Subunit vaccines against enveloped viruses: virosomes, micelles and other protein complexes

Characterization of purified gp 51 from bovine leukemia virus integrated into iscom. Physicochemical properties and serum antibody response to the integrated gp51

It is proposed that the envelope glycoprotein, gp 51, is the protective antigen of bovine leukemia virus (BLV). An experimental iscom vaccine has been prepared from immunoaffinity purified gp 51. To overcome the problem of integrating a nonamphipathic protein, gp 51 was partially denatured at pH 2.4 before integration into the iscom. The recovery of gp 51 into the iscom was calculated to be 85%. The gp 51 incorporated into iscom retained its physicochemical properties and the neutralizing epitopes F, G and H were found to be intact. The iscom preparation was shown to induce a specific immune response to gp 51 after inoculation into mice and calves, as tested by ELISA and Western blotting. Sera from the immunized calves specifically inhibited the VSV-(BLV) pseudotypes. Thus the gp 51-iscom preparations appear to be highly immunogenic and to induce a gp 51 specific response.

A polymer containing a repeating peptide sequence can stimulate T-cell-independent IgG antibody production in vivo

The immunogenicity of a CD4 peptide sequence 303-315 (V4 domain) was determined for three forms of the peptide: (a) a polymer consisting of repeating peptide units, (b) a peptide linked to a large protein carrier, chicken serum albumin, and (c) unmodified free peptide. Two in vivo systems were used: a T-cell-competent BALB/c mouse and a T-cell-deficient nude mouse. In BALB/c mice the IgG antibody responses to the peptide-CSA conjugate were at least 100-fold greater than the response to the polymer, and the free peptide gave no response. However, in contrast to the normal BALB/c mice, in the nude mice the polymer produced the only significant response. Nude mice immunized with the polymer produced a predominantly IgG response with almost equal amounts of IgG1 and IgG 2a + 2b. This IgG subclass distribution was very similar to that obtained in the BALB/c for the peptide-CSA conjugate. Positive sera from both groups were able to react with immobilized CD4 molecule on Western blots, confirming the specificity of both the T-cell-independent as well as T-cell-dependent response. These results suggest that repeating epitopes on the same peptide polymer molecule may cause cross-linking of antigen-specific immunoglobin receptors on B-cells, and thus behave as a relatively T-cell-independent immunogen which can induce isotype switching.

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

In the iscom, antigen is attached by hydrophobic interactions to a matrix which is built up by the adjuvant Quil A and lipids. Thus, the iscom presents antigen in multiple copies on a small particle with a built-in adjuvant. By studying the specific antibody response, in vitro proliferation and IL-2 secretion by splenocytes from mice following different in vivo treatments with iscoms and/or matrix, we attempted to distinguish between nonspecific stimulatory effects, caused by the matrix or iscoms, and specific responses to the antigens incorporated into iscoms. The results strongly suggest that matrix and also iscoms exert a nonspecific adjuvant activity by a transient high spontaneous proliferation of cells collected within 2 weeks after administration of iscoms or matrix. This high rate of proliferation was preceded by suppressed proliferation, 3 days after injection with matrix or iscom. The adjuvant component included in iscoms, i.e., the matrix, does not excert a mitogenic stimulation in vitro or influence the levels of specific antibodies in serum. Specific responses to the antigens included in iscoms were recorded both as increasing levels of serum antibodies and as iscom-induced proliferation of immune spleen cells in vitro. The recruitment of IL-2 was only related to the specific stimulation induced by the antigens in iscom.

Defining minimal requirements for antibody production to peptide antigens

The role that individual determinants play in modulating the immune response of an organism to a pathogen is often obscured because of the complexity of the pathogen. In order to gain a better appreciation of the role of individual determinants in the immune response, a pathogen may be dissociated into smaller components, for example peptides representing specific epitopes. These isolated components are often poorly immunogenic and historically have required the use of adjuvants to stimulate antibody production. This report defines the minimal essential requirements for antibody production to a peptide in this system. These are the ability to stimulate both B- and T-helper lymphocytes, anchorage in a phospholipid complex and multivalency within the complex. When these conditions are met, no additional adjuvants are necessary. This procedure has allowed us to identify three distinct T-helper cell epitopes from HIV gp160. In addition, this information has been used to produce a simple, totally synthetic and highly immunogenic preparation for the production of antibodies to peptides.

