A Phase 2a Randomized, Double-Blind, Dose-Optimizing Study to Evaluate the Immunogenicity and Safety of a Bivalent DNA Vaccine for Hemorrhagic Fever with Renal Syndrome Delivered by Intramuscular Electroporation

Hantaan virus (HTNV) and Puumala virus (PUUV) are pathogenic hantaviruses found in Asia and Europe, respectively. DNA vaccines targeting the envelope glycoproteins of these viruses have been constructed and found to elicit neutralizing antibodies when delivered to humans by various technologies including intramuscular electroporation. Here, we report findings from a Phase 2a clinical trial of a combined HTNV/PUUV DNA vaccine delivered at varying doses and administration schedules using the Ichor Medical Systems TriGrid intramuscular electroporation delivery technology. The study was designed to characterize the effects of DNA vaccine dose and number of administrations on the frequency and magnitude of immunological response. Subjects (n = 120) were divided into four cohorts. Cohorts 1 and 2 received a dose of 2 mg of DNA (1 mg per plasmid), and cohorts 3 and 4 received a dose of 1 mg of DNA (0.5 mg per plasmid) each vaccination. Each of the four cohorts received a series of four administrations (days 0, 28, 56 and 168). For cohorts 1 and 3, the DNA vaccine candidate was delivered at each of the four administrations. For cohorts 2 and 4, in order to maintain blinding, subjects received the DNA vaccine on days 0, 56 and 168, but on day 28 received only the phosphate buffered saline vehicle rather the DNA vaccine. Sera were collected on days 0, 28, 56, 84, 140, 168, 196, 252 and 365 and evaluated for the presence of neutralizing antibodies by PUUV and HTNV pseudovirion neutralization assays (PsVNAs). Day 84 was also evaluated by a plaque reduction neutralization test (PRNT). Overall the PsVNA50 geometric mean titers (GMTs) and seropositivity rates among cohorts were similar. Cohort 3 exhibited the highest frequency of subjects that became seropositive to both PUUV and HTNV after vaccination, the highest peak GMT against both viruses, and the highest median titers against both viruses.

Andes virus M genome segment is not sufficient to confer the virulence associated with Andes virus in Syrian hamsters

Sin Nombre virus (SNV) and Andes virus (ANDV), members of the genus Hantavirus, in the family Bunyaviridae, are causative agents of hantavirus pulmonary syndrome (HPS) in North and South America, respectively. Although ANDV causes a lethal HPS-like disease in hamsters, SNV, and all other HPS-associated hantaviruses that have been tested, cause asymptomatic infections of laboratory animals, including hamsters. In an effort to understand the pathogenicity of ANDV in the hamster model, we generated ANDV/SNV reassortant viruses. Plaque isolation of viruses from cell cultures infected with both parental viruses yielded only one type of stable reassortant virus: large (L) and small (S) segments of SNV and M segment of ANDV. This virus, designated SAS reassortant virus, had in vitro growth and plaque morphology characteristics similar to those of ANDV. When injected into hamsters, the SAS reassortant virus was highly infectious and elicited high-titer, ANDV-specific neutralizing antibodies; however, the virus did not cause HPS and was not lethal. These data indicate that the ANDV M genome segment is not sufficient to confer the lethal HPS phenotype associated with ANDV.

Smallpox DNA vaccine protects nonhuman primates against lethal monkeypox

Two decades after a worldwide vaccination campaign was used to successfully eradicate naturally occurring smallpox, the threat of bioterrorism has led to renewed vaccination programs. In addition, sporadic outbreaks of human monkeypox in Africa and a recent outbreak of human monkeypox in the U.S. have made it clear that naturally occurring zoonotic orthopoxvirus diseases remain a public health concern. Much of the threat posed by orthopoxviruses could be eliminated by vaccination; however, because the smallpox vaccine is a live orthopoxvirus vaccine (vaccinia virus) administered to the skin, the vaccine itself can pose a serious health risk. Here, we demonstrate that rhesus macaques vaccinated with a DNA vaccine consisting of four vaccinia virus genes (L1R, A27L, A33R, and B5R) were protected from severe disease after an otherwise lethal challenge with monkeypox virus. Animals vaccinated with a single gene (L1R) which encodes a target of neutralizing antibodies developed severe disease but survived. This is the first demonstration that a subunit vaccine approach to smallpox-monkeypox immunization is feasible.

Active and passive vaccination against hantavirus pulmonary syndrome with Andes virus M genome segment-based DNA vaccine

Hantavirus pulmonary syndrome (HPS) is a rapidly progressing human disease with one of the highest case fatality rates (30 to 50%) of any acute viral disease known. There are no vaccines, effective antiviral drugs, or immunologics to prevent or treat HPS. In an attempt to develop HPS medical countermeasures, we constructed an expression plasmid, pWRG/AND-M, that contains the full-length M genome segment of Andes virus (ANDV), a South American hantavirus. Transfection experiments in cell culture indicated that both the G1 and G2 glycoproteins are expressed from pWRG/AND-M. Rhesus macaques vaccinated by gene gun with pWRG/AND-M developed remarkably high levels of neutralizing antibodies that not only neutralized ANDV but also cross-neutralized other HPS-associated hantaviruses, including Sin Nombre virus. To determine if the antibodies elicited in the monkeys could confer protection, we performed a series of passive-transfer experiments using a recently described lethal HPS animal model (i.e., adult Syrian hamsters develop HPS and die within 10 to 15 days after challenge with ANDV). When injected into hamsters 1 day before challenge, sera from the vaccinated monkeys either provided sterile protection or delayed the onset of HPS and death. When injected on day 4 or 5 after challenge, the monkey sera protected 100% of the hamsters from lethal disease. These data provide a proof of concept for a gene-based HPS vaccine and also demonstrate the potential value of a postexposure immunoprophylactic to treat individuals after exposure, or potential exposure, to these highly lethal hantaviruses.

A lethal disease model for hantavirus pulmonary syndrome

Hantaviruses are associated with two human diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Development of vaccines and therapies to prevent and treat HFRS and HPS have been hampered by the absence of a practical animal model. Here we report that Andes virus (ANDV), a South American hantavirus, is highly lethal in adult Syrian hamsters. The characteristics of the disease in hamsters, including the incubation period, symptoms of rapidly progressing respiratory distress, and pathologic findings of pulmonary edema and pleural effusion, closely resemble HPS in humans. This is the first report of a lethal disease model for hantaviruses that causes HPS.

