Effect of iscoms and their adjuvant moiety (matrix) on the initial proliferation and IL-2 responses: comparison of spleen cells from mice inoculated with iscoms and/or matrix

Nasal Vaccine Delivery

The mucosal surfaces represent the major site of entry of many pathogens, and major challenges in vaccine development include safety and stability in a suitable dosage form. Micro- and nanocarrier-based delivery systems as nasal vaccines induce humoral, cellular, and mucosal immunity. The nasal route of vaccination could also offer immunity at several distant mucosal sites (oral, rectal, vaginal, and pulmonary), which is considered a simplified and cost-effective mode of vaccination with enhanced patient compliance. Most of the nasal vaccine delivery systems in the form of microparticulates, nanoparticulates, and liposomes are currently under development and prove to offer immunity in animal models. The importance and potential of the nasal route of administration for vaccines is unexplored, and this chapter outlines the opportunities, challenges, and potential delivery solutions to facilitate the development of improved nasal vaccines for infectious diseases.

ISCOMs and ISCOMATRIX

Immunostimulatory complexes (ISCOMs) are particulate antigen delivery systems composed of antigen, cholesterol, phospholipid and saponin, while ISCOMATRIX is a particulate adjuvant comprising cholesterol, phospholipid and saponin but without antigen. The combination of an antigen with ISCOMATRIX is called an ISCOMATRIX vaccine. ISCOMs and ISCOMATRIX combine the advantages of a particulate carrier system with the presence of an in-built adjuvant (Quil A) and consequently have been found to be more immunogenic, while removing its haemolytic activity of the saponin, producing less toxicity. ISCOMs and ISCOMATRIX vaccines have now been shown to induce strong antigen-specific cellular or humoral immune responses to a broad range of antigens of viral, bacterial, parasite origin or tumor in a number of animal species including non-human primates and humans. These vaccines produced by well controlled and reproducible processes have also been evaluated in human clinical trials. In this review, we summarize the recent progress of ISCOMs and ISCOMATRIX, including preparation technology as well as their application in humans and veterinary vaccine designs with particular emphasis on the current understanding of the properties and features of ISCOMs and ISCOMATRIX vaccines to induce immune responses. The mechanisms of adjuvanticity are also discussed in the light of recent findings.

Quillaja saponin can modulate ovalbumin-induced IgE allergic responses through regulation of Th1/Th2 balance in a murine model

Quillaja saponin is the extract from the balk of a South American tree, and it is considered to modulate immunological responses. We hypothesized that Quillaja saponin may change allergy-associated cytokine profile and antigen-specific immune responses. The purpose of this study is to investigate whether Quillaja saponin can suppress ovalbumin (OVA)-induced IgE-mediated allergic responses through promoting a dominant Th1 immune response. The spleen cells from BALB/c mice, which were primed by OVA, were used for an in vitro challenge test. The level of total and OVA-specific IgE, IL-4, IFN-gamma, and IL-12 was determined by enzyme-linked immunosorbent assay (ELISA). BALB/c mice were orally administered with saponin for 35 days. The mice were immunized intraperitoneally with OVA on days 14 and 21. After intraperitoneal challenge with OVA on day 35, anaphylactic symptoms were monitored. Total and specific IgE and IgG, specific IgG1 and IgG2a, and histamine levels in serum were analyzed by ELISA. The increase of IL-12 and IFN-gamma levels was observed in the presence of Quillaja saponin, while the IL-4 level was decreased. Furthermore, Quillaja saponin suppressed total and OVA-specific IgE secretion in spleen cells. Balb/c mice that were orally administered Quillaja saponin exhibited lower total and OVA-specific IgE and OVA-specific IgG secretions, whereas total IgG levels remained unchanged. Suppression of OVA-specific IgG1 and an increase of OVA-IgG2a were observed in mice fed saponin. Quillaja saponin also decreased serum histamine levels and diminished anaphylactic symptoms. The present study indicates that Quillajasaponin can suppress allergen-specific IgE-mediated reactivity in a murine model of food allergy, which results from shifting from a Th2-dominated to a Th1-dominated immune response.

