Human parainfluenza virus type 1 immunization of infant mice protects from subsequent Sendai virus infection

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.

Sendai virus as a backbone for vaccines against RSV and other human paramyxoviruses

Human paramyxoviruses are the etiological agents for life-threatening respiratory virus infections of infants and young children. These viruses, including respiratory syncytial virus (RSV), the human parainfluenza viruses (hPIV1-4) and human metapneumovirus (hMPV), are responsible for millions of serious lower respiratory tract infections each year worldwide. There are currently no standard treatments and no licensed vaccines for any of these pathogens. Here we review research with which Sendai virus, a mouse parainfluenza virus type 1, is being advanced as a Jennerian vaccine for hPIV1 and as a backbone for RSV, hMPV and other hPIV vaccines for children.

Relationships among dissemination of primary parainfluenza virus infection in the respiratory tract, mucosal and peripheral immune responses, and protection from reinfection: a noninvasive bioluminescence-imaging study

Respiratory paramyxoviruses such as respiratory syncytial virus (RSV) and human parainfluenza virus type 1 (HPIV1) to HPIV4 infect virtually all children by the age of 2 to 5 years, leading to partial but incomplete protection from reinfection. Here, we used luciferase-expressing reporter Sendai viruses (the murine counterpart of HPIV1) to noninvasively measure primary infection, immune responses, and protection from reinfection by either a lethal challenge or natural transmission in living mice. Both nonattenuated and attenuated reporter Sendai viruses were used, and three inoculation strategies were employed: intramuscular (i.m.), intranasal (i.n.) at a low dose and low volume, and i.n. at a high dose and high volume. High-dose, high-volume i.n. inoculation resulted in the highest levels of antibody responses and protection from reinfection. Low-dose, low-volume i.n. inoculation afforded complete protection from contact transmission and protection from morbidity, mortality, and viral growth during lethal challenge. i.m. inoculation was inferior to i.n. inoculation at inducing antibody responses and protection from challenge. For individual mice and across groups, the levels of serum binding and neutralizing antibody responses correlated with primary infection and protection from reinfection in the lungs. Contact transmission, the predominant mode of parainfluenza virus transmission, was modeled accurately by direct i.n. inoculation of Sendai virus at a low dose and low volume and was completely preventable by i.n. vaccination of an attenuated virus at a low dose and low volume. The data highlight differences in infection and protection from challenge in the upper versus lower respiratory tract and bear upon live attenuated vaccine development.

IMPORTANCE

There are currently no licensed vaccines against HPIVs and human RSV (HRSV), important respiratory pathogens of infants and children. Natural infection leads to partial but incomplete protective immunity, resulting in subsequent reinfections even in the absence of antigenic drift. Here, we used noninvasive bioluminescence imaging in a mouse model to dissect relationships among (i) the mode of inoculation, (ii) the dynamics of primary infection, (iii) consequent immune responses, and (iv) protection from high-dose, high-volume lethal challenge and contact transmission, which we find here to be similar to that of a mild low-dose, low-volume upper respiratory tract (URT)-biased infection. Our studies demonstrate the superiority of i.n. versus i.m. vaccination in protection against both lethal challenge and contact transmission. In addition to providing correlates of protection that will assist respiratory virus vaccine development, these studies extend the development of an increasingly used technique for the study of viral infection and immunity, noninvasive bioluminescence imaging.

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.

Intranasal administration of retinyl palmitate with a respiratory virus vaccine corrects impaired mucosal IgA response in the vitamin A-deficient host

Our previous studies showed that intranasal vaccination of vitamin A-deficient (VAD) mice failed to induce normal levels of upper respiratory tract IgA, a first line of defense against respiratory virus infection. Here we demonstrate that the impaired responses in VAD animals are corrected by a single intranasal application of retinyl palmitate with the vaccine. Results encourage the clinical testing of intranasal vitamin A supplements to improve protection against respiratory viral disease in VAD populations.

