Protein subunit vaccines of parainfluenza type 3 virus: immunogenic effect in lambs and mice

The Current Status of COVID-19 Vaccines

The current COVID-19 pandemic has substantially accelerated the demands for efficient vaccines. A wide spectrum of approaches includes live attenuated and inactivated viruses, protein subunits and peptides, viral vector-based delivery, DNA plasmids, and synthetic mRNA. Preclinical studies have demonstrated robust immune responses, reduced viral loads and protection against challenges with SARS-CoV-2 in rodents and primates. Vaccine candidates based on all delivery systems mentioned above have been subjected to clinical trials in healthy volunteers. Phase I clinical trials have demonstrated in preliminary findings good safety and tolerability. Evaluation of immune responses in a small number of individuals has demonstrated similar or superior levels of neutralizing antibodies in comparison to immunogenicity detected in COVID-19 patients. Both adenovirus- and mRNA-based vaccines have entered phase II and study protocols for phase III trials with 30,000 participants have been finalized.

Development of oligomannose-coated liposome-based nasal vaccine against human parainfluenza virus type 3

Human parainfluenza viruses (HPIVs) are the etiologic agents of lower respiratory infections and pneumonia in infants, young children and immunocompromised hosts. The overarching goal for the prevention of HPIV infection is the development of an effective vaccine against HPIVs. In the present study, we investigated the effectiveness of oligomannose-coated liposomes (OMLs) as an antigen-delivery system in combination with a synthetic double-stranded RNA analog for the induction of mucosal and systematic immunity against HPIV3. Full-length hemagglutinin-neuraminidase (HN) protein was synthesized using the wheat germ cell-free protein production system and then encapsulated into OML to serve as the antigen. Intranasal administration of the HN-filling OML (OML-HN) with the synthetic double-stranded RNA adjuvant, polyriboinosinic-polyribocytidylic acid [poly(I:C)] generated significant viral-specific systemic and mucosal immune responses as evidenced by the prominent induction of serum IgG and nasal wash IgA, respectively. On the other hand, no significant immune responses were observed in mice immunized with OML-HN without the adjuvant. Furthermore, serum from mice immunized with OML-HN plus poly(I:C) significantly suppressed viral infection in cell culture model. Our results provide the first evidence that intranasal co-administration of OML-encapsulated HN with the poly(I:C) adjuvant augments the viral-specific immunity against HPIV3.

Parainfluenza viruses

Human parainfluenza viruses (HPIV) were first discovered in the late 1950s. Over the last decade, considerable knowledge about their molecular structure and function has been accumulated. This has led to significant changes in both the nomenclature and taxonomic relationships of these viruses. HPIV is genetically and antigenically divided into types 1 to 4. Further major subtypes of HPIV-4 (A and B) and subgroups/genotypes of HPIV-1 and HPIV-3 have been described. HPIV-1 to HPIV-3 are major causes of lower respiratory infections in infants, young children, the immunocompromised, the chronically ill, and the elderly. Each subtype can cause somewhat unique clinical diseases in different hosts. HPIV are enveloped and of medium size (150 to 250 nm), and their RNA genome is in the negative sense. These viruses belong to the Paramyxoviridae family, one of the largest and most rapidly growing groups of viruses causing significant human and veterinary disease. HPIV are closely related to recently discovered megamyxoviruses (Hendra and Nipah viruses) and metapneumovirus.

The immunostimulating complex (ISCOM) is an efficient mucosal delivery system for respiratory syncytial virus (RSV) envelope antigens inducing high local and systemic antibody responses

ISCOM is an efficient mucosal delivery system for RSV envelope proteins as measured by antibody responses in respiratory tract secretions and in sera of mice following two intranasal (i.n.) administrations. Intranasally administered RSV ISCOMs induced high levels of IgA antibodies both in the upper respiratory tract and in the lungs. In the lungs, a prominent and long-lasting IgA response was recorded, which still persisted 22 weeks after the second i.n. immunization when the experiment ended. Subcutaneous (s.c.) immunization only induced low IgA titres in the upper respiratory tract and no measurable response to RSV was found in the lungs. Differences were also noticed in serum between the i.n. and s.c. modes of immunization. ISCOMs given intranasally induced earlier, higher and longer lasting IgM and IgG1 serum anti-RSV antibody responses than those induced by the s.c. mode of administration. A low serum IgE response was only detectable at 2 weeks after i.n. immunization with ISCOMs and after s.c. immunization with an inactivated virus, but no IgE response was detectable after s.c. injection of ISCOMs. The serum IgA response was more pronounced following s.c. injection of inactivated virus than after i.n. application of ISCOMs, and a clear-cut booster effect was obtained with a second immunization. Virtually no serum IgA response was detected after the s.c. administration of ISCOMs. In conclusion, the high immune responses induced by RSV ISCOMs in the respiratory tract and serum after i.n. administration indicate prominent mucosal delivery and adjuvant properties of the ISCOMs, warranting further studies.

