Long-term protection from SARS coronavirus infection conferred by a single immunization with an attenuated VSV-based vaccine

Chimeric coronavirus-like particles carrying severe acute respiratory syndrome coronavirus (SCoV) S protein protect mice against challenge with SCoV

We tested the efficacy of coronavirus-like particles (VLPs) for protecting mice against severe acute respiratory syndrome coronavirus (SCoV) infection. Coexpression of SCoV S protein and E, M and N proteins of mouse hepatitis virus in 293T or CHO cells resulted in the efficient production of chimeric VLPs carrying SCoV S protein. Balb/c mice inoculated with a mixture of chimeric VLPs and alum twice at an interval of four weeks were protected from SCoV challenge, as indicated by the absence of infectious virus in the lungs. The same groups of mice had high levels of SCoV-specific neutralizing antibodies, while mice in the negative control groups, which were not immunized with chimeric VLPs, failed to manifest neutralizing antibodies, suggesting that SCoV-specific neutralizing antibodies are important for the suppression of viral replication within the lungs. Despite some differences in the cellular composition of inflammatory infiltrates, we did not observe any overt lung pathology in the chimeric-VLP-treated mice, when compared to the negative control mice. Our results show that chimeric VLP can be an effective vaccine strategy against SCoV infection.

Severe acute respiratory syndrome coronavirus as an agent of emerging and reemerging infection

Before the emergence of severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) in 2003, only 12 other animal or human coronaviruses were known. The discovery of this virus was soon followed by the discovery of the civet and bat SARS-CoV and the human coronaviruses NL63 and HKU1. Surveillance of coronaviruses in many animal species has increased the number on the list of coronaviruses to at least 36. The explosive nature of the first SARS epidemic, the high mortality, its transient reemergence a year later, and economic disruptions led to a rush on research of the epidemiological, clinical, pathological, immunological, virological, and other basic scientific aspects of the virus and the disease. This research resulted in over 4,000 publications, only some of the most representative works of which could be reviewed in this article. The marked increase in the understanding of the virus and the disease within such a short time has allowed the development of diagnostic tests, animal models, antivirals, vaccines, and epidemiological and infection control measures, which could prove to be useful in randomized control trials if SARS should return. The findings that horseshoe bats are the natural reservoir for SARS-CoV-like virus and that civets are the amplification host highlight the importance of wildlife and biosecurity in farms and wet markets, which can serve as the source and amplification centers for emerging infections.

Attenuation of recombinant vesicular stomatitis virus-human immunodeficiency virus type 1 vaccine vectors by gene translocations and g gene truncation reduces neurovirulence and enhances immunogenicity in mice

Recombinant vesicular stomatitis virus (rVSV) has shown great potential as a new viral vector for vaccination. However, the prototypic rVSV vector described previously was found to be insufficiently attenuated for clinical evaluation when assessed for neurovirulence in nonhuman primates. Here, we describe the attenuation, neurovirulence, and immunogenicity of rVSV vectors expressing human immunodeficiency virus type 1 Gag. These rVSV vectors were attenuated by combinations of the following manipulations: N gene translocations (N4), G gene truncations (CT1 or CT9), noncytopathic M gene mutations (Mncp), and positioning of the gag gene into the first position of the viral genome (gag1). The resulting N4CT1-gag1, N4CT9-gag1, and MncpCT1-gag1 vectors demonstrated dramatically reduced neurovirulence in mice following direct intracranial inoculation. Surprisingly, in spite of a very high level of attenuation, the N4CT1-gag1 and N4CT9-gag1 vectors generated robust Gag-specific immune responses following intramuscular immunization that were equivalent to or greater than immune responses generated by the more virulent prototypic vectors. MncpCT1-gag1 also induced Gag-specific immune responses following intramuscular immunization that were equivalent to immune responses generated by the prototypic rVSV vector. Placement of the gag gene in the first position of the VSV genome was associated with increased in vitro expression of Gag protein, in vivo expression of Gag mRNA, and enhanced immunogenicity of the vector. These findings demonstrate that through directed manipulation of the rVSV genome, vectors that have reduced neurovirulence and enhanced immunogenicity can be made.

