Long-lasting balanced immunity and protective efficacy against respiratory syncytial virus in mice induced by a recombinant protein G1F/M2

RSV recombinant candidate vaccine G1F/M2 with CpG as an adjuvant prevents vaccine-associated lung inflammation, which may be associated with the appropriate types of immune memory in spleens and lungs

Respiratory syncytial virus (RSV) is a major respiratory pathogen in infants. The early formalin-inactivated RSV not only failed to protect infants against infection, but also was associated with enhanced pulmonary inflammatory disease upon natural infection. A safe and effective vaccine should prevent the inflammatory disease and provide protection. Immune memory is the cornerstone of vaccines. In this study, we evaluated three types of immune memory T cells, antibodies, and lung inflammation of a vaccine candidate G1F/M2, which includes a neutralizing epitope fragment of RSV G protein and a cytotoxic T lymphocyte epitope of M2 protein, with toll-like receptor 9 agonist CpG2006 as an adjuvant by intranasal (i.n.) and intraperitoneal (i.p.) immunization protocols. The results indicated that immunization of mice with G1F/M2 + CpG i.p. induced significantly higher level of CD4⁺ or CD8⁺ central memory (TCM), Th1-type effector memory (TEM), and balanced ratio of IgG1/IgG2a, but lower level of lung tissue-resident memory (TRM), compared with immunization with G1F/M2 + CpG i.n., G1F/M2 i.n., or G1F/M2 i.p. Following RSV challenge, the mice immunized with G1F/M2 + CpG i.p. showed higher level of Th1-type responses, remarkably suppressed inflammatory cytokines and histopathology in lungs, compared with mice immunized with G1F/M2 + CpG i.n., G1F/M2 i.n., or G1F/M2 i.p. These results suggested that high level of TCM and Th1 type of TEM in spleens may contribute to inhibition of lung inflammation, while high level of TRM in lungs and lack of or weak Th1-type immune memory in spleens may promote lung inflammation following RSV challenge.

Simultaneous Administration of Recombinant Measles Viruses Expressing Respiratory Syncytial Virus Fusion (F) and Nucleo (N) Proteins Induced Humoral and Cellular Immune Responses in Cotton Rats

We previously reported that recombinant measles virus expressing the respiratory syncytial virus (RSV) fusion protein (F), MVAIK/RSV/F, induced neutralizing antibodies against RSV, and those expressing RSV-NP (MVAIK/RSV/NP) and M2-1 (MVAIK/RSV/M2-1) induced RSV-specific CD8⁺/IFN-γ⁺ cells, but not neutralizing antibodies. In the present study, MVAIK/RSV/F and MVAIK/RSV/NP were simultaneously administered to cotton rats and immune responses and protective effects were compared with MVAIK/RSV/F alone. Sufficient neutralizing antibodies against RSV and RSV-specific CD8⁺/IFN-γ⁺ cells were observed after re-immunization with simultaneous administration. After the RSV challenge, CD8⁺/IFN-γ⁺ increased in spleen cells obtained from the simultaneous immunization group in response to F and NP peptides. Higher numbers of CD8⁺/IFN-γ⁺ and CD4⁺/IFN-γ⁺ cells were detected in lung tissues from the simultaneous immunization group after the RSV challenge. No detectable RSV was recovered from lung homogenates in the immunized groups. Mild inflammatory reactions with the thickening of broncho-epithelial cells and the infiltration of inflammatory cells were observed in lung tissues obtained from cotton rats immunized with MVAIK/RSV/F alone after the RSV challenge. No inflammatory responses were observed after the RSV challenge in the simultaneous immunization groups. The present results indicate that combined administration with MVAIK/RSV/F and MVAIK/RSV/NP induces humoral and cellular immune responses and shows effective protection against RSV, suggesting the importance of cellular immunity.

Design and Evaluation of a Multi-Epitope Peptide of Human Metapneumovirus

OBJECTIVES

No licensed vaccines or therapeutic agents for human metapneumovirus (hMPV) infection exist to date. We aimed to construct a multi-epitope peptide (MEP) of hMPV to show promising results for epitope-based vaccine development.

METHODS

Six independent algorithms were screened to predict B-cell epitopes of hMPV, and three algorithms were used to predict cytotoxic T lymphocyte and T helper (Th) lymphocyte epitopes. Predicted epitopes were assembled in series with the spacers GPGPG and KK introduced, termed MEP. Recombinant mep genes were inserted into pET32a(+) plasmid and expressed in Escherichia coli strain BL21 (DE3). BALB/c mice were immunized with MEP with different adjuvants. Antibody titer, lymphocyte proliferation, cytotoxic T lymphocyte (CTL) activity and splenocyte cytokines were detected 2 weeks later after the last immunization. Microneutralization assay was used to detect neutralizing antibodies.

RESULTS

Six B-cell epitopes, four CTL epitopes and two Th epitopes were screened to construct the mep gene. Expressed MEP induced >104 antibodies in BALB/c mice, and produced anti-MEP antibody reacting with hMPV strains specifically as detected in indirect fluorescent assay (the titer was 160). The lymphocyte proliferation index, CTL activity and splenocyte cytokines of the MEP immunization groups were higher than in the control group (p < 0.05). Both IgG1 and IgG2a antibodies could be detected in the different groups, and balanced Th1/Th2 cytokines were secreted by splenocytes in these groups. The mean neutralizing titers of the MEP+CpG ODN, MEP+Alum and MEP+Alum+ CpG ODN groups were 87 (95% CI 50-126), 93 (95% CI 67-121) and 96 (95% CI 69-147), respectively.

