Specificity of antibodies elicited by a synthetic peptide having a sequence in common with a fragment of a virus protein, the hepatitis B surface antigen

On the meaning of affinity limits in B-cell epitope prediction for antipeptide antibody-mediated immunity

B-cell epitope prediction aims to aid the design of peptide-based immunogens (e.g., vaccines) for eliciting antipeptide antibodies that protect against disease, but such antibodies fail to confer protection and even promote disease if they bind with low affinity. Hence, the Immune Epitope Database (IEDB) was searched to obtain published thermodynamic and kinetic data on binding interactions of antipeptide antibodies. The data suggest that the affinity of the antibodies for their immunizing peptides appears to be limited in a manner consistent with previously proposed kinetic constraints on affinity maturation in vivo and that cross-reaction of the antibodies with proteins tends to occur with lower affinity than the corresponding reaction of the antibodies with their immunizing peptides. These observations better inform B-cell epitope prediction to avoid overestimating the affinity for both active and passive immunization; whereas active immunization is subject to limitations of affinity maturation in vivo and of the capacity to accumulate endogenous antibodies, passive immunization may transcend such limitations, possibly with the aid of artificial affinity-selection processes and of protein engineering. Additionally, protein disorder warrants further investigation as a possible supplementary criterion for B-cell epitope prediction, where such disorder obviates thermodynamically unfavorable protein structural adjustments in cross-reactions between antipeptide antibodies and proteins.

The position of the LysN epsilon H2-grafted antigens along the sequential oligopeptide carrier, Ac-(Aib-Lys-Aib-Gly)n (SOCn-II), influences the antibody recognition: application to the Sm main autoimmune epitope

A sequential oligopeptide carrier of antigenic peptides is presented, incorporating two Aib residues in each repetitive moiety: Ac-(Aib-Lys-Aib-Gly)(n) (SOC(n) -II; n = 2-4). The conformational study, by (1)H-nmr, CD, and Fourier transform ir spectroscopy, indicated that the SOC(n) -II carrier displays a pronounced 3(10)-helix, compared to the Ac-(Lys-Aib-Gly)(n) (SOC(n) -I) carrier of the same approximately backbone length, previously reported. One of the dominant autoimmune epitopes of the Sm and U1RNP cellular components, the PPGMRPP sequence, was coupled to the Lys-N(epsilon)H(2) groups of the SOC(n) -II carrier and used as antigenic substrate for detecting anti-Sm/U1RNP autoantibodies in ELISA assays. Anti-Sm antibodies are highly specific for systemic lupus erythematosus, while anti-U1RNP are specific for mixed connective tissue disease. The anti-(PPGMRPP)(5)-SOC(n) -II ELISA was compared with the anti-(PPGMRPP)(n) -SOC(n) -I ELISA, provided that both antigenic substrates possess the same amount of the epitope replicates. The significance of the lysine positions along the oligopeptide backbone of the carrier for a favorable antibody recognition of the anchored antigens is also examined.

Peptide immunogen mimicry of putative E1 glycoprotein-specific epitopes in hepatitis C virus

Hepatitis C virus (HCV) accounts for most cases of acute and chronic non-A and non-B hepatitis with serious consequences that may lead to hepatocellular carcinoma. The putative envelope glycoproteins (E1 and E2) of HCV probably play a role in the pathophysiology of the virus. In order to map the immunodominant domains of the E1 glycoprotein, two epitopes from amino acid residues 210 to 223 (P1) and 315 to 327 (P2) were predicted from the HCV sequence. Immunization of mice with the synthetic peptides conjugated to bovine serum albumin induced an antibody response, and the antisera immunoprecipitated the E1 glycoprotein (approximately 33 kDa) of HCV expressed by recombinant vaccinia virus. A panel of HCV-infected human sera was also tested with the synthetic peptides by enzyme-linked immunosorbent assay for epitope-specific responses. Of 38 infected serum samples, 35 (92.1%) demonstrated a spectrum of reactivity to the P2 peptide. On the other hand, only 17 of 38 (44.7%) serum samples were reactive to the P1 peptide. Strains of HCV exhibit a striking genomic diversity. The predicted P1 epitope showed localization in the sequence-variable region, and the P2 epitope localized in a highly conserved domain. Results from this study suggest that the E1 glycoprotein of HCV contains at least two potential antigenic epitopes. Synthetic peptides corresponding to these epitopes and antisera to these peptides may serve as the monospecific immunological reagents to further determine the role of E1 glycoprotein in HCV infection.

