Preliminary human trial of inactivated golden hamster kidney cell (GHKC) vaccine against haemorrhagic fever with renal syndrome (HFRS)

Antiviral Therapy of Haemorrhagic Fevers and Arbovirus Infections

RNA viruses of the families Arena-, Bunya-, Filo-, Flavi-and Togaviridae cause illness in humans ranging from mild, non-specific febrile syndromes to fulminant, lethal haemorrhagic fever. They are transmitted from animals to humans and from human to human by arthropods, aerosols or contact with body fluids. Antiviral compounds, convalescent plasma and interferon inhibit many of these agents in vitro and in virus-infected animals. Drug or plasma treatment is now in use for several human diseases, and would probably be beneficial for a number of others for which there is only limited treatment experience. Success is linked to early diagnosis and initiation of therapy. Ribavirin is used to treat Lassa fever and haemorrhagic fever with renal syndrome, and would probably be effective for Crimean-Congo haemorrhagic fever and for all New World arenavirus diseases. The value of ribavirin in the early treatment of hantavirus pulmonary syndrome is under evaluation. Convalescent plasma is the therapy of choice for Argentine haemorrhagic fever, and would also probably be effective for other New World arenaviruses and some other infections if a safe supply of plasma could be maintained. Ribavirin and interferon-α have both shown protective efficacy in non-human primates infected with Rift Valley fever virus. No effective therapy has yet been identified for filovirus infections, but results in animal models are encouraging. More clinical research is urgently needed. Even if placebo-controlled drug trials cannot be performed, conscientious reports of the results of therapy in limited numbers of patients can still provide evidence of antiviral drug effects.

Screening and Identification of an H-2Kb-Restricted CTL Epitope within the Glycoprotein of Hantaan Virus

The cytotoxic T lymphocyte (CTL) response plays a key role in controlling viral infection, but only a few epitopes within the HTNV glycoprotein (GP) that are recognized by CTLs have been reported. In this study, we identified one murine HTNV GP-derived H2-K^b-restricted CTL epitope in C57BL/6 mice, which could be used to design preclinical studies of vaccines for HTNV infection. First, 15 8-mer peptides were selected from the HTNV GP amino acid sequence based on a percentile rank of <=1% by IEDB which is the most comprehensive collection of epitope prediction and analysis tool. A lower percentile rank indicates higher affinity and higher immune response. In the case of the consensus method, we also evaluated the binding score of peptide-binding affinity by the BIMAS software to confirm that all peptides were able to bind H2-K^b. Second, one novel GP-derived CTL epitope, GP6 aa456-aa463 (ITSLFSLL), was identified in the splenocytes of HTNV-infected mice using the IFN-γ ELISPOT assay. Third, a single peptide vaccine was administered to C57BL/6 mice to evaluate the immunogenic potential of the identified peptides. ELISPOT and cell-mediated cytotoxicity assays showed that this peptide vaccine induced a strong IFN-γ response and potent cytotoxicity in immunized mice. Last, we demonstrated that the peptide-vaccinated mice had partial protection from challenge with HTNV. In conclusion, we identified an H2-K^b-restricted CTL epitope with involvement in the host immune response to HTNV infection.

A single immunization with a recombinant canine adenovirus type 2 expressing the seoul virus Gn glycoprotein confers protective immunity against seoul virus in mice

Seoul virus (SEOV), a member of hantavirus genus, is one of the causative agents of hemorrhagic fever with renal syndrome (HFRS) and afflicts tens of thousands of people annually. In this paper, we evaluate the immune response induced by a replication-competent recombinant canine adenovirus type 2 expressing the Gn protein of SEOV (rCAV-2-Gn) in BALB/c mice. Sera from immunized mice contained neutralizing antibodies that could specifically recognize SEOV and neutralize its infectivity in vitro. Moreover, the recombinant virus induced complete protection against a lethal challenge with the highly virulent SEOV strain CC-2. Protective level neutralizing antibodies were maintained for at least 20 weeks. The efficacy of the recombinant was similar to that induced by a currently available inactivated HFRS vaccine. This recombinant virus is therefore a potential alternative to the inactivated vaccine.

