Enhancement of rotavirus immunogenicity by microencapsulation

Nasal delivery of PLG microparticle encapsulated defensin peptides adjuvanted gp41 antigen confers strong and long-lasting immunoprotective response against HIV-1

Defensins display immunostimulatory activities including a chemotactic effect for T lymphocytes/immature dendritic cells and secretion of pro-inflammatory cytokines suggest their role in bridging innate and adaptive immunity. We hypothesized whether defensins with separately emulsified HIV-1 immunogen would elicit peptide-specific systemic and mucosal antibody response in mice. The HIV-1 peptide alone in microsphere showed low peptide-specific antibody response in sera and different washes, while the presence of defensins markedly increased the antibody peak titre both in sera (102,400-409,600) (p < 0.05) and in washes (800-25,600) (p < 0.001). Defensins with HIV-1 peptide were showing 43.0-83.2% and 38.7-72.3% in vitro neutralization against laboratory isolates in serum and lavage samples, respectively, higher than HIV-1 peptide alone. Our findings may have implications in the development of new mucosal adjuvant for AIDS vaccination.

Improved Immunogenicity of Biodegradable Polymer Particles Entrapped Rotavirus Vaccine

Rotavirus (RV) entrapped in polylactide (PLA) and polylactide-coglycolide (PLGA) polymer particles were formulated and evaluated in mice for improved immunogenicity using oral, intranasal (IN), and intramuscular (IM) routes of administration. Microparticles of size ranges between 1 and 8 µm were prepared using double emulsion solvent evaporation technique. Stabilizers like mouse serum albumin, sucrose, and sodium bicarbonate that were used during particle formulation helped in minimizing the denaturation of the entrapped antigen. Immunization with 20 µg of antigen entrapped in polymeric particles through various routes of administration elicited measurable amount of antibody titer in mice. The immunoglobulin A (IgA) and immunoglobulin G (IgG) titer (≥4-fold rise between pre and post immunized sera) was analyzed by the use of enzyme-linked immunosorbent assay. PLGA encapsulated RV microparticles elicited better antibody response through IN route (90%) where as PLA encapsulated RV microparticles showed improved response when administrated through oral route (83.3%). Overall, the performance of IN route based immunization was significantly higher than oral and IM route ( p<0.001) with both the polymers. The results are of indication that, PLGA encapsulated RV microparticles have greater potential for vaccine formulation to combat rotavirus infection.

Microencapsulation of bacteriophage felix O1 into chitosan-alginate microspheres for oral delivery

This paper reports the development of microencapsulated bacteriophage Felix O1 for oral delivery using a chitosan-alginate-CaCl(2) system. In vitro studies were used to determine the effects of simulated gastric fluid (SGF) and bile salts on the viability of free and encapsulated phage. Free phage Felix O1 was found to be extremely sensitive to acidic environments and was not detectable after a 5-min exposure to pHs below 3.7. In contrast, the number of microencapsulated phage decreased by 0.67 log units only, even at pH 2.4, for the same period of incubation. The viable count of microencapsulated phage decreased only 2.58 log units during a 1-h exposure to SGF with pepsin at pH 2.4. After 3 h of incubation in 1 and 2% bile solutions, the free phage count decreased by 1.29 and 1.67 log units, respectively, while the viability of encapsulated phage was fully maintained. Encapsulated phage was completely released from the microspheres upon exposure to simulated intestinal fluid (pH 6.8) within 6 h. The encapsulated phage in wet microspheres retained full viability when stored at 4 degrees C for the duration of the testing period (6 weeks). With the use of trehalose as a stabilizing agent, the microencapsulated phage in dried form had a 12.6% survival rate after storage for 6 weeks. The current encapsulation technique enables a large proportion of bacteriophage Felix O1 to remain bioactive in a simulated gastrointestinal tract environment, which indicates that these microspheres may facilitate delivery of therapeutic phage to the gut.

Delivery systems and adjuvants for oral vaccines

The oral route is the ideal means of delivering prophylactic and therapeutic vaccines, offering significant advantages over systemic delivery. Most notably, oral delivery is associated with simple administration and improved safety. In addition, unlike systemic immunisation, oral delivery can induce mucosal immune responses. However, the oral route of vaccine delivery is the most difficult because of the numerous barriers posed by the gastrointestinal tract. To facilitate effective immunisation with peptide and protein vaccines, antigens must be protected, uptake enhanced and the innate immune response activated. Numerous delivery systems and adjuvants have been evaluated for oral vaccine delivery, including live vectors, inert particles and bacterial toxins. Although developments in oral vaccines have been disappointing so far, in terms of the generation of products, the availability of a range of novel delivery systems offers much greater hope for the future development of improved oral vaccines.