Purification and characterization of the Sin Nombre virus nucleocapsid protein expressed in Escherichia coli

Sin Nombre virus is a member of the Hantavirus genus, family Bunyaviridae, and is an etiologic agent of hantavirus pulmonary syndrome. The hantavirus nucleocapsid (N) protein plays an important role in the encapsidation and assembly of the viral negative-sense genomic RNA. The Sin Nombre N protein was expressed as a C-terminal hexahistidine fusion in Escherichia coli and initially purified by nickel-affinity chromatography. We developed methods to extract the soluble fraction and to solubilize the remainder of the N protein using denaturants. Maximal expression of protein from native purification was observed after a 1.5-h induction with IPTG (2.4 mg/L). The zwitterionic detergent Chaps did not enhance the yield of native purifications, but increased the yield of protein obtained from insoluble purifications. Both soluble and insoluble materials, purified by nickel-affinity chromatography, were also subjected to Hi Trap SP Sepharose fast-flow (FF) chromatography. Both soluble and insoluble proteins had a similar A(280) profile on the Sepharose FF column, and both suggested the presence of a nucleic acid contaminant. The apparent dissociation constant of the N protein, purified by nickel-affinity and SP Sepharose FF chromatography, and the 5' end of the viral S-segment genome were measured using a filter binding assay. The N protein-vRNA complex had an apparent dissociation constant of 140 nM.

DNA vaccination with the Hantaan virus M gene protects Hamsters against three of four HFRS hantaviruses and elicits a high-titer neutralizing antibody response in Rhesus monkeys

Four hantaviruses-Hantaan virus (HTNV), Seoul virus (SEOV), Dobrava virus (DOBV) and Puumala virus-are known to cause hemorrhagic fever with renal syndrome (HFRS) in Europe and Asia. HTNV causes the most severe form of HFRS (5 to 15% case-fatality rate) and afflicts tens of thousands of people annually. Previously, we demonstrated that DNA vaccination with a plasmid expressing the SEOV M gene elicited neutralizing antibodies and protected hamsters against infection with SEOV and HTNV. Here, we report the construction and evaluation of a DNA vaccine that expresses the HTNV M gene products, G1 and G2. DNA vaccination of hamsters with the HTNV M gene conferred sterile protection against infection with HTNV, SEOV, and DOBV. DNA vaccination of rhesus monkeys with either the SEOV or HTNV M gene elicited high levels of neutralizing antibodies. These are the first immunogenicity data for hantavirus DNA vaccines in nonhuman primates. Because a neutralizing antibody response is considered a surrogate marker for protective immunity in humans, our protection data in hamsters combined with the immunogenicity data in monkeys suggest that hantavirus M gene-based DNA vaccines could protect humans against the most severe forms of HFRS.

Persistent hantavirus infections: characteristics and mechanisms

Hantaviruses include serious human pathogens that are maintained in nature in persistently infected rodents and that can also persistently infect cultured mammalian cells, causing little or no cytopathology. The mechanisms of hantavirus persistence are only beginning to be explored. Recent data point to subtle changes in the viral genome that might result in the differential regulation of replication and lead to persistence.

DNA vaccination with vaccinia virus L1R and A33R genes protects mice against a lethal poxvirus challenge

Previously we found that passive transfer of monoclonal antibodies (MAbs) specific to either the vaccinia virus (VACV) L1R or A33R gene product protected mice from challenge with VACV. The L1R-specific MAbs, which bind the intracellular mature virion (IMV), neutralized virus in cell culture, whereas the A33R-specific MAbs, which bind extracellular enveloped virions (EEV), did not. To investigate whether a protective response could be generated by vaccination with these genes, we constructed and evaluated DNA vaccines expressing the VACV L1R and/or A33R genes under control of a cytomegalovirus promoter. Mice were vaccinated with DNA-coated gold beads by using a gene gun and then challenged with VACV (strain WR) intraperitoneally. Mice vaccinated with L1R alone developed neutralizing antibodies and were partially protected. Mice vaccinated with a combination of both genes loaded on the same gold beads developed a robust anti-A33R response; however, no neutralizing antibody response was detected, and the mice were not protected. In contrast, when mice were vaccinated with L1R and A33R loaded on different gold beads, neutralizing (presumably anti-L1R) and anti-A33R antibody responses were detected, and protection was markedly improved. Our results indicated that vaccination with both L1R and A33R proteins, intended to evoke mechanistically distinct and complementary forms of protection, was more effective than vaccination with either protein by itself.

Clinical evaluation of a vaccinia-vectored Hantaan virus vaccine

We evaluated a vaccinia-vectored vaccine for hemorrhagic fever with renal syndrome in clinical trials. A Phase I dose-escalation study in 16 volunteers divided into four groups demonstrated that subcutaneous inoculation of approximately 10(7) plaque-forming units of the recombinant virus was safe and immunogenic. Vaccination of a fifth group of 12 volunteers indicated that neutralizing antibody titers to both vaccinia virus and Hantaan virus were enhanced after a second inoculation. Comparing two routes of vaccination showed that scarification effectively induced neutralizing antibodies in vaccinia virus-naive volunteers but that subcutaneous inoculation was superior to scarification in vaccinia virus-immune individuals. A Phase II, double-blinded, placebo-controlled clinical trial was conducted among 142 volunteers. Two subcutaneous vaccinations were administered at 4-week intervals. Neutralizing antibodies to Hantaan virus or to vaccinia virus were detected in 72% or 98% of vaccinia virus-naive volunteers, respectively. In contrast, only 26% of the vaccinia virus-immune volunteers developed neutralizing antibody responses to Hantaan virus. J. Med. Virol. 60:77-85, 2000. Published 2000 Wiley-Liss, Inc.

