Characterization of the expression and immunogenicity of poliovirus replicons that encode simian immunodeficiency virus SIVmac239 Gag or envelope SU proteins

Kunjin replicon-based simian immunodeficiency virus gag vaccines

An RNA-based, non-cytopathic replicon vector system, based on the flavivirus Kunjin, has shown considerable promise as a new vaccine delivery system. Here we describe the testing in mice of four different SIVmac239 gag vaccines delivered by Kunjin replicon virus-like-particles. The four vaccines encoded the wild type gag gene, an RNA-optimised gag gene, a codon-optimised gag gene and a modified gag-pol gene construct. The vaccines behaved quite differently for induction of effector memory and central memory responses, for mediation of protection, and with respect to insert stability, with the SIV gag-pol vaccine providing the optimal performance. These results illustrate that for an RNA-based vector the RNA sequence of the antigen can have profound and unforeseen consequences on vaccine behaviour.

Immunogenicity of West Nile virus infectious DNA and its noninfectious derivatives

The exceptionally high virulence of the West Nile NY99 strain makes its suitability in the development of a live WN vaccine uncertain. The aim of this study is to investigate the immunogenicity of noninfectious virus derivatives carrying pseudolethal mutations, which preclude virion formation without affecting preceding steps of the viral infectious cycle. When administered using DNA immunization, such constructs initiate an infectious cycle but cannot lead to a viremia. While the magnitude of the immune response to a noninfectious replication-competent construct was lower than that of virus or infectious DNA, its overall quality and the protective effect were similar. In contrast, a nonreplicating construct of similar length induced only a marginally detectable immune response in the dose range used. Thus, replication-competent noninfectious constructs derived from infectious DNA may offer an advantageous combination of the safety of noninfectious formulations with the quality of the immune response characteristic of infectious vaccines.

Expression of a membrane-anchored glycoprotein, the influenza virus hemagglutinin, by dicistronic replicons derived from the poliovirus genome

Mono- and dicistronic poliovirus replicons were constructed to express the influenza virus hemagglutinin, retaining its signal peptide and transmembrane region. Picornavirus genomes do not normally encode glycoproteins, and only the dicistronic replicon, in which the foreign and poliovirus sequences were separated by the encephalomyocarditis virus internal ribosomal entry site, replicated and expressed glycosylated hemagglutinin.

Membrane-associated respiratory syncytial virus F protein expressed from a human rhinovirus type 14 vector is immunogenic

Human rhinovirus (HRV) replicons have the potential to serve as respiratory vaccine vectors for mucosal immunization in humans. However, since many vaccine immunogens of interest are glycosylated, an important concern is whether HRV replicons are capable of expressing glycosylated proteins. The human respiratory syncytial virus (RSV) fusion (F) protein was chosen as a model glycoprotein and the HRV replicon DeltaP1FVP3 was generated by inserting the F protein-coding sequence in frame and in lieu of the 5' proximal 1489 nucleotides of the capsid-coding segment in the HRV-14 genome. When transfected into H1-HeLa cells, DeltaP1FVP3 replicated and led to the expression of the F protein. Inhibition with guanidine demonstrated that F-protein expression was dependent on DeltaP1FVP3 replication and did not result from translation of input RNA. Although most of the F protein remained as an immature, glycosylated precursor (F0), a readily detectable fraction of the protein was processed into the mature glycosylated subunit F1, an event known to occur within the Golgi apparatus. Packaged DeltaP1FVP3 replicons were generated in transfected HeLa cells by coexpression of homologous HRV capsid proteins using the vaccinia virus/T7 RNA polymerase hybrid system. Packaged replicon RNAs were capable of infecting fresh cells, leading to accumulation of the F protein as in RNA-transfected cells. Mice immunized with HeLa cell lysates containing F protein expressed from DeltaP1FVP3 produced neutralizing antibodies against RSV. These results indicate that an HRV-14 replicon can express a foreign glycosylated protein, providing further support for the potential of HRV replicons as a vaccine delivery system.

Vaccination of macaques against pathogenic simian immunodeficiency virus with Venezuelan equine encephalitis virus replicon particles

Vaccine vectors derived from Venezuelan equine encephalitis virus (VEE) that expressed simian immunodeficiency virus (SIV) immunogens were tested in rhesus macaques as part of the effort to design a safe and effective vaccine for human immunodeficiency virus. Immunization with VEE replicon particles induced both humoral and cellular immune responses. Four of four vaccinated animals were protected against disease for at least 16 months following intravenous challenge with a pathogenic SIV swarm, while two of four controls required euthanasia at 10 and 11 weeks. Vaccination reduced the mean peak viral load 100-fold. The plasma viral load was reduced to below the limit of detection (1,500 genome copies/ml) in one vaccinated animal between 6 and 16 weeks postchallenge and in another from week 6 through the last sampling time (40 weeks postchallenge). The extent of reduction in challenge virus replication was directly correlated with the strength of the immune response induced by the vectors, which suggests that vaccination was effective.

