Antigen-specific increases in the number of splenocytes expressing MHC class II molecules following restimulation with antigen in various physical forms

Adjuvants modulating mucosal immune responses or directing systemic responses towards the mucosa

In developing veterinary mucosal vaccines and vaccination strategies, mucosal adjuvants are one of the key players for inducing protective immune responses. Most of the mucosal adjuvants seem to exert their effect via binding to a receptor/or target cells and these properties were used to classify the mucosal adjuvants reviewed in the present paper: (1) ganglioside receptor-binding toxins (cholera toxin, LT enterotoxin, their B subunits and mutants); (2) surface immunoglobulin binding complex CTA1-DD; (3) TLR4 binding lipopolysaccharide; (4) TLR2-binding muramyl dipeptide; (5) Mannose receptor-binding mannan; (6) Dectin-1-binding ss 1,3/1,6 glucans; (7) TLR9-binding CpG-oligodeoxynucleotides; (8) Cytokines and chemokines; (9) Antigen-presenting cell targeting ISCOMATRIX and ISCOM. In addition, attention is given to two adjuvants able to prime the mucosal immune system following a systemic immunization, namely 1alpha, 25(OH)2D3 and cholera toxin.

Review of novel particulate antigen delivery systems with special focus on treatment of type I allergy

For the treatment of infectious diseases, cancer and allergy, the directed induction of an appropriate immune response is the ultimate goal. Therefore, with the development of pure, often very small proteins, peptides or DNA by molecular biology techniques, the research for suitable adjuvants or delivery systems became increasingly important. Particle formulations are made of a variety of materials, including lipids, proteins or amino acids, polysaccharides, polyacrylic substances or organic acids. Microparticles serve as vehicles and provide a depot for the entrapped or coupled antigen. The release occurs in a pulsatile or continuous manner, a feature, which is well controllable for many particulate systems. Particles attract antigen presenting cells to the administration site, thereby guaranteeing the efficient presentation of the antigen to the immune system. Importantly, particles also protect the entrapped substance. This is especially necessary after oral application to avoid gastric or tryptic breakdown. In this article, the design and construction of different antigen delivery systems and their immune effects, with special focus on the suitability for allergy treatment, are discussed.

Current status and potential application of ISCOMs in veterinary medicine

The immune stimulating complex (ISCOM) is a 40 nm nanoparticle used as a delivery system for vaccine antigens, targeting the immune system both after parenteral and mucosal administration. The ISCOM is made up of saponin, lipids and antigen usually held together by hydrophobic interaction between these three components. The compulsory elements to form the ISCOM structure are cholesterol and saponin. When the antigen is omitted the ISCOM-MATRIX is formed. There are a number of saponins that can form ISCOMs, and many other substances (including antigens, targeting and immuno-modulating molecules) can be incorporated into the ISCOM provided they are hydrophobic or rendered to be hydrophobic. Thus, it is possible to create ISCOM particles with different properties. After parenteral immunisation of the ISCOM, the T cell response is first detected in the draining lymph node. Subsequently, the T cell response is localised to the spleen, while the B cell response is first found both in the draining lymph nodes and in the spleen. Up to 50 days later, the majority of the antibody producing cells is found in the bone marrow (BM). In contrast, antigens that have been adjuvanted in an oil emulsion, limit the T cell response to the draining lymph nodes while the B cell response is found in the draining lymph nodes and spleen, but not in the BM. The ISCOM efficiently evokes CD8+, MHC class 1 restricted T cell response. The deposit of antigens both to the endosomal vesicles and to the cytosol of antigen presenting cells (APCs) explains why both T helper cells (vesicles) and cytotoxic T lymphocytes (cytosol) are efficiently induced by ISCOMs. The T helper (Th) cell response is balanced in the sense that both Th1 and Th2 cells are induced. Prominent IL-12 production by cells in the innate system is a characteristic reaction induced by ISCOMs, promoting the development of a strong Th1 response. After mucosal administration by the intranasal or the intestinal routes, the ISCOM induces strong specific mucosal IgA responses in local and remote mucosal surfaces. Also T cell responses are evoked by the mucosal administration. A large number of experimental ISCOM vaccines have been tested and protection has been induced against a number of pathogens in various species including chronic and persistent infections exemplified by human immune deficiency virus 1 (HIV-1), and 2 (HIV-2) and simian immune deficiency virus (SIV) in primates, and various herpes virus infections in several species. In contrast to a conventional rabies virus vaccine the ISCOM rabies formulation protected mice after exposure to the virulent virus. Recently, experimental ISCOM vaccines were shown to efficiently induce immune response in newborns of murine and bovine species in the presence of maternal antibodies, while conventional vaccines have failed. ISCOM vaccines are on the market for horses and cattle and several other ISCOM vaccines are under development. Since the ISCOM and the ISCOM-MATRIX can be blended with live attenuated vaccine antigens without hampering the proliferation of the live vaccine antigens, it opens the possibility to use the ISCOM adjuvant system in a mixture of live and killed vaccine antigens.