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.

Parainfluenza virus type 3 (PIV3)-specific and non-virus-specific delayed type hypersensitivity responses in cotton rats given different PIV3 antigen preparations

Virus-specific, T-lymphocyte-mediated delayed type hypersensitivity (DTH) responses were studied in cotton rats using replicating (wild-type parainfluenza virus type 3 (PIV3) and recombinant vaccinia virus expressing PIV3 haemagglutinin-neuraminidase (HN) or fusion (F) glycoproteins), and non-replicating (detergent-solubilized, affinity chromatography purified HN and F glycoproteins or inactivated whole PIV3) virus preparations. Significant virus-specific DTH responses were observed in all test groups 1-2 weeks after a single antigen inoculation or 5 days after two inoculations given 3 weeks apart. Peak swelling of ear pinnas in these animals generally occurred 24 h after elicitation and was marked by a cellular infiltration consisting of mono- and polymorphonuclear leucocytes. A considerable non-virus-specific inflammatory response, presumably due to tissue culture or media components in the priming antigen preparations, was observed 3 weeks after priming. No significant differences in DTH responses were observed in cotton rats primed with any of the PIV3 preparations. The possible roles and significance of both the virus-specific and non-virus-specific DTH responses in paramyxovirus-induced disease in humans and cotton rats are discussed.

An immune stimulating complex (ISCOM) subunit rabies vaccine protects dogs and mice against street rabies challenge

Dogs and mice were immunized with either a rabies glycoprotein subunit vaccine incorporated into an immune stimulating complex (ISCOM) or a commercial human diploid cell vaccine (HDCV) prepared from a Pitman Moore (PM) rabies vaccine strain. Pre-exposure vaccination of mice with two intraperitoneal (i.p.) doses of 360 ng ISCOM or 0.5 ml HDCV protected 95% (38/40) and 90% (36/40) of mice, respectively, against a lethal intracerebral (i.c.) dose with challenge virus strain (CVS). One 360 ng i.p. dose of ISCOM protected 87.5% (35/40) of mice against i.c. challenge with CVS. Three groups of five dogs were vaccinated intramuscularly (i.m.) with 730 ng of rabies ISCOM prepared from either the PM or the CVS rabies strains, and they resisted lethal street rabies challenge. Postexposure treatment of mice with three or four 120 ng i.m. doses of ISCOM protected 90% (27/30) and 94% (45/48), respectively, of mice inoculated in the footpad with street rabies virus, but three doses of HDCV conferred no protection. When four doses of HDCV were administered postexposure, 78% (32/41) of the mice died of anaphylactic shock; 21% (11/52) of mice had already died of rabies 4 days after the third vaccine dose was administered.

Comparative analysis of the immunostimulatory properties of different adjuvants on the immunogenicity of a prototype parainfluenza virus type 3 subunit vaccine

The immunogenicity of a parainfluenza virus type 3 (PIV-3) subunit vaccine consisting of affinity-purified haemagglutinin-neuraminidase (HN) and fusion (F) surface glycoproteins was tested in guinea-pigs and hamsters. The ability of several different immunopotentiating agents to enhance the antibody response of animals to the PIV-3 surface glycoproteins was evaluated. The immunity induced by HN and F alone was compared with the response elicited by purified proteins combined with Freund's complete adjuvant, aluminium phosphate, Syntex's threonyl-muramyl dipeptide (MDP) SAF-MF formulation, or Ribi's adjuvant formulation containing BCG cell wall skeleton (CWS), trehalose dimycolate (TDM) and monophosphoryl lipid A (MPL) in a 2% squalene-in-water emulsion. Purified proteins were also incorporated into three different liposome formulations prepared by the detergent dialysis procedure. Immunization of guinea-pigs and hamsters with two 15 micrograms doses of the PIV-3 surface glycoproteins administered in the absence of adjuvant elicited high haemagglutination inhibition, neutralization and anti-fusion titres. The liposome preparations failed to enhance the antibody titres. Ribi's adjuvant formulation was effective at inducing a good secondary response to the purified proteins while the immunostimulatory effects of aluminium phosphate, Syntex and Freund's adjuvants were clearly demonstrated in both primary and secondary responses. When administered without adjuvant, a 15 microgram dose of the HN and F mixture was capable of protecting hamsters against live virus challenge. The immunoprotective dose of the purified proteins could be reduced to at least 0.1 microgram by the addition of aluminium phosphate, Syntex or Freund's adjuvants.