Mode of parainfluenza virus transmission determines the dynamics of primary infection and protection from reinfection

Little is known about how the mode of respiratory virus transmission determines the dynamics of primary infection and protection from reinfection. Using non-invasive imaging of murine parainfluenza virus 1 (Sendai virus) in living mice, we determined the frequency, timing, dynamics, and virulence of primary infection after contact and airborne transmission, as well as the tropism and magnitude of reinfection after subsequent challenge. Contact transmission of Sendai virus was 100% efficient, phenotypically uniform, initiated and grew to robust levels in the upper respiratory tract (URT), later spread to the lungs, grew to a lower level in the lungs than the URT, and protected from reinfection completely in the URT yet only partially in the lungs. Airborne transmission through 7.6-cm and 15.2-cm separations between donor and recipient mice was 86%-100% efficient. The dynamics of primary infection after airborne transmission varied between individual mice and included the following categories: (a) non-productive transmission, (b) tracheal dominant, (c) tracheal initiated yet respiratory disseminated, and (d) nasopharyngeal initiated yet respiratory disseminated. Any previous exposure to Sendai virus infection protected from mortality and severe morbidity after lethal challenge. Furthermore, a higher level of primary infection in a given respiratory tissue (nasopharynx, trachea, or lungs) was inversely correlated with the level of reinfection in that same tissue. Overall, the mode of transmission determined the dynamics and tropism of primary infection, which in turn governed the level of seroconversion and protection from reinfection. These data are the first description of the dynamics of respiratory virus infection and protection from reinfection throughout the respiratory tracts of living animals after airborne transmission. This work provides a basis for understanding parainfluenza virus transmission and protective immunity and for developing novel vaccines and non-pharmaceutical interventions.

Epitope mapping of the nucleocapsid protein of sendai virus and application of antigenic epitopes for the ELISA-based diagnosis of sendai virus infection

Sendai virus (SeV) is one of the most prevalent viral pathogens infecting laboratory mice and rats. To date, mature SeV virions have been used as antigens for serological diagnosis. To develop antigens that are more specific and easier to prepare for diagnosis, we examined the antigenic sites in the nucleocapsid protein (NP) of SeV with antisera from experimentally SeV-infected mice and a peptide array membrane containing overlapping 10-mer peptides covering the entire NP. We found antigenic linear sequences in two regions, amino acids 120-160 and 420-500, of the SeV-NP. From these antigenic sequences, we applied two synthesized peptides, IVKTRDMEYERTTEWL and FVTLHGAERLEEETNDE, which correspond to positions 119-134 and 458-474 of the SeV-NP, respectively, as antigens in an enzyme-linked immunosorbent assay (ELISA). Evaluation of the ELISAs using these peptides revealed that they were specific to anti-SeV antisera. Furthermore, the ELISAs using these peptides were able to distinguish between SeV-positive and SeV-negative mouse sera to the same extent as a commercial ELISA kit. These results indicate that these peptides are useful for the serological diagnosis of SeV infection.

Respiratory syncytial virus: current progress in vaccine development

Respiratory syncytial virus (RSV) is the etiological agent for a serious lower respiratory tract disease responsible for close to 200,000 annual deaths worldwide. The first infection is generally most severe, while re-infections usually associate with a milder disease. This observation and the finding that re-infection risks are inversely associated with neutralizing antibody titers suggest that immune responses generated toward a first RSV exposure can significantly reduce morbidity and mortality throughout life. For more than half a century, researchers have endeavored to design a vaccine for RSV that can mimic or improve upon natural protective immunity without adverse events. The virus is herein described together with the hurdles that must be overcome to develop a vaccine and some current vaccine development approaches.