A polytope DNA vaccine elicits multiple effector and memory CTL responses and protects against human papillomavirus 16 E7-expressing tumour

Vaccine-induced CD8 T cells directed to tumour-specific antigens are recognised as important components of protective and therapeutic immunity against tumours. Where tumour antigens have pathogenic potential or where immunogenic epitopes are lost from tumours, development of subunit vaccines consisting of multiple individual epitopes is an attractive alternative to immunising with whole tumour antigen. In the present study we investigate the efficacy of two DNA-based multiepitope ('polytope') vaccines containing murine (H-2b) and human (HLA-A*0201)-restricted epitopes of the E7 oncoprotein of human papillomavirus type 16, in eliciting tumour-protective cytotoxic T-lymphocyte (CTL) responses. We show that the first of these polytopes elicited powerful effector CTL responses (measured by IFN-gamma ELISpot) and long-lived memory CTL responses (measured by functional CTL assay and tetramers) in immunised mice. The responses could be boosted by immunisation with a recombinant vaccinia virus expressing the polytope. Responses induced by immunisation with polytope DNA alone partially protected against infection with recombinant vaccinia virus expressing the polytope. Complete protection was afforded against challenge with an E7-expressing tumour, and reduced growth of nascent tumours was observed. A second polytope differing in the exact composition and order of CTL epitopes, and lacking an inserted endoplasmic reticulum targeting sequence and T-helper epitope, induced much poorer CTL responses and failed to protect against tumour challenge. These observations indicate the validity of a DNA polytope vaccine approach to human papillomavirus E7-associated carcinoma, and underscore the importance of design in polytope vaccine construction.

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.

Influence of adjuvant-active peptidoglycan monomer on specific T cell responses in mice

Peptidoglycan monomer (PGM) originating from Brevibacterium divaricatum is a non-toxic, non-pyrogenic, water-soluble immunostimulator. It potentiates humoral immune response to ovalbumin (OVA) in mice upregulating both immunoglobulin (IgG) 1 and IgG2a antibody subclasses. This study concerns the influence of PGM on T cell activation and cytokine networks in response to OVA. OVA-specific proliferative response as well as interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) secretion in lymph node cell cultures of immunised mice were studied. Due to pharmacokinetic properties of PGM, namely its fast metabolism and excretion, special emphasis was on choosing the appropriate time for lymph node removal and duration of cell cultivation for each cytokine. PGM treatment in addition to OVA resulted in an increase of lymph node cellularity, stimulation of OVA-specific IFN-gamma and IL-4 production as well as of OVA-specific proliferative response. Results demonstrate that PGM stimulated both Th1 and Th2 subpopulations.

Limitations of HLA-transgenic mice in presentation of HLA-restricted cytotoxic T-cell epitopes from endogenously processed human papillomavirus type 16 E7 protein

We investigated the use of mice transgenic for human leucocyte antigen (HLA) A*0201 antigen-binding domains to test vaccines composed of defined HLA A*0201-restricted cytotoxic T-lymphocyte (CTL) epitopes of human papillomavirus (HPV) type 16 E7 oncoprotein. HPV is detected in >90% of cervical carcinomas. HPV16 E7 oncoprotein transforms cells of the uterine cervix and functions as a tumour-associated antigen to which immunotherapeutic strategies may be directed. We report that although the HLA A*0201 E7 epitope peptides function both to prime for E7 CTL responses, and to sensitize target cells for E7-directed CTL killing in situations where antigen processing is not required, the epitopes are not processed out of either endogenously expressed or immunization-introduced E7, by the mouse antigen-processing and presentation machinery. Thus (1) CTL induced by HLA A*0201 peptide immunization killed E7 peptide-pulsed target cells, but did not kill target cells expressing whole E7; (2) immunization with whole E7 protein did not elicit CTL directed to HLA A*0201-restricted E7 CTL epitopes; (3) HLA A*0201-restricted CTL epitopes expressed in the context of a DNA polytope vaccine did not activate E7-specific T cells either in 'conventional' HLA A*0201 transgenic (A2.1Kb) mice, or in HHD transgenic mice in which expression of endogenous H-2 class 1 is precluded; and (4) HLA A*0201 E7 peptide epitope immunization was incapable of preventing the growth of an HLA A*0201- and E7-expressing tumour. There are generic implications for the universal applicability of HLA-class 1 transgenic mice for studies of human CTL epitope presentation in murine models of human infectious disease where recognition of endogenously processed antigen is necessary. There are also specific implications for the use of HLA A2 transgenic mice for the development of E7-based therapeutic vaccines for cervical cancer.

Immunisation of mice against neosporosis

In the present study a murine encephalitis model was used to investigate if protection against neosporosis could be achieved by immunisation. Groups of 10 mice were immunised with a sublethal dose of live Neospora caninum tachyzoites, N. caninum antigens incorporated into iscoms, N. caninum lysate mixed with Quil A, or N. caninum lysate in PBS. Control mice were given Quil A only. Challenge infection with 2.5x10(6) N. caninum tachyzoites resulted in clinical symptoms that remained until the end of the experiment in the controls. In contrast, mice immunised with live parasites or parasite lysate in Quil A only showed mild and transient symptoms. Of nine mice immunised with N. caninum iscoms, seven recovered while two died. Most severely affected were the mice immunised with parasite lysate only; all of them died within 28 days post-infection. Histological examination and scoring of brain lesions gave a significantly lower (P<0.0001) lesion score in mice immunised with live parasites than in controls. The groups immunised with iscoms or lysate and Quil A also had reduced lesion scores (P<0.04 and 0.07, respectively) but not the group given parasite lysate alone. The lesions seen in the latter group differed from those in the other groups. There was less cellular reaction and more tachyzoites indicating an active infection. The N. caninum specific antibody responses and cytokine production (IFN-gamma, IL-4 and IL-5) of splenocytes were analysed at the time of challenge infection. The results suggest a correlation between protection and high levels of IFN-gamma. Also, the immune responses recorded in mice immunised with parasite lysate without adjuvant were relatively weak and more towards the Th2 type, when compared with the other immunisation schedules. This is consistent with the weaker inflammatory response observed in the brains of these mice.

