Construction and characterization of recombinant vaccinia viruses co-expressing a respiratory syncytial virus protein and a cytokine

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.

Brief History and Characterization of Enhanced Respiratory Syncytial Virus Disease

In 1967, infants and toddlers immunized with a formalin-inactivated vaccine against respiratory syncytial virus (RSV) experienced an enhanced form of RSV disease characterized by high fever, bronchopneumonia, and wheezing when they became infected with wild-type virus in the community. Hospitalizations were frequent, and two immunized toddlers died upon infection with wild-type RSV. The enhanced disease was initially characterized as a "peribronchiolar monocytic infiltration with some excess in eosinophils." Decades of research defined enhanced RSV disease (ERD) as the result of immunization with antigens not processed in the cytoplasm, resulting in a nonprotective antibody response and CD4(+) T helper priming in the absence of cytotoxic T lymphocytes. This response to vaccination led to a pathogenic Th2 memory response with eosinophil and immune complex deposition in the lungs after RSV infection. In recent years, the field of RSV experienced significant changes. Numerous vaccine candidates with novel designs and formulations are approaching clinical trials, defying our previous understanding of favorable parameters for ERD. This review provides a succinct analysis of these parameters and explores criteria for assessing the risk of ERD in new vaccine candidates.

Virus-encoded ectopic CD74 enhances poxvirus vaccine efficacy

Vaccinia virus (VV) has been used globally as a vaccine to eradicate smallpox. Widespread use of this viral vaccine has been tempered in recent years because of its immuno-evasive properties, with restrictions prohibiting VV inoculation of individuals with immune deficiencies or atopic skin diseases. VV infection is known to perturb several pathways for immune recognition including MHC class II (MHCII) and CD1d-restricted antigen presentation. MHCII and CD1d molecules associate with a conserved intracellular chaperone, CD74, also known as invariant chain. Upon VV infection, cellular CD74 levels are significantly reduced in antigen-presenting cells, consistent with the observed destabilization of MHCII molecules. In the current study, the ability of sustained CD74 expression to overcome VV-induced suppression of antigen presentation was investigated. Viral inhibition of MHCII antigen presentation could be partially ameliorated by ectopic expression of CD74 or by infection of cells with a recombinant VV encoding murine CD74 (mCD74-VV). In contrast, virus-induced disruptions in CD1d-mediated antigen presentation persisted even with sustained CD74 expression. Mice immunized with the recombinant mCD74-VV displayed greater protection during VV challenge and more robust anti-VV antibody responses. Together, these observations suggest that recombinant VV vaccines encoding CD74 may be useful tools to improve CD4⁺ T-cell responses to viral and tumour antigens.

Respiratory syncytial virus: immunopathology and control

Respiratory syncytial virus (RSV) is the primary cause of serious upper and lower respiratory tract infections in infants and children worldwide. RSV infection in infancy may lead to the onset of asthma or other health problems later in life. An effective vaccine is not yet available against RSV infection. Humans respond to RSV infection by mounting an immune response, but the antiviral immunity is incomplete, thus repeat RSV infections continue throughout life. The precise mechanism of RSV-induced infection and immunopathology remains unclear. The limited knowledge of RSV immunity is a major problem in designing a protective vaccine. In this review, the biology of RSV infection, its immunopathology, the role of innate and adaptive immunity, as well as the understanding of how to control RSV infection based on prophylactic and therapeutic approaches are discussed.