Determination of efficiency of attachment of biotinylated antibodies to avidin-linked, aqueous-based microcapsules by flow cytometry

We used flow cytometry to determine the percentage of aqueous-based microcapsules bearing antibodies specific for various antigen-presenting cells (APCs) within a given population of putative APC-specific microcapsules. Flow cytometry offers a high-throughput, rapid and simple method to analyze antibody binding to noncellular, nonspherical material.

Protective effects of oral microencapsulated Mycoplasma hyopneumoniae vaccine prepared by co-spray drying method

The efficacy of Mycoplasma hyopneumoniae oral vaccine was investigated in microsphere dosage form. A co-spray drying process was used to apply an encapsulating material, Eudragit L30 D-55, to microspheres containing Mycoplasma hyopneumoniae antigens. The microspheres were generally effective (>93%) with protein release at pH 7.4, but almost none were released at pH 1.2, for 3 hr in an in vitro dissolution test. An SPF-swine model was used to evaluate the effectiveness of the microspheres as an oral vaccine, and the related immune responses. The serum's systemic IgG against M. hyopneumoniae was evoked by ELISA analysis, after a 2nd immunization of all pigs. The vaccinated groups' mean lesion score was significantly lower after the Mycoplasma hyopneumoniae challenge than that of the nonvaccinated/challenged groups (P<0.05). This study strongly suggests that the oral microspheres vaccine prepared by a co-spray drying method can provide effective protection against M. hyopneumoniae infection in pigs.

Development of oral microencapsulated forms for delivering viral vaccines

Rapid development in biotechnology during the last decade has allowed novel ideas in the development of antiviral vaccines to be considered and provides interesting technological approaches to their realization. Designing of microencapsulated forms for delivering bacterial and viral antigens or antigenic complexes using biodegradable biopolymers is an important novel direction. This approach involves the production of polymeric spherical particles with a diameter of 1 microm to 3 mm, containing isolated viral antigens or whole viral particles. Microencapsulated antigens administered orally are protected from low pH values of the gastric juice, bile acids, their salts and proteolytic enzymes of the gastrointestinal tract. The ability to drastically potentiate the immune response to encapsulated antigens, together with the ability to penetrate into the intestinal and respiratory mucosae upon oral and tracheal administrations, respectively, with induction of local and systemic immune reactions are the special merits of such polymers. However, the majority of data on microencapsulated viral vaccines has so far been obtained in animal models, as well as a limited number of studies on the protective effect they elicit. Certain success in the development of vaccines against a number of human viral infections, such as hepatitis B, cytomegalovirus and rotavirus, gives hope to successful completion of this research. Presumably, such vaccines will be safe and innocuous, simple in administration and capable of inducing both the systemic and local immune responses at the primary portal of viral infection.

Induction of mucosal immune responses following enteric immunization with antigen delivered in alginate microspheres

Oral immunization is the most effective way of inducing immune responses in the intestinal tract. Biodegradable microspheres have been used extensively for the delivery of antigens to the Peyer's patches (PPs) within the gut-associated lymphoid tissue (GALT). We evaluated various formulations of alginate microspheres for their capacity to induce mucosal immune responses in vivo. Multiple intestinal "loops" each containing a single PP, were surgically prepared in lambs. We have previously showed that PP in individual intestinal loops function as independent sites for the induction of immune responses. This animal model provides a system for directly comparing different antigen formulations within the same animal. Individual intestinal loops were injected with a model antigen, porcine serum albumin (PSA) encapsulated in three different formulations of alginate micropsheres. Three weeks after immunization, PSA-specific immune responses were assayed with antibody secreting cell (ASC) ELISPOT, lymphocyte proliferative responses (LPRs), IFN-gamma production and antibody secreted into intestinal loops. PSA encapsulated in alginate micropsheres or in saline induced humoral immune responses as indicated by the presence of numerous ASC. However, PSA-specific T-cell responses (LPR and IFN-gamma production) were not induced.

