The 22,000-kilodalton protein of respiratory syncytial virus is a major target for Kd-restricted cytotoxic T lymphocytes from mice primed by infection

In utero tobacco smoke exposure alters lung inflammation, viral clearance, and CD8+T-cell responses in neonatal mice infected with respiratory syncytial virus

Maternal smoking during pregnancy and exposure of infants to cigarette smoke are strongly associated with adverse health effects in childhood including higher susceptibility to respiratory viral infections. Human respiratory syncytial virus (HRSV) is the most important cause of lower respiratory tract infection among young infants. Exacerbation of respiratory disease, including HRSV bronchiolitis and higher susceptibility to HRSV infection, is well correlated with previous smoke exposure. The mechanisms of recurrence and susceptibility to viral pathogens after passive smoke exposure are multifactorial and include alteration of the structural and immunologic host defenses. In this work, we used a well-established mouse model of in utero smoke exposure to investigate the effect of in utero smoke exposure in HRSV-induced pathogenesis. Sample analysis indicated that in utero exposure led to increased lung inflammation characterized by an increased influx of neutrophils to the airways of the infected mice and a delayed viral clearance. On the other hand, decreased HRSV-specific CD8+T-cell response was observed. These findings indicate that cigarette smoke exposure during pregnancy alters HRSV-induced disease as well as several aspects of the neonatal immune responses.

Vaccination with a Single-Cycle Respiratory Syncytial Virus Is Immunogenic and Protective in Mice

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory tract infection in infants and young children, but no vaccine is currently available. Live-attenuated vaccines represent an attractive immunization approach; however, balancing attenuation while retaining sufficient immunogenicity and efficacy has prevented the successful development of such a vaccine. Recently, a recombinant RSV strain lacking the gene that encodes the matrix (M) protein (RSV M-null) was developed. The M protein is required for virion assembly following infection of a host cell but is not necessary for either genome replication or gene expression. Therefore, infection with RSV M-null produces all viral proteins except M but does not generate infectious virus progeny, resulting in a single-cycle infection. We evaluated RSV M-null as a potential vaccine candidate by determining its pathogenicity, immunogenicity, and protective capacity in BALB/c mice compared with its recombinant wild-type control virus (RSV recWT). RSV M-null-infected mice exhibited significantly reduced lung viral titers, weight loss, and pulmonary dysfunction compared with mice infected with RSV recWT. Despite its attenuation, RSV M-null infection induced robust immune responses of similar magnitude to that elicited by RSV recWT. Additionally, RSV M-null infection generated serum Ab and memory T cell responses that were similar to those induced by RSV recWT. Importantly, RSV M-null immunization provided protection against secondary viral challenge by reducing lung viral titers as efficiently as immunization with RSV recWT. Overall, our results indicate that RSV M-null combines attenuation with high immunogenicity and efficacy and represents a promising novel live-attenuated RSV vaccine candidate.

Recombinant baculovirus-based vaccine expressing M2 protein induces protective CD8+ T-cell immunity against respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is an important cause of acute lower respiratory tract disease in infants, young children, immunocompromised individuals, and the elderly. However, despite ongoing efforts to develop an RSV vaccine, there is still no authorized RSV vaccine for humans. Baculovirus has attracted attention as a vaccine vector because of its ability to induce a high level of humoral and cellular immunity, low cytotoxicity against various antigens, and biological safety for humans. In this study, we constructed a recombinant baculovirus- based vaccine expressing the M2 protein of RSV under the control of cytomegalovirus promoter (Bac_RSVM2) to induce CD8+ T-cell responses which play an important role in viral clearance, and investigated its protective efficacy against RSV infection. Immunization with Bac_RSVM2 via intranasal or intramuscular route effectively elicited the specific CD8+ T-cell responses. Most notably, immunization with Bac_RSVM2 vaccine almost completely protected mice from RSV challenge without vaccine-enhanced immunopathology. In conclusion, these results suggest that Bac_RSVM2 vaccine employing the baculovirus delivery platform has promising potential to be developed as a safe and novel RSV vaccine that provides protection against RSV infection.

Novel HLA-A2-restricted human metapneumovirus epitopes reduce viral titers in mice and are recognized by human T cells

Human metapneumovirus (HMPV) is a major cause of morbidity and mortality from acute lower respiratory tract illness, with most individuals seropositive by age five. Despite the presence of neutralizing antibodies, secondary infections are common and can be severe in young, elderly, and immunocompromised persons. Preclinical vaccine studies for HMPV have suggested a need for a balanced antibody and T cell immune response to enhance protection and avoid lung immunopathology. We infected transgenic mice expressing human HLA-A*0201 with HMPV and used ELISPOT to screen overlapping and predicted epitope peptides. We identified six novel HLA-A2 restricted CD8(+) T cell (TCD8) epitopes, with M39-47 (M39) immunodominant. Tetramer staining detected M39-specific TCD8 in lungs and spleen of HMPV-immune mice. Immunization with adjuvant-formulated M39 peptide reduced lung virus titers upon challenge. Finally, we show that TCD8 from HLA-A*0201 positive humans recognize M39 by IFNγ ELISPOT and tetramer staining. These results will facilitate HMPV vaccine development and human studies.

Recent advances in the development of subunit-based RSV vaccines

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections causing pneumonia and bronchiolitis in infants. RSV also causes serious illness in elderly populations, immunocompromised patients and individuals with pulmonary or cardiac problems. The significant morbidity and mortality associated with RSV infection have prompted interest in RSV vaccine development. In the 1960s, a formalin-inactivated vaccine trial failed to protect children, and indeed enhanced pathology when naturally infected later with RSV. Hence, an alternative approach to traditional killed virus vaccines, which can induce protective immunity without serious adverse events, is desired. Several strategies have been explored in attempts to produce effective vaccine candidates including gene-based and subunit vaccines. Subunit-based vaccine approaches have shown promising efficacy in animal studies and several have reached clinical trials. The current stage of development of subunit-based vaccines against RSV is reviewed in this article.

Animal models of respiratory syncytial virus infection and disease

The study of human respiratory syncytial virus pathogenesis and immunity has been hampered by its exquisite host specificity, and the difficulties encountered in adapting this virus to a murine host. The reasons for this obstacle are not well understood, but appear to reflect, at least in part, the inability of the virus to block the interferon response in any but the human host. This review addresses some of the issues encountered in mouse models of respiratory syncytial virus infection, and describes the advantages and disadvantages of alternative model systems.

