Poliovirus antigen chimeras

In vitro disassembly of a parvovirus capsid and effect on capsid stability of heterologous peptide insertions in surface loops

We have analyzed the in vitro disassembly of the capsid of the minute virus of mice, and the stability of capsid chimeras carrying heterologous epitope insertions. Upon heating in a physiological buffer, empty capsids formed by 60 copies of protein VP2 underwent first a reversible conformational change with a small enthalpy change detected by fluorescence. This change was associated with, but not limited to, externalization of the VP2 N terminus. Irreversible capsid dissociation as detected by changes in fluorescence, hemagglutination activity, and electrophoretic mobility occurred at much higher temperatures. Differential scanning calorimetry in the same conditions indicated that the dissociation/denaturation transition involved a high enthalpy change and proceeded through one or more intermediates. In contrast, in the presence of 1.5 M guanidinium chloride, heat-induced disassembly fitted a two-state irreversible process. Both thermally and chemically induced dissociation/denaturation yielded a form that had lost a part of the tertiary structure, but still retained the native secondary structure. Data from chemical dissociation indicates this form may correspond to a molten globule-like monomeric state of the capsid protein. All five antigenic peptide insertions attempted in exposed loops, despite being perhaps among the least disruptive, led to defects in folding/assembly of the capsid and, in most cases, to reduced capsid stability against thermal dissociation. The results with one of the simplest viral capsids reveal a complex pathway for disassembly, and a reduction in capsid assembly and stability upon insertion of peptides, even within the most exposed capsid loops.

Characterization of the immune response to canine parvovirus induced by vaccination with chimaeric plant viruses

NIH mice were vaccinated subcutaneously or intranasally with chimaeric cow pea mosaic virus (CPMV) constructs expressing a 17-mer peptide sequence from canine parvovirus (CPV) as monomers or dimers on the small or large protein surface subunits. Responses to the chimaeric virus particles (CVPs) were compared with those of mice immunized with the native virus or with parvovirus peptide conjugated to keyhole limpet haemocyanin (KLH). The characteristics of the immune response to vaccination were examined by measuring serum and mucosal antibody responses in ELISA, in vitro antigen-induced spleen cell proliferation and cytokine responses. Mice made strong antibody responses to the native plant virus and peptide-specific responses to two of the four CVP constructs tested which were approximately 10-fold lower than responses to native plant virus. The immune response generated by the CVP constructs showed a marked TH1 bias, as determined by a predominantly IgG(2a) isotype peptide-specific antibody response and the release of IFN-gamma but not IL-4 or IL-5 from lymphocytes exposed to antigen in vitro. In comparison, parvovirus peptide conjugated to KLH generated an IgG(1)-biased (TH2) response. These data indicate that the presentation of peptides on viral particles could be used to bias the immune response in favor of a TH1 response.Anti-viral and anti-peptide IgA were detected in intestinal and bronchial lavage fluid of immunized mice, demonstrating that a mucosal immune response to CPV can be generated by systemic and mucosal immunization with CVP vaccines. Serum antibody from both subcutaneously-vaccinated and intranasally-vaccinated mice showed neutralizing activity against CPV in vitro.

Inactivated recombinant plant virus protects dogs from a lethal challenge with canine parvovirus

A vaccine based upon a recombinant plant virus (CPMV-PARVO1), displaying a peptide derived from the VP2 capsid protein of canine parvovirus (CPV), has previously been described. To date, studies with the vaccine have utilized viable plant chimaeric particles (CVPs). In this study, CPMV-PARVO1 was inactivated by UV treatment to remove the possibility of replication of the recombinant plant virus in a plant host after manufacture of the vaccine. We show that the inactivated CVP is able to protect dogs from a lethal challenge with CPV following parenteral immunization with the vaccine. Dogs immunized with the inactivated CPMV-PARVO1 in adjuvant displayed no clinical signs of disease and shedding of CPV in faeces was limited following CPV challenge. All immunized dogs elicited high titres of peptide-specific antibody, which neutralized CPV in vitro. Levels of protection, virus shedding and VP2-specific antibody were comparable to those seen in dogs immunized with the same VP2- peptide coupled to keyhole limpet hemocyanin (KLH). Since plant virus-derived vaccines have the potential for cost-effective manufacture and are not known to replicate in mammalian cells, they represent a viable alternative to current replicating vaccine vectors for development of both human and veterinary vaccines.