Engineered human vaccines

The limitations of human vaccines in use at present and the design requirements for a new generation of human vaccines are discussed. The progress in engineering of human vaccines for bacteria, viruses, parasites, and cancer is reviewed, and the data from human studies with the engineered vaccines are discussed, especially for cancer and AIDS vaccines. The final section of the review deals with the possible future developments in the field of engineered human vaccines and the requirement for effective new human adjuvants.

Hybrid hepatitis B virus nucleocapsid bearing an immunodominant region from hepatitis B virus surface antigen

A hepatitis B core antigen (HBcAg) gene bearing the 39-amino-acid-long domain A of hepatitis B surface antigen (HBsAg) within the HBcAg immunodominant loop has been constructed and expressed in Escherichia coli. Chimeric capsids demonstrated HBs but not HBc antigenicity and elicited in mice B-cell and T-cell responses against native HBcAg and HBsAg.

Markedly prolonged incubation period of hepatitis B in a chimpanzee passively immunized with a human monoclonal antibody to the a determinant of hepatitis B surface antigen

The protective efficacy of a human monoclonal antibody directed against the a determinant of hepatitis B virus (HBV) surface antigen was studied in a chimpanzee. A single high dose of 5 mg/kg (body weight) of monoclonal antibody SDZ OST 577 was intravenously administered to a chimpanzee, followed by intravenous challenge with 10(3.5) chimpanzee infectious doses of a wild-type HBV, the MS-2 strain (ayw subtype). The passively acquired antibody to HBV surface antigen could be detected for 40 weeks. Serum HBV DNA tested by a "nested" polymerase chain reaction assay was negative through the 36th week after virus challenge but became positive by the 38th week. The chimpanzee subsequently developed acute hepatitis B approximately 1 year after challenge. The nucleotide sequence of the a determinant of the surface gene of the replicated virus was identical with that of the inoculated wild-type virus. Thus, a human monoclonal antibody directed against the a determinant of HBV surface antigen delayed but did not prevent experimental infection of HBV and hepatitis in the chimpanzee. Our results indicate an incomplete ability of this antibody to protect against HBV infection in vivo after a single infusion.

Genetic alterations in the gene encoding the major HBsAg: DNA and immunological analysis of recurrent HBsAg derived from monoclonal antibody-treated liver transplant patients

A gene region encoding a segment of the major surface protein, HBsAg, of hepatitis B virus was analyzed from serum samples after orthotopic liver transplantation of three hepatitis B virus chronic carrier patients treated with a human anti-hepatitis B virus monoclonal antibody (SDZ OST 577). Each of these three patients became HBsAg negative after transplantation and therapy with the human anti-hepatitis B virus monoclonal antibody but returned to HBsAg positivity (first detected 143,251 and 252 days after the transplantation). Polymerase chain reaction DNA amplification was performed on DNA from serum samples showing low levels of recurrent HBsAg and reduced antigen reactivity with SDZ OST 577 antibody. Polymerase chain reaction DNA included a 230-bp highly conserved, major S gene region that was cloned into M13 bacteriophage; analysis of this DNA segment provided a consensus of DNA sequences for the serum samples exhibiting altered reactivity with the therapeutic monoclonal. Analysis of independent DNA clones from serum samples of patients exhibiting low but detectable recurrent serum levels of posttherapy HBsAg revealed the presence of S protein variant sequences when compared with polymerase chain reaction DNA derived from the original infected liver or pretherapy serum HBsAg. Genetic variation was predominant in a highly conserved peptide domain that has previously been implicated in antibody binding and neutralizing antibody epitopes. In independent patients infected with either adw or ayw hepatitis B virus subtypes, single nucleotide changes resulted in one to two amino acid differences for each variant allele (residues 124, 129, 131, 137, 140 and/or 145) when compared with pretherapy viral DNA. Administration of serum containing one of these variant viruses to a single hepatitis B-naive chimpanzee resulted in subclinical hepatitis and detectable levels of circulating anti-HBs and anti-HBc antibodies 49 and 70 days after virus administration, respectively. Hepatitis B virus DNA was recovered on liver biopsy between 6 and 8 wk after inoculation, although the animal remained persistently seronegative for HBsAg. DNA sequence analysis of both primate and patient liver hepatitis B virus confirmed the presence of the DNA encoding the S protein variant and associates this DNA with the predominant hepatotropic virus in liver infection.