Production of antibodies to recombinant antigens from Lucilia cuprina following cutaneous immunisation of sheep

Immunological control of cutaneous myiasis of sheep caused by Lucilia cuprina larvae has been an elusive goal. Antibody to antigens derived from the peritrophic membrane can stunt or kill larvae in a dose dependent fashion. Thus efficacy of vaccines employing these antigens may be limited by the amount of antibody in skin available for ingestion by larvae. The potential for elevating antibody concentrations in skin by intradermal immunisation with the recombinant peritrophic membrane antigens peritrophin-44, peritrophin-48 and peritrophin-95 was therefore examined. Using within-animal comparisons, specific antibody was significantly higher in skin transudates from locally immunised sites than from adjacent adjuvant control sites. It was concluded that cutaneous immunisation may assist immunological control of blowfly larvae.

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.

Nonspecific down-regulation of CD8+ T-cell responses in mice expressing human papillomavirus type 16 E7 oncoprotein from the keratin-14 promoter

The E7 oncoprotein of human papillomavirus 16 (HPV16) transforms basal and suprabasal cervical epithelial cells and is a tumor-specific antigen in cervical carcinoma, to which immunotherapeutic strategies aimed at cytotoxic T-lymphocyte (CTL) induction are currently directed. By quantifying major histocompatibility complex class I tetramer-binding T cells and CTL in mice expressing an HPV16 E7 transgene from the keratin-14 (K14) promoter in basal and suprabasal keratinocytes and in thymic cortical epithelium, we show that antigen responsiveness of both E7- and non-E7-specific CD8+ cells is down-regulated compared to non-E7 transgenic control mice. We show that the effect is specific for E7, and not another transgene, expressed from the K14 promoter. Down-regulation did not involve deletion of CD8+ T cells of high affinity or high avidity, and T-cell receptor (TCR) Vbeta-chain usage and TCR receptor density were similar in antigen-responsive cells from E7 transgenic and non-E7 transgenic mice. These data indicate that E7 expressed chronically from the K14 promoter nonspecifically down-regulates CD8+ T-cell responses. The in vitro data correlated with the failure of immunized E7 transgenic mice to control the growth of an E7-expressing tumor challenge. We have previously shown that E7-directed CTL down-regulation correlates with E7 expression in peripheral but not thymic epithelium (T. Doan et al., J. Virol. 73:6166-6170, 1999). The findings have implications for the immunological consequences of E7-expressing tumor development and E7-directed immunization strategies. Generically, the findings illustrate a T-cell immunomodulatory function for a virally encoded human oncoprotein.

Induction of antibody and T-cell responses by immunization with ISCOMS containing the 38-kilodalton protein of Mycobacterium tuberculosis

In this study, we investigated the influence of different amounts of N-(palmitoyloxy) succinimide (PA-NHS): attachment of lipid tails to the protein and Quil A on the immunogenicity of the 38-kDa mycobacterial protein incorporated into immunostimulating complexes (ISCOMS; 38-kDa ISCOMS). The addition of higher amounts of Quil A during the ISCOMS preparation increased the amount of protein incorporated into ISCOMS, whereas the use of higher amounts of PA did not influence this parameter. Low antibody responses were observed after primary immunization with all 38-kDa ISCOMS preparations which, however, strongly increased after booster injections. IgG2a is the major subclass IgG induced by these ISCOMS preparations. There were only slight differences between the various ISCOMS formulations in their capacity to induce cytotoxic T-lymphocytes (CTLs). Spleen cells primed with ISCOMS prepared with the highest amount of Quil A produced high levels of IFN-gamma after stimulation with T helper cell type one (Th1) peptide of the 38-kDa protein (aa 70-84), 38-kDa protein or purified protein derivate (PPD). Spleen cells primed with ISCOMS prepared with the lowest amount of Quil A only substantial IFN-gamma levels were detected after stimulation with 38-kDa protein. IL-4 secretion was very low or not detectable with all ISCOM preparations. These results therefore demonstrated that all 38 kDa-ISCOMS preparations were: (1) immunogenic by inducing antibodies, Th1 and CTL responses; (2) that the way in which the ISCOMS were prepared, e.g. the amount of Quil A used, modulates the epitope specificity of the Th1 response.

