Restoration of virulence in the attenuated Candid#1 vaccine virus requires reversion at both positions 168 and 427 in the envelope glycoprotein GPC.

Live-attenuated virus vaccines provide long-lived protection against viral disease but carry inherent risks of residual pathogenicity and genetic reversion. The live-attenuated Candid#1 vaccine was developed to protect Argentines against lethal infection by the Argentine hemorrhagic fever arenavirus, Junín virus. Despite its safety and efficacy in Phase III clinical study, the vaccine is not licensed in the US, in part due to concerns regarding the genetic stability of attenuation. Previous studies had identified a single F427I mutation in the transmembrane domain of the Candid#1 envelope glycoprotein GPC as the key determinant of attenuation, as well as the propensity of this mutation to revert upon passage in cell culture and neonatal mice. To ascertain the consequences of this reversion event, we introduced the I427F mutation into recombinant Candid#1 (I427F rCan) and investigated the effects in two validated small-animal models: in mice expressing the essential virus receptor (human transferrin receptor 1; huTfR1) and in the conventional guinea pig model. We report that I427F rCan displays only modest virulence in huTfR1 mice and appears attenuated in guinea pigs. Reversion at another attenuating locus in Candid#1 GPC (T168A) was also examined, and a similar pattern was observed. By contrast, virus bearing both revertant mutations (A168T+I427F rCan) approached the lethal virulence of the pathogenic Romero strain in huTfR1 mice. Virulence was less extreme in guinea pigs. Our findings suggest that genetic stabilization at both positions is required to minimize the likelihood of reversion to virulence in a second-generation Candid#1 vaccine.IMPORTANCELive-attenuated virus vaccines, such as measles/mumps/rubella and oral poliovirus, provide robust protection against disease but carry with them the risk of genetic reversion to the virulent form. Here, we analyze the genetics of reversion in the live-attenuated Candid#1 vaccine that is used to protect against Argentine hemorrhagic fever, an often-lethal disease caused by the Junín arenavirus. In two validated small-animal models, we find that restoration of virulence in recombinant Candid#1 viruses requires back-mutation at two positions specific to the Candid#1 envelope glycoprotein GPC, at positions 168 and 427. Viruses bearing only a single change showed only modest virulence. We discuss strategies to genetically harden Candid#1 GPC against these two reversion events in order to develop a safer second-generation Candid#1 vaccine virus.

Seminario Fiebre Hemorrágica Argentina en Provincia de Buenos Aires: nuestro desafío

Destinado a todo el personal de salud, Alejandra Rodríguez aborda aspectos epidemiológicos de la Fiebre Hemorrágica Argentina, la Dra. Andrea Uboldi diserta sobre la vacuna y la Dra. Alejandra Gaiano sobre los desafíos futuros

Host receptor-targeted therapeutic approach to counter pathogenic New World mammarenavirus infections.

Five New World mammarenaviruses (NWMs) cause life-threatening hemorrhagic fever (HF). Cellular entry by these viruses is mediated by human transferrin receptor 1 (hTfR1). Here, we demonstrate that an antibody (ch128.1/IgG1) which binds the apical domain of hTfR1, potently inhibits infection of attenuated and pathogenic NWMs in vitro. Computational docking of the antibody Fab crystal structure onto the known structure of hTfR1 shows an overlapping receptor-binding region shared by the Fab and the viral envelope glycoprotein GP1 subunit that binds hTfR1, and we demonstrate competitive inhibition of NWM GP1 binding by ch128.1/IgG1 as the principal mechanism of action. Importantly, ch128.1/IgG1 protects hTfR1-expressing transgenic mice against lethal NWM challenge. Additionally, the antibody is well-tolerated and only partially reduces ferritin uptake. Our findings provide the basis for the development of a novel, host receptor-targeted antibody therapeutic broadly applicable to the treatment of HF of NWM etiology.

Antibody-Based Inhibition of Pathogenic New World Hemorrhagic Fever Mammarenaviruses by Steric Occlusion of the Human Transferrin Receptor 1 Apical Domain.