Evaluation of the immunogenicity and protective efficacy of a candidate parainfluenza virus type 3 subunit vaccine in cotton rats

A parainfluenza virus type 3 (PIV3) subunit vaccine consisting of detergent-solubilized, affinity-purified haemagglutinin-neuraminidase (HN) and fusion (F) surface glycoproteins was tested in cotton rats for immunogenicity, short-term effects on virus-induced immunopathology and protective efficacy. Groups of animals were immunized twice, 4 weeks apart, with graded doses of vaccine administered either alone or with aluminium phosphate (AlPO4). The minimum immunogenic dose of vaccine was 0.1 microgram HN and F when the vaccine was given alone and 0.01 microgram when the vaccine was administered with AlPO4 adjuvant. Antibody responses in animals immunized with 1 microgram HN and F mixed with adjuvant were similar to those in control animals infected with live PIV3 intranasally. Pulmonary and nasal wash PIV3 titres generally were inversely correlated with serum antibody levels. Virus titres were significantly reduced in all groups of animals immunized with greater than or equal to 0.1 microgram HN and F compared with control animals immunized with vehicle only. Four days after virus challenge, there was no evidence of enhanced histopathology in lung sections from animals immunized with the candidate vaccine.

Preparation of proteosome-based vaccines. Correlation of immunogenicity with physical characteristics

In order to facilitate the use of proteosome-based vaccines, we have identified and analyzed the parameters that affect their immunogenicity. As a model system we used synthetic peptides (LCF6) containing sequences from the immunodominant (NANP)n tandem repeat region of the P. falciparum circumsporozoite protein, hydrophobically complexed to multimeric protein preparations (proteosomes) of meningococcal outer membrane proteins (OMP), since we have previously shown that high levels of anti-(NANP)n IgG can be elicited in mice by use of this novel adjuvant system (Lowell et al., 1988a). We have now examined these preparations by velocity sedimentation and measured their ability to elicit an IgG response in mice. Velocity sedimentation of freshly mixed OMP and LCF6, without dialysis, produced a limited number of small complexes, whereas dialysis of the mixture for 4 d yielded heterogeneously sized complexes that became more homogeneous when the dialysis was carried out for 7 or 10 days. The most homogeneous of these peptide-proteosome complexes (those dialyzed for 10 days) induced substantial levels of anti-(NANP)n IgG in mice, and shorter periods of dialysis resulted in vaccines that induced proportionately lower titers. Analysis of a series of preparations with varying LCF6: OMP ratios (w/w) showed that the degree of peptide substitution of the proteosomes was inversely proportional to the rate of sedimentation of the complexes and that there exists an optimal degree of lipopeptide complexing to the proteosomes. Our results suggest that the parameters affecting the immunogenicity of the peptide-proteosome complexes are: (i) hapten density, and (ii) size of the complex. Furthermore, sedimentation analysis of peptide-proteosome immunogens may serve as a rapidly performed assay of immunogenic potency.

Specificity and in vitro transfer of the immunosuppressive effect of detergent-disrupted influenza virus vaccine

Primed murine splenocytes give an in vitro antibody response to influenza whole virus vaccine (WVV), as measured by enzyme immunoassay (EIA). When subunit vaccine (SV) of either influenza A or influenza B virus was added to in vitro splenocyte cultures stimulated with WVV, the EIA antibody response to homologous WVV was reduced. This reduction in antibody response was observed when SV was prepared using zwitterionic detergent (empigen BB), non-ionic detergent (triton-X-100) or cationic detergent cetyl-trimethyl ammonium bromide (CTAB); it was found to be effected only by SV of strains of the same virus subtype--when SVs prepared from a heterotypic (H3N2) strain, an H1N1 strain and an influenza B strain were added to splenocyte cultures in the presence of WVV. When splenocytes from immunologically naive mice, exposed in vitro to SV, were transferred to secondary cultures of primed splenocytes, the antibody response to WVV in the secondary cultures was also reduced. Mechanisms that may suppress the in vitro antibody response are discussed.

