vaccine protocols

1 Overview of Vaccines Gordon Ada 1, Patterns of Infectious Processes Most vaccines are designed as a prophylactic measure, that is, to stimulate the immune response so that on subsequent exposure to the particular infec- tious agent, the extent of infection in the vaccinated individual is so low that disease does not occur. There is also increasing interest in designing vaccines that may be effective as a therapeutic measure. There are two contrasting types of infectious processes. 1.1. Intracellular vs Extracellular Patterns Some organisms, including all viruses and some bacteria, are obligate intrac- ellular parasites in that they only replicate inside a susceptible cell. Some para- sites, e.g., malarta, have an intracellular phase as one part of their life cycle. In contrast, many bacteria and parasites replicate extracellularly. Because of these differences, the immune responses required to control the infection may differ. 1.2. Acute vs Persistent Infections In the case of an acute infection, exposure of a naive individual to a suble- thal dose of the infectious agent may cause disease, but the immune response so generated will clear the infection within days or weeks. Death may occur if the infecting dose is so high that the immune response is qualitatively or quan- titatively insufficient to prevent continuing replication of the agent so that the host is overwhelmed. In contrast, many infections persist for months or years if the process of infection by the agent results in the evasion or the subversion of what would normally be an effective immune control reaction(s). Most of the vaccines registered for use in developed countries, and discussed briefly in the next section, are designed to prevent/control acute human infections. From. Methods m Molecular Medme: Vaccrne Protocols Edited by A Robmson, G Farrar, and C Wlblrn Humana Press Inc , Totowa, NJ 2 Ada Table 1 Currently Registered Viral and Bacterial Vaccines Viral Bacterial Love attenuated Vaccmia PO110 (OPV) Measles Adeno Yellow fever Mumps Rubella Inactivated, whole organism Influenza Rabies Japanese encephalitis Polio (IPV) Subunit Hepatitis B Influenza Conjugates (polysaccharides/protem carrier) Toxoids Combmations Measles, mumps, rubella (MMR) General reference (43) 2. Types of Vaccines Almost all of the vaccines m use today are against viral or bacterial mfec- tions (Table 1). They are of three types-live, attenuated microorganisms; inactivated whole microorganisms; and subunit preparations. 2.1. Live, Attenuated Microorganisms Some live viral vaccines are regarded by many as the most successful of all human vaccines, with one or two administrations conferring long-lasting immumty. Four general approaches to develop such vaccines have been used: 1. One approach, pioneered by Edward Jenner, is to use a vuus that is a natural pathogen in another host as a vaccine in humans. Examples of this approach are BCG Salmonella (Ty2 1 a) Vibno cholerae Bordetella pertussis Yersinia pestis Streptococcus pneumonzae Salmonella typhl VI carbohydrate Haemophilus vzfluenzae, type b Acellular B pertusszs Nelsseria meningldltis (A,C) H injluenzae, type b (Hib) Clostridlum tetanl Corynebactenum diphthenae Diphtheria, pertussis, tetanus VT) DPT, H injluenzae, type b (Hib) Overview of Vaccine 3 the use of cowpox and parainfluenza viruses in humans and the turkey herpes virus in chickens. More recently, the use of avipox viruses, such as fowlpox and canarypox, which undergo an abortive infection in humans, has given encourag- ing results in human trials (I). 2. The polio, measles, and yellow fever vaccines typify the second approach. The wild-type viruses are extensively passaged in tissue-culture/ammal hosts until a balance is reached between loss of virulence and retention of immunogenic- ity m humans. 3. Type 2 poho vnus is a naturally occurring attenuated strain that has been highly successful More recently, rotavirus strains of low virulence have been recovered from children’s nurseries during epidemics (2). 