Vaccines

Much progress has been made towards reaching an understanding of immune responses at the molecular level. This has provided much needed information for identifying the antigens which will afford protection against diseases such as rabies, malaria, whooping cough, hepatitis and acquired immune deficiency syndrome, and for presenting them to the immune system.

Structural and serological evidence for a novel mechanism of antigenic variation in foot-and-mouth disease virus

Changes resulting in altered antigenic properties of viruses nearly always occur on their surface and have been attributed to the substitution of residues directly involved in binding antibody. To investigate the mechanism of antigenic variation in foot-and-mouth disease virus (FMDV), variants that escape neutralization by a monoclonal antibody have been compared crystallographically and serologically with parental virus. FMDVs form one of the four genera of the Picornaviridae. The unenveloped icosahedral shell comprises 60 copies each of four structural proteins VP1-4. Representatives from each of the genera have similar overall structure, but differences in the external features. For example, human rhinovirus has a pronounced 'canyon' that is proposed to contain the cell attachment site, whereas elements of the attachment site for FMDV, which involves the G-H loop (residues 134-160) and C-terminus (200-213) of VP1, are exposed on the surface. Moreover, this G-H loop, which is a major antigenic site of FMDV, forms a prominent, highly accessible protrusion, a feature not seen in other picornaviruses. It is this loop that is perturbed in the variant viruses that we have studied. The amino acid mutations characterizing the variants are not at positions directly involved in antibody binding, but result in far-reaching perturbations of the surface structure of the virus. Thus, this virus seems to use a novel escape mechanism whereby an induced conformational change in a major antigenic loop destroys the integrity of the epitope.

"Instant-mix" whole brain photon with neutron boost radiotherapy for malignant gliomas

From July 1985 through March 1987, 44 consecutive patients with supratentorial, nonmetastatic anaplastic astrocytoma (AA) and glioblastoma multiforme (GBM) were treated with whole brain photon irradiation with concomitant neutron boost at the University of Chicago. All patients had biopsy proven disease and surgery ranged from biopsy to total gross excision. Whole brain photon radiation was given at 1.5 Gy per fraction, 5 days weekly for a total dose of 45 Gy in 6 weeks. Neutron boost radiation was prescribed to a target minimum dose that included the pre-surgical CT tumor volume plus 1 cm margin. Neutrons were administered 5-20 minutes prior to photon radiation twice weekly and a total dose of 5.2 Gyn gamma was administered over 6 weeks. Median follow-up was 36 months. The median survival was 40.3 months for anaplastic astrocytoma (10 patients) and 11 months for glioblastoma multiforme (34 patients) and 12 months for the overall group. Variables that predicted longer median survival included histology (AA vs. GBM), age (less than or equal to 39 years vs. older), and extent of surgery (total gross or partial excision vs. biopsy) whereas tumor size and Karnofsky performance status did not have a significant influence. The median survival of the anaplastic astrocytoma group was better than expected compared to the RTOG 80-07 study (a dose-finding study of similar design to this study) and historical data. Reasons for this are discussed.

Expression in yeast of amino-terminal peptide fusions to hepatitis B core antigen and their immunological properties

Hepatitis B core protein (HBcAg) is a potent antigen that gives both a T-cell-dependent and a T-cell-independent antibody response. It has been shown that a foreign epitope can be fused to the amino terminus of HBcAg without affecting particle integrity, and that the resulting chimaeric cores retain the immunogenicity of the foreign epitope. Here we describe the efficient expression in yeast of two different chimaeric cores, carrying epitopes of Foot and Mouth Disease Virus (FMDV) or human chorionic gonadotrophin (hCG), which are candidates for FMD and contraceptive vaccines, respectively. These cores could not be produced in E. coli in soluble form but were expressed to high levels in yeast. We constructed a yeast expression vector that allows rapid production of different chimaeric cores by cloning in cassettes encoding foreign epitopes. Both FMDV and hCG-cores were shown to present the epitopes at the surface of the particles. The FMDV-cores produced in yeast were efficient inducers of neutralising antibodies in guinea-pigs after one low dose.

