Evaluation of a novel immunogenic vaccine platform based on a genome replication-deficient Sendai vector.

We developed a novel vaccine platform based on a paramyxoviral, genome replication-deficient Sendai virus vector that can express heterologous genes inserted into the genome. To validate the novel approach in vivo, we generated a combined vaccine candidate against human respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (PIV3). The present study compares two different methods of displaying heterologous antigens: (i) the RSV fusion (F) protein, encoded as a secretable version in an additional transcription unit, serves as an antigen only after being expressed in infected cells; (ii) PIV3 fusion (F) and hemagglutinin-neuraminidase (HN) genes, replacing Sendai counterparts in the vector genome, are also expressed as structural components on the surface of vaccine particles. The efficacy of this prototype vaccine was assessed in a mouse model after mucosal administration. The vaccine candidate was able to elicit specific mucosal, humoral and T cell-mediated immune responses against RSV and PIV3. However, PIV3 antigen display on the vaccine particles' surface induced higher antibody titers than the RSV antigen, being expressed only after cell infection. Consequently, this construct induced an adequate neutralizing antibody response only to PIV3. Finally, replicating virus particles were not detected in the lungs of immunized mice, confirming the genome stability and replication deficiency of this vaccine vector in vivo. Both factors can contribute substantially to the safety profile of vaccine candidates. In conclusion, this replication-deficient Sendai vector represents an efficient platform that can be used for vaccine developments against various viral pathogens.

Evaluation of nucleocapsid and phosphoprotein p functionality as critical factors during the early phase of paramyxoviral infection.

In the beginning of a paramyxovirus infection after cell entry viral survival depends on efficient primary (1°) transcription and on the stability of only one input nucleocapsid. Here we examined the influence of the viral polymerase co-factor phosphoprotein P on the very early phase of an infection, i.e. before progeny nucleocapsids are synthesized. We used a novel set-up with Sendai virus (SeV) mutants incapable of genome replication: SeV-ΔP with the entire P ORF deleted, SeV-PΔ2-77 with the deletion of aa 2-77. These mutants allow maintaining the state of the very beginning of an infection when statistically one viral genome is present in the cell. This single genome serves as template for transcription. During SeV-ΔP infections only early 1° transcription takes place at low levels. However, when the truncated P protein is expressed in SeV-PΔ2-77 infections, 1° transcription levels rise significantly up to an 8-fold increased amount of viral mRNA. This shows that the P protein is able to support transcription and thereby mediates the transition from early to late 1° transcription. Importantly, nucleocapsids of both mutants could be shown to remain stable and functional for at least 5 days - even without de novo P protein synthesis. These results describe a novel function of the P protein: enhancing viral gene expression even before genome replication has started. Thus, the since long postulated supportive function of the P protein is not related to stabilization of the nucleocapsid but rather enhances the processivity of the viral polymerase during late 1° and secondary (2°) transcription and genome replication.

Recombinant Sendai virus induces T cell immunity against respiratory syncytial virus that is protective in the absence of antibodies.

Respiratory syncytial virus (RSV) causes severe respiratory disease in infants and a vaccine is highly desirable. The fusion (F) protein of RSV is an important vaccine target, but the contribution of F-specific T cells to successful vaccination remains unclear. We studied the immune response to vaccination of mice with a recombinant Sendai virus expressing RSV F (rSeV F). rSeV F induced protective neutralizing antibody and RSV F-specific CTL responses. T cell immunity was stronger than that induced by recombinant vaccinia virus (rVV F), a well characterized reference vector. Vaccination of antibody-deficient mice showed that vaccine-induced RSV F-specific T cells were sufficient for protective immunity. rSeV F induced T cell immunity in the presence of neutralizing antibodies, which did not impair the vaccine response. Although the F protein only contains a subdominant CTL epitope, vaccination with rSeV F is sufficient to induce protective T cell immunity against RSV in mice.

De novo synthesis of N and P proteins as a key step in Sendai virus gene expression.

Among the members of the paramyxovirus family, the transcription process and the components involved have been studied under in vitro conditions thus far. Here, we reexamined the function of the viral RNA-dependent RNA polymerase through infection studies with Sendai virus (SeV) N and P deletion (Delta) mutants. To elucidate solely transcription-specific processes, all virus mutants also were rendered deficient in genome replication. Using mutant SeV DeltaP, the earlier suspected supplemental role of P protein was clearly demonstrated to be essential during viral gene expression. Moreover, when SeV DeltaN or DeltaN PDelta2-77 (with the 5' end of the P gene deleted) mutant was used for infections, a completely unexpected new and essential role for N protein was discovered for viral gene expression. In the early phases of an infection and in the absence of de novo viral protein synthesis, primary transcription occurs at hardly detectable levels. In contrast, if newly synthesized N protein is present, primary viral transcription reaches normal levels. From our data, we conclude that de novo synthesis of SeV N and P proteins is a key step for viral gene expression that facilitates the transition from preliminary to normal primary transcriptional activity.