Pathogenic clade B New World mammarenaviruses (NWM) can cause Argentine, Venezuelan, Brazilian, and Bolivian hemorrhagic fevers. Sequence variability among NWM glycoproteins (GP) poses a challenge to the development of broadly neutralizing therapeutics against the entire clade of viruses. However, blockade of their shared binding site on the apical domain of human transferrin receptor 1 (hTfR1/CD71) presents an opportunity for the development of effective and broadly neutralizing therapeutics. Here, we demonstrate that the murine monoclonal antibody OKT9, which targets the apical domain of hTfR1, can sterically block cellular entry by viral particles presenting clade B NWM glycoproteins (GP1-GP2). OKT9 blockade is also effective against viral particles pseudotyped with glycoproteins of a recently identified pathogenic Sabia-like virus. With nanomolar affinity for hTfR1, the OKT9 antigen binding fragment (OKT9-Fab) sterically blocks clade B NWM-GP1s and reduces infectivity of an attenuated strain of Junin virus. Binding of OKT9 to the hTfR1 ectodomain in its soluble, dimeric state produces stable assemblies that are observable by negative-stain electron microscopy. A model of the OKT9-sTfR1 complex, informed by the known crystallographic structure of sTfR1 and a newly determined structure of the OKT9 antigen binding fragment (Fab), suggests that OKT9 and the Machupo virus GP1 share a binding site on the hTfR1 apical domain. The structural basis for this interaction presents a framework for the design and development of high-affinity, broadly acting agents targeting clade B NWMs. IMPORTANCE Pathogenic clade B NWMs cause grave infectious diseases, the South American hemorrhagic fevers. Their etiological agents are Junin (JUNV), Guanarito (GTOV), Sabiá (SABV), Machupo (MACV), Chapare (CHAV), and a new Sabiá-like (SABV-L) virus recently identified in Brazil. These are priority A pathogens due to their high infectivity and mortality, their potential for person-to-person transmission, and the limited availability of effective therapeutics and vaccines to curb their effects. While low homology between surface glycoproteins of NWMs foils efforts to develop broadly neutralizing therapies targeting NWMs, this work provides structural evidence that OKT9, a monoclonal antibody targeting a single NWM glycoprotein binding site on hTfR1, can efficiently prevent their entry into cells.

Second-Generation Live-Attenuated Candid#1 Vaccine Virus Resists Reversion and Protects against Lethal Junín Virus Infection in Guinea Pigs.

Live-attenuated virus vaccines are highly effective in preventing viral disease but carry intrinsic risks of residual virulence and reversion to pathogenicity. The classically derived Candid#1 virus protects seasonal field workers in Argentina against zoonotic infection by Junín virus (JUNV) but is not approved in the United States, in part due to the potential for reversion at the attenuating locus, a phenylalanine-to-isoleucine substitution at position 427 in the GP2 subunit of the GPC envelope glycoprotein. Previously, we demonstrated facile reversion of recombinant Candid#1 (rCan) in cell culture and identified an epistatic interaction between the attenuating I427 and a secondary K33S mutation in the stable signal peptide (SSP) subunit of GPC that imposes an evolutionary barrier to reversion. The magnitude of this genetic barrier is manifest in our repeated failures to rescue the hypothetical revertant virus. In this study, we show that K33S rCan is safe and attenuated in guinea pigs and capable of eliciting potent virus-neutralizing antibodies. Immunized animals are fully protected against lethal challenge with virulent JUNV. In addition, we employed a more permissive model of infection in neonatal mice to investigate genetic reversion. RNA sequence analysis of the recovered virus identified revertant viruses in pups inoculated with the parental rCan virus and none in mice receiving K33S rCan (P < 0.0001). Taken together, our findings support the further development of K33S rCan as a safe second-generation JUNV vaccine. IMPORTANCE Our most successful vaccines comprise weakened strains of virus that initiate a limited and benign infection in immunized persons. The live-attenuated Candid#1 strain of Junín virus (JUNV) was developed to protect field workers in Argentina from rodent-borne hemorrhagic fever but is not licensed in the United States, in part due to the likelihood of genetic reversion to virulence. A single-amino-acid change in the GPC envelope glycoprotein of the virus is responsible for attenuation, and a single nucleotide change may regenerate the pathogenic virus. Here, we take advantage of a unique genetic interaction between GPC subunits to design a mutant Candid#1 virus that establishes an evolutionary barrier to reversion. The mutant virus (K33S rCan) is fully attenuated and protects immunized guinea pigs against lethal JUNV infection. We find no instances of reversion in mice inoculated with K33S rCan. This work supports the further development of K33S rCan as a second-generation JUNV vaccine.

