Adjuvanticity and protective immunity elicited by Bordetella pertussis antigens encapsulated in poly(DL-lactide-co-glycolide) microspheres

Stimulation of mucosal and systemic antibody responses against Bordetella pertussis filamentous haemagglutinin and recombinant pertussis toxin after nasal administration with chitosan in mice

Mice were intranasally immunised with a mixture of Bordetella pertussis filamentous haemagglutinin (FHA) and recombinant pertussis toxin, PT-9K/129G (rPT) in combination with chitosan. For both antigens, this formulation induced systemic responses as measured by serum IgG and also mucosal responses as measured by secretory IgA in lung lavage and nasal washes. Immunosorbant assays were used to measure these responses. Both the systemic and mucosal responses were considerably higher than those produced when a mixture of rPT and FHA was administered nasally without chitosan. In comparison, intraperitoneally administered rPT/FHA adsorbed to Alhydrogel elicited only a systemic response, and nasal chitosan solution produced neither systemic nor mucosal response. This study clearly demonstrated that chitosan potentiated the serum and mucosal immune responses to nasally administered FHA and rPT in mice. Hence, this nasal chitosan delivery system has potential as a new non-injectable vaccine for the prophylaxis of whooping cough.

Polymer-grafted starch microparticles for oral and nasal immunization

Microparticle delivery systems for oral vaccine administration are receiving considerable attention. A novel silicone polymer-grafted starch microparticle system was developed that is efficacious both orally and intranasally. Unlike most other microparticle systems, this novel system does not appear to retard the release of antigen or to protect antigen from degradation. The results indicate that a unique physiochemical relationship occurs between protein antigen and silicone in a starch matrix that facilitates the mucosal immunogenicity of antigen. This leads to predominance of Th2 antibody response. Taken together, these findings indicate that this novel microparticle system may be advantageous for the delivery of small quantities of antigen, especially intranasally, and may be useful for the induction of oral tolerance.

Mucosal immunogenicity elicited in mice by oral vaccination with phosphorylcholine encapsulated in poly (D,L-lactide-co-glycolide) microspheres

Poly(D,L-lactide-co-glycolide) microspheres loaded with phosphorylcholine linked to thyroglobulin (PC-Thyr) as protein carrier were prepared. The entrapment efficiency reached 80% when the initial protein:polymer ratio was 1:8. Ninety-four percent of the loaded microspheres had a diameter < or = 10 microns. The encapsulation process did not alter PC-Thyr absorbance nor PC antigenic reactivity. Oral administration of these microspheres induced a specific IgA response in intestinal, pulmonary and vaginal secretions, as well as a strong specific systemic immune response in female Balb/c mice. This suggests the need to explore further the potential ability of PC-Thyr loaded microspheres to protect against infections caused by PC-bearing microorganisms which invade or colonize different mucosal sites.

Intranasal immunization of mice with herpes simplex virus type 2 recombinant gD2: the effect of adjuvants on mucosal and serum antibody responses

Mucosal immunization offers the potential for inducing IgA antibody responses in the vagina, the site of infection for many viruses, including herpes simplex type 2 (HSV-2). To investigate this possibility, mice were immunized intranasally with 10 micrograms glycoprotein D2 (gD2) from HSV combined with a series of adjuvants of proven efficacy; the oil in water emulsion MF59, poly(D,L-lactide-co-glycolide) microparticles (PLG) (encapsulated or co-administered), immune-stimulating complexes (iscoms) (incorporated or co-administered with iscomatrix) and the genetically detoxified enterotoxin from Escherichia coli, LT-K63. Encapsulation of gD2 into PLG microparticles, incorporation of gD2 into iscoms and co-administration of gD2 with LT-K63 induced mucosal IgA antibody responses (nasal wash, saliva and vaginal wash) which were greater than those induced by intramuscular administration of gD2 with MF59. Intranasal immunization with these formulations also induced substantial levels of serum IgG and neutralizing antibodies. These studies demonstrated that intranasal immunization with potent adjuvants is an effective means to induce mucosal antibody responses, even in the lower genital tract.