4. A fourth approach has been to select mutants that will grow at low temperatures and very poorly above 37’C (Chapter 2). The cold-adapted strains of influenza vuus grow at 25°C and have mutations in four of the internal viral genes (3). Although such strains were first described in the late 1960s and have since under- gone extensive clnncal trials in adults and children, they are not yet registered for human use. In contrast to the above successes, BCG for the control of tuberculosis remained until comparatively recently the only example of a live attenuated bacterial vaccine. Although still widely used in the WHO Expanded Programme of Immunization (EPI) for children, it has given very variable results in adult human trials. However, prolonged studies to make other attenuated bacterial vaccines, especially against Salmonella infections, have led more recently to a general approach involving the selective deletion or inactivation of groups of genes (4 and see Chapter 4). The first success was with the strain Ty2la, which has a faulty galactose metabolism, the success of which led to the development of strains with other gene deletions. This approach also shows promise for complex viruses. Thus, 18 open reading frames have been selectively deleted from the Copenhagen strain of vaccinia virus, including six genes involved in nucleotide metabolism, to form a preparation that 1s of very low virulence, but retains immunogenicity (5). The selective deletion of specific nucleic acid sequences is also being tried with simian immunodeficiency virus with some Initial success (6). This approach offers the prospect of a selective and repro- ducible means of producing adequately attenuated viral and bacterial prepara- tions. Live attenuated vaccines have the potential of stimulating the widest range of different immune responses, which may be effective in preventing, controlling, and clearing a later infection. 2.2. Inactivated Whole Microorganisms Inactivation of viruses, such as polio, influenza, rabies, and Japanese encephalitis vu-uses, and some bacteria, including Bordetella pertussis and Vzbrio cholerae, is the basis of vaccines with varying efficacy. Compared to 4 Ada the attenuated preparations, these vaccines need to be administered in substan- tially larger doses and sometimes more frequently. The viral vaccines are gen- erally effective in preventing disease, the low efficacy (70%) of the influenza viral vaccine being in part owing to the continuing antigenic drift to which this virus is subject. In contrast, the only bacterial vaccine of this nature still in wide use is the pertussis vaccine, which is highly effective, but has already been replaced by a subunit preparation in some countries because of adverse side effects attributed to the whole-cell vaccine (7). Inactivated whole vaccines generally induce many of the desirable immune responses, particularly infectivity-neutralizing antibody, but generally do not generate a class I MIX-restricted cytotoxic T-cell (CTL) response, which has been shown to be the major response required to clear intracellular infections by many viruses and some bacteria and parasites. 2.3. Subunit Vaccines The generation of antibody that prevents infection by both intra- and extra- cellular microorganisms has been regarded as the prime requirement of a vac- cine. The epitopes recognized by such antibodies are most usually confined to one or a few proteins or carbohydrate moieties present at the external surface of the microorganism. Isolation (or synthesis) of such components formed the basis of the first viral and bacterial subunit vaccines. Viral vaccines were com- posed of the influenza surface antigens, the hemagglutinin and neuraminidase, and the hepatitis B surface antigen (HBsAg). Bacterial vaccines contained the different oligosaccharide-based preparations from encapsulated bacteria (Chapter 8). In the latter case, immunogenicity was greatly increased, espe- cially for infants, by coupling the haptenic moiety (carbohydrate) to a protein carrier, thereby ensuring the involvement of T helper cells (Th-ceils) in the production of different classes of immunoglobulin (Ig), particularly IgG. The two bacterial toxoids, tetanus and diphtheria, represent a special situation where the primary requirement was neutralization of the activity of the toxin secreted by the invading bacteria (Chapter 7). HBsAg is present as such in the blood of hepatitis B virus-infected people, which was the source of antigen for the first vaccines. A major advance occurred when the same product was made from yeast cells transfected with DNA coding for this antigen, initiating the era of genetically engineered vaccines (8). Up to 17% of adults receiving this vaccine turn out to be poor or nonresponders, because of the age of the recipients and their genetic makeup (9). 