Peptides bound to proteosomes via hydrophobic feet become highly immunogenic without adjuvants.

Addition of either a lauroyl or a pentapeptide (FLLAV) hydrophobic foot to the NH2 terminus of a small, synthetic peptide allowed the peptide to hydrophobically complex to meningococcal outer membrane protein proteosomes by simple dialysis. Both conventional and LPS-hyporesponsive mice immunized with these complexes without any adjuvants developed high-titered and persistent anti-peptide IgG. Since proteosomes have been safely given to many people and since important antigenic determinants are generally hydrophilic, this system should be widely applicable to the development of peptide vaccines for human use.

Proteosome-lipopeptide vaccines: enhancement of immunogenicity for malaria CS peptides.

Proteosomes are hydrophobic, membranous, multimolecular preparations of meningococcal outer membrane proteins that are also B cell mitogens. These characteristics suggested that proteosomes may serve as carrier proteins and adjuvants to enhance peptide immunogenicity. Although high titers of malaria circumsporozoite (CS) antibodies protect against malaria, vaccines thus far tested in humans have been insufficiently immunogenic to be clinically useful. Here it is shown that synthetic CS peptides hydrophobically complexed to proteosomes by way of lauroyl-cysteine become highly immunogenic in mice without other adjuvants. The high titers of antibodies produced and the safety of proteosomes in humans suggest that this novel system is widely applicable for the development of peptide vaccines to protect against many diseases.

Immunoglobulin allotypes and immune response to meningococcal group B polysaccharide.

Serum samples were collected from 120 healthy adult volunteers (105 Caucasians and 15 Negros) before and after immunization with meningococcal polysaccharide (MPS) group B vaccine. Antibodies to MPS group B were measured and sera were typed for several Gm and Km(1) allotypes. A significant association was found between the Km(1) allotype and immune response to MPS group B in Caucasians.

Complex of meningococcal group B polysaccharide and type 2 outer membrane protein immunogenic in man.

A noncovalent complex of meningococcal group B polysaccharide and type 2 outer membrane protein has been characterized and its potential as a vaccine against group B meningococcal disease investigated. The polysaccharide component was found to have a partition coefficient, K(d), of 0.34 on Sepharose CL-4B in the presence of sodium deoxycholate. The protein consisted of four to five major proteins including the principal outer membrane protein. Hydrophobic binding between the protein and polysaccharide was demonstrated by gel filtration and isopycnic CsCl density gradient centrifugation and found to involve all of the proteins. After demonstrating safety and immunogenicity in animals, two lots of vaccine were tested in a total of eight volunteers. Two 120-mug doses were given subcutaneously at 0 and 5 wk. Mild local reactions occurred in all eight volunteers, but no systemic reactions were observed. 2 wk after the first dose, six of the volunteers had increased levels of bactericidal antibodies against both the group B polysaccharide and the outer membrane proteins. Antibody rises to the group B polysaccharide (mean 6-fold) were confirmed by passive hemagglutination assays and rises to the proteins (mean 10-fold) by a solid phase radioimmunoassay. The second dose resulted in little or no increase in antibody titers. Antibody titers declined over a period of 14 wk but mostly remained above preimmunization levels. Bactericidal antibodies with specificity for the group B polysaccharide were mostly of the immunoglobulin (Ig)M class, and were directed against a determinant associated only with high molecular weight polysaccharides. We conclude that both the group B polysaccharide and the outer membrane protein are immunogenic in man when presented as a complex and that the complex warrants further testing and development as a vaccine against group B meningococcal disease.

A rapid and sensitive PCR strategy employed for amplification and sequencing of porA from a single colony-forming unit of Neisseria meningitidis.