Characterization of the Hantaan nucleocapsid protein-ribonucleic acid interaction

The nucleocapsid (N) protein functions in hantavirus replication through its interactions with the viral genomic and antigenomic RNAs. To address the biological functions of the N protein, it was critical to first define this binding interaction. The dissociation constant, K(d), for the interaction of the Hantaan virus (HTNV) N protein and its genomic S segment (vRNA) was measured under several solution conditions. Overall, increasing the NaCl and Mg(2+) in these binding reactions had little impact on the K(d). However, the HTNV N protein showed an enhanced specificity for HTNV vRNA as compared with the S segment open reading frame RNA or a nonviral RNA with increasing ionic strength and the presence of Mg(2+). In contrast, the assembly of Sin Nombre virus N protein-HTNV vRNA complexes was inhibited by the presence of Mg(2+) or an increase in the ionic strength. The K(d) values for HTNV and Sin Nombre virus N proteins were nearly identical for the S segment open reading frame RNA, showing weak affinity over several binding reaction conditions. Our data suggest a model in which specific recognition of the HTNV vRNA by the HTNV N protein resides in the noncoding regions of the HTNV vRNA.

Comparison of the protective efficacy of naked DNA, DNA-based Sindbis replicon, and packaged Sindbis replicon vectors expressing Hantavirus structural genes in hamsters

Seoul virus (SEOV) is a member of the Hantavirus genus (family Bunyaviridae) and an etiological agent of hemorrhagic fever with renal syndrome. The medium (M) and small (S) gene segments of SEOV encode the viral envelope glycoproteins and nucleocapsid protein, respectively. We compared the immunogenicity and protective efficacy of naked DNA (pWRG7077), DNA-based Sindbis replicon (pSIN2.5), and packaged Sindbis replicon vectors (pSINrep5), containing either the M or S gene segment of SEOV in Syrian hamsters. All of the vectors elicited an anti-SEOV immune response to the expressed SEOV gene products. Vaccinated hamsters were challenged with SEOV and monitored for evidence of infection. Protection from infection was strongly associated with M-gene vaccination. A small number of S-gene-vaccinated animals also were protected. Hamsters vaccinated with the pWRG7077 vector expressing the M gene demonstrated the most consistent protection from SEOV infection and also were protected from heterologous hantavirus (Hantaan virus) infection.

Human memory cytotoxic T-lymphocyte (CTL) responses to Hantaan virus infection: identification of virus-specific and cross-reactive CD8(+) CTL epitopes on nucleocapsid protein

Hantaan virus, the prototypic member of the Hantavirus genus, causes hemorrhagic fever with renal syndrome in humans. We examined the human memory T-lymphocyte responses of three donors who had previous laboratory-acquired infections with Hantaan virus. We demonstrated virus-specific responses in bulk cultures of peripheral blood mononuclear cells (PBMC) from all donors. Bulk T-cell responses were directed against either Hantaan virus nucleocapsid (N) or G1 protein, and these responses varied between donors. We established both CD4(+) and CD8(+) N-specific cell lines from two donors and CD4(+) G1-specific cell lines from a third donor. All CD8(+) cytotoxic T-lymphocyte (CTL) lines recognized one of two epitopes on the nucleocapsid protein: one epitope spanning amino acids 12 to 20 and the other spanning amino acids 421 to 429. The CTL lines specific for amino acids 12 to 20 were restricted by HLA B51, and those specific for amino acids 421 to 429 were restricted by HLA A1. The N-specific CTL lines isolated from these two donors included both Hantaan virus-specific CTLs and hantavirus cross-reactive CTLs. Responses to both epitopes are detectable in short-term bulk cultures of PBMC from one donor, and precursor frequency analysis confirms that CTLs specific for these epitopes are present at relatively high precursor frequencies in the peripheral T-cell pool. These data suggest that infection with Hantaan virus results in the generation of CTL to limited epitopes on the nucleocapsid protein and that infection also results in the generation of cross-reactive T-cell responses to distantly related hantaviruses which cause the distinct hantavirus pulmonary syndrome. This is the first demonstration of human T-lymphocyte responses to Hantaan virus.

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.

A colorimetric PCR-enzyme immunoassay to identify hantaviruses

BACKGROUND

Hantaviruses cause two serious human diseases: hantavirus pulmonary syndrome and hemorrhagic fever with renal syndrome. At least nine hantaviruses are known to be pathogenic for humans and numerous others, with unknown disease potential, have been detected in rodents. Assays to quickly identify specific hantaviruses would be useful both for clinical diagnosis and in risk assessment studies.

OBJECTIVES

The goal of our study was to develop and test a specific and sensitive PCR-based assay for identification and differentiation of hantaviruses.

STUDY DESIGN

We developed an assay that combined RNA-PCR amplification and colorimetric enzymatic detection to identify representative European, Asian, and north American hantaviruses. RNAs from 18 hantavirus strains of nine species were amplified in the presence of digoxigenin-dUTP by using a single pair of oligonucleotide primers and polymerase chain reaction (PCR) performed by using rTth DNA polymerase. Digoxigenin-labeled PCR products were hybridized in solution to virus type-specific biotinilated probes, captured onto streptavidin-coated microtiter plates and detected by horseradish peroxidase-labeled anti-digoxigenin antibodies and a chromogenic substrate.

RESULTS AND CONCLUSIONS

The assay correctly identified each homologous virus type tested. The detection limit of the assay was approximately 15 PFU or at least 50 copies of the viral genome. The assay is simple and strain-specific and is adaptable for automation, making it more practical than other available techniques for accurate and reliable diagnosis and typing of hantaviruses.

Characterization of Langat virus antigenic determinants defined by monoclonal antibodies to E, NS1 and preM and identification of a protective, non-neutralizing preM-specific monoclonal antibody

Hybridomas secreting monoclonal antibodies (MAb) to the tick-borne encephalitis (TBE) group virus, Langat virus (LGTV), were prepared. Of more than 200 MAb screened, 19 antibodies, which cross-reacted with the etiologic agent of Central European encephalitis, were selected for further characterization. Of these MAb, 15 were specific for LGTV E glycoprotein, two for the NS1 protein, and three for preM protein. The two NS1-specific MAb and two of the E-specific MAb reacted with all six of the other TBE group viruses tested while the remainder of the E-specific MAb failed to recognize at least one of the viruses. None of the MAb neutralized LGTV in cell culture assays, but one of the preM-specific MAb protected weanling mice against a virulent LGTV challenge. Although protective antibodies to E and NS1 proteins of TBE viruses were reported, our data provided the first evidence for protection by a non-neutralizing antibody to the preM or M protein of any of the tick-borne flaviviruses.

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.