Increased immunogenicity of a non-amphipathic protein (BSA) after inclusion into iscoms

Bovine serum albumin (BSA) was used as a non-amphipathic model protein to be included into iscoms. Pretreatment at an acidic pH (2.5) was used to reveal hydrophobic regions, after which BSA could be integrated. In immunization experiments in mice the BSA iscoms induced long lasting and considerably higher serum antibody responses than non-treated monomeric BSA or BSA aggregated by acidic treatment.

Virosomes reconstituted from human immunodeficiency virus proteins and lipids

Purified Human Immunodeficiency Virus (HIV) was solubilized in octylglucopyranoside. After centrifugation, the supernatant was added to lipid-detergent mixed micelles. Formation of virosomes occurred during overnight dialysis. Centrifugation on a continuous glycerol gradient showed that envelope glycoproteins (gp120 and gp41) and matrix protein p17 but not core protein p25 were associated to virosomes. Proteolytic treatment of virosomes indicates that gp120 is oriented toward the outside as in the virus particles, whereas p17 protein is anchored on both sides of the liposomal membrane. Virosomes are spherical vesicles with approximately the size of the virus as shown by electron microscopy.

Free haemagglutinin in inactivated whole virus influenza vaccines

While studying the haemagglutinin content of whole virus inactivated influenza vaccines by the single radial diffusion test and quantitative electron microscopy, it was found that not all haemagglutinin measured by single radial diffusion was bound to virions, a part of it being in a free state. The influence of unbound haemagglutinin on the immunogenicity of whole virus inactivated influenza vaccine is discussed. In addition, the use of single radial diffusion for the assessment of unbound haemagglutinin is suggested.

Prospects for the control of AIDS patients by introducing defective-HIV harbouring leukocytes

Introduction of leukocytes harbouring an artificially constructed defective HIV provirus into AIDS patients may result in inducing superinfection resistance against HIV and interfering with HIV receptors or replication of HIV. All these may slow down progression of the disease.

The influence of different adjuvants on the immune response to a synthetic peptide comprising amino acid residues 9-21 of herpes simplex virus type 1 glycoprotein D

The immuno-modulating properties of different adjuvant systems on the murine humoral and cellular immune response to a synthetic peptide comprising amino acid residues 9-21 of glycoprotein D of herpes simplex virus type 1 (HSV-1) were investigated. For immunization, the peptide was conjugated to ovalbumin or bovine serum albumin by glutaraldehyde and the adjuvants used in this study were Freund's complete adjuvant (FCA), aluminium hydroxide, the Ribi adjuvant system (RAS) and two non-ionic block polymer surfactants, viz. L101 and 31R1, in oil in water emulsions. High anti-peptide antibody titers were obtained after immunization with FCA, aluminium hydroxide, RAS and L101. All adjuvants, except RAS, stimulated the induction of delayed type hypersensitivity obtained after immunization with peptide 9-21 coupled to ovalbumin and elicited by injection of purified HSV-1 virions in the footpad. Challenge with a lethal dose of HSV-1 showed that mice immunized with peptide 9-21 coupled to ovalbumin in combination with FCA, RAS and L101, respectively, were significantly protected. Although immunization with peptide 9-21 coupled to ovalbumin combined with aluminium hydroxide stimulated induction of delayed type hypersensitivity, no significant protective immunity against the challenge was generated.

Trial of a novel experimental Toxoplasma iscom vaccine in pregnant sheep

Fifteen vaccinated ewes (group 1) and 13 unvaccinated ewes (group 2) were each challenged orally with 2000 sporulated Toxoplasma gondii oocysts at 91 (+/- 1) days' gestation. Another four pregnant ewes acted as unvaccinated unchallenged controls. Lamb mortality in group 1 was 36.4% after a mean gestation of 141 days while in group 2 it was 64.7% after a mean gestation of 131.5 days. These differences were not statistically significant. However, substantially more specific antibody was detected in precolostral sera from live lambs from vaccinated ewes than in live lambs from unvaccinated ewes in group 2.