The predicted amino acid sequence was determined for the class-1 outer membrane protein, PorA, from a B:15:P1.7,3 strain of Neisseria meningitidis that is currently causing an epidemic of meningitis in Northern Chile. The P1.7,3 PorA showed a unique sequence in the exposed loop 4 of the putative porin structure that is different from all the reported PorA sequences. Based on the nucleotide (nt) sequence of the P1.7,3 porA, we designed two sets of PCR (polymerase chain reaction) primers that specifically amplified porA from any N. meningitidis strain, and a third set of primers that amplified porA only from the P1.7,3 strain. Using these primers, we developed a sensitive double hot-start nested PCR (HNPCR) strategy that could amplify porA and generate nt sequence from as low as a single colony-forming unit. This strategy consisted of three phases of PCR. The first two phases were designed to generate amplified target DNA that could be directly visualized by ethidium bromide staining starting from one to two molecules of Neisseria genome. The third phase was designed to generate a sequence of several hundred nt directly from the amplified DNA. A number of culture-negative cerebrospinal fluid samples from individuals suspected of meningitis during a vaccine trial were analyzed by this strategy to obtain more accurate information on the actual number of cases that occurred in the study and the non-study populations. The basic HNPCR strategy described here could be applied to amplify and sequence target DNAs from any low-copy-number biological sample.

Use of a zwitterionic detergent for the restoration of the antibody-binding capacity of electroblotted meningococcal outer membrane proteins.

A method is described for the partial restoration of the antibody-binding capacity of meningococcal class 2 outer membrane proteins (40-42 K molecular weight) following denaturation (dissociation) in boiling sodium dodecyl sulfate (SDS). The method relies on the presence of 0.1-0.4% zwitterionic detergent in the electrode buffer during the electroblot transfer of proteins from SDS-polyacrylamide gels to nitrocellulose paper. Meningococcal class 2 proteins which had lost their earlier capacity to bind mouse monoclonal antibodies in the normal blot procedure after SDS-polyacrylamide gel electrophoresis, bound monoclonal antibodies following the addition of the zwitterionic detergent to the blot buffer. Human post-vaccination anti-class 2 protein antibodies reacted with serotype 2a class 2 protein in a similar manner. This simple modification to the electroblot procedure proved helpful in identifying mouse monoclonal antibodies and human antibodies specific for native meningococcal class 2 proteins.

A general approach to standardization of the solid-phase radioimmunoassay for quantitation of class-specific antibodies.

The feasibility of using an anti-human immunoglobulin/human immunoglobulin/[125I]anti-human immunoglobulin 'sandwich' in a solid-phase radioimmunoassay to produce a standard curve which could be used to quantitate antigen-specific antibody of a particular immunoglobulin class was investigated. The amount of secondary antibody (SAb) bound was determined as a function of whether the primary antibody (PAb) was bound to its specific solid-phase antigen or by a solid-phase anti-human immunoglobulin. No significant difference between the two values was observed. Quantitation of antitetanus toxoid antibody by this method was in good agreement with quantitative precipitin tests. Comparison of SAb binding as a function of the way the PAb is bound was extended to class-specific PAb by use of murine monoclonal antibodies to meningococcal antigens. In most cases somewhat greater binding of SAb occurred when PAb was bound to antigen, but in several cases where low avidity antibody and/or poor quality antigens were used, greater SAb binding occurred when PAb was bound by anti-mouse immunoglobulin. The results indicate that this approach may be useful as a general method for standardizing the SPRIA and other solid-phase immunoassays such as the ELISA to measure class-specific antibody.

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.

Lipo-oligosaccharide immunotyping of Neisseria meningitidis by a whole-cell ELISA with monoclonal antibodies.

To assess the applicability of a whole-cell ELISA (WCE) with monoclonal antibodies (MAbs) for lipo-oligosaccharide (LOS) immunotyping of Neisseria meningitidis, 675 meningococcal isolates obtained in 1989 and 1990 in the Netherlands and 57 isolates collected in 1974, of which the immunotype had been determined previously by microprecipitation, were analysed. Despite the lack of specific MAbs for L2 and L4, an algorithm was developed for the assignment of immunotypes on the basis of the reaction patterns of the reference strains and these isolates to a combination of 14 MAbs. The immunotypes found by WCE were in accordance with those obtained by microprecipitation and the results from WCE were reproducible. The distribution of immunotypes among isolates of the various serogroups in the Netherlands in 1989-1990 is presented. Based on the reaction patterns of the isolates, two main categories of related immunotypes could be distinguished among isolates of serogroups B and C: L2/L4 and L3/L1/L8. Some isolates of the latter category were of one immunotype, but many isolates expressed one or two additional immunotypes, either strongly or weakly, indicating that the differences in this category are quantitative rather than qualitative. The results of this study have demonstrated that the WCE method for LOS immunotyping is easily applicable and provides better definition of test strains for in-vitro bactericidal assays and research into pathogenesis.