Clonally related CD8+ T cells responsible for rapid population of both diffuse nasal-associated lymphoid tissue and lung after respiratory virus infection

The immune system has evolved to use sophisticated mechanisms to recruit lymphocytes to sites of pathogen exposure. Trafficking pathways are precise. For example, lymphocytes that are primed by gut pathogens can, in some cases, be imprinted with CCR9 membrane receptors, which can influence migration to the small intestine. Currently, little is known about T cell trafficking to the upper respiratory tract or the relationship between effectors that migrate to the diffuse nasal-associated lymphoid tissue (d-NALT), the lower airways, and the lung. To determine whether a T cell primed by Ag from a respiratory pathogen is imprinted for exclusive trafficking to the upper or lower respiratory tract or whether descendents from that cell have the capacity to migrate to both sites, we inoculated mice by the intranasal route with Sendai virus and conducted single-cell-sequencing analyses of CD8(+) T lymphocytes responsive to a K(b)-restricted immunodominant peptide, FAPGNYPAL (Tet(+)). Cells from the d-NALT, lung airways (bronchoalveolar lavage), lung, and mediastinal lymph node were examined 10 d postinfection to determine TCR usage and clonal relationships. We discovered that 1) Tet(+) cells were heterogeneous but preferentially used TCR elements TRAV6, TRAV16, and TRBD1; 2) both N and C termini of Vα and Vβ TCR junctions frequently encompassed charged residues, perhaps facilitating TCR αβ pairing and interactions with a neutral target peptide; and 3) T cells in the d-NALT were often clonally related to cells in the lower respiratory tract.

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.

Host specificity of the anti-interferon and anti-apoptosis activities of parainfluenza virus P/C gene products

Human parainfluenza virus type 1 (HPIV-1) and Sendai virus (SeV) are highly homologous in structure and sequence, whilst maintaining distinct host ranges. These viruses express accessory proteins from their P/C gene that are known to have activities against innate immunity. The accessory proteins expressed from the P/C gene of these viruses are different. In addition to the nested set of C proteins, SeV expresses V protein from edited P mRNA, which is not expressed by HPIV-1. This study evaluated the host specificity and role of the P/C gene products in anti-interferon (IFN) and anti-apoptosis activity by characterizing a recombinant SeV, rSeVhP, in which the SeV P/C gene was replaced with that of HPIV-1. Unlike SeV, rSeVhP infection strongly activated IFN regulatory transcription factor (IRF)-3 and nuclear factor-kappaB, resulting in an increased level of IFN-beta induction compared with SeV in murine cells. In contrast, activation of IRF-3 was not observed in rSeVhP-infected human A549 cells. rSeVhPSV, which expressed SeV V protein from an inserted gene in rSeVhP, induced less IFN-beta than rSeVhP, suggesting that V contributes to the suppression of IFN production in murine cells. Furthermore, rSeVhP induced apoptotic cell death in murine but not in A549 cells. These data indicate the functional difference in P/C gene products from SeV and HPIV-1 in antagonizing IFN induction and apoptosis, which is likely to be one of the major factors for pathogenicity in specific hosts.

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.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

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.

Respiratory Vaccination of Mice Against Influenza Virus: Dissection of T- and B-Cell Priming Functions

We find that a single respiratory administration of replicationally inactivated influenza A viral particles most often elicits a waning serum antibody response, as the long-sustained bone marrow antiviral plasma cell populations characteristically induced by viral infection are lacking, though antiviral plasma cells at other sites may occasionally persist for a long time. To determine whether this alteration in the pattern of the B-cell response is a reflection of the nature of T-helper (Th) priming, we simultaneously primed B cells with inactivated influenza A/PR8(H1N1) and Th cells with infectious A/x31(H3N2). We show that Th cells cross-react extensively between these two viruses, although the antibody response to viral envelope glycoproteins is completely non-cross-reactive. Th cells primed by infectious A/x31 have little impact on the antibody response specifically elicted from naïve B cells by inactivated A/PR8 viruses, suggesting that the characteristic vigour of the antibody response to influenza viral infection depends on the direct interaction of antiviral B cells with virally infected dendritic cells. Memory B cells primed by inactivated influenza viral particles however, respond rapidly to secondary challenge with live or inactivated viruses, promptly populating bone marrow with antiviral plasma cells. Moreover, Th cells primed by previous live A/x31 viral challenge alter the pattern of the response of naïve B cells to live A/PR8 challenge by accelerating the appearance of anti-H1/N1 plasma cells in bone marrow, eliminating the early spike of anti-H1/N1 plasma cells in the mediastinal node, and generally diminishing the magnitude of the lymph node response. Inactivated A/PR8 and infectious A/x31 are both effective vaccines against A/PR8 infection, as mice preimmunized with either vaccine exhibit much more rapid viral clearance from the lung after infectious A/PR8 challenge. In fact, even when given during a course of anti-CD8 treatment to preempt cross-reactive cytotoxic T cells, live A/x31 is a more effective vaccine against A/PR8 infection than is inactivated A/PR8 itself.