The structure of foot-and-mouth disease virus: implications for its physical and biological properties

The structure of foot-and-mouth disease virus has been solved at a resolution of 2.9 A by X-ray diffraction techniques. The overall structural organisation of the particle is similar to that seen in other picornaviruses but there are several unique features. Many of these help to explain its characteristic physical and biological properties. In particular the canyon or pit found at the surface of other picornaviruses is lacking, which has important implications for cell attachment and the process of infection. Also there are 60 large disordered protrusions at the surface corresponding to the major antigenic site. This disorder is of particular interest in relation to the striking ability of linear synthetic peptides to induce protective immunity against foot-and-mouth disease.

Presentation and immunogenicity of viral epitopes on the surface of hybrid hepatitis B virus core particles produced in bacteria

We recently reported the enhanced immunogenicity of a peptide epitope when it was presented as a fusion protein with hepatitis B core antigen. In those experiments the fusion protein was expressed in vaccinia virus. We have now refined the system so that large amounts of highly immunogenic particles can be produced using a simple bacterial expression system. We describe the expression of three different viral epitopes as chimeric particles that induce good antibody responses to each epitope after one dose of low amounts of antigen. Finally we demonstrate that the immunogenicity is a reflection of both T helper cell sites within the core protein and also the particulate nature of the immunogens.

Immunological properties of hepatitis B core antigen fusion proteins

The immunogenicity of a 19 amino acid peptide from foot-and-mouth disease virus has previously been shown to approach that of the inactivated virus from which it was derived after multimeric particulate presentation as an N-terminal fusion with hepatitis B core antigen. In this report we demonstrate that rhinovirus peptide-hepatitis B core antigen fusion proteins are 10-fold more immunogenic than peptide coupled to keyhole limpet hemocyanin and 100-fold more immunogenic than uncoupled peptide with an added helper T-cell epitope. The fusion proteins can be readily administered without adjuvant or with adjuvants acceptable for human and veterinary application and can elicit a response after nasal or oral dosing. The fusion proteins can also act as T-cell-independent antigens. These properties provide further support for their suitability as presentation systems for "foreign" epitopes in the development of vaccines.

Neutralizing antibodies to all seven serotypes of foot-and-mouth disease virus elicited by synthetic peptides

Uncoupled peptides from all seven serotypes of foot-and-mouth disease virus (FMDV) protein VP1 have been used to elicit neutralizing antibody responses in guinea-pigs. The responses were largely serotype specific, although some significant cross-neutralization was observed. Dimeric tandem peptides have also been used to simultaneously elicit neutralizing antibodies to two different FMDV serotypes. The possible existence of structural features common to the B-cell neutralization sites or the guinea-pig helper T-cell sites within all seven peptides are analysed and discussed.

Chemically synthesized peptides elicit neutralizing antibody to bovine enterovirus

Synthetic peptides representing 14 regions of the bovine enterovirus structural proteins were used to raise antibodies in mice. The peptides were predicted using amino acid sequence alignments with the position of antigenic sites on other picornaviruses. Five of the anti-peptide antibodies reacted with the virus in an immunoprecipitation test. Furthermore, each of these anti-peptide antibodies neutralized virus infectivity; those directed against peptides of VP2 and VP3 neutralized to a greater extent than those directed against peptides of VP1. The positions of these epitopes in the viral structural proteins are discussed in relation to corresponding positions in other picornaviruses.

Serological prospects for peptide vaccines against foot-and-mouth disease virus

Antibodies to a synthetic peptide corresponding to the 141 to 160 amino acid sequence of the protein VP1 of type O foot-and-mouth disease virus (FMDV) neutralize a wider range of type O isolates than anti-virion serum. Extending this peptide at the amino terminus reduced the number of strains neutralized by the antipeptide sera. Reactions with antisera to peptides representing non-contiguous native sequences showed that it was also possible to increase the number of strains effectively neutralized. Selected substitutions of a single amino acid at position 148 markedly altered the neutralizing specificity of antibodies elicited by the 141 to 160 peptide. In particular, a peptide with an L----S substitution at this position induced antibodies which neutralized a type O and a type A virus equally, and guinea-pigs inoculated with it were protected from challenge with either virus. Attempts to isolate variant viruses resistant to neutralization with anti-peptide antibody indicated that these occurred at low frequency, and there was some evidence that resistance may be partially conferred by mutations outside the peptide sequence.