Recent approaches in hantavirus vaccine development

Rodent-borne hantaviruses are associated with two main clinical disorders in humans: hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome. Although hantavirus diseases can be life threatening and numerous research efforts are focused on the development of hantavirus prevention, no specific antiviral therapy is yet available and, at this time, no WHO-approved vaccine has gained widespread acceptance. This review will summarize the current knowledge and recent progress as well as new speculative approaches in the development of hantavirus vaccines.

A pseudotype vesicular stomatitis virus containing Hantaan virus envelope glycoproteins G1 and G2 as an alternative to hantavirus vaccine in mice

We examined whether a vesicular stomatitis virus (VSV) pseudotype bearing the hantavirus envelope glycoproteins (GPs) G1 and G2 (VSVdeltaG*HTN) could be used as a safe and effective alternative to native hantavirus. Mice were immunized with purified particles of VSVdeltaG*HTN. After the second immunization, all mice produced anti-GP antibody as detected in ELISA and a neutralization test. After the third immunization, the mice were challenged with Hantaan virus. Neither anti-NP antibody production nor Hantaan virus-specific CD8 T-cell reactions were detected in these mice. The present study demonstrated the potential of using a pseudotype VSV system as a tool for developing a hantavirus vaccine.

Immunogenicity of SARS inactivated vaccine in BALB/c mice

Severe acute respiratory syndrome (SARS) is a serious infectious threat to public health. To create a novel trial vaccine and evaluate its potency, we attempted to generate a SARS inactivated vaccine using SARS coronavirus (SARS-CoV) strain F69 treated with formaldehyde and mixed with Al(OH)3. Three doses of the vaccine were used to challenge three groups of BALB/c mice. We found that the mice exhibited specific IgM on day 4 and IgG on day 8. The peak titers of IgG were at day 47 in low-dose group (1:19,200) and high-dose group (1:38,400) whereas in middle-dose group (1:19,200), the peak was at day 40. On day 63, the IgG levels reached a plateau. Neutralization assay demonstrated that the antisera could protect Vero-E6 cells from SARS-CoV's infection. Analysis of the antibody specificity revealed that the mouse antisera contained a mixture of antibodies specifically against the structure proteins of SARS-CoV. Furthermore, the mouse antisera conferred higher amount of antibodies against protein N, polypeptide S4 and S2 than those of proteins M and 3CL. These findings suggest that the inactivated SARS-CoV could preserve its antigenicity and the inactivated vaccine can stimulate mice to produce high levels of antibodies with neutralization activity. Results also suggest that polypeptides originating from protein N or S might be a potential target for the generation of a recombinant SARS vaccine.

Hantaviruses: Immunology, Treatment, and Prevention

Hantaviruses are rodent-borne bunyaviruses that are associated with two main clinical diseases in humans: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. It has been suggested that host-related immune mechanisms rather than direct viral cytopathology may be responsible for the principal abnormality (vascular dysfunction) in these syndromes. This review summarizes the current knowledge on hantaviral host immune responses, immune abnormalities, laboratory diagnosis, and antiviral therapy as well as the current approaches in vaccine development.

Hantavirus infections and their prevention

Hantaviruses are rodent-borne bunyaviruses which cause haemorrhagic fever with renal syndrome and Hantavirus pulmonary syndrome in humans. This review covers the host interactions of the viruses, including the rodent reservoirs, the clinical outcome of human infections as well as the pathogenesis and laboratory diagnosis of infections. The current stage in prophylaxis and therapy of hantaviral diseases is described and different approaches in vaccine development are discussed.

Molecular cloning and high-level expression of G2 protein of hantaan (HTN) virus 76-118 strain in the yeast Pichia pastoris KM71

Hantaan viral G2 envelope gene, which is known to be one of major antigens and induce neutralizing antibodies, was cloned into expression vector pHIL-S1 which consists of AOX1 promoter, PHO1 signal sequence, HIS4 gene and other components. The recombined plasmid was transformed into methylotropic yeast, Pichia pastoris of KM71 and recombinant strains harboring multi-copy of G2 gene were selected. Expression of the cloned G2 gene was confirmed with Western blot analysis using anti-sera of guinea pig immunized with the carboxyl terminal region of G2 protein expressed in Escherichia coli. The expression of G2 gene from the recombinant strain was tightly repressed by dextrose and effectively induced by methanol, an inducer of AOX1 promoter. The highest expression level was observed from 1 day after induction and maintained at the same level for up to 4 days.

