Meningococcal outer membrane vesicle vaccine given intranasally can induce immunological memory and booster responses without evidence of tolerance

Outer membrane vesicle-based intranasal vaccines

Delivery of vaccines via the mucosal route is regarded as the most effective mode of immunization to counteract infectious diseases that enter via mucosal tissues, including oral, nasal, pulmonary, intestinal, and urogenital surfaces. Mucosal vaccines not only induce local immune effector elements, such as secretory Immunoglobulin A (IgA) reaching the luminal site of the mucosa, but also systemic immunity. Moreover, mucosal vaccines may trigger immunity in distant mucosal tissues because of the homing of primed antigen-specific immune cells toward local and distant mucosal tissue via the common mucosal immune system. While most licensed intramuscular vaccines induce only systemic immunity, next-generation mucosal vaccines may outperform parenteral vaccination strategies by also eliciting protective mucosal immune responses that block infection and/or transmission. Especially the nasal route of vaccination, targeting the nasal-associated lymphoid tissue, is attractive for local and distant mucosal immunization. In numerous studies, bacterial outer membrane vesicles (OMVs) have proved attractive as vaccine platform for homologous bacterial strains, but also as antigen delivery platform for heterologous antigens of nonbacterial diseases, including viruses, parasites, and cancer. Their application has also been extended to mucosal delivery. Here, we will summarize the characteristics and clinical potential of (engineered) OMVs as vaccine platform for mucosal, especially intranasal delivery.

Lipid membrane-based therapeutics and diagnostics

Success rates in drug discovery are extremely low, and the imbalance between new drugs entering clinical research and their approval is steadily widening. Among the causes of the failure of new therapeutic agents are the lack of safety and insufficient efficacy. On the other hand, timely disease diagnosis may enable an early management of the disease, generally leading to better and less costly outcomes. Several strategies have been explored to overcome the barriers for drug development and facilitate diagnosis. Using lipid membranes as platforms for drug delivery or as biosensors are promising strategies, due to their biocompatibility and unique physicochemical properties. We examine some of the lipid membrane-based strategies for drug delivery and diagnostics, including their advantages and shortcomings. Regarding synthetic lipid membrane-based strategies for drug delivery, liposomes are the archetypic example of a successful approach, already with a long period of well-succeeded clinical application. The use of lipid membrane-based structures from biological sources as drug carriers, currently under clinical evaluation, is also discussed. These biomimetic strategies can enhance the in vivo lifetime of drug and delivery system by avoiding fast clearance, consequently increasing their therapeutic window. The strategies under development using lipid membranes for diagnostic purposes are also reviewed.

Isolation and Functions of Extracellular Vesicles Derived from Parasites: The Promise of a New Era in Immunotherapy, Vaccination, and Diagnosis

Experimental and epidemiological evidence shows that parasites, particularly helminths, play a central role in balancing the host immunity. It was demonstrated that parasites can modulate immune responses via their excretory/secretory (ES) and some specific proteins. Extracellular vesicles (EVs) are nano-scale particles that are released from eukaryotic and prokaryotic cells. EVs in parasitological studies have been mostly employed for immunotherapy of autoimmune diseases, vaccination, and diagnosis. EVs can carry virulence factors and play a central role in the development of parasites in host cells. These molecules can manipulate the immune responses through transcriptional changes. Moreover, EVs derived from helminths modulate the immune system via provoking anti-inflammatory cytokines. On the other hand, EVs from parasite protozoa can induce efficient immunity, that makes them useful for probable next-generation vaccines. In addition, it seems that EVs from parasites may provide new diagnostic approaches for parasitic infections. In the current study, we reviewed isolation methods, functions, and applications of parasite's EVs in immunotherapy, vaccination, and diagnosis.