Immunostimulating complexes (ISCOMs) for nasal vaccination

The immunostimulating complex (ISCOM) is documented as a strong adjuvant and delivery system for parenteral immunization. Its effectiveness for mucosal immunization has also been proven with various incorporated antigens. Lövgren et al. were the first to demonstrate the capacity of influenza virus ISCOMs to induce mucosal immune response and protection after one comparatively low nasal dose. Further studies show that similar to Cholera toxin (CT) and Escherichia coli heat-labile toxin (LT), ISCOMs break immunological tolerance and exert strong mucosal adjuvant activity, resulting in secretory IgA and systemic immune responses. Striking is the capacity of ISCOMs to induce CTL response also after nasal administration. In contrast to CT, ISCOMs initiate mucosal as well as systemic immune responses in an IL-12 dependent manner but independently of IL-4. The recombinant B subunit of cholera toxin (rCTB) was incorporated in the same ISCOM particle to explore symbiotic effects. The IgA response to rCTB in lungs was increased 100-fold when rCTB was administered nasally in ISCOMs and more than 10-fold in the remote mucosa of the genital tract. An enhanced IgA response to a passenger antigen OVA was recorded in the remote genital tract. After i.n. administration of the envelope proteins of respiratory syncytial virus in ISCOMs, high serum antibodies were induced, almost at the same levels as those following parenteral immunization and potent IgA responses were also evoked both at the local respiratory mucosa, and in the cases tested at the distant mucosae of the genital and intestinal tracts. Similar results have also been recorded with ISCOMs containing envelope proteins from Herpes simplex virus, Influenza virus and Mycoplasma mycoides. The mucosal targeting property of envelope proteins of RSV was utilized in an HIV-gp120 RSV ISCOM formulation. After nasal administration an enhanced mucosal IgA response to gp120 was observed in the female reproductive tract. In general, antigens derived from envelope viruses or cell membranes incorporated into ISCOMs retain their biological activity and conformation, encompassing the mucosal targeting and virus neutralizing properties.

Immunomodulation by iscoms, immune stimulating complexes

The iscom is a uniform stable complex consisting of cholesterol, phospholipid, adjuvant-active saponin, and antigen. The iscom matrix is a particulate complex with identical composition, shape, and morphology, but lacking the incorporated antigen. The assembly of the complex is based on hydrophobic interactions, but antigens that are not hydrophobic can be conjugated with a hydrophobic tail or hidden hydrophobic regions can be exposed, e.g., by acid treatment, to facilitate the incorporation into iscoms. The functional aspects of iscoms are described emphasizing immunomodulation in mouse models. Iscoms prominently enhance the antigen targeting, uptake, and activity of antigen presenting cells including dendritic and B cells and macrophages resulting in the production of proinflammatory cytokines, above all interleukin (IL)-1, IL-6, and IL-12. The expression of costimulatory molecules major histocompatibility complex (MHC) class II, B7.1 and B7.2, is also enhanced. The latter partly explains why the iscom is an efficient adjuvant for elderly mice. Iscoms enhance the Th1 type of response with increased production of IL-2 and interferon gamma. However, with some antigens and particularly in monkeys immunized with HIV iscoms, the production of IL-4 was enhanced. IL-4, IL-2, and interferon gamma (IFNgamma) together with the beta chemokines MIP-1alpha and MIP-1beta correlated with protection against challenge infection with a chimeric virus (simian immunodeficiency virus-human immunodeficiency virus). Iscoms were also shown to induce a potent immune response in the newborn and to be an efficient delivery system for mucosal administration. Technical information is given about formulation of iscoms and about handling of antigens to optimize their incorporation into iscoms.

Internalization of iscom-borne antigens and presentation under MHC class I or class II restriction