The CD4 T cell response to respiratory syncytial virus infection

Respiratory syncytial virus (RSV) can induce severe lower respiratory tract infections in infants and is the leading cause of bronchiolitis in children worldwide. RSV-induced inflammation is believed to contribute substantially to the severity of disease. T helper (Th)2-, Th9-, and Th17-related cytokines are all observed in infants hospitalized following a severe RSV infection. These cytokines cause an influx of inflammatory cells, resulting in mucus production and reduced lung function. Consistent with the data from RSV-infected infants, CD4 T cell production of Interleukin (IL)-9, IL-13, and IL-17 has all been shown to contribute to RSV-induced disease in a murine model of RSV infection. Conversely, murine studies indicate that the combined actions of regulatory factors such as CD4 regulatory T cells and IL-10 inhibit the inflammatory cytokine response and limit RSV-induced disease. In support of this, IL-10 polymorphisms are associated with susceptibility to severe disease in infants. Insufficient regulation and excess inflammation not only impact disease following primary RSV infection it can also have a major impact following vaccination. Prior immunization with a formalin-inactivated (FI-RSV) vaccine resulted in enhanced disease in infants following a natural RSV infection. A Th2 CD4 T cell response has been implicated to be a major contributor in mediating vaccine-enhanced disease. Thus, future RSV vaccines must induce a balanced CD4 T cell response in order to facilitate viral clearance while inducing proper regulation of the immune response.

Advances in and the potential of vaccines for respiratory syncytial virus

Respiratory syncytial virus (RSV) is the leading cause of serious lower respiratory track illness causing bronchiolitis and some mortality in infants and the elderly. Despite decades of research there is no licensed RSV vaccine. To enable the development of RSV vaccines, several major obstacles must be overcome including immature and waning immunity to RSV infection, the capacity of RSV to evade immunity and the failure of RSV infection to induce robust enduring immunity. Since the failure of the formalin-inactivated RSV vaccine trial, more cautious and deliberate progress has been made toward RSV vaccine development using a variety of experimental approaches. The scientific rational and the state of development of these approaches are reviewed in this article.

Determining the breadth of the respiratory syncytial virus-specific T cell response

Respiratory syncytial virus (RSV) is the most common cause of viral lower respiratory tract infections in infants and children under the age of 5. Studies examining RSV infection in susceptible BALB/c mice indicate that both CD4 and CD8 T cells not only contribute to viral clearance but also facilitate RSV-induced disease. However, efforts to understand the mechanisms by which RSV-specific T cells mediate disease following acute RSV infection have been hampered by the lack of defined RSV-specific T cell epitopes. Using an overlapping peptide library spanning each of the RSV-derived proteins, intracellular cytokine staining for gamma interferon was utilized to identify novel RSV-specific CD4 and CD8 T cell epitopes. Five novel CD8 T cell epitopes were revealed within the RSV fusion (F) protein and glycoprotein (G). In addition, five previously unidentified CD4 T cell epitopes were discovered, including epitopes in the phosphoprotein (P), polymerase protein (L), M2-1 protein, and nucleoprotein (N). Though the initial CD4 T cell epitopes were 15 amino acids in length, synthesis of longer peptides increased the frequency of responding CD4 T cells. Our results indicate that CD4 T cell epitopes that are 17 amino acids in length result in more optimal CD4 T cell stimulation than the commonly used 15-mer peptides.

IMPORTANCE

Respiratory syncytial virus (RSV) is the leading cause of hospitalization for lower respiratory tract infection in children. T cells play a critical role in clearing an acute RSV infection, as well as contributing to RSV-induced disease. Here we examined the breadth of the RSV-specific T cell response, using for the first time an overlapping peptide library spanning the entire viral genome. We identified 5 new CD4 and 5 new CD8 T cell epitopes, including a CD8 T cell epitope within the G protein that was previously believed not to elicit a CD8 T cell response. Importantly, we also demonstrated that the use of longer, 17-mer peptides elicits a higher frequency of responding CD4 T cells than the more commonly used 15-mer peptides. Our results demonstrate the breadth of the CD4 and CD8 T cell response to RSV and demonstrate the importance of using longer peptides when stimulating CD4 T cell responses.

Neonatal calf infection with respiratory syncytial virus: drawing parallels to the disease in human infants

Respiratory syncytial virus (RSV) is the most common viral cause of childhood acute lower respiratory tract infections. It is estimated that RSV infections result in more than 100,000 deaths annually worldwide. Bovine RSV is a cause of enzootic pneumonia in young dairy calves and summer pneumonia in nursing beef calves. Furthermore, bovine RSV plays a significant role in bovine respiratory disease complex, the most prevalent cause of morbidity and mortality among feedlot cattle. Infection of calves with bovine RSV shares features in common with RSV infection in children, such as an age-dependent susceptibility. In addition, comparable microscopic lesions consisting of bronchiolar neutrophilic infiltrates, epithelial cell necrosis, and syncytial cell formation are observed. Further, our studies have shown an upregulation of pro-inflammatory mediators in RSV-infected calves, including IL-12p40 and CXCL8 (IL-8). This finding is consistent with increased levels of IL-8 observed in children with RSV bronchiolitis. Since rodents lack IL-8, neonatal calves can be useful for studies of IL-8 regulation in response to RSV infection. We have recently found that vitamin D in milk replacer diets can be manipulated to produce calves differing in circulating 25-hydroxyvitamin D3. The results to date indicate that although the vitamin D intracrine pathway is activated during RSV infection, pro-inflammatory mediators frequently inhibited by the vitamin D intacrine pathway in vitro are, in fact, upregulated or unaffected in lungs of infected calves. This review will summarize available data that provide parallels between bovine RSV infection in neonatal calves and human RSV in infants.

Immunoprotectivity of HLA-A2 CTL peptides derived from respiratory syncytial virus fusion protein in HLA-A2 transgenic mouse

Identification of HLA-restricted CD8⁺ T cell epitopes is important to study RSV-induced immunity and illness. We algorithmically analyzed the sequence of the fusion protein (F) of respiratory syncytial virus (RSV) and generated synthetic peptides that can potentially bind to HLA-A*0201. Four out of the twenty-five 9-mer peptides tested: peptides 3 (F33–41), 13 (F214–222), 14 (F273–281), and 23 (F559–567), were found to bind to HLA-A*0201 with moderate to high affinity and were capable of inducing IFN-γ and IL-2 secretion in lymphocytes from HLA-A*0201 transgenic (HLA-Tg) mice pre-immunized with RSV or recombinant adenovirus expressing RSV F. HLA-Tg mice were immunized with these four peptides and were found to induce both Th1 and CD8⁺ T cell responses in in vitro secondary recall. Effector responses induced by these peptides were observed to confer differential protection against live RSV challenge. These peptides also caused better recovery of body weight loss induced by RSV. A significant reduction of lung viral load was observed in mice immunized with peptide 23, which appeared to enhance the levels of inflammatory chemokines (CCL17, CCL22, and IL-18) but did not increase eosinophil infiltration in the lungs. Whereas, significant reduction of infiltrated eosinophils induced by RSV infection was found in mice pre-immunized with peptide 13. Our results suggest that HLA-A2-restricted epitopes of RSV F protein could be useful for the development of epitope-based RSV vaccine.