Newcastle disease virus, a host range-restricted virus, as a vaccine vector for intranasal immunization against emerging pathogens

The international outbreak of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) in 2002-2003 highlighted the need to develop pretested human vaccine vectors that can be used in a rapid response against newly emerging pathogens. We evaluated Newcastle disease virus (NDV), an avian paramyxovirus that is highly attenuated in primates, as a topical respiratory vaccine vector with SARS-CoV as a test pathogen. Complete recombinant NDV was engineered to express the SARS-CoV spike S glycoprotein, the viral neutralization and major protective antigen, from an added transcriptional unit. African green monkeys immunized through the respiratory tract with two doses of the vaccine developed a titer of SARS-CoV-neutralizing antibodies comparable with the robust secondary response observed in animals that have been immunized with a different experimental SARS-CoV vaccine and challenged with SARS-CoV. When animals immunized with NDV expressing S were challenged with a high dose of SARS-CoV, direct viral assay of lung tissues taken by necropsy at the peak of viral replication demonstrated a 236- or 1,102-fold (depending on the NDV vector construct) mean reduction in pulmonary SARS-CoV titer compared with control animals. NDV has the potential for further development as a pretested, highly attenuated, intranasal vector to be available for expedited vaccine development for humans, who generally lack preexisting immunity against NDV.

Vesicular stomatitis virus vectors expressing avian influenza H5 HA induce cross-neutralizing antibodies and long-term protection

Given the lethality of H5N1 avian influenza viruses (AIV) and the recurring spread from poultry to humans, an effective vaccine against H5N1 viruses may be needed to prevent a pandemic. We generated experimental vaccine vectors based on recombinant vesicular stomatitis virus (VSV) expressing the H5 hemagglutinin (HA) from an H5N1 virus isolated in 1997. The HA gene was expressed either from an attenuated wild-type VSV vector or from a single-cycle vector containing a deletion of the VSV G gene. We found that all of the vectors induced potent neutralizing antibody titers against the homologous and antigenically heterologous H5N1 viruses isolated in 2004 and 2005. Vaccination of mice with any combination of prime or prime/boost vectors provided long-lasting protection (>7 months) against challenge with AIV, even in animals receiving a single dose of single-cycle vaccine. Our data indicate that these recombinants are promising vaccine candidates for pandemic influenza.

Animal models and vaccines for SARS-CoV infection

We summarize findings of SARS-CoV infections in several animal models each of which support viral replication in lungs accompanied by histopathological changes and/or clinical signs of illness to varying degrees. New findings are reported on SARS-CoV replication and associated pathology in two additional strains (C57BL/6 and 129S6) of aged mice. We also provide new comparative data on viral replication and associated pathology following infection of golden Syrian hamsters with various SARS-CoV strains and report the levels of neutralizing antibody titers following these infections and the cross-protective efficacy of infection with these strains in protecting against heterologous challenge. Finally, we summarize findings of a variety of vaccine approaches and discuss the available in vitro and in vivo data addressing the potential for disease enhancement following re-infection in animals previously vaccinated against or infected with SARS-CoV.

Requirement for CD4 T Cell Help in Maintenance of Memory CD8 T Cell Responses Is Epitope Dependent

CD4 Th cells play critical roles in stimulating Ab production and in generating primary or maintaining memory CTL. The requirement for CD4 help in generating and maintaining CTL responses has been reported to vary depending on the vector or method used for immunization. In this study, we examined the requirement for CD4 T cell help in generating and maintaining CTL responses to an experimental AIDS vaccine vector based on live recombinant vesicular stomatitis virus (VSV) expressing HIV Env protein. We found that primary CD8 T cell responses and short-term memory to HIV Env and VSV nucleocapsid (VSV N) proteins were largely intact in CD4 T cell-deficient mice. These responses were efficiently recalled at 30 days postinfection by boosting with vaccinia recombinants expressing HIV Env or VSV N. However, by 60 days postinfection, the memory/recall response to VSV N was lost in CD4-deficient mice, while the recall response HIV Env was partially maintained in the same animals for at least 90 days. This result indicates that there are epitope-specific requirements for CD4 help in the maintenance of memory CD8 T cell responses. Our results also suggest that choice of epitopes might be critical in an AIDS vaccine designed to protect against disease in the context of reduced or declining CD4 T cell help.