Parainfluenza viruses

Human parainfluenza viruses (HPIV) were first discovered in the late 1950s. Over the last decade, considerable knowledge about their molecular structure and function has been accumulated. This has led to significant changes in both the nomenclature and taxonomic relationships of these viruses. HPIV is genetically and antigenically divided into types 1 to 4. Further major subtypes of HPIV-4 (A and B) and subgroups/genotypes of HPIV-1 and HPIV-3 have been described. HPIV-1 to HPIV-3 are major causes of lower respiratory infections in infants, young children, the immunocompromised, the chronically ill, and the elderly. Each subtype can cause somewhat unique clinical diseases in different hosts. HPIV are enveloped and of medium size (150 to 250 nm), and their RNA genome is in the negative sense. These viruses belong to the Paramyxoviridae family, one of the largest and most rapidly growing groups of viruses causing significant human and veterinary disease. HPIV are closely related to recently discovered megamyxoviruses (Hendra and Nipah viruses) and metapneumovirus.

Dendritic cell influx differs between the subglottic and glottic mucosae during acute laryngotracheitis induced by a broad spectrum of stimuli

Clinically, the subglottic and glottic mucosae may react differently, eg, during acute laryngotracheitis. In healthy rats, we showed previously that the composition of the mucosal immune system of the larynx also differs between these areas. Neutrophils, lymphocytes, and dendritic cells (DCs) are part of this mucosal immune system. In particular, DCs occupy a key function. They migrate into inflamed mucosae during the early phase of the immune response, which is normally characterized by an influx of neutrophils. Thus, they help to overcome the time lag between the innate and the adaptive immune responses. In the present study, the influx of DCs, neutrophils, and T lymphocytes into the subglottic and glottic mucosae of rats was examined at different time points after challenge with a broad spectrum of stimuli such as dead Moraxella catarrhalis, viable Bordetella pertussis, viable Sendai virus, and the soluble protein ovalbumin. The number of DCs increased rapidly after the application of the antigens. This increase was as rapid as the increase in neutrophils. Depending on the kind of antigen, their number in the mucosa increased up to 1,000 cells per 0.1 mm2 (Sendai virus). The comparison of different mucosal areas shows that an overwhelming number of immunocompetent cells entered the subglottic mucosa, whereas only a few cells migrated into the adjacent glottic mucosa. In conclusion, after inhalation of different kinds of antigens, the subset of immunocompetent cells investigated in this study entered the laryngeal mucosa in high numbers. The number of DCs entering the laryngeal mucosa was higher than the numbers of the other immune cells investigated. This finding underlines their function as first-line sentinels of the mucosal immune system of the larynx. The observation that the number of cells entering the laryngeal mucosa is location-dependent indicates the ability of adjacent laryngeal regions to react differently. This is similar to the clinical observation of a selective subglottic reaction during acute laryngotracheitis.

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.

Acute laryngotracheitis in the rat induced by Sendai virus: the influx of six different types of immunocompetent cells into the laryngeal mucosa differs strongly between the subglottic and the glottic compartment

OBJECTIVES

Acute laryngotracheitis is a disease in which mainly the subglottic area is infected, whereas adjacent parts of the larynx, especially the narrow glottic fold, remain unaffected. The reason for the difference between these two directly adjacent regions is unknown. Therefore, in the present study the influx of dendritic cells, neutrophils, T and B lymphocytes, natural killer cells, and macrophages into the mucosa of different laryngeal compartments was investigated after Sendai virus infection in the rat. The aims were to study both the influx of immunocompetent cells and the adhesion of the pathogen and to correlate them to the different reactions of the laryngeal areas during pseudocroup.

