Vaccines: New concepts and developments

Conference Vaccines: New Concepts and Developments 1 4 - 1 7 July, 1986, Buffalo, New York The theme of the 10th International Convocation on Immunology, organized by the Ernest Witebsky Center for Immunology, was vaccines but in a very broad sense ranging from manipulating immunoglobulins, defining antigens and antigenic determinants, the basis of antigen recognition and antigen carriers to potential vaccines. A few of the numerous, exciting and interesting papers will be briefly summarized here. Typically antibodies only have a binding capacity. Lerner (Scripps Clinic and ResearchFoundation) described experiments in which it is possible to obtain monoclonal antibodies (MCA) which will transcend the binding to do chemical work. The MCAs were directed against a tetrahedral intermediate in the reaction of one planar molecule going to another. In the presence of such MCAs, the reaction could actually be brought about. Thus, the results suggest there is potential for developing antibodies to direct very specific chemical reactions for which no enzymes exist. Using cytochrome c as a model antigen, Margoliash (Northwestern University) has defined the minimal length of a peptide capable of activating T-helper cells as about 10 amino acids. Although the mechanism of activation and binding of the peptide fragment to the surface of T-cells is unknown, results from this laboratory implicate a 72-74 kDa protein in peptide binding. Antibody to this protein appears to specifically block antigen presentation. Experiments by Atassi (Baylor College of Medicine) using myoglobin in mice confirm the optimal peptide size to be about 14 amino acids. These antigenic sites are all on the surface of the molecule. It is possible to map the T-sites within the antigenic sites; however, there are also T-sites for which there is not a corresponding antigenic type for a specific mouse type. That is, mouse types differ in the repertoire of antigenic sites which they recognize; some would appear to have holes in their repertoire. Klinman (Scripps Clinic and Research Foundation) discussed the problem of immunizing the young which simply do not have the repertoire of an adult because they do not have the number of B-cells. The repertoire that they do recognize is also non-random. It was pointed out by Ogra (State University of New York at Buffalo) that

most infections, both bacterial and viral, are acquired via the mucosal route. Comparison has been made of live versus killed vaccines and oral versus parenteral routes of immunization. It would seem that live oral vaccination gives the desired effect without the unwanted side-effects of parenteral vaccines. Also oral immunization gives responses at different mucosal surfaces but the level of the response may vary. The use of live oral vaccines was also stressed by Curtiss (Washington University, St. Louis) and Manning (University of Adelaide). Both are working with attenuated live salmonellae as carriers for foreign antigens. Curtiss has assessed the usefulness of a variety of mutations (asd, thyA, aroA, purA and galE) singly and in combination as attenuating markers. (A poster describing temperature-sensitive mutants as a means of attenuation was also presented, by Hooke). The combination of aroA and purA gives a strain capable of good colonization and which can generate a high level of cell mediated immunity. Curtiss has introduced the genes for two proteins of Streptococcus mutans into such strains and finds the proteins to be immunogenic and antibodies to be protective. Manning described development of a cholera vaccine based on introducing the genes for surface antigens of Vibrio cholerae into galE salmonellae. One of these antigens, the O-antigen of the lipopolysaccharide, can induce the production of protective antibodies. An attenuated salmonella expressing this antigen is being tested for immunogenicity in humans: it has none of the disadvantages of cholera toxin deletion mutants which still produce some diarrhoea in a significant proportion of volunteers. Further use of recombinant D N A technology was elegantly demonstrated by the work of Young (Massachusetts Institute of Technology). He described the use of ~.gtll for the isolation of phage ~. clones expressing Mycobacteriurn antigens. It is known that cell mediated immunity is the predominant important response in tuberculosis (M. tuberculosis) and leprosy (M. leprae) and they used gene fusions to produce sufficient amounts of antigen which could be presented to T cell clones to look for stimulation. They then raised MCAs to identify the antigenic epitopes