Complete nucleotide sequences of the M and S segments of two hantavirus isolates from California: evidence for reassortment in nature among viruses related to hantavirus pulmonary syndrome

We report the complete nucleotide sequence of the M and the S genome segments and a portion of the L segments of two hantavirus isolates from Peromyscus maniculatus trapped in eastern California. The isolates, Convict Creek 107 and 74 (CC107 and CC74) are genetically similar to viruses known to cause hantavirus pulmonary syndrome in New Mexico. CC107 and CC74 each have an M segment consisting of 3696 nucleotides with a coding potential of 1140 amino acids in the virus complementary-sense RNA (cRNA). The S segments of CC107 and CC74 are 2083 and 2047 nucleotides long, respectively, and each has an ORF in the cRNA capable of encoding a protein of 428 amino acids. Unusually long 3' noncoding regions of 757 and 721 nucleotides follow the S segment ORF of CC107 and CC74, respectively, and include numerous imperfect repetitive sequences. Whereas the M and S segments of any given hantavirus typically appear to diverge at comparable rates from homologous genes of any other hantavirus, CC107 and CC74 have M segments that differ by only 1% from one another but S segments that differ by 13%. After trivial explanations are rendered improbable, i.e., by consideration of the genetics of closely and distantly related hantaviruses, the most likely explanation for our data is that hantavirus genome segment reassortment occurred within rodent populations in California.

Short report: prevalence of hantavirus infection in rodents associated with two fatal human infections in California

Rodents living near two fatal human cases of hantavirus pulmonary syndrome in California were surveyed for evidence of hantavirus infection. Seventeen (15%) (14 Peromyscus maniculatus and one each of P. truei, Eutamias minimus, and Microtus californicus) of 114 rodents tested had evidence (enzyme-linked immunosorbent assay or polymerase chain reaction) of hantavirus infection. This suggests that Peromyscus mice, and P. maniculatus in particular, may be the reservoir for the virus causing this newly recognized disease in California, as previously reported for New Mexico and Arizona.

Isolation and initial characterization of a newfound hantavirus from California

A fatal case of hantavirus pulmonary syndrome (HPS) in northern California prompted our attempt to isolate viruses from local rodents. From tissues of two deer mice, Peromyscus maniculatus, two hantaviruses (Convict Creek virus 107 and 74, CC107 and CC74) were established in cell culture. Viral antigens, proteins, and RNAs of the first and archetypical isolate (CC107) were examined, and portions of the medium (M) and small (S) genome segments of both isolates were sequenced. Antigenically, CC107 virus and the second isolate, CC74 virus, were more closely related to Puumala virus than Hantaan (HTN) virus, though distinct from both. Northern blots of viral RNAs showed the large and M segments of CC107 to be the same size as those of HTN virus, whereas the S segment was larger. Protein gels did not reveal CC107 to have a substantially larger nucleocapsid protein than HTN virus. Partial nucleotide sequence comparisons of CC107 and CC74 viruses revealed their M segments to be highly similar to one another, while their S segments differed by more than 10%. Nucleotide and deduced amino acid sequence comparisons showed the California isolates to be closely related to the newfound hantaviruses first detected in the Four Corners area and since incriminated in HPS through wide areas of the United States.

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.

Serological relationships among viruses in the Hantavirus genus, family Bunyaviridae

We examined the serological relationships among 32 hantavirus isolates collected from numerous geographic regions and hosts. We prepared rat immune sera to each virus and used these sera in hemagglutination inhibition (HAI) tests, enzyme-linked immunosorbent assays (ELISA), and plaque-reduction neutralization tests to establish the antigenic relationships among the isolates. Our studies included viruses that had been partially characterized previously, as well as isolates for which little or no serological data were available. Our results indicate that, in addition to the four established serological groups of hantaviruses, represented by Hantaan, Seoul, Puumala, and Prospect Hill viruses, there exist at least two other distinct groups of hantaviruses. These groups are represented by Thailand 749 virus, an isolate from Bandicota in Thailand, and by Thottapalayam virus, an isolate from Suncus in India. To compare more closely the antigenic relationships of the isolates to prototype Hantaan virus, we examined the reactivities of Hantaan G1- or G2-specific monoclonal antibodies with the envelope proteins of a number of the isolates. We found that several epitopes defined by monoclonal antibodies to the G2 protein were highly conserved as detected by HAI tests and ELISA. Almost all of the isolates could be neutralized by at least one G2-specific monoclonal antibody. In contrast, epitopes defined by G1 monoclonal antibodies were conserved only among Hantaan-like viruses.

Expression strategy of the M genome segment of Hantaan virus

The medium (M) genome segment of Hantaan virus encodes the envelope glycoproteins, G1 and G2, in a continuous open reading frame with a gene order of 5'-G1-G2-3' with respect to the virus-complementary sense RNA. Because potential translation initiation codons and amino acids constituting typical signal sequences precede both the G1 and G2 genes, we sought to determine if G1 and G2 can be expressed independently. To investigate translational requirements for G1 and G2, we constructed M segment genes in which portions of the coding information were mutated or deleted, and transiently expressed these genes in eukaryotic cells by using a vaccinia virus/T7 RNA polymerase system. We found that G2 expression can occur by ribosomal access to the translation initiation codon preceding the G2 signal sequence (nucleotides 1934-1936), but that other upstream AUG codons cannot be used as efficiently. The presence of this codon, however, was not required for G2 expression because changing nucleotides 1934-1936 to CUG, GCG or AUG did not abrogate expression of G2. We also found that leaky ribosomal scanning, rather than internal initiation of translation was the most likely explanation for the observed independent translational initiation of G2, but that not all upstream, in-frame AUGs could serve as initiator codons. To assess the requirement for a continuous open reading frame for G1 and G2 expression, we expressed a gene which had G1 and G2 coding information in different reading frames. Although G1 was expressed at apparently normal levels, little or no G2 was expressed. In contrast, only G2 was expressed from a gene in which the carboxy-terminal G1 coding information was deleted and the remaining, truncated G1 was placed out of frame with respect to G2. These data suggest that reinitiation of translation may occur under some, but not all, circumstances when the polyprotein coding information is perturbed. Our results are consistent with biogenesis of G1 and G2 primarily or entirely according to the ribosomal scanning model.

