A Highly Immunogenic and Protective Middle East Respiratory Syndrome Coronavirus Vaccine Based on a Recombinant Measles Virus Vaccine Platform.

UNLABELLED: In 2012, the first cases of infection with the Middle East respiratory syndrome coronavirus (MERS-CoV) were identified. Since then, more than 1,000 cases of MERS-CoV infection have been confirmed; infection is typically associated with considerable morbidity and, in approximately 30% of cases, mortality. Currently, there is no protective vaccine available. Replication-competent recombinant measles virus (MV) expressing foreign antigens constitutes a promising tool to induce protective immunity against corresponding pathogens. Therefore, we generated MVs expressing the spike glycoprotein of MERS-CoV in its full-length (MERS-S) or a truncated, soluble variant of MERS-S (MERS-solS). The genes encoding MERS-S and MERS-solS were cloned into the vaccine strain MVvac2 genome, and the respective viruses were rescued (MVvac2-CoV-S and MVvac2-CoV-solS). These recombinant MVs were amplified and characterized at passages 3 and 10. The replication of MVvac2-CoV-S in Vero cells turned out to be comparable to that of the control virus MVvac2-GFP (encoding green fluorescent protein), while titers of MVvac2-CoV-solS were impaired approximately 3-fold. The genomic stability and expression of the inserted antigens were confirmed via sequencing of viral cDNA and immunoblot analysis. In vivo, immunization of type I interferon receptor-deficient (IFNAR(-/-))-CD46Ge mice with 2 × 10(5) 50% tissue culture infective doses of MVvac2-CoV-S(H) or MVvac2-CoV-solS(H) in a prime-boost regimen induced robust levels of both MV- and MERS-CoV-neutralizing antibodies. Additionally, induction of specific T cells was demonstrated by T cell proliferation, antigen-specific T cell cytotoxicity, and gamma interferon secretion after stimulation of splenocytes with MERS-CoV-S presented by murine dendritic cells. MERS-CoV challenge experiments indicated the protective capacity of these immune responses in vaccinated mice. IMPORTANCE: Although MERS-CoV has not yet acquired extensive distribution, being mainly confined to the Arabic and Korean peninsulas, it could adapt to spread more readily among humans and thereby become pandemic. Therefore, the development of a vaccine is mandatory. The integration of antigen-coding genes into recombinant MV resulting in coexpression of MV and foreign antigens can efficiently be achieved. Thus, in combination with the excellent safety profile of the MV vaccine, recombinant MV seems to constitute an ideal vaccine platform. The present study shows that a recombinant MV expressing MERS-S is genetically stable and induces strong humoral and cellular immunity against MERS-CoV in vaccinated mice. Subsequent challenge experiments indicated protection of vaccinated animals, illustrating the potential of MV as a vaccine platform with the potential to target emerging infections, such as MERS-CoV.

Evaluation of a modified vaccinia virus Ankara (MVA)-based candidate pandemic influenza A/H1N1 vaccine in the ferret model.

The zoonotic transmissions of highly pathogenic avian influenza viruses of the H5N1 subtype that have occurred since 1997 have sparked the development of novel influenza vaccines. The advent of reverse genetics technology, cell-culture production techniques and novel adjuvants has improved the vaccine strain preparation, production process and immunogenicity of the vaccines, respectively, and has accelerated the availability of pandemic influenza vaccines. However, there is still room for improvement, and alternative vaccine preparations can be explored, such as viral vectors. Modified vaccinia virus Ankara (MVA), originally developed as a safe smallpox vaccine, can be exploited as a viral vector and has many favourable properties. Recently, we have demonstrated that an MVA-based vaccine could protect mice and macaques against infection with highly pathogenic influenza viruses of the H5N1 subtype. In the present study, recombinant MVA expressing the haemagglutinin (HA) gene of pandemic influenza A/H1N1 virus was evaluated in the ferret model. A single immunization induced modest antibody responses and afforded only modest protection against the development of severe disease upon infection with a 2009(H1N1) strain. In contrast, two immunizations induced robust antibody responses and protected ferrets from developing severe disease, confirming that MVA is an attractive influenza vaccine production platform.

Evaluation of vaccination strategies against infection with feline immunodeficiency virus (FIV) based on recombinant viral vectors expressing FIV Rev and OrfA.

In recent years it has become clear that cell-mediated immunity is playing a role in the control of lentivirus infections. In particular, cytotoxic T lymphocyte responses have been associated with improved outcome of infection, especially those directed against the regulatory proteins like Rev and Tat, which are expressed early after infection. Therefore, there is considerable interest in lentiviral vaccine candidates that can induce these types of immune responses. In the present study, we describe the construction and characterisation of expression vectors based on recombinant Semliki Forest virus system and modified vaccinia virus Ankara for the expression of feline immunodeficiency virus (FIV) accessory proteins Rev and OrfA. These recombinant viral vectors were used to immunize cats using a prime-boost regimen and the protective efficacy of this vaccination strategy was assessed after challenge infection of immunized cats with FIV.

T cell responses to respiratory syncytial virus fusion and attachment proteins in human peripheral blood mononuclear cells.

The cellular immune response to respiratory syncytial virus (RSV) is considered important in both protection and immunopathogenesis. We have studied the HLA class I- and class II-restricted T cell responses to RSV fusion (F) and attachment (G) proteins in peripheral blood mononuclear cells (PBMCs) obtained from healthy young adults. PBMCs were stimulated with autologous cells infected with recombinant modified vaccinia virus Ankara (rMVA) expressing RSV F (rMVA-F) or G (rMVA-G). In rMVA-F-stimulated bulk cultures F-specific CD4(+) and CD8(+) T cell responses were demonstrated, whereas in rMVA-G-stimulated cultures only G-specific CD4(+) T cell responses were detected. Using a set of overlapping peptides spanning the F protein, a number of the F-specific T cell responses could be mapped to different antigenic regions, whereas for the G protein only CD4(+) T cell responses recognizing the central conserved domain could be detected. These results suggest that the RSV glycoprotein-specific T cell response is directed to a number of different epitopes. Further studies must be performed to confirm the apparent inability of the RSV G protein to induce CD8(+) T cell responses. The rMVA-based in vitro stimulation protocol will be useful to define protein-specific T cell responses in different viral systems.