A new synthetic functionalized antigen carrier

A new synthetic functionalized antigen carrier is described. It consists of a core of seven branched lysine residues, of which each of the four N-terminal lysine residues contains two N-(S-acetylmercaptoacetyl)-glutamyl residues. After removal of the protecting S-acetyl groups affording eight thiol functions, the carrier can easily be conjugated to a properly functionalized antigen, e.g. an S-(Npys)-cysteinyl peptide, thus affording a high molecular weight conjugate with an unusually high antigen content.

Competition between tuftsin and HBV S-protein sequences

The syntheses of HBV S-protein partial sequences: Thr-Lys-Pro-Thr (I), Thr-Lys-Pro-Thr-Asp (II), and Thr-Lys-Pro-Thr-Asp-Gly (III) and also of pentapeptide Thr-Lys-Pro-Gly-Arg (IV), are described. For the peptides II and III inhibitory activity against tuftsin was found. Peptide IV (an analogue of tuftsin-inhibitor Thr-Lys-Pro-Pro-Arg) demonstrated a tuftsin-like activity in the phagocytosis experiments.

Synthesis of peptide-immunogens corresponding to amino acid sequences from human histocompatibility class II membrane glycoproteins

Six peptides with amino acid sequences of human histocompatibility Class II membrane glycoproteins were synthesized by conventional solution methods. Five peptides were prepared by stepwise procedures from the carboxyterminus. The sixth was synthesized by fragment condensation (5 + 10 coupling). Antibodies to synthetic peptides were then used to locate exposed and buried regions in the membrane glycoproteins.

Controlled peptide-protein conjugation by means of 3-nitro-2-pyridinesulfenyl protection-activation

The disulfide bond in S-3-nitro-2-pyridinesulfenyl (S-Npys) compounds is stable towards the acid treatment used in solid-phase peptide synthesis, yet the liability of S-Npys-peptides towards nucleophiles enables the conjugation to proteins to proceed under mild conditions. Thus Boc-Cys(Npys)-OH was coupled as N-terminal residue to a resin-linked peptide chain. After deprotection and cleavage from the resin the Npys-cysteinylpeptide was attached to a properly functionalized protein by reaction with a mercapto group. The amount of peptide conjugated to the protein was determined by measuring the amount of 3-nitro-2-thiopyridone liberated. The cysteinylpeptide which was detached from the protein by reduction of the disulfide bond was shown to be identical with the product obtained by reduction of the Npys-cysteinylpeptide.

Translational selection in the expression of the hepatitis B virus envelope proteins

The region of the hepatitis B virus (HBV) genome coding for the viral envelope proteins contains three inphase ATGs that are conserved among viral subtypes. Each of these ATGs can be used as mRNA initiation codons. The three translated proteins share a carboxy-terminal region (the S protein) and extend amino-terminally to include the pre-S2 region in the middle (M) protein, and the pre-S1 and pre-S2 regions in the large (L) protein. We have inserted the HBV DNA coding for the M protein into a baculovirus expression vector. Infected insect cells transcribe a mRNA that is initiated solely within a baculovirus promoter, and that contains the initiator codons for both M and S proteins. Although these cells primarily secrete the M protein, the major translational product is the S protein, which is not secreted. This preferential translation, the result of the use of an internal initiator codon, demonstrates that the regulation of HBV envelope protein production can occur at the translational level.