Meningococcal vaccines--present and future.

Over 20 years after the development of the meningococcal A and C vaccines, an effective vaccine against Neisseria meningitidis group B is still lacking. Major obstacles in the development of a B vaccine have been the remarkable capacity of the organism to evade the immune defences of the host and the lack of a predictive animal model. Three group B vaccines based on outer membrane proteins have been, or are currently being, evaluated in field trials. Nevertheless, a number of important questions remain such as the identity of the active components, the degree of efficacy against heterologous group B subtypes, and the duration of protection. In addition, work on a variety of alternative approaches to a group B vaccine is rapidly progressing. Among these are use of chemically modified group B polysaccharide, synthetic or natural lipopolysaccharide epitopes, synthetic peptides corresponding to bactericidal epitopes on the class 1 outer membrane protein, and iron binding proteins. Although each of these approaches has some problems associated with it, the prospects remain good for an effective solution to the group B problem.

Proteosome-hydrophobic 'foot' malaria peptide vaccines for Plasmodium falciparum and P. vivax.

The immunogenicity of synthetic peptides representing the repeating portions of circumsporozoite proteins of Plasmodium sporozoites was greatly increased by complexing them to proteosomes via hydrophobic moieties added to their amino termini. Proteosomes have been used safely in people in the development of meningococcal vaccines and therefore proteosome-peptide vaccines are prime candidates for use against malaria.

The use of filter paper monoclonal antibodies in a Dot-blot test for typing Neisseria meningitidis B.

A simple method for the collection, preservation, shipment, and testing of minute amounts of dried monoclonal antibodies for typing Neisseria meningitidis B is described. The monoclonal antibodies collected on filter paper were extracted in PBS and evaluated by Dot-blot employing whole cells of N. meningitidis B as antigen. The dried filter paper with monoclonal antibodies could be stored at room temperature for as long as 30 days without detectable changes in antibody response when used for typing outer membrane antigens of N. meningitidis B.

A phase 1 study of a meningococcal native outer membrane vesicle vaccine made from a group B strain with deleted lpxL1 and synX, over-expressed factor H binding protein, two PorAs and stabilized OpcA expression.

This phase I clinical trial assessed the safety and immunogenicity of a native outer membrane vesicle (NOMV) vaccine prepared from an lpxL1(-) synX(-) mutant of strain 8570(B:4:P1.19,15:L8-5) of Neisseria meningitidis. Additional mutations enhance the expression of factor H binding protein variant 1 (fHbp v.1), stabilize expression of OpcA and introduce a second PorA (P1.22,14). Thirty-six volunteers were assigned to one of four dose groups (10, 25, 50 and 75 mcg, based on protein content) to receive three intramuscular injections at six week intervals with aluminum hydroxide adjuvant. Specific local and systemic adverse events were solicited by diary and at visits on days 2, 7, and 14 after each vaccination. Blood chemistries, complete blood count, and coagulation studies were measured on each vaccination day and again 2 and 14 days later. Blood for ELISA and serum bactericidal assays was drawn two and six weeks after each vaccination. The proportion of volunteers who developed a fourfold or greater increase in bactericidal activity to the wild type parent of the vaccine strain at two weeks after the third dose was 27 out of 34 (0.79, 95% C.I. 0.65-0.93). Against four other group B strains the response rate ranged from 41% to 82% indicating a good cross reactive antibody response. Depletion assays show contributions to bactericidal activity from antibodies to lipooligosaccharide (LOS), fHbp v.1 and OpcA.

Human immune response to meningococcal outer membrane protein epitopes after natural infection or vaccination.