Synergistic attenuation of vesicular stomatitis virus by combination of specific G gene truncations and N gene translocations

A variety of rational approaches to attenuate growth and virulence of vesicular stomatitis virus (VSV) have been described previously. These include gene shuffling, truncation of the cytoplasmic tail of the G protein, and generation of noncytopathic M gene mutants. When separately introduced into recombinant VSV (rVSV), these mutations gave rise to viruses distinguished from their "wild-type" progenitor by diminished reproductive capacity in cell culture and/or reduced cytopathology and decreased pathogenicity in vivo. However, histopathology data from an exploratory nonhuman primate neurovirulence study indicated that some of these attenuated viruses could still cause significant levels of neurological injury. In this study, additional attenuated rVSV variants were generated by combination of the above-named three distinct classes of mutation. The resulting combination mutants were characterized by plaque size and growth kinetics in cell culture, and virulence was assessed by determination of the intracranial (IC) 50% lethal dose (LD(50)) in mice. Compared to virus having only one type of attenuating mutation, all of the mutation combinations examined gave rise to virus with smaller plaque phenotypes, delayed growth kinetics, and 10- to 500-fold-lower peak titers in cell culture. A similar pattern of attenuation was also observed following IC inoculation of mice, where differences in LD(50) of many orders of magnitude between viruses containing one and two types of attenuating mutation were sometimes seen. The results show synergistic rather than cumulative increases in attenuation and demonstrate a new approach to the attenuation of VSV and possibly other viruses.

Utility of the aged BALB/c mouse model to demonstrate prevention and control strategies for severe acute respiratory syndrome coronavirus (SARS-CoV)

The causative agent of Severe Acute Respiratory Syndrome (SARS) was identified as a coronavirus (CoV) following the outbreak of 2002–2003. There are currently no licensed vaccines or treatments for SARS-CoV infections. Potential prevention and control strategies that show promise in vitro must be evaluated in animal models. The aged BALB/c mouse model for SARS supports a high level of viral replication in association with clinical illness and disease that mimics SARS in the elderly. We tested two preventive strategies, vaccination and passive transfer of serum antibody, to determine the extent of protection achieved against SARS-CoV challenge in this model. These approaches were able to achieve or induce antibody titers sufficient to reduce viral load, protect from weight loss and reduce or eliminate histopathologic changes in the lungs of aged mice. This study validates the utility of the aged BALB/c mouse model for evaluation of the efficacy of vaccines and immunoprophylaxis.

Replication and propagation of attenuated vesicular stomatitis virus vectors in vivo: vector spread correlates with induction of immune responses and persistence of genomic RNA

Live-attenuated vesicular stomatitis virus (VSV) vectors expressing foreign antigens induce potent immune responses and protect against viral diseases in animal models. Highly attenuated (VSV-CT1) or single-cycle VSV (VSVDeltaG) vectors induce immune responses lower than those generated by attenuated wild-type VSV vectors when given intranasally. We show here that reduced spread of the more highly attenuated or single-cycle vectors to other organs, including lymph nodes, correlates with the reduction in the immune responses. A reverse transcription, real-time PCR assay for VSV genomic RNA (gRNA) sequences showed long-term persistence of gRNA from replicating vectors in lymph nodes, long after viral clearance. Such persistence may be important for induction of potent immune responses by VSV vectors.

Vaccine efficacy in senescent mice challenged with recombinant SARS-CoV bearing epidemic and zoonotic spike variants

BACKGROUND

In 2003, severe acute respiratory syndrome coronavirus (SARS-CoV) was identified as the etiological agent of severe acute respiratory syndrome, a disease characterized by severe pneumonia that sometimes results in death. SARS-CoV is a zoonotic virus that crossed the species barrier, most likely originating from bats or from other species including civets, raccoon dogs, domestic cats, swine, and rodents. A SARS-CoV vaccine should confer long-term protection, especially in vulnerable senescent populations, against both the 2003 epidemic strains and zoonotic strains that may yet emerge from animal reservoirs. We report the comprehensive investigation of SARS vaccine efficacy in young and senescent mice following homologous and heterologous challenge.