In vivo and in vitro comparisons of spray-drying and solvent- evaporation preparation of microencapsulated Mycoplasma hyopneumoniae for use as an orally administered vaccine for pigs

OBJECTIVE

To evaluate the efficacy of an orally administered vaccine of Mycoplasma hyopneumoniae that was prepared by spray drying or solvent evaporation.

ANIMALS

Thirty 6-week-old, crossbred, specific-pathogen-free (SPF) pigs.

PROCEDURE

Pigs were randomly allocated into 5 groups and housed in an SPF facility. Pigs in 2 groups (groups AQ and CAP) were fed M hyopneumoniae enteric-coated vaccine on days 0, 10, and 20. A third group (group IM) received an IM injection of M hyopneumoniae vaccine with aluminium hydroxide as an adjuvant on days 0, 10, and 20. The last 2 groups (non-vaccinated-challenged [NV-C] and nonchallenged [NC]) were fed a sham treatment. All 24 pigs in groups AQ, CAFP IM, and NV-C were challenge exposed with 5 ml of a 10% pneumonic lung suspension administered on day 40 via intubation of the trachea. All pigs were slaughtered and the lungs removed and examined for lesions on day 68.

RESULTS

In vitro studies indicated that these 2 microencapsulation techniques formed an effective shell and protected mycoplasmal antigen from gastric acid. Results of inoculation and challenge tests indicated that microencapsulated M hyopneumoniae were sufficiently potent to induce an immune response and provide good protection.

CONCLUSIONS AND CLINICAL RELEVANCE

Orally administered microencapsulated M hyopneumoniae vaccines induced an immune response and reduced the severity of lung lesions in challenge-exposed pigs. Results suggest that this novel method can be applied to other antigens, because the spray-drying process yielded an orally administered M hyopneumoniae vaccine that induced a good immune response.

Approaches to development of microencapsulated form of the live measles vaccine

Development of delivery of antigens and antigenic complexes using microcapsules or microgranules made of pH-dependent polymers is one of several high priority directions of modern vaccinology. These polymers should protect the virus from acid gastric medium, dissolve or swell readily in weakly alkaline intestinal medium, in no way decrease the specific activities of viral antigens, promote their penetration into intestinal mucosa, and possess adjuvant properties. The State Research Center Vector and "DELSI" are developing the technology for production of microencapsulated form of the live measles vaccine L-16 viruses for oral administration. The authors have so far succeeded in selecting and characterizing a number of polymers that are promising for microencapsulated vaccine and for testing of virus titers and immune response of experimental samples of a new vaccine in animals. Control of samples in guinea pigs demonstrated that the encapsulated measles virus retained its specific activity and capability for inducing immune response in experimental animals.

Induction of systemic and mucosal immune response in cattle by intranasal administration of pig serum albumin in alginate microparticles

Biodegradable microparticles are an efficient mucosal delivery system that protect antigens from the harsh mucosal environment and facilitate their uptake by M cells at the epithelium of mucosal-associated lymphoid tissue. In this study, we determined the systemic and mucosal immune response in calves following intranasal and oral immunization with pig serum albumin (PSA) encapsulated in alginate microparticles. The size of the particles ranged from 1 to 50 microm in diameter, with 95% of the particles being smaller than 5 microm. High levels of anti-PSA IgG1 antibodies were found in the serum, nasal secretions, and to a less extent in saliva of calves vaccinated intranasally, but not orally, with PSA-microparticles. There was no significant increase of PSA-specific IgA. A weak lymphocyte proliferative immune response was observed in peripheral blood mononuclear cells (PBMCs), and few anti-PSA antibody-secreting cells (ASC) were detected in the blood of calves immunized intranasally. The combined systemic and mucosal response observed in intranasally immunized animals may be attributed to the wide variation in the size of the alginate microparticles, with smaller particles translocating to regional lymph nodes and inducing a systemic immune response, and larger particles being retained in the NALT and inducing a mucosal immune response. The procedure presented here may be useful as an intranasal vaccine against respiratory diseases in cattle.