Phylogenetic analyses of virus isolates in the genus Hantavirus, family Bunyaviridae

We constructed a phylogenic tree by pairwise comparison of the deduced amino acid sequences encoded in the medium (M) genome segments of 13 hantaviruses. Five distinct branches were identified, four of which are represented by Hantaan, Seoul, Puumala, and Prospect Hill viruses. These groups corresponded to those previously established by serological and genetic means. In addition, we present sequence information for the M segment of Thailand virus and demonstrate that it represents a unique, fifth branch on the dendrogram. We show that a tree nearly identical to that constructed from the deduced amino acids encoded in the M segments of these viruses can be constructed by comparing nucleotide sequences of a 333-bp region of the M segments of the same hantaviruses. This region can be amplified, for most hantaviruses, by reverse transcriptase-polymerase chain reaction (RT-PCR) techniques, using a single primer pair. By using this method, we constructed a consensus tree for 30 hantaviruses, including 15 isolates for which we PCR-amplified and sequenced the 333-bp region. In addition to the five branches described above, we identified a sixth unique hantavirus group represented by Dobrava virus, an Apodemus isolate from Slovenia. Although we were unable to PCR-amplify the M segment of Thottapalayam virus, a distantly related hantavirus isolated from a shrew captured in India, we were able to amplify, clone, and sequence a portion of the small (S) segment of that virus. When we compared our Thottapalayam sequence to corresponding S segment sequences of other hantaviruses, the results indicated that this virus may represent a seventh, distinct group of hantaviruses.

Epitope mapping studies with neutralizing and non-neutralizing monoclonal antibodies to the G1 and G2 envelope glycoproteins of Hantaan virus

Epitopes recognized by three G1-specific and two G2-specific neutralizing monoclonal antibodies to Hantaan virus were mapped by sequence analyses of the complete M genome segments of neutralization escape variant viruses. For each variant, we detected nucleotide sequence substitutions which resulted in a single amino acid change in either the G1 or G2 protein. Serological properties of the variant viruses correlated with changes identified by nucleotide sequence analyses. To map epitopes recognized by three G1-specific and six G2-specific, non-neutralizing monoclonal antibodies, we prepared genes, truncated at the carboxy terminal coding regions of G1 or G2, and expressed them with baculovirus recombinants or transiently in a vaccinia/T7 RNA polymerase system. Reactivities of the monoclonal antibodies with the truncated proteins were monitored by immune precipitation of the radiolabeled, truncated glycoproteins. We determined that all three of the G1-specific antibodies reacted with truncated proteins, which retained the amino terminal one-third of G1, but lost reactivity with shorter G1 proteins. The G2-specific antibodies only recognized G2 proteins, which retained approximately 80% of the G2 gene.

Nucleotide and deduced amino acid sequences of the M and S genome segments of two Puumala virus isolates from Russia

Hemorrhagic fever with renal syndrome (HFRS) is caused by viruses in the Hantavirus genus, family Bunyaviridae. Three serologically distinct hantaviruses, Hantaan, Seoul and Puumala viruses, are known to cause HFRS. We report here, for the first time, gene sequences of two human Puumala virus isolates, P360 and K27, obtained in an HFRS endemic region of the former Soviet Union. We compared the nucleotide sequences and the derived amino acid sequences of their gene products to a Puumala virus isolate from rodents.

Molecular and antigenic characterization of HV114, a hantavirus isolated from a patient with haemorrhagic fever with renal syndrome in China

The relationship of a Hantaan-like virus (HV114), isolated from a patient with haemorrhagic fever with renal syndrome in Hubei Province, People's Republic of China, to other pathogenic hantaviruses was evaluated by cross-neutralization studies and nucleotide sequence analysis of the M genome segment. Plaque reduction neutralization assays indicated that HV114 is closely related to prototype Hantaan (HTN) virus, strain 76-118, which was originally isolated from an Apodemus field mouse in Korea. Comparison of the M genome segments of HTN 76-118 and HV114 revealed sequence identity of 84.7% and 95.4% for nucleotides and deduced amino acids, respectively. These data demonstrate that HV114 and 76-118 are two closely related but different isolates of HTN virus, establishing the scientific basis for testing and future use in China of a recombinant vaccine expressing the genome of HTN virus strain 76-118.

Expression of non-conserved regions of the S genome segments of three hantaviruses: evaluation of the expressed polypeptides for diagnosis of haemorrhagic fever with renal syndrome

Haemorrhagic fever with renal syndrome (HFRS) is a serious and often fatal disease caused by viruses in the Hantavirus genus of the family Bunyaviridae. We expressed the entire coding region of the small (S) genome segments of three serologically distinct hantaviruses as soluble proteins in Escherichia coli and evaluated the expressed nucleocapsid proteins (NPs) as antigens for diagnosis of HFRS. We also prepared novel diagnostic antigens by expressing truncated genes from which we deleted amino acid coding regions that were highly conserved among the three viruses. These antigens were analysed for their potential to detect and differentiate between antisera to various hantaviruses by ELISA. ELISA results obtained with HFRS patient sera or with sera from naturally or experimentally infected animals indicate that homologous antigens and antisera reacted to high titre. The truncated NPs were more specific than the complete NPs in distinguishing between possible aetiological agents of HFRS. Our findings demonstrate that prokaryotic expression of portions of the NPs of specific hantaviruses can be used to generate, readily and efficiently, large quantities of antigen that is both sensitive and specific in diagnostic assays for HFRS.

Cloning and sequence analysis of the genes encoding the nonstructural proteins of Langat virus and comparative analysis with other flaviviruses

Langat virus, a member of the family Flaviviridae is antigenically very similar to highly pathogenic tick-borne encephalitis viruses. We cloned and sequenced the complete nonstructural gene-coding region of Langat virus (strain TP21) and compared the deduced amino acid sequences of each nonstructural protein to those of other flaviviruses. By alignment with the reported amino acid sequences of the nonstructural proteins of several flaviviruses, we were able to predict proteolytic cleavage sites and identify sequence motifs, which are highly conserved among flaviviruses. Sequence similarity calculations revealed that the NS3 and NS5 proteins are the most highly conserved of the flavivirus nonstructural proteins. The NS3 and NS5 proteins of Langat virus contained specific peptide sequences that have been demonstrated to be associated with helicase or polymerase activities, respectively. The NS1 protein of Langat virus displayed complete homology of potential N-linked glycosylation sites and cysteine residues with the NS1 proteins of other tick-borne flaviviruses, suggesting a highly conserved NS1 protein structure. The data presented in this report serve to complete the entire sequence of the Langat virus-coding region and provide the basis for comparison of this naturally attenuated virus to the other highly virulent tick-borne flaviviruses.

