocytes. The most reactive peptides, J1, J3, and J7, elicited antibody responses in rabbits that recognized the peptide immunogen and both recombinant and parasite AMA1. Human antibodies in plasma samples from individuals exposed to chronic malaria reacted with J1 and J7 peptides and were isolated using immobilized peptide immunoadsorbents. Both rabbit and human antibodies specific for J1 and J7 peptides were able to inhibit the invasion of erythrocytes by P. falciparum merozoites. This is the first example of phage-derived peptides that mimic an important epitope of a blood-stage malaria vaccine candidate, inducing and isolating functional protective antibodies. Our data support the use of J1 and J7 peptide mimics as in vitro correlates of protective immunity in future AMA1 vaccine trials.

The molecular basis of the antigenic cross-reactivity between measles and cowpea mosaic viruses

Two nonrelated viruses, cowpea mosaic virus (wtCPMV) and measles virus (MV), were found to induce cross-reactive antibodies. The nature of this cross-reactivity was studied and results are presented here demonstrating that antiserum raised against wtCPMV reacted with peptide from the fusion (F) protein of MV. Furthermore, the F protein of MV was shown to share an identical conformational B cell epitope with the small subunit of CPMV coat protein. Passive transfer of anti-wtCPMV antibodies into BALB/c mice conferred partial protection against measles virus induced encephalitis. The results are discussed in the context of cross-protection.

Rational design and molecular diversity for the construction of anti-alpha-bungarotoxin antidotes with high affinity and in vivo efficiency

The structure of peptide p6.7, a mimotope of the nicotinic receptor ligand site that binds alpha-bungarotoxin and neutralizes its toxicity, was compared to that of the acetylcholine binding protein. The central loop of p6.7, when complexed with alpha-bungarotoxin, fits the structure of the acetylcholine binding protein (AChBP) ligand site, whereas peptide terminal residues seem to be less involved in toxin binding. The minimal binding sequence of p6.7 was confirmed experimentally by synthesis of progressively deleted peptides. Affinity maturation was then achieved by random addition of residues flanking the minimal binding sequence and by selection of new alpha-bungarotoxin binding peptides on the basis of their dissociation kinetic rate. The tetra-branched forms of the resulting high-affinity peptides were effective as antidotes in vivo at a significantly lower dose than the tetra-branched lead peptide.

The LTR72 mutant of heat-labile enterotoxin of Escherichia coli enhances the ability of peptide antigens to elicit CD4(+) T cells and secrete gamma interferon after coapplication onto bare skin

Application of antigens with an adjuvant onto bare skin is a needle-free and pain-free immunization procedure that delivers antigens to the immunocompetent cells of the epidermis. We tested here the immunogenicity and adjuvanticity of two mutants of heat-labile enterotoxin (LT) of Escherichia coli, LTK63 and LTR72. Both mutants were shown to be immunogenic, inducing serum and mucosal antibody responses. The application of LTK63 and LTR72 to bare skin induced significant protection against intraperitoneal challenge with a lethal dose of LT. In addition, both LT mutants enhanced the capacity of peptides TT:830-843 and HA:307-319 (representing T-helper epitopes from tetanus toxin and influenza virus hemagglutinin, respectively) to elicit antigen-specific CD4(+) T cells after coapplication onto bare skin. However, only mutant LTR72 was capable of stimulating the secretion of high levels of gamma interferon. These findings demonstrate that successful skin immunization protocols require the selection of the right adjuvant in order to induce the appropriate type of antigen-specific immune responses in a selective and reliable way. Moreover, the use of adjuvants such the LTK63 and LTR72 mutants, with no or low residual toxicity, holds a lot of promise for the future application of vaccines to the bare skin of humans.