Neutralizing epitopes of type O foot-and-mouth disease virus. I. Identification and characterization of three functionally independent, conformational sites

Eleven neutralizing monoclonal antibodies (MAbs) were produced to the O1BFS 1860/67 strain of foot-and-mouth disease virus (FMDV), and were characterized for their ability to bind viral and subviral antigens in different ELISA tests and to neutralize heterologous type O isolates. Neutralization escape variants of the homologous virus, isolated under pressure from five of these MAbs, were used in cross-neutralization tests with all of the 11 antibodies. These studies identified three functionally independent, conformational, neutralizing sites. The most conformationally dependent site bound antibody which neutralized a range of type O virus isolates. A second site was less dependent on conformation and was recognized by antibody that was strain-specific. The least conformational site bound MAbs which showed limited cross-neutralization of other type O strains. This latter site appeared to be immunodominant and contained several overlapping epitopes which showed some differences in their specificities. Isoelectrofocusing and sequencing studies of the variants strongly suggested that polypeptide VP2 contributes to the immunodominant site.

Neutralizing epitopes of type O foot-and-mouth disease virus. II. Mapping three conformational sites with synthetic peptide reagents

Four neutralizing monoclonal antibodies (MAbs), recognizing three functionally independent, conformational sites on type O foot-and-mouth disease virus (FMDV) failed to react with immobilized structural proteins or synthetic peptides but bound to the isolated capsid protein VP1 and peptides in solution. Inhibition ELISA techniques were, therefore, applied using peptide antigens and anti-peptide sera to block MAb binding to virus particles, permitting the identification of those portions of the VP1 protein contributing to the epitopes. The binding site of one MAb, which neutralized a range of type O FMDV isolates, was shown to have components within regions 146 to 150 and 200 to 213 of VP1 with a critical involvement of the amino acids at positions 146 and 206 or 207. The determinants recognized by two other MAbs which were directed at similar, but not identical, epitopes from a second site included components from the 200 to 213 and 143 to 146 regions with amino acids 143 and 144, respectively, appearing critical for the inhibition of the virus binding of the two antibodies. These results demonstrate that the two previously identified immunogenic tracts of VP1 are brought into proximity in the quaternary structure of the virion to form an antigenic domain containing several conformational epitopes, some of which are functionally independent. A fourth, strain-specific MAb was effectively blocked from reacting with virus by peptides corresponding to residues 161 to 180 and 200 to 213.

Helper T-cell determinants in vaccine design

Mice belonging to the H-2d haplotype do not respond to the 141-160 peptide of foot-and-mouth disease virus protein VP1. However, when defined 'foreign' helper T-cell determinants from ovalbumin or sperm whale myoglobin are added they do respond. These observations are likely to have important implications for the design of peptide vaccines.

The cell attachment site on foot-and-mouth disease virus includes the amino acid sequence RGD (arginine-glycine-aspartic acid)

The amino acid sequence RGD (arginine-glycine-aspartic acid) is highly conserved in the VP1 protein of foot-and-mouth disease virus (FMDV), despite being situated in the immunodominant hypervariable region between amino acids 135 and 160. RGD-containing proteins are known to be important in promoting cell attachment in several different systems, and we report here that synthetic peptides containing this sequence are able to inhibit attachment of the virus to baby hamster kidney (BHK) cells. Inhibition was dose-dependent and could be reversed on removal of the peptide. A synthetic peptide corresponding to a portion of the same hypervariable region but not containing the RGD sequence did not inhibit virus attachment under the same conditions. Antibody against the RGD region of VP1 blocked attachment of the virus to BHK cells, and neutralizing monoclonal antibodies, which neutralize virus by preventing cell attachment, were blocked by RGD-containing peptides from binding virus in an ELISA test. Cleavage of the C-terminal region of virus VP1 in situ with proteolytic enzymes reduced cell attachment, and antiserum against a peptide corresponding to this region was also able to inhibit attachment of virus to BHK cells. These results indicate that the amino acid sequence RGD at positions 145 to 147 and amino acids from the C-terminal region of VP1 (positions 203 to 213) contribute to the cell attachment site on FMDV for BHK cells.

The three-dimensional structure of foot-and-mouth disease virus at 2.9 A resolution

The structure of foot-and-mouth disease virus has been determined at close to atomic resolution by X-ray diffraction without experimental phase information. The virus shows similarities with other picornaviruses but also several unique features. The canyon or pit found in other picornaviruses is absent; this has important implications for cell attachment. The most immunogenic portion of the capsid, which acts as a potent peptide vaccine, forms a disordered protrusion on the virus surface.