Intranasal vaccination with leishmanial antigens protects golden hamsters (Mesocricetus auratus) against Leishmania (Viannia) Braziliensis infection

Background

Previous results have shown that oral and intranasal administration of particulate Leishmania (Leishmania) amazonensis antigens (LaAg) partially protects mice against L. amazonensis infection. However, vaccination studies on species of the subgenus Viannia, the main causative agent of cutaneous and mucosal leishmaniasis in the Americas, have been hampered by the lack of easy-to-handle bio-models that accurately mimic the human disease. Recently, we demonstrated that the golden hamster is an appropriate model for studying the immunopathogenesis of cutaneous leishmaniasis caused by L. (Viannia) braziliensis. Using the golden hamster model, our current study investigated whether the protective effect of intranasal immunisation with LaAg can be extended to L. braziliensis infection.

Methodology/Principal Findings

Golden hamsters vaccinated with either two intranasal (IN) doses of LaAg (10 µg) or two intramuscular doses of LaAg (20 µg) were challenged 2 weeks post-vaccination with L. braziliensis. The results showed that IN immunisation with LaAg significantly reduced lesion growth and parasitic load as well as serum IgG and IgG2 levels. At the experimental endpoint on day 114 post-infection, IN-immunised hamsters that were considered protected expressed IFN-γ and IL10 mRNA levels that returned to uninfected skin levels. In contrast to the nasal route, intramuscular (IM) immunisation failed to provide protection.

Conclusions/Significance

These results demonstrate for the first time that the nasal route of immunisation can induce cross protection against L. braziliensis infection.

Leishmaniasis is a disease that is common in most tropical countries. In Brazil, the cutaneous form of the disease is highly prevalent, with approximately 28,000 new cases reported annually. L. (Viannia) braziliensis is the main causative agent of cutaneous leishmaniasis; however, vaccine studies against protozoans of the subgenus Viannia have been largely neglected, mainly due to the high resistance of most mouse strains to the infection. Here, the authors used the golden hamster, which is highly susceptible to dermotropic Leishmania spp infection. It was previously shown that oral and intranasal vaccination with whole L. (Leishmania) amazonensis antigens (LaAg) protected mice against L. amazonensis infection. In the present study, the authors investigated whether the protective effect of intranasal immunisation with LaAg can be extended to L. braziliensis infection using the golden hamster model. The results showed that intranasal immunisation with LaAg significantly reduced lesion growth and parasitic load as well as IgG and IgG2 serum levels. At the endpoint of the experiment, intranasally immunised hamsters that were considered protected expressed IFN-γ and IL10 mRNA at levels similar to those in uninfected skin. These data show that the use of a proper animal model and/or different vaccination strategies may facilitate the development of an effective vaccine against L. braziliensis.

Discovery of Salmonella virulence factors translocated via outer membrane vesicles to murine macrophages

Salmonella enterica serovar Typhimurium, an intracellular pathogen and leading cause of food-borne illness, encodes a plethora of virulence effectors. Salmonella virulence factors are translocated into host cells and manipulate host cellular activities, providing a more hospitable environment for bacterial proliferation. In this study, we report a new set of virulence factors that is translocated into the host cytoplasm via bacterial outer membrane vesicles (OMV). PagK (or PagK1), PagJ, and STM2585A (or PagK2) are small proteins composed of ∼70 amino acids and have high sequence homology to each other (>85% identity). Salmonella lacking all three homologues was attenuated for virulence in a mouse infection model, suggesting at least partial functional redundancy among the homologues. While each homologue was translocated into the macrophage cytoplasm, their translocation was independent of all three Salmonella gene-encoded type III secretion systems (T3SSs)-Salmonella pathogenicity island 1 (SPI-1) T3SS, SPI-2 T3SS, and the flagellar system. Selected methods, including direct microscopy, demonstrated that the PagK-homologous proteins were secreted through OMV, which were enriched with lipopolysaccharide (LPS) and outer membrane proteins. Vesicles produced by intracellular bacteria also contained lysosome-associated membrane protein 1 (LAMP1), suggesting the possibility of OMV convergence with host cellular components during intracellular trafficking. This study identified novel Salmonella virulence factors secreted via OMV and demonstrated that OMV can function as a vehicle to transfer virulence determinants to the cytoplasm of the infected host cell.