Antibody levels in 41 sets of human acute- and convalescent-phase meningococcal sera were compared with those in 23 sets of human prevaccination and 2-week postvaccination sera. We used a modification of a solid-phase radioimmunoassay (SPRIA) technique to test each of the human serum samples as inhibitors of monoclonal antibodies (MAbs) that bind (HIMSPRIA) to the outer membrane complex from a 2a:P1.2:P5.1 strain. We used three murine MAbs specific for the 2a, P1.2, and P5.1 epitopes on meningococcal class 1, 2, and 5 proteins, respectively, to detect antibodies with similar specificities in human sera. Each of 40 available matching strains from patients were also screened with the three MAbs in a nitrocellulose spot blot assay. A total of 37 (92%) were positive for the 2a epitope, 36 (90%) were positive for the P1.2 epitope, and 16 (40%) were positive for the P5.1 epitope. Of 38 available convalescent-phase sera, 27 (71%) matched with these strains and had detectable inhibiting antibody for each of the MAb-defined protein epitopes of the infecting strain. Three convalescent-phase sera had no HIMSPRIA activity for MAb-defined epitopes that were present on the infecting strain; others had activity for one or two of the epitopes. The results were similar for pre- and postvaccination sera. The average level of HIMSPRIA activity for the P1.2 epitope was greater than fivefold higher in postvaccination sera compared with that in convalescent-phase sera. Sera with distinct patterns of HIMSPRIA activity also were tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis and showed a correlation between the HIMSPRIA activity for particular epitopes and the level of antibody binding to the immunoblotted proteins possessing those epitopes. A comparison of the HIMSPRIA and the bactericidal activity of selected postvaccination sera indicated a possible correlation between HIMSPRIA and bactericidal activity, but it also suggested the presence of bactericidal antibodies with specificities other than those defined by the MAbs.

Lipopolysaccharide serotyping of Neisseria meningitidis by hemagglutination inhibition.

The method of hemagglutination inhibition was used to investigate the antigenic diversity of lipopolysaccharide (LPS) from Neisseria meningitidis and to develop a serotyping systems based on this antigen. The system uses outer membrane complex prepared by a simple extraction procedure to inhibit homologous hemagglutination reactions involving sheep erythrocytes sensitized with purified LPS and rabbit antiserum raised to whole meningococci. Antisera with specificity for eight different LPS determinants were used as typing sera to serotype a cross section of 67 meningococcal strains. Only two strains (both group A) were not typable with the eight sera, and most strains had more than one type. Comparison of LPS type and bactericidal serotype suggests that the LPS and protein serotypes are independent serological markers.

Importance of complement source in bactericidal activity of human antibody and murine monoclonal antibody to meningococcal group B polysaccharide.

The bactericidal activity of human antibody and murine monoclonal antibody to meningococcal group B polysaccharide was investigated as a function of the complement source. The immunoglobulin M murine monoclonal antibody 2-2-B was shown by several different methods to be highly specific for meningococcal group B and Escherichia coli K1 capsular polysaccharides. It had strong bactericidal activity in conjunction with either rabbit or human complement, but gave a higher titer with rabbit complement. A strong prozone was observed in each case. Human postvaccination antibody to meningococcal group B polysaccharide was strongly bactericidal with rabbit complement, but had little or no bactericidal activity in conjunction with human complement. Antibodies in adult normal human sera that were bactericidal with rabbit complement were also found to be predominantly directed against the meningococcal group B capsular polysaccharide. Human antibodies that were bactericidal with human complement appeared to be primarily directed against noncapsular antigens.

Outer-membrane protein and lipopolysaccharide serotyping of Neisseria meningitidis by inhibition of a solid-phase radioimmunoassay.

A new procedure involving inhibition of a solid-phase radioimmunoassay was developed for specific determination of the outer-membrane protein and the lipopolysaccharide (LPS) serotypes of meningococci. Antigen was allowed to bind to the wells of a polyvinyl microtiter plate and then reacted with a limiting amount of homologous antibody which had been preincubated with buffer or a standard concentration of inhibiting antigen. The amount of antibody bound per well was quantitated by incubation with excess 125I-labeled goat anti-rabbit immunoglobulin. Typing sera for detecting eight LPS antigens and 18 protein antigens were made in rabbits by use of both the group C and group B bactericidal serotyping strains. Reactions between unabsorbed sera and purified LPS were inhibited in the LPS typing system, whereas reactions between absorbed sera and outer-membrane complex were inhibited in the protein typing system. Outer-membrane complex was used as the inhibiting antigen in both cases. Approximately 97% of the 80 group B and C strains tested were LPS typable, and 80% were protein typable. Of 51 group A strains tested, however, only 22% were LPS typable and 14% were protein typable. Several nonreciprocal correlations between the occurrence of particular LPS and protein serotype antigens on the same strain were observed, but in general the protein and LPS serotype antigens appeared to occur independently.

Type-specific antigens of group A Neisseria meningitidis: lipopolysaccharide and heat-modifiable outer membrane proteins.