3. Vaccine Safety All available data concerning the efficacy and safety of a candidate vaccine are reviewed by regulatory authorities before registration (Chapter 20). At that Overview of Vaccine 5 stage, potential safety hazards, which occur at a frequency of perhaps l/10,000, should have been detected. There are examples of undesirable side effects occurring at much lower frequencies, which are seen only during immuno- surveillance following registration, but these may be so low that their occur- rence as a consequence of vaccination is difficult to prove. For example, following the mass vaccmation program of people in the United States with swine influenza vaccine m 1976-1977, a small proportion developed the Guillain-Barre syndrome (10). This has turned out to be an isolated event. In the prolonged absence of frequent outbreaks of disease by specific vaccine- preventable infections following successful vaccination campaigns, the occur- rence of low levels of undesirable side effects following vaccination gains notoriety. The evidence bearing on causality and specific adverse health out- comes following vaccination against a number of childhood viral and bacterial infections, mainly in the United States, has recently been evaluated by an expert committee for the Institute of Medicine in the United States (II). The possibility of adverse neurological effects was of particular concern, and evidence for these, as well as several immunological reactions, such as anaphylaxis and delayed- type hypersensitivity (DTH), was examined in detail. In the great majority of cases, there was insufficient evidence to support a causal relationship, and where the data were more persuasive, the risk was considered to be extraordinarily low. Measles has provided an interesting example of vaccine safety. The WHO/EPI has provided data illustrating the remarkable safety of the standard vaccine (12). Furthermore, although natural measles infection induces an immunosup- pressive state from which most children recover, the above study recorded only two cases of immunosuppression in tmmunocompromised children following vaccination (II). In many developing countries, measles vaccmation is given at 9 mo of age: This delay is necessary to allow a sufficient decay of maternally acquired antibody. This decay to low levels occurs earlier in some infants, allow- mg an opportunity for infection by circulating wild-type virus before 9 mo. This factor contributes significantly to the l-2 million deaths/yr from measles infec- tion worldwide. To lessen this risk, “high-titer” measles vaccines were devel- oped that could be effective in 54mo-old children. Trials in several countries showed their apparent safety and ability to induce satisfactory immune respon- ses in this age group, so their general use was authorized by the WHO in 1989. Unfortunately, reports later appeared recording unexpected cases of mortality following vaccination, especially in young girls in disadvantaged populations (13), leading to the withdrawal of these vaccines from use. One possibility is that the high-titer vaccine caused a degree of immunosuppression sufficient to allow infections by other agents to occur. Inactivation of a whole microorganism, even a relatively sample virus, does not guarantee safety, Immunization of infants with mactivated measles or res- 6 Ada piratory syncytial vnus (RSV) preparations sensitized some recipients to severe reactions when they were later exposed to the wild-type virus (e.g., 14). Never- theless, the great safety record of the subunit viral vaccines is one factor con- tributing to the attractiveness of the subunit approach to vaccine development. 4. Efficacy There could be no more persuasive evidence of the worth of an immuniza- tion program as a very effective public health procedure than the eradication/ elimination of an mfectious agent. Global eradication was first achieved in 1977 when the last case of endemic smallpox was detected, slightly more than 10 years after the intensified WHO campaign was initiated. Followmg mten- sive immunization campaigns, the last case of endemic polio m the Americas was detected more than three years ago (1.5). Clearly, the smallpox and poho vn-us vaccines used in these campaigns are/were highly efficacious, although both elicited some undesirable side effects (16,17). The eradication of polio in the Americas is of itself remarkable and has led to intensified efforts in other regions, although it is recognized that global eradication of polio is a substan- tially greater challenge compared to smallpox. Nevertheless, the success in the Americas with poliomyelitis has led to the next challenge in that region-can measles, another viral infection specific for humans, also be eliminated in the Americas (18)? These achievements, together with the emergence of such diseases as AIDS, have greatly increased interest in all aspects of “vaccinology.” The following sections discuss the need for improved and new vaccmes against a variety of infectious agents, some of the new approaches now available for vaccine development, the properties and functions of different immune responses, and some of the obstacles that still face the vaccine developer. 