Major histocompatibility complex-dependent cytotoxic T lymphocyte repertoire and functional avidity contribute to strain-specific disease susceptibility after murine respiratory syncytial virus infection

Susceptibility to respiratory syncytial virus (RSV) infection in mice is genetically determined. While RSV causes little pathology in C57BL/6 mice, pulmonary inflammation and weight loss occur in BALB/c mice. Using major histocompatibility complex (MHC)-congenic mice, we observed that the H-2(d) allele can partially transfer disease susceptibility to C57BL/6 mice. This was not explained by altered viral elimination or differences in the magnitude of the overall virus-specific cytotoxic T lymphocyte (CTL) response. However, H-2(d) mice showed a more focused response, with 70% of virus-specific CTL representing Vβ8.2(+) CTL directed against the immunodominant epitope M2-1 82, while in H-2(b) mice only 20% of antiviral CTL were Vβ9(+) CTL specific for the immunodominant epitope M187. The immunodominant H-2(d)-restricted CTL lysed target cells less efficiently than the immunodominant H-2(b) CTL, probably contributing to prolonged CTL stimulation and cytokine-mediated immunopathology. Accordingly, reduction of dominance of the M2-1 82-specific CTL population by introduction of an M187 response in the F1 generation of a C57BL/6N × C57BL/6-H-2(d) mating (C57BL/6-H-2(dxb) mice) attenuated disease. Moreover, disease in H-2(d) mice was less pronounced after infection with an RSV mutant failing to activate M2-1 82-specific CTL or after depletion of Vβ8.2(+) cells. These data illustrate how the MHC-determined diversity and functional avidity of CTL responses contribute to disease susceptibility after viral infection.

Conserved cysteine residues within the attachment G glycoprotein of respiratory syncytial virus play a critical role in the enhancement of cytotoxic T-lymphocyte responses

The cytotoxic T-lymphocyte (CTL) response plays an important role in the control of respiratory syncytial virus (RSV) replication and the establishment of a Th1-CD4+ T cell response against the virus. Despite lacking Major Histocompatibility Complex I (MHC I)-restricted epitopes, the attachment G glycoprotein of RSV enhances CTL activity toward other RSV antigens, and this effect depends on its conserved central region. Here, we report that RSV-G can also improve CTL activity toward antigens from unrelated pathogens such as influenza, and that a mutant form of RSV-G lacking four conserved cysteine residues at positions 173, 176, 182, and 186 fails to enhance CTL responses. Our results indicate that these conserved residues are essential for the wide-spectrum pro-CTL activity displayed by the protein.

Genetic susceptibility to the delayed sequelae of neonatal respiratory syncytial virus infection is MHC dependent

Respiratory syncytial virus (RSV) is a major cause of respiratory morbidity, resulting in hospitalization for bronchiolitis in some infected infants that is associated with wheeze in later life. Genetic factors are known to affect the severity of the sequelae after RSV infection, but the complexity of the temporal and genetic effects makes it difficult to analyze this response in studies in man. Therefore, we developed a murine genetic model to analyze the sequelae occurring after RSV infection in early life. Haplotype-based genetic analysis of interstrain differences in severity identified the MHC as an important genetic determinant. This was confirmed by analysis of responses in congenic mice with different MHC haplotypes. We also found that susceptible strains had high CD8 levels during secondary infection. Analysis of first filial generation, second filial generation, and back-cross progeny produced by intercrossing resistant (H-2(k), C3H/HeN) and sensitive (H-2(b), BALB/c) strains indicated that susceptibility to sequelae after RSV infection was dominantly inherited but also segregated in a non-MHC-dependent manner. Thus, MHC haplotype and its effect on CD8 cell response is an important determinant of the outcome of neonatal RSV infection.

Prospects for defined epitope vaccines for respiratory syncytial virus

The history of vaccines for respiratory syncytial virus (RSV) illustrates the complex immunity and immunopathology to this ubiquitous virus, starting from the failed formalin-inactivated vaccine trials performed in the 1960s. An attractive alternative to traditional live or killed virus vaccines is a defined vaccine composed of discrete antigenic epitopes for which immunological activities have been characterized as comprehensively as possible. Here we present cumulative data on murine and human CD4, CD8 and neutralization epitopes identified in RSV proteins along with information regarding their associated immune responses and host-dependent variability. Identification and characterization of RSV epitopes is a rapidly expanding topic of research with potential contributions to the tailored design of improved safe and effective vaccines.

Pulmonary infection of mice with human metapneumovirus induces local cytotoxic T-cell and immunoregulatory cytokine responses similar to those seen with human respiratory syncytial virus

Human metapneumovirus (hMPV) is a major cause of upper and lower respiratory-tract infection in infants, the elderly and immunocompromised individuals. Virus-directed cellular immunity elicited by hMPV infection is poorly understood, in contrast to the phylogenetically and clinically related pathogen human respiratory syncytial virus (hRSV). In a murine model of acute lower respiratory-tract infection with hMPV, we demonstrate the accumulation of gamma interferon (IFN-gamma)-producing CD8+ T cells in the airways and lungs at day 7 post-infection (p.i.), associated with cytotoxic T lymphocytes (CTLs) directed to an epitope of the M2-1 protein. This CTL immunity was accompanied by increased pulmonary expression of Th1 cytokines IFN-gamma and interleukin (IL)-12 and antiviral cytokines (IFN-beta), as well as chemokines Mip-1alpha, Mip-1beta, Mig, IP-10 and CX3CL1. There was also a moderate increase in Th2-type cytokines IL-4 and IL-10 compared with uninfected mice. At 21 days p.i., a strong CTL response could be recalled from the spleen. A similar pattern of CTL induction to the homologous M2-1 CTL epitope of hRSV, and of cytokine/chemokine induction, was observed following infection with hRSV, highlighting similarities in the cellular immune response to the two related pathogens.

The host response and molecular pathogenesis associated with respiratory syncytial virus infection

Since the isolation of respiratory syncytial virus (RSV) in 1956, its significance as an important human pathogen in infants, the elderly and the immunocompromised has been established. Many important mechanisms contributing to RSV infection, replication and disease pathogenesis have been uncovered; however, there is still insufficient knowledge in these and related areas, which must be addressed to facilitate the development of safe and effective vaccines and therapeutic treatments. A better understanding of the molecular pathogenesis of RSV infection, particularly the host-cell response and transcription profiles to RSV infection, is required to advance disease intervention strategies. Substantial information is accumulating regarding how RSV proteins modulate molecular signaling and regulation of cytokine and chemokine responses to infection, molecular signals regulating programmed cell death, and innate and adaptive immune responses to infection. This review discusses RSV manipulation of the host response to infection and related disease pathogenesis.