Antibody responses in humans to an inactivated hantavirus vaccine (Hantavax)

Hantaviruses cause haemorrhagic fever with renal syndrome (HFRS) and result in severe human morbidity and mortality. Safe and effective vaccines are needed urgently in order to reduce the incidence of human illness. Hitherto studies of hantavirus vaccine efficiency have been limited to individuals at low risk of infection. In this study the immune response to an inactivated hantavirus vaccine was measured in 64 human volunteers at high risk of infection by virtue of residence and occupation. 30 d after vaccination, 79% of subjects developed a significant hantavirus antibody titre as measured by immunofluorescence (IFA) and 62% by enzyme linked immunosorbent assay (ELISA). Seroconversion rates increased to 97% one month after the booster dose. Neutralising antibody titres paralleled this trend with 13% of vaccine recipients producing neutralising antibody one month after the first dose and 75% of vaccine recipients responding one month after boosting. Antibody titres had declined by one year, however, with only 37% and 43% of sera positive by IFA and ELISA, respectively. Re-vaccination at this time produced a vigorous anamnestic response with 94% and 100% of vaccine recipients yielding positive antibody titres. Only 50% of the sampled population, however, produced neutralising antibodies following the booster dose one year later. The vaccine was well tolerated and there were no apparent differences in the responses of males and females. However, further improvement of this vaccine is necessary in order to induce a more longlasting humoral immune response.

DNA vaccination with hantavirus M segment elicits neutralizing antibodies and protects against seoul virus infection

Seoul virus (SEOV) is one of four known hantaviruses causing hemorrhagic fever with renal syndrome (HFRS). Candidate naked DNA vaccines for HFRS were constructed by subcloning cDNA representing the medium (M; encoding the G1 and G2 glycoproteins) or small (S; encoding the nucleocapsid protein) genome segment of SEOV into the DNA expression vector pWRG7077. We vaccinated BALB/c mice with three doses of the M or S DNA vaccine at 4-week intervals by either gene gun inoculation of the epidermis or needle inoculation into the gastrocnemius muscle. Both routes of vaccination resulted in antibody responses as measured by ELISA; however, gene gun inoculation elicited a higher frequency of seroconversion and higher levels of antibodies in individual mice. We vaccinated Syrian hamsters with the M or S construct using the gene gun and found hantavirus-specific antibodies in five of five and four of five hamsters, respectively. Animals vaccinated with the M construct developed a neutralizing antibody response that was greatly enhanced in the presence of guinea pig complement. Immunized hamsters were challenged with SEOV and, after 28 days, were monitored for evidence of infection. Hamsters vaccinated with M were protected from infection, but hamsters vaccinated with S were not protected.

Nucleotide sequence and phylogenetic analysis of the medium (M) genomic RNA segments of three hantaviruses isolated in China

The medium (M) genome segment of hantaviruses (family Bunyaviridae) encodes the two virion glycoproteins. G1 and G2, as a precursor protein in the complementary sense RNA. We determined the nucleotide sequences of the M genome segments of three Chinese hantavirus isolates, a Hantaan-type (HTN) virus designated A9 and two Seoul-type (SEO) viruses designated L99 and HB55, and compared them to those of other HTN or SEO viruses isolated in Eastern Asia. The M segment of A9 is 3616 nucleotides in length and shows 99.5% identity at the nucleotide level and 99.1% identity at the amino acid level to that of the Chinese HTN isolate HV114. The M segments of L99 and HB55 are 3652 nucleotides in length, one nucleotide longer than the M segments of other sequenced SEO isolates such as SEO 80-39, SR-11, and Biken-1. The Chinese SEO isolates showed 95% nucleotide sequence identity and 99% amino acid sequence identity to SEO 80-39. We also sequenced a 736 nucleotides region of the M genome segment of another Chinese SEO isolate, R22, which revealed errors in the published data. Phylogenetic analysis of the available sequences indicated that both the Chinese HTN- and SEO-type viruses form lineages distinct from those of the isolates from other parts of Eastern Asia.