Differential effects of the type I interferons alpha4, beta, and epsilon on antiviral activity and vaccine efficacy

The type I IFNs exert a range of activities that include antiviral, antiproliferative, and immunomodulatory effects. To study this further, we have constructed recombinant vaccinia viruses expressing HIV or hemagglutinin (HA) Ags along with murine type I IFNs, IFN-alpha(4) (HA-VV-IFN-alpha(4)), IFN-beta (HA-VV-IFN-beta), or IFN-epsilon (HIV-VV-IFN-epsilon), a recently discovered member of this family. Our aims were to characterize IFN-epsilon functionality as a type I IFN and also to study the biological properties of these factors toward the development of safer and more effective vector-based vaccines. HIV-VV-IFN-epsilon and HA-VV-IFN-beta grew to lower titers than did their parental controls in murine cell lines. In vivo, however, HIV-VV-IFN-epsilon growth was not attenuated, while IFN-beta demonstrated potent local antiviral activity with no replication of HA-VV-IFN-beta detected. Flow cytofluorometric analysis of B lymphocytes incubated with virally encoded IFN-epsilon showed up-regulation of activation markers CD69 and CD86, while RT-PCR of IFN-epsilon-treated cells revealed that gene expression levels of antiviral proteins were elevated, indicating the induction of an antiviral state. The use of these constructs in a poxvirus prime-boost immunization regime led to robust humoral and cellular immune responses against the encoded Ags, despite the lack of replication in the case of HA-VV-IFN-beta. Thus, coexpression of these factors may be beneficial in the design of safer vector-based vaccines. Our data also indicate that while IFN-epsilon exhibits certain biological traits similar to other type I IFNs, it may also have a specific role in mucosal immune regulation that is quite distinct.

Pulmonary eosinophilia requires interleukin-5, eotaxin-1, and CD4+ T cells in mice immunized with respiratory syncytial virus G glycoprotein

Severe illness, type 2 cytokine production, and pulmonary eosinophilia are adverse immune responses resulting from respiratory syncytial virus (RSV) challenge of vvGs-immunized mice. We have shown IL-4 and IL-13 activity must be simultaneously inhibited to reduce disease severity. We now address the contributions of IL-5, eotaxin-1, and CD4+ and CD8+ T cells to the induction of disease-enhancing immune responses. Depletion of CD4+ T cells during immunization prevented IL-4, IL-13, and eotaxin-1 production, diminished eosinophilia, and reduced weight loss. Conversely, CD8+ T cell depletion did not decrease eosinophilia, weight loss, or type 2 cytokines but did dramatically reduce mucus production and increase eotaxin production. Anti-IL-5 administration at immunization or challenge significantly decreased pulmonary eosinophilia. Strikingly, there were not concomitant decreases in weight loss. Following RSV challenge eotaxin-1-deficient mice immunized with vvGs exhibited significantly less eosinophilia without decreased weight loss or type 2 cytokine production. We conclude CD4+ T cell production of IL-5 and induction of eotaxin-1 are required for vvGs-induced eosinophilia following RSV challenge, while CD8+ T cells appear to down-regulate eotaxin-1 and mucus production. In summary, we demonstrate that pulmonary eosinophilia 1) is a by-product of memory CD4+ T cell activation, 2) does not necessarily correlate with mucus production, and, most importantly, 3) is not required for the RSV G-induced illness in mice. These findings have important implications for the evaluation of candidate RSV vaccines.

Skin inflammation in RelB−/− mice leads to defective immunity and impaired clearance of vaccinia virus

BACKGROUND

Atopic dermatitis (AD) is an inflammatory skin disorder occurring in genetically predisposed individuals with a systemic T(H)2 bias. Atopic dermatitis patients exposed to the smallpox vaccine, vaccinia virus (VV), occasionally develop eczema vaccinatum (EV), an overwhelming and potentially lethal systemic infection with VV.

OBJECTIVE

To establish a murine model of EV and examine the effects of skin inflammation on VV immunity.

METHODS

The skin of RelB(-/-) mice, like that of chronic AD lesions in humans, exhibits thickening, eosinophilic infiltration, hyperkeratosis, and acanthosis. RelB(-/-) and wild-type (WT) control mice were infected with VV via skin scarification. Viral spread, cytokine levels, IgG2a responses and VV-specific T cells were measured.