Report

in protein fusions, derived from fusions with gene subfragments. A vaccine containing a 65 kDa antigen has been constructed. This protein is a strong immunogen and highly crossreactive amongst medically significant Mycobacterium spp. It may represent the antigen responsible for cross-protection between tuberculosis and leprosy. Vaccinia would seem to be a suitable vehicle for delivering this antigen. Paoletti (New York State Department of Health) and Smith (University of Cambridge) both spoke on the potential of vaccinia virus as a carrier for genes encoding protective antigens from other viral or parasitic infections. The great advantage of vaccinia is its proven success in eliminating smallpox, the ease of administration and the relative ease of genetic manipulations. The only major misgiving is the incidence (one in a million) of serious complications and sometimes death. A review of the AIDS virus and related retroviruses was presented by Montagnier (Pasteur Institute). He also discussed the prospects and difficulties of being able to vaccinate against the disease. One suggestion was to introduce the gene for the envelope protein into vaccinia. Hilleman (Merck Institute for Therapeutic Research) on the other hand suggested that a subunit vaccine produced via recombinant D N A technology was the way to go with AIDS as well as the retroviruses involved in multiple sclerosis and nonA, nonB hepatitis. He also pointed out that the best hope was for vaccination prior to infection but that almost any approach may be met with difficulty because of the hypervariability of the major envelope glycoproteins. Possibly the best chance is to not worry about antibodies to the virus itself but to hope that other antigens are inserted into the membrane of the infected cells which could then be eliminated. A number of lectures were based on idiotypes and anti-idiotypes and the prospects of idiotype vaccines. Roitt (The Middlesex Hospital Medical School) discussed the control of the immune response by antigen and idiotypic networks and how an anti-idiotype can function like an antigen without looking like the antigen. That is antiidiotypes may be structually dissimilar but functionally identical. Bona (Mount Sinai School of Medicine) extended this theme with the use of anti-idiotype antibodies to combat the antigenically variable influenza virus. Dreesman (Southwest Foundation of Biomedical Research) described results with an anti-idiotype antibody to hepatitis B virus surface antigen. This antibody deVaccine, Vol. 5, June 1987

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Conference Report tects the cross-reacting major epitope essential for inducing protection. It has been shown to be capable of conferring immunity in chimpanzees. Lambert (University of Geneva) presented evidence for the utility of anti-idiotype vaccines against parasitic infections to avoid the various immune response escape mechanisms of different parasites. Possible advantages which he saw were that it can be used to influence immunoglobulin isotype, bypass genetic restriction and avoid adjuvants. However, there is a potential problem of idiotype-anti-idiotype complexes. Krhler (Roswell Park Memorial Institute) also saw a role for anti-idiotype vaccines in the case of non-responders whether this be due to genetic reasons, an immature immune system, immunosuppression or being immunocompromized (as in AIDS, tumour and cancer patients). Synthetic peptides were also discussed in terms of vaccines and as carriers for antigens. Arnon (Weizmann Institute of Science) presented results with two different peptides. The first consists of a very immunogenic peptide present in numerous H3 type strains of influenza virus. Antibodies to this peptide produce a 50% reduction specific for the H3 type. The second peptide corresponds to residues 50-64 of the B subunit of cholera toxin. Antibodies have significant neutralizing capacity against the toxin and its effects as well as against the related LT toxin of enterotoxigenic Escherichia coli. Another peptide corresponding to the GM1 ganglioside binding domain of the B subunit of cholera toxin has been shown (Reid, Tseng, Hooper and Brewer, Walter Reed Army Institute of Research) to serve as a carrier for synthetic antigens during in vitro immunization. Apparent molecular mimicry of a host antigen by a pathogen also poses a problem and the example presented was the heart muscle determinant shared by group A streptococci (Cunningham, University of Oklahoma Health Sciences Center; Stinson, State University of New York at Buffalo). During acute rheumatic heart disease (S. pyogenes) and subacute bacterial endocarditis (S. mutans) heart reactive, i.e. autoantibodies, are detected. The myosin antibodies are not related to streptococci and streptococcal antibodies cannot react with cardiac muscle. The cause is not understood, but two possibilities seem likely; either the nonspecific activation of self reactive B-lymphocytes by bacterial components or tissue damage may cause the exposure of normally hidden self antigens. Both lead to the production of autoantibodies. The Ernest Witebsky Memorial Lecture was presented by Dr Jonathon Uhr (University of Texas Health Science