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.

Immune stimulating complexes as mucosal vaccines

There is a need for non-living adjuvant vectors that will allow a full range of local and systemic immune responses to orally administered purified antigens. Here we describe our experience with lipophilic immune-stimulating complexes (ISCOMs) containing the saponin adjuvant Quil A. When given orally, ISCOMs containing the model protein antigen ovalbumin (OVA) induce a wide range of systemic immune responses, including Th1 and Th2 CD4-dependent activity, serum IgG antibodies and class I MHC-restricted cytotoxic T cell responses. In addition, there is local production of secretory IgA antibodies in the intestine itself, as well as priming of CD4 and CD8 T cell responses in the draining lymphoid tissues. Preliminary results indicate that the mucosal adjuvant properties of ISCOMs may reflect their ability to deliver antigen combined with the pro-inflammatory properties of Quil A in a particulate form. Of the many inflammatory mediators induced, interleukin-12, derived from dendritic cells and/or macrophages, appears to be of central importance. These results indicate that ISCOMs may prove to be useful mucosal vaccine vectors with functions which are distinct from existing vectors of this type.

Mice expressing the E7 oncogene of HPV16 in epithelium show central tolerance, and evidence of peripheral anergising tolerance, to E7-encoded cytotoxic T-lymphocyte epitopes

In order to derive mice which expressed both the E7 open reading frame transgene of human papillomavirus type 16 in skin and MHC class 1 restriction elements for several E7-encoded cytotoxic T-lymphocyte (CTL) epitopes, K14.HPV16E7 mice which express E7 in basal keratinocytes were crossed to the F1 generation with A2.1 Kb transgenic mice which express the MHC binding cleft domains of human HLA A*0201, and murine H-2b. F1 mice (denoted K14E7 x A2.1) expressed E7 in the thymus at least as early as 2-5 days before birth. Immunisation of FVB x A2.1 control mice (transgenic for HLA A*0201 and H-2b but not for E7), with two HLA A*0201-restricted epitopes of E7 and one H-2b-restricted CTL epitope of E7, gave strong primary CTL responses recognising epitope-pulsed or constitutively E7-expressing syngeneic target cells. In contrast, in immunised K14E7 x A2.1 mice, the CTL responses to the H-2b epitope and one of the HLA A*0201 CTL epitopes were strongly down-regulated, and to the other HLA A*0201 epitope, completely abolished, as demonstrated by percentage specific killing by bulk splenocyte cultures in cytotoxicity assays, and by CTL precursor frequency analysis. In thymus-transplanted bone marrow radiation chimeras in which the immune system of K14E7 x A2.1 mice was replaced by a FVB x A2.1 immune system, specific immunisation did not result in reemergence of strong E7-directed CTL responses. In agreement with these in vitro findings, specific immunisation failed to significantly alter the course of E7-associated tumour development in K14E7 x A2.1 mice. These data are consistent with a model of central deletional CTL tolerance to E7-encoded epitopes recognised in the context of two distinct MHC class 1 restriction elements, and with the possibility of peripheral T-cell anergy maintained by expression of E7 in the skin.

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.

Flow cytometric analysis of cellular changes in mice after intradermal inoculation with a liposome-iscom adjuvanted vaccine

As it is not known what changes to leucocyte homeostasis are mandatory for effective adjuvant action, the biological relevance of systemic changes elicited by different vaccine formulations can only be interpreted in the context of the immunological outcomes. We used flow cytometry to quantify the changes in leucocyte subsets induced in mice intradermally immunized with SAMA4 (adjuvant group), outer membrane proteins (OMP) purified from Actinobacillus pleuropneumoniae (OMP antigen group), SAMA4 adjuvanted OMP (OMP vaccine group), or phosphate-buffered saline (PBS: control group). This approach allowed direct comparisons to be made between the effects of antigen, adjuvant or antigen-adjuvant complexes on immune effector cell populations. Antigens complexed with the liposome-iscom hybrid adjuvant, SAMA4, generated strong antibody responses and cytotoxic T-cell activity in animals immunized intradermally, reflecting remobilization and recruitment of specific cell populations. Splenomegaly, due to granulocytosis, monocytosis and megakaryocytosis, was most prominent in the OMP vaccine group. Histological examination of spleen sections confirmed that these changes were due primarily to splenic haematopoiesis. Circulating numbers of granulocytes and monocytes increased significantly (P < 0.05) in the blood of the OMP vaccine group, as did granulocyte numbers in the lungs (P < 0.05). No changes in T- and B-cell numbers were detected by flow cytometry in the spleens, lungs or blood over the 28-day period in any treatment group. Thymocyte numbers (predominantly CD4+CD8+ cells) in the OMP vaccine group fell by 95% within 3 days of immunization. Identical cellular responses were obtained when an innocuous antigen, ovalbumin, was complexed with SAMA4 instead of OMP, thus demonstrating that the adjuvant effects of SAMA4 were due to synergistic interaction between antigen and adjuvant and not due to the presence of toxic components. The association of strong adaptive immune responses with such complex changes in leucocyte homeostasis induced by complexing adjuvant and antigen suggested that the changes were important for effective vaccination and were not purely circumstantial.