RESULTS

Cutaneously VV-infected RelB(-/-), but not WT mice, exhibited weight loss, markedly impaired systemic clearance of the virus and increased contiguous propagation from the inoculation site. This was associated with a dramatically impaired generation of IFN-gamma-producing CD8(+) vaccinia-specific T cells along with decreased secretion of IFN-gamma by VV-stimulated splenocytes. The T(H)2 cytokines-IL-4, IL-5, IL-13, and IL-10-on the other hand, were overproduced. When infected intraperitoneally, RelB(-/-) mice generated robust T cell responses with good IFN-gamma production.

CONCLUSION

Allergic inflammation in RelB(-/-) mice is associated with dysregulated immunity to VV encountered via the skin. We speculate that susceptibility of AD patients to overwhelming vaccinia virus infection is similarly related to ineffective T cell responses.

CLINICAL IMPLICATIONS

The susceptibility of patients with AD to EV following cutaneous contact with VV is related to ineffective antiviral immune responses.

Respiratory syncytial virus (RSV) evades the human adaptive immune system by skewing the Th1/Th2 cytokine balance toward increased levels of Th2 cytokines and IgE, markers of allergy--a review

Infection of infants in their first year of life, children and elderly people with the respiratory syncytial virus (RSV) endangers the life of the patient. An attempt to develop a formalin-inactivated RSV (FI-RSV) vaccine during the 1960s resulted in an aggravated infection in immunized children, leading to hospitalization, while infection of non-immunized children produced much milder symptoms. The reason for this remained an enigma, one which was gradually solved over the last decade by many researchers who studied the molecular biology of RSV infection of respiratory ciliary cells. Clinical studies of RSV-infected patients indicated increased levels of Th2 cytokines and IgE in the patients' sera, suggesting that an allergy-like condition developed during infection. The biomarkers of allergy caused by endogenous or environmental allergens include a marked increase of the Th2 cytokine IL-4 and IgE non-neutralizing antibodies to the allergen. The way allergens trigger allergy was deciphered recently, and will be discussed later. Studies of RSV infection led to the suggestion that RSV patients suffer from allergy prior to RSV infection, a concept that was later abandoned. Studies on HIV-1 [Y. Becker, Virus Genes 28, 319-331 (2005)] research led me to the hypothesis that since HIV-1 infection induces a marked increase of IL-4 and IgE in serum, an allergy-like condition, the AIDS stage is the result of an allergen motif that is embedded in the shed viral gp120 molecules. It is hypothesized that the viral-soluble G glycoprotein (sG) contains a T cell superantigen (Tsag) that is capable of binding to the V(H)3 domain of IgE/FcepsilonRI(+) hematopoietic cells, basophils, mast cells and monocytes, similar to the case of allergens, and that this aggregation causes these innate system cells to degranulate and release large amounts of Th2 cytokines (IL-4, IL-5, IL-10, IL-13) into the blood. The way these Th2 cytokines skew the Th1/Th2 balance toward Th2 > Th1 will be discussed. The aim of the present review is to base RSV pathogenicity on the numerous very good analyses of the virus genes and to suggest a therapeutic approach to treatment that is directed at preventing the inhibitory effects of Th2 cytokines on the adaptive immune system of the patients, instead of inhibiting RSV replication by antivirals. The review of the molecular research on the role of the viral fusion (F) and attachment (G) glycoproteins of RSV provided information on their role in the virus infection: early in infection the F glycoprotein induces Th1 cells to release the Th1 cytokines IL-2, IL-12 and IFN-gamma to activate precursors CTLs (pCTLs) to become anti-RSV CTLs. The G and sG glycoproteins attach to FKNR1(+) ciliary respiratory epithelial cells as well as directly to eosinophils to the lungs. The sG T cell antigen can also induce the release of large amounts of Th2 cytokines from CD4(+) T cells and from FCepsilonRI(+) mast cells, basophils and monocytes. By comparison to HIV-1 gp120 it is possible to show that in the G and sG proteins the T cell antigen resembles the CD4(+) T cell superantigen (=allergen) domain of HIV-1 gp120 which aggregates with IgE/FCepsilonRI(+) hematopoietic cells. The increased IL-4 level in the serum inhibits the adaptive immune response: IL-4Ralpha(+) Th1 cells stop Th1 cytokine synthesis and IL-4Ralpha(+) B cells stop the synthesis of antiviral IgG and IgA and switch to IgE synthesis. In addition, the hematopoietic cells release histamine and prostaglandin which induce wheezing. The gradual increase of sG molecules creates a gradient of fractalkine (FKN) which directs IL-5-activated eosinophils to the lungs of the patient.