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.

Influenza virus ISCOMs: biochemical characterization

Immunostimulating complexes (ISCOMs) have been prepared from influenza A virus envelope glycoproteins, i.e. haemagglutinin (HA) and neuraminidase (NA). An ISCOM consists of a matrix, which is the micellar form of the glycoside, Quil A, in hydrophobic interaction with both the envelope glycoproteins (HA/NA). The Quil A bound to the ISCOM amounted to 50 micrograms mg-1 (5%) of ISCOM protein. ISCOMs were morphologically identified as symmetrical cage-like structures of approximately equal to 40 nm in diameter with hexagonal or pentagonal subunits of approximately equal to 12 nm. The sedimentation coefficient was approximately equal to 19 S as compared to 30 S for the glycoprotein micelles. The biological activities of the HA and NA are preserved in both ISCOMs and micelles.

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).

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.

Structural proteins of bovine parainfluenza-3 virus

Six structural proteins of bovine parainfluenza-3 virus (PI-3V) labeled with [35S]-methionine could be resolved by polyacrylamide gel electrophoresis (PAGE). Five structural proteins of this virus had been previously reported. The 6 proteins found in this study were: L, a 180,000 (180 kD) molecular weight (MW) large protein; P, 83 kD phosphoprotein; HN, 69 kD hemagglutinin-neuraminidase glycoprotein; NP, 66 kD nucleocapsid protein; F, 55 kD fusion glycoprotein; and M, 38 kD matrix protein. Selective labeling with [2-3H]-mannose revealed only HN and F glycoprotein bands. A cellular actin protein (43 kD), associated with many enveloped viruses, was also found as a seventh protein in bovine PI-3V.

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.

Protection of weanling hamsters from experimental infection with wild-type parainfluenza virus type 3 (para 3) by cold-adapted mutants of para 3

Parainfluenza virus type 3 (para 3) was adapted to replicate at 20 degrees C, a nonpermissive temperature for wild-type (wt) para 3. Serial passage at 20 degrees C resulted in the generation of cold-adapted (ca) and temperature-sensitive (ts) mutants. These mutant viruses have been characterized both in vitro and in vivo [Belshe and Hissom (1982): Journal of Medical Virology 10:235-242; Crookshanks and Belshe (1984): Journal of Medical Virology 13:243-249]. We now report the evaluation of three mutants (clone 1150, passaged 12 times in the cold [cp12], clone 1146, passaged 18 times in the cold [cp18], and clone 1328, passaged 45 times in the cold [cp45]) for their ability to protect hamsters from infection by wild-type para 3. Ether-anesthetized male syrian hamsters were intranasally vaccinated with either wt para 3 (clone 127) or one of the ca para 3 mutants and on day 28 post-vaccination; each animal was intranasally challenged with 10(5.0) pfu of wt para 3. On days 1, 2, 3, and 4 post-challenge, 4 to 13 hamsters from each group were sacrificed, and the quantity of para 3 in the nasal turbinates and lungs was determined. Wt virus induced protection from challenge. cp12, cp18, and cp45 reduced the peak titer of wt replication in the lungs by greater than 100-fold, tenfold, and tenfold, respectively. The duration of virus replication was shortened also by intranasal vaccination with the mutants. These data give evidence of an inverse relationship between the degree of protection induced by vaccination with cold-adapted mutants and the number of passages of the virus in the cold.

Monoclonal antibodies reveal extensive antigenic differences between the hemagglutinin-neuraminidase glycoproteins of human and bovine parainfluenza 3 viruses

A panel of twenty monoclonal antibodies to the hemagglutinin-neuraminidase (HN) glycoprotein of human parainfluenza 3 (PI3) virus has been obtained and tentatively classified into four different groups based on reactivity in hemagglutination inhibition (HI), neuraminidase inhibition (NI), and plaque neutralization (NT) tests. The antibodies were tested for cross-reactivity with bovine PI3 virus, Sendai virus, and simian virus 5 (SV5). Only two of these antibodies showed similar reactivities with human and bovine PI3 viruses in HI and NT tests; a few other antibodies showed low levels of reactivity with the heterologous viruses in HI tests. A competitive binding assay further suggested that the two cross-reactive antibodies are directed against the same domain of the HN molecule. Therefore, the HN glycoproteins of human and bovine PI3 viruses appear to be antigenically dissimilar, although they share at least one common epitope.