Recent advances in vaccine adjuvants for systemic and mucosal administration

Although vaccines produced by recombinant DNA technology are safer than traditional vaccines, which are based on attenuated or inactivated bacteria or viruses, they are often poorly immunogenic. Therefore, adjuvants are often required to enhance the immunogenicity of these vaccines. A number of adjuvants which are particulates of defined dimensions (<5 microm) have been shown to be effective in enhancing the immunogenicity of weak antigens in animal models. Two novel adjuvants which possess significant potential for the development of new vaccines include an oil-in-water microemulsion (MF59) and polymeric microparticles. MF59 has been shown to be a potent and safe adjuvant in human subjects with several vaccines (for example HSV-2, HIV-1 and influenza virus). An MF59 adjuvanted influenza has been recommended for approval in Italy. Microparticles prepared from the biodegradable polymers the poly(lactide-co-glycolides) (PLG) are currently undergoing extensive pre-clinical evaluation as vaccine adjuvants. Because of their controlled release characteristics, microparticles also possess considerable potential for the development of single dose vaccines. The development of single dose vaccines would offer significant advantages and would improve vaccination uptake rates in at risk populations, particularly in the developing world. In addition to systemic administration, microparticles have also also been shown to enhance the immunogenicity of vaccines when administered by mucosal routes. Therefore microparticles may allow the development of novel vaccines which can be administered by non-parenteral routes. Mucosal administration of vaccines would significantly improve patient compliance by allowing immunization to be achieved without the use of needles. An alternative approach to the development of mucosally administered vaccines involves the production of genetically detoxified toxins. Heat labile enterotoxin (LT) from Escherichia coli and cholera toxin from Vibrio cholerae are two closely related bacterially produced toxins, which are the most potent adjuvants available. However, these molecules are too toxic to be used in the development of human vaccines. Nevertheless, these toxins have been modified by site-directed mutagenesis to produce molecules which are adjuvant active, but non-toxic. The most advanced of these molecules (LTK63), which has a single amino acid substitution in the enzymatically active subunit of LT, is active as an adjuvant, but non-toxic in pre-clinical models. The approach of genetically detoxifying bacterial toxins to produce novel adjuvants offers significant potential for the future development of mucosally administered vaccines.

A nasal whole-cell pertussis vaccine can induce strong systemic and mucosal antibody responses which are not enhanced by cholera toxin

The immunogenicity of formaldehyde-inactivated Bordetella pertussis (Bp) delivered by the intranasal or colonic-rectal routes in BALB/c mice was studied by immunization four times at weekly intervals with Bp alone, or with Bp mixed with cholera toxin (CT) as a mucosal adjuvant. Mice given Bp subcutaneously, and untreated mice served as controls. Antibody responses in serum, saliva, bronchoalveolar lavage (BAL) fluids and extracts of faeces were measured by enzyme-linked immunosorbent assay. Nasal immunizations with Bp alone induced high levels of IgG antibodies to Bp in serum and BAL fluids, as well as IgA antibodies in serum, saliva, BAL fluids and extracts of faeces. The IgA responses were significantly reduced, and the IgG responses were not increased, when CT was given intranasally together with Bp. However, CT increased the IgA responses to Bp in faeces when both antigens were given rectally, while rectal administration of Bp alone did not induce significant serum or secretory antibody responses. However, when mixed with Bp, the CT itself induced antibodies to CT in serum and samples representing secretions after both nasal and rectal administrations. Thus, Bp is strongly immunogenic when applied intranasally, but not when presented into the intestinal lumen via the rectal route. It appears that CT, which is known to be a mucosal adjuvant and which in itself is a strong mucosal immunogen, will inhibit the immune responses of other strong immunogens when applied on the nasal mucosa.

Protective immunity against Salmonella typhimurium elicited in mice by oral vaccination with phosphorylcholine encapsulated in poly(DL-lactide-co-glycolide) microspheres

Encapsulation of vaccines in biodegradable microspheres provides excellent mucosal immunogens with a high potential for immunization against bacterial infections. We tested the protective immunity elicited by intragastric vaccination with phosphorylcholine (PC) encapsulated in poly(DL-lactide-co-glycolide) (DL-PLG) microspheres against Salmonella typhimurium in a mouse model of invasive intestinal infection. We chose PC as the antigen because it was found to elicit an immune response after intestinal exposure of mice to PC-bearing S. typhimurium and because anti-PC immunity protects mice against Streptococcus pneumoniae, another PC-bearing microorganism. Mice were primed intragastrically on days 1, 2, and 3 and boosted on days 28, 29, and 30 with PC (280 microg) coupled to porcine thyroglobulin (PC-thyr) encapsulated in DL-PLG microspheres, free PC-thyr, or blank microspheres. A significant rise in anti-PC immunoglobulin A (IgA) titers, as measured by an enzyme-linked immunosorbent assay, was observed in the intestinal secretions after immunization with PC-loaded microspheres, compared to the titers of mice immunized with free PC-thyr or blank microspheres. This antibody response peaked 14 days after the last boost and correlated with a highly significant resistance to oral challenge by S. typhimurium C5 (P < 10(-3)). Control mice were primed intraperitoneally on day 1 with 15 microg of PC in complete Freund's adjuvant and boosted on days 10, 14, and 20 with the same dose without adjuvant but via the same route. In these mice, the levels of anti-PC IgA in intestinal secretions were equivalent to those of the mice intragastrically immunized with PC-loaded microspheres, but protection was significantly weaker, suggesting that either the IgAs were not functional or that other immune mechanisms are important in protection. Taken together, our results highlight the potential of antigen encapsulation in DL-PLG microspheres for eliciting protective immunity against invasive intestinal bacterial diseases and suggest that a similar strategy could be used against diseases caused by other PC-bearing microorganisms.