Therapy for Argentine hemorrhagic fever in nonhuman primates with a humanized monoclonal antibody.

The COVID-19 pandemic has reemphasized the need to identify safe and scalable therapeutics to slow or reverse symptoms of disease caused by newly emerging and reemerging viral pathogens. Recent clinical successes of monoclonal antibodies (mAbs) in therapy for viral infections demonstrate that mAbs offer a solution for these emerging biothreats. We have explored this with respect to Junin virus (JUNV), an arenavirus classified as a category A high-priority agent and the causative agent of Argentine hemorrhagic fever (AHF). There are currently no Food and Drug Administration-approved drugs available for preventing or treating AHF, although immune plasma from convalescent patients is used routinely to treat active infections. However, immune plasma is severely limited in quantity, highly variable in quality, and poses significant safety risks including the transmission of transfusion-borne diseases. mAbs offer a highly specific and consistently potent alternative to immune plasma that can be manufactured at large scale. We previously described a chimeric mAb, cJ199, that provided protection in a guinea pig model of AHF. To adapt this mAb to a format more suitable for clinical use, we humanized the mAb (hu199) and evaluated it in a cynomolgus monkey model of AHF with two JUNV isolates, Romero and Espindola. While untreated control animals experienced 100% lethality, all animals treated with hu199 at 6 d postinoculation (dpi) survived, and 50% of animals treated at 8 dpi survived. mAbs like hu199 may offer a safer, scalable, and more reproducible alternative to immune plasma for rare viral diseases that have epidemic potential.

Glycoprotein N-linked glycans play a critical role in arenavirus pathogenicity.

Several arenaviruses cause hemorrhagic fevers in humans with high case fatality rates. A vaccine named Candid#1 is available only against Junin virus (JUNV) in Argentina. Specific N-linked glycans on the arenavirus surface glycoprotein (GP) mask important epitopes and help the virus evade antibody responses. However the role of GPC glycans in arenavirus pathogenicity is largely unclear. In a lethal animal model of hemorrhagic fever-causing Machupo virus (MACV) infection, we found that a chimeric MACV with the ectodomain of GPC from Candid#1 vaccine was partially attenuated. Interestingly, mutations resulting in acquisition of N-linked glycans at GPC N83 and N166 frequently occurred in late stages of the infection. These glycosylation sites are conserved in the GPC of wild-type MACV, indicating that this is a phenotypic reversion for the chimeric MACV to gain those glycans crucial for infection in vivo. Further studies indicated that the GPC mutant viruses with additional glycans became more resistant to neutralizing antibodies and more virulent in animals. On the other hand, disruption of these glycosylation sites on wild-type MACV GPC rendered the virus substantially attenuated in vivo and also more susceptible to antibody neutralization, while loss of these glycans did not affect virus growth in cultured cells. We also found that MACV lacking specific GPC glycans elicited higher levels of neutralizing antibodies against wild-type MACV. Our findings revealed the critical role of specific glycans on GPC in arenavirus pathogenicity and have important implications for rational design of vaccines against this group of hemorrhagic fever-causing viruses.

South American Hemorrhagic Fevers: A summary for clinicians.

OBJECTIVES: This article is one of a series on acute, severe diseases of humans caused by emerging viruses for which there are no or limited licensed medical countermeasures. We approached this summary on South American Hemorrhagic Fevers (SAHF) from a clinical perspective that focuses on pathogenesis, clinical features, and diagnostics with an emphasis on therapies and vaccines that have demonstrated potential for use in an emergency situation through their evaluation in nonhuman primates (NHPs) and/or in humans. METHODS: A standardized literature review was conducted on the clinical, pathological, vaccine, and treatment factors for SAHF as a group and for each individual virus/disease. RESULTS: We identified 2 treatments and 1 vaccine platform that have demonstrated potential benefit for treating or preventing infection in humans and 4 other potential treatments currently under investigation. CONCLUSION: We provide succinct summaries of these countermeasures to give the busy clinician a head start in reviewing the literature if faced with a patient with South American Hemorrhagic Fever. We also provide links to other authoritative sources of information.