5. Opportunities for Improved and New Vaccines There are clearly two possible requirements for vaccine development. One 1s to develop improved vaccines to replace some existing vaccines. The other, even more pressing need, is for vaccines against the many infectious agents that still cause considerable morbidity and in some cases mortality. Table 2 lists examples of diseases where improved vaccines are desirable, and some viral, bacterial, and other infections for which vaccines are not yet available. The rationale for the need for improved compared to current vaccines var- ies. For example, despite the efficacy and safety of the standard measles vac- cine, there is a need for an (additional?) vaccine that would be effective in the presence of maternal antibody. A genetically more stable type 3 live polio virus and a means to make the oral polio vaccine and other live vaccines more heat- stable would be desirable. The standard Japanese encephalitis viral vaccine is Overview of Vaccine 7 Table 2 Opportunities for Improved and New Vaccines Improved Viral Influenza A and B Japanese encephalms Polio Rabies Measles New Corona Cytomegalo Dengue Hepatitis A and C HIVland2 Hantan Herpes Norwalk agent Papilloma Parainfluenza Respriatory syncytial Rota Varicella Bacterial Cholera Meningococcus M. tuberculosis B. pertussis Others Chlamydia E. coli Group A and B streptococcus Haemophilus ducreyi Mycobacteria leprae Menmgococcus B Neisseria gonorrhoeae Shigella Malaria Schistosomiasis Giardia Filariasis Treponema B. burgdorferi produced from infected baby mouse brains, surely now an out-of-date approach. However, above all, fulfillment of the aim of the Children’s Vac- cine Initiative, i.e., to produce a formulation of children’s vaccines that can be administered at a smgle visit at or near birth and provide effective immunity against numerous diseases (19), is likely in the long term to result in major changes. Vaccines against many of the other agents in Table 2 are unlikely to be made using traditional techniques. For example, Mycobacterium leprue cannot be produced in sufficient quantity to make a whole-organism vaccine to admmis- 8 Ada ter to >lOO million people. It may also be impractical to produce large quanti- ties of some viruses to form the basis of a vaccine, but above all, some of the new approaches to develop vaccines hold out so much promise that they are bound to influence future manufacturing practices greatly. 6. New Approaches to Vaccine Development There are basically three new approaches that are being investigated. 1. The use of anti-idiotype antibody preparations to mimic B-cell epitopes. 2. The synthesis of ohgo/polypeptides, which reflect naturally occurrmg ammo acid sequences m proteins of the pathogen (Chapter 6). 3. The use of recombinant DNA (rDNA) technology (Chapter 5) to obtain DNA/ cDNA coding for antigen(s) of different pathogens or other factors, such as cytokines, and to use these m mainly three different ways: a. To transfect cells so that the inserted DNA/cDNA is translated and expressed. b. To insert the DNA/cDNA into the genome of other viruses or bacteria, which are usually chosen as vectors because of then record as effective and safe vaccines. Such clnmenc constructs are potential new vaccines (Chapters 3-5) c. A plasmid contannng the DNA/cDNA can be directly injected into cells in viva, where it is translated and expressed and immune responses nntiated (Chapter 21). 6.7. Anti-ldiofypes The attractions of this approach included the fact that the anti-idiotype should mimic (1) both carbohydrate and peptide-based epitopes; and (2) the conformation of the epitope in question. Despite such advantages, this approach has never really prospered. 6.2. O/igo/Po/ypepfides The sequences may contain either B- or both B-cell epitopes and T-cell determinants. Sequences containing B-cell epitopes may be conjugated to car- rier proteins that frequently act as a source of T-cell determinants or assembled in different configurations to achieve particular configurations or produce mul- tiple determinants. Some of the obvious advantages of this approach include the fact that the final product contains the critical components of the antigen, which offers the possibility of removal of segments mimicking host sequences. Multimerm constructs, such as Multiple Antigemc Peptide Systems (MAPS) can be highly immunogenic (20). In addition, recent work has shown that immunogemcity of important “cryptic” sequences may sometimes be enhanced by deletion of other segments of a molecule (21), and new methods of synthe- sis offer the possibility of more closely mimicking conformational patterns in the original protein (e.g., 22). This is now a very active field, and peptide-based vaccines seem to be assured of a significant share of the future vaccine market. Overview of Vaccine Table 3 Some Live Viral and Bacterial Vectors Viruses Vaccinia, fowlpox, canarypox, adenovlrus, polio, herpes, influenza Bacteria BCG, Salmonella, E. colt 6.3. Transfection of Cells with DNA/cDNA Three cell types have been used-prokaryotes; lower eukaryotes, mainly yeast; and mammalian cells, either primary cells (e.g., monkey kidney), cell strains (with a finite replicating ability), or cell lines (immortalized cells, such as Chinese hamster ovary [CHO] cells). Each has its own advantages, and bac- terial, yeast, and different mammalian cells are now widely used. As a general rule, other bacterial proteins should preferably be made in transfected bacterial cells and human viral antigens, especially glycoproteins, m mammalian cells, because of the substantial differences in properties, such as posttranslational modification in different cell types (23). 6.4. Live Viral and Bacterial Vectors Table 3 lists the viruses and bacteria mostly used for this purpose. Most experience has been with vaccinia virus, since it is very convenient to use, has a wide host range, possesses about 100 different promoters, and, as already stated, substantial amounts of DNA can be removed from it, leaving room for inserted DNA coding for at least 10 average-sized proteins. Several of the vec- tors, such as adenovirus, polio virus, and SuZmonelZu, should be ideal for deliv- ery via a mucosal route, although both vaccinia and BCG have also been given orally and intranasally. Making chimeric vectors has also been an effective way of assessing the potential role in immune processes of different cytokines. Inserting cDNA cod- ing for a particular cytokine as well as that for the foreign antigen results in synthesis and secretion of the cytokine at the site of infection. One of the more interesting recent findings is that inclusion of the cDNA coding for IL-6 greatly enhances production of sIgA specific for the viral antigens (24). 6.5. “Naked” DNA The most fascinating of recent approaches has been the injection of plas- mids containing the DNA of interest, either directly into muscle cells or as DNA-coated microgold particles via a “gene-gun” into skin cells. In the latter case, some beads are taken up by dendritic-like cells and transported to the 10 Ada Table 4 Properties and Functions of Different Components of the Immune Response Type of Type of response infection Cytokine profile Stages of infectious process Prevent Limit Reduce Clear Nonadaptive I E Adaptive Antibody I E CD4+ Th2 I E CD4+ Thl I E CD8+CTLs I E - ++ - ? +++ ++ +++ +++ IL-3,4,5,6,10,13 TNFa IL-2,3, IFNy, TNFa - ++ J-w - +++ IL-2, IFNy, TNFP +++ _ - - + - ? - ++ H- +++ ++-I- ++ ++? +-k+ +++ +++ ++-I- - - I, mtracellular mfectlon, E, extracellular mfectlon, IL, mnterleukm, IFN, Interferon, TNF, tumor necrosis factor draining lymph nodes. This procedure has resulted in quite prolonged humoral and cell-mediated immune responses. One of the potential benefits is that the induction of such responses should also occur in the presence of specific anti- body. The fact that a recent issue of a relevant scientific journal consists entirely of articles describing the use of this approach reflects the widespread interest in this approach (25). 7. Properties and Functions of Different Components of the Immune Response 7.1. Classes of Lymphocytes Our knowledge of the properties of lymphocytes, the cell type of major importance in vaccine development, has increased enormously in recent years. The major role of B-lymphocytes 1s the production of antibodies of different isotypes and, of course, specrficity. The other class of lymphocytes, the T-cells, consist of two main types. One, with the cell-surface marker CD4, exists in two subclasses, the Thl- and ThZcells (h standing for helper activity). A major role of Th2-cells is to “help” B-cells differentiate, replicate, and secrete anti- body. They do this in part by the secretion of different cytokines (interleukins, ILs), which are listed in Table 4. Thl-cells also have a small, but important role in helping B-cells produce antibody of certain isotypes, but the overall pattern of cytokine secretion is markedly different. Such factors as IEN-7, TNF-a, [...]... to lifelong mfectlon, unlessthe vaccine greatly hmits this and/or suchcells are readily destroyed Overview of Vaccine 13 9 Promising Further Developments Despite the above constraints, there are also some promising further developments of a general nature 9.1 Combination Vaccines Delivery of the vaccine can be a major cost component in vaccination programs Combining vaccines so that three or more can... Clark, H F and Offit, P A (1994) Rotavirus vaccines, in Vaccines, 2nd ed (Plotkin, S A and Mortimer, E A., eds.),Saunders,Philadelphia, pp 809-822 3 Maassab,H F., Shaw, M W., and Heilman, C A (1994) Live influenza virus vaccine, in Vaccines, 2nd ed (Plotkin, S.A andMortrmer, E A., eds.),Saunders, Philadelphia, pp 78l-801, 14 Ada 4 Levme, M M (1994) Typhoid fever vaccines, in Vucclnes, 2nd ed (Plotkm, S... response ISCOMS and QS21 may Induce a CD8+ CTL response (38) 8 Some Factors Affecting the Ease of Development of Vaccines Although the new technologies have effectively made it possible to develop vaccines to most infectious agents, many other factors may influence the speed at which such vaccines can be developed (39) Some of these factors are: 1 The simpler the agent,the more straightforward it 1slikely... S C., Sehgal, P K , and Desrosiers, R C (1992) Protective effects of a live attenuated SIV vaccine with a deletion in the nef gene Science 258,1938-1940 7 Mortimer, E A (1994) Pertussis vaccine, m Vaccznes, 2nd ed (Plotkm, S A and Mortimer, E A., eds.), Saunders, Philadelphia, pp 91-136 8 Hllleman, M R (1992) Vaccine perspectives from the vantage of hepatitis B Vaccwe Res 1, 1-15 9 Egea, E , Iglesias,... hepatitis B vaccine m humans J Exp Med 173, 531-542 10 Langmuir, I D., Bregman, D J., Kurland, L D., Nathanson, N., and Victor, M (1984) An epidemiologlcal and clinical evaluation of Guillam-Barre syndrome reported m association with the admmistration of swine influenza vaccine J Epzdemiol 119,841-879 11 Stratton, K R., Howe, C J., and Johnston, R B (1994) Adverse events associated with childhood vaccines... American Health Organization, Washmgton 16, l-2 19 Douglas, R G (1993) The children’s vaccine initiative-will it work? J InjI Dzs 168,269 274 20 Tam, J P (1988) Synthetic peptide vaccine design: synthesis and properties of a high density multiple antlgemc peptide system Proc Natl Acad Scz USA 85, 5409-5413 Overview of Vaccine 15 21 Pruksakorn, S., Cume, B., Brandt, E., Martm, D., Galbraith, A , Phornphutkul,... G., and Scott, P (1994) The adJuvant effect of mterleukm-12 in a vaccine agamst Leishmania major Science 263,235-237 16 Ada 38 Cooper, P D (1994) The selective mductron of dtfferent immune responses by vaccme adjuvants, m Strategies in Vaccine Deszgn (Ada, G L., ed.), Landes, Austin, TX, pp 129-158 39 Ada, G L (1995) The development of new vaccines, in Vaccination and World Health (Cutts, F and Smith,... 168,306-3 13 43 Plotkin, S A and Morttmer, E A (eds.) (1994) Vaccznes W B Saunders, Phrladelphra 2 Temperature-Sensitive Mutant Vaccines Craig R Pringle 1, Introduction Many live virus vaccines derived by empirical routes exhibit temperaturesensitive (ts) phenotypes The live virus vaccines that have been outstandingly successful in controlling poliomyelitis are the prime example of this phenomenon The three... neurovirulence Concomitantly, all three vaccine strains developed ts characteristics, a phenotype that correlated well with loss of neurovirulence, The reproductive capacity at supraoptimal(4O”C) temperature, the ret phenotype, proved to be a useful property for monitoring the genetic stability of the attenuated virus during propagation, vaccine production, and replication in vaccinees Nucleotide sequencing... from a vaccine- associated case of paralysis and assayin primates of the neurovirulence of recombinant viruses prepared from infectious cDNA established that two of the 10 mutations in the type-three vaccine strain were associated with the loss of neurovirulence The mutation conferring temperature sensitivity was one of these mutations (I) Since all three independently modified poliomyelitis virus vaccines . two possible requirements for vaccine development. One 1s to develop improved vaccines to replace some existing vaccines. The other, even more pressing need, is for vaccines against the many infectious. bacterial subunit vaccines. Viral vaccines were com- posed of the influenza surface antigens, the hemagglutinin and neuraminidase, and the hepatitis B surface antigen (HBsAg). Bacterial vaccines contained. for vaccine development, the properties and functions of different immune responses, and some of the obstacles that still face the vaccine developer. 5. Opportunities for Improved and New Vaccines