A vaccinia virus-vectored Hantaan virus vaccine protects hamsters from challenge with Hantaan and Seoul viruses but not Puumala virus

To investigate the ability of a vaccinia virus-vectored vaccine expressing the M and the S segments of Hantaan (HTN) virus (C. S. Schmaljohn, S. E. Hasty, and J. M. Dalrymple, Vaccine 10:10-13, 1992) to elicit a protective immune response against other hantaviruses, we vaccinated hamsters with the recombinant vaccine and challenged them with HTN, Seoul (SEO), or Puumala (PUU) virus. Neutralizing antibodies to HTN virus were found in all vaccinated hamsters both before and after challenge. Neutralizing antibody titers to SEO virus were present at low levels or were undetectable after two immunizations with the vaccine but were positive in all vaccinated hamsters after challenge with SEO virus and were also positive in control animals that were not challenged. Neutralizing antibodies to PUU virus were observed only in hamsters previously challenged with PUU virus. To assay for virus in the blood and tissues of the hamsters, we developed a nested reverse transcriptase (RT)-PCR with cross-reactive outer primers and serotype-specific inner primers. The RT-PCR specifically detected as little as 1 PFU of virus in serum containing high-titer neutralizing antibodies and was more sensitive than immunofluorescent antibody staining for detecting virus in lung and kidney specimens of infected hamsters. By using the RT-PCR, we found that vaccinated hamsters, challenged with HTN or SEO virus, neither were viremic nor had evidence of virus in their lungs or kidneys. In contrast, vaccinated hamsters challenged with PUU virus were viremic and had PUU virus-specific nucleic acid in their organs.

Prevalence of serum IgG antibodies to Puumala virus (haemorrhagic fever with renal syndrome) in northern Sweden

A stratified and randomly-selected population sample was identified in 1990 in order to study the seroprevalence of nephropathia epidemica (haemorrhagic fever with renal syndrome) in Northern Sweden. Sera from 1538 subjects (750 men, 788 women), 25-64 years of age, were analysed for the presence of Puumala virus (PUV) specific-IgG by the indirect immunofluorescence antibody test. Specific IgG was detected in sera from 83 subjects (5.4%). Men and women had similar seroprevalence rates. The highest seroprevalences were found in subjects 55 years or older (8.0%) and among farmers and forestry workers (15.9%). The geographic distribution of seropositive individuals was uneven and there were significantly more seropositive persons in rural than in urban areas (P < 0.05).

Antigenic and molecular characterization of hantavirus isolates from China

Hemorrhagic fever with renal syndrome (HFRS) is caused by certain viruses in the genus Hantavirus, family Bunyaviridae, and is a major public health problem in China. By using molecular and serological tests, we characterized 15 hantaviruses isolated either from patients with HFRS or from rodents captured in endemic areas of China. By cross plaque-reduction neutralization tests performed with rabbit immune sera, we identified two serologically distinct groups of viruses, comprised of those related to Hantaan virus, and those related to Seoul virus. To study the genetic relationships among these viruses, we amplified a 330 base pair region of the medium (M) genome segment of each isolate by reverse transcription and polymerase chain reaction (PCR) and compared the nucleotide sequences to those of other, well-characterized hantaviruses. In addition, we PCR-amplified and analyzed the entire coding region of the small (S) genome segment of each isolate by restriction enzyme digestion with a battery of enzymes. The results of our genetic analyses of both the M and S segments of these isolates confirmed our serological data, indicating that Hantaan and Seoul viruses co-circulate in endemic disease regions of China. We constructed a phylogenetic tree based on multiple alignment of the partial M segment sequences. The resulting dendrogram distinguished three genetic subtypes of Hantaan viruses and one type of Seoul virus.