In vitro hepatitis B virus suppression of erythropoiesis is dependent on the multiplicity of infection and is reversible with anti-HBs antibodies

Exposure of human bone marrow mononuclear cells to hepatitis B virus results in the suppression of the in vitro growth of several hematopoietic progenitor cells. We studied the degree of inhibition of erythroid progenitor cells that results as a function of the time of exposure of mononuclear cells to hepatitis B virus and the ratio of virus to mononuclear cells, the multiplicity of infection. With an overnight incubation of mononuclear cells with hepatitis B virus-containing sera, a multiplicity of infection of greater than one virus per mononuclear cell is required to observe significant inhibition of erythroid colony formation. This multiplicity of infection effect is also observed with purified Dane particles. Exposure of mononuclear cells to an increasing number of Dane particles results in a dose-dependent suppression of erythroid colony formation with significant inhibition observed with a multiplicity of infection of virus to mononuclear cells as low as 5:1. Murine monoclonal antibodies to HBsAg completely neutralize the hepatitis B virus-mediated inhibition of CFU-E while control antibodies do not. Purified HBsAg has no effect on colony formation. In conclusion, the hepatitis B virus-mediated inhibition of erythrogenesis in vitro provides a basis for understanding the bone marrow depression observed during hepatitis B virus infections and may provide an in vitro model for examining hepatitis B virus infection.

Antibodies recognizing human serum albumin are not elicited by immunization with preS2 sequences of the hepatitis B virus envelope protein

Antibodies to the preS2 region of the hepatitis B virus (HBV) envelope protein and to human serum albumin (HSA) were allegedly detected at about the same level in sera of humans with acute or chronic hepatitis B [Hellström et al., 1986]. It was claimed that anti-HSA arises as a result of an immune response to the preS2 sequence and that it was involved in hepatocellular damage. Over 100 sera from animals and humans immunized with HBsAg containing preS2 sequences, or with synthetic peptides from the preS1, preS2, and S regions of the HBV env protein were assayed for anti-HSA. The results revealed the following: 1) Immunization with the native preS2 sequence or with unconjugated synthetic peptides derived from that sequence does not result in elicitation of anti-HSA. Therefore the alleged appearance of anti-HSA during hepatitis B cannot be directly related to an anti-preS2-specific immune response. 2) Some synthetic peptides, whether or not they were derived from the preS2 sequence, when linked to certain carriers, but not to others, elicited in rabbits an anti-HSA response, which was markedly lower than the response to the homologous peptide. These anti-HSA antibodies could be separated from anti-preS2-specific antibodies by affinity chromatography and did not recognize the synthetic peptide used for immunization. The use in active immunoprophylaxis of hepatitis B of unconjugated peptides from the preS2 sequence with proven high immunogenicity will avoid carrier/linker-mediated induction of antibodies not relevant to protection against HBV.

A synthetic vaccine constructed by copolymerization of B and T cell determinants

Synthetic vaccines are based on the identification of short peptide sequences responsible for inducing a protective immune response. These sequences could contain B and/or T cell determinants. In this study, we have examined the recognition by B and T mouse lymphocytes of several synthetic peptides corresponding to regions of a bacterial and two viral proteins. These include a streptococcal S-34 peptide, H(99-121) and two other synthetic hepatitis B virus surface peptides. A lymph node proliferation assay was employed to detect T cell determinants. Limiting dilution analysis was used to estimate the frequency of clonal precursor B cells specific for an antigenic determinant. This study indicates that the synthetic hepatitis B virus surface peptides are recognized by B cells but not by T cells, whereas the S-34 peptide possesses both B and T epitopes. The copolymerization of the B determinant H(99-121) with S-34 has conferred immunogenicity to the H(99-121) peptide. After copolymerization, the synthetic hybrid molecule retained the S-34 T epitope and acquired a new determinant recognized by T cells. These results demonstrate that synthetic vaccines could be constructed by appropriate selection and organization of B and T determinants.