Mucosal immunity and tolerance: relevance to vaccine development

The mucosal immune system of mammals consists of an integrated network of lymphoid cells which work in concert with innate host factors to promote host defense. Major mucosal effector immune mechanisms include secretory antibodies, largely of immunoglobulin A (IgA) isotype, cytotoxic T cells, as well as cytokines, chemokines and their receptors. Immunologic unresponsiveness (tolerance) is a key feature of the mucosal immune system, and deliberate vaccination or natural immunization by a mucosal route can effectively induce immune suppression. The diverse compartments located in the aerodigestive and genitourinary tracts and exocrine glands communicate via preferential homing of lymphocytes and antigen-presenting cells. Mucosal administration of antigens may result in the concomitant expression of secretory immunoglobulin A (S-IgA) antibody responses in various mucosal tissues and secretions, and under certain conditions, in the suppression of immune responses. Thus, developing formulations based on efficient delivery of selected antigens/tolerogens, cytokines and adjuvants may impact on the design of future vaccines and of specific immunotherapeutic approaches against diseases associated with untoward immune responses, such as autoimmune disorders, allergic reactions, and tissue-damaging inflammatory reactions triggered by persistent microorganisms.

Production of recombinant subunit vaccines: protein immunogens, live delivery systems and nucleic acid vaccines

The first scientific attempts to control an infectious disease can be attributed to Edward Jenner, who, in 1796 inoculated an 8-year-old boy with cowpox (vaccinia), giving the boy protection against subsequent challenge with virulent smallpox. Thanks to the successful development of vaccines, many major diseases, such as diphtheria, poliomyelitis and measles, are nowadays kept under control, and in the case of smallpox, the dream of eradication has been fulfilled. Yet, there is a growing need for improvements of existing vaccines in terms of increased efficacy and improved safety, besides the development of completely new vaccines. Better technological possibilities, combined with increased knowledge in related fields, such as immunology and molecular biology, allow for new vaccination strategies. Besides the classical whole-cell vaccines, consisting of killed or attenuated pathogens, new vaccines based on the subunit principle, have been developed, e.g. the Hepatitis B surface protein vaccine and the Haemophilus influenzae type b vaccine. Recombinant techniques are now dominating in the strive for an ideal vaccine, being safe and cheap, heat-stable and easy to administer, preferably single-dose, and capable of inducing broad immune response with life-long memory both in adults and in infants. This review will describe different recombinant approaches used in the development of novel subunit vaccines, including design and production of protein immunogens, the development of live delivery systems and the state-of-the-art for nucleic acids vaccines.

Construction and characterization of encapsidated poliovirus replicons that express biologically active murine interleukin-2

Poliovirus genomes have been constructed in which the capsid genes have been substituted with the murine gene encoding interleukin-2 (IL-2) (referred to as replicons). One replicon contained the gene for IL-2 in place of the poliovirus capsid VP2 and VP3 genes, and a second replicon was constructed that contained the murine IL-2 substituted for the poliovirus VP3 and VP1 genes. The IL-2 genes were cloned into the replicon so as to maintain the translational reading frame with the remaining poliovirus proteins. Transfection of either replicon into cells resulted in the expression of replicon-encoded proteins and replication of replicon RNA. Using a procedure developed in this laboratory, we have encapsidated these replicons into authentic polio virions by passaging the replicons in the presence of a recombinant vaccinia virus, VVP1, which expresses the capsid precursor, P1, protein. Using a quantitative immunoassay, we determined that the majority of the IL-2 produced remained intracellular, with approximately 1%-2% released from the infected cells, and that the IL-2 was biologically active. The results of these studies demonstrate the utility of poliovirus replicons for expression of small bioactive molecules and are discussed with respect to future applications as immune adjuvants as well as potential new tumor therapies.

Demonstration of the specificity of poliovirus encapsidation using a novel replicon which encodes enzymatically active firefly luciferase

The specificity of poliovirus encapsidation has been studied using a novel chimeric genome in which the gene encoding firefly luciferase has been substituted for the VP2-VP3-VP1 genes of the poliovirus capsid (P1) gene. Transfection of RNA transcribed in vitro from this genome resulted in a VP4-luciferase fusion protein which retained luciferase enzyme activity. Since the detection of enzyme activity was dependent upon replication of the transfected RNA genome, we refer to these genomes as replicons. The replicon encoding luciferase was encapsidated upon transfection of the genomic RNA into cells previously infected with a recombinant vaccinia virus, VV-P1, which encodes the poliovirus type 1 capsid proteins (P1). Infection of cells with each serial passage, followed by analysis of luciferase enzyme activity, revealed that encapsidated replicons could be detected at the first passage with VV-P1. Amplification of the titer of encapsidated replicons occurred upon serial passage with VV-P1, as evidenced by the high expression levels of luciferase enzyme activity following infection. Serial passage of the luciferase replicons with poliovirus type 1, 2, or 3 resulted in the trans encapsidation into the type 1, 2, or 3 capsids, respectively. In contrast, serial passage with bovine enterovirus, Coxsackievirus A21 or B3, or enterovirus 70 did not result in trans encapsidation, even though co-infection of cells with the replicon and different enteroviruses resulted in high-level expression of luciferase. The results of this study highlight the specificity of poliovirus encapsidation and point to the use of encapsidated replicons encoding luciferase as a reagent for dissecting elements of replication and encapsidation.

Recombinant viruses as vaccines and immunological tools

Recombinant viruses have been investigated as candidate vaccines, and have also been used extensively as immunological tools. Recent advances in this area include the following: the construction and testing of a recombinant simian immunodeficiency virus encoding human interferon-gamma; the development of new vectors such as recombinant poliovirus; and the generation of polyepitope vaccines. Basic immunological research has benefited from the use of recombinant viruses to further understand the role of molecules such as CD40 ligand, nitric oxide and interleukin-4.