CONCLUSION

MEP of hMPV elicited both strong humoral immunity and cell-mediated immunity in mice. The anti-MEP serum could neutralize hMPV infection in vitro. Joint use of CpG ODN and aluminum hydroxide adjuvants obtained the best immune effects. This study may contribute to hMPV epitope-based vaccine development.

Recombinant measles viruses expressing respiratory syncytial virus proteins induced virus-specific CTL responses in cotton rats

Respiratory syncytial virus (RSV) is a common cause of serious lower respiratory tract illnesses in infants. Natural infections with RSV provide limited protection against reinfection because of inefficient immunological responses that do not induce long-term memory. RSV natural infection has been shown to induce unbalanced immune response. The effective clearance of RSV is known to require the induction of a balanced Th1/Th2 immune response, which involves the induction of cytotoxic T lymphocytes (CTL). In our previous study, recombinant AIK-C measles vaccine strains MVAIK/RSV/F and MVAIK/RSV/G were developed, which expressed the RSV fusion (F) protein or glycoprotein (G). These recombinant viruses elicited antibody responses against RSV in cotton rats, and no infectious virus was recovered, but small amounts of infiltration of inflammatory cells were observed in the lungs following RSV challenge. In the present study, recombinant AIK-C measles vaccine strains MVAIK/RSV/M2-1 and MVAIK/RSV/NP were developed, expressing RSV M2-1 or Nucleoprotein (NP), respectively. These viruses exhibited temperature-sensitivity (ts), which was derived from AIK-C, and expressed respective RSV antigens. The intramuscular inoculation of cotton rats with the recombinant measles virus led to the induction of CD8(+) IFN-γ(+) cells. No infectious virus was recovered from a lung homogenate following the challenge. A Histological examination of the lungs revealed a significant reduction in inflammatory reactions without alveolar damage. These results support the recombinant measles viruses being effective vaccine candidates against RSV that induce RSV-specific CTL responses with or without the development of an antibody response.

A novel influenza virus hemagglutinin-respiratory syncytial virus (RSV) fusion protein subunit vaccine against influenza and RSV

Influenza A virus and respiratory syncytial virus (RSV) cause substantial morbidity and mortality afflicting the ends of the age spectrum during the autumn through winter months in the United States. The benefit of vaccination against RSV and influenza using a subunit vaccine to enhance immunity and neutralizing antibody was investigated. Influenza virus hemagglutinin (HA) and RSV fusion (F) protein were tested as vaccine components alone and in combination to explore the adjuvant properties of RSV F protein on HA immunity. Mice vaccinated with HA and F exhibited robust immunity that, when challenged, had reduced viral burden for both influenza and RSV. These studies show an enhancing and cross-protective benefit of F protein for anti-HA immunity.

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 immunity and immunopathology: lessons from respiratory syncytial virus

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants and is an important source of morbidity and mortality in the elderly and immunocompromised. This review will discuss the humoral and cellular adaptive immune responses to RSV infection and how these responses are shaped in the immature immune system of the infant and the aged environment of the elderly. Furthermore, we will provide an overview of our current understanding of the role the various arms of the adaptive immune response play in mediating the delicate balance between the successful elimination of the virus from the host and the induction of immunopathology. Efficacious immunization against RSV remains a high priority within the field and we will highlight recent advances made in vaccine design.

Respiratory syncytial virus impairs T cell activation by preventing synapse assembly with dendritic cells

Respiratory syncytial virus (RSV) infection is one of the leading causes of infant hospitalization and a major health and economic burden worldwide. Infection with this virus induces an exacerbated innate proinflammatory immune response characterized by abundant immune cell infiltration into the airways and lung tissue damage. RSV also impairs the induction of an adequate adaptive T cell immune response, which favors virus pathogenesis. Unfortunately, to date there are no efficient vaccines against this virus. Recent in vitro and in vivo studies suggest that RSV infection can prevent T cell activation, a phenomenon attributed in part to cytokines and chemokines secreted by RSV-infected cells. Efficient immunity against viruses is promoted by dendritic cells (DCs), professional antigen-presenting cells, that prime antigen-specific helper and cytotoxic T cells. Therefore, it would be to the advantage of RSV to impair DC function and prevent the induction of T cell immunity. Here, we show that, although RSV infection induces maturation of murine DCs, these cells are rendered unable to activate antigen-specific T cells. Inhibition of T cell activation by RSV was observed independently of the type of TCR ligand on the DC surface and applied to cognate-, allo-, and superantigen stimulation. As a result of exposure to RSV-infected DCs, T cells became unresponsive to subsequent TCR engagement. RSV-mediated impairment in T cell activation required DC-T cell contact and involved inhibition of immunological synapse assembly among these cells. Our data suggest that impairment of immunological synapse could contribute to RSV pathogenesis by evading adaptive immunity and reducing T cell-mediated virus clearance.