Regulation of immunity to respiratory syncytial virus by dendritic cells, toll-like receptors, and notch

The activation and maintenance of pulmonary viral disease is regulated at multiple levels and determined by the early innate response to the pathogenic stimuli. Subsequent activation events that rely directly and indirectly on the virus itself can alter the development and severity of the ensuing immunopathologic responses. In the present review we outline several interconnected mechanisms that rely on the early recognition of viral nucleic acid for the most appropriate anti-viral immune responses, including TLRs and Notch activation in DCs and T cells. Deviation or persistence of the immune response to respiratory viruses may impact significantly on the severity of the responses. While these mechanisms are likely similar in most respiratory viral infections, this review will focus on findings with respiratory syncytial virus (RSV) infections.

Enhancement of the CD8+ T cell response to a subdominant epitope of respiratory syncytial virus by deletion of an immunodominant epitope

Cytotoxic T lymphocytes (CTLs) are critical for the control of respiratory syncytial virus infection (RSV) in humans and mice. Recently, we identified a new H-2K(d)-restricted subdominant epitope in the respiratory syncytial virus M2 protein. In this study, we investigated if modification of anchor residues at positions 2 and 9 in the dominant M2(82-90) epitope in the M2 protein would alter the CTL epitope dominance hierarchy following immunization with plasmid DNA encoding M2 proteins. We showed that immunogenicity of the subdominant epitope M2(127-135) was enhanced when the anchor residues of the dominant epitope were mutated, suggesting that the immunodominant epitope induces a suppression of response to the subdominant epitope.

Overcoming T cell-mediated immunopathology to achieve safe RSV vaccination

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in young children. Premature infants, immunocompromised individuals, and the elderly exhibit an increased risk for the development of severe disease after RSV infection. Currently, there is not a safe and effective RSV vaccine available, in part due to our incomplete understanding of how severe immunopathology was induced following RSV infection of children previously immunized with a formalin-inactivated RSV vaccine. Much of our current understanding of RSV vaccine-enhanced disease can be attributed to the establishment of multiple mouse models of RSV vaccination. Studies analyzing the RSV-specific immune response in mice have clearly demonstrated that both CD4 and CD8 memory T cells contribute to RSV-induced immunopathology. In this review we will focus our discussion on data generated from the mouse models of RSV immunization that have advanced our understanding of how virus-specific T cells mediate immunopathology and RSV vaccine-enhanced disease.

Human and bovine respiratory syncytial virus vaccine research and development

Human (HRSV) and bovine (BRSV) respiratory syncytial viruses (RSV) are two closely related viruses, which are the most important causative agents of respiratory tract infections of young children and calves, respectively. BRSV vaccines have been available for nearly 2 decades. They probably have reduced the prevalence of RSV infection but their efficacy needs improvement. In contrast, despite decades of research, there is no currently licensed vaccine for the prevention of HRSV disease. Development of a HRSV vaccine for infants has been hindered by the lack of a relevant animal model that develops disease, the need to immunize immunologically immature young infants, the difficulty for live vaccines to find the right balance between attenuation and immunogenicity, and the risk of vaccine-associated disease. During the past 15 years, intensive research into a HRSV vaccine has yielded vaccine candidates, which have been evaluated in animal models and, for some of them, in clinical trials in humans. Recent formulations have focused on subunit vaccines with specific CD4+ Th-1 immune response-activating adjuvants and on genetically engineered live attenuated vaccines. It is likely that different HRSV vaccines and/or combinations of vaccines used sequentially will be needed for the various populations at risk. This review discusses the recent advances in RSV vaccine development.

Mapping and characterization of the primary and anamnestic H-2(d)-restricted cytotoxic T-lymphocyte response in mice against human metapneumovirus

Cytotoxic T lymphocytes (CTLs) are important for the control of virus replication during respiratory infections. For human metapneumovirus (hMPV), an H-2(d)-restricted CTL epitope in the M2-2 protein has been described. In this study, we screened the hMPV F, G, N, M, M2-1, and M2-2 proteins using three independent algorithms to predict H-2(d) CTL epitopes in BALB/c mice. A dominant epitope (GYIDDNQSI) in positions 81 to 89 of the antitermination factor M2-1 and a subdominant epitope (SPKAGLLSL) in N(307-315) were detected during the anti-hMPV CTL response. Passive transfer of CD8(+) T-cell lines against M2-1(81-89) and N(307-315) protected Rag1(-/-) mice against hMPV challenge. Interestingly, diversification of CTL targets to include multiple epitopes was observed after repetitive infections. A subdominant response against the previously described M2-2 epitope was detected after the third infection. An understanding of the CTL response against hMPV is important for developing preventive and therapeutic strategies against the virus.

The stability of human respiratory syncytial virus is enhanced by incorporation of the baculovirus GP64 protein

Current efforts to develop a vaccine against human respiratory syncytial virus (HRSV) are focused on live attenuated strains. However, the unstable nature of HRSV is a major challenge for the preparation, storage and distribution of live vaccine candidates. We report here that the stability of HRSV can be improved by incorporation of the GP64 glycoprotein from baculovirus Autographa californica multiple nucleopolyhedrovirus. GP64 was incorporated in place of or in addition to the homologous HRSV glycoproteins and was either expressed from the HRSV genome or provided by propagating the virus in a Vero cell line constitutively expressing GP64 (Vbac cells). The infectivity of the different virus stocks was monitored after storage at 4 degrees, 22 degrees or 37 degrees C, over a period of 8 weeks. The results showed that the infectivity of HRSV could be stabilized by up to 10,000-fold by the GP64 protein, when stored at 22 degrees C for 6 weeks. This approach for stabilizing live HRSV may be important for vaccine development and may also prove useful for stabilizing other enveloped viruses.