Formation and characterization of FeLV ISCOMs

Immunostimulating complexes (ISCOMs) have been prepared from feline leukaemia virus (FeLV) envelope proteins. The ISCOMs were characterized biochemically in SDS-polyacrylamide gel electrophoresis showing the presence of proteins of estimated molecular weights of 15,000, 27,000 and 70,000. Immunoblotting showed that both the transmembrane protein p15E and the external glycoprotein gp70 (making up the gp85 protein) were present in the ISCOM. Furthermore, a degradation product of gp70 with an estimated molecular weight of 32,000 was identified in the immunoblot. The FeLV ISCOM was shown by electron microscopy to have the characteristic cage-like structure of an ISCOM with a mean diameter of 37 nm. About 10% of the total amount of gp70 in the culture fluid was recovered in the ISCOMs. The largest loss was encountered during the sedimentation of the virus. In a preliminary immunization experiment in mice the FeLV ISCOMs elicited after a booster gave a clear-cut immune response against gp70.

Intranasal immunization with proteoliposomes protects against influenza

Worldwide, influenza virus remains a serious disease which has successfully eluded numerous attempts to design a consistently effective vaccine. In part, these attempts have been thwarted because of a lack of basic understanding of the mechanisms which mediate protection and recovery from influenza infection. A better understanding of the roles of secretory antibody, serum antibody and cell mediated immunity vis-à-vis protection and recovery from influenza infection has allowed us more rationally to approach the design and administration of a vaccine for influenza. We have constructed a vaccine composed of glycoproteins from the envelopes of either influenza of Sendai virus embedded in a lipid bilayer (immunosomes) mimicking the presentation of the virus to the cells during natural infection. Intranasal immunization with these immunosomes induces an adequate systemic Ir compared with intramuscular immunization and a superior local IgA response. These animals were specifically protected from virus challenge.

Bovine leukaemia virus ISCOMs: biochemical characterization

The glycoprotein gp51 of bovine leukaemia virus (BLV) has been included in an immunostimulating complex (ISCOM). The ISCOM was characterized biochemically in SDS-polyacrylamide gel electrophoresis showing the presence of proteins of estimated molecular weights of 50 and 30 kDa. Immunoblotting showed that gp51 was present in the ISCOM. The BLV-ISCOM had a S-value of 19 S and the electronmicrograph showed the cage-like structure as previously reported for other ISCOMs. About 17% of the total amount of gp51 in the cell culture fluid was recovered in the ISCOMs. The largest loss of gp51 was encountered during the sedimentation of the virus. An ELISA, utilizing monoclonal antibodies to defined epitopes for capture was developed to control the antigenicity of epitopes, e.g. those known to induce neutralizing antibodies. Using this device as a quality control for epitopes the following could be stated. First, ISCOMs prepared from virus solubilized with the non-ionic detergents Triton X-100 or MEGA did not react with neutralizing monoclonal antibodies. In contrast, ISCOMs prepared from virus solubilized with the non-ionic detergents Tween-20, Tween-80 or octyl glucoside did react with the neutralizing antibodies. Second, the neutralizing epitopes were better exposed in ISCOMs than the other epitopes of gp51. In a preliminary experiment it was shown that gp51 in ISCOMs was highly immunogenic.

Controlled organization of multimolecular complexes of enveloped virus glycoproteins: study of immunogenicity

Some technological and immunological problems facing the preparation of subunit viral vaccines are discussed. Solubilization of enveloped virus glycoproteins with various detergents has been studied. It has been demonstrated that a novel non-ionic detergent, MESK, can be used to prepare the glycoproteins of enveloped viruses in defined supramolecular forms: monomers, micelles, liposomes and multimeric complexes. These preparations have been tested for immunogenicity. It has been shown that the immunogenicity of glycoproteins in micellar form or in liposomes is comparable with that of the whole virus. The immunogenicity of the glycoprotein complex with the glycoside Quil A appeared to be significantly higher in comparison with the whole virus and was similar to the immunogenicity of glycoproteins mixed with Freund's complete adjuvant.

