Petra de Vries

Canine Distemper Virus (CDV) immune-stimulating complexes (iscoms), but not measles virus iscoms, protect dogs against CDV infection.

The potential of immune-stimulating complexes (iscoms), a novel form of antigenic presentation, for the induction of protective immunity against morbillivirus infection was shown by immunizing dogs with canine distemper virus (CDV) iscoms, which contained the fusion (F) protein and a minor amount of the haemagglutinin of the virus. The immunized dogs developed CDV-neutralizing antibodies but, in contrast to non-immunized dogs, did not develop viraemia or clinical signs of infection upon intranasal challenge with the virulent Snyder Hill strain of CDV. Immunization of dogs with measles virus (MV) iscoms, prepared either from affinity-purified MV F protein or from purified whole virus, resulted in partial protection against challenge with CDV. The data presented clearly show that the iscom form of antigenic presentation may be considered a serious candidate for subunit vaccines against morbillivirus infection.

In vivo antibody response and in vitro CTL activation induced by selected measles vaccine candidates, prepared with purified Quil A components.

Semipurified Quil A and purified Quil A were used to prepare well-characterized subunit vaccine candidates against measles. Variation in the relative amounts of the measles virus (MV) fusion (F) protein, Quil A-components and lipids did not influence induction of antibody responses in mice, but had a pronounced effect on the capacity to induce cytotoxic T cell (CTL) activity of a CD8(+) MV F-protein specific human T cell clone in vitro. A characteristic MV iscom preparation based on the combined use of HPLC-purified Quil A-components QA-3 and QA-22 (QA-3/22) efficiently induced CTL activity in vitro. Comparable results were obtained by mixing beta-propiolactone inactivated MV with iscom-matrix QA-3/22 or free QA-22. On the basis of the data presented it was concluded that these three preparations are interesting MV vaccine candidates for further evaluation in pre-clinical experiments in a primate model.

Immunogenicity studies with a genetically engineered hexavalent PorA and a wild-type meningococcal group B outer membrane vesicle vaccine in infant cynomolgus monkeys

The immunogenicity of two meningococcal outer membrane vesicle (OMV) vaccines, namely the Norwegian wild-type OMV vaccine and the Dutch hexavalent PorA OMV vaccine, were examined in infant cynomolgus monkeys. For the first time, a wild-type- and a recombinant OMV vaccine were compared. Furthermore, the induction of memory and the persistence of circulating antibodies were measured. The Norwegian vaccine contained all four classes of major outer membrane proteins (OMP) and wild-type L3/L8 lipopolysaccharide (LPS). The Dutch vaccine consisted for 90% of class 1 OMPs, had low expression of class 4 and 5 OMP, and GalE LPS. Three infant monkeys were immunised with a human dose at the age of 1.5, 2.5 and 4.5 months. Two monkeys of each group received a fourth dose at the age of 11 months. In ELISA, both OMV vaccines were immunogenic and induced booster responses, particularly after the fourth immunisation. The Norwegian vaccine mostly induced sero-subtype P1.7,16 specific serum bactericidal antibodies (SBA), although some other SBA were induced as well. The antibody responses against P1.7,16, induced by the Norwegian vaccine, were generally higher than for the Dutch vaccine. However, the Dutch vaccine induced PorA specific SBA against all six sero-subtypes included in the vaccine showing differences in the magnitude of SBA responses to the various PorAs.

Protection of macaques against simian immunodeficiency virus infection with inactivated vaccines: comparison of adjuvants, doses and challenge viruses

Nine European laboratories contributed a total of 98 macaques towards a collaborative trial to study the ability of formaldehyde-inactivated or subunit SIV vaccines to protect immunized animals against live virus challenges. Four adjuvants, three dose levels and two immunization schedules were compared. Fifty-two of 61 (85%) immunized animals were protected against infection after challenge with either homologous or heterologous virus strains grown in human cells. Optimum protection required a high dose of antigen and a prolonged immunization schedule. On the day of challenge the titres of antibodies to SIV and to host cell components, as well as the titres of neutralizing antibodies, were significantly higher in the protected animals than in the non-protected. Forty-four vaccinated macaques (of which 36 were protected against previous challenges grown in human cells) and 28 naive animals were then challenged with extracellular or cell-associated SIV grown in simian cells. All naive animals and all vaccinees challenged with extracellular SIV became infected. Four of the eight animals challenged with cell-associated viruses were protected. These results clearly indicate that vaccines which potently protect against SIV grown in human cells, do not protect against SIV grown in simian cells. The cell substrate on which challenge viruses are grown is clearly significant in interpreting the results of vaccine trials. This trial has demonstrated that SIV vaccines using different adjuvants can protect macaques against SIV grown in human cells but not against extracellular SIV grown in simian cells. These results have important relevance to the development of HIV vaccines for humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of rhesus macaques from SIV infection by immunization with different experimental SIV vaccines.