Biological Threat Characterization Research: A Critical Component of National Biodefense

Biological warfare (BW) threat assessments identify and prioritize BW threats to civilian and military populations. In an ideal world, they provide policymakers with clear and compelling guidance to prioritize biodefense research, development, testing, evaluation, and acquisition of countermeasures. Unfortunately, the biodefense community does not exist in an ideal world. National security professionals responsible for crafting BW threat assessments often are challenged by factors that limit the clarity and/or timeliness of those assessments. Moreover, the potential for life science advances to enhance threats enabled by state programs and the possibility that non-state actors may pursue crude but effective BW methodologies will drastically expand the scope of the perceived threat. Appropriate investment of federal biodefense funds will require some mechanism for validating and prioritizing present and future threats. Ideally, such a mechanism will incorporate empirical data targeted to elucidate actual hazards. In this regard, the Department of Homeland Security's creation of a Biological Threat Characterization Program for the technical validation of threat agents will be a valuable addition to the nation's overall biodefense strategy. This article articulates the need for a coordinated national biological threat characterization program, discusses some of the principal challenges associated with such research, and suggests a few options for their resolution.

Enhanced humoral HIV-1-specific immune responses generated from recombinant rhabdoviral-based vaccine vectors co-expressing HIV-1 proteins and IL-2

Recombinant rabies virus (RV) vaccine strain-based vectors expressing HIV-1 antigens have been shown to induce strong and long-lasting cellular but modest humoral responses against the expressed antigens in mice. However, an effective vaccine against HIV-1 may require stronger responses, and the development of such an immune response may depend on the presence of certain cytokines at the time of the inoculation. Here, we describe several new RV-based vaccine vehicles expressing HIV-1 Gag or envelope (Env) and murine IL-2 or IL-4. Cells infected with recombinant RVs expressed high levels of functional IL-2 or IL-4 in culture supernatants in addition to HIV-1 proteins. The recombinant RV expressing IL-4 was highly attenuated in a cytokine-independent manner, indicating that the insertion of two foreign genes into the RV genome is mainly responsible for the attenuation observed. The expression of IL-4 resulted in a decrease in the cellular immune response against HIV-1 Gag and Env when compared with the parental virus not expressing IL-4 and only 2 of 20 mice seroconverted to HIV-1 Env after two inoculations. The IL-2-expressing RV was completely apathogenic after direct intracranial inoculation of mice. In addition, mice immunized with IL-2 maintained strong anti-HIV-1 Gag and Env cellular responses and consistently induced seroconversion against HIV-1 Env after two inoculations. This suggests the potential use of IL-2 in RV-based HIV-1 vaccine strategies, which may require the induction of both arms of the immune response.

Modified vaccinia virus Ankara immunization protects against lethal challenge with recombinant vaccinia virus expressing murine interleukin-4