Preparation of candidate vaccinia-vectored vaccines for haemorrhagic fever with renal syndrome

Two vaccinia-vectored candidate vaccines for haemorrhagic fever with renal syndrome were prepared by inserting cDNA, representing the medium (M) genome segment, or the M and the small (S) genome segments of Hantaan virus into the thymidine kinase gene of the Connaught vaccine strain of vaccinia virus. In the single recombinant, the M segment was placed under control of the vaccinia virus 7.5 kDa promoter. In the double recombinant, the M and S segments were placed under control of the vaccinia virus 7.5 kDa and 11 kDa promoters, respectively. An immunoplaque assay technique was developed to select recombinants without the need for expression of irrelevant genes or use of potential mutagens. Proteins indistinguishable from authentic viral envelope glycoproteins and nucleocapsid protein were observed by immunoprecipitation with antibodies to Hantaan virus. The recombinant expressing both the M and the S segments was selected for further development and testing as a human vaccine.

Coexpression of the membrane glycoproteins G1 and G2 of Hantaan virus is required for targeting to the Golgi complex

To study the intracellular transport and targeting to the Golgi complex of the membrane glycoproteins G1 and G2 of Hantaan virus, we have expressed them together and separately using recombinant vaccinia viruses. When expressed from the same recombinant vaccinia virus, G1 and G2 were localized to the Golgi complex as analyzed by both immunofluorescence and subcellular fractionation. However, when the glycoproteins were expressed from separate recombinant viruses, both proteins remained in the endoplasmic reticulum. Using several monoclonal antibodies, it was found that G1 expressed alone did not acquire its correct conformation. Finally, if cells were coinfected with G1- and G2-expressing recombinant viruses, the proteins were again targeted to the Golgi complex. The N-linked glycans remained in all cases largely endoglycosidase-H sensitive. With none of the recombinant viruses were expression of the glycoproteins observed on the cell surface. Neither did chasing in the presence of cycloheximide result in the surface expression of G1 or G2. Our results indicate that for transport out of the endoplasmic reticulum and proper targeting to the Golgi complex, the two glycoproteins have to be coexpressed. The most likely interpretation is that G1 and G2 have to interact with each other in the endoplasmic reticulum in order to become transport competent.

Antigenic subunits of Hantaan virus expressed by baculovirus and vaccinia virus recombinants

Baculovirus and vaccinia virus vectors were used to express the small (S) and medium (M) genome segments of Hantaan virus. Expression of the complete S or M segments yielded proteins electrophoretically indistinguishable from Hantaan virus nucleocapsid protein or envelope glycoproteins (G1 and G2), and expression of portions of the M segment, encoding either G1 or G2 alone, similarly yielded proteins which closely resembled authentic Hantaan virus proteins. The expressed envelope proteins retained all antigenic sites defined by a panel of monoclonal antibodies to Hantaan virus G1 and G2 and elicited antibodies in animals which reacted with authentic viral proteins. A Hantaan virus infectivity challenge model in hamsters was used to assay induction of protective immunity by the recombinant-expressed proteins. Recombinants expressing both G1 and G2 induced higher titer antibody responses than those expressing only G1 or G2 and protected most animals from infection with Hantaan virus. Baculovirus recombinants expressing only nucleocapsid protein also appeared to protect some animals from challenge. Passively transferred neutralizing monoclonal antibodies similarly prevented infection, suggesting that an antibody response alone is sufficient for immunity to Hantaan virus.

Coding properties of the S and the M genome segments of Sapporo rat virus: comparison to other causative agents of hemorrhagic fever with renal syndrome

Three serologically distinct groups of hantaviruses have been associated with severe, moderate, and mild forms of hemorrhagic fever with renal syndrome (HFRS). To gain a better understanding of the genetic variation among these viruses, we cloned and sequenced the M and the S genome segments of Sapporo rat virus, an etiologic agent of moderate HFRS, and compared the predicted gene products to those of Hantaan virus, and the Hällnäs strain of Puumala virus, which are etiologic agents of severe and mild HFRS, respectively. The SR-11 S segment consisted of 1769 nucleotides and had an open reading frame (ORF) in the virus-complementary sense RNA with a coding capacity of 429 amino acids. Deduced amino acids from the SR-11 S segment ORF displayed 83% homology with those of Hantaan nucleocapsid (N) protein. Comparison of the S segment ORFs of all three viruses revealed 58% homology. No evidence for additional nonstructural protein(s) encoded by the SR-11 S segment was obtained. The SR-11 M segment consisted of 3651 nucleotides and had an ORF in the virus-complementary sense RNA with a coding capacity of 1134 amino acids. Amino acid sequences predicted from the SR-11 M segment ORF were 75% homologous with those encoding Hantaan G1 and G2 envelope glycoproteins. Comparison of the deduced amino acid sequences of the M segment ORFs of SR-11, Hantaan, and Hällnäs viruses revealed a 43% homology for amino acids constituting the G1 proteins and a 55% homology for amino acids constituting the G2 proteins of the three viruses. The envelope proteins of SR-11 virus were localized within the M segment ORF by amino-terminal sequence analysis of purified G1 and G2. G1 initiated at amino acid 17 and G2 at amino acid 647 within the ORF. Five potential asparagine-linked glycosylation sites were identified in the SR-11 G1 coding sequences, four of which were conserved between Hantaan and SR-11 viruses and three of which were conserved among all three viruses. One potential glycosylation site was identified in the SR-11 G2 coding sequences and was conserved among Hantaan, SR-11 and Hällnäs viruses. Cysteine residues were highly conserved within the M segment ORFs of all three viruses, suggesting a similar structure and function of the G1 and G2 proteins.