METHODS AND FINDINGS

Using Venezuelan equine encephalitis virus replicon particles (VRP) expressing the 2003 epidemic Urbani SARS-CoV strain spike (S) glycoprotein (VRP-S) or the nucleocapsid (N) protein from the same strain (VRP-N), we demonstrate that VRP-S, but not VRP-N vaccines provide complete short- and long-term protection against homologous strain challenge in young and senescent mice. To test VRP vaccine efficacy against a heterologous SARS-CoV, we used phylogenetic analyses, synthetic biology, and reverse genetics to construct a chimeric virus (icGDO3-S) encoding a synthetic S glycoprotein gene of the most genetically divergent human strain, GDO3, which clusters among the zoonotic SARS-CoV. icGD03-S replicated efficiently in human airway epithelial cells and in the lungs of young and senescent mice, and was highly resistant to neutralization with antisera directed against the Urbani strain. Although VRP-S vaccines provided complete short-term protection against heterologous icGD03-S challenge in young mice, only limited protection was seen in vaccinated senescent animals. VRP-N vaccines not only failed to protect from homologous or heterologous challenge, but resulted in enhanced immunopathology with eosinophilic infiltrates within the lungs of SARS-CoV-challenged mice. VRP-N-induced pathology presented at day 4, peaked around day 7, and persisted through day 14, and was likely mediated by cellular immune responses.

CONCLUSIONS

This study identifies gaps and challenges in vaccine design for controlling future SARS-CoV zoonosis, especially in vulnerable elderly populations. The availability of a SARS-CoV virus bearing heterologous S glycoproteins provides a robust challenge inoculum for evaluating vaccine efficacy against zoonotic strains, the most likely source of future outbreaks.

Neurovirulence properties of recombinant vesicular stomatitis virus vectors in non-human primates

Although vesicular stomatitis virus (VSV) neurovirulence and pathogenicity in rodents have been well studied, little is known about VSV pathogenicity in non-human primates. To address this question, we measured VSV viremia, shedding, and neurovirulence in macaques. Following intranasal inoculation, macaques shed minimal recombinant VSV (rVSV) in nasal washes for 1 day post-inoculation; viremia was not detected. Following intranasal inoculation of macaques, wild type (wt) VSV, rVSV, and two rVSV-HIV vectors showed no evidence of spread to CNS tissues. However, macaques inoculated intrathalamically with wt VSV developed severe neurological disease. One of four macaques receiving rVSV developed clinical and histological signs similar to the wt group, while the remaining three macaques in this group and all of the macaques in the rVSV-HIV vector groups showed no clinical signs of disease and reduced severity of histopathology compared to the wt group. The implications of these findings for rVSV vaccine development are discussed.

Receptor-binding domain of SARS-CoV spike protein induces long-term protective immunity in an animal model

Development of effective vaccines against severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) is still a priority in prevention of re-emergence of SARS. Our previous studies have shown that the receptor-binding domain (RBD) of SARS-CoV spike (S) protein elicits highly potent neutralizing antibody responses in the immunized animals. But it is unknown whether RBD can also induce protective immunity in an animal model, a key aspect for vaccine development. In this study, BALB/c mice were vaccinated intramuscularly (i.m.) with 10 μg of RBD-Fc (RBD fused with human IgG1 Fc) and boosted twice at 3-week intervals and one more time at 12th month. Humoral immune responses of vaccinated mice were investigated for up to 12 months at a 1-month interval and the neutralizing titers of produced antibodies were reported at months 0, 3, 6 and 12 post-vaccination. Mice were challenged with the homologous strain of SARS-CoV 5 days after the last boost, and sacrificed 5 days after the challenge. Mouse lung tissues were collected for detection of viral load, virus replication and histopathological effects. Our results showed that RBD-Fc vaccination induced high titer of S-specific antibodies with long-term and potent SARS-CoV neutralizing activity. Four of five vaccinated mice were protected from subsequent SARS-CoV challenge because no significant virus replication, and no obvious histopathological changes were found in the lung tissues of the vaccinated mice challenged with SARS-CoV. Only one vaccinated mouse had mild alveolar damage in the lung tissues. In contrast, high copies of SARS-CoV RNA and virus replication were detected, and pathological changes were observed in the lung tissues of the control mice. In conclusion, our findings suggest that RBD, which can induce protective antibodies to SARS-CoV, may be further developed as a safe and effective SARS subunit vaccine.