Comparison of poly(acryl starch) and poly(lactide-co-glycolide) microspheres as drug delivery system for a rotavirus vaccine

Drug delivery systems allowing controlled release of antigen are of particular interest in the development of vaccines. We have compared poly(acrylic starch) microspheres (PAS) and poly(lactide-co-glycolide) microspheres (PLG) as drug delivery systems for a rotavirus vaccine. The polymers are both biodegradable but have different degradation mechanisms and antigen release profiles. PAS are enzymatically degraded and have a continuous fast antigen release rate compared to the hydrolytically degraded PLG which release the incorporated antigen in a pulsatile manner. In this study mice were immunised intramuscularly and orally on three occasions with formalin-inactivated rotavirus (FRRV) incorporated in PAS and PLG and with FFRV alone. Serum and faeces samples were collected and analysed by ELISA for rotavirus specific IgG and IgA antibodies. A neutralising assay was also conducted on both serum and faeces antibodies. The two different polymer drug delivery systems induced different immune responses depending on administration route. PAS elicited significant antibody levels and neutralising effect after oral administration while PLG showed high antibody levels after intramuscular administration. The immune response appears to be dependent on the differences in antigen release and degradation mechanism for the two polymer systems.

A quantitative luminescence assay for measuring cell uptake of aqueous-based microcapsules in vitro

We recently developed a system of microencapsulation consisting of aqueous-based polymers (e.g. alginate) and aqueous amines (e.g. spermine). We found that microencapsulation enhanced virus-specific protective immune responses. In addition, we found that microencapsulation may enhance virus-specific immune responses by selecting for antigen-presenting cells (APC) that are more efficient at processing and presenting viral antigens than those involved after natural infection. To determine the intracellular trafficking patterns and fate of microcapsules within APC, we developed a luminescence assay that permits the determination of specific quantities of proteins introduced into cells by microcapsules. We found that the time-dependent uptake of horseradish peroxidase (HRP)-labeled microcapsules was accurately detected in lysates of peritoneal exudate cells using luminol. The amplitude of HRP-catalyzed chemiluminescence in cell lysates correlated with the capture efficiency and retention kinetics of HRP in three different microcapsule preparations. HRP was most efficiently captured and retained by linking biotinylated HRP to microcapsulses chemically modified at the amine moiety with egg avidin. This preparation yielded more accurate and sensitive quantitation of HRP contained within cells than preparations capturing HRP or HRP-conjugated goat antibody into the microcapsular matrix by ionic interactions.

Water-based microsphere delivery system for proteins

This paper describes formulation of a model protein, horseradish peroxidase (HRP), in a water based microcapsule delivery system and demonstrates the utility of this delivery system for proteins. Aqueous solutions (1 mg/mL) of the enzyme were separately blended with aqueous solutions of the neutral sodium salt of the anionic polymer iota carrageenan (0.6 mM in repeat unit). These blends were instilled as uniform microdroplets into aqueous solutions of a series of eleven mono-, di-, or oligo-amines (as neutral hydrochloride or acetate salts). Essentially instantaneous salt exchange interaction of the sodium salt of anionic polymer with amine hydrochloride resulted in formation of microparticles of amine/polymer complex. The enzyme was captured in the resulting capsules. The particles were washed by repeated centrifugation and resuspension in water and their particle size distribution was determined. HRP in washed pelleted microspheres was analyzed for fragmentation/aggregation by SDS-PAGE and size exclusion chromatography, for unfolding by fluorescence spectroscopy, and for specific enzymatic activity, capture efficiency and release studies by absorbance spectroscopy. Dependent on amine employed, capture efficiencies ranged from 1 to 72%. Encapsulation produced no adverse effect on protein size as no molecular fragments or aggregates were visible below or above 44 kDa. The tryptophan fluorescence spectrum of the protein did not change after encapsulation indicating no conformational change in tertiary structure. There was an apparent substrate diffusion related reduction in activity of encapsulated HRP, but almost 100% of activity was recovered on lysis of the capsules. It is concluded that water based charged film encapsulation used as a drug delivery system for proteins does not alter structural conformation or specific activity of the model protein tested and provides protein release at a constant rate.

Rotavirus infections: guidelines for treatment and prevention

The classification of rotaviruses as well as the pathogenesis and the diagnosis of rotavirus infections are briefly reviewed. Treatment of rotavirus disease consists mainly of oral or intravenous rehydration, using World Health Organization-recommended oral rehydration solutions or lactated Ringer's solutions, respectively. Specific antivirals have been tried in animal models but are not used for human treatment at present. The epidemiology of rotaviruses is complex as at any one time and in any geographical area different types co-circulate. The development of rotavirus candidate vaccines is reviewed, one of which, the tetravalent, rhesus rotavirus-based human reassortant vaccine, was licensed for universal use in the US in 1998. Its implementation requires careful surveillance of co-circulating rotavirus types (molecular epidemiology) as well as of any potential adverse effects not previously detected.