Tissue-specific regulation of CD8+ T-lymphocyte immunodominance in respiratory syncytial virus infection

Cytotoxic T lymphocytes (CTLs) are critical for control of respiratory syncytial virus (RSV) infection in humans and mice. To investigate cellular immune responses to infection, it is important to identify major histocompatibility complex (MHC) class I-restricted CTL epitopes. In this study, we identified a new RSV-specific, H-2K(d)-restricted subdominant epitope in the M2 protein, M2(127-135) (amino acids 127 to 135). This finding allowed us to study the frequency of T lymphocytes responding to two H-2K(d)-presented epitopes in the same protein following RSV infection by enzyme-linked immunospot (ELISPOT) and intracellular cytokine assays for both lymphoid and nonlymphoid tissues. For the subdominant epitope, we identified an optimal nine-amino-acid peptide, VYNTVISYI, which contained an H-2K(d) consensus sequence with Y at position 2 and I at position 9. In addition, an MHC class I stabilization assay using TAP-2-deficient RMA-S cells transfected with K(d) or L(d) indicated that the epitope was presented by K(d). The ratios of T lymphocytes during the peak CTL response to RSV infection that were specific for M2(82-90) (dominant) to T lymphocytes specific for M2(127-135) (subdominant) were approximately 3:1 in the spleen and 10:1 in the lung. These ratios were observed consistently in primary or secondary infection by the ELISPOT assay and in secondary infection by MHC/peptide tetramer staining. The number of antigen-specific T lymphocytes dropped in the 6 weeks after infection; however, the proportions of T lymphocytes specific for the immunodominant and subdominant epitopes were maintained to a remarkable degree in a tissue-specific manner. These studies will facilitate investigation of the regulation of immunodominance of RSV-specific CTL epitopes.

Differential immune responses and pulmonary pathophysiology are induced by two different strains of respiratory syncytial virus

In this study we performed comparisons of pulmonary responses between two different respiratory syncytial virus (RSV) antigenic subgroup A strains, A2 and Line 19. Line 19 strain induced significant dose-responsive airway hyperreactivity (AHR) in BALB/c mice at days 6 and 9 after infection, whereas the A2 strain induced no AHR at any dose. Histological examination indicated that A2 induced no goblet cell hyper/metaplasia, whereas the Line 19 induced goblet cell expansion and significant increases in gob5 and MUC5AC mRNA and protein levels in vivo. When examining cytokine responses, A2 strain induced significant interleukin (IL)-10 expression, whereas Line 19 strain induced significant IL-13 expression. When IL-13-/- mice were infected with Line 19 RSV, the AHR responses were abrogated along with gob5 gene expression. There was little difference in viral titer throughout the infection between the line 19- and A2-infected mice. However, the A2 strain grew to significantly higher titers than the Line 19 strain in HEp-2 cells in vitro. Thus, RSV Line 19-induced airway dysfunction does not correlate with viral load in vivo. These data demonstrate that different RSV strains of the same antigenic subgroup can elicit differential immune responses that impact the phenotypic expression of RSV-induced illness.

The cysteine-rich region and secreted form of the attachment G glycoprotein of respiratory syncytial virus enhance the cytotoxic T-lymphocyte response despite lacking major histocompatibility complex class I-restricted epitopes

The cytotoxic T-lymphocyte (CTL) response is important for the control of viral replication during respiratory syncytial virus (RSV) infection. The attachment glycoprotein (G) of RSV does not encode major histocompatibility complex class I-restricted epitopes in BALB/c mice (H-2(d)). Furthermore, studies to date have described an absence of significant CTL activity directed against this protein in humans. Therefore, G previously was not considered necessary for the generation of RSV-specific CTL responses. In this study, we demonstrate that, despite lacking H-2(d)-restricted epitopes, G enhances the generation of an effective CTL response against RSV. Furthermore, we show that this stimulatory effect is independent of virus titers and RSV-induced inflammation; that it is associated primarily with the secreted form of G; and that the effect depends on the cysteine-rich region of G (GCRR), a segment conserved in wild-type isolates worldwide. These findings reveal a novel function for the GCRR with potential implications for the generation of protective cellular responses and vaccine development.

Respiratory Syncytial Virus G Protein and G Protein CX3C Motif Adversely Affect CX3CR1+T Cell Responses

Interactions between fractalkine (CX3CL1) and its receptor, CX3CR1, mediate leukocyte adhesion, activation, and trafficking. The respiratory syncytial virus (RSV) G protein has a CX3C chemokine motif that can bind CX3CR1 and modify CXCL1-mediated responses. In this study, we show that expression of the RSV G protein or the G protein CX3C motif during infection is associated with reduced CX3CR1+ T cell trafficking to the lung, reduced frequencies of RSV-specific, MHC class I-restricted IFN-gamma-expressing cells, and lower numbers of IL-4- and CX3CL1-expressing cells. In addition, we show that CX3CR1+ cells constitute a major component of the cytotoxic response to RSV infection. These results suggest that G protein and the G protein CX3C motif reduce the antiviral T cell response to RSV infection.

Identification of an H-2D(b)-restricted CD8+ cytotoxic T lymphocyte epitope in the matrix protein of respiratory syncytial virus

Cytotoxic T lymphocytes (CTL) play a significant role in the clearance of respiratory syncytial virus (RSV) infection in humans and mice. Identification of class I MHC-restricted CTL epitopes is critical in elucidating mechanisms of CTL responses against viral infections. However, only four H-2d-restricted epitopes have been reported in mice. Because of the diversity of transgenic and knockout mice available to study immune responses, new epitopes in additional strains of mice must be identified. We therefore attempted to discover novel CTL epitopes in C57Bl/6 mice. Our efforts revealed a new H-2D(b)-restricted CTL epitope from the RSV M protein, corresponding to aa 187-195 (NAITNAKII). Also, M187-195-specific CTLs were activated with kinetics similar to the immunodominant BALB/c epitope, M2 82-90. This is the first RSV-specific CTL epitope described in a strain of mice other than BALB/c. Furthermore, identification of this H-2b-restricted CTL epitope provides access to genetically modified H-2b mice for more detailed studies of CTL mechanisms in RSV infection.

Induction of balanced immunity in BALB/c mice by vaccination with a recombinant fusion protein containing a respiratory syncytial virus G protein fragment and a CTL epitope

Respiratory syncytial virus (RSV), an important pathogen of the lower respiratory tract, is responsible for severe illness both in new born and young children and in elderly people. However, development of a RSV vaccine has been hampered by the outcome of the infant trials in the 1960s with a formalin-inactivated RSV (FI-RSV) preparation. Previous studies in mice indicated that G protein immunization resulted in antibody and Th2-type response and failed to induce MHC I-restricted CD8(+) T-cell response. Vaccines designed to induce CD8(+) T-cell along with antibody response might be ideal. In the present report, a fusion protein G1F/M2 containing a RSV-G protein fragment (G: 125-225 amino acid) and a CD8(+) T-cell epitope from RSV-M2 protein was investigated. G1F/M2 was cloned, expressed in E. coli, purified and renaturated. In BALB/c mice, G1F/M2 induced not only humoral immunity but also cellular immunity. In addition, interestedly, G1F/M2 elicited balanced IgG1/IgG2a response. These results suggest that the fusion protein G1F/M2 is potential as a RSV subunit vaccine.