Emerging respiratory viruses: challenges and vaccine strategies

The current threat of avian influenza to the human population, the potential for the reemergence of severe acute respiratory syndrome (SARS)-associated coronavirus, and the identification of multiple novel respiratory viruses underline the necessity for the development of therapeutic and preventive strategies to combat viral infection. Vaccine development is a key component in the prevention of widespread viral infection and in the reduction of morbidity and mortality associated with many viral infections. In this review we describe the different approaches currently being evaluated in the development of vaccines against SARS-associated coronavirus and avian influenza viruses and also highlight the many obstacles encountered in the development of these vaccines. Lessons learned from current vaccine studies, coupled with our increasing knowledge of the host and viral factors involved in viral pathogenesis, will help to increase the speed with which efficacious vaccines targeting newly emerging viral pathogens can be developed.

Recombinant vesicular stomatitis virus as an HIV-1 vaccine vector

Recombinant vesicular stomatitis virus (rVSV) is currently under evaluation as a human immunodeficiency virus (HIV)-1 vaccine vector. The most compelling reasons to develop rVSV as a vaccine vector include a very low seroprevalence in humans, the ability to infect and robustly express foreign antigens in a broad range of cells, and vigorous growth in continuous cell lines used for vaccine manufacture. Numerous preclinical studies with rVSV vectors expressing antigens from a variety of human pathogens have demonstrated the versatility, flexibility, and potential efficacy of the rVSV vaccine platform. When administered to nonhuman primates (NHPs), rVSV vectors expressing HIV-1 Gag and Env elicited robust HIV-1-specific cellular and humoral immune responses, and animals immunized with rVSV vectors expressing simian immunodeficiency virus (SIV) Gag and HIV Env were protected from AIDS after challenge with a pathogenic SIV/HIV recombinant. However, results from an exploratory neurovirulence study in NHPs indicated that these prototypic rVSV vectors might not be adequately attenuated for widespread use in human populations. To address this safety concern, a variety of different attenuation strategies, designed to produce a range of further attenuated rVSV vectors, are currently under investigation. Additional modifications of further attenuated rVSV vectors to upregulate expression of HIV-1 antigens and coexpress molecular adjuvants are also being developed in an effort to balance immunogenicity and attenuation.

An optimized vaccine vector based on recombinant vesicular stomatitis virus gives high-level, long-term protection against Yersinia pestis challenge

We have developed recombinant vesicular stomatitis virus (VSV) vectors expressing the Yersinia pestis lcrV gene. These vectors, given intranasally to mice, induced high antibody titers to the LcrV protein and protected against intranasal (pulmonary) challenge with Y. pestis. High-level protection was dependent on using an optimized VSV vector that expressed high levels of the LcrV protein from an lcrV gene placed in the first position in the VSV genome, followed by a single boost. This VSV-based vaccine vector system has potential as a plague vaccine protecting against virulent strains lacking the F1 protein.

Animal models and antibody assays for evaluating candidate SARS vaccines: summary of a technical meeting 25-26 August 2005, London, UK

Severe acute respiratory syndrome (SARS) emerged in the Guangdong province of China in late 2002 and spread to 29 countries. By the end of the outbreak in July 2003, the CDC and WHO reported 8437 cases with a 9.6% case fatality rate. The disease was caused by a previously unrecognized coronavirus, SARS-CoV. Drawing on experience with animal coronavirus vaccines, several vaccine candidates have been developed and evaluated in pre-clinical trials. Available data suggest that vaccines should be based on the the 180kDa viral spike protein, S, the only significant neutralization antigen capable of inducing protective immune responses in animals. In the absence of clinical cases of SARS, candidate vaccines should be evaluated for efficacy in animal models, and although it is uncertain whether the United States Food and Drug Administration's "animal rule" would apply to licensure of a SARS vaccine, it is important to develop standardized animal models and immunological assays in preparation for this eventuality. This report summarizes the recommendations from a WHO Technical Meeting on Animal Models and Antibody Assays for Evaluating Candidate SARS Vaccines held on 25-26 August 2005 in South Mimms, UK, provides guidance on the use of animal models, and outlines the steps to develop standard reagents and assays for immunological evaluation of candidate SARS vaccines.

Is there an ideal animal model for SARS?