Expression of the Bacillus anthracis protective antigen gene by baculovirus and vaccinia virus recombinants

The gene encoding Bacillus anthracis protective antigen (PA) was modified by site-directed mutagenesis, subcloned into baculovirus and vaccinia virus plasmid transfer vectors (pAcYM1 and pSC-11, respectively), and inserted via homologous recombinations into baculovirus Autographa californica nuclear polyhedrosis virus or vaccinia virus (strains WR and Connaught). Expression of PA was detected in both systems by immunofluorescence assays with antisera from rabbits immunized with B. anthracis PA. Western blot (immunoblot) analysis showed that the expressed product of both systems was slightly larger (86 kilodaltons) than B. anthracis-produced PA (83.5 kilodaltons). Analysis of trypsin digests of virus-expressed and authentic PA suggested that the size difference was due to the presence of a signal sequence remaining with the virus-expressed protein. Immunization of mice with either recombinant baculovirus-infected Spodoptera frugiperda cells or with vaccinia virus recombinants elicited a high-titer, anti-PA antibody response.

Baculovirus expression of the M genome segment of Rift Valley fever virus and examination of antigenic and immunogenic properties of the expressed proteins

Autographa californica nuclear polyhedrosis viral recombinants containing coding information for the Rift Valley fever virus (RVFV) envelope glycoproteins (G1 and G2) and varying amounts of preglycoprotein coding sequences were prepared by using transfer vectors pAc373 or pAcYM1. Expression products were processed to yield proteins indistinguishable from authentic G1 and G2 by gel electrophoresis. The immunogenic properties of the expressed proteins were assessed by immunizing mice and challenging with RVFV. A single inoculation with lysates of cells infected with recombinants expressing both G1 and G2 induced neutralizing antibody responses in mice and protected them from an otherwise lethal challenge with RVFV. Lysates of cells infected with a recombinant expressing only G2 also induced a protective response after two immunizations. Survivors displayed elevated antibody titers to G1 and G2 and also developed antibodies to the RVFV nucleocapsid protein, the latter allowing discrimination from vaccinated mice and indicating that animals had survived infection. Nonimmune mice were protected from lethal RVFV infection by passive transfer of sera from animals immunized with recombinant antigens, indicating that a humoral immune response is sufficient to protect against RVFV.

Characterization of Hantaan virus envelope glycoprotein antigenic determinants defined by monoclonal antibodies

A panel of 24 monoclonal antibodies (MAbs) to the G1 or G2 envelope glycoproteins of Hantaan virus were used to determine the surface topography and functional properties of antigenic sites. Nine distinct, partially overlapping antigenic sites, two on G1 and seven on G2, were demonstrated by competitive binding assays. Analyses of the antigenic sites by haemagglutination (HA) inhibition and plaque-reduction neutralization tests showed that all of the sites, except one on G1, were related to viral HA. Only one of the G1 antigenic sites and two of the G2 sites were involved in virus neutralization. These results suggest that certain epitopes related to HA were not critical for virus neutralization. The nine antigenic sites could be further divided into 13 based upon the serological cross-reactivity of MAbs with viruses representative of each of the four known antigenic groups within the Hantavirus genus of Bunyaviridae, i.e. Hantaan, Seoul, Puumala and Prospect Hill viruses.

Conservation of antigenic properties and sequences encoding the envelope proteins of prototype Hantaan virus and two virus isolates from Korean haemorrhagic fever patients

Viruses isolated from the blood of two Korean haemorrhagic fever patients were propagated in cell culture and compared to prototype Hantaan virus which was isolated from Apodemus mice. The antigenic properties of the human isolates were found to be closely related to Hantaan virus by plaque reduction neutralization, haemagglutination inhibition and fluorescent antibody staining with both polyclonal and monoclonal antibodies. The medium genome segment of each human isolate was sequenced and compared to that of Hantaan virus. Nucleotides comprising the Hantaan virus G1 and G2 envelope protein-coding regions differed from those of the other viruses by only 5.4% and 5.7%. The human isolates differed from one another by 1.6%. The nucleotide differences resulted in predicted amino acid variations of 1.3% to 2.3% among the three viruses, with the majority occurring as conservative substitutions in G1.

Baculovirus expression of the small genome segment of Hantaan virus and potential use of the expressed nucleocapsid protein as a diagnostic antigen

Autographa californica nuclear polyhedrosis virus (AcNPV) was used as an expression vector for the nucleocapsid protein gene of Hantaan virus. Two different cDNA clones representing the small genome segment of Hantaan virus were inserted into the transfer vector pAcYM1, and recombinants were generated by replacement of a portion of the baculovirus polyhedrin gene with the foreign, Hantaan virus gene. Recombinants containing both the first and second ATG initiation codons of the Hantaan virus gene produced nucleocapsid protein, while those containing only the second codon did not. The expressed nucleocapsid protein was evaluated as a potential diagnostic antigen with a variety of hantavirus-immune sera. The high levels of expression obtained, specific serological reactivity with immune sera and the low level of biological containment required for production of this protein all suggest a significant advantage over authentic viral antigen for diagnosis of hantavirus infection.

Expression of the Hantaan virus M genome segment by using a vaccinia virus recombinant

A cDNA containing the complete open reading frame of the Hantaan virus (HTN) M genome segment has been cloned into vaccinia virus. This recombinant virus expresses two glycoproteins which are similar to the HTN structural glycoproteins, G1 and G2, in molecular weight, cleavage pattern, and cellular distribution. Both HTN and recombinant vaccinia virus glycoproteins are exclusively associated with the Golgi apparatus of the cell. Despite this intracellular restriction, mice inoculated with the recombinant vaccinia virus raised neutralizing antibodies against HTN. The specificity of virus neutralization appears to reside in the HTN glycoproteins, since a vaccinia virus recombinant expressing the HTN nucleocapsid protein was unable to elicit a neutralizing antibody response.

Detection of hantaviruses with RNA probes generated from recombinant DNA

Radiolabeled RNA probes generated from cDNA clones of the M and S genome segments of Hantaan virus readily detected Hantaan virus and two isolates from Korean hemorrhagic fever patients but were less effective in detecting four other hantaviruses.