Immune responses and disease enhancement during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.

Altered function in CD8+ T cells following paramyxovirus infection of the respiratory tract

For many respiratory pathogens, CD8+ T cells have been shown to play a critical role in clearance. However, there are still many unanswered questions with regard to the factors that promote the most efficacious immune response and the potential for immunoregulation of effector cells at the local site of infection. We have used infection of the respiratory tract with the model paramyxovirus simian virus 5 (SV5) to study CD8+ T-cell responses in the lung. For the present study, we report that over time a population of nonresponsive, virus-specific CD8+ T cells emerged in the lung, culminating in a lack of function in approximately 85% of cells specific for the immunodominant epitope from the viral matrix (M) protein by day 40 postinfection. Concurrent with the induction of nonresponsiveness, virus-specific cells that retained function at later times postinfection exhibited an increased requirement for CD8 engagement. This change was coupled with a nearly complete loss of functional phosphoprotein-specific cells, a response previously shown to be almost exclusively CD8 independent. These studies add to the growing evidence for immune dysregulation following viral infection of the respiratory tract.

Respiratory syncytial virus-induced immunoprotection and immunopathology

Respiratory syncytial virus (RSV), a member of the Paramyxoviridae family, is a major clinical problem causing yearly epidemics of severe lower airway disease in both infants and the elderly. Attempts at vaccination have been frustrated by both the poor immunogenicity of this virus, and the severe immunopathology observed in early vaccine trials. Primary infection generally occurs in infancy, with approximately 5% of infected infants requiring hospitalization. Equally problematic is the apparent link between severe RSV disease and the later development of allergy and asthma. While there is no evidence that natural infection promotes Th2 predominance, development of enhanced eosinophilic disease in children receiving inactivated virus administered with a commonly used adjuvant demonstrated how easily the balance between immune-mediated protection and immune-mediated pathology can be perturbed. In this review we have focused on studies carried out in the mouse model aimed at determining the correlates of RSV protection and explaining the mechanism of vaccine enhanced immunopathology.

Gene-gun DNA vaccination aggravates respiratory syncytial virus-induced pneumonitis

A CD8+ T-cell memory response to respiratory syncytial virus (RSV) was generated by using a DNA vaccine construct encoding the dominant Kd-restricted epitope from the viral transcription anti-terminator protein M2 (M282–90), linked covalently to human β 2-microglobulin (β 2m). Cutaneous gene-gun immunization of BALB/c mice with this construct induced an antigen-specific CD8+ T-cell memory. After intranasal RSV challenge, accelerated CD8+ T-cell responses were observed in pulmonary lymph nodes and virus clearance from the lungs was enhanced. The construct induced weaker CD8+ T-cell responses than those elicited with recombinant vaccinia virus expressing the complete RSV M2 protein, but stronger than those induced by a similar DNA construct without the β 2m gene. DNA vaccination led to enhanced pulmonary disease after RSV challenge, with increased weight loss and cell recruitment to the lung. Depletion of CD8+ T cells reduced, but did not abolish, enhancement of disease. Mice vaccinated with a construct encoding a class I-restricted lymphocytic choriomeningitis virus epitope and β 2m suffered more severe weight loss after RSV infection than unvaccinated RSV-infected mice, although RSV-specific CD8+ T-cell responses were not induced. Thus, in addition to specific CD8+ T cell-mediated immunopathology, gene-gun DNA vaccination causes non-specific enhancement of RSV disease without affecting virus clearance.

Pathogenesis of Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is recognized as the most important cause of serious lower respiratory tract illness in infants and young children worldwide causing repeat infections throughout life with serious complications occurring in the elderly and immune compromised patient. The level of disease pathogenesis associated with RSV infection is balanced between virus elimination and the nature of the immune response to infection. The innate and adaptive immune responses to RSV infection are not fully elucidated; however, significant progress has been made in understanding the virus-host relationship and mechanisms associated with disease pathogenesis. This review summarizes important aspects of these findings, and provides current perspective on processes that may contribute to RSV disease pathogenesis.

Latency and persistence of respiratory syncytial virus despite T cell immunity

Respiratory syncytial virus (RSV) causes bronchiolitis in infants, which is associated with recurrent wheezing in later childhood. There is mounting evidence that the virus becomes latent or persists in vivo, but little is known about the mechanisms of its latency, persistence, and immune evasion. We therefore infected BALB/c mice intranasally with human RSV, analyzed sequential tissue samples by direct culture and polymerase chain reaction for viral and messenger RNA, and monitored antiviral immune responses. Virus could not be detected in bronchoalveolar lavage samples beyond Day 14, but viral genomic and messenger RNA was present in lung homogenates for 100 days or more; combined depletion of CD4 and CD8 T cells allowed infective virus to be recovered. Neutralizing antibody and memory cytotoxic T cell responses were intact in mice with latent infections, and latent viral genome contained an authentic nonmutated M2 82-91 K(d) cytotoxic T lymphocyte epitope. A mutation of this epitope, detected in one clone, did not assist evasion. We suggest that RSV latency depends on persistence in privileged sites rather than on viral mutation.

CD8 T cell responses to infectious pathogens

CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.

Respiratory syncytial virus nucleoprotein-specific cytotoxic T-cell epitopes in a South African population of diverse HLA types are conserved in circulating field strains

This study identifies memory cytotoxic T lymphocyte (CTL) epitopes to respiratory syncytial virus (RSV) in healthy South African adults and demonstrates the conservation of those epitopes in circulating field strains of RSV in South Africa. Thirty-seven healthy adults from a population with diverse HLA backgrounds were screened by gamma interferon (IFN-gamma) enzyme-linked immunospot for memory CTL activity in response to overlapping peptides representing the complete nucleoprotein (N) of RSV. Responses of more than 40 spot-forming cells/million cells were detectable in 21 individuals. The significant responses were further characterized, and 14-mer peptides were identified that induced cytolytic activity. Fine mapping of peptides with the highest cytolytic activity identified an HLA-B(*)08-restricted RSV-specific CTL epitope. The extended 14-mer peptide containing this epitope also induced lysis in the context of A(*)02-restricted target cells in some individuals. These HLA types are common in the target population; thus, the epitope is useful for studies of CTL responses to RSV in humans. The epitope was detected in healthy adults, reflecting the response generated in the course of previous natural RSV infection. We obtained a large panel of naturally occurring isolates of RSV to determine whether there was evidence of escape from CTL activity in circulating strains. We found that this epitope and a previously identified B(*)07-restricted N protein epitope were conserved in RSV field strains representing the diversity of circulating genotypes. This work suggests that escape from CTL activity is not common for this acute respiratory infection.