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Center) on the topic 'Immunotoxins: new pharmacologic agents for the treatment of cancer and immune dysfunction'. He discussed the construction and use of ricin-coupled specific-antibodies as a means of selectively eliminating cells carrying the corresponding antigen. It was suggested that FAB fragments are preferable to whole Ig molecules and proposed a scheme by which these immunotoxins could be produced. This involved constructing a hybrid gene consisting of VH CH coding region coupled via a D N A linker to the coding region of the A chain of ricin. If this was transfected into a hybridoma secreting L chain (VL CL) then the appropriate FAB-ricin molecule would be made. Results of a phase 1 trial, in which

similar molecules directed against a melanoma were used, gave promise. However, the period of regression of the tumour took weeks instead of the predicted few days. The diversity of technologies and approaches presented at the meeting gives hope for a wealth of effective vaccines against a wide range of diseases. All the lectures and poster abstracts presented at the meeting are to be published in mid-1987 by Longmans, UK (Eds H. Krhler and P.T. LoVerde).

P.A. Manning University of Adelaide, Australia

22nd US-Japan Cholera Conference 20-23 July 1986, Toyama, Japan The annual conferences (held alternately in the US and Japan) organized by the cholera panel of the US-Japan Cooperative Medical Science Program do not just discuss Vibrio cholerae but encompass a broad range of bacterial diarrhoeal pathogens. The areas covered include epidemiology, pathology and immunology, molecular biology and molecular genetics. Together they are aiming to present a coherent picture of the interactions of the bacterium with its host and the role of the molecules involved in pathogenesis and immunity. Such an understanding is clearly providing guidelines for vaccine development and treatment of the diseases. The number of Vibrio spp. and the variety of the diseases they produce was demonstrated by the report of vibrios associated with cholecystitis (Yamagistu, Toyama Medical and Pharmaceutical University) and the wealth of toxins found (Honda, Osaka University). These toxins include cholera-like toxins, haemolysin, thermostable direct haemolysin, heat stable toxin, shiga-like toxin and protease. The ecology of non-01 V. cholera and V. mimicus in various waters and fish and the seasonal variability was described (Kodama, Toyama Institute of Health). Also the role of factors such as chitin and its derivatives in maintaining viability of vibrios was discussed (Amako, Kyushu University). Several papers were presented which related to cholera vaccines or potential protective antigens which should be present in a vaccine. Kaper (Center for Vaccine Development) presented data on another cholera toxin deletion strain which was less reactogenic than previous strains. However, some residual

diarrhoea is still detected (1 out of 9 volunteers) and the factor(s) responsible for this are not known. Clemens (ICDDR, Bangladesh) revealed results of the 1985 field trial in Bangladesh of the oral B-subunit killed whole cell (BSWC) and killed whole cell (WC) cholera vaccines. Protection of 85% with BSWC and 58% with WC was reported. The question, however, must be raised as to whether this level of protection would be obtained in an unprimed population, Another approach to a cholera vaccine was described by Manning (University of Adelaide). This involves introducing V. cholerae surface antigens into attenuated salmonellae to be used as live oral vaccines. He described molecular cloning of genes for two antigens, an outer membranes protein and the O-antigen of the lipopolysaccharide. Antibodies to this latter antigen are highly protective in animal models. Interestingly, an apparently unrelated marine vibrio shares O-antigenic determinants with V. cholerae 01 (Hisatsune, Josai University). Another antigen relevant to vaccines may be timbriae, and Ehara (Nagasaki University) presented data strongly implicating timbriae as important for ~dherence and antibodies to fimbriae being protective. Cholera toxin may have other effects besides that on the adenylate cyclase system. Zinnaka (National Defense Medical College) demonstrated a suppressive effect on cellular immunity and Taguchi (Kyorin University School of Medicine) suggested that cholera toxin promotes intra-intestinal growth of V. cholerae in a model animal system. Also using an animal model, Miura (Keio University School of Medicine) showed that both somatostatin and loperamide almost completely inhibited the secre-