Bivalent Junin & Machupo experimental vaccine based on alphavirus RNA replicon vector.

Junin (JUNV) and Machupo (MACV), two mammalian arenaviruses placed on the 2018 WHO watch list, are prevalent in South America causing Argentine and Bolivian hemorrhagic fevers (AHF and BHF), respectively. The live attenuated JUNV vaccine, Candid #1, significantly reduced the incidence of AHF. Vaccination induces neutralizing antibody (nAb) responses which effectively target GP1 (the viral attachment glycoprotein) pocket which accepts the tyrosine residue of the cellular receptor, human transferrin receptor 1 (TfR1). In spite of close genetic relationships between JUNV and MACV, variability in the GP1 receptor binding site (e.g., MACV GP1 loop 10) results in poor MACV neutralization by Candid #1-induced nAbs. Candid #1 is not recommended for vaccination of children younger than 15 years old (a growing "at risk" group), pregnant women, or other immunocompromised individuals. Candid #1's primary reliance on limited missense mutations for attenuation, genetic heterogeneity, and potential stability concerns complicate approval of this vaccine in the US. To address these issues, we applied alphavirus RNA replicon vector technology based on the human Venezuelan equine encephalitis vaccine (VEEV) TC-83 to generate replication restricted virus-like-particles vectors (VLPVs) simultaneously expressing cellular glycoprotein precursors (GPC) of both viruses, JUNV and MACV. Resulting JV&MV VLPVs were found safe and immunogenic in guinea pigs. Immunization with VLPVs induced humoral responses which correlated with complete protection against lethal disease after challenge with pathogenic strains of JUNV (Romero) and MACV (Carvallo).

Monoclonal Antibodies with Neutralizing Activity and Fc-Effector Functions against the Machupo Virus Glycoprotein.

Machupo virus (MACV), the causative agent of Bolivian hemorrhagic fever (BHF), is a New World arenavirus that was first isolated in Bolivia from a human spleen in 1963. Due to the lack of a specific vaccine or therapy, this virus is considered a major risk to public health and is classified as a category A priority pathogen by the U.S. National Institutes of Health. In this study, we used DNA vaccination against the MACV glycoprotein precursor complex (GPC) and murine hybridoma technology to generate 25 mouse monoclonal antibodies (MAbs) against the GPC of MACV. Out of 25 MAbs, five were found to have potent neutralization activity in vitro against a recombinant vesicular stomatitis virus expressing MACV GPC (VSV-MACV) as well as against authentic MACV. Furthermore, the five neutralizing MAbs exhibited strong antibody-dependent cellular cytotoxicity (ADCC) activity in a reporter assay. When tested in vivo using VSV-MACV in a Stat2-/- mouse model, three MAbs significantly lowered viral loads in the spleen. Our work provides valuable insights into epitopes targeted by neutralizing antibodies that could be potent targets for vaccines and therapeutics and shed light on the importance of effector functions in immunity against MACV.IMPORTANCE MACV infections are a significant public health concern and lead to high case fatality rates. No specific treatment or vaccine for MACV infections exist. However, cases of Junin virus infection, a related virus, can be treated with convalescent-phase serum. This indicates that a MAb-based therapy for MACV could be effective. Here, we describe several MAbs that neutralize MACV and could be used for this purpose.

Description and characterization of a novel live-attenuated tri-segmented Machupo virus in Guinea pigs.

BACKGROUND: Machupo virus (MACV) is a member of the Mammarenavirus genus, Arenaviridae family and is the etiologic agent of Bolivian hemorrhagic fever, which causes small outbreaks or sporadic cases. Several other arenaviruses in South America Junín virus (JUNV) in Argentina, Guanarito in Venezuela, Sabiá in Brazil and Chapare in Bolivia, also are responsible for human hemorrhagic fevers. Among these arenaviruses, JUNV caused thousands of human cases until 1991, when the live attenuated Candid #1 vaccine, was used. Other than Candid #1 vaccine, few other therapeutic or prophylactic treatments exist. Therefore, new strategies for production of safe countermeasures with broad spectrum activity are needed. FINDINGS: We tested a tri-segmented MACV, a potential vaccine candidate with several mutations, (r3MACV). In cell culture, r3MACV showed a 2-log reduction in infectious virus particle production and the MACV inhibition of INF-1ß was removed from the construct and produced by infected cells. Furthermore, in an animal experiment, r3MACV was able to protect 50% of guinea pigs from a simultaneous lethal JUNV challenge. Protected animals didn't display clinical symptoms nor were virus particles found in peripheral blood (day 14) or in organs (day 28 post-inoculation). The r3MACV provided a higher protection than the Candid #1 vaccine. CONCLUSIONS: The r3MACV provides a potential countermeasure against two South America arenaviruses responsible of human hemorrhagic fever.