Isolation and studies of myxovirus glycoproteins

The isolation of ortho- and paramyxovirus glycoproteins using a new nonionic detergent (MESK) is reported. MESK was shown to solubilize most of the viral envelope glycoproteins without decreasing their biologic activity. Solubilized glycoproteins are not contaminated by any internal viral proteins or by appreciable quantities of viral envelope lipids. The removal of MESK by dialysis resulted in the formation of glycoprotein micelles. The immunogenic activity of isolated glycoproteins was compared to that of virus particles. Immunization with isolated glycoproteins was shown to protect mice against a lethal influenza infection. Virions were treated with MESK in the presence of exogenous egg phosphatidylcholine, detergent was removed by dialysis and the glycoprotein was reconstituted in the vesicles. This reconstitution was accompanied by restoration of the haemolytic activity of Sendai virus proteins up to that of native virus particles. The level of activity, also the morphology and buoyant density of the vesicle were dependent on the protein/lipid ratio. MESK proved to be of value for the selective solubilization of the surface glycoproteins of animal enveloped viruses and their reconstitution in liposomes.

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

The envelope proteins (the peplomers) of enveloped viruses are the components that are important for induction of protective immunity. This article reviews methods and problems of making subunit vaccines of peplomers. In the first section, the solubilization of enveloped viruses with detergent is discussed. The preparation of envelope proteins into defined different physical forms is described, i.e. monomeric and micelle forms and the reconstitution of the protein into lipid vesicles (virosomes). Finally, the preparation of a new type of complex is described (named iscom), which is highly immunogenic. In the following sections the efficacy of the different physical forms are reviewed and it is concluded that monomeric forms must be avoided since they are poorly immunogenic and they may even have a suppressive effect on the immune response. The multimeric micelles, virosomes and iscoms are all immunogenic. The iscom is an interesting new concept that can be used to produce efficient subunit vaccines.

Structural characterization of virion proteins and genomic RNA of human parainfluenza virus 3

The virion proteins and genomic RNA of human parainfluenza virus 3 have been characterized. The virion contains seven major and two minor proteins. Three proteins of 195 X 10(3) molecular weight (195K), 87K, and 67K are associated with the nucleocapsid of the virion and have been designated L, P, and NP, respectively. Three proteins can be labeled with [14C]glucosamine and have molecular weights of 69K, 60K, and 46K. We have designated these proteins as HN, F0, and F1, respectively. HN protein has interchain disulfide bonds, but does not participate in disulfide bonding to form homomultimeric forms. F1 appears to be derived from a complex, F1,2, that has an electrophoretic mobility similar to that of F0 under nonreducing conditions. A protein of 35K is associated with the envelope components of the virion and aggregates under low-salt conditions; this protein has been designated M. The genome of human parainfluenza virus 3 is a linear RNA molecule with a molecular weight of approximately 4.6 X 10(6).

Iscom, a novel structure for antigenic presentation of membrane proteins from enveloped viruses

We describe here a novel type of immunostimulating complex, called 'iscom', in which virus membrane proteins are presented in a multimeric form. The matrix of the iscom is the glycoside Quil A (Spikoside; Iscotec AB), extracted from the bark of Quillaja saponaria Molina, which forms micelles at the critical micellar concentration of 0.03%. In micelle form, Quil A probably has regions accessible for hydrophobic interaction with the membrane proteins so that it can form complexes with them. Iscoms have been prepared with membrane proteins of para-influenza-3 (PI-3), measles and rabies viruses, and their immunizing potency tested in animals. In these experiments, iscoms prove to be at least 10 times more potent than micelles formed by aggregation of the membrane proteins alone. Iscoms of PI-3 and measles viruses also stimulate the formation of antibody to the fusion (F) protein, which is considered to be poorly immunogenic. No side effects of iscoms or of protein micelles have been observed.