The solid-phase radioimmunoassay inhibition method was used to analyze the noncapsular surface antigens of group A Neisseria meningitidis for type specificity. By use of antisera prepared against group A strains, three serologically distinct lipopolysaccharide antigens and five outer membrane protein antigens were identified among group A strains from a variety of geographical origins. Two of the lipopolysaccharide antigens were unique to group A strains while the third was similar to those on strains of other meningococcal serogroups. Fractionation of outer membrane proteins in the presence of 2% sodium deoxycholate followed by quantitative inhibition of the typing reactions with the subfractions revealed that the protein responsible for type specificity was not the principal outer membrane protein, but, most likely, the 31,000-dalton, heat-modifiable outer membrane protein. Thus, although group A strains may share a common principal outer membrane protein, typing is feasible using other surface antigens. In a survey of 82 group A strains, 93% were typable with respect to outer membrane proteins.

Comparison of cysteine and tryptophan content of insoluble proteins derived from wild-type and mi-1 strains of Neurospora crassa.

The possibility of an amino acid substitution (cysteine for tryptophan) in a membrane protein of the [mi-1] strain of Neurospora crassa has been investigated in detail by using a double radioactive labeling procedure. Auxotrophic strains of Neurospora having wild-type [+] or [mi-1] cytoplasm have been grown under conditions which result in the specific labeling of protein tryptophan with (3)H and protein cysteine with (35)S. Although the least soluble 1 to 20% of the [mi-1] mitochondrial membrane protein was usually found to have a higher Cys/Trp ratio (ratio of cysteine plus half-cystine to tryptophan) than the corresponding [+] fraction, it has been shown that these differences were due mainly to the presence of differential amounts of a very insoluble, cysteine-rich (Cys-rich) material. The same Cys-rich material was found in variable amounts in both [+] and [mi-1] cultures, but the concentration was usually higher in the [mi-1] cultures. The Cys-rich material is clearly distinct from "structural protein" on the basis of amino acid composition and appears to have no direct relationship to the [mi-1] phenotype. In the absence of the Cys-rich material, no difference between the Cys/Trp ratios of corresponding [+] and [mi-1] membrane proteins could be detected. We conclude, therefore, that the previously postulated amino acid substitution of cysteine for tryptophan in [mi-1] membrane protein is incorrect.

Analysis of parameters affecting the solid phase radioimmunoassay quantitation of antibody to meningococcal antigens.

An indirect solid phase radioimmunassay (SPRIA) performed in flexible polyvinyl microtiter plates was modified for quantitative determination of antibodies to various bacterial antigens. Parameters affecting quantitation of the assay were investigated by using meningococcal serotype antigens and rabbit antisera plate was essentially complete after 1 hr at 37 degrees C, and only 4 to 8% of the bound antigen was released during the course of the assay. About 90% of the specific primary antibody (PAb) added to the antigen-coated wells was bound after overnight incubation at room temperature, whereas, 10 to 25% of the bound PAb was released before completion of the assay. Under conditions of limiting PAb the time required for saturation binding of 125I-anti-immunoglobulin (secondary antibody = SAb) to the PAb was dependent on the concentration of SAb. At a concentration of 20 ng SAb/25 mul, maximum binding occurred in 12 to 16 hr at 22 degrees C. Uncer conditions of extreme SAb excess the cpm of 125I-SAb bound was directly proportional to the amount of PAb bound. Under these conditions the cpm of 125I-SAb bound per well can be related to the amount of PAb added per well by a time-dependent calibration coefficient K(t) which is the product of three parameters: 1) the specific activity of the 125I-SAb, 2) the ratio of PAb bound to SAb bound and, 3) the fraction of added PAb remaining bound to the plate. Experimentally determined values for these parameters were used to calculate K(t) and quantitate the specific antibody in nine rabbit antisera with the SPRIA. A close correlation (r=0.985) was found between these results and the results of quantitative precipitin tests performed by using the same antisera and antigens. Although the SPRIA results were an average of 33% lower, a more accurate value for K(t) can easily be determined by performing the SPRIA on several sera calibrated by the quantitative test. Reproducibility of the SPRIA for 10 replicate determinations was +/- 6.7%. The assay described is capable of measuring a minimum of about 0.5 mug antibody/ml of serum and appears to be applicable to many different antigens.