The yellow fever 17D vaccine virus as a vector for the expression of foreign proteins: development of new live flavivirus vaccines

The Flaviviridae is a family of about 70 mostly arthropod-borne viruses many of which are major public health problems with members being present in most continents. Among the most important are yellow fever (YF), dengue with its four serotypes and Japanese encephalitis virus. A live attenuated virus is used as a cost effective, safe and efficacious vaccine against YF but no other live flavivirus vaccines have been licensed. The rise of recombinant DNA technology and its application to study flavivirus genome structure and expression has opened new possibilities for flavivirus vaccine development. One new approach is the use of cDNAs encopassing the whole viral genome to generate infectious RNA after in vitro transcription. This methodology allows the genetic mapping of specific viral functions and the design of viral mutants with considerable potential as new live attenuated viruses. The use of infectious cDNA as a carrier for heterologous antigens is gaining importance as chimeric viruses are shown to be viable, immunogenic and less virulent as compared to the parental viruses. The use of DNA to overcome mutation rates intrinsic of RNA virus populations in conjunction with vaccine production in cell culture should improve the reliability and lower the cost for production of live attenuated vaccines. The YF virus despite a long period ignored by researchers probably due to the effectiveness of the vaccine has made a come back, both in nature as human populations grow and reach endemic areas as well as in the laboratory being a suitable model to understand the biology of flaviviruses in general and providing new alternatives for vaccine development through the use of the 17D vaccine strain.

Cowpea mosaic virus as a vaccine carrier of heterologous antigens

The plant virus, cowpea mosaic virus (CPMV), has been developed as an expression and presentation system to display antigenic epitopes derived from a number of vaccine targets including infectious disease agents and tumors. These chimeric virus particles (CVPs) could represent a cost-effective and safe alternative to live replicating virus and bacterial vaccines. A number of CVPs have now been generated and their immunogenicity examined in a number of animal species. This review details the humoral and cellular immune responses generated by these CVPs following both parenteral and mucosal delivery and highlights the potential of CVPs to elicit protective immunity from both viral and bacterial infection.

Replacement of the F and G proteins of respiratory syncytial virus (RSV) subgroup A with those of subgroup B generates chimeric live attenuated RSV subgroup B vaccine candidates

Human respiratory syncytial virus (RSV) exists as two antigenic subgroups, A and B, both of which should be represented in a vaccine. The F and G glycoproteins are the major neutralization and protective antigens, and the G protein in particular is highly divergent between the subgroups. The existing system for reverse genetics is based on the A2 strain of RSV subgroup A, and most efforts to develop a live attenuated RSV vaccine have focused on strain A2 or other subgroup A viruses. In the present study, the development of a live attenuated subgroup B component was expedited by the replacement of the F and G glycoproteins of recombinant A2 virus with their counterparts from the RSV subgroup B strain B1. This gene replacement was initially done for wild-type (wt) recombinant A2 virus to create a wt AB chimeric virus and then for a series of A2 derivatives which contain various combinations of A2-derived attenuating mutations located in genes other than F and G. The wt AB virus replicated in cell culture with an efficiency which was comparable to that of the wt A2 and B1 parents. AB viruses containing temperature-sensitive mutations in the A2 background exhibited levels of temperature sensitivity in vitro which were similar to those of A2 viruses bearing the same mutations. In chimpanzees, the replication of the wt AB chimera was intermediate between that of the A2 and B1 wt viruses and was accompanied by moderate rhinorrhea, as previously seen in this species. An AB chimeric virus, rABcp248/404/1030, which was constructed to contain a mixture of attenuating mutations derived from two different biologically attenuated A2 viruses, was highly attenuated in both the upper and lower respiratory tracts of chimpanzees. This attenuated AB chimeric virus was immunogenic and conferred a high level of resistance on chimpanzees to challenge with wt AB virus. The rABcp248/404/1030 chimeric virus is a promising vaccine candidate for RSV subgroup B and will be evaluated next in humans. Furthermore, these results suggest that additional attenuating mutations derived from strain A2 can be inserted into the A2 background of the recombinant chimeric AB virus as necessary to modify the attenuation phenotype in a reasonably predictable manner to achieve an optimal balance between attenuation and immunogenicity in a virus bearing the subgroup B antigenic determinants.