METHODS

Acute laryngotracheitis was induced by intranasal application of Sendai virus in brown Norway rats. This virus is exclusively pneumotropic in rodents and belongs to the parainfluenza virus type 1, the main pathogen of acute laryngotracheitis in children. The numbers of dendritic cells, neutrophils, T and B lymphocytes, natural killer cells, and macrophages were determined in the supraglottic, glottic, subglottic, and tracheal mucosa on days 2, 5, 7, and 14 after virus application. Furthermore, the nucleoprotein of the virus and major histocompatibility complex (MHC) Class II expression were detected immunohistologically on the laryngeal epithelium.

RESULTS

All cell subsets entered the laryngeal mucosa during inflammation. The highest influx was detected among dendritic cells subglottically. This was accompanied by a strong virus adhesion and MHC Class II expression on the subglottic epithelium. In contrast, only a few immunocompetent cells entered the adjacent glottic mucosa, and on the glottic epithelium staining for virus nucleoprotein and MHC Class II expression was weak.

CONCLUSIONS

The inflammatory response of the laryngeal mucosa shows great regional differences in this animal model during experimental viral infection. The response was characterized by a strong subglottic and a weak glottic reaction. A possible reason for this difference might be region-specific viral adhesion on the epithelium of the laryngeal areas, as well as differences in MHC Class II expression. Thus, these data agree with the clinical observation during acute laryngotracheitis and may explain why the subglottic part of the larynx is affected preferentially during pseudocroup. The molecular mechanisms mediating the different reactions await clarification.

Effect of Staphylococcus enterotoxin B on the concurrent CD8(+) T cell response to influenza virus infection

Bacterial superantigens have potent in vivo effects. Respiratory viral infections are often associated with secondary bacterial infections, raising the likelihood of exposure to bacterial superantigens after the initiation of the anti-viral immune response. In this study, the general and V beta-specific effects of exposure to Staphylococcal enterotoxin B (SEB) during influenza virus infection on both the ongoing acute and the subsequent recall CD8(+) T cell responses were analyzed, using the well-characterized murine influenza model system and tetrameric MHC/peptide reagents to directly identify virus-specific T cells. The results show that although superantigen exposure during the primary viral infection caused delayed viral clearance, there was remarkably little effect of SEB on the magnitude or TCR repertoire of the ongoing cytolytic T cell response or on the recall response elicited by secondary viral infection. Thus, despite the well-characterized immunomodulatory effects of SEB, there was surprisingly little interference with concurrent anti-viral immunity.

CD4+ T cell priming accelerates the clearance of Sendai virus in mice, but has a negative effect on CD8+ T cell memory

Current vaccines designed to promote humoral immunity to respiratory virus infections also induce potent CD4+ T cell memory. However, little is known about the impact of primed CD4+ T cells on the immune response to heterologous viruses that are serologically distinct, but that share CD4+ T cell epitopes. In addition, the protective capacity of primed CD4+ T cells has not been fully evaluated. In the present study, we addressed these two issues using a murine Sendai virus model. Mice were primed with an HN421-436 peptide that represents the dominant CD4+ T cell epitope on the hemagglutinin-neuraminidase (HN) of Sendai virus. This vaccination strategy induced strong CD4+ T cell memory to the peptide, but did not induce Abs specific for the Sendai virus virion. Subsequent Sendai virus infection of primed mice resulted in 1) a substantially accelerated virus-specific CD4+ T cell response in the pneumonic lung; 2) enhanced primary antiviral Ab-forming cell response in the mediastinal lymph nodes; and 3) accelerated viral clearance. Interestingly, the virus-specific CD8+ T cell response in the lung and the development of long-term memory CD8+ T cells in the spleen were significantly reduced. Taken together, our data demonstrate that primed CD4+ T cells, in the absence of pre-existing Ab, can have a significant effect on the subsequent immune responses to a respiratory virus infection.