Partial nucleotide sequence of the Japanese encephalitis virus genome

Approximately 10 kb of the estimated 10.9-kb genome of the Japanese encephalitis virus (JE; Nakayama strain) has been cloned as cDNA; the uncloned portion includes 430 bases at the 5'-terminus and 450 bases at the 3'-end. A map of the genome has been developed through nucleotide sequencing and in vivo expression with the Escherichia coli expression vector lambda gt11 and immunological identification. Sequence results for 4320 nucleotides suggest the JE genome organization is very similar to those of three other flaviviruses for which sequence information is available. Like the other flaviviruses, the JE proteins are encoded by a single open reading frame that continues uninterrupted throughout the region sequenced. Considerable homology exists between the JE RNA and protein sequences and those of the other characterized flaviviruses. Comparative nucleotide and (amino acid) homology values for the M-E-NS1-ns2 segment of JE are approximately MVE, 70% (80%), WN, 68% (76%), and YF, 50% (45%). Even greater homology is suggested when the protein hydrophobicity profiles are compared. The molecular relationships are consistent with the established serological relationships among JE, MVE, and WN viruses and argue that these flaviviruses may have been derived from a common evolutionary ancestor.

Hantaan virus M RNA: coding strategy, nucleotide sequence, and gene order

The M genome segment of Hantaan virus was molecularly cloned and the nucleotide sequence of cDNA was determined. The virion RNA is 3616 bases long with 3'- and 5'-terminal nucleotide sequences complementary for 18 bases. A single long open reading frame in the viral complementary-sense RNA had the potential to encode 1135 amino acids or a polypeptide of 126,000 Da. Amino-terminal sequences of isolated G1 and G2 envelope glycoproteins were determined, revealing a gene order with respect to message sense RNA of 5'-G1-G2-3'. Mature G1 begins 18 amino acids beyond the first AUG of the open reading frame, preceded by a short, hydrophobic leader sequence. G2 begins at the 649th amino acid of the open reading frame and also follows a hydrophobic sequence. Carboxy termini of G1 and G2 were localized and gene order was verified by immune precipitation of Hantaan proteins with antisera to synthetic peptides generated by using amino acid sequences derived from the cDNA sequence. The antipeptide sera were also reactive by immunoblotting with SDS-denatured G1 and G2. Molecular weights of 64,000 and 53,700 were calculated for the G1 and G2 glycoproteins, respectively, from their predicted amino acid sequences. Five potential asparagine-linked glycosylation sites were contained within the G1 amino acid sequence and two within the G2 sequence. These data are consistent with our previous estimates of the molecular weights and extent of glycosylation of the Hantaan envelope glycoproteins.

Coding strategy of the S genome segment of Hantaan virus

Hantaan virus is the type species of the recently recognized Hantavirus genus of Bunyaviridae. The small (S) RNA segment of the negative-sense, tripartite genome was molecularly cloned and the nucleotide sequence was determined. The RNA sequence derived from the cDNA copy was found to contain 1696 nucleotides. A single open reading frame of sufficient size to encode the virus nucleocapsid protein was detected in the cDNA corresponding to viral complementary-sense RNA. RNA transcripts of the cDNA were synthesized with SP6 polymerase and were used to program cell-free reticulocyte lysate translation systems. Viral complementary-sense transcripts served as efficient messages in translation systems and generated Hantaan nucleocapsid protein. No translation products were detected when lysates were programmed with viral-sense transcripts. This coding assignment of the nucleocapsid protein to the viral complementary-sense RNA of the S genome segment is consistent with those of other members of this family. Unlike other Bunyaviridae, which encode both a nucleocapsid protein and a nonstructural (NSs) protein of similar sizes, a NSs protein has not been identified for Hantaan virus. Furthermore, other than the nucleocapsid protein gene sequence, the only potential open reading frame in Hantaan S RNA encoded a short, 48-amino acid polypeptide which initiated two codons beyond the termination of the nucleocapsid protein in the same reading frame. These data demonstrate that the coding strategy of the Hantaan virus S RNA is different than those reported for other viruses in this family.

Hantaan virus replication: effects of monensin, tunicamycin and endoglycosidases on the structural glycoproteins

The monovalent ionophore monensin, which interferes with cellular transport pathways, and the antibiotic tunicamycin, which prevents glycosylation of newly synthesized proteins, were used to examine Hantaan virus particle formation and polypeptide synthesis. Viral replication in the presence of either drug resulted in reduced antigen production as well as reduced yields of both intracellular and extracellular infectious virus. Analysis of viral polypeptides synthesized in the presence of the drugs suggested differential effects of monensin and tunicamycin on Hantaan virus. Although reduced levels of the three major structural proteins were detected with increasing concentrations of monensin, the electrophoretic migrations of the polypeptides synthesized were unaltered. In contrast, after tunicamycin treatment, G1 was no longer detectable and G2 displayed both a quantitative reduction and an apparent molecular weight reduction of approximately 3000. Both G1 and G2 were sensitive to endoglycosidases H and F with resultant electrophoretic mobility shifts corresponding to molecular weights of approximately 7000 for G1 and 3000 for G2. Oligosaccharides appeared to be mostly, but not entirely, of the high-mannose type.

Antigenic and genetic properties of viruses linked to hemorrhagic fever with renal syndrome

Hemorrhagic fever with renal syndrome (HFRS) comprises a variety of clinically similar diseases of viral etiology that are endemic to and sporadically epidemic throughout the Eurasian continent and Japan. Although HFRS has not been reported in North America, viruses that are antigenically similar to HFRS agents were recently isolated from rodents in the United States. Examination and comparison of eight representative isolates from endemic disease areas and from regions with no known associated HFRS indicate that these viruses represent a new and unique group that constitutes a separate genus in the Bunyaviridae family of animal viruses.

Characterization of Hantaan virions, the prototype virus of hemorrhagic fever with renal syndrome

Hantaan virus, strain 76-118, was propagated to high titer in a clone of Vero cells, and infectious virions were successfully concentrated and purified. Infectivity and virus antigenic activity were closely associated with a virus particle that exhibited a sedimentation rate indistinguishable from a representative member of the Bunyaviridae. Purified virions sedimented to a density of 1.16-1.17 in sucrose and 1.20-1.21 in cesium chloride. Detergent disruption of virions resulted in a nucleocapsid structure (density, 1.18 in sucrose and 1.25 in cesium chloride) and soluble protein antigens. Three separate nucleocapsids were resolved by rate-zonal centrifugation and contained a single but common polypeptide of 50,000 daltons. Electrophoresis of radiolabeled RNA extracted from purified virions yielded a profile of three RNA species with apparent molecular weights of 2.7, 1.2, and 0.6 X 10(6). These data support earlier electron microscopy reports which suggested that Hantaan virus has characteristics similar to some members of the virus family Bunyaviridae.