Polynucleotide vaccines: potential for inducing immunity in animals

Polynucleotide immunization has been described as the Third Revolution in Vaccinology. Early studies suggest the potential benefits of this form of immunization including: long-lived immunity, a broad-spectrum of immune responses (both cell mediated immunity, and humoral responses) and the simultaneous induction of immunity to a variety of pathogens through the use of multivalent vaccines. Using a murine model, we studied methods to enhance and direct the immune response to polynucleotide vaccines. We demonstrated the ability to modulate the magnitude and direction of the immune response by co-administration of plasmid encoded cytokines and antigen. Also, we clearly demonstrated that the cellular components (cytosolic, membrane-anchored, or extracellular) to which the expressed antigen is delivered determines the types of immune responses induced. Since induction of immunity at mucosal surfaces (route of entry for many pathogens) is critical to prevent infection, various methods of delivering polynucleotide vaccines to mucosal surfaces have been attempted and are described. Expansion of studies in various species, using natural models, should be extremely helpful in demonstrating the universality of this approach to immunization and more importantly, accurately identify parameters that are critical for the development of protective immunity.

Novel approaches for oral delivery of macromolecules

Traditional forms of administrations of nonabsorbable drugs and peptides often rely on their parenteral injection, since the intestinal epithelium is poorly permeable to these therapeutical agents. A number of innovative drug delivery approaches have been recently developed, including the drug entrapment within small vesicles or their passage through the intestinal paracellular pathway. Zonula occludens toxin, a recently discovered protein elaborated by Vibrio cholerae, provided tools to gain more insights on the pathophysiology of the regulation of intestinal permeability through the paracellular pathway and to develop alternative approaches for the oral delivery of drugs and macromolecules normally not absorbed through the intestine.

Influence of dextran molecular weight on capture in and release from decylamine carboxymethylcellulose capsules

A series of dextran molecular weight markers were encapsulated in decylamine carboxymethylcellulose microcapsules to serve as probes of capsule retentivity. The capsules were prepared by allowing microdrops of aqueous sodium carboxymethylcellulose to fall into aqueous decylamine acetate solution. Salt exchange reaction at the droplet pseudointerface resulted in self-assembling films which essentially instantaneously enclosed the droplets. Concentrations of anionic polymer were varied in the range from 1-3%. Chromophore-bearing dextrans were incorporated into these capsules by blending the dextrans with the carboxymethylcellulose prior to the encapsulation step. Four dextrans of differing (light scattering) molecular weights were used: 2 x 10(6), 6 x 10(5), 7 x 10(4), and 1.9 x 10(4) amu. The mass balance of dextran retained in the capsules, released on washing the capsules or which escaped encapsulation was determined spectrophotometrically. To measure total dextran in a population of washed capsules, the capsules were lysed in a 0.3 M solution of sodium chloride. To monitor dextran release, washed capsules were suspended in water and dextran concentration in the supernatant was measured. Encapsulation efficiency exceeded 80% for high molecular weight dextran but was lower with the smaller dextrans.

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.

Effect of water-based microencapsulation on protection against EDIM rotavirus challenge in mice

We determined the capacity of microcapsules formed by the combination of sodium alginate, an aqueous anionic polymer, and spermine hydrochloride, an aqueous cationic amine, to enhance protection against rotavirus challenge in mice. Adult BALB/c mice were orally inoculated with either free or microencapsulated rotavirus (simian rotavirus strain RRV) and challenged 6 or 16 weeks later with murine rotavirus strain EDIM. Virus-specific humoral immune responses were determined at the time of challenge and 4 days after challenge by intestinal fragment culture. We found that spermine-alginate microcapsules enhanced protection against challenge 16 weeks after immunization but not 6 weeks after immunization. Quantities of virus-specific immunoglobulin A produced by small intestinal lamina propria lymphocytes were correlated with the degree of protection against challenge afforded by spermine-alginate microcapsules. Possible mechanisms by which microcapsules enhance protection against rotavirus challenge are discussed.

Innovative strategies for the oral delivery of drugs and peptides

Conventional forms of administration for nonabsorbable drugs and peptides often rely on parenteral injection, because the intestinal epithelium represents a major barrier to the oral absorption of these therapeutic agents. Recently, a number of innovative drug-delivery approaches have been developed, including entrapment within small vesicles and passage through the space between adjacent intestinal cells. This article reviews some of the most promising techniques currently available for oral delivery and their possible practical applications for the delivery of vaccines and drugs for the treatment of clinical conditions that require frequent, chronic parenteral administration.