Recent advances in vaccine adjuvants: the development of MF59 emulsion and polymeric microparticles

Vaccines produced by recombinant DNA technology are safer than 'traditional' vaccines but they are often poorly immunogenic, requiring adjuvants to enhance their immunogenicity. Particulate adjuvants of defined dimensions (< 5 microns) have been shown to be effective in enhancing the immunogenicity of 'weak' antigens in animal models. Two novel adjuvants that possess significant potential for the development of new vaccines are the MF59 sub-microemulsion and polymeric microparticles. MF59 is an oil-in-water emulsion and has been shown to be both potent and safe in human subjects with several vaccines. Microparticles prepared from the biodegradable polymer poly(lactide-co-glycolide) have been shown to enhance immunogenicity when administered by mucosal routes, such as oral and intranasal, and they also possess considerable potential for the development of single-dose vaccines through the use of controlled-release technology.

Nasal lymphoid tissue, intranasal immunization, and compartmentalization of the common mucosal immune system

Mucosal application of vaccines with an appropriate adjuvant can induce immune responses at both systemic and mucosal sites, and therefore may prevent not only infectious disease, but also colonization of mucosal surfaces. Intranasal is more effective than intragastric immunization at generating earlier and stronger mucosal immune response. Nasal lymphoid tissue (NALT) and its local draining lymph nodes may retain long-term immune memory. IgA isotype switching, and the differentiation and maturation of IgA antibody-secreting cells (ASC) may occur before these cells migrate out of NALT, whereas IgG ASC responses require passage of the cells through draining lymph nodes of the NALT. Knowledge of whether immune memory cells can recirculate to and reside in the inductive sites other than their origin after encountering antigen will be helpful for understanding the compartmentalization of the common mucosal immune system as well as for determining the best route for delivering a mucosal vaccine against a particular pathogen.

Immunogenicity and efficacy against lethal aerosol staphylococcal enterotoxin B challenge in monkeys by intramuscular and respiratory delivery of proteosome-toxoid vaccines

Staphylococcal enterotoxin B (SEB), a primary cause of food poisoning, is also a superantigen that can cause toxic shock after traumatic or surgical staphylococcal wound [correction of would] infections or viral influenza-associated staphylococcal superinfections or when aerosolized for use as a potential biologic warfare threat agent. Intranasal or intramuscular (i.m.) immunization with formalinized SEB toxoid formulated with meningococcal outer membrane protein proteosomes has previously been shown to be immunogenic and protective against lethal respiratory or parenteral SEB challenge in murine models of SEB intoxication. Here, it is demonstrated that immunization of nonhuman primates with the proteosome-SEB toxoid vaccine is safe, immunogenic, and protective against lethal aerosol challenge with 15 50% lethal doses of SEB. Monkeys (10 per group) were primed i.m. and given booster injections by either the i.m. or intratracheal route without adverse side effects. Anamnestic anti-SEB serum immunoglobulin G (IgG) responses were elicited in all monkeys, but strong IgA responses in sera and bronchial secretions were elicited both pre- and post-SEB challenge only in monkeys given booster injections intratracheally. The proteosome-SEB toxoid vaccine was efficacious by both routes in protecting 100% of monkeys against severe symptomatology and death from aerosolized-SEB intoxication. These data confirm the safety, immunogenicity, and efficacy in monkeys of parenteral and respiratory vaccination with the proteosome-SEB toxoid, thereby supporting clinical trials of this vaccine in humans. The safety and enhancement of both bronchial and systemic IgA and IgG responses by the proteosome vaccine delivered by a respiratory route are also encouraging for the development of mucosally delivered proteosome vaccines to protect against SEB and other toxic or infectious respiratory pathogens.

Pertussis antigens that abrogate bacterial adherence and elicit immunity

Infectious disease processes follow the initial steps of adherence of the organism to host tissues and subsequent colonization of the target tissues that can occur through specific adhesion-receptor systems. Bordetella pertussis, the human pathogen that causes whooping cough, has evolved a genetically controlled system whereby adhesins are expressed when they enter the human host. Two adhesins, filamentous hemagglutinin (FHA) and pertactin, mediate the adherence of the bacterium to eukaryotic cells through varied attachment mechanisms, including lectin-like binding sites that interact with sulfated sugars on cell surface glycoconjugates and the ARG-GLY-ASP binding sequence, which recognizes a family of integrins found on the cell surface. The differential expression of relevant receptors by various eukaryotic cells likely plays a role in the pathogenesis and immune response to the bacterium by the host, directing the organism to specific cell types and to specific tissue sites. Substantial evidence exists that the B. pertussis adhesins, FHA and pertactin, elicit immune responses that are protective in animal models for the disease, including serum antibody production and local immune responses in the respiratory tract following nasal administration of encapsulated antigens. Both of these adhesins are components of new acellular pertussis vaccines that have proven safe and highly effective for prevention of serious disease in infants.