Cellular immune responses in the murine lung to local immunization with influenza A virus glycoproteins in micelles and immunostimulatory complexes (iscoms)

Primary immunization with a single inoculum of either micelles or iscoms containing influenza A virus glycoproteins failed to induce either B or cytotoxic T (Tc) cell responses. In contrast, immunization with two inocula of iscoms, but not micelles, resulted in the appearance of influenza virus-specific antibody-secreting cells (ASC) but not Tc cells in the lung. There was a 10-fold increase in Tc cell precursor frequency and an increase in ASC generated by secondary in vitro stimulation of lung cell cultures obtained from mice primed with iscoms but not micelles. In mice primed with infectious virus, secondary immunization with either micelles or iscoms increased the number of ASC in the lung and elicited virus-specific Tc cell responses. In contrast homologous virus challenge failed to induce detectable secondary B or Tc cell responses.

The iscom antigen-presenting system

The immunostimulating complex, or iscom, provides an effective means of presenting antigens to the immune system. Vaccines for influenza, hepatitis B and AIDS are in the offing.

The serum antibody response distributed in subclasses and isotypes after intranasal and subcutaneous immunization with influenza virus immunostimulating complexes

Immunostimulating complexes (iscoms) were prepared from influenza virus glycoproteins (A/PR8(H1N1]. Mice were inoculated with iscoms by local (oral or intranasal) as well as by subcutaneous administration. It was shown that one subcutaneous or intranasal inoculation induced serum antibody responses of similar magnitude. The intranasal administration, however, induced somewhat higher IgA and IgM titres than that induced subcutaneously. After a second intranasal or subcutaneous inoculation a prominent increase of the IgG isotypes was found. The secondary IgA and IgM responses were of similar magnitude as those induced after the primary inoculation. The antibody responses induced were evenly distributed within the IgG isotypes, although the highest titres recorded were of the IgG1 and IgG2 isotypes.

Influenza virus ISCOMs: antibody response in animals

A monovalent experimental ISCOM vaccine has been prepared with the envelope glycoproteins haemagglutinin and neuraminidase of the equine virus strain A/Solvalla/79 (H3N8). In vaccination trials on BALB/c mice the ISCOM vaccine induced more than ten times higher serum antibody titres measured in ELISA than a corresponding experimental micelle vaccine. Similarly, in guinea-pigs the ISCOMs induced about tenfold higher haemagglutination inhibition (HI) and neuraminidase inhibition (NI) titres than a micelle vaccine or a conventional killed influenza whole virus vaccine. Horses vaccinated with a divalent experimental ISCOM vaccine, containing the equine strains A/Prague/56 (H7N7) and A/Solvalla/79 (H3N8), responded with ELISA antibody titres against haemagglutinin which were higher and lasted considerably longer than those in horses vaccinated with conventional whole virus vaccine. ISCOMs induced complete immunoprotection in mice vaccinated with a dose of 1 microgram envelope glycoproteins of the mouse pathogenic strain A/PR/8/34 (H1N1).

New approaches to animal vaccines utilizing genetic engineering

Control of infectious diseases in livestock is an important determinant in the success of a nation's effort to efficiently meet its need for animal products. Genetic engineering offers many new options in the design of animal vaccines. Monoclonal antibodies, DNA cloning, recombination, and transfection are examples of techniques that facilitate innovative strategies in antigen identification, production, and delivery. This article reviews the use of genetic engineering in the production of vaccines directed against foot-and-mouth disease virus and other important pathogens of animals. The advantages and disadvantages of vaccines produced through the use of genetic engineering are discussed.

Impairment of immunogenicity by antigen presentation in liposomes made from dimyristoylphosphatidylethanolamine linked to the secretion of prostaglandins by macrophages

The induction of antibody response in syngeneic rats by the Gross virus cell surface antigen (GCSAa) was dependent on the presentation of GCSAa into liposomes made from distearoylphosphatidylcholine (DSPC). GCSAa liposomes made from dimyristoylphosphatidylethanolamine (DMPE) were nonimmunogenic, even when used as anamnestic immunogens. Spleen cells, from rats twice immunized with GCSAa-DSPC-liposomes and used to transfer the anti-GCSAa immune response into naive recipients after a tertiary immunostimulation in vitro in the presence of naive peritoneal exudate cells (PEC), responded to soluble GCSAa only after irradiation at 500 rds and to GCSAa-DMPE-liposomes only when indomethacin was added during the in vitro stimulation. The preincubation of these cells with empty DMPE liposomes or the addition of supernatant from PEC fed with DMPE liposomes abrogated the response to GCSAa-DSPC liposomes. Using a specific radioimmunoassay, prostaglandin E2 was demonstrated to be produced by PEC when fed with DMPE liposomes, and not when fed with DSPC liposomes. This prostaglandin E2 secretion by PEC induced by DMPE liposomes was inhibited by indomethacin.