The outbreak of severe acute respiratory syndrome (SARS) in 2003 was controlled by public health measures at a time when specific interventions such as antiviral drugs, vaccines and immunotherapy were not available. Since then, several animal models have been developed for the study of SARS and, although no model replicates the human disease in all aspects, the use of animal models for SARS has led to the establishment of several important principles for vaccine and immunotherapy. Consistency and reproducibility of findings in a given model must be demonstrated to establish the superiority of one model over others. Here, we suggest aspects of an ideal animal model for studies of SARS pathogenesis and vaccine development and present our assessment of the strengths and limitations of the current animal models for SARS.

Recombinant vesicular stomatitis virus vectors expressing herpes simplex virus type 2 gD elicit robust CD4+ Th1 immune responses and are protective in mouse and guinea pig models of vaginal challenge

Recombinant vesicular stomatitis virus (rVSV) vectors offer an attractive approach for the induction of robust cellular and humoral immune responses directed against human pathogen target antigens. We evaluated rVSV vectors expressing full-length glycoprotein D (gD) from herpes simplex virus type 2 (HSV-2) in mice and guinea pigs for immunogenicity and protective efficacy against genital challenge with wild-type HSV-2. Robust Th1-polarized anti-gD immune responses were demonstrated in the murine model as measured by induction of gD-specific cytotoxic T lymphocytes and increased gamma interferon expression. The isotype makeup of the serum anti-gD immunoglobulin G (IgG) response was consistent with the presence of a Th1-CD4+ anti-gD response, characterized by a high IgG2a/IgG1 IgG subclass ratio. Functional anti-HSV-2 neutralizing serum antibody responses were readily demonstrated in both guinea pigs and mice that had been immunized with rVSV-gD vaccines. Furthermore, guinea pigs and mice were prophylactically protected from genital challenge with high doses of wild-type HSV-2. In addition, guinea pigs were highly protected against the establishment of latent infection as evidenced by low or absent HSV-2 genome copies in dorsal root ganglia after virus challenge. In summary, rVSV-gD vectors were successfully used to elicit potent anti-gD Th1-like cellular and humoral immune responses that were protective against HSV-2 disease in guinea pigs and mice.

Induction of protective immunity against severe acute respiratory syndrome coronavirus (SARS-CoV) infection using highly attenuated recombinant vaccinia virus DIs

SARS-coronavirus (SARS-CoV) has recently been identified as the causative agent of SARS. We constructed a series of recombinant DIs (rDIs), a highly attenuated vaccinia strain, expressing a gene encoding four structural proteins (E, M, N and S) of SARS-CoV individually or simultaneously. These rDIs elicited SARS-CoV-specific serum IgG antibody and T-cell responses in vaccinated mice following intranasal or subcutaneous administration. Mice that were subcutaneously vaccinated with rDIs expressing S protein with or without other structural proteins induced a high level of serum neutralizing IgG antibodies and demonstrated marked protective immunity against SARS-CoV challenge in the absence of a mucosal IgA response. These results indicate that the potent immune response elicited by subcutaneous injection of rDIs containing S is able to control mucosal infection by SARS-CoV. Thus, replication-deficient DIs constructs hold promise for the development of a safe and potent SARS vaccine.

Immunization with SARS-CoV S DNA vaccine generates memory CD4+ and CD8+ T cell immune responses

An effective vaccine for severe acute respiratory syndrome (SARS) will probably require the generation and maintenance of both humoral and cellular immune responses. It has been reported that after natural infection in humans and immunization in animals with SARS-CoV vaccine, antibody is produced and persistent for a long period of time. In the present study, mice were immunized i.m. with SARS-CoV S DNA vaccine, and three different methods (ELISA, ELISPOT and FACS) were used to evaluate the immune responses when the cells were stimulated in vitro with a pool of peptides overlapping entire SARS spike protein. The results show that prime-immunization with SARS-CoV S DNA vaccine can induce both CD4⁺ and CD8⁺ T cell responses. Boosting with the same vaccine enhances CD4⁺ and CD8⁺ T cell responses in both lymphoid and nonlymphoid organs and were persistent over two months. The SARS-CoV S-specific CD4⁺ and CD8⁺ T cells were CD62L⁻, a marker for memory cells, and −30 to 50% of the cells expressed IL-7Rα (CD127), a marker for the capacity of effector cells to develop into memory cells. In addition, immunization with the DNA vaccine elicited high levels of antibody production. Taken together, these data demonstrate that immunization with SARS-CoV S DNA vaccine can generate antigen-specific humoral and cellular immune responses that may contribute to long-term protection.