Quantitation of virus-specific classes of antibodies following immunization of mice with attenuated equine herpesvirus 1 and viral glycoprotein D

The antibody responses of CBA/J mice infected intranasally (i.n.) with either the attenuated KyA strain or the pathogenic RacL11 strain of equine herpesvirus 1 (EHV-1) or immunized with recombinant glycoprotein D (rgD) were investigated using the ELISPOT assay to measure EHV-1-specific antibody-secreting cells (ASC) in the regional lymphoid tissue of the respiratory tract. IgG, IgA, and IgM ASC specific for EHV-1 were detected in the mediastinal lymph nodes (MLN) and lungs 2 weeks after i.n. infection with EHV-1 strain KyA or RacL11, or immunization with heat-killed KyA or rgD. EHV-1-specific ASC were present in the MLN and lungs at 4 and 8 weeks, but declined in frequency by fivefold in the lung at 8 weeks. However, i.n. immunized (2 x 10(6) pfu KyA or 50 microgram rgD/mouse) mice infected at 8 weeks with pathogenic EHV-1 RacL11 resisted challenge and showed eight- and tenfold increases in MLN ASC and lung ASC, respectively, by 3 days after challenge. In contrast to the intranasal route of immunization, intraperitoneal immunization yielded ASC frequencies in the MLN and lungs that were only slightly above those of nonimmunized control mice. These data indicate that immunization with infectious or heat-killed EHV-1 KyA, or rgD, induces significant levels of virus-specific ASC both in the MLN and lungs, a specific memory B-cell response, and long-term protective immunity. The finding that the numbers of ASC induced by the pathogenic strain versus the attenuated strain of EHV-1, which were virtually identical, indicated that the ability to generate a B-cell response is independent of and does not contribute to EHV-1 virulence.

Thymic lymphoproliferative disease after successful correction of CD40 ligand deficiency by gene transfer in mice

Inherited deficiency of the CD40 ligand (X-linked hyper-IgM syndrome) is characterized by failure of immunoglobulin isotype switching and severe defects of cell-mediated immunity. To test the potential for gene transfer therapy to correct this disorder, we transduced murine bone marrow or thymic cells with a retroviral vector containing the cDNA for the murine CD40 ligand (CD40L) and injected them into CD40L-/- mice. Even low-level, constitutive expression of the transgene stimulated humoral and cellular immune functions in these mice. With extended follow-up, however, 12 of 19 treated mice developed T-lymphoproliferative disorders, ranging from polyclonal increases of lymphoblasts to overt monoclonal T-lymphoblastic lymphomas that involved multiple organs. Our findings show that constitutive (rather than tightly regulated), low-level expression of CD40L can produce abnormal proliferative responses in developing T lymphocytes, apparently through aberrant interaction between CD40L+ and TCRalphabeta+CD40+ thymocytes. Current methods of gene therapy may prove inappropriate for disorders involving highly regulated genes in essential positions in proliferative cascades.

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.

Inter- and intra-patient sequence diversity among parainfluenza virus-type 1 nucleoprotein genes

Parainfluenza viruses (PIV) have been categorized into four discrete types (types 1-4), based on antigenic similarities. Here is described an evaluation of nucleoprotein (NP) sequence variability among nine patients infected with the type 1 virus. The examination of short segments of the NP sequence was sufficient to define significant variability both within and between patient samples. These data, in conjunction with previous studies of hemagglutinin-neuraminidase and fusion protein sequences from PIV-infected patient populations suggest a lack of absolute stability among isolates within each virus type. Potentially, antigenic variability exists to the extent that an immune response elicited toward one isolate may not be fully protective against another of the same type. Thus, sequence variability could contribute to natural re-infections with PIV, as well as to previous vaccine failures. Results highlight the importance of analyzing viruses that break through vaccine-induced immunity, in order to measure the influence of virus diversity on PIV vaccine outcome.