Protection against lethal measles virus infection in mice by immune-stimulating complexes containing the hemagglutinin or fusion protein

The importance of each of the two surface glycoproteins of measles virus in active and passive immunization was examined in mice. Infected-cell lysates were depleted of either the hemagglutinin (H) or fusion (F) glycoprotein by using multiple cycles of immunoaffinity chromatography. The products were used to prepare immune-stimulating complexes (iscoms) containing either F or H glycoprotein. Such complexes are highly immunogenic, possibly as a result of effective presentation of viral proteins to the immune system [B. Morein, B. Sundquist, S. Höglund, K. Dalsgaard, and A. Osterhaus, Nature (London) 308:457-460, 1984]. Groups of 3-week-old BALB/c mice were inoculated with the iscom preparations. All animals developed hemolysis-inhibiting antibodies, whereas only sera of animals immunized with the iscoms containing the H glycoprotein had hemagglutination-inhibiting antibodies. Sera from animals immunized with the H or F preparation only precipitated the homologous glycoprotein in radioimmune precipitation assays. The immunized animals were challenged with a lethal dose of the hamster neurotropic variant of measles virus. Of the 7-week-old animals in the nonimmunized control group, 50% died within 10 days after challenge. No animals in the immunized groups showed symptoms of disease throughout the observation period of 3 months. Passive administration of anti-H monoclonal antibodies gave full protection against the 100% lethal acute infection with the hamster neurotropic variant of measles virus in newborn mice, whereas anti-F monoclonal antibodies failed to protect the animals. This study emphasizes that both H and F glycoproteins need to be considered in the development of measles virus subunit vaccines.

Potentiation of the immune response by immunization with antigens in defined multimeric physical forms

Conventional vaccines consisting of whole microorganisms have in many cases proven ineffective. This has led to the development of subunit vaccines which contain defined protective antigens. However, subunit vaccines are frequently poorly immunogenic, requiring the addition of adjuvants and/or their formation into forms such as micelles or virosomes. Ideally a vaccine should be limited to the desired antigens, incorporated in a multimeric physically defined form into which the adjuvant is built. This is possible through use of the ISCOM (immuno-stimulating complex), a matrix of the glycoside Quil A, onto which antigens are attached by hydrophobic interaction. Experiments involving ISCOMs prepared using membrane proteins from several viruses are described. The ISCOM system can be used to enhance immune response to antigens prepared from microorganisms and cells as well as peptides and other small molecules.

Vaccination of rabbits with a bovine herpesvirus type 1 subunit vaccine: adjuvant effect of ISCOMs

Bovine herpesvirus type 1 has two major immunogenic surface glycoproteins: a 90 kDa haemagglutinin and the 130 (74 + 54) kDa glycoprotein. These proteins were purified by rate zonal sucrose density gradient centrifugation after extraction with nonionic detergent Triton X-100. For the preparation of ISCOMs, the glycoproteins were further adsorbed during a second rate zonal centrifugation, to micelles of Quil A glycoside, already added to the gradient. Haemagglutinating peaks were collected and used as subunit vaccine in rabbits: groups of three animals were injected with 50, 10 and 5 micrograms protein. Seroconversion was followed by ELISA, haemagglutination inhibition, neutralizing and plaque reduction assays. ISCOMs and unadsorbed subunits were efficient in inducing neutralizing as well as haemagglutination inhibiting antibodies: ISCOMs gave a higher level of response. The efficiency demonstrated by ISCOMs suggests their potential as a subunit vaccine.