Development of a Genetically-Engineered, Candidate Polio Vaccine Employing the Self-Assembling Properties of the Tobacco Mosaic Virus Coat Protein

A synthetic gene coding for the coat protein of tobacco mosaic virus (TMVCP) was expressed in E. coli under the direction of the lacUV5 promoter. Modification of the 3' end of the TMVCP gene by insertion of a region coding for an antigenic epitope from poliovirus type 3 resulted in the production of a hybrid TMVCP (TMVCP-polio 3). Both the E. coli-produced TMVCP and TMVCP-polio 3 were shown to assemble into virus-like rods under acidic conditions in E. coli extracts. Their purification was accomplished in a single step by chromatography on Sepharose 6B. TMVCP-polio 3 induced the formation of poliovirus neutralizing antibodies following injection into rats. The level of immune response was related to the degree of polymerization of the TMVCP-polio 3 preparations.

The hepatitis B virus

DNA recombinant technology has radically changed hepatitis B virus (HBV) virology. The genetic organization, transcription and replication of the virus are basically understood, structures of integrated HBV sequences in hepatocellular carcinoma have been characterized, and new vaccines produced by recombinant DNA technique are being developed.

Hepatitis B virus contains pre-S gene-encoded domains

One of the open reading frames on hepatitis B virus (HBV) DNA comprises the coding region (designated the env gene) for the virus envelope proteins. Studies on messenger RNA transcription suggest that this gene has the potential to code for three related proteins: (1) a protein of 226 amino acids identified as a major protein constituent of the HBV envelope, termed S-protein; (2) a protein with 55 additional amino acids at the N-terminal coded for by a portion of the env gene upstream of the S-gene (pre-S); (3) a protein corresponding to the entire env gene (pre-S + S). Synthetic peptides from the N-terminals of proteins (2) and (3), and antisera to them have been used to study the occurrence and properties of pre-S sequences. The results presented here provide unambiguous evidence that all three env encoded proteins are present in HBV particles; synthetic peptides corresponding to the gene encoding pre-S are highly immunogenic and can be used in diagnostic tests for detection in human sera of antibodies preferentially recognizing HBV; such antibodies, specific for pre-S determinants, are elicited during hepatitis B infection and by immunization with HBV proteins (2) and (3); the hepatitis B vaccine licensed in the United States does not contain pre-S proteins; and the pre-S proteins of the HBV envelope contain domains specifically recognized by liver cells. These findings suggest that pre-S determinants are important in virus-neutralizing responses and should be present in HBV vaccines.

Delineation and conformational analysis of two synthetic peptide models of antigenic sites on rodent cytochrome c

Two regions of rodent cytochrome c, one within the first four residues of the molecule, which is N-acetylated, and one at a beta bend around residue 44, are known to be immunogenic and antigenic in rabbits. Using sequential peptide synthesis, we have determined the residues required for linear synthetic peptides within these sequences to bind to antibody raised in rabbits to intact rat cytochrome c. The residues that were important in binding the N-terminal peptides were N-acetylglycine at position 1 and valine at position 3. The smallest peptide sequence around residue 44 that would bind to antibodies was Gln-Ala-Ala-Gly-Phe. A theoretical conformational analysis of these peptides showed that the amino-terminal tetrapeptide adopts a wide statistical ensemble of conformational states and that the addition of residues beyond 41 and 45 in the other sequence does not appear to stabilize longer peptides in the native beta-bend conformation. Thus, the antigenicity conferred by Phe-46 and Gln-42 in this peptide is most likely due to the direct interaction of the side chains of these residues with the antibody binding site. The demonstration here that native conformation is not essential for antigenic peptides to bind to antibodies raised against the whole protein indicates that the association energy between antigen and antibody can be sufficient to induce conformation in conformationally flexible peptides. This supports the concept that anti-protein and anti-peptide antibodies may invoke conformational changes in cross-reactive protein antigens and may explain why longer peptides, which may adopt stable nonnative secondary structure, often do not bind to antibodies raised to the whole molecule.