Recent events have raised concern over the use of pathogens, including variola virus, as biological weapons. Vaccination with Dryvax is associated with serious side effects and is contraindicated for many people, and the development of a safer effective smallpox vaccine is necessary. We evaluated an attenuated vaccinia virus, modified vaccinia virus Ankara (MVA), by use of a murine model to determine its efficacy against an intradermal (i.d.) or intranasal (i.n.) challenge with vaccinia virus (vSC8) or a recombinant vaccinia virus expressing murine interleukin-4 that exhibits enhanced virulence (vSC8-mIL4). After an i.d. challenge, 15 of 16 mice who were inoculated with phosphate-buffered saline developed lesions, one dose of intramuscularly administered MVA was partially protective (3 of 16 mice developed lesions), and the administration of two or three doses of MVA was completely protective (0 of 16 mice developed lesions). In unimmunized mice, an i.n. challenge with vSC8 caused a significant but self-limited illness, while vSC8-mIL4 resulted in lethal infections. Immunization with one or two doses of MVA prevented illness and reduced virus titers in mice who were challenged with either vSC8 or vSC8-mIL4. MVA induced a dose-related neutralizing antibody and vaccinia virus-specific CD8+-T-cell response. Mice immunized with MVA were fully protected from a low-dose vSC8-mIL4 challenge despite a depletion of CD4+ cells, CD8+ cells, or both T-cell subsets or an antibody deficiency. CD4+- or CD8+-T-cell depletion reduced the protection against a high-dose vSC8-mIL4 challenge, and the depletion of both T-cell subsets was associated with severe illness and higher vaccinia virus titers. Thus, MVA induces broad humoral and cellular immune responses that can independently protect against a molecularly modified lethal poxvirus challenge in mice. These data support the continued development of MVA as an alternative candidate vaccine for smallpox.

Vbeta14(+) T cells mediate the vaccine-enhanced disease induced by immunization with respiratory syncytial virus (RSV) G glycoprotein but not with formalin-inactivated RSV

Mice immunized with respiratory syncytial virus (RSV) G glycoprotein or with formalin-inactivated RSV (FI-RSV) exhibit severe disease following RSV challenge. This results in type 2 cytokine production and pulmonary eosinophilia, both hallmarks of vaccine-enhanced disease. RSV G-induced T-cell responses were shown to be restricted to CD4(+) T cells expressing Vbeta14 in the T-cell receptor (TCR), and the deletion of these T cells resulted in less severe disease. We therefore examined the role of Vbeta14(+) T cells in FI-RSV-induced disease. BALB/c mice were immunized with vaccinia virus expressing secreted RSV G (vvGs) or with FI-RSV. At the time of challenge with live RSV, mice were injected with antibody to the Vbeta14 component of the TCR. vvGs-immunized mice treated with anti-Vbeta14 had reduced cytokine levels in the lung. Eosinophil recruitment to the lung was also significantly reduced. In contrast, depletion of Vbeta14(+) T cells in FI-RSV-immunized mice had little impact on cytokine production or pulmonary eosinophilia. An analysis of TCR Vbeta chain usage confirmed a bias toward Vbeta14 expression on CD4(+) T cells from vvGs-immunized mice, whereas the CD4(+) T cells in FI-RSV-immunized mice expressed a diverse array of Vbeta chains. These data show that although FI-RSV and vvGs induce responses resulting in similar immunopathology, the T-cell repertoire mediating the response is different for each immunogen and suggest that the immune responses elicited by RSV G are not the basis for FI-RSV vaccine-enhanced disease.

Respiratory syncytial virus, pneumonia virus of mice, and influenza A virus differently affect respiratory allergy in mice

BACKGROUND

Respiratory viral infections in early childhood may interact with the immune system and modify allergen sensitization and/or allergic manifestations. In mice, respiratory syncytial virus (RSV) infection during allergic provocation aggravates the allergic T helper (Th) 2 immune response, characterized by the production of IL-4, IL-5, and IL-13, and inflammatory infiltrates. However, it is unclear whether the RSV-enhanced respiratory allergic response is a result of non-specific virus-induced damage of the lung, or virus-specific immune responses.

OBJECTIVE

In the present study we investigated whether RSV, pneumonia virus of mice (PVM) and influenza A virus similarly affect the allergic response.