Vaccine-elicited receptor-binding site antibodies neutralize two New World hemorrhagic fever arenaviruses.

While five arenaviruses cause human hemorrhagic fevers in the Western Hemisphere, only Junin virus (JUNV) has a vaccine. The GP1 subunit of their envelope glycoprotein binds transferrin receptor 1 (TfR1) using a surface that substantially varies in sequence among the viruses. As such, receptor-mimicking antibodies described to date are type-specific and lack the usual breadth associated with this mode of neutralization. Here we isolate, from the blood of a recipient of the live attenuated JUNV vaccine, two antibodies that cross-neutralize Machupo virus with varying efficiency. Structures of GP1-Fab complexes explain the basis for efficient cross-neutralization, which involves avoiding receptor mimicry and targeting a conserved epitope within the receptor-binding site (RBS). The viral RBS, despite its extensive sequence diversity, is therefore a target for cross-reactive antibodies with activity against New World arenaviruses of public health concern.

Epistastic Interactions within the Junín Virus Envelope Glycoprotein Complex Provide an Evolutionary Barrier to Reversion in the Live-Attenuated Candid#1 Vaccine.

The Candid#1 strain of Junín virus was developed using a conventional attenuation strategy of serial passage in nonhost animals and cultured cells. The live-attenuated Candid#1 vaccine is used in Argentina to protect at-risk individuals against Argentine hemorrhagic fever, but it has not been licensed in the United States. Recent studies have revealed that Candid#1 attenuation is entirely dependent on a phenylalanine-to-isoleucine substitution at position 427 in the fusion subunit (GP2) of the viral envelope glycoprotein complex (GPC), thereby raising concerns regarding the potential for reversion to virulence. In this study, we report the identification and characterization of an intragenic epistatic interaction between the attenuating F427I mutation in GP2 and a lysine-to-serine mutation at position 33 in the stable signal peptide (SSP) subunit of GPC, and we demonstrate the utility of this interaction in creating an evolutionary barrier against reversion to the pathogenic genotype. In the presence of the wild-type F427 residue, the K33S mutation abrogates the ability of ectopically expressed GPC to mediate membrane fusion at endosomal pH. This defect is rescued by the attenuating F427I mutation. We show that the recombinant Candid#1 (rCan) virus bearing K33S GPC is viable and retains its attenuated genotype under cell culture conditions that readily select for reversion in the parental rCan virus. If back-mutation to F427 offers an accessible pathway to increase fitness in rCan, reversion in K33S-GPC rCan is likely to be lethal. The epistatic interaction between K33S and F427I thus may minimize the likelihood of reversion and enhance safety in a second-generation Candid#1 vaccine.IMPORTANCE The live-attenuated Candid#1 vaccine strain of Junín virus is used to protect against Argentine hemorrhagic fever. Recent findings that a single missense mutation in the viral envelope glycoprotein complex (GPC) is responsible for attenuation raise the prospect of facile reversion to pathogenicity. Here, we characterize a genetic interaction between GPC subunits that evolutionarily forces retention of the attenuating mutation. By incorporating this secondary mutation into Candid#1 GPC, we hope to minimize the likelihood of reversion and enhance safety in a second-generation Candid#1 vaccine. A similar approach may guide the design of live-attenuated vaccines against Lassa and other arenaviral hemorrhagic fevers.

Protocol for the Production of a Vaccine Against Argentinian Hemorrhagic Fever.