HBsAg-serum protein complexes stimulate immune T lymphocytes more efficiently than do pure HBsAg

HBsAg from plasma of chronic hepatitis B carriers was purified by affinity chromatography using a mouse monoclonal antibody specific for HBsAg. Elution with buffer at two different pH values separated HBsAg into two fractions: one contained high amounts of immune complexes associated with HBsAg; the other contained larger quantities of the HBsAg polypeptides P24 and GP27 and only small amounts of immunoglobulin. When compared for effects on stimulating the proliferative response of freshly isolated lymphocytes and an HBsAg-specific T cell clone, the HBsAg fraction containing a high proportion of immunoglobulin was much more potent than HBsAg with low amounts of immunoglobulins or pure HBsAg, which was isolated from the culture supernatant of the human hepatoma cell line (PLC/PRF/5). The plasma-derived HBsAg with low amounts of complexed immunoglobulins became more immunogenic in the presence of an anti-HBsAg monoclonal IgG. The present results, combined with earlier findings, suggest that HBsAg associated with immune complexes is a more potent stimulator of T cells than purer HBsAg preparations due to an increase in the efficiency of monocytes to capture the antigen through binding to immune complexes for subsequent processing and presentation of the antigen. These observations could be of relevance for the preparation of effective hepatitis B vaccines from recombinant DNA and peptide synthesis technologies.

The impact of new technologies on vaccine development

The ability to move genetic determinants between species using in vitro gene-manipulation techniques has opened up new approaches to vaccine development. This has rapidly grown into an exciting area of research in both academic and industrial laboratories. There are numerous scientific challenges which require multidisciplinary teams to solve problems in creating new immunogens. This has challenged our existing knowledge about protein structure and conformation, microbial pathogenicity and the immune system. Recombinant-DNA techniques are invaluable as tools of analysis and antigen production. The surface of micro-organisms can also be minutely explored with the use of synthetic peptides and monoclonal antibodies. Nevertheless, these new technologies do not allow us to circumvent the need for detailed understanding of pathogens and the disease process. What is apparent from the work carried out so far is that there are few easy answers to vaccine development and it is not realistic to expect rapid solutions to these problems. As there are many potential targets for constructing novel vaccines for both human and animal diseases, it is helpful to establish some priorities. There is a tendency to look at the existing effective vaccines and simply direct research at producing them more economically or with enhanced safety and stability. The advantage of this approach is that considerable background work will have already been carried out establishing the basis for the application of recombinant DNA techniques. However, this can also lead to conflicts (often within the same institute or company) between the new and old technologies. This could be to the detriment of the new technologies which are still only partly developed and may not be good enough yet to compete with existing vaccines in cost or efficacy. The more ambitious, and eventually more rewarding, approach is to attempt to develop new vaccines where none had existed before. There is a vast untapped market, especially in the parasitic diseases, but the scientific problems may be considerable and much more background work is likely to be necessary. Indeed, most of the work in this area is more accurately referred to as basic research rather than vaccine development as totally new, effective vaccines are still some way off. Having directed research towards a specific organism or disease there are still many options available as to the scientific strategy to adopt. As discussed in this review it may be possible to consider subunits, synthetic antigens and live (attenuated or heterologous) organisms as possible vaccines.(ABSTRACT TRUNCATED AT 400 WORDS)