Expression and immunogenicity of pertussis toxin S1 subunit-tetanus toxin fragment C fusions in Salmonella typhi vaccine strain CVD 908

Salmonella typhi vaccine strain CVD 908 can deliver heterologous antigens to the host immune system following mucosal immunization. Stable expression of foreign proteins in Salmonella cells often requires antigen-specific engineering strategies. Fusion of antigens to stabilizing proteins has proven to be a successful strategy for rescuing otherwise unstable proteins. We designed plasmids to allow the fusion of antigens to the amino terminus or carboxyl terminus of fragment C of tetanus toxin, separated by a 4-amino-acid hinge region. Towards the ultimate goal of developing a live oral diphtheria-pertussis-tetanus vaccine, we used these plasmids to stably express the S1 subunit of pertussis toxin in CVD 908. Driven by the anaerobically inducible nirB promoter, the S1 subunit alone was expressed poorly in Salmonella cytoplasm. In contrast, hybrid proteins with S1 fused to either the amino or carboxyl terminus of fragment C were expressed at a high level in CVD 908 and were recognized in Western blot (immunoblot) analysis by monoclonal antibodies directed to S1 and to fragment C. Mice were immunized by the oral or intranasal routes with CVD 908 derivatives harboring these recombinant plasmids. All fusion proteins elicited serum antibody responses to fragment C following intranasal immunization, whereas oral inoculation did not. The configuration of antigens constituting the fusion was critical; S1 fused to the amino terminus of fragment C was less effective than S1 fused to the carboxyl terminus in generating anti-fragment C antibodies. CVD 908 expressing truncated S1 fused to the carboxyl terminus of fragment C elicited neutralizing serum pertussis antitoxin following intranasal immunization of mice.

Intranasal and intramuscular proteosome-staphylococcal enterotoxin B (SEB) toxoid vaccines: immunogenicity and efficacy against lethal SEB intoxication in mice

Intranasal or intramuscular (i.m.) immunization of mice and i.m. immunization of rabbits with formalinized staphylococcal enterotoxin B (SEB) toxoid in saline elicited higher anti-SEB serum immunoglobulin G (IgG) titers when the toxoid was formulated with proteosomes. In addition, intranasal immunization of mice with this proteosome-toxoid vaccine elicited high levels of anti-SEB IgA in lung and intestinal secretions, whereas the toxoid without proteosomes did not. Two i.m. immunizations with proteosome-toxoid plus alum also induced higher murine serum responses than alum-adjuvanted toxoid without proteosomes. Furthermore, proteosome-toxoid delivered intranasally in saline or i.m. with either saline or alum afforded significant protection against lethal SEB challenge in two D-galactosamine-sensitized murine models of SEB intoxication, i.e., the previously described i.m. challenge model and a new respiratory challenge model of mucosal SEB exposure. Efficacy correlated with the induction of high serum levels of anti-SEB IgG. In contrast, intranasal or i.m. immunization with toxoid in saline without proteosomes was not significantly protective in either challenge model. Proteosome-toxoid plus alum given i.m. also elicited more significant protection against respiratory challenge than the alum-adjuvanted toxoid alone. The capacity of proteosomes to enhance both i.m. and intranasal immunogenicity and efficacy of SEB toxoid indicates that testing such proteosome-SEB toxoid vaccines in the nonhuman primate aerosol challenge model of SEB intoxication prior to immunogenicity trials in humans is warranted. These data expand the applicability of the proteosome mucosal vaccine delivery system to protein toxoids and suggest that respiratory delivery of proteosome vaccines may be practical for enhancement of both mucosal and systemic immunity against toxic or infectious diseases.

Orally administered microencapsulated Bordetella pertussis fimbriae protect mice from B. pertussis respiratory infection

Fimbriae from Bordetella pertussis have been encapsulated in poly(lactide-co-glycolide) microparticles of a size appropriate for uptake by the immune inductive tissues of the gastrointestinal tract. Mice were immunized by oral gavage with a single dose of 10 micrograms of microencapsulated fimbriae. The resulting immune responses were compared with those resulting from intraperitoneal injection of mice with equivalent amounts of fimbriae absorbed onto alhydrogel. The examination of serum and mucosal secretions, collected over a 6-week period, for specific antifimbrial antibodies clearly demonstrated that only orally immunized animals mounted measurable immune responses in external secretions. Six weeks after immunization, all immunized animals were protected against intranasal challenge with live B. pertussis.