Recognition of bovine respiratory syncytial virus proteins by bovine CD8+ T lymphocytes

CD8+ T lymphocytes play a major role in the clearance of bovine respiratory syncytial virus (BRSV), an important respiratory pathogen of young calves that shares many of the epidemiological and pathological features of human respiratory syncytial virus (HRSV) in infants. Recombinant vaccinia virus (rVV) and recombinant fowlpox virus (rFPV), expressing individual BRSV proteins, were used to demonstrate that the F, N and M2 proteins were the major antigens recognized by bovine CD8+ T cells in major histocompatibility complex (MHC)-defined cattle. BRSV protein recognition by CD8+ T cells was analysed using cytotoxic T lymphocyte (CTL) assays or by the production of interferon-gamma (IFN-gamma) following restimulation with BRSV proteins. Strong recognition of the G protein by CD8+ T cells was observed in cattle that had been vaccinated with rVV expressing this protein and subsequently challenged with BRSV. Although there is variation in the number of expressed MHC genes in cattle with different class I haplotypes, this did not appear to influence BRSV protein recognition by CD8+ T cells. Knowledge of the antigenic specificity of BRSV-specific CD8+ T cells will facilitate the qualitative and quantitative analysis of BRSV-specific CD8+ T-cell memory in cattle and help to ensure that potential vaccines induce a qualitatively appropriate CD8+ T-cell response.

Enhanced immune protection by a liposome-encapsulated recombinant respiratory syncytial virus (RSV) vaccine using immunogenic lipids from Deinococcus radiodurans

The radiation-resistant bacterium, Deinococcus radiodurans contains a variety of phospho-, glyco- and phosphoglycolipids, the structures of which appear to be largely unique in nature. We show here that such lipids are immunogenic when administered as liposomes intranasally in mice, as evidenced by the induction of serum antibodies which recognize D. radiodurans lipids but not other lipids by thin layer chromatographic immunostaining. By modifying a liposomal vaccine against respiratory syncytial virus (RSV) we find that vaccine efficacy is markedly enhanced by the inclusion of lipids isolated from D. radiodurans. Using dioleoylphosphatidylcholine (DOPC) or D. radiodurans lipids, liposomes were prepared which encapsulated a soluble fragment of the RSV G protein (G(128-188)) fused with a portion of the bacterial thioredoxin (Trx) protein. Mice immunized intranasally with D. radiodurans liposomes showed markedly greater protection against RSV challenge over mice immunized with DOPC liposomes. Enhanced vaccine efficacy was achieved using liposomes prepared from either whole D. radiodurans lipids or from a single isolated phosphoglycolipid previously identified as alpha-galactosylphosphatidylglyceroylalkylamine (lipid 7). Mice immunized and protected against RSV challenge were free of pulmonary eosinophilic infiltration, an undesirable consequence of many RSV vaccines. The results provide further support for liposome-based vaccines for RSV and underline the importance of lipid composition in liposome formulations.

Respiratory syncytial virus infection suppresses lung CD8+ T-cell effector activity and peripheral CD8+ T-cell memory in the respiratory tract

Respiratory syncytial virus (RSV) is a major cause of morbidity from respiratory infection in infants, young children and the elderly. No effective vaccine against RSV is currently available and studies of the natural history of RSV infection suggest repeated infections with antigenically related virus strains are common throughout an individual's lifetime. We have studied the CD8+ T-cell response during experimental murine RSV infection and found that RSV inhibits the expression of effector activity by activated RSV-specific CD8+ T cells infiltrating the lung parenchyma and the development of pulmonary CD8+ T-cell memory by interfering with TCR-mediated signaling. These data suggest a possible mechanism to explain the limited duration of protective immunity in RSV infection.

Visualization and characterization of respiratory syncytial virus F-specific CD8(+) T cells during experimental virus infection

CTL play a major role in the clearance of respiratory syncytial virus (RSV) during experimental pulmonary infection. The fusion (F) glycoprotein of RSV is a protective Ag that elicits CTL and Ab response against RSV infection in BALB/c mice. We used the strategy of screening a panel of overlapping synthetic peptides corresponding to the RSV F protein and identified an immunodominant H-2K(d)-restricted epitope (F(85-93); KYKNAVTEL) recognized by CD8(+) T cells from BALB/c mice. We enumerated the F-specific CD8(+) T cell response in the lungs of infected mice by flow cytometry using tetramer staining and intracellular cytokine synthesis. During primary infection, F(85-93)-specific effector CD8(+) T cells constitute approximately 4.8% of pulmonary CD8(+) T cells at the peak of the primary response (day 8), whereas matrix 2-specific CD8(+) T cells constituted approximately 50% of the responding CD8(+) T cell population in the lungs. When RSV F-immune mice undergo a challenge RSV infection, the F-specific CD8(+) T cell response is accelerated and dominates, whereas the primary response to the matrix 2 epitope in the lungs is reduced by approximately 20-fold. In addition, we found that activated F-specific effector CD8(+) T cells isolated from the lungs of RSV-infected mice exhibited a lower than expected frequency of IFN-gamma-producing CD8(+) T cells and were significantly impaired in ex vivo cytolytic activity compared with competent F-specific effector CD8(+) T cells generated in vitro. The significance of these results for the regulation of the CD8(+) T cell response to RSV is discussed.

Long-term persistence and reactivation of T cell memory in the lung of mice infected with respiratory syncytial virus

In mice acutely infected with respiratory syncytial virus (RSV), more than 20% of pulmonary CD8(+) T cells, but only 2-3% of CD8(+) T cells in the draining lymph node secreted interferon-gamma in response to a single peptide. Surprisingly, the percentage of virus-specific T cells in the lung remained at these high levels long after the acute infection. Pulmonary memory T cells were further studied in a sensitive adoptive transfer system, which allows visualizing polyclonal CD4(+) and CD8(+) virus-specific memory T cell responses. Fifty days after infection, persisting RSV-specific pulmonary T cells remained CD69(hi) CD62L(lo), but had returned to a resting memory state according to functional criteria. In the absence of neutralizing antibodies reinfection first induced cell division among virus-specific memory T cells 3 days after infection predominantly in the local lymph node. However, divided cells then rapidly accumulated in the lung without significantly increasing in the lymph node. These results suggest rapid export of reactivated cells from the lymph node to the target organ. Thus, although memory T cells can be maintained in the infected organ after a localized virus infection, amplification of a recall response appears to be most effective in organized lymphoid tissue.