Live recombinant vaccinia virus protects chimpanzees against hepatitis B

Hepatitis B virus (HBV) is an important human pathogen responsible for over 200 million cases of chronic infection, many of which progress to hepatocellular carcinoma. Although HBV cannot be propagated in tissue culture, highly effective subunit vaccines obtained from the plasma of chronically infected patients have been developed and licensed. Such vaccines are safe but their expense and limited quantities make them unavailable to most Third World countries. Other approaches to vaccine construction, including purification of the HBV surface antigen (HBsAg) from genetically engineered eukaryotic cells and the synthesis of peptides predicted from the nucleotide sequence of the HBsAg gene, are still under evaluation. Another potential application of recombinant DNA technology to vaccine development is the use of live virus vectors to express foreign genes. An infectious vaccinia virus recombinant that expressed the HBsAg in animal cells and which stimulated the production of antibody to HBsAg (anti-HBs) in rabbits represented a novel candidate vaccine of this class. As a continuation of our earlier study, we now present evidence that chimpanzees vaccinated with a live recombinant vaccinia virus protected against hepatitis following challenge with HBV.

Affinity of antibody responses in man to hepatitis B vaccine determined with synthetic peptides

The affinity and level of antibody to hepatitis B surface antigen (anti-HBs) in recipients of a plasma-derived hepatitis B vaccine were determined with three different antigens. The first two antigens were prepared by chemical synthesis, to represent linear or cyclical forms of aminoacid sequences 139 to 147 of the major hepatitis B surface antigen (HBsAg) polypeptide. The binding of antibodies to these synthetic peptides was compared with that to a third antigen, prepared by solubilisation of the naturally occurring HBsAg, the basic component of the currently licensed hepatitis B vaccine in the United Kingdom. Antibody levels, expressed as total antibody combining sites (Abt) in fixed volumes of immune sera, increased throughout the course of immunisation and correlated with the development of antibody as measured by a commercially available radioimmunoassay. Abt values were similar for both forms of the synthetic peptide, although higher affinity values were found with the cyclical structure, which illustrates the importance of protein conformation in antibody responses to HBsAg. Antibody affinity for the three antigens increased progressively throughout the immunisation schedule but the pattern of affinity maturation varied according to the peptide used as an antigen probe and between subjects. Most subjects showed a significant rise in antibody affinity after the third (booster) dose of vaccine given at six months. The use of synthetic peptides allowed a quantitative and qualitative assessment of antibody responses to hepatitis B vaccine and confirmed that selected peptides corresponding to relevant HBsAg epitopes may be useful as alternative hepatitis B vaccines.

Use of peptide synthesis to probe viral antigens for epitopes to a resolution of a single amino acid

A procedure is described for rapid concurrent synthesis on solid supports of hundreds of peptides, of sufficient purity to react in an enzyme-linked immunosorbent assay. Interaction of synthesized peptides with antibodies is then easily detected without removing them from the support. In this manner an immunogenic epitope of the immunologically important coat protein of foot-and-mouth disease virus (type O1) is located with a resolution of seven amino acids, corresponding to amino acids 146-152 of that protein. Then, a complete replacement set of peptides in which all 20 amino acids were substituted in turn at every position within the epitope was synthesized, and the particular amino acids conferring specificity for the reaction with antibody were determined. It was found that the leucine residues at positions 148 and 151 were essential for reaction with antisera raised against intact virus. A lesser contribution was derived from the glutamine and alanine residues at positions 149 and 152, respectively. Aside from the practical significance for locating and examining epitopes at high resolution, these findings may lead to better understanding of the basis of antigen-antibody interaction and antibody specificity.

Hepatitis B virus infection. Current concepts of chronicity and immunity

Among the three types of viral hepatitis agents-A, B and non-A, non-B-the hepatitis B virus (HBV) has been best characterized by immunologic and recombinant DNA technologies. The indefinite persistence of hepatitis B virus infection in 85% to 90% of perinatally infected infants and in about 10% of those infected later in life accounts for a worldwide epidemiologic reservoir of more than 200 million carriers who are at a high risk for the development of delta-infection, chronic liver disease and hepatocellular carcinoma. Active immunization with a safe and effective vaccine, derived from the plasma of carriers of hepatitis B surface antigen (HBsAg), is envisaged to avoid viral hepatitis type B and its chronic sequelae. In addition to serologic and immunohistochemical markers of hepatitis B virus infection, hybridization assays using cloned HBV DNA have provided new insight into the biology of this virus, its persistence and its oncogenic potential in humans and in animal models. Genetic similarities have been recognized between HBV and the antigenically distinct non-A, non-B agents implicated in some cases of transfusion-associated chronic hepatitis. Structurally this unique group of HBV and HBV-like agents are DNA viruses with functional attributes of integration and replication analogous to the retroviruses.