Molecular detection of measles virus in primary cell cultures of otosclerotic tissue.

CONCLUSION: Primary cell cultures were established from otosclerotic/otospongiotic footplate bone particles. Although this procedure is time-consuming, the quality and quantity of RNA isolated from these cells were much higher in comparison with the direct isolation of RNA from footplate bone samples and the preparation was more suitable for the detection of measles virus (MeV) RNA. OBJECTIVE: Morphological and biochemical investigations suggest that persistent MeV infection participates in the development of otosclerotic foci. However, this hypothesis is controversial because the detection of MeV in otosclerotic foci is inconsistent since the results are dependent on the presence and stage of foci in the investigated bone particles. Unfortunately, this cannot be confirmed before investigation. To study the presence of the MeV by different techniques in otosclerotic foci, stapes footplate fragments were collected during stapedectomy from patients suffering from clinical otosclerosis. MATERIALS AND METHODS: MeV-specific RT-PCR was performed on total RNA isolated directly from four fresh frozen footplate bone fragments and from the cells of 16 primary cultures of otosclerotic tissue samples. In order to rescue persisting MeV, the primary footplate cells were cocultured with MeV permissive B95a cells. RESULTS: MeV was not detected in RNA from fresh frozen otosclerotic materials, but analysis of the RNA from 5 of the 16 primary cell cultures showed MeV-positive results. Nucleotide sequencing of a 317 bp MeV-specific RT-PCR fragment confirmed the presence of the MeV RNA genome. Here, we report the first determination of MeV sequences in total RNA isolated from primary cells cultured from otosclerotic tissue. Persisting MeV in primary footplate cells could not be recovered by coculturing with B95a cells.

Severe impairment of dendritic cell allostimulatory activity by Sendai virus vectors is overcome by matrix protein gene deletion.

Delivery of Ags to dendritic cells (DCs) plays a pivotal role in the induction of efficient immune responses ranging from immunity to tolerance. The observation that certain viral pathogens are able to infect DCs has led to a concept in which applications of recombinant viruses are used for Ag delivery with the potential benefit of inducing potent Ag-specific T cell responses directed against multiple epitopes. As a prerequisite for such an application, the infection of DCs by recombinant viruses should not interfere with their stimulatory capacity. In this context, we could show that an emerging negative-strand RNA viral vector system based on the Sendai virus (SeV) is able to efficiently infect monocyte-derived human DCs (moDCs). However, after infection with SeV wild type, both the response of DCs to bacterial LPS as a powerful mediator of DC maturation and the allostimulatory activity were severely impaired. Interestingly, using various recombinant SeV vectors that were devoid of single viral genes, we were able to identify the SeV matrix (M) protein as a key component in moDC functional impairment after viral infection. Consequently, use of M-deficient SeV vectors preserved the allostimulatory activity in infected moDCs despite an efficient expression of all other virally encoded genes, thereby identifying M-deficient vectors as a highly potent tool for the genetic manipulation of DCs.

A chimeric respiratory syncytial virus fusion protein functionally replaces the F and HN glycoproteins in recombinant Sendai virus.

Entry of most paramyxoviruses is accomplished by separate attachment and fusion proteins that function in a cooperative manner. Because of this close interdependence, it was not possible with most paramyxoviruses to replace either of the two protagonists by envelope glycoproteins from related paramyxoviruses. By using reverse genetics of Sendai virus (SeV), we demonstrate that chimeric respiratory syncytial virus (RSV) fusion proteins containing either the cytoplasmic domain of the SeV fusion protein or in addition the transmembrane domain were efficiently incorporated into SeV particles provided the homotypic SeV-F was deleted. In the presence of SeV-F, the chimeric glycoproteins were incorporated with significantly lower efficiency, indicating that determinants in the SeV-F ectodomain exist that contribute to glycoprotein uptake. Recombinant SeV in which the homotypic fusion protein was replaced with chimeric RSV fusion protein replicated in a trypsin-independent manner and was neutralized by antibodies directed to RSV-F. However, replication of this virus also relied on the hemagglutinin-neuraminidase (HN) as pretreatment of cells with neuraminidase significantly reduced the infection rate. Finally, recombinant SeV was generated with chimeric RSV-F as the only envelope glycoprotein. This virus was not neutralized by antibodies to SeV and did not use sialic acids for attachment. It replicated more slowly than hybrid virus containing HN and produced lower virus titers. Thus, on the one hand RSV-F can mediate infection in an autonomous way while on the other hand it accepts support by a heterologous attachment protein.