Severe acute respiratory syndrome (SARS) coronavirus: application of monoclonal antibodies and development of an effective vaccine

SARS-CoV is a new type of human coronavirus identified as a causative agent of severe acute respiratory syndrome (SARS). On the occasion of the SARS outbreak, various monoclonal antibodies (mAbs) against SARS-CoV have been developed and applied for diagnosis, clinical management and basic research. In this review, we overview the biochemical and functional properties and applications of these SARS-CoV mAbs. We also focus on a variety of vaccines currently under development and discuss the immune response elicited by these vaccines in animal models, hopefully to better understand what we need to do next to fight against newly emerging pathogens in the future.

Use of recombinant virus-vectored tuberculosis vaccines for respiratory mucosal immunization

Recombinant virus-vectored TB vaccines represent the most promising vaccine platform for boosting the protective immunity mediated by parenteral BCG prime immunization. A major advantage associated with virus-vectored vaccines is that they are potent respiratory mucosa-deliverable vaccines. A recombinant replication-deficient adenoviral (Ad) vector was engineered to express Mycobacterium tuberculosis (M.tb) Ag85A. Single administration of this Ad vaccine via the intranasal, but not intramuscular, route provided potent immune protection from pulmonary M.tb challenge. Respiratory mucosal boosting immunization with Ad vaccine was effective in enhancing T-cell activation and immune protection following parenteral DNA or BCG prime immunization. We have also recently developed a recombinant vesicular stomatitis virus-vectored (VSV) TB vaccine. Ad and VSV vector systems will be complementary to each other for BCG prime-virus vaccine boost immunization protocols.

Coronavirus pathogenesis and the emerging pathogen severe acute respiratory syndrome coronavirus

Coronaviruses are a family of enveloped, single-stranded, positive-strand RNA viruses classified within the Nidovirales order. This coronavirus family consists of pathogens of many animal species and of humans, including the recently isolated severe acute respiratory syndrome coronavirus (SARS-CoV). This review is divided into two main parts; the first concerns the animal coronaviruses and their pathogenesis, with an emphasis on the functions of individual viral genes, and the second discusses the newly described human emerging pathogen, SARS-CoV. The coronavirus part covers (i) a description of a group of coronaviruses and the diseases they cause, including the prototype coronavirus, murine hepatitis virus, which is one of the recognized animal models for multiple sclerosis, as well as viruses of veterinary importance that infect the pig, chicken, and cat and a summary of the human viruses; (ii) a short summary of the replication cycle of coronaviruses in cell culture; (iii) the development and application of reverse genetics systems; and (iv) the roles of individual coronavirus proteins in replication and pathogenesis. The SARS-CoV part covers the pathogenesis of SARS, the developing animal models for infection, and the progress in vaccine development and antiviral therapies. The data gathered on the animal coronaviruses continue to be helpful in understanding SARS-CoV.

Coronavirus pathogenesis and the emerging pathogen severe acute respiratory syndrome coronavirus

Coronaviruses are a family of enveloped, single-stranded, positive-strand RNA viruses classified within the Nidovirales order. This coronavirus family consists of pathogens of many animal species and of humans, including the recently isolated severe acute respiratory syndrome coronavirus (SARS-CoV). This review is divided into two main parts; the first concerns the animal coronaviruses and their pathogenesis, with an emphasis on the functions of individual viral genes, and the second discusses the newly described human emerging pathogen, SARS-CoV. The coronavirus part covers (i) a description of a group of coronaviruses and the diseases they cause, including the prototype coronavirus, murine hepatitis virus, which is one of the recognized animal models for multiple sclerosis, as well as viruses of veterinary importance that infect the pig, chicken, and cat and a summary of the human viruses; (ii) a short summary of the replication cycle of coronaviruses in cell culture; (iii) the development and application of reverse genetics systems; and (iv) the roles of individual coronavirus proteins in replication and pathogenesis. The SARS-CoV part covers the pathogenesis of SARS, the developing animal models for infection, and the progress in vaccine development and antiviral therapies. The data gathered on the animal coronaviruses continue to be helpful in understanding SARS-CoV.