Prospects for vaccines against rotaviruses

Candidate vaccines against rotavirus-caused diarrhoea have been under development for more than ten years. Recent research has helped to identify virological and immunological parameters which are most likely to be correlates of protection from rotavirus infection and disease. Large double-blind, placebo-controlled trials in the United States and Venezuela have resulted in successful protection from severe disease and dehydration after immunisation with live-attenuated rhesus rotavirus-based monovalent and tetravalent vaccine candidates. The tetravalent vaccine is now submitted for regulatory approval in the United States. The anticipated widespread use of such a vaccine will need careful safety and effectiveness surveillance as the enormous diversity of rotavirus antigenicity may affect efficacy in different geographical regions. To proceed from licensure to reduction of disease a series of goals must be achieved: the vaccine must be recommended by major immunisation advisory committees, be financed in both the public and private sectors, be integrated into existing vaccination schedules, be promoted, find parental acceptance and achieve a high level of coverage. Copyright 1998 John Wiley & Sons, Ltd.

Aqueous-based microcapsules are detected primarily in gut-associated dendritic cells after oral inoculation of mice

We previously found that aqueous-based microencapsulation enhanced virus-specific humoral immune responses after oral inoculation of mice. However, the mechanism by which microencapsulation enhances immunogenicity remains unclear. We found that spermine-alginate microcapsules were detected primarily in gut-associated dendritic cells (i.e. CD11c/CD18+, Ia+, CD11b-, CD45R-) after oral inoculation of adult mice. Microencapsulation may enhance immunogenicity by involving antigen presenting cells which are more efficient than those recruited during natural infection.

Effect of microencapsulation on immunogenicity of a bovine herpes virus glycoprotein and inactivated influenza virus in mice

We previously found that aqueous-based spermine-alginate or spermine-chondroitin sulfate microcapsules enhanced rotavirus-specific humoral immune responses after intramuscular inoculation of mice. To extend our observations with whole, infectious rotavirus to vaccine strategies which include inactivated virus and purified proteins, we determined the capacity of aqueous-based microcapsules to enhance virus-specific immune responses to bovine herpes virus type 1 glycoprotein D (BHV-1-gD) or ether-treated influenza virus. We found that spermine-alginate microcapsules decreased the quantity of BHV-1-gD necessary to induce protein-specific antibodies about 5000-fold. However, spermine-alginate microcapsules did not enhance influenza virus-specific antibody responses. Microcapsules composed of spermine-chondroitin sulfate did not enhance either BHV-1-gD or influenza virus-specific immune responses. Possible mechanisms of enhancement of virus-specific antibody responses by microencapsulation are discussed.

Rotavirus virus-like particles administered mucosally induce protective immunity

We have evaluated the immunogenicity and protective efficacy of rotavirus subunit vaccines administered by mucosal routes. Virus-like particles (VLPs) produced by self-assembly of individual rotavirus structural proteins coexpressed by baculovirus recombinants in insect cells were the subunit vaccine tested. We first compared the immunogenicities and protective efficacies of VLPs containing VP2 and VP6 (2/6-VLPs) and G3 2/6/7-VLPs mixed with cholera toxin and administered by oral and intranasal routes in the adult mouse model of rotavirus infection. VLPs administered orally induced serum antibody and intestinal immunoglobulin A (IgA) and IgG. The highest oral dose (100 microg) of VLPs induced protection from rotavirus challenge (> or = 50% reduction in virus shedding) in 50% of the mice. VLPs administered intranasally induced higher serum and intestinal antibody responses than VLPs administered orally. All mice receiving VLPs intranasally were protected from challenge; no virus was shed after challenge. Since there was no difference in immunogenicity or protective efficacy between 2/6- and 2/6/7-VLPs, protection was achieved without inclusion of the neutralization antigens VP7 and VP4. We also tested the immunogenicities and protective efficacies of 2/6-VLPs administered intranasally without the addition of cholera toxin. 2/6-VLPs administered intranasally without cholera toxin induced lower serum and intestinal antibody titers than 2/6-VLPs administered with cholera toxin. The highest dose (100 microg) of 2/6-VLPs administered intranasally without cholera toxin resulted in a mean reduction in shedding of 38%. When cholera toxin was added, higher levels of protection were achieved with 10-fold less immunogen. VLPs administered mucosally offer a promising, safe, nonreplicating vaccine for rotavirus.