Sendai virus trailer RNA simultaneously blocks two apoptosis-inducing mechanisms in a cell type-dependent manner.

Induction of apoptosis during Sendai virus (SeV) infection has previously been documented to be triggered by initiator caspases (for strain F) or by a contribution of the cellular protein TIAR (T-cell-activated intracellular antigen-related) (for strain Z). Here, evidence was provided that both TIAR and caspases are simultaneously involved in apoptosis induction as a result of infection with SeV strain F. SeV F infection induced death in all tested cell lines, which could only be partially prevented through the pan-caspase inhibitor z-VAD-fmk. However, infection of seven different cell lines with the SeV mutant Fctr48z overexpressing a TIAR-sequestering RNA from the modified leader resulted in a cell type-dependent reduced cytopathic effect (CPE); in an earlier study a similar mutant derived from SeV Z was shown to prevent the induction of any CPE. Finally, blocking of caspases through z-VAD-fmk combined with Fctr48z infection led to complete abrogation of CPE, clearly demonstrating the existence of two separate mechanisms inducing cell death during SeV F infections. Interestingly, a cell type-specific interference between these two mechanisms could be detected during infection with the mutant virus Fctr48z: RNA transcribed from the mutated leader was able to trans-dominantly inhibit caspase-mediated apoptosis. Thus, virus-expressed factors enabling a well-balanced ratio of suppression and triggering of apoptosis seem to be essential for optimal virus replication.

Recombinant Sendai virus for efficient gene transfer to human airway epithelium.

Recombinant Sendai virus (rSeV) infects respiratory epithelial cells in animal models and cultures of undifferentiated human nasal cells. It was the aim of this study to investigate the capability of rSeV to express a transgene in human airway epithelium. Differentiated human airway epithelial cells were generated using air-liquid interface culture techniques. Application of rSeV coding for green fluorescence protein (GFP) onto the apical surface (using a multiplicity of infection of 3) resulted in expression of the transgene in more than 90% of the cells followed by decreasing numbers of positive cells during the observation time of 3 weeks. The infection of human respiratory epithelial cells is mediated by sialic acid residues at the apical surface. Despite the secretion of interleukin (IL)-8 and the replication of rSeV in the epithelial cells, the authors could not detect any cytopathic effect after the infection. In conclusion, rSeV infects differentiated human airway epithelial cells with high efficiency. Transgene expression is transient and accompanied by the secretion of an inflammatory cytokine.

Efficient propagation of single gene deleted recombinant Sendai virus vectors.

Recombinant Sendai virus vectors (SeVV) have become an attractive tool for basic virological as well as for gene transfer studies. However, to (i) reduce the cellular injury induced by basic recombinant SeV vectors (encoding all six SeV genes as being present in SeV wild-type (wt) genomes) and to (ii) improve SeV vector safety, deletions of viral genes are necessary for the construction of superior SeVV generations. As a strong expression system recombinant replication-incompetent adenoviruses, coding for SeV proteins hemagglutinin-neuraminidase (HN), fusion (F), or matrix (M), were generated and successfully employed for the propagation of single gene deleted (DeltaHN, DeltaF, DeltaM) recombinant SeVV. Further investigations of the propagation procedures required for single gene deleted recombinant SeVV demonstrated (i) modifications of the cell culture medium composition as well as (ii) incubation with vitamin E as crucial steps for the enhancement of SeVV-DeltaHN, -DeltaF, or -DeltaM viral particle yield. Such optimized propagation procedures even led to a successful propagation of HN-deleted viral particles (SeVV-DeltaHN), which has not been reported before.

Sendai virus vectors as an emerging negative-strand RNA viral vector system.

The power to manipulate the genome of negative-strand RNA viruses, including the insertion of additional non-viral genes, has led to the development of a new class of viral vectors for gene transfer approaches. The murine parainfluenza virus type I, or Sendai virus (SeV), has emerged as a prototype virus of this vector group, being employed in numerous in vitro as well as animal studies over the last few years. Extraordinary features of SeV are the remarkably brief contact time that is necessary for cellular uptake, a strong but adjustable expression of foreign genes, efficient infection in the respiratory tract despite a mucus layer, transduction of target cells being independent of the cell cycle, and an exclusively cytoplasmic replication cycle without any risk of chromosomal integration. In this review we describe the current knowledge of Sendai virus vector (SeVV) development as well as the results of first-generation vector applications under both in vitro and in vivo conditions. So far, Sendai virus vectors have been identified to be a highly efficient transduction tool for a broad range of different tissues and applications. Future directions in vector design and development are discussed.

Cell cycle independent infection and gene transfer by recombinant Sendai viruses.

A common problem for viral vectors in the field of somatic gene therapy is the dependence of an efficient cellular transduction on the cell cycle phase of target cells. An optimized viral vector system should therefore transduce cells in different cell cycle phases equally to improve transduction efficiencies. Recent observations that recombinant Sendai viruses (SeV) can infect a broad range of different tissues suggested SeV to be a good candidate for future gene therapeutic strategies in which dividing and non-dividing cells have to be reached. However, detailed data on the influence of distinct cell cycle phases on the infection of SeV or related viruses are missing. We report that synchronization of NIH 3T3 cells as well as contact inhibition of human fibroblast cells did not exhibit any negative influence on SeV infection rates. Furthermore, different attractive target tissues like human umbilical cord derived cells or primary human hepatocytes can be reached by SeV efficiently. As an important information for further cell cycle studies of paramyxoviruses we discovered surprisingly that the DNA polymerase inhibitor aphidicolin (induces a G(1)/M arrest) functions as an inhibitor of SeV but not of an adenoviral expression vector. In conclusion, the results demonstrate SeV based vector particles to be an ideal tool to reach equally cells coexisting in different cell cycle phases.

Negative-strand RNA viral vectors: intravenous application of Sendai virus vectors for the systemic delivery of therapeutic genes.

Treatment by gene replacement is critical in the field of gene therapy. Suitable vectors for the delivery of therapeutic genes have to be generated and tested in preclinical settings. Recently, extraordinary features for a local gene delivery by Sendai virus vectors (SeVV) have been reported for different tissues. Here we show that direct intravenous application of SeVV in mice is not only feasible and safe, but it results in the secretion of therapeutic proteins to the circulation, for example, human clotting Factor IX (hFIX). In vitro characterization of first-generation SeVV demonstrated that secreted amounts of hFIX were at least comparable to published results for retroviral or adeno-associated viral vectors. Furthermore, as a consideration for application in humans, SeVV transduction led to efficient hFIX synthesis in primary human hepatocytes, and SeVV-encoded hFIX proteins could be shown to be functionally active in the human clotting cascade. In conclusion, our investigations demonstrate for the first time that intravenous administration of negative-strand RNA viral vectors may become a useful tool for the wide area of gene replacement requirements.

Different substitutions at conserved amino acids in domains II and III in the Sendai L RNA polymerase protein inactivate viral RNA synthesis.

The Sendai virus RNA polymerase is a complex of two virus-encoded proteins, the phosphoprotein (P) and the large (L) protein, where L is believed to possess all the enzymatic activities necessary for viral transcription and replication. The alignment of amino acid sequences of L proteins from negative-sense RNA viruses shows six regions, designated domains I-VI, of good conservation which have been proposed to be important for the various enzymatic activities of the polymerase. To directly address the role(s) of domains II and III, site-directed mutations were constructed by the substitution of multiple amino acids at 13 highly or mostly conserved residues. Analysis of in vitro viral transcription and replication showed that the majority of the mutations completely inactivated the L protein for all aspects of RNA synthesis, thus conservation correlated with the essential nature of the amino acid. At some positions different phenotypes, from inactivation to partial activities, were observed which depended on the nature of the amino acid that was substituted. Two mutants, K543R and K666V, could synthesize some leader RNA, but were defective in mRNA synthesis and replication. K666R and G737E had significantly reduced replication compared to transcription in vitro, but replicated genome RNA much more efficiently in vivo. K666A gave transcription, but no replication. Representative inactive L mutants, however, were still able to bind P protein and the polymerase complex was capable of binding nucleocapsids, so the defect appeared to be in the initiation of RNA synthesis.

Caspase-8 and Apaf-1-independent caspase-9 activation in Sendai virus-infected cells.

Apoptotic cell death is of central importance in the pathogenesis of viral infections. Activation of a cascade of cysteine proteases, i.e. caspases, plays a key role in the effector phase of virus-induced apoptosis. However, little is known about pathways leading to the activation of initiator caspases in virus-infected host cells. Recently, we have shown that Sendai virus (SeV) infection triggers apoptotic cell death by activation of the effector caspase-3 and initiator caspase-8. We now investigated mechanisms leading to the activation of another initiator caspase, caspase-9. Unexpectedly we found that caspase-9 cleavage is not dependent on the presence of active caspases-3 or -8. Furthermore, the presence of caspase-9 in mouse embryonic fibroblast (MEF) cells was a prerequisite for Sendai virus-induced apoptotic cell death. Caspase-9 activation occurred without the release of cytochrome c from mitochondria and was not dependent on the presence of Apaf-1 or reactive oxygen intermediates. Our results therefore suggest an alternative mechanism for caspase-9 activation in virally infected cells beside the well characterized pathways via death receptors or mitochondrial cytochrome c release.