The immunogenicity and efficacy of an inactivated whole SIVmac (32H) preparation adjuvanted with muramyl dipeptide (SIV-MDP) and a gp120-enriched SIVmac (32H) ISCOM preparation (SIV-ISCOM), were compared by immunizing four rhesus macaques (Macaca mulatta) four times with SIV-MDP and four others in the same way with SIV-ISCOM. Two monkeys immunized with whole inactivated measles virus (MV) adjuvanted with MDP (MV-MDP) and two monkeys immunized with MV-ISCOM served as controls. In the SIV-ISCOM-immunized monkeys higher SIV-specific serum antibody titres were found than in the SIV-MDP-immunized monkeys. In contrast to the MV-immunized monkeys all SIV-MDP- and SIV-ISCOM-immunized monkeys were protected against intravenous challenge 2 weeks after the last immunization with 10 median monkey infectious doses (MID50) of a cell-free SIVmac (32H) challenge stock propagated in the human T-cell line C8166. After 43 weeks the protected monkeys were reboosted and 2 weeks later rechallenged with 10 MID50 of the same virus produced in peripheral blood mononuclear cells (PBMC) from a rhesus macaque. None of these animals proved to be protected against this challenge. In a parallel experiment in which the same numbers of monkeys were immunized in the same way, the animals were challenged intravenously with 10 MID50 of PBMC from an SIVmac (32H)-infected rhesus macaque. Two out of four SIV-MDP- and two out of four SIV-ISCOM-immunized monkeys proved to be protected from SIV infection.

Vaccination against acute respiratory virus infections and measles in man

Several viruses may cause more or less severe acute respiratory infections in man, some of which are followed by systemic infection. Only for influenza and measles are licensed vaccines available at present. The protection induced by influenza vaccines, which are based on inactivated whole virus or viral subunits, depends largely on the matching of vaccine strain and circulating virus. Measles vaccines, which are based on attenuated live virus, have been quite effective in controlling the disease in vaccinated populations in the industrialized world. In developing countries, severe measles infections occur in infants from six to nine months of age, which necessitates the vaccination of children of less than six months. At that time maternal antibodies, that may interfere with the induction of protection, may still be present. Therefore, instead of using the parenteral route, the possibility to use the mucosal route of primary immunization is also investigated for vaccination with attenuated live measles vaccines. The use of inactivated measles vaccines has resulted in a state of immunity which upon exposure to the virus may induce an atypical measles syndrome including a severe pneumonia. Measles virus proteins presented in an iscom matrix have recently been shown to induce functional B and T cell responses to both the surface glycoproteins of the virus. These responses could also be induced in the presence of virus neutralizing antibodies and they proved to be protective in several animal model systems. Many of the problems that have been encountered in the development of measles vaccines, proved to be similar in the development of vaccines against other paramyxoviruses causing acute respiratory infections in man, including respiratory syncytial virus. Parenteral application of inactivated and attenuated live vaccines against these paramyxoviruses has generally had little success. Topical application of attenuated live vaccines has been more successful, and also the use of vaccinia recombinant viruses expressing foreign paramyxoviral glycoproteins has shown promising results in laboratory animals. Live vaccines based on adenovirus types 4 and 7 in oral enteric-coated vaccines, which lead to virus replication in the intestines but not in the respiratory tract have been included in military vaccination programs. The possibility to replace e.g. the E3 region with foreign DNA makes adenoviruses also suitable as cloning vectors for proteins of other respiratory viruses. Although live attenuated vaccines against some of the serotypes of rhinoviruses have shown promising results, the generation of a multivalent vaccine against this epidemiologically most significant cause of acute respiratory infections will be almost impossible, due to the multiplicity of serotypes involved.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigenicity and immunogenicity of recombinant envelope glycoproteins of SIVmac32H with different in vivo passage histories.

Shortly after infection of two rhesus monkeys (Macaca mulatta) either with a SIVmac32H challenge stock or with the same virus that had been passaged in another rhesus monkey for 11 months, SIV-envelope genes were cloned from their peripheral blood mononuclear cells and subsequently expressed by recombinant vaccinia viruses. The molecular weights and antigenicities of the thus produced envelope glycoproteins were largely identical to those of the native SIV. The envelope glycoprotein derived from the in vivo passaged virus proved to be poorly recognized by virus neutralizing monoclonal antibodies directed against one of the seven antigenic sites for which monoclonal antibodies were available. Immunization studies in rats showed that this protein was also less efficient in inducing antibodies against this antigenic site, and that it induced significantly lower levels of virus neutralizing antibodies than the other SIV-envelope glycoprotein. The immunogenicity of the SIV-envelope glycoprotein incorporated into immune stimulating complexes (iscoms) was compared to that of the same protein presented with Quil A or MDP-tsl.

Vaccines against Morbillivirus Infections

Members of the genus Morbillivirus classified within the family of Paramyxoviridae are rinderpest virus (RPV), peste des petits ruminants (PPRV), canine distemper virus (CDV), and measles virus (MV) (16). Recently, other morbilliviruses have been isolated from aquatic mammals, like seals (phocid distemper virus, PDV) and dolphins (14,38). All viruses are highly contagious for their natural hosts and may cause serious, acute diseases that may result in high mortality rates. At present vaccination programs with live attenuated vaccines have proven to be the most effective approach to prevent RPV infection in cattle or domestic buffalo populations, PPRV infection in goats and sheep, CDV infection in dogs, and MV infection in humans. The use of live vaccines still has several disadvantages: they are less effective in the presence of maternal antibodies or intercurrent virus infections, may cause severe side-effects in immunocompromized hosts, and need a cold-chain during transport and storage. The use of live attenuated vaccines for use in wild species should not be advocated, as calamities in different wild species with live CDV vaccines have been reported (29). The introduction of Tween-ether- or formaldehyde-inactivated morbillivirus vaccines has been accompanied by serious problems. Animals or humans were shown to be insufficiently protected and in some cases illness following exposure to live virus was more severe than that in nonvaccinated individuals. As a result of new developments in biology and technology, also in the field of morbillivirus vaccines, the development is rapidly changing from the use of conventional methods to novel approaches for vaccine strategies.