Chimeric plant virus particles administered nasally or orally induce systemic and mucosal immune responses in mice

The humoral immune responses to the D2 peptide of fibronectin-binding protein B (FnBP) of Staphylococcus aureus, expressed on the plant virus cowpea mosaic virus (CPMV), were evaluated after mucosal delivery to mice. Intranasal immunization of these chimeric virus particles (CVPs), either alone or in the presence of ISCOM matrix, primed CPMV-specific T cells and generated high titers of CPMV- and FnBP-specific immunoglobulin G (IgG) in sera. Furthermore, CPMV- and FnBP-specific IgA and IgG could also be detected in the bronchial, intestinal, and vaginal lavage fluids, highlighting the ability of CVPs to generate antibody at distant mucosal sites. IgG2a and IgG2b were the dominant IgG subclasses in sera to both CPMV and FnBP, demonstrating a bias in the response toward the T helper 1 type. The sera completely inhibited the binding of human fibronectin to the S. aureus FnBP. Oral immunization of the CVPs also generated CPMV- and FnBP-specific serum IgG; however, these titers were significantly lower and more variable than those generated by the intranasal route, and FnBP-specific intestinal IgA was undetectable. Neither the ISCOM matrix nor cholera toxin enhanced these responses. These studies demonstrate for the first time that recombinant plant viruses have potential as mucosal vaccines without the requirement for adjuvant and that the nasal route is most effective for the delivery of these nonreplicating particles.

Peptide display on functional tailspike protein of bacteriophage P22

The tailspike protein (TSP) of Salmonella typhimurium P22 bacteriophage is a multifunctional homotrimer, 6 copies of which are non-covalently attached to the capsid to form the virion tail in the last reaction of phage assembly. An antigenic peptide of foot-and-mouth disease virus (FMDV), aa 134-156 of protein VP1, has been joined to the carboxy terminus of TSP, and produced as a fusion protein in Escherichia coli directed by the trp promoter. The resulting fusion protein is soluble, stable, non-toxic, and can be easily purified by standard procedures. Moreover, both the endorhamnosidase and capsid assembly activities of the TSP are conserved, permitting the fusion protein to reconstitute infectious viruses by in vitro association with tailless particles. In both free TSP and P22 chimeric virions, the foreign peptide is solvent-exposed and highly antigenic, indicating that P22 TSP could be an appropriate carrier protein for multimeric peptide display.

An HTLV-I vaccine: why, how, for whom?

Endemic infection with the human T cell leukemia/lymphoma viruses I and II (HTLV-I/II) is now recognized to be worldwide, and is becoming epidemic among intravenous drug abusers (IVDAs) in the United States and Europe. The number of people around the world infected with HTLV-I can be estimated as between 10 and 20 million (Table 1). HTLV-I causes a rapidly progressing adult T cell leukemia/lymphoma (ATLL), and an incurable progressive neuromyelopathy named tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM), as well as a number of less well-studied syndromes. There is evidence that coinfection with HTLV-I or -II accelerates progression to AIDS. The cumulative lifetime risk of developing ATLL or TSP/HAM is around 5%, which, in terms of the induction of serious diseases, places HTLV-I in the same category of viruses for which efficient vaccines are made and used. Furthermore, there are factors favoring the feasibility of a vaccine against HTLV-I, in that the virus displays relatively low antigenic variability, natural immunity occurs in humans, and experimental vaccination with the envelope (Env) antigen is successful in animal models. A vaccine against HTLV-I would be of significant public health value in the fields of oncology, neurology, and AIDS, and it would serve as a pathfinder for a vaccine against HIV.