Outer membrane vesicles of Neisseria lactamica as a potential mucosal adjuvant

The muscosal delivery of vaccines has many advantages including ease of administration and the induction of a mucosal immune response at the natural site of infection for many pathogens. Mice were immunised with outer membrane vesicles (OMV) prepared from Neisseria lactamica or Neisseria meningitidis by subcutaneous (SC) or intranasal (IN) routes, or live cells of N. lactamica given IN or by SC injection. A systemic IgG and mucosal IgA response was demonstrated and N. lactamica OMV induced antibodies cross-reactive with N. meningitidis; however, a cross-reactive response following IN administration was only evident after three doses of vaccine. OMV from both organisms were also an effective intranasal adjuvant for a co-administered model antigen, hepatitis B surface antigen (HBsAg), inducing systemic IgG against HBsAg and IgA in lung and vaginal washes. IN administration of N. meningitidis OMV elicited serum antibodies that were bactericidal for meningococci and provided passive protection in an infant rat model of meningococcal bacteraemia. The antibody response to N. lactamica OMV given IN was only weakly bactericidal but still afforded passive protection. Thus, OMV from N. lactamica given IN elicit immune responses cross-reactive with N. meningitidis and act as an effective mucosal adjuvant.

Comparison of immune responses to gonococcal PorB delivered as outer membrane vesicles, recombinant protein, or Venezuelan equine encephalitis virus replicon particles

Porin (PorB) is a major outer membrane protein produced by all Neisseria gonorrhoeae strains and has been a focus of intense interest as a vaccine candidate. In this study, the immunogenicity of PorB in mice was investigated after several immunization regimens. Outer membrane vesicles (OMV), recombinant renatured PorB (rrPorB), and PorB-expressing Venezuelan equine encephalitis (VEE) virus replicon particles (PorB VRP) were delivered intranasally (i.n.) or subcutaneously (s.c.) into the dorsal area or the hind footpad in three-dose schedules; the PorB VRP-immunized mice were given a single additional booster dose of rrPorB in Ribi adjuvant. Different delivery systems and administration routes induced different immune responses. Mice immunized s.c. with rrPorB in Ribi had the highest levels of PorB-specific serum immunoglobulin G (IgG) by enzyme-linked immunosorbent assay. Surprisingly, there was an apparent Th1 bias, based on IgG1/IgG2a ratios, after immunization with rrPorB in Ribi in the footpad while the same vaccine given in the dorsal area gave a strongly Th2-biased response. PorB VRP-immunized mice produced a consistent Th1 response with a high gamma interferon response in stimulated splenic lymphocytes and very low IgG1/IgG2a ratios. Immunization by OMV delivered i.n. was the only regimen that resulted in a serum bactericidal response, and it generated an excellent mucosal IgA response. Serum from mice immunized with rrPorB preferentially recognized the surface of whole gonococci expressing a homologous PorB, whereas serum from PorB VRP-immunized mice had relatively low whole-cell binding activity but recognized both heterologous and homologous PorB equally. The data resulting from this direct comparison suggested that important aspects of the immune response can be manipulated by altering the form of the antigen and its delivery. This information coupled with an understanding of protective antigonococcal immune responses will enable the design of the optimal vaccine for N. gonorrhoeae.

Immunoglobulin-A antibodies in upper airway secretions may inhibit intranasal influenza virus replication in mice but not protect against clinical illness

Mice immunized intranasally with a formalin-inactivated A/PR/8/34 (H1N1) influenza whole virus vaccine adjuvanted with cholera toxin, outer membrane vesicles from group B meningococci or formalin-inactivated whole cell Bordetella pertussis were protected against replication of the homologous virus in the nasal cavity. Only some mice were protected against clinical illness measured as weight loss and lowered body temperature. All mice immunized subcutaneously with one-tenth the intranasal vaccine dose without adjuvant were protected against clinical illness but not against local mucosal viral replication. Replicating virus was primarily found in animals with low concentrations of immunoglobulin (Ig)-A antibodies in saliva regardless of concentrations of IgG antibodies in serum. Clinical illness was seen only in those with low serum antibodies regardless of antibody levels in saliva. Nonreplicating nasal vaccines may not be sufficiently protective unless they also have a substantial influence on systemic immunity.