Immunomodulation using bacterial enterotoxins

Immunologic unresponsiveness (tolerance) is a key feature of the mucosal immune system, and deliberate vaccination by a mucosal route can effectively induce immune suppression. However, some bacterial-derived proteins, e.g. cholera toxin and the heat labile toxin of Escherichia coli, are immunogenic and immunomodulatory at mucosal surfaces and can effectively adjuvant immune responses to codelivered bystander antigens. This review summarizes some of the structural and biological characteristics of these toxins and provides examples of how these properties have been exploited for tolerance induction and mucosal vaccine development.

Mucosal delivery of a respiratory syncytial virus CTL peptide with enterotoxin-based adjuvants elicits protective, immunopathogenic, and immunoregulatory antiviral CD8+ T cell responses

In an effort to develop a safe and effective vaccine against respiratory syncytial virus (RSV), we used Escherichia coli heat-labile toxin (LT), and LTK63 (an LT mutant devoid of ADP-ribosyltransferase activity) to elicit murine CD8(+) CTL responses to an intranasally codelivered CTL peptide from the second matrix protein (M2) of RSV. M2(82-90)-specific CD8(+) T cells were detected by IFN-gamma enzyme-linked immunospot and (51)Cr release assay in local and systemic lymph nodes, and their induction was dependent on the use of a mucosal adjuvant. CTL elicited by peptide immunization afforded protection against RSV challenge, but also enhanced weight loss. CTL-mediated viral clearance was not dependent on IFN-gamma since depletion using specific mAb during RSV challenge did not affect cellular recruitment or viral clearance. Depletion of IFN-gamma did, however, reduce the concentration of TNF detected in lung homogenates of challenged mice and largely prevented the weight loss associated with CTL-mediated viral clearance. Mice primed with the attachment glycoprotein (G) develop lung eosinophilia after intranasal RSV challenge. Mucosal peptide vaccination reduced pulmonary eosinophilia in mice subsequently immunized with G and challenged with RSV. These studies emphasize that protective and immunoregulatory CD8(+) CTL responses can be mucosally elicited using enterotoxin-based mucosal adjuvants but that resistance against viral infection may be accompanied by enhanced disease.

Characterization of a novel respiratory syncytial virus-specific human cytotoxic T-lymphocyte epitope

Respiratory syncytial virus (RSV) infection is a major cause of morbidity in childhood worldwide. The first human RSV-specific cytotoxic T-lymphocyte epitope to be defined is described. This HLA B7-restricted epitope in nucleoprotein (NP) was detectable in four healthy, B7-positive adult subjects using B7-RSV-NP tetrameric complexes to stain CD8(+) T cells.

CD4(+) T-cell-mediated antiviral protection of the upper respiratory tract in BALB/c mice following parenteral immunization with a recombinant respiratory syncytial virus G protein fragment

We analyzed the protective mechanisms induced against respiratory syncytial virus subgroup A (RSV-A) infection in the lower and upper respiratory tracts (LRT and URT) of BALB/c mice after intraperitoneal immunization with a recombinant fusion protein incorporating residues 130 to 230 of RSV-A G protein (BBG2Na). Mother-to-offspring antibody (Ab) transfer and adoptive transfer of BBG2Na-primed B cells into SCID mice demonstrated that Abs are important for LRT protection but have no effect on URT infection. In contrast, RSV-A clearance in the URT was achieved in a dose-dependent fashion after adoptive transfer of BBG2Na-primed T cells, while it was abolished in BBG2Na-immunized mice upon in vivo depletion of CD4(+), but not CD8(+), T cells. Furthermore, the conserved RSV-A G protein cysteines and residues 193 and 194, overlapping the recently identified T helper cell epitope on the G protein (P. W. Tebbey et al., J. Exp. Med. 188:1967-1972, 1998), were found to be essential for URT but not LRT protection. Taken together, these results demonstrate for the first time that CD4(+) T cells induced upon parenteral immunization with an RSV G protein fragment play a critical role in URT protection of normal mice against RSV infection.

CTL epitopes identified with a defective recombinant adenovirus expressing measles virus nucleoprotein and evaluation of their protective capacity in mice

Cytotoxic T-lymphocyte (CTL) responses to measles virus (MV) play an important role in recovery from infection, with one of the major target proteins for CTL activity being the nucleoprotein (Np). In this report, a replication-deficient adenovirus-5 recombinant, expressing for MV Np (Rad68) was tested for in vivo priming of MV Np-specific CTL responses in BALB/c and CBA mice. In both strains of mice strong Np-specific CTL responses were induced and these responses were shown to be MHC class I restricted. Using overlapping 15mer peptides spanning residues 1-505 of MV Np a single epitope comprising residues 281-295 was identified in BALB/c mice whereas, in CBA mice two epitopes comprising residues 51-65 and 81-95, were identified. These epitopes were found to contain class I motifs for H-2L(d) and H-2K(k) MHC molecules, respectively. Immunization of BALB/c and CBA mice with the respective CTL epitopes resulted in the in vivo induction of peptide-and MV Np-specific CTL responses. In addition, the identified H-2K(k) restricted CTL epitopes conferred some protection against encephalitis induced following intracerebral challenge with a lethal dose of canine distemper virus (the Np of which shares 70% sequence homology with MV Np). These findings highlight the potential of using well-defined CTL epitopes to control virus infection.

Transfer of the Enhancing Effect of Respiratory Syncytial Virus Infection on Subsequent Allergic Airway Sensitization by T Lymphocytes

In mice, respiratory syncytial virus (RSV) infection enhances allergic airway sensitization, resulting in lung eosinophilia and in airway hyperresponsiveness (AHR). The mechanisms by which RSV contributes to development of asthma and its effects on allergic airway sensitization in mice are not known. We tested whether these consequences of RSV infection can be adoptively transferred by T cells and whether depletion of T cell subsets prevents the effects of RSV infection on subsequent airway sensitization. Mononuclear cells, T lymphocytes, or CD4 or CD8 T cells from peribronchial lymph nodes (PBLN) of RSV-infected mice were transferred into naive BALB/c mice which were then exposed to OVA via the airways. Additionally, RSV-infected mice were depleted of CD4 or CD8 T cells following acute RSV infection but prior to airway sensitization. Following sensitization, airway responsiveness to inhaled methacholine, numbers of lung eosinophils, and levels of IFN-γ, IL-4, and IL-5 in PBLN cell cultures were monitored. Transfer of T cells from RSV-infected mice resulted in increased eosinophil influx into the lungs, increased IL-5 production, and development of AHR following airway sensitization to allergen. Transfer of CD8 but not CD4 T cells from the PBLN of RSV-infected mice also resulted in AHR following 10 days of OVA exposure. Further, depletion of CD8 T cells prevented these consequences of RSV infection while CD4 T cell depletion reduced them. We conclude that T cells, in particular CD8 T cells, are critical in mediating RSV-induced development of lung eosinophilia and AHR following allergic airway sensitization.