Adjuvant effects of orally administered saponins on humoral and cellular immune responses in mice

We have described adjuvant effects of orally administered Quillaja saponins on the immune responses of mice fed inactivated rabies antigen (AG). The in vivo lymphocyte proliferation in mice fed antigen + saponin (AG + SAP) was significantly greater than that in mice fed antigen (AG) alone. Further, the mitogen-induced cell proliferative responses in animals primed with AG + SAP was markedly increased compared with those in the AG group. These changes in clonal expansion were associated with an enhanced helper T cell (Th) and B cell co-operation. The in vivo cell proliferation and in vitro mitogen-induced responses of mice fed AG + SAP correlated with enhanced antibody synthesis. In mice fed saponin alone, there were significant increases in clonal expansion and lymphocyte function. Our present data indicate that the immunocompetence in animals fed AG + SAP was indeed evoked by saponins. Cytotoxic T lymphocyte activity in mice fed SAP or AG + SAP was detected 7 days after booster, in contrast to 21 days in mice fed AG alone. The natural killer cell activity in mice fed SAP alone was greatly enhanced and persisted for an extended period of time.

Antigenic presentation of small molecules and peptides conjugated to a preformed iscom as carrier

The aim of the present study was to elaborate a carrier system for haptens and synthetic peptides, making them immunogenic without addition of Freund's adjuvants. As carriers, preformed iscoms and micelles as well as BSA have been compared. The iscoms and micelles were prepared with envelope proteins of an influenza virus. As a model hapten, the small molecules of biotin were coupled to iscoms to determine the optimum epitope density for induction of an enhanced antibody response to the hapten. The most efficient carrier tested was the preformed iscom at an epitope density of ten biotin molecules per viral protein in the iscom. This carrier system exceeded the efficacy of both the preformed micelles and BSA, the latter with or without addition of Freund's adjuvant. A favourable epitope density could not be achieved when each of two different synthetic peptides was conjugated to iscoms. Epitope densities higher than one to three peptide molecules per protein lead to polymerization of either the peptide or the carrier. The coupling agent was glutardialdehyde.

Immunogenic activity of gonococcal protein I in mice with three different lipoidal adjuvants delivered in liposomes and in complexes

For several reasons the major outer membrane protein from Neisseria gonorrhoeae (gonococcal protein [PI]) is an attractive component for a gonococcal vaccine. This paper describes the influence of two different physical forms of PI on its immunogenic activity. To this end PI was delivered in liposomes and in protein-detergent complexes. In both forms PI was present in a multimeric form. The liposomes were composed of phosphatidylcholine and cholesterol. The effect of dicetylphosphate as a negatively charged amphiphile and three lipoidal adjuvants was investigated. Two lipoidal adjuvants (Avridine and dimethyldioctadecylammoniumbromide) were positively charged amphiphiles, whereas the third one (tridecyl N-acetylmuramyl-L-alanyl-D-isoglutaminate) was neutral. The protein-detergent complexes were also tested in the presence of the lipoidal adjuvants and in an AlPO4-adsorbed form. The liposome preparations were characterized for their size, charge, and residual amount of detergent. The immunogenic activity of PI in all forms was tested in mice. The results of the antibody assays showed that PI in the liposomes was more immunogenic than PI in the complexes. A second dose with liposomes induced only a small booster effect, whereas such a dose with the complexes produced pronounced booster effects. The incorporation of the positively charged lipoidal adjuvants in the liposomes resulted in enhanced booster effects. The highest immunogenic activity of PI after two injections, however, was observed in the complexed form adsorbed to AlPO4.

Characterization and immunogenicity of HSV-1 antigens obtained following zwitterionic detergent treatment

A preparation was obtained from herpesvirus hominis type 1 (HSV-1) infected cells using the zwitterionic detergent, Empigen BB. The preparation was partially purified by ultracentrifugation over a cushion of 20% sucrose. Serological characterization by ELISA and immuno double diffusion, using both polyclonal and monoclonal antibodies shows this preparation to contain HSV glycoproteins, including gC, gD and gE. Immunization of Balb/c mice elicited serum antibody responses against both HSV-1 and HSV-2 viruses, complete protection against HSV-1 (strain WAL) and partial protection against HSV-2 (strain 333).

Properties of monospecific antibodies to the glycoprotein of western equine encephalitis virus

Monospecific (MSp-) antisera against E1 and E2 glycoproteins of western equine encephalitis (WEE) virus were prepared and examined for binding activities to whole virions, hemagglutination-inhibition (HI), neutralization (NT) and protection. Both anti-E1 and anti-E2 MSp-Abs protected mice against WEE virus challenge. A competition experiment with monoclonal antibodies showed that these MSp-antisera appear to lack the antibody population for some epitopes involved in viral neutralization.