Intranasal vaccination against cutaneous leishmaniasis with a particulated leishmanial antigen or DNA encoding LACK

We have previously demonstrated that oral delivery of a disease-promoting particulated antigen of Leishmania amazonensis (LaAg) partially protects mice against cutaneous leishmaniasis. In the present work, we sought to optimize a mucosal vaccine by using the intranasal route for delivery of different antigen preparations, including (i) LaAg, (ii) soluble recombinant p36/LACK leishmanial antigen (LACK), and (iii) plasmid DNA encoding LACK (LACK DNA). BALB/c mice that received two intranasal doses of 10 microg of LaAg and were challenged 1 week postvaccination with L. amazonensis developed delayed but effective control of lesion growth. A diminished parasite burden was accompanied by enhancement of both gamma interferon (IFN-gamma) and interleukin-10 levels in the lesion-draining lymph nodes. The vaccine efficacy improved with time. At 4 months postvaccination, when a strong parasite-specific TH1-type response was present in vivo, the infection was controlled for at least 5 months after challenge. In contrast to the particulated LaAg, soluble LACK (10 microg/dose) had no effect. Interestingly, LACK DNA (30 microg/dose), but not empty DNA, promoted rapid and durable protective immunity. Parasite growth was effectively controlled, and at 5 months after challenge LACK-reactive cells in both the mucosal and lesion-draining lymph nodes produced high levels of IFN-gamma. These results demonstrate for the first time the feasibility of using the intranasal route for long-lived memory vaccination against cutaneous leishmaniasis with adjuvant-free crude antigens or DNA.

Improved methods for producing outer membrane vesicles in Gram-negative bacteria

Outer membrane vesicle formation occurs during Gram-negative bacterial growth. However, natural production of large amounts of outer membrane vesicles has only been described in a few bacterial genera. The purified vesicles of some bacterial pathogens have shown potential applications in vaccinology and in antibiotic therapy. This study focused on the development of a gene expression system able to induce production of large amounts of outer membrane vesicles. The Tol-Pal system of Escherichia coli, required to maintain outer membrane integrity, is composed of five cell envelope proteins, TolA, TolB, TolQ, TolR and Pal. Tol proteins are parasitized by filamentous bacteriophages and by colicins. The phage infection process and colicin import require, respectively, the N-terminal domain of the minor coat g3p protein and the translocation domain of colicins, with both domains interacting with Tol proteins. In this study, we show that the periplasmic production of either Tol, g3p or colicin domains was able to specifically destabilize the E. coli or Shigella flexneri cell envelope and to induce production of high amounts of vesicles. This technique was further found to work efficiently in Salmonella enterica serovar Typhimurium.

Local and systemic antibody responses in mice immunized intranasally with native and detergent-extracted outer membrane vesicles from Neisseria meningitidis

The mouse humoral immune response toward native or detergent-extracted outer membrane vesicles (NOMVs and DOMVs, respectively) from Neisseria meningitidis was determined after intranasal immunization. Both preparations elicited high frequencies of NOMV-specific antibody-forming cells (AFCs) locally in the nasal associated lymphoid tissue (NALT) after three or four weekly doses. The diffuse NALT (D-NALT) contained ca. 10-fold more NOMV-specific AFCs than those observed in the mediastinal lymph node, spleen, and bone marrow. AFCs observed in the D-NALT were primarily immunoglobulin A positive (IgA(+)) and were maintained for at least 1 month. In contrast, the organized NALT (O-NALT) contained low numbers of AFCs, and the response was relatively short-lived. In other lymphoid tissues, AFCs producing various IgG subclasses and IgM were present with IgG2b-producing AFCs being dominant or codominant with IgA or IgG2a. In serum and in all of the tissues examined, with the exception of the NALT, NOMVs clearly induced a stronger antibody response and a broader range of antibody isotypes than DOMVs. The development of NOMV-specific AFCs in spleen and bone marrow after intranasal immunization was slow compared to intravenous immunization but, once established, the intranasally elicited responses increased steadily for at least 75 days. NOMV-specific antibodies induced via several routes of immunization had high bactericidal activities in serum. Our results indicated that intranasally administered OMVs induced strong local and systemic antibody responses in mice that were relatively long-lived.