Exogenous nonreplicating antigens (Ag) incorporated into immunostimulating complexes (iscoms) induce CTL responses under MHC class I restriction. A requirement for inducing CTL responses is that the Ag is delivered to the cytosol of antigen-presenting cells (APC), a route restricted to endogenously produced Ag. To investigate the mechanisms by which iscoms elicit MHC class I-restricted responses, the intracellular distribution of influenza virus envelope proteins incorporated in iscoms (flu-iscoms) or in micelles (flumicelles) was studied in vitro using murine peritoneal cells (PEC). Ultrathin sections of cells pulsed with biotinylated flu-iscoms or flu-micelles were analyzed by electron microscopy after detection of the biotin label by reaction with streptavidin-gold. PEC pulsed with flu-iscoms showed a pattern of scattered gold particles distributed in clear and dense vesicles as well as in the intracellular space but not associated with organelles. In cells pulsed with flu-micelles, Ag was also detected in most cellular compartments but at a considerably lower concentration. The intracellular distribution of particulate Ag in iscom or micelle form was confirmed by lysis and differential centrifugation of Ag-pulsed APC. Furthermore, P815 cells pulsed with flu-iscoms were lysed by specific immune effectors showing that the iscom-Ag was processed and presented by class I-expressing APC. Flu-iscoms were internalized about 50-fold more efficiently than ovalbumin iscoms (ovaiscoms) suggesting that the nature of the protein and/or the presence of cellular receptors are important factors influencing the capacity of APC to take up iscom-borne proteins. PEC accounted for the most active internalization of iscom-borne Ag, although splenic dendritic cells and B cells also took up fluiscoms with remarkable efficiency.

Effect of ethanol on B cell expression of major histocompatibility class II proteins in immunized mice

Acute or chronic exposure to ethanol (EtOH), as well as other stimuli that induce a neuroendocrine stress response, can decrease the expression of MHC class II proteins (immune-associated antigens, Ia) on B cells and macrophages. In a mouse model for binge drinking, it has been shown that this decrease is caused by EtOH-induced increases in endogenous glucocorticoids. Decreased Ia expression would be expected to suppress T-dependent humoral responses, and such suppression has been noted in our model. However, it has been reported that activated B cells are much less susceptible to glucocorticoid-induced decreases in Ia expression than are resting B cells. Thus, it is not clear that the decreased Ia observed in our previous studies with non-immunized mice could account for decreased humoral responses, because it has not been directly determined that decreased Ia expression occurs in immunized mice. To examine this issue, splenocytes from mice immunized with sheep erythrocytes were studied by flow cytometry. Mice were treated with EtOH by gavage and immunized 12 h later, because our previous results indicate that this produces maximal suppression of the humoral response. In immunized mice, EtOH decreased Ia expression on B cells at 6 and 12 h after immunization, but not at 24 or 74 h. In a dose-response study, a substantial decrease in Ia expression on B cells was observed at an EtOH dosage of 6.0 or 7.0 g/kg. Thus, decreased Ia expression is a potential mechanism for EtOH-induced suppression of the humoral response. A glucocorticoid antagonist (RU 486) partially blocked the EtOH-induced decrease in Ia expression, suggesting that glucocorticoids are involved in the reduction of Ia expression in immunized mice. Direct administration of corticosterone to produce blood levels comparable to those noted in EtOH-treated mice did not significantly decrease Ia expression, but Ia expression tended to be lower in mice treated with corticosterone. Taken together, these results indicate that glucocorticoids play some role in decreasing Ia expression in immunized mice, but they are less important than in non-immunized mice.

Kinetics, localization and cytokine profile of T cell responses to immune stimulating complexes (iscoms) containing human influenza virus envelope glycoproteins

Immune stimulating complexes (iscoms) are 40 nm particles combining adjuvant-active Quillaja saponins and multimeric presentation of antigens. The distribution in mice of influenza virus iscoms and the resulting T cell responses in the lymph nodes (LN) and spleen were characterized. After a single subcutaneous injection, iscoms were delivered to the draining LN where they induced a transient population of LN cells which responded with proliferation and secretion of interleukin-2 (IL-2), gamma-interferon (IFN-gamma) and interleukin-4 (IL-4) after restimulation. The response in the spleen developed more slowly, sustained for 12 weeks and was characterized by cells producing in particular IL-2 and IFN-gamma but also IL-4. A booster resulted in a dramatic enhancement of the production of IFN-gamma, indicating that iscoms efficiently recruit cells with Th1 properties. Comparisons of T cell responses to iscoms and to influenza virus antigen in Freund's complete adjuvant demonstrate that these adjuvants affect both the localization and cytokine profile of T cell responses.

Iscoms in parasitological research

During the history of vaccine development, a number of adjuvants and adjuvant formulations have been tested and evaluated for their ability to increase the immunogenicity of different antigens. In this review, Anna Lundén, Karin Lövgren Bengtsson, Anders Sjölander and Arvid Uggla focus on iscoms (immune stimulating complexes), their characteristics and applications to different types of parasitic antigens.

Adjuvant activity of iscoms; effect of ratio and co-incorporation of antigen and adjuvant

We have studied the importance of co-incorporation of antigen and adjuvant in iscoms and the effects of different ratios of adjuvant and antigen in the iscom particles. Immune responses to influenza virus antigens (flu-Ag) in iscoms were compared to those induced by flu-Ag mixed with iscom-matrix, i.e. antigen and adjuvant delivered in separate packages. Higher doses of Quil A were required with iscom-matrix to induce strong immune responses compared to iscoms containing the same amount of antigen. The immunogenic properties of iscoms were affected by the ratio between antigen and adjuvant in the particles. Both iscoms and flu-Ag mixed with iscom-matrix induced antigen-specific antibodies with similar IgG subclass distribution and activated spleen cells producing high levels of IL-2 and IFN-gamma in vitro.