METHODS

BALB/c mice were sensitized and challenged with ovalbumin (OVA), and inoculated with virus during the challenge period. Pulmonary inflammation, lung cytokine mRNA responses, and IgE production in serum were assessed after the last OVA-challenge.

RESULTS

Like RSV, PVM enhanced the OVA-induced pulmonary IL-4, IL-5, and IL-13 mRNA expression, which was associated with enhanced perivascular inflammation. In addition, PVM increased the influx of eosinophils in lung tissue. In contrast, influenza virus decreased the Th2 cytokine mRNA expression in the lungs. However, like PVM, influenza virus enhanced the pulmonary eosinophilic infiltration in OVA-allergic mice.

CONCLUSION

The Paramyxoviruses RSV and PVM both are able to enhance the allergic Th2 cytokine response and perivascular inflammation in BALB/c mice, while the Orthomyxovirus influenza A is not.

Vaccinia virus pathogenicity in atopic dermatitis is caused by allergen-induced immune response that prevents the antiviral cellular and humoral immunity

Atopic dermatitis (AD) serves as a contraindication for the immunization of AD patients with a live vaccinia virus (VV) vaccine. The antiallergen IgE interacts with the Fc receptors (FcepsilonRI) on dendritic cell (DC) membranes and with allergen molecules. The immunological events that lead to AD disease, the activation of the T-helper 2 (Th2) immune response, the synthesis of the cytokines IL-4, IL-5, IL-13, and the inhibition of the T-helper 1 (Th1) damage the capacity of the host to develop anti-VV cytotoxic cells (CTLs). In the presence of Th2-derived cytokine IL-4 in the AD skin and the synthesis of VV proteins that interfere recruitment of DCs by host cytokines, the VV can cause a generalized infection. Conceptually, new VV recombinants may be needed for human immunization. Such VV recombinants should lack the genes that interfere with the host immune system and express a mutated human IL-4 cytokine gene that will prevent negative regulatory mechanisms. Such improved VV recombinants may be used to express genes from pathogenic viruses.

Contribution of respiratory syncytial virus G antigenicity to vaccine-enhanced illness and the implications for severe disease during primary respiratory syncytial virus infection

BACKGROUND

Immunization of BALB/c mice with vaccinia virus expressing the G glycoprotein (vvG) of respiratory syncytial virus (RSV) or with formalin-inactivated alum-precipitated RSV (FI-RSV) predisposes for severe illness, type 2 cytokine production and pulmonary eosinophilia after challenge with live RSV. This similar disease profile has led to the proposal that the presence of the G glycoprotein in the FI-RSV preparation was the immunologic basis for the vaccine-associated enhancement of disease observed in the failed clinical trials of the 1960s. However, processes of disease pathogenesis observed in FI-RSV- and vvG-immunized mice suggest that FI-RSV and vvG immunizations induce immune responses of different compositions and requirements that converge to produce similar disease outcomes upon live virus challenge.

METHODS

The potential role of RSV G present in FI-RSV preparations in increasing postimmunization disease severity was explored in mice.

RESULTS

The absence of RSV G or its immunodominant epitope during FI-RSV immunization does not reduce disease severity after RSV challenge. Furthermore although depletion of V beta 14+ T cells during RSV challenge modulates disease in G-primed mice, minimal impact on disease in FI-RSV-immunized mice is observed.

CONCLUSION

FI-RSV vaccine-enhanced illness is not attributable to RSV G. Furthermore formulation of a safe and effective RSV vaccine must ensure RSV antigen production, processing and presentation via the endogenous pathways. Thus gene delivery by vector, by DNA or by live attenuated virus are attractive vaccine approaches.