Retention of trypsin activity in spermine alginate microcapsules

We have previously shown virus particles encapsulated in aqueous spermine alginate constructs retain immunogenicity and infectivity both in vitro and in vivo. However, because virions are complex structures with multiple reinforcing components, it was uncertain if isolated single proteins would retain functional integrity when similarly encapsulated. To examine this question trypsin, used as a model protein, was blended with aqueous sodium alginate and the blend was dispersed as fine droplets in aqueous spermine hydrochloride to generate self-assembling, trypsin-containing microcapsules. Trypsin was assayed spectrophotometrically for retention of enzymatic activity using N-alpha-p-tosyl-L-arginine methyl ester as substrate. Neither of the encapsulating reagents alone inhibited enzyme activity. Enzyme that escaped capture was assayed directly in the manufacturing supernatant. In mass balance studies we found that about 20-30% of activity was retained in intact capsules with the remainder resident in the aqueous manufacturing supernatant and washes. However, we found that the capsule wall appeared to inhibit enzyme activity by retarding substrate diffusion into and product diffusion out from the capsules, as evidenced by an increase in activity on lysis. Thus, it is clear that a single protein, as represented by trypsin, can retain functional integrity when encapsulated in this all aqueous system.

Orally administered microencapsulated reovirus can bypass suckled, neutralizing maternal antibody that inhibits active immunization of neonates

Purified reovirus serotype 1, encapsulated in biodegradable aqueous microcapsules, was found to bypass maternal antibody passively transferred by suckling to neonates. Genetically identical, immunocompetent F1 scid/+ mice were generated by the reciprocal crosses of C.B17 scid/scid and normal congenic +/+ adult mice. The immunocompetent +/+ dams were either orally infected with reovirus prior to mating or not. Thus, these immunocompetent F1 pups developed either in the absence or in presence of passively transferred maternal immunity. The F1 mice were orally immunized on day 10 with either live virus, microencapsulated reovirus, or empty microcapsules plus live virus. The immune responses were assessed in the neonatal gut-associated lymphoid tissues (GALT). Examination of reovirus specific immunoglobulin A in the serum and GALT, taken on days 7, 14, and 21 postimmunization, clearly demonstrated that microencapsulated reovirus could bypass the normal effect of maternal antibodies, passively acquired by suckling, to inhibit active priming of neonates by oral route. These observations seem relevant to the development of efficacious oral vaccines that also allow passive, protective immunity via suckled maternal antibodies while permitting active oral immunization of neonates.

Controlled delivery of antigens and adjuvants in vaccine development

Advances in the understanding of the pathogenesis of infectious diseases and cancer immunology have inspired many new approaches to vaccine development. Many subunit antigens and peptides that are effective for vaccination have been discovered. These subunit antigens in tum stimulate synthesis of effective adjuvants to enhance their immunogenicity. Controlled-release technology offers the potential of further improving the efficacy of conventional vaccine formulations by optimizing the temporal and spatial presentation of the-antigens and adjuvants to the immune system. The combination of sustained release and depot effect may also reduce the amount of antigens or adjuvants needed and eliminate the booster shots that are necessary for the success of many vaccinations. This review examines the contribution controlled release technology can make in various areas of vaccination, with an emphasis on tumor vaccines.

Aqueous-based microencapsulation enhances virus-specific humoral immune responses in mice after parenteral inoculation

Vaccines are commonly administered by the parenteral route. Therefore, adjuvant strategies which include parenteral immunization may improve the efficacy of a number of current vaccines. The capacity of aqueous-based microencapsulation to enhance virus-specific IgG responses in mice inoculated intramuscularly with small quantities of antigen was evaluated. Mice were inoculated with either 10(4), 10(3), or 10(2) p.f.u. of microencapsulated rotavirus (bovine strain WC3), placebo microcapsules plus free virus, or virus alone. Mice were subsequently bled 1, 2, 4, 6, and 9 months after inoculation. Microencapsulation of rotavirus enhanced virus-specific humoral immune responses. In addition, virus-containing microcapsules composed of spermine-chondroitin sulfate induced levels of virus-specific antibodies greater than those found after inoculation with virus-containing microcapsules composed of spermine-alginate. Mechanisms by which microencapsulation may enhance virus-specific humoral immunity are discussed.