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 containing purified Quillaja saponins upregulate both Th1-like and Th2-like immune responses

The immune stimulating complex (iscom) is built up by antigen, cholesterol, phospholipids, and adjuvant active Quillaja saponins. Previous studies have shown that iscoms containing Quil A (a semipurified preparation of saponins) efficiently induce antibody and cell-mediated immune responses. In this study, we demonstrate that iscoms containing a mixture of two purified low toxicity Quillaja saponin fractions (ISCOPREP 703) are able to upregulate both Th1-like and Th2-like immune responses. Thus, ovalbumin (OVA) iscoms induced higher levels of antigen-specific IgG1 and IgG2a antibodies and increased the production of both IFN-gamma and IL-4 compared with OVA administered without adjuvant. In contrast, OVA formulated in Al(OH)3 elicited IgG1 and IgE antibodies and primed spleen cells producing IL-4 and IL-10, suggesting the activation of primarily Th2-like cells. These findings underline that adjuvants are able to alter the character of immune responses and may be used to generate responses with desired properties.

Immunomodulating effects after perinatal exposure to methylmercury in mice

The influence of methylmercury on the developing immune system was studied in offspring from Balb/c mice exposed to 0, 0.5 or 5 mg Hg/kg as methylmercury in the diet. Dams were exposed for 10 weeks prior to mating, during gestation and lactation. Pups were exposed to mercury until day 15 of lactation, thereafter the pups were given control milk and control diet. Samples for mercury analysis were collected from the pups on days 22 and 50, and for immunological studies on days 10, 22 and 50. The exposure resulted in significantly increased total Hg concentrations in whole blood on day 22 and 50 in offspring from the 5 mg Hg/kg group, and in offspring from the 0.5 mg Hg/kg group on day 22. On day 50, blood mercury levels had decreased to background levels in the 0.5 mg Hg/kg group. Increased numbers of splenocytes and thymocytes were found in offspring from the 0.5 mg Hg/kg group. Flow cytometry analysis of thymocytes revealed increased numbers and altered proportions of lymphocyte subpopulations within the thymus in offspring from both of the exposed groups. The proliferative response of splenocytes to the B-cell mitogen LPS was increased in offspring from dams exposed to 5 mg Hg/kg, and the primary antibody response to a viral antigen was stimulated in pups from dams exposed to 0.5 mg Hg/kg. The present results indicate that placental and lactational transfer of mercury affects thymocyte development and stimulates certain mitogen- or antigen-induced lymphocyte activities in mice.

Modulation of immune responses by bovine beta-casein

The present reports the influence of bovine beta-casein on in vitro and in vivo immune responses. Bovine beta-casein showed an inhibitory effect on ovine neutrophil chemotaxis but had an enhancing effect on superoxide production by neutrophils. In response to mitogenic stimulation, the proliferative response of both T and B lymphocytes was significantly enhanced by beta-casein. While beta-casein had no significant effects on IFN gamma production by ovine blood lymphocytes, and TNF alpha production and MCH Class II antigen expression by ovine bronchoalveolar macrophages, it enhanced IL-1 beta production by the macrophages, beta-casein also had no influence on bovine NK cell activity against a virally-infected cell line. Interestingly, beta-casein was found to reduce the adjuvant effect of matrix immune stimulating complexes (ISCOM) on anti-ovalbumin antibody response in mice when given intramuscularly. Taken together, the results suggest that bovine beta-casein had selective modulating effects in vitro on both innate and adaptive immune responses in ruminants, whereas systemic administration of beta-casein, that might have a depressive effect on adjuvant activity, requires further study.

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.

Prenatal exposure of Balb/c mice to ochratoxin A: effects on the immune system in the offspring