IL-13 is sufficient for respiratory syncytial virus G glycoprotein-induced eosinophilia after respiratory syncytial virus challenge

Although well studied in settings of helminth infection and allergen sensitization, the combined contributions of IL-4 and IL-13 and their signaling pathways in models of viral pathogenesis have not been reported. Using a murine model of respiratory syncytial virus (RSV) infection, we evaluated the contribution of IL-13, alone and in conjunction with IL-4, during immunization with recombinant vaccinia virus expressing RSV G glycoprotein (vvGs) or with formalin-inactivated RSV (FI-RSV). We showed that both IL-4 and IL-13 activity must be inhibited to modulate G-specific responses resulting in severe RSV-induced disease. Inhibition of IL-4 or IL-13 activity alone had minimal impact on disease in vvGs-immunized mice. However, treatment of IL-4-deficient mice with IL-13Ra during vvGs immunization reduced IL-5, IL-13, and eotaxin production and pulmonary eosinophilia after RSV challenge. In contrast, FI-RSV-induced immune responses were diminished when either IL-4 or IL-13 activity was blocked. After RSV challenge, these type 2 T cell responses were also diminished in vvGs-primed IL-4Ralpha-deficient mice. Our data suggest that secreted vvGs uses mechanisms requiring signaling through the IL-4Ralpha-chain by either IL-4 or IL-13 for induction of eosinophilia and is the first description of the relative contributions of IL-4, IL-13, and their receptors in viral pathogenesis.

Gamma interferon-dependent protection of the mouse upper respiratory tract following parenteral immunization with a respiratory syncytial virus G protein fragment

The protective mechanisms induced in the mouse upper respiratory tract (URT) after intraperitoneal immunization with G2Na, a recombinant respiratory syncytial virus (RSV) G protein fragment (amino acid residues 130 to 230), were investigated. This protection was recently shown to be mediated by CD4(+) T cells and to be critically dependent on the cysteines and amino acids 193 and 194 (H. Plotnicky-Gilquin, A. Robert, L. Chevalet, J.-F. Haeuw, A. Beck, J.-Y. Bonnefoy, C. Brandt, C.-A. Siegrist, T. N. Nguyen, and U. F. Power, J. Virol. 74:3455-3463, 2000). On G2Na, we identified a domain (amino acid residues 182 to 198) responsible for the T-helper-cell activity. This region coincided with a peptide designed AICK (residues 184 to 198) which includes the previously identified murine and human T-helper-cell epitope on the native G protein (P. W. Tebbey, M. Hagen, and G. E. Hancock, J. Exp. Med. 188:1967-1972, 1998). Immunization with AICK, in alum or complete Freund's adjuvant, significantly reduced nasal RSV titers in normal BALB/c mice. However, although lung protection was induced, in contrast to the case with live RSV, neither AICK nor G2Na was able to prevent nasal infection in gamma interferon (IFN-gamma)-knockout mice. Anti-IFN-gamma neutralizing antibodies partially inhibited URT protection after administration to G2Na-immunized BALB/c mice. Furthermore, while purified CD4(+) T cells from BALB/c mice immunized with G2Na or AICK significantly reduced lung and nasal infection of naive recipient mice after adoptive transfer, the cells from IFN-gamma-knockout mice had no effect. Together, these results demonstrated for the first time that the T-helper-cell epitope of RSV G protein induces URT protection in mice after parenteral immunization through a Th1-type, IFN-gamma-dependent mechanism.

Current concepts on active immunization against respiratory syncytial virus for infants and young children

Respiratory syncytial virus (RSV) is the most important causative agent of viral respiratory tract infections in infants and young children. Passive immunization against RSV became available recently, but this does not apply to an effective vaccine as a result of dramatic adverse results of immunization with a RSV candidate vaccine in the 1960s and the lack of full knowledge of the immune response induced by RSV. Nonetheless intensive research during the past two decades has resulted in several interesting candidate vaccines, of which some have gone through testing in humans. These include the subunit vaccines PFP-1, PFP-2, BBG2Na and cold-passaged/temperature-sensitive mutants. The development of candidate vaccines against RSV is discussed. Because of questions, uncertainties and difficulties with the development of effective vaccines against RSV, it will probably be at least another 5 to 10 years before routine immunization against RSV becomes available.