Antigen presentation by naive macrophages, dendritic cells and B cells to primed T lymphocytes and their cytokine production following exposure to immunostimulating complexes

Influenza virus envelope proteins incorporated into immunostimulating complexes (iscoms) are taken up and processed by various kinds of antigen-presenting cells (APC), encompassing peritoneal cells (PEC), unfractionated splenocytes, splenic dendritic cells (DC) or B cells. The iscom-pulsed naive APC stimulated primed T cells to proliferate and produce cytokine in vitro. In contrast, only DC and B cells pulsed with the same antigen (Ag) in the micelle form functioned as accessory cells stimulating the primed T cells to proliferate and produce cytokine. In general, iscoms were better inducers of cell proliferation than micelles. Iscoms stimulated more secretion of IL-2 and interferon-gamma (IFN-gamma) than the micelles, but both antigenic forms stimulated secretion of IL-4. DC and B cells pulsed with iscoms stimulated most efficiently the secretion of IL-2 and IFN-gamma. DC were superior to the other APC in stimulating primed T cells to secrete IFN-gamma. On the other hand, micelles stimulated more efficiently than iscoms splenic T cells from micelle-primed as well as iscom-primed mice to secrete IL-10. These data indicate that influenza virus envelope proteins incorporated in iscoms stimulate a broad T cell response, possibly emphasizing a Th1 type of response. The same Ag in a micelle form induce a more prominent Th2 type of T cell response. The results indicate that the administration of an Ag in an adjuvant formulation can superimpose a different cytokine profile on the immune response than that induced by the protein Ag alone.

Protection of mice against an influenza virus infection by oral vaccination with viral nucleoprotein incorporated into immunostimulating complexes

Influenza A virus nucleoprotein (NP) was integrated into immunostimulating complexes (ISCOMs) after attachment of bacterial lipopolysaccharide to the antigen. Oral immunization with these NP-ISCOMs protected mice fully against an otherwise lethal challenge infection with an unrelated influenza virus subtype without the appearance of severe clinical signs or extensive pathological lesions in the lungs. Mice immunized with analogous bovine serum albumine-incorporated ISCOMs all died. After oral immunization, high titers of NP-specific antibodies, particularly IgA, could be detected in the bronchoalveolar fluid and in the blood serum. No cytotoxic lymphocytes could be demonstrated in the spleens or the lungs of vaccinated mice, and no anti-NP antibody-dependent cytolysis of infected host cells was mediated by complement or in the form of an antibody-dependent cell cytotoxicity. However, a vigorous delayed-type hypersensitivity reaction was produced after probing vaccinated animals with purified NP. No comparable protective immunity or antibody response was induced by a strictly intragastric administration of NP-ISCOMs. It appears, therefore, that the general and local immune response in the lungs was primarily stimulated through contact of NP-ISCOMs with the mucous membrane of the oro-pharyngeal cavity and that cytotoxic effects did not play a major role for the establishment of the protective immunity. Partial protection against a lethal challenge was observed in chickens immunized with NP-ISCOMs in the drinking water.

The induction of cell-associated and secreted IL-1 by iscoms, matrix or micelles in murine splenic cells

The kinetics of the expression of membrane-associated IL-1 (mIL-1) and soluble IL-1 (sIL-1) was studied in in vitro stimulated spleen cells from non-primed mice or from mice primed with influenza virus antigens incorporated in the immuno-stimulating complexes (iscoms) or as micelles. Matrix, which is the carrier structure for the antigens in the iscom, was used as a non-antigen stimulus. The IL-1 produced was assayed in an IL-1-dependent cell line and the specificity was demonstrated in a blocking experiment with antiserum to IL-1 alpha. Soluble IL-1 alpha was also quantified in ELISA. Iscoms and matrix induced production of mIL-1 and sIL-1 in cultures from non-treated mice as well as from mice primed 4 days before with iscoms or micelles. Micelles were a less strong stimulus and did not induce production of sIL-1. Micelles induced production of mIL-1 in cultures from non-primed mice or from mice which were recently immunized with micelles. No mIL-1 expression was induced by micelles if the spleen cells originated from mice immunized shortly before with iscoms. Depletion experiments demonstrated that sIL-1 was produced by adherent cells upon stimulation with iscoms or matrix. However, factor(s) from the non-adherent cells seem to be necessary for optimal secretion of sIL-1.