Immunisation schedules for non-replicating nasal vaccines can be made simple by allowing time for development of immunological memory

Mice immunised intranasally with multiple doses of outer membrane vesicles (OMVs) from group B meningococci developed antibody responses that depended on the interval between doses. High levels of antibodies in saliva and extracts of faeces were induced within 4 weeks after an OMV vaccine had been given at weekly intervals, whereas the antibody responses in these samples were negligible when given four times at 1-day or 1-h intervals, or as one large dose. Only modest responses were obtained in serum after 4 weeks, however, whether the vaccine had been given repeatedly at any schedule, including the 1-week interval, or as one dose. On the other hand, two large doses given 8 weeks apart induced booster antibody responses in both serum and secretions that matched the responses from a second series of the four smaller doses. Intranasal immunisations may thus stimulate immunological memory more rapidly in secretions than in serum. In order to secure adequate systemic responses by a minimum of doses, nasal vaccines should therefore be given at intervals longer than 4 weeks, in harmony with the intervals recommended for injectable vaccines.

Meningococcal conjugate vaccines

Neisseria meningitidis is a leading cause of bacterial meningitis and sepsis in the US, Europe and in many other parts of the world, including parts of sub-Saharan Africa (known as the African 'meningitis belt'). There are > 500000 cases of meningococcal disease annually with an estimated death toll of 135000 worldwide. Approximately 10 - 15 % of survivors experience significant morbidity in the form of neurological sequelae, including hearing loss, speech disorders, loss of limbs, mental retardation and paralysis. Disease is usually caused by N. meningitidis serogroups A, B, C, Y or W-135. Prevention of meningococcal disease includes isolation, chemoprophylaxis and vaccination with available polysaccharide vaccines. However, the polysaccharide meningococcal vaccines (i.e., A and C; A, C and W-135; or A, C, Y and W-135) initially developed in the 1970s are generally poorly immunogenic in children or require repeated doses and do not produce long-lasting immunity. Conjugate vaccine technology has been very successfully used in childhood vaccines for the prevention of other bacterial meningitis pathogens, including vaccines against Haemophilus influenzae serotype b (Hib) and more recently, the seven- and nine-valent conjugate pneumococcal vaccines. Newly released meningococcal conjugate vaccines against N. meningitidis serogroup C have been highly efficacious in young children and adolescents, with minimal side effects. Conjugate vaccines targeting other important meningococcal serogroups (e.g., N. meningitidis serogroup A, responsible for the large pandemic outbreaks and the majority of disease in sub-Saharan Africa and serogroups Y and W-135) are under development and together with the serogroup C conjugates, have the potential to significantly impact worldwide sporadic and epidemic meningococcal disease. The search for an effective serogroup B meningococcal vaccine remains elusive. This manuscript reviews the conjugate meningococcal vaccines and their potential for meningococcal disease prevention.