Argentinian hemorrhagic Fever (AHF) is a febrile, acute disease caused by Junín virus (JUNV), a member of the Arenaviridae. Different approaches to obtain an effective antigen to prevent AHF using complete live or inactivated virus, as well as molecular constructs, have reached diverse development stages. This chapter refers to JUNV live attenuated vaccine strain Candid #1, currently used in Argentina to prevent AHF. A general standardized protocol used at Instituto Nacional de Enfermedades Virales Humanas (Pergamino, Pcia. Buenos Aires, Argentina) to manufacture the tissue culture derived Candid #1 vaccine is described. Intermediate stages like viral seeds and cell culture bank management, bulk vaccine manufacture, and finished product processing are also separately presented in terms of Production and Quality Control/Quality Assurance requirements, under the Adminitracion Nacional de Medicamentos, Alimentos y Tecnología Medica (ANMAT), the Argentine national regulatory authority.

[Stability of Candid#1 vaccine to prevent Argentine Hemorrhagic Fever]. / Estabilidad de la vacuna CANDID#1 para prevenir la Fiebre Hemorrágica Argentina.

Candid#1 is the first live attenuated vaccine produced and registered in Argentina. Produced since 2003 at the INEVH to prevent Argentine hemorrhagic fever, it is obtained by harvesting supernatants of diploid cells infected with an attenuated strain of Junin virus and subsequent lyophilization. The stability of this vaccine is crucial to ensure its effectiveness. This study was aimed to evaluate the stability of Candid#1 by exposing it to different time and temperature conditions. Three vaccine batches produced in 2003 were analysed according to the following storage scheme: (a) reconstituted vaccine at 2 °C to 8 °C for 8 days; (b) lyophilized vaccine at 2 °C to 8 °C for 6 months; (c) lyophilized vaccine at -18 °C to -20 °C for 10 years. The potency was assessed in Vero cell monolayers under agar. The results were: (a) reconstituted vaccine was stable between 2 °C and 8 °C for 8 days, (b) lyophilized vaccine was stable between 2 °C and 8 °C for 2 months, and (c) lyophilized vaccine was stable 9 years between -18 °C and -20 °C, keeping all its properties. These results allowed us to establish the following storage conditions and expiration times for Candid#1: (a) reconstituted: 12 hours between 2 °C and 8 °C, (b) lyophilized: 30 days between 2 °C and 8 °C and (c) lyophilized: 9 years between -18 °C and -20 °C. Based on our results, favorable changes were made in the conditions of transport, storage and distribution of the vaccine. Domestic freezers in strategically located centers were installed, allowing the preservation of vaccine stocks for distribution to secondary vaccination centers.

Estabilidad de la vacuna Candid#1 para prevenir la fiebre hemorrágica Argentina / Stability of Candid#1 vaccine to prevent Argentine Hemorrhagic Fever

Candid#1 es la primera vacuna a virus vivo atenuado producida y registrada en Argentina. Se produce en el INEVH desde 2003 para prevenir la fiebre hemorrágica argentina y se obtiene mediante cosecha de sobrenadantes de cultivos de células diploides infectadas con una cepa atenuada del virus Junín, formulación y posterior liofilización. Su estabilidad es crucial para asegurar su efectividad. El objetivo de este trabajo fue evaluar la estabilidad de Candid#1 exponiéndola a distintas condiciones de temperatura y tiempo. Tres lotes producidos en 2003 fueron sometidos al siguiente esquema de almacenamiento: (a) vacuna reconstituida conservada entre 2 °C y 8 °C durante 8 días, (b) vacuna liofilizada conservada entre 2 °C y 8 °C durante 6 meses, y (c) vacuna liofilizada conservada entre -18 °C y -20 °C durante 10 años. La potencia fue evaluada en monocapa de células Vero bajo agar. Los resultados fueron: (a) Candid#1 reconstituida fue estable 8 días entre 2 °C y 8 °C, (b) Candid#1 liofilizada fue estable 2 meses entre 2 °C y 8 °C y (c) Candid#1 liofilizada fue estable 9 años entre -18 °C y -20 °C manteniendo todos sus atributos. Estos resultados permitieron establecer las siguientes condiciones de almacenamiento: reconstituida 12 horas entre 2 °C y 8 °C, liofilizada 30 días entre 2 °C y 8 °C y 9 años entre -18 °C y -20 °C. A la luz de estos resultados, se generaron cambios favorables en las condiciones de transporte, almacenamiento y distribución de la vacuna. Se implementó la instalación de freezers domésticos en centros estratégicamente distribