The hemagglutinin-neuraminidase glycoproteins of human parainfluenza virus type 1 and Sendai virus have high structure-function similarity with limited antigenic cross-reactivity

Unraveling dynamics of paramyxovirus-receptor interactions using nanoparticles displaying hemagglutinin-neuraminidase

Sialoglycan-binding enveloped viruses often possess receptor-destroying activity to avoid being immobilized by non-functional decoy receptors. Sialic acid (Sia)-binding paramyxoviruses contain a hemagglutinin-neuraminidase (HN) protein that possesses both Sia-binding and -cleavage activities. The multivalent, dynamic receptor interactions of paramyxovirus particles provide virion motility and are a key determinant of host tropism. However, such multivalent interactions have not been exhaustively analyzed, because such studies are complicated by the low affinity of the individual interactions and the requirement of high titer virus stocks. Moreover, the dynamics of multivalent particle-receptor interactions are difficult to predict from Michaelis-Menten enzyme kinetics. Therefore, we here developed Ni-NTA nanoparticles that multivalently display recombinant soluble HN tetramers via their His tags (HN-NPs). Applying this HN-NP platform to Newcastle disease virus (NDV), we investigated using biolayer interferometry (BLI) the role of important HN residues in receptor-interactions and analyzed long-range effects between the catalytic site and the second Sia binding site (2SBS). The HN-NP system was also applicable to other paramyxoviruses. Comparative analysis of HN-NPs revealed and confirmed differences in dynamic receptor-interactions between type 1 human and murine parainfluenza viruses as well as of lab-adapted and clinical isolates of human parainfluenza virus type 3, which are likely to contribute to differences in tropism of these viruses. We propose this novel platform to be applicable to elucidate the dynamics of multivalent-receptor interactions important for host tropism and pathogenesis, particularly for difficult to grow sialoglycan-binding (paramyxo)viruses.

Immunogenicity and Therapeutic Efficacy of a Sendai-Virus-Vectored HSV-2 Vaccine in Mouse and Guinea Pig Models

BACKGROUND

To date, there is no licensed vaccine for preventing herpes simplex virus type 2 (HSV-2). The current treatment to address the infection and prevent its transmission is not always satisfactory.

METHODS

We constructed two recombinant vectors, one encoding HSV-2 glycoprotein D (gD, SeV-dF/HSV-2-gD) and one encoding HSV-2-infected cell protein 27 (ICP27, SeV-dF/HSV-2-ICP27), based on a replication-defective Sendai virus through reverse genetics, collectively comprising a combinatorial HSV-2 therapeutic vaccine candidate. The immunogenicity and proper immunization procedure for this vaccine were explored in a murine model. The therapeutic effect that helps prevent recurrent HSV-2 disease was evaluated in HSV-2-infected guinea pigs.

RESULTS

Both a robust humoral immune response and a cellular immune response, characterized by the neutralizing antibody titer and the IFN-γ level, respectively, were elicited in BALB/c mice. A further study of cellular immunogenicity in mice revealed that T lymphocytes were successfully enhanced with the desirable secretion of several cytokines. In HSV-2-seropositive guinea pigs, vaccination could reduce the severity of HSV-2 in terms of recurrent lesions, duration of recurrent outbreak, and frequency of recurrence by 58.66%, 45.34%, and 45.09%, respectively, while viral shedding was also significantly inhibited in the vaccine-treated group compared to the group treated with phosphate-buffered saline.

CONCLUSIONS

The replication-defective recombinant Sendai viruses conveying HSV-2-gD and ICP27 proteins showed great immunogenicity and potential for preventing recurrent HSV-2 disease.

Solid-Phase Binding Assay for Ganglioside Binding of Human Respiroviruses

Human parainfluenza virus types 1 (hPIV-1) and 3 (hPIV-3) belong to the family Paramyxoviridae, subfamily Paramyxoviridae, and genus Respirovirus. The viruses enter by utilizing glycoproteins or glycosphingolipids (gangliosides) containing sialic acid on the cell membrane. We developed a solid-phase binding assay to evaluate hPIV-1, hPIV-3, and Sendai virus' abilities to bind to different types of gangliosides. hPIV1 and hPIV3 show strong binding to neolacto-series gangliosides containing a non-reducing terminal sialic acid residue and different specificity regarding the sialic acid linkages. This solid-phase binding assay is suitable to evaluate other orthomyxoviruses and paramyxoviruses' binding specificities utilizing sialic acids.

Sendai Virus-Vectored Vaccines That Express Envelope Glycoproteins of Respiratory Viruses

Human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), and human parainfluenza viruses (HPIVs) are leading causes of respiratory disease in young children, the elderly, and individuals of all ages with immunosuppression. Vaccination strategies against these pneumoviruses and paramyxoviruses are vast in number, yet no licensed vaccines are available. Here, we review development of Sendai virus (SeV), a versatile pediatric vaccine that can (a) serve as a Jennerian vaccine against HPIV1, (b) serve as a recombinant vaccine against HRSV, HPIV2, HPIV3, and HMPV, (c) accommodate foreign genes for viral glycoproteins in multiple intergenic positions, (d) induce durable, mucosal, B-cell, and T-cell immune responses without enhanced immunopathology, (e) protect cotton rats, African green monkeys, and chimpanzees from infection, and (f) be formulated into a vaccine cocktail. Clinical phase I safety trials of SeV have been completed in adults and 3–6-year-old children. Clinical testing of SeVRSV, an HRSV fusion (F) glycoprotein gene recombinant, has also been completed in adults. Positive results from these studies, and collaborative efforts with the National Institutes of Health and the Serum Institute of India assist advanced development of SeV-based vaccines. Prospects are now good for vaccine successes in infants and consequent protection against serious viral disease.

A Respiratory Syncytial Virus Vaccine Vectored by a Stable Chimeric and Replication-Deficient Sendai Virus Protects Mice without Inducing Enhanced Disease

Respiratory syncytial virus (RSV) is a major cause of severe respiratory infections in children and elderly people, and no marketed vaccine exists. In this study, we generated and analyzed a subunit vaccine against RSV based on a novel genome replication-deficient Sendai virus (SeV) vector. We inserted the RSV F protein, known to be a genetically stable antigen, into our vector in a specific way to optimize the vaccine features. By exchanging the ectodomain of the SeV F protein for its counterpart from RSV, we created a chimeric vectored vaccine that contains the RSV F protein as an essential structural component. In this way, the antigen is actively expressed on the surfaces of vaccine particles in its prefusion conformation, and as recently reported for other vectored vaccines, the occurrence of silencing mutations of the transgene in the vaccine genome can be prevented. In addition, its active gene expression contributes to further stimulation of the immune response. In order to understand the best route of immunization, we compared vaccine efficacies after intranasal (i.n.) or intramuscular (i.m.) immunization of BALB/c mice. Via both routes, substantial RSV-specific immune responses were induced, consisting of serum IgG and neutralizing antibodies, as well as cytotoxic T cells. Moreover, i.n. immunization was also able to stimulate specific mucosal IgA in the upper and lower respiratory tract. In virus challenge experiments, animals were protected against RSV infection after both i.n. and i.m. immunization without inducing vaccine-enhanced disease. Above all, the replication-deficient SeV appeared to be safe and well tolerated.IMPORTANCE Respiratory syncytial virus (RSV) is a major cause of respiratory diseases in young children and elderly people worldwide. There is a great demand for a licensed vaccine. Promising existing vaccine approaches based on live-attenuated vaccines or viral vectors have suffered from unforeseen drawbacks related to immunogenicity and attenuation. We provide a novel RSV vaccine concept based on a genome replication-deficient Sendai vector that has many favorable vaccine characteristics. The specific vaccine design guarantees genetic stability of the transgene; furthermore, it supports a favorable presentation of the antigen, activating the adaptive response, features that other vectored vaccine approaches have often had difficulties with. Wide immunological and pathological analyses in mice confirmed the validity and efficacy of this approach after both parenteral and mucosal administration. Above all, this concept is suitable for initiating clinical studies, and it could also be applied to other infectious diseases.

Preparation for a first-in-man lentivirus trial in patients with cystic fibrosis

We have recently shown that non-viral gene therapy can stabilise the decline of lung function in patients with cystic fibrosis (CF). However, the effect was modest, and more potent gene transfer agents are still required. Fuson protein (F)/Hemagglutinin/Neuraminidase protein (HN)-pseudotyped lentiviral vectors are more efficient for lung gene transfer than non-viral vectors in preclinical models. In preparation for a first-in-man CF trial using the lentiviral vector, we have undertaken key translational preclinical studies. Regulatory-compliant vectors carrying a range of promoter/enhancer elements were assessed in mice and human air–liquid interface (ALI) cultures to select the lead candidate; cystic fibrosis transmembrane conductance receptor (CFTR) expression and function were assessed in CF models using this lead candidate vector. Toxicity was assessed and ‘benchmarked’ against the leading non-viral formulation recently used in a Phase IIb clinical trial. Integration site profiles were mapped and transduction efficiency determined to inform clinical trial dose-ranging. The impact of pre-existing and acquired immunity against the vector and vector stability in several clinically relevant delivery devices was assessed. A hybrid promoter hybrid cytosine guanine dinucleotide (CpG)- free CMV enhancer/elongation factor 1 alpha promoter (hCEF) consisting of the elongation factor 1α promoter and the cytomegalovirus enhancer was most efficacious in both murine lungs and human ALI cultures (both at least 2-log orders above background). The efficacy (at least 14% of airway cells transduced), toxicity and integration site profile supports further progression towards clinical trial and pre-existing and acquired immune responses do not interfere with vector efficacy. The lead rSIV.F/HN candidate expresses functional CFTR and the vector retains 90–100% transduction efficiency in clinically relevant delivery devices. The data support the progression of the F/HN-pseudotyped lentiviral vector into a first-in-man CF trial in 2017.

First-in-Human Evaluation of the Safety and Immunogenicity of an Intranasally Administered Replication-Competent Sendai Virus-Vectored HIV Type 1 Gag Vaccine: Induction of Potent T-Cell or Antibody Responses in Prime-Boost Regimens

Background. We report the first-in-human safety and immunogenicity assessment of a prototype intranasally administered, replication-competent Sendai virus (SeV)–vectored, human immunodeficiency virus type 1 (HIV-1) vaccine.

Methods. Sixty-five HIV-1–uninfected adults in Kenya, Rwanda, and the United Kingdom were assigned to receive 1 of 4 prime-boost regimens (administered at 0 and 4 months, respectively; ratio of vaccine to placebo recipients, 12:4): priming with a lower-dose SeV-Gag given intranasally, followed by boosting with an adenovirus 35–vectored vaccine encoding HIV-1 Gag, reverse transcriptase, integrase, and Nef (Ad35-GRIN) given intramuscularly (S_LA); priming with a higher-dose SeV-Gag given intranasally, followed by boosting with Ad35-GRIN given intramuscularly (S_HA); priming with Ad35-GRIN given intramuscularly, followed by boosting with a higher-dose SeV-Gag given intranasally (AS_H); and priming and boosting with a higher-dose SeV-Gag given intranasally (S_HS_H).

Results. All vaccine regimens were well tolerated. Gag-specific IFN-γ enzyme-linked immunospot–determined response rates and geometric mean responses were higher (96% and 248 spot-forming units, respectively) in groups primed with SeV-Gag and boosted with Ad35-GRIN (S_LA and S_HA) than those after a single dose of Ad35-GRIN (56% and 54 spot-forming units, respectively) or SeV-Gag (55% and 59 spot-forming units, respectively); responses persisted for ≥8 months after completion of the prime-boost regimen. Functional CD8⁺ T-cell responses with greater breadth, magnitude, and frequency in a viral inhibition assay were also seen in the S_LA and S_HA groups after Ad35-GRIN boost, compared with those who received either vaccine alone. SeV-Gag did not boost T-cell counts in the AS_H group. In contrast, the highest Gag-specific antibody titers were seen in the AS_H group. Mucosal antibody responses were sporadic.

Conclusions. SeV-Gag primed functional, durable HIV-specific T-cell responses and boosted antibody responses. The prime-boost sequence appears to determine which arm of the immune response is stimulated.

Clinical Trials Registration. NCT01705990.

Development of an AIDS vaccine using Sendai virus vectors

Development of an effective AIDS vaccine is crucial for the control of global human immunodeficiency virus type 1 (HIV-1) prevalence. We have developed a novel AIDS vaccine using a Sendai virus (SeV) vector and investigated its efficacy in a macaque AIDS model of simian immunodeficiency virus (SIV) infection. Its immunogenicity and protective efficacy have been shown, indicating that the SeV vector is a promising delivery tool for AIDS vaccines. Here, we describe the potential of SeV vector as a vaccine antigen delivery tool to induce effective immune responses against HIV-1 infection.

Timing is everything: Fine-tuned molecular machines orchestrate paramyxovirus entry

The Paramyxoviridae include some of the great and ubiquitous disease-causing viruses of humans and animals. In most paramyxoviruses, two viral membrane glycoproteins, fusion protein (F) and receptor binding protein (HN, H or G) mediate a concerted process of recognition of host cell surface molecules followed by fusion of viral and cellular membranes, resulting in viral nucleocapsid entry into the cytoplasm. The interactions between the F and HN, H or G viral glycoproteins and host molecules are critical in determining host range, virulence and spread of these viruses. Recently, atomic structures, together with biochemical and biophysical studies, have provided major insights into how these two viral glycoproteins successfully interact with host receptors on cellular membranes and initiate the membrane fusion process to gain entry into cells. These studies highlight the conserved core mechanisms of paramyxovirus entry that provide the fundamental basis for rational anti-viral drug design and vaccine development.

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New structural and functional insights into paramyxovirus entry mechanisms.

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Current data on paramyxovirus glycoproteins suggest a core conserved entry mechanism.

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Diverse mechanisms preventing premature fusion activation exist in these viruses.

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Precise spacio-temporal interplay between paramyxovirus glycoproteins initiate entry.

Sweet Is the Memory of Past Troubles: NK Cells Remember

Natural killer (NK) cells are important in host defense against tumors and microbial pathogens. Recent studies indicate that NK cells share many features with the adaptive immune system, and like B cells and T cells, NK cells can acquire immunological memory. Here, we review evidence for NK cell memory and the molecules involved in the generation and maintenance of these self-renewing NK cells that provide enhanced protection of the host.

Safety and immunogenicity of an intranasal Sendai virus-based human parainfluenza virus type 1 vaccine in 3- to 6-year-old children

Human parainfluenza virus type 1 (hPIV-1) is the most common cause of laryngotracheobronchitis (croup), resulting in tens of thousands of hospitalizations each year in the United States alone. No licensed vaccine is yet available. We have developed murine PIV-1 (Sendai virus [SeV]) as a live Jennerian vaccine for hPIV-1. Here, we describe vaccine testing in healthy 3- to 6-year-old hPIV-1-seropositive children in a dose escalation study. One dose of the vaccine (5 × 10(5), 5 × 10(6), or 5 × 10(7) 50% egg infectious doses) was delivered by the intranasal route to each study participant. The vaccine was well tolerated by all the study participants. There was no sign of vaccine virus replication in the airway in any participant. Most children exhibited an increase in antibody binding and neutralizing responses toward hPIV-1 within 4 weeks from the time of vaccination. In several children, antibody responses remained above incoming levels for at least 6 months after vaccination. Data suggest that SeV may provide a benefit to 3- to 6-year-old children, even when vaccine recipients have preexisting cross-reactive antibodies due to previous exposures to hPIV-1. Results encourage the testing of SeV administration in young seronegative children to protect against the serious respiratory tract diseases caused by hPIV-1 infections.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.

Sendai virus-based RSV vaccine protects against RSV challenge in an in vivo maternal antibody model

Respiratory syncytial virus (RSV) is the cause of significant morbidity and mortality among infants, and despite decades of research there remains no licensed vaccine. SeVRSV is a Sendai virus (SeV)-based live intranasal vaccine that expresses the full length RSV fusion (F) gene. SeV is the murine counterpart of human parainfluenza virus type 1. Given that the target population of SeVRSV is young infants, we questioned whether maternal antibodies typical of this age group would inhibit SeVRSV vaccine efficacy. After measuring SeV- and RSV-specific serum neutralizing antibody titers in human infants, we matched these defined titers in cotton rats by the passive transfer of polyclonal or monoclonal antibody products. Animals were then vaccinated with SeVRSV followed by a 3 month rest period to allow passively transferred antibodies to wane. Animals were finally challenged with RSV to measure the de novo vaccine-induced immune responses. Despite the presence of passively-transferred serum neutralizing antibodies at the time of vaccination, SeVRSV induced immune responses that were protective against RSV challenge. The data encourage advancement of SeVRSV as a candidate vaccine for the protection of children from morbidity and mortality caused by RSV.

Genetic analysis of human parainfluenza viruses circulating in Korea, 2006

Human parainfluenza viruses (HPIV) are important causes of respiratory tract infections in young children. To characterize the molecular epidemiology of an HPIV outbreak occurring in Korea during 2006, genetic analysis of 269 cell culture isolates from HPIV-infected children, was conducted using nested reverse transcription-PCR (RT-PCR). HPIV-1 was detected in 70.3% of tested samples (189/269). The detection rate of HPIV-2 and HPIV-3 was 1.5% (4/269) and 9.3% (25/269), respectively. Mixed HPIV-1, -2 and -3 infections were detected in 19.0% (51/269): HPIV-1 and HPIV-2 in 15, HPIV-1 and HPIV-3 in 26, HPIV-2 and HPIV-3 in 6, and HPIV-1, -2 and -3 in 4. Of these positive samples for three different types HIPV-1, -2, and -3, two each representative strains were selected, the full length of hemagglutinin-neuraminidase (HN) gene for HPIV was amplified by RT-PCR, and sequenced. Multiple alignment analysis, based on reference sequence of HPIV-1, -2, and -3 strains available in GenBank, showed that the identity of nucleotide and deduced amino acid sequences was 92.4-97.6% and 92.7-97.9%, respectively, for HPIV-1, 88.5-99.8% and 88.6-100% for HPIV-2, and 96.3-99.5% and 95.0-99.3% for HPIV-3, respectively. Phylogenetic analysis showed that HPIV-1, -2, and -3 strains identified in this study were closely related among the strains in the same type with no significant genetic variability. These results show that HPIV of multiple imported sources was circulating in Korea.

Differential Susceptibility of Cells Expressing Allogeneic MHC or Viral Antigen to Killing by Antigen-Specific CTL

CD8(+) cytotoxic T lymphocytes (CTLs) generated by immunization with allogeneic cells or viral infection are able to lyse allogeneic or virally infected in vitro cells (e.g., lymphoma and mastocytoma). In contrast, it is reported that CD8(+) T cells are not essential for allograft rejection (e.g., heart and skin), and that clearance of influenza or the Sendai virus from virus-infected respiratory epithelium is normal or only slightly delayed after a primary viral challenge of CD8-knockout mice. To address this controversy, we generated H-2(d)-specific CD8(+) CTLs by a mixed lymphocyte culture and examined the susceptibility of a panel of H-2(d) cells to CTL lysis. KLN205 squamous cell carcinoma, Meth A fibrosarcoma, and BALB/c skin components were found to be resistant to CTL-mediated lysis. This resistance did not appear to be related to a reduced expression of MHC class I molecules, and all these cells could block the recognition of H-2(d) targets by CTLs in cold target inhibition assays. We extended our observation by persistently infecting the same panel of cell lines with defective-interfering Sendai virus particles. The Meth A and KLN205 lines infected with a variant Sendai virus were resistant to lysis by Sendai virus-specific CTLs. The Sendai virus-infected Meth A and KLN205 lines were able to block the lysis of Sendai virus-infected targets by CTLs in cold target inhibition assays. Taken together, these results suggest that not all in vivo tissues may be sensitive to CTL lysis.

Critical role of the fusion protein cytoplasmic tail sequence in parainfluenza virus assembly

Interactions between viral glycoproteins, matrix protein and nucleocapsid sustain assembly of parainfluenza viruses at the plasma membrane. Although the protein interactions required for virion formation are considered to be highly specific, virions lacking envelope glycoprotein(s) can be produced, thus the molecular interactions driving viral assembly and production are still unclear. Sendai virus (SeV) and human parainfluenza virus type 1 (hPIV1) are highly similar in structure, however, the cytoplasmic tail sequences of the envelope glycoproteins (HN and F) are relatively less conserved. To unveil the specific role of the envelope glycoproteins in viral assembly, we created chimeric SeVs whose HN (rSeVhHN) or HN and F (rSeVh(HN+F)) were replaced with those of hPIV1. rSeVhHN grew as efficiently as wt SeV or hPIV1, suggesting that the sequence difference in HN does not have a significant impact on SeV replication and virion production. In sharp contrast, the growth of rSeVh(HN+F) was significantly impaired compared to rSeVhHN. rSeVh(HN+Fstail) which expresses a chimeric hPIV1 F with the SeV cytoplasmic tail sequence grew similar to wt SeV or rSeVhHN. Further analysis indicated that the F cytoplasmic tail plays a critical role in cell surface expression/accumulation of HN and F, as well as NP and M association at the plasma membrane. Trafficking of nucelocapsids in infected cells was not significantly affected by the origin of F, suggesting that F cytoplasmic tail is not involved in intracellular movement. These results demonstrate the role of the F cytoplasmic tail in accumulation of structural components at the plasma membrane assembly sites.

HIV epidemic in Asia: optimizing and expanding vaccine development

The recent evidence in Thailand for protection from acquisition of HIV through vaccination in a mostly heterosexual population has generated considerable hope. Building upon these results and the analysis of the correlates of risk remains among the highest priorities. Improved vaccine concepts including heterologous prime-boost regimens, improved proteins with potent adjuvants and new vectors expressing mosaic antigens may soon enter clinical development to assess vaccine efficacy in men who have sex with men. Identifying heterosexual populations with sufficient HIV incidence for the conduct of efficacy trials represents perhaps the main challenge in Asia. Fostering translational research efforts in Asian countries may benefit from the development of master strategic plans and program management processes.

Mucosal immunity against influenza induced by attenuated recombinant Sendai virus

Live-attenuated influenza vaccines (LAIVs) have been shown to be more immunogenic and capable of inducing a broader immune response than inactivated vaccine. However, use of LAIVs is still limited owing to the safety concerns. Le et al. generated an attenuated recombinant Sendai virus - GP42-H1 expressing the hemagglutinin (HA) gene of influenza A virus. The HA protein was expressed on the cell surface of CV-1 cells infected with GP42-H1. Intranasal immunization of mice with GP42-H1 induced HA-specific IgG and IgA antibodies in sera and mucosal sites without causing any disease symptoms. Immunized mice were also protected from lethal dose challenge of influenza A virus.

Induction of influenza-specific mucosal immunity by an attenuated recombinant Sendai virus

BACKGROUND

Many pathogens initiate infection at the mucosal surfaces; therefore, induction of mucosal immune responses is a first level of defense against infection and is the most powerful means of protection. Although intramuscular injection is widely used for vaccination and is effective at inducing circulating antibodies, it is less effective at inducing mucosal antibodies.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report a novel recombinant, attenuated Sendai virus vector (GP42-H1) in which the hemagglutinin (HA) gene of influenza A virus was introduced into the Sendai virus genome as an additional gene. Infection of CV-1 cells by GP42-H1 resulted in cell surface expression of the HA protein. Intranasal immunization of mice with 1,000 plaque forming units (pfu) of GP42-H1 induced HA-specific IgG and IgA antibodies in the blood, bronchoalveolar lavage fluid, fecal pellet extracts and saliva. The HA-specific antibody titer induced by GP42-H1 closely resembles the titer induced by sublethal infection by live influenza virus; however, in contrast to infection by influenza virus, immunization with GP42-H1 did not result in disease symptoms or the loss of body weight. In mice that were immunized with GP42-H1 and then challenged with 5LD(50) (1250 pfu) of influenza virus, no significant weight loss was observed and other visual signs of morbidity were not detected.

CONCLUSIONS

These results demonstrate that the GP42-H1 Sendai virus recombinant is able to confer full protection from lethal infection by influenza virus, supporting the conclusion that it is a safe and effective mucosal vaccine vector.

Identification of a natural human serotype 3 parainfluenza virus

Parainfluenza virus is an important pathogen threatening the health of animals and human, which brings human many kinds of disease, especially lower respiratory tract infection involving infants and young children. In order to control the virus, it is necessary to fully understand the molecular basis resulting in the genetic diversity of the virus. Homologous recombination is one of mechanisms for the rapid change of genetic diversity. However, as a negative-strand virus, it is unknown whether the recombination can naturally take place in human PIV. In this study, we isolated and identified a mosaic serotype 3 human PIV (HPIV3) from in China, and also provided several putative PIV mosaics from previous reports to reveal that the recombination can naturally occur in the virus. In addition, two swine PIV3 isolates transferred from cattle to pigs were found to have mosaic genomes. These results suggest that homologous recombination can promote the genetic diversity and potentially bring some novel biologic characteristics of HPIV.

Replicating viral vectors as HIV vaccines: summary report from the IAVI-sponsored satellite symposium at the AIDS vaccine 2009 conference

In October 2009, The International AIDS Vaccine Initiative (IAVI) convened a satellite symposium entitled 'Replicating Viral Vectors for use in AIDS Vaccines' at the AIDS Vaccine 2009 Conference in Paris. The purpose of the symposium was to gather together researchers, representatives from regulatory agencies, and vaccine developers to discuss issues related to advancement of replication-competent viral vector- based HIV vaccines into clinical trials. The meeting introduced the rationale for accelerating the development of replicating viral vectors for use as AIDS vaccines. It noted that the EMEA recently published draft guidelines that are an important first step in providing guidance for advancing live viral vectors into clinical development. Presentations included case studies and development challenges for viral vector-based vaccine candidates. These product development challenges included cell substrates used for vaccine manufacturing, the testing needed to assess vaccine safety, conducting clinical trials with live vectors, and assessment of vaccination risk versus benefit. More in depth discussion of risk and benefit highlighted the fact that AIDS vaccine efficacy trials must be conducted in the developing world where HIV incidence is greatest and how inequities in global health dramatically influence the political and social environment in developing countries.

Phenotypes and functions of persistent Sendai virus-induced antibody forming cells and CD8+ T cells in diffuse nasal-associated lymphoid tissue typify lymphocyte responses of the gut

Lymphocytes of the diffuse nasal-associated lymphoid tissue (d-NALT) are uniquely positioned to tackle respiratory pathogens at their point-of-entry, yet are rarely examined after intranasal (i.n.) vaccinations or infections. Here we evaluate an i.n. inoculation with Sendai virus (SeV) for elicitation of virus-specific antibody forming cells (AFCs) and CD8(+) T cells in the d-NALT. Virus-specific AFCs and CD8(+) T cells each appeared by day 7 after SeV inoculation and persisted for 8 months, explaining the long-sustained protection against respiratory virus challenge conferred by this vaccine. AFCs produced IgM, IgG1, IgG2a, IgG2b and IgA, while CD8+ T cells were cytolytic and produced low levels of cytokines. Phenotypic analyses of virus-specific T cells revealed striking similarities with pathogen-specific immune responses in the intestine, highlighting some key features of adaptive immunity at a mucosal site.

Robust IgA and IgG-producing antibody forming cells in the diffuse-NALT and lungs of Sendai virus-vaccinated cotton rats associate with rapid protection against human parainfluenza virus-type 1

Sendai virus (SeV), a natural mouse pathogen, shows considerable promise as a candidate vaccine for human parainfluenza virus-type 1 (hPIV-1), and also as a vaccine vector for other serious pathogens of infants including respiratory syncytial virus (RSV). In an effort to define correlates of immunity, we examined the virus-specific serum antibody of cotton rats inoculated intranasally (I.N.) with SeV. Virus-specific antibody forming cells (AFCs) were also measured in the bone marrow, because these are considered responsible for durable serum antibody levels in other viral systems. Results showed that a single SeV inoculation was sufficient to induce virus-specific serum antibodies and bone marrow-resident AFCs that persisted for as many as 8 months post-vaccination. Given that the predominant SeV-specific serum antibody isotype was IgG, an isotype that traffics poorly to the upper respiratory tract (URT), we asked if local nasal and lung-associated antibodies and AFCs were also present. Studies showed that: (i) SeV-specific antibodies appeared in the URT and lower respiratory tract (LRT) within 7 days after immunization, (ii) corresponding AFCs were present in the diffuse-NALT (d-NALT) and lung, (iii) AFCs in the d-NALT and lung peaked at approximately 6 weeks and persisted for the lifetime of the animal, reaching a level exceeding that of the bone marrow by an order of magnitude, (iv) IgA was the dominant isotype among AFCs in the d-NALT and lung at 4-weeks post-vaccination and thereafter, and (v) antibody and AFC responses associated with the prevention of lung infection when animals were challenged with hPIV-1 just 1 week after vaccination.

Residues in the heptad repeat a region of the fusion protein modulate the virulence of Sendai virus in mice

While the molecular basis of fusion (F) protein refolding during membrane fusion has been studied extensively in vitro, little is known about the biological significance of membrane fusion activity in parainfluenza virus replication and pathogenesis in vivo. Two recombinant Sendai viruses, F-L179V and F-K180Q, were generated that contain F protein mutations in the heptad repeat A region of the ectodomain, a region of the protein known to regulate F protein activation. In vitro, the F-L179V virus caused increased syncytium formation (cell-cell membrane fusion) yet had a rate of replication and levels of F protein expression and cleavage similar to wild-type virus. The F-K180Q virus had a reduced replication rate along with reduced levels of F protein expression, cleavage, and fusogenicity. In DBA/2 mice, the hyperfusogenic F-L179V virus induced greater morbidity and mortality than wild-type virus, while the attenuated F-K180Q virus was much less pathogenic. During the first week of infection, virus replication and inflammation in the lungs were similar for wild-type and F-L179V viruses. After approximately 1 week of infection, the clearance of F-L179V virus was delayed, and more extensive interstitial inflammation and necrosis were observed in the lungs, affecting entire lobes of the lungs and having significantly greater numbers of syncytial cell masses in alveolar spaces on day 10. On the other hand, the slower-growing F-K180Q virus caused much less extensive inflammation than wild-type virus, presumably due to its reduced replication rate, and did not cause observable syncytium formation in the lungs. Overall, the results show that residues in the heptad repeat A region of the F protein modulate the virulence of Sendai virus in mice by influencing both the spread and clearance of the virus and the extent and severity of inflammation. An understanding of how the F protein contributes to infection and inflammation in vivo may assist in the development of antiviral therapies against respiratory paramyxoviruses.

Human PIV-2 recombinant Sendai virus (rSeV) elicits durable immunity and combines with two additional rSeVs to protect against hPIV-1, hPIV-2, hPIV-3, and RSV

The human parainfluenza viruses (hPIVs) and respiratory syncytial viruses (RSVs) are the leading causes of hospitalizations due to respiratory viral disease in infants and young children, but no vaccines are yet available. Here we describe the use of recombinant Sendai viruses (rSeVs) as candidate vaccine vectors for these respiratory viruses in a cotton rat model. Two new Sendai virus (SeV)-based hPIV-2 vaccine constructs were generated by inserting the fusion (F) gene or the hemagglutinin-neuraminidase (HN) gene from hPIV-2 into the rSeV genome. The inoculation of either vaccine into cotton rats elicited neutralizing antibodies toward both homologous and heterologous hPIV-2 virus isolates. The vaccines elicited robust and durable antibodies toward hPIV-2, and cotton rats immunized with individual or mixed vaccines were fully protected against hPIV-2 infections of the lower respiratory tract. The immune responses toward a single inoculation with rSeV vaccines were long-lasting and cotton rats were protected against viral challenge for as long as 11 months after vaccination. One inoculation with a mixture of the hPIV-2-HN-expressing construct and two additional rSeVs (expressing the F protein of RSV and the HN protein of hPIV-3) resulted in protection against challenge viruses hPIV-1, hPIV-2, hPIV-3, and RSV. Results identify SeV vectors as promising vaccine candidates for four different paramyxoviruses, each responsible for serious respiratory infections in children.

Development of recombinant Sendai virus vaccines for prevention of human parainfluenza and respiratory syncytial virus infections

Respiratory syncytial virus (RSV) and human parainfluenza viruses (hPIVs) are the most important causes of hospitalization for viral respiratory tract diseases in infants and young children. Unfortunately, there are currently no licensed vaccines for prevention of these infections. Researchers at St. Jude Children's Research Hospital are now developing Sendai virus (SV), a natural respiratory pathogen of mice, as a Jennerian vaccine for hPIV-1, and as a vaccine backbone for the prevention of RSV and other hPIVs. Unmodified SV is currently being tested in the clinic. Thus far, the vaccine has been well tolerated. Preclinical studies also continue and have demonstrated that intranasal vaccinations with recombinant SV expressing an RSV antigen are sufficient to activate high-magnitude RSV-specific neutralizing B- and T-cell activities in a cotton rat system. Furthermore, vaccinated animals are completely protected against RSV challenges. As clinical safety studies progress, St. Jude Children's Research Hospital researchers are also working to formulate a SV-based cocktail vaccine designed to prevent several hPIV and RSV infections in humans.

Mutation at residue 523 creates a second receptor binding site on human parainfluenza virus type 1 hemagglutinin-neuraminidase protein

The paramyxovirus hemagglutinin-neuraminidase (HN) is a multifunctional protein mediating hemagglutination (HA), neuraminidase (NA), and fusion promotion activities. It has been a matter of debate whether HN contains combined or separate sites for HA and NA activities. To clear the issue, we determined the presence of the second binding site on human parainfluenza virus (hPIV) type 1, 2, and 3 and Sendai virus (SeV) HN proteins. Results of virus elution from erythrocytes at an elevated temperature and HA inhibition by NA inhibitor BCX-2798 suggest that all hPIVs bind to the receptor only through the NA catalytic site, while SeV HN has an additional receptor binding site. Comparison of SeV and hPIV1 HN sequences revealed two amino acid differences at residues 521 and 523 in the region close to the second binding site identified in Newcastle disease virus HN. We mutated hPIV1 HN at position 523 from Asn to the residue of SeV HN, Asp, and rescued a recombinant SeV that carries the mutated hPIV1 HN by a reverse genetics system. The hPIV1 HN with Asp at position 523 hemagglutinated in the presence of BCX-2798, suggesting that the amino acid difference at position 523 is critical for the formation of a second binding site. Creation of the second binding site on hPIV1 HN, however, did not significantly affect the growth or fusion activity of the recombinant virus. Our study indicates that the presence and requirement of a second binding site vary among paramyxoviruses.

Role of sialic acid-containing molecules in paramyxovirus entry into the host cell: A minireview

Sialic acid-containing compounds play a key role in the initial steps of the paramyxovirus life cycle. As enveloped viruses, their entry into the host cell consists of two main events: binding to the host cell and membrane fusion. Virus adsorption occurs at the surface of the host cell with the recognition of specific receptor molecules located at the cell membrane by specific viral attachment proteins. The viral attachment protein present in some paramyxoviruses (Respirovirus, Rubulavirus and Avulavirus) is the HN glycoprotein, which binds to cellular sialic acid-containing molecules and exhibits sialidase and fusion promotion activities. Gangliosides of the gangliotetraose series bearing the sialic acid N-acetylneuraminic (Neu5Ac) on the terminal galactose attached in alpha2-3 linkage, such as GD1a, GT1b, and GQ1b, and neolacto-series gangliosides are the major receptors for Sendai virus. Much less is known about the receptors for other paramyxoviruses than for Sendai virus. Human parainfluenza viruses 1 and 3 preferentially recognize oligosaccharides containing N-acetyllactosaminoglycan branches with terminal Neu5Acalpha2-3Gal. In the case of Newcastle disease virus, has been reported the absence of a specific pattern of the gangliosides that interact with the virus. Additionally, several works have described the use of sialylated glycoproteins as paramyxovirus receptors. Accordingly, the design of specific sialic acid analogs to inhibit the sialidase and/or receptor binding activity of viral attachment proteins is an important antiviral strategy. In spite of all these data, the exact nature of paramyxovirus receptors, apart from their sialylated nature, and the mechanism(s) of viral attachment to the cell surface are poorly understood.

Recombinant Sendai virus as a novel vaccine candidate for respiratory syncytial virus

Respiratory syncytial virus (RSV) is among the most important and serious pediatric respiratory diseases, and yet after more than four decades of research an effective vaccine is still unavailable. This review examines the role of the immune response in reducing disease severity; considers the history of RSV vaccine development; and advocates the potential utility of Sendai virus (a murine paramyxovirus) as a xenogenic vaccine vector for the delivery of RSV antigens. The immunogenicity and protective efficacy of RSV-recombinant Sendai virus vectors constructed using reverse genetics is examined. RSV-recombinant Sendai virus is easy to grow (i.e., achieves extremely high titers in eggs), is easy to administer (intranasal drops), and elicits both B- and T-cell responses leading to protection from RSV challenge in a small-animal model. Unmodified Sendai virus is currently being studied in clinical trials as a vaccine for its closely related human cognate (human parainfluenza virus type 1). Sendai virus may prove an enormously valuable vaccine platform, permitting the delivery of recombinants targeting important pediatric respiratory pathogens, RSV chief among them.

IFN-γ: A Cytokine Essential for Rejection of CTL-Resistant, Virus-Infected Cells

We recently demonstrated differential susceptibility of cells expressing viral antigen to killing by antigen-specific cytotoxic T lymphocytes (CTLs). In addition, interferon-gamma (IFN-gamma) has been implicated in the clearance of some viruses from tissues. We explored the role of IFN-gamma in the cytotoxicity of Sendai virus-specific CTLs against virus-infected RL(male symbol)1 (T cell leukemia) or Meth A (fibrosarcoma) cells, as well as the growth of subcutaneously (s.c.) transplanted, virus-infected cells in IFN-gamma(+/+) or IFN-gamma(/) mice of the syngeneic strain (BALB/c). Sendai virus-specific CTLs were cytotoxic against virus-infected RL(male symbol)1 cells, and s.c. transplanted, virus-infected RL(male symbol)1 cells were acutely rejected from IFN-gamma(+/+) or IFN-gamma(/) mice. In contrast, the CTLs were inactive toward virus-infected Meth A cells, but s.c. transplanted, virus-infected Meth A cells were acutely rejected from IFN-gamma(+/+) but not IFN-gamma(/) mice. The s.c. growth of virus-infected Meth A cells in the mutant mice was markedly inhibited by s.c. injections of IFN-gamma, and the rejection from IFN-gamma(+/+) mice was delayed after specific elimination of macrophages by intravenous (i.v.) injections of dichloromethylene diphosphonatecontaining liposomes. These results suggest an essential role of IFN-gamma and involvement of macrophage in the rejection of CTL-resistant, virus-infected cells.

Safety and immunogenicity of intranasal murine parainfluenza virus type 1 (Sendai virus) in healthy human adults

Human parainfluenza virus-type 1 (hPIV-1) is the most common cause of pediatric laryngotracheobronchitis (croup) and results in close to 30,000 US hospitalizations each year. No effective vaccine is available. We examined murine PIV-1 (Sendai virus, SeV) as a live, xenotropic vaccine for the closely related human PIV-1 in a phase I, dose escalation study in healthy adults. Intranasal Sendai virus was uniformly well-tolerated and showed evidence of immunogenicity in three of nine vaccinees despite pre-existing, cross-reactive immunity presumably induced by previous exposure to human PIV-1. Results encourage future trials to evaluate the efficacy of Sendai virus in preventing human PIV-1 infection in infants and children.

Peptides from common viral and bacterial pathogens can efficiently activate diabetogenic T-cells

Cross-reactivity between an autoantigen and unknown microbial epitopes has been proposed as a molecular mechanism involved in the development of insulin-dependent diabetes (type 1 diabetes). Type 1 diabetes is an autoimmune disease that occurs in humans and the nonobese diabetic (NOD) mouse. BDC2.5 is an islet-specific CD4+ T-cell clone derived from the NOD mouse whose natural target antigen is unknown. A biometrical analysis of screening data from BDC2.5 T-cells and a positional scanning synthetic combinatorial library (PS-SCL) was used to analyze and rank all peptides in public viral and bacterial protein databases and identify potential molecular mimic sequences with predicted reactivity. Selected sequences were synthesized and tested for stimulatory activity with BDC2.5 T-cells. Active peptides were identified, and some of them were also able to stimulate spontaneously activated T-cells derived from young, pre-diabetic NOD mice, indicating that the reactivity of the BDC2.5 T-cell is directed at numerous mouse peptides. Our results provide evidence for their possible role as T-cell ligands involved in the activation of diabetogenic T-cells.

Sialidase, receptor-binding and fusion-promotion activities of Newcastle disease virus haemagglutinin–neuraminidase glycoprotein: a mutational and kinetic study

Mutations were generated in residues at the putative catalytic site of the haemagglutinin–neuraminidase (HN) protein of Newcastle disease virus Clone 30 strain (Arg498, Glu258, Tyr262, Tyr317 and Ser418) and their effects on its three associated activities were studied. Expression of the mutant proteins at the surface of HeLa cells was similar to that of the wild-type. Sialidase, receptor-binding and fusion-promotion activities were affected to different degrees for all mutants studied. Mutant Arg498Lys lost most of its sialidase activity, although it retained most of the receptor-binding activity, suggesting that, for the former activity, besides the presence of a basic residue, the proximity to the substrate molecule is also important, as Lys is shorter than Arg. Proximity also seems to be important in substrate recognition, since Tyr262Phe retained most of its sialidase activity while Tyr262Ser lost most of it. Also, Ser418Ala displayed most of the wild-type sialidase activity. However, a kinetic and thermodynamic study of the sialidase activity of the Tyr262Ser and Ser418Ala mutants was performed and revealed that the hydroxyl group of these residues also plays an important role in catalysis, since such activity was much less effective than that of the wild-type and these mutations modified their activation energy for sialidase catalysis. The discrepancy of the modifications in sialidase and receptor-binding activities in the mutants analysed does not account for the topological coincidence of the two sites. These results also suggest that the globular head of HN protein may play a role in fusion-promotion activity.

Sequence analysis of the Washington/1964 strain of human parainfluenza virus type 1 (HPIV1) and recovery and characterization of wild-type recombinant HPIV1 produced by reverse genetics

A complete consensus sequence was determined for the genomic RNA of human parainfluenza virus type 1 (HPIV1) strain Washington/20993/1964 (HPIV1 WASH/64), a clinical isolate that previously was shown to be virulent in adults. The sequence exhibited a high degree of relatedness to both Sendai virus, a PIV1 virus recovered from mice, and human PIV3 (HPIV3) with regard to cis-acting regulatory regions and protein-coding sequences. This consensus sequence was used to generate a full-length antigenomic cDNA and to recover a recombinant wild-type HPIV1 (rHPIV1). Interestingly, the rHPIV1 could be rescued from full-length antigenomic rHPIV1 cDNA using HPIV3 support plasmids, HPIV1 support plasmids, or a mixture thereof. The replication of rHPIV1 in vitro and in the respiratory tract of hamsters was similar to that of its biologically derived parent virus. The similar biological properties of rHPIV1 and HPIV1 WASH/64 in vitro and in vivo, together with the previous demonstration of the virulence of this specific isolate in humans, authenticates the rHPIV1 sequence as that of a wild-type virus. This rHPIV1 can now be used to study the biological properties of HPIV1 and as a substrate to introduce attenuating mutations for the generation of live-attenuated HPIV1 vaccine candidates.

Sendai virus, a murine parainfluenza virus type 1, replicates to a level similar to human PIV1 in the upper and lower respiratory tract of African green monkeys and chimpanzees

Human parainfluenza virus type 1 (HPIV1), a major cause of croup in infants and young children, accounts for 6% of hospitalizations for pediatric respiratory tract disease. The antigenically related Sendai virus, referred to here as murine PIV1 (MPIV1), is being considered for use as a live-attenuated vaccine to protect against HPIV1 (J. L. Hurwitz, K. F. Soike, M. Y., Sangster, A. Portner, R. E. Sealy, D. H. Dawson, and C. Coleclough, 1997, Vaccine 15(5), 533-540) and also as a recombinant vaccine vector expressing antigens to protect against viral disease in humans. However, in the 1950s MPIV1 was reported to have been isolated from humans, suggesting that zoonotic transmission might have occurred. It is therefore important to examine the ability of MPIV1 to replicate in nonhuman primates, i.e., surrogate hosts for humans. In the present study the level of replication of MPIV1 and HPIV1 was compared in African green monkeys and chimpanzees. Surprisingly, MPIV1 replicated as efficiently as HPIV1 in the upper and lower respiratory tract of African green monkeys at doses of 10(4) and 10(6) and replicated only slightly less efficiently at both sites in chimpanzees. African green monkeys immunized with MPIV1 were highly resistant to subsequent challenge with HPIV1 even though MPIV1 did not induce a detectable HPIV1-neutralizing antibody response. The high level of replication of MPIV1 observed in the upper and lower respiratory tract of these primates suggests that MPIV1 likely would require significant attenuation before it could be given to humans as a vaccine against HPIV1 or as a vaccine vector. Its ability to efficiently replicate in nonhuman primates suggests that MPIV1 lacks a significant host range restriction in primates and could theoretically cause zoonotic disease in humans.

Functional properties of the fusion and attachment glycoproteins of Nipah virus

Nipah virus (NV) and Hendra virus (HV) are recently emergent, related viruses that can cause severe disease in humans and animals. The goal of this study was to investigate the immunogenic and functional properties of the fusion (F) and attachment (G) glycoproteins of NV. Vaccination of mice with recombinant vaccinia viruses (rVVs) expressing either the F (rVV/NV-F) or G (rVV/NV-G) proteins of NV induced neutralizing antibody responses to NV, with higher titers produced after vaccination with rVV/NV-G. When the homologous pairs of F and G proteins from either HV or NV were coexpressed in a transient expression system, fusion was detected in less than 12 h. An equivalent amount of fusion was observed when the heterologous pairs of F and G proteins from HV and NV were coexpressed. Membrane fusion was inhibited by antiserum from mice vaccinated with rVV/NV-G and rVV/NV-F. Therefore, as with other paramyxoviruses, the membrane glycoproteins of NV are the targets of neutralizing antibodies and membrane fusion mediated by NV requires the presence of both the F and the G proteins. Data from these biological assays support the taxonomic grouping of both HV and NV in the new genus, Henipavirus, within the family Paramyxoviridae.

A single amino acid alteration in the human parainfluenza virus type 3 hemagglutinin-neuraminidase glycoprotein confers resistance to the inhibitory effects of zanamivir on receptor binding and neuraminidase activity

Entry and fusion of human parainfluenza virus type 3 (HPF3) requires interaction of the viral hemagglutinin-neuraminidase (HN) glycoprotein with its sialic acid receptor. 4-Guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid (4-GU-DANA; zanamivir), a sialic acid transition-state analog designed to fit the influenza virus neuraminidase catalytic site, possesses antiviral activity at nanomolar concentrations in vitro. We have shown previously that 4-GU-DANA also inhibits both HN-mediated binding of HPF3 to host cell receptors and HN's neuraminidase activity. In the present study, a 4-GU-DANA-resistant HPF3 virus variant (ZM1) was generated by serial passage in the presence of 4-GU-DANA. ZM1 exhibited a markedly fusogenic plaque morphology and harbored two HN gene mutations resulting in two amino acid alterations, T193I and I567V. Another HPF3 variant studied in parallel, C-0, shared an alteration at T193 and exhibited similar plaque morphology but was not resistant to 4-GU-DANA. Neuraminidase assays revealed a 15-fold reduction in 4-GU-DANA sensitivity for ZM1 relative to the wild type (WT) and C-0. The ability of ZM1 to bind sialic acid receptors was inhibited 10-fold less than for both WT and C-0 in the presence of 1 mM 4-GU-DANA. ZM1 also retained infectivity at 15-fold-higher concentrations of 4-GU-DANA than WT and C-0. A single amino acid alteration at HN residue 567 confers these 4-GU-DANA-resistant properties. An understanding of ZM1 and other escape variants provides insight into the effects of this small molecule on HN function as well as the role of the HN glycoprotein in HPF3 pathogenesis.

Receptor specificities of human respiroviruses

Through their hemagglutinin-neuraminidase glycoprotein, parainfluenza viruses bind to sialic acid-containing glycoconjugates to initiate infection. Although the virus-receptor interaction is a key factor of infection, the exact nature of the receptors that human parainfluenza viruses recognize has not been determined. We evaluated the abilities of human parainfluenza virus types 1 (hPIV-1) and 3 (hPIV-3) to bind to different types of gangliosides. Both hPIV-1 and hPIV-3 preferentially bound to neolacto-series gangliosides containing a terminal N-acetylneuraminic acid (NeuAc) linked to N-acetyllactosamine (Galbeta1-4GlcNAc) by the alpha2-3 linkage (NeuAcalpha2-3Galbeta1-4GlcNAc). Unlike hPIV-1, hPIV-3 bound to gangliosides with a terminal NeuAc linked to Galbeta1-4GlcNAc through an alpha2-6 linkage (NeuAcalpha2-6Galbeta1-4GlcNAc) or to gangliosides with a different sialic acid, N-glycolylneuraminic acid (NeuGc), linked to Galbeta1-4GlcNAc (NeuGcalpha2-3Galbeta1-4GlcNAc). These results indicate that the molecular species of glycoconjugate that hPIV-1 recognizes are more limited than those recognized by hPIV-3. Further analysis using purified gangliosides revealed that the oligosaccharide core structure is also an important element for binding. Gangliosides that contain branched N-acetyllactosaminoglycans in their core structure showed higher avidity than those without them. Agglutination of human, cow, and guinea pig erythrocytes but not equine erythrocytes by hPIV-1 and hPIV-3 correlated well with the presence or the absence of sialic acid-linked branched N-acetyllactosaminoglycans on the cell surface. Finally, NeuAcalpha2-3I, which bound to both viruses, inhibited virus infection of Lewis lung carcinoma-monkey kidney cells in a dose-dependent manner. We conclude that hPIV-1 and hPIV-3 preferentially recognize oligosaccharides containing branched N-acetyllactosaminoglycans with terminal NeuAcalpha2-3Gal as receptors and that hPIV-3 also recognizes NeuAcalpha2-6Gal- or NeuGcalpha2-3Gal-containing receptors. These findings provide important information that can be used to develop inhibitors that prevent human parainfluenza virus infection.

Structural and functional relationship between the receptor recognition and neuraminidase activities of the Newcastle disease virus hemagglutinin-neuraminidase protein: receptor recognition is dependent on neuraminidase activity

The terminal globular domain of the paramyxovirus hemagglutinin-neuraminidase (HN) glycoprotein spike has a number of conserved residues that are predicted to form its neuraminidase (NA) active site, by analogy to the influenza virus neuraminidase protein. We have performed a site-directed mutational analysis of the role of these residues in the functional activity of the Newcastle disease virus (NDV) HN protein. Substitutions for several of these residues result in a protein lacking both detectable NA and receptor recognition activity. Contribution of NA activity, either exogenously or by coexpression with another HN protein, partially rescues the receptor recognition activity of these proteins, indicating that the receptor recognition deficiencies of the mutated HN proteins result from their lack of detectable NA activity. In addition to providing support for the homology-based predictions for the structure of HN, these findings argue that (i) the HN residues that mediate its NA activity are not critical to its attachment function and (ii) NA activity is required for the protein to mediate binding to receptors.

Molecular cloning and expression of human parainfluenza virus type 1 L gene

The large (L) protein, a subunit of paramyxovirus RNA polymerase complex is responsible for the majority of enzymic activities involved in viral replication and transcription. To gain insight of the functions of the L protein, we cloned the L gene of human parainfluenza virus type 1 (hPIV1) and sequenced the entire gene. The L gene, which was 6800 nucleotides, encoded a protein of 2223 residues with a calculated molecular weight of 253657. The predicted amino acid sequence was highly homologous with that of Sendai virus (SV) L (86% identity). The hPIV1 L protein expressed from the cloned L gene bound hPIV1 P expressed in the same cells. When cells were transfected with hPIV1 L, P and NP genes together with SV minigenome RNA containing a chloramphenicol acetyltransferase (CAT) gene (Send-CAT), RNA was transcribed, and CAT proteins were detected. These results indicate that the protein encoded by the cloned hPIV1 L gene was biologically functional and that the hPIV1 polymerase complex recognized SV transcription initiation and termination sequences to produce viral transcripts.

Rapid molecular epidemiologic studies of human parainfluenza viruses based on direct sequencing of amplified DNA from a multiplex RT-PCR assay

Sequencing studies of limited regions of the human parainfluenza viruses (HPIVs) genomes have helped describe patterns of virus circulation and characterize institutional outbreaks of HPIVs-associated respiratory illness. In this study, we sequenced reverse transcription polymerase chain reaction (RT-PCR)-amplified HPIVs RNA obtained from a multiplex RT-PCR assay described previously for simultaneous detection of HPIV-1, 2 and 3. Differences in the nucleotide sequences of limited regions of the HN gene allowed us to distinguish temporally and geographically diverse HPIV isolates (43 HPIV-1, 7 HPIV-2, 12 HPIV-3 isolates from this and previously published studies). In addition, an outbreak of HPIV-3-associated illness among infants on a pediatric ward was investigated by comparing sequences of three ward isolates with three matched community controls. Sequences of all ward isolates were identical and differed from those of the community controls, suggesting a single introduction and nosocomial transmission of the virus. Combining multiplex reverse transcription polymerase chain reaction (RT-PCR) assays with direct sequencing of the PCR products can provide an integrated system for rapid diagnosis and characterization of HPIVs.

The use of a quantitative fusion assay to evaluate HN-receptor interaction for human parainfluenza virus type 3

Sialic acid is the receptor determinant for the human parainfluenza virus type 3 (HPF3) hemagglutinin-neuraminidase (HN) glycoprotein, the molecule responsible for binding of the virus to cell surfaces. In order for the fusion protein (F) of HPF3 to promote membrane fusion, HN must interact with its receptor. In addition to its role in receptor binding and fusion promotion, the HPF3 HN molecule contains receptor-destroying (sialidase) activity. The putative active sites are in the extracellular domain of this type II integral membrane protein. However, HN is not available in crystalline form; the exact locations of these sites, and the structural requirements for binding to the cellular receptor, which has not yet been isolated, are unknown. Nor have small molecular synthetic inhibitors of attachment or fusion that would provide insight into these processes been identified. The strategy in the present study was to develop an assay system that would provide a measure of a specific step in the viral cycle-functional interaction between viral glycoproteins and the cell during attachment and fusion-and serve to screen a variety of substances for inhibitory potential. The assay is based on our previous finding that CV-1 cells persistently infected (p.i.) with HPF3 do not fuse with one another but that the addition of uninfected CV-1 cells, supplying the critical sialic acid containing receptor molecules that bind HN, results in rapid fusion. In the present assay two HeLa cell types were used: we persistently infected HeLa-LTR-betagal cells, assessed their fusion with uninfected HeLa-tat cells, and then quantitated the beta-galactosidase (betagal) produced as a result of this fusion. The analog alpha-2-S-methyl-5-N-thioacetylneuraminic acid (alpha-Neu5thioAc2SMe) interfered with fusion, decreasing betagal production by 84% at 50 mM and by 24% at 25 mM. In beginning to extend our studies to different types of molecules, we tested an unsaturated derivative of sialic acid, 2,3-dehydro-2-deoxy-n-acetyl neuraminic acid (DANA), which is known to inhibit influenza neuraminidase by virtue of being a transition-state analog. We found that 10 mM DANA inhibited neuraminidase activity in HPF3 viral preparations. More significantly, this compound was active in our assay of HN-receptor interaction; 10 mM DANA completely blocked fusion and betagal production, and hemadsorption inhibition by DANA suggested that DANA blocks attachment. In plaque reduction assays performed with the compounds, the active analog alpha-Neu5thioAc2SMe reduced plaque formation by 50% at a 50 mM concentration; DANA caused a 90% inhibition in the plaque reduction assay at a concentration of 25 mM. Our results indicate that specific sialic acid analogs that mimic the cellular receptor determinant of HPF3 can block virus cell interaction and that an unsaturated n-acetyl-neuraminic acid derivative with affinity to the HN site responsible for neuraminidase activity also interferes with HN-receptor binding. Strategies suggested by these findings are now being pursued to obtain information regarding the relative locations of the active sites of HN and to further elucidate the relationship between the receptor-binding and receptor-destroying activities of HN during the viral life cycle. The quantitative assay that we describe is of immediate applicability to large-scale screening for potential inhibitors of HPF3 infection in vivo.

A multiplex RT-PCR for the detection of parainfluenza viruses 1-3 in clinical samples

Parainfluenza viruses (PIV) are an important cause of respiratory morbidity. Conventional diagnostic methods for detection of PIV are time consuming or lack sensitivity. A multiplex PCR that detects PIV 1-3 was developed using novel primers for PIV viruses 1 and 2 and primers for PIV 3 described previously. Following RNA extraction a single multiplex reverse transcription was undertaken using antisense primers specific for each virus type. This was followed by a 40-cycle multiplex PCR using primers directed towards the haemagglutinin-neuraminidase coding region of each virus type. Products were probed with type-specific fluorescein labelled internal probes and detected by chemiluminescence. Cultured PIV viruses were detectable to a sensitivity of 1 TCID50. The technique was applied to 57 nasal aspirates taken from children presenting with various acute respiratory conditions and analysed previously by culture, immunofluorescence and/or serology. It was possible to detect PIV 1, 2 or 3 in 13/13 samples found previously positive for PIV by tissue culture, 13/15 found previously positive by immunofluorescence and 6/10 that coincided with positive serology. None of the samples found previously positive for other viruses (26) or negative to virus detection (6) were found positive by RT-PCR. It is concluded that this method is as sensitive as combined immunofluorescence and tissue culture for the detection of the PIV viruses 1-3 and should be useful for rapid diagnosis of PIV 1-3 infections.

Cytoplasmic domain of Sendai virus HN protein contains a specific sequence required for its incorporation into virions

In the assembly of paramyxoviruses, interactions between viral proteins are presumed to be specific. The focus of this study is to elucidate the protein-protein interactions during the final stage of viral assembly that result in the incorporation of the viral envelope proteins into virions. To this end, we examined the specificity of HN incorporation into progeny virions by transiently transfecting HN cDNA genes into Sendai virus (SV)-infected cells. SV HN expressed from cDNA was efficiently incorporated into progeny Sendai virions, whereas Newcastle disease virus (NDV) HN was not. This observation supports the theory of a selective mechanism for HN incorporation. To identify the region on HN responsible for the selective incorporation, we constructed chimeric SV and NDV HN cDNAs and evaluated the incorporation of expressed proteins into progeny virions. Chimera HN that contained the SV cytoplasmic domain fused to the transmembrane and external domains of the NDV HN was incorporated to SV particles, indicating that amino acids in the cytoplasmic domain are responsible for the observed specificity. Additional experiments using the chimeric HNs showed that 14 N-terminal amino acids are sufficient for the specificity. Further analysis identified five consecutive amino acids (residues 10 to 14) that were required for the specific incorporation of HN into SV. These residues are conserved among all strains of SV as well as those of its counterpart, human parainfluenza virus type 1. These results suggest that this region near the N terminus of HN interacts with another viral protein(s) to lead to the specific incorporation of HN into progeny virions.

Simultaneous detection and identification of human parainfluenza viruses 1, 2, and 3 from clinical samples by multiplex PCR

Reverse transcription (RT)-PCR assays have been widely described for use in the diagnosis of human parainfluenza viruses (HPIVs) and other respiratory virus pathogens. However, these assays are mostly monospecific, requiring separate amplifications for each HPIV type. In the present work, we describe multiplex RT-PCR assays that detect and differentiate HPIV serotypes 1, 2, and 3 in a combined reaction. Specifically, a mixture of three pairs of primers to conserved regions of the hemagglutinin-neuraminidase gene of each HPIV serotype was used for primary amplification, yielding amplicons with similar sizes. For typing, a second amplification was performed with a mixture of nested primers, yielding amplicons with sizes easily differentiated by agarose gel electrophoresis. A modified single-amplification RT-PCR assay with fluorescence-labeled nested primers, followed by analysis of the labeled products on an automated sequencing gel, was also evaluated. Fifteen temporally and geographically diverse HPIV isolates from the Centers for Disease Control and Prevention archives and 26 of 30 (87%) previously positive nasopharyngeal specimens (8 of 10 positive for HPIV serotype 1 [HPIV1], 9 of 10 positive for HPIV2, and 9 of 10 positive for HPIV3) were positive and were correctly typed by both assays. Negative results were obtained with naso- or oropharyngeal specimens and/or culture isolates of 33 unrelated respiratory tract pathogens, including HPIV4, enterovirus, rhinovirus, respiratory syncytial virus, adenovirus, influenza virus, and Streptococcus pneumoniae. Our multiplex RT-PCR assays provide sensitive, specific, and simplified tools for the rapid diagnosis of HPIV infections.

The transmembrane domain in viral fusion: essential role for a conserved glycine residue in vesicular stomatitis virus G protein

The transmembrane (TM) domains of viral fusion proteins are required for fusion, but their precise role is unknown. G protein, the fusion protein of vesicular stomatitis virus, was previously shown to lose syncytia-forming ability if six residues (GLIIGL) were deleted from its TM domain. The 20-residue TM domain of wild-type (TM20) G protein was thus changed into a TM domain of 14 residues (TM14). To assess possible sequence specificity for this loss of function, the two Gly residues in TM20 were replaced with either Ala or Leu. Both mutations resulted in complete loss of fusion activity, as measured by fusion-dependent reporter gene transfer. Single substitutions decreased activity by about half. TM14 was weakly active (15%) but reintroduction of a Gly residue into TM14 by a single Ile --> Gly substitution increased activity to 80%. All mutants retained normal hemifusion activity, i.e., lipid mixing between the outer leaflets of the reacting membranes. Thus, at least one TM Gly residue is required for a late step in fusion mediated by G protein. Gly residues were significantly (2.6-fold; P = 0.004) more abundant in the TM domains of viral fusion proteins than in those of nonfusion proteins and were distributed differently within the TM domain. Thus, Gly residues in the TM domain of other viral fusion proteins may also prove to be important for fusion activity.

Elevated expression of the human parainfluenza virus type 1 F gene downregulates HN expression

Interactions involved in the expression of parainfluenza glycoproteins were examined by expressing cDNA clones of the HN and F genes from human parainfluenza virus type-1 (hPIV1) or Sendai virus (SV) in recombinant Semliki Forest virus (recSFV) or vaccinia-T7 expression vectors. We found that expression of a cloned F protein gene of hPIV1 resulted in downregulation of the HN proteins of hPIV1 or SV. Compared to the amount of HN expressed in the absence of F, coexpression of HN and F led to about 70% reduction in HN. This reduction of HN was observed in both total cell lysates and in protein localized on the cell surface. In contrast to hPIV1 F, SV F did not suppress the expression of HN. Northern blot analysis indicated that similar levels of HN mRNA accumulated in the absence or presence of hPIV1 F. The reduction of HN protein expression by hPIV1 F was detectable after as little as a 10-min labeling period, suggesting that downregulation occurred at the level of translation or at an early stage of protein folding. In hPIV1-infected cells, the amount of F protein synthesized was only about 15% of that of HN, whereas SV F is expressed at high levels. When the level of F in hPIV1-infected cells was artificially increased by recSFV, HN expression was suppressed. The reduction of F protein production in hPIV1-infected cells was regulated at the level of transcription. Characterization of mRNAs produced in hPIV1-infected cells showed that only 20% of the hPIV1 F mRNAs were monocistronic transcripts; 80% were bicistronic M-F readthrough mRNAs. Because proteins are suggested to be synthesized from only the first cistron of bicistronic mRNA in paramyxovirus (T. C. Wong and A. Hirano (1987) J. Virol. 61, 584-589), production of F protein is likely suppressed by transcriptional regulation in hPIV1-infected cells. These results suggest that F is capable of downregulating the synthesis of HN, but that this is normally prevented in hPIV1-infected cells by suppression of F protein synthesis by transcriptional regulation.

Intranasal Sendai virus vaccine protects African green monkeys from infection with human parainfluenza virus-type one

Human parainfluenza virus-type I (hPIV-1) infections are a common cause of "group" and hospitalizations among young children. Here we address the possibility of using the xenotropic Sendai virus [a mouse parainfluenza virus (PIV)] as a vaccine for hPIV-1. Sendai virus was administered to six African green monkeys (Cercopithecus aethiops) by the intranasal (i.n.) route. A long lasting virus-specific antibody response was elicited, both in the serum and nasal cavity. Sendai virus caused no apparent clinical symptoms in the primates, but live virus was detected in the nasal cavity for several days after inoculation. No virus was detected after a second dose of Sendai virus was administered on day 126 after the initial priming. Animals were challenged with hPIV-1 i.n. on day 154. All six vaccinated animals were fully protected from infection while six of six control animals were infected with hPIV-1. The antibody responses induced by Sendai virus immunizations proved to be greater than those induced by hPIV-1. These results demonstrate that unmanipulated Sendai virus is an effective vaccine against hPIV-1 in a primate model and may constitute a practical vaccine for human use.