Peptide dendrimers: applications and synthesis

Peptide dendrimers are radial or wedge-like branched macromolecules consisting of a peptidyl branching core and/or covalently attached surface functional units. The multimeric nature of these constructs, the unambiguous composition and ease of production make this type of dendrimer well suited to various biotechnological and biochemical applications. Applications include use as biomedical diagnostic reagents, protein mimetics, anticancer and antiviral agents, vaccines and drug and gene delivery vehicles. This review focuses on the different types of peptide dendrimers currently in use and the synthetic methods commonly employed to generate peptide dendrimers ranging from stepwise solid-phase synthesis to chemoselective and orthogonal ligation.

Parenteral and mucosal prime-boost immunization strategies in mice with hepatitis B surface antigen and CpG DNA

Synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs (CpG ODN) are potent adjuvants to protein antigens administered by parenteral or mucosal routes to BALB/c mice. To date, there have been no studies using combined parenteral/mucosal approaches with CpG DNA as adjuvant. In this study we evaluated different parenteral prime-mucosal boost and mucosal prime-parenteral boost strategies using hepatitis B surface antigen (HBsAg) alone or with different adjuvants: aluminum hydroxide (alum), cholera toxin (CT), CpG ODN. In addition, since CpG ODN has previously been shown to act synergistically with other adjuvants after parenteral or mucosal delivery, we also evaluated adjuvant combinations: alum+CpG ODN and CT+CpG ODN. The effects of adjuvant and administration strategy on systemic and mucosal humoral responses were measured, as well as cell-mediated immune responses (cytotoxic T lymphocyte activity). These results were compared to parenteral only or mucosal only strategies. Our findings demonstrate that parenteral immunization can prime for mucosal responses even when different lymph nodes were being targeted. HBsAg-specific immune responses (IgG in plasma, cytotoxic T lymphocytes) induced by parenteral prime could all be significantly enhanced by mucosal boosting and despite the fact that intramuscular immunization alone could not induce mucosal IgA, it could prime for a subsequent mucosal boost. In addition, the presence of adjuvant at time of boosting could influence the nature of subsequent immune responses (Th1 vs. Th2). Mice primed intranasally could have their systemic immune responses boosted with a parenteral administration and it was also possible to enhance mucosal responses induced by intranasal prime with an intramuscular boost.

Immunization onto bare skin with synthetic peptides: immunomodulation with a CpG-containing oligodeoxynucleotide and effective priming of influenza virus-specific CD4+ T cells

Exploiting the immune system of the skin for vaccine administration offers an attractive alternative to the currently used invasive immunization procedures. In this study we report that a synthetic peptide representing a T-helper (Th) epitope from influenza virus haemagglutinin (aa 307--319) can be an effective immunogen when coapplied with cholera toxin (CT) onto bare skin. Proliferation of both peptide- and influenza virus-specific CD4+ T cells was measured in lymphocyte cultures from spleens and regional lymph nodes. The presence of the CpG oligodeoxynucleotide 1826 in the peptide/CT formulation, enhanced the proliferation of peptide- and virus-specific T cells as measured by the conventional [(3)H]thymidine uptake and interleukin (IL)-2 assays. Furthermore, the bias towards Th2-type of responses stimulated by CT was shifted towards Th1 as demonstrated (i) by the increase of interferon-gamma and decrease of IL-4 cytokine levels measured in culture supernatants, (ii) by the predominance of IG2a anti-CT antibodies in the serum, and (iii) by the down-regulation of total serum IgE antibody levels. These findings demonstrate the potential of the bare skin as a non-invasive route for administration of small molecular size peptide antigens. Furthermore, with the selection and combination of the appropriate type of adjuvants, immune responses can be modulated towards the desired type of Th phenotype.