Evidence for Naturally Acquired T Cell-Mediated Mucosal Immunity toNeisseria meningitidis

Naturally acquired protective immunity against Neisseria meningitidis is thought to partially explain the disparity between the high levels of carriage in the human nasopharynx and the rare incidence of disease. To investigate this immunity to Neisseria meningitidis at the mucosal level, in vitro cellular responses to outer membrane vesicle preparations derived from this pathogen were examined using mononuclear cells from the palatine tonsils of adults and children. Characterization of these responses was achieved by depletion of CD45RA(+), CD45RO(+), and CD19(+) populations and outer membrane vesicles derived from isogenic mutants expressing different serosubtypes of the major outer membrane protein, porin A (PorA), no PorA and membrane preparations from a mutant with no LPS (LpxA(-)). The magnitude of cellular proliferative responses against the outer membrane vesicles were strongly associated with age and were largely T cell mediated, involving both CD45RO(+) and CD45RA(+) T cell phenotypes. Responses were not dependent on LPS but consisted of both PorA cross-specific and non-PorA-dependent responses. Cellular immunity against Neisseria meningitidis was found to be frequently associated with systemic IgG Abs but was not associated with serum bactericidal Abs. For the first time our results demonstrate an age-associated acquisition of mucosal T effector/memory cell responses to Neisseria meningitidis. This mucosal cellular immunity can be present in the absence of serum bactericidal Abs, a classical marker of protective immunity.

Mucosal vaccination against encapsulated respiratory bacteria--new potentials for conjugate vaccines?

Polysaccharide (PS)-encapsulated bacteria such as Haemophilus influenzae type b (Hib), Streptococcus pneumoniae (pneumococcus), Neisseria meningitides (meningococcus) and group B streptococcus (GBS), cause a major proportion of disease in early childhood. Native PS vaccines are immunogenic and provide protection against disease in healthy adults but do not induce immunological memory. PSs are T-cell-independent antigens and do not elicit antibodies in infants and young children, but by conjugating PS to proteins they become T-cell dependent and immunogenic at an early age. Despite excellent efficacy of PS-protein conjugate vaccines against invasive disease, protection against mucosal infections such as pneumococcal otitis media has been less efficacious. Circulating PS-specific antibodies may protect against infections at mucosal sites, but mucosal immunoglobulin A antibodies may also contribute significantly to protection against mucosal infections. Mucosal immunization of experimental animals with conjugate vaccines against Hib, pneumococcus, meningococcus and GBS induces systemic and mucosal immune responses, which provide protection against carriage, otitis media and invasive disease in a variety of challenge models, providing new means for protection against encapsulated bacteria. In addition, mucosal immunization of neonatal mice with a pneumococcal conjugate and the nontoxic adjuvant LT-K63 has been superior to parenteral immunization in eliciting protective antibodies and PS-specific memory, and thus circumventing the limitations of antibody responses to PS that are responsible for enhanced susceptibility of neonates and infants to infections caused by encapsulated bacteria. Through T-cell dependent enhanced immunogenicity of PS-protein conjugate vaccines, mucosal immunization could be an attractive approach for early life immunization against encapsulated bacteria.

Can nonliving nasal vaccines be made to work?

Nasal vaccines consisting of nonliving particulate formulations can induce immune responses of importance for protection against infection. The most promising results have been obtained with vaccines against influenza, pertussis and group B meningococcal disease. So far, however, the results do not challenge the standing of corresponding injectable vaccines, although results of experiments in animals do indicate that effective nonliving nasal vaccines may soon be developed. This will depend on refined immunization schedules to benefit from immunological memory and on formulations to make the vaccines more accessible to the immune system by way of mucosal adjuvants or immune modulators.

Bacteria-derived particles as adjuvants for non-replicating nasal vaccines

In attempts to mimic natural infections, vaccines consisting of microbial particles may be delivered directly to mucosal surfaces. In this way, the mucosal as well as the systemic immune systems can be activated. Even non-living particles of bacterial origin have been shown to elicit strong immune responses when administered intranasally. However, some particles such as formalin-inactivated influenza virus may need a mucosal adjuvant to be effective. The bacteria-derived particles seem to possess such an adjuvant activity when mixed with and given intranasally with the less immunogenic killed virus. Possibly, the bacterial particles facilitate uptake of the virus through the mucosal membranes, although an additional influence on the immune response to the virus might be mediated in the lymphoid tissue below the mucosal surface. Bacteria-derived particles in nasal vaccines may thus serve as an alternative adjuvant to derivatives of cholera toxin or the heat-labile toxin from E. coli.