Effects of prenatal exposure to the mycotoxin ochratoxin A (OA) on the immune system were evaluated in Balb/c mice. Dams were exposed to OA in their diet at doses of 0.18 (control), 30 or 200 micrograms/kg before and during gestation. At birth, pups were cross-fostered to non-exposed dams. OA exposure of the dams did not influence reproductive outcome, that is, the numbers of litters, litter sizes and body weight of the pups. Flow cytomety analysis of T-lymphocyte subpopulations on days 14 and 28 postpartum revealed a decrease in the percentages of splenic CD4+ and CD8+ cells in offspring from the high-dose group (200 micrograms/kg diet), but no significant alterations in absolute numbers of these cell populations nor in the total numbers of splenocytes were observed. In the thymus, a relative as well as an absolute increase in the CD4+ subpopulation was seen in exposed pups on day 14. On day 28, the absolute numbers of CD4+, CD8+ and CD4+CD8+ (double positive) cells were increased, reflecting an elevated number of thymocytes in the high-dose group. No significant differences were found in the proliferative responses of splenic or thymic lymphocytes to mitogens, or in the production of interleukin-2 in concanavalin A-stimulated cell cultures. Further, the plaque-forming cell response to sheep red blood cells and the humoral antibody response to the viral antigen PR8 were not affected by prenatal exposure to OA. No significant differences in natural killer cell activity were observed. The results indicate that exposure of dams to relatively low levels of dietary OA alters absolute and relative numbers of lymphocyte subpopulations in lymphoid organs, but does not suppress immune functions in the offspring.

Effects of ochratoxin A on the rat immune system after perinatal exposure

Effects on the immune system after perinatal exposure to ochratoxin A (OA) were studied in Sprague-Dawley rats after single or repeated exposure of the dams. In a short-term study, dams with litters were given a single dose of OA (0, 10, 50 or 250 micrograms/kg body weight) on day 11 of lactation. The effects on cell numbers in spleen and thymus añd on the mitogen responses of lymphocytes were evaluated in the suckling pups on day 14 of lactation. The proliferative response of splenocytes to the T-cell mitogen Concanavalin A (Con A) was significantly stimulated in pups from dams given 10 or 50 micrograms OA/kg body weight as compared to control pups. In addition, proliferation of thymocytes in response to Con A was stimulated in pups from dams exposed to 50 micrograms OA/kg body weight. In a long-term, cross-fostering study comparing pre- and postnatal exposure, half of the dams received 50 micrograms OA/kg body weight 5 days a week by gastric intubation 2 weeks before mating, during gestation and then 7 days a week until weaning. Effects on immune parameters were studied in the pups on day 14 of lactation and at 13 weeks of age. Suppressed mitogenic responses were seen to both lipopolysaccharide (LPS) and Con A in prenatally exposed pups sampled on day 14 of lactation. At 13 weeks the response of splenocytes to LPS was still impaired. The primary antibody response to a viral antigen was also lower in the prenatally exposed pups than in the control pups. These effects on the immune response were not seen in the groups of pups exposed postnatally or both pre- and postnatally, although blood concentrations of OA were higher in these groups at the time of the first sampling. This indicates that the decrease in proliferation and antibody production resulted from prenatal modulation of the immune system. The results show that prenatal exposure to relatively low doses of OA may induce immunosuppression. In contrast, short-term exposure of suckling pups to OA via the milk stimulates the proliferative responses of lymphocytes to polyclonal activation.

ISCOMs (immunostimulating complexes): the first decade

A little over a decade ago, novel immunostimulating complexes (ISCOMs) were described. This review examines the position and progress that ISCOM technology has achieved in the fields of vaccine research and medicine over this period. Much of the work on ISCOMs has remained in the area of vaccine research where there is still an urgent need for improved adjuvants to help combat important diseases such as AIDS, malaria and influenza. Currently the only widely licensed adjuvants for human use are the aluminium salts, but with the trend towards highly purified subunit vaccines, which are inherently less immunogenic than some of the older vaccines, potent adjuvants capable of promoting specific immune responses are required. ISCOMs are one such technology that offers many of these requirements and as their use in vaccines enters its second decade clinical trials are commencing that will establish whether these submicron, non-living particles composed of saponin, cholesterol, phospholipid and in many cases protein, are useful components for a range of human vaccines.

Effects of ochratoxin A on the mouse immune system after subchronic exposure

The effects on the immune system of oral, subchronic exposure to ochratoxin A (OA) at 6, 250 or 2600 micrograms/kg diet were studied in female Balb/c mice. After 28 days of exposure, antibody production plague-forming cells/spleen, was suppressed in a dose-dependent manner which was significant in the two highest exposure groups. In addition, a decrease in thymocyte cell counts was seen in the 250-micrograms/kg group. After 90 days exposure, flow cytometry analysis of thymic lymphocyte subpopulations revealed a decreased proportion of mature (CD4+ or CD8+) cells. Furthermore, the mitogenic responsiveness of thymocytes and splenocytes to concanavalin A (Con A) was significantly decreased. This effect was observed in all three treatment groups. Interleukin-2 production of Con A-stimulated lymphocytes, natural killer cell activity, and humoral antibody titres to a viral antigen were not affected by OA treatment. The present results indicate that subchronic, oral exposure to OA affects certain immune functions in mice at exposure levels that may be found in contaminated food products.

Induction of Th1 and Th2 CD4+ T cell responses by oral or parenteral immunization with ISCOMS

We examined the ability of oral or parenteral immunization with immune stimulating complexes containing ovalbumin (ISCOMS-OVA) to prime T cell proliferative and cytokine responses. A single subcutaneous immunization with ISCOMS-OVA primed potent antigen-specific proliferative responses in the draining popliteal lymph node, which were entirely dependent on the presence of CD4+ T cells. CD8+ T cells did not proliferate in vitro even in the presence of the appropriate peptide epitope and exogenous interleukin (IL)-2. Primed popliteal lymph node cells produced IL-2, IL-5 and interferon (IFN)-gamma, but not IL-4 when restimulated with OVA in vitro. Serum antigen-specific IgG1 and IgG2a antibody responses were also primed by subcutaneous immunization with ISCOMS-OVA, confirming the stimulation of both Th1 and Th2 cells in vivo. Spleen cells from subcutaneously primed mice produced a similar pattern of cytokines, indicating that disseminated priming had occurred. Oral immunization with ISCOMS-OVA also primed local antigen-specific proliferative responses in the mesenteric lymph node and primed an identical pattern of systemic cytokine responses in the spleen. The ability of ISCOMS to prime both Th1 and Th2 CD4+ T cell responses may be central to their potent adjuvant activities and confirm the potential of ISCOMS as future oral vaccine vectors.

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.

Adjuvant activity of non-toxic Quillaja saponaria Molina components for use in ISCOM matrix

It is well established that ISCOMs function efficiently as an antigen-presenting system and protective immunity has been evoked against a variety of infectious agents. The built-in saponin adjuvant from Quillaja saponaria Molina is responsible for the strong immunoenhancing activity displayed by the ISCOM. However, to allow the use of ISCOMs in human vaccines it is necessary to determine the immunological properties and toxicity of chemically defined Quillaja components. Thus, the present study was carried out in a mouse model to determine the adjuvant activity and toxicity of "free", isolated Quillaja components, as well as formulated into particles, i.e. ISCOM matrix. The purified Quillaja components and the ISCOM matrix formulations were examined for their adjuvant activity in a model system consisting of purified influenza virus antigen and Quillaja saponins. It was demonstrated that a Quillaja component, designated QH-C, either as a "free" component or in an ISCOM matrix, has a strong adjuvant activity, but little or no toxicity in the doses tested. In addition, QH-C in the form of ISCOM matrix does not induce any local reactions at the site of injection. Thus, ISCOMs containing the QH-C component, devoid of toxicity, but with strong adjuvant activity, can prove to be useful in adjuvant formulations for human use.

Effects of subchronic exposure to Caramel Colour III on the immune system in mice

Administration of Caramel Colour III is associated with lymphopenia in laboratory animals, especially if the animals are fed a vitamin B6-deficient diet. Recently, functional immunological alterations in rats exposed to Caramel Colour III have been reported. The component of Caramel Colour III that is responsible for the immunological effects has been shown to be 2-acetyl-4-tetrahydroxybutyl imidazole (THI). In the present study, female Balb/c mice fed a diet with a relatively high vitamin B6 content were exposed to 2 or 10% of a commercial Caramel Colour III preparation with a low THI content (less than 25 ppm) in the drinking water for 9 wk. Although this treatment did not induce a lymphopenia in the exposed mice, flow cytometric analysis of lymphocyte subpopulations demonstrated reductions in the CD4+ and CD8+ cell populations. In addition, the proliferative response of spleen cells to B and T cell mitogens was significantly reduced in the mice exposed to 2% Caramel Colour III. No changes were observed in natural killer cell activity or in the humoral antibody response to a viral antigen. The results indicate that Caramel Colour III that meets the specified limit of less than 25 mg THI/kg may, nevertheless, interfere with the lymphoid system in mice with an adequate vitamin B6 status.

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.

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

To understand how a presentation system for antigens initiates an immune response and why it has a strong adjuvant activity, a number of parameters need to be analysed. In this study the frequency of spleen cells expressing MHC class II (Ia antigen) was determined after immunization of mice and restimulation of their spleen cells, in vitro, with influenza virus envelope proteins in different physical forms, namely iscoms, micelles and virus particles. All three forms of the antigen stimulated, in an antigen-specific manner, an increased proportion of spleen cells expressing MHC class II in the restimulation experiments. The induction of increased MHC class II expression was at least partly dependent on antigen-specific induction of IFN-gamma since an antibody to IFN-gamma partly inhibited the increase of MHC class II+ cells induced by iscom or by Concanavalin A. The iscom-borne antigens were superior to micelles to prime the immune response in vitro, indicating a capacity to induce memory cells. This primed immune response was readily recalled in vitro, as measured by IFN-gamma production and an increased number of MHC class II positive cells.

Involvement of interleukin-2 and interferon-gamma in the immune response induced by influenza virus iscoms

Splenocytes from mice primed with influenza virus envelope proteins incorporated in iscoms, as micelles or as infectious virus, were restimulated in vitro with the same antigen. Interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) were assayed in the supernatants of such cultures. Influenza virus iscoms induced IL-2 and IFN-gamma responses in restimulation experiments that were antigen specific and significantly higher than those induced by micelles or infectious virus. Serum samples collected at the end of the experiments were analysed for the antibody response and profile. The antibody titres induced by iscoms were of a similar order of magnitude as those induced by infectious virus, and were about 18 times higher than the titres induced by micelles. In mice immunized with iscoms or infectious virus the most abundant antibodies were of the IgG1 and IgG2a isotype, and the IgE response was low. We conclude that immunization with iscoms stimulates the Th1-like subtype of murine T lymphocytes.

Measles virus transmembrane fusion protein synthesized de novo or presented in immunostimulating complexes is endogenously processed for HLA class I- and class II-restricted cytotoxic T cell recognition

The routes used by antigen-presenting cells (APC) to convert the transmembrane fusion glycoprotein (F) of measles virus (MV) to HLA class I and class II presentable peptides have been examined, using cloned cytotoxic T lymphocytes in functional assays. Presentation by Epstein-Barr virus-transformed B lymphoblastoid cell lines was achieved using live virus, ultraviolet light-inactivated virus, and purified MV-F delivered either as such or incorporated in immunostimulating complexes (MV-F-ISCOM). Only live virus and MV-F-ISCOM allow presentation by class I molecules, while all antigen preparations permit class II-restricted presentation. We observe presentation of MV-F from live virus and as MV-F-ISCOM by class II molecules in a fashion that is not perturbed by chloroquine. Our studies visualize novel presentation pathways of type I transmembrane proteins.

Interactions between immune-stimulating complexes (ISCOMs) and peritoneal mononuclear leucocytes

Studies were undertaken in mice using immune-stimulating complexes (ISCOMs) or micelles prepared from envelope glycoproteins of human influenza virus (PR8) and matrix (i.e., ISCOM skeleton without incorporated antigen). Electron microscopic studies showed that ISCOMs, in contrast to micelles, have a remarkable affinity for cell membranes and seem to rapidly promote their own internalization by cells to which they adhere. PR8 ISCOMs, but not matrix nor micelles, significantly increased the expression of membrane Ia by peritoneal mononuclear leucocytes 24 hr after intraperitoneal immunization.

Initiation of cytotoxic T-cell response and protection of Balb/c mice by vaccination with an experimental ISCOMs respiratory syncytial virus subunit vaccine

Respiratory syncytial virus is an important human pathogen causing serious lower respiratory tract infections of children and elderly people. Previous studies on the development of experimental subunit vaccines either expressed by recombinant DNA technology or prepared from purified viral proteins absorbed on adjuvant (ISCOMs) have shown promise. The present work reports on the effectiveness of an experimental ISCOMs vaccine in initiating humoral and cell-mediated immune responses and in providing overall protection upon live virus challenge in Balb/c mice; results indicate that vaccination by the intramuscular route is more effective, even if vaccination by the intranasal route also significantly reduced virus shedding.

The influence of the adjuvant Quil A on the epitope specificity of meningococcal lipopolysaccharide anti-carbohydrate antibodies

Rabbits were immunized with immunotype L3,7,9 phosphoethanolamine (PEA) group containing oligosaccharide-tetanus toxoid conjugates both with and without the addition of the adjuvant Quil A. The epitope specificity of the antibodies present in these antisera was analysed in an immunotype L2 and L3,7,9 specific inhibition ELISA using the homologous and heterologous lipopolysaccharide, oligosaccharide and partial dephosphorylated oligosaccharide as inhibitors. Two groups of antisera could be identified. In one group of antisera, at least two antibody populations are present, namely directed against the PEA group containing determinants on immunotype L3,7,9 lipopolysaccharide and against immunotype L2 specific epitopes in which no PEA group is present. In the second group of antisera, one but probably more antibody populations are detected with a similar specificity towards the conserved epitopes of both immunotypes. In general, immunization with the conjugates only resulted in the induction of antibodies against the PEA group containing epitopes on the L3,7,9 lipopolysaccharide (80%). Antibodies directed against the conserved epitopes of both immunotypes are mainly evoked with the conjugates in combination with the adjuvant Quil A (80%). Although these results suggest that the epitope specificity of the antibodies induced depends on the use of Quil A, the influence of genetic factors cannot be excluded. At the moment it is not known whether the differences in epitope specificities are reflected in biological function of these antibodies. However, the induction of antibodies with clearly different epitope specificities after immunization of different rabbits with the same antigen stresses the importance of this kind of analysis when developing a vaccine based on oligosaccharide-protein conjugates.