Hepatitis B viral antigenic structure: signature analysis by monoclonal radioimmunoassays

An approach has been developed for the analysis of hepatitis B viral (HBV) antigenic structure that creates numerical "signatures" of HBV strains. This technique employs high-affinity IgM and IgG monoclonal antibodies (anti-HBsAg) directed toward distinct and separate determinants on hepatitis B surface antigen (HBsAg). Such antibodies have been used to develop sensitive and specific radioimmuno-assays for measurement of HBsAg-associated determinants in serum. In performing "signature" analysis separate binding curves for each monoclonal anti-HBsAg are generated by measuring immunoreactivity in serial dilutions of HBsAg-positive serum. Since the HBsAg concentration in serum is unknown, the binding profiles of groups of samples from the same "classic" HBV subtype are aligned by an iterative maximum likelihood procedure to give the numerical signature of that HBV subtype. By using this approach, HBsAg shows far more antigenic heterogeneity than previously recognized by polyvalent anti-HBsAg antibodies. Indeed, there are subgroups within the classic HBsAg subtypes. In addition, the a domain (common to all known subtypes or strains of HBV) has been shown to be multideterminant. Thus, these studies have demonstrated heretofore unrecognized differences in HBV subtypes. This approach also has broader significance for the study of subtle or major antigenic changes among other viral agents since it is not necessary to know the concentration of virus or viral protein in complex protein mixtures.

Antibodies against synthetic peptides of the B subunit of cholera toxin: crossreaction and neutralization of the toxin

Six peptides corresponding to various segments of the B subunit of cholera toxin have been synthesized and covalently linked to tetanus toxoid. Of the antibodies raised in rabbits against these conjugates, four crossreacted to different extents with the intact B subunit and whole native cholera toxin. Antisera to the peptide of sequence 75-85 were not crossreactive, whereas elongation by six amino acid residues resulted in a peptide (69-85) leading to antibodies crossreactive with the cholera toxin. Of most interest was peptide CTP3 (50-64), which was the only one that reacted with antisera to cholera toxin and which led to antibodies reacting with the cholera toxin to a similar level as its homologous peptide-antipeptide reaction. Indeed, antisera to CTP3 neutralized significantly the biological activity of cholera toxin, as followed by skin vascular permeability and by fluid accumulation in ligated small intestinal loops of rabbits.

H-2 linked genetic control of immune responsiveness to hepatitis B surface antigen (HBsAg) in mice

Recent data suggest that genes involved in the control of (1) immune responses of humans to HBsAg and (2) the susceptibility to the development of chronic hepatitis B are linked to the major HLA histocompatibility complex. Studies on the genetic regulation of anti-HBs responses and on the possible abrogation of nonresponsiveness to HBsAg in humans are difficult. In an attempt to develop a relevant animal model system, the anti-HBs response of inbred and congenic strains of mice was investigated. A great variation in anti-HBs responses among individual mice belonging to the same strains was observed. Nevertheless, it was possible to rank the inbred mouse strains studied according to their decreasing anti-HBs responses as follows: BALB/c[d] congruent to SWR/J[q] greater than C57BL/6J[b] congruent to DBA/2J[a] greater than AKR/J[k] greater than A/J[a] greater than CBA/CaJ[k] greater than SJL/J[s]. (Letters in brackets indicate H-2 haplotype). Only a small proportion of SJL mice had an anti-HBs response. Therefore, this strain may serve as a model for human nonresponders. Studies with the congenic strains B10.D2[d] and B10.S[s] indicated that genes conferring responsiveness to HBsAg are linked to the H-2 histocompatibility complex. However, genes not linked to H-2 also probably play a role in regulating anti-Hbs responses.