Nasal delivery of epitope based vaccines

Essentially all of the currently available vaccines are based on the use of inactivated or live-attenuated pathogens. However, these vaccines have several shortcomings, such as difficulties of in vitro culturing, biohazard risks, as well as loss of efficacy due to the genetic variations seen in many viruses. These problems may potentially be solved by immunising with epitope-based vaccines consisting of rationally designed protective epitopes, appropriately presented and easy to deliver, which are capable of stimulating effective B-cell, T-cell and cytotoxic immune responses whilst avoiding potentially hazardous and undesirable effects. Furthermore, the use of a mixture of defined epitopes could lead to an effective broad range immune response which has the potential to overcome both strain specificity of the pathogen and the MHC restriction of the host. Epitope-based vaccines can be designed to involve the use of synthetic materials that can be available in unlimited quantities and posing no biohazard. Other approaches include the use of naked DNA or recombinant viruses or bacteria expressing the epitopes. An important objective in the development of such vaccines is that they should be effective when delivered via the mucosal route and effective in the presence of maternal antibodies. In this review, we present examples of the use of various epitope-based vaccine constructs, focussing particularly upon their intranasal delivery to the immune system.

Nasal vaccines

The nasal route for vaccination offers some important opportunities, especially for the prophylaxis of respiratory diseases. Vaccination via the respiratory tract is reviewed and the deposition and clearance of antigens in the deep lung and nose are described and contrasted. Lymphoid structures in the respiratory tract differ according to species; the rat and mouse have a well developed nose-associated lymphoid tissue, while in man, the structure known as Waldeyer's ring (that includes the tonsils), is important as an induction site. The immune response following intranasal administration can provide protection at the administration site and at various effector sites as part of the common mucosal immune system. A number of formulation considerations are important when designing novel systems for nasal administration as are physiological factors such as mucociliary clearance.

The bare skin and the nose as non-invasive routes for administering peptide vaccines

Among the different technologies currently tested for the development of novel vaccines, synthetic peptides represent a promising option, since they are chemically pure and induce immune responses of predetermined specificity. Furthermore, they can be replaced with pseudopeptides or peptide mimetics that contain changes in the amide bond, resulting in more stable and immunogenic molecules. Administration of peptide vaccines via non-invasive routes, such as the nose or the bare skin, allows the efficient uptake of antigen by antigen-presenting cells, which are abundant in the associated lymphoid tissues, ensuring the induction of effective systemic and mucosal immune responses. Using non-invasive routes could be advantageous for vaccination programs in third-world countries, since vaccine administration is simple, painless and economical. In this review, we discuss and present some preliminary data on the advantages of synthetic peptides and peptidomimetics as candidate vaccines, and their potential for administration via the skin and the nose.

Immunization onto bare skin with heat-labile enterotoxin of Escherichia coli enhances immune responses to coadministered protein and peptide antigens and protects mice against lethal toxin challenge

In this study, the potential of the bare skin as a non-invasive route for vaccination was examined. Following application of heat-labile enterotoxin (LT) of Escherichia coli onto bare skin of BALB/c mice, strong serum anti-LT antibody responses were observed, and mucosal immunoglobulin A (IgA) and IgG antibodies were measured in vagina washes. In addition, LT enhanced the serum and mucosal antibody and proliferative T-cell responses to the model protein antigen beta-galactosidase (beta-gal) when coadministered onto bare skin, highlighting its potential to exert an adjuvant effect. When a peptide representing a T-helper epitope (aa 307-319) from the haemagglutinin of influenza virus was applied onto bare skin with LT or cholera toxin (CT), it primed effectively peptide- and virus-specific T cells, as measured in vitro by the interleukin-2 (IL-2) secretion assay. LT was shown to be as immunogenic as CT. Binding activity to GM1 gangliosides was essential for effective induction of anti-CT serum and mucosal antibody responses. Finally, mice immunized onto bare skin with LT were protected against intraperitoneal challenge with a lethal dose of the homologous toxin. These findings give further support to a growing body of evidence on the potential of skin as a non-invasive route for vaccine delivery. This immunization strategy might be advantageous for vaccination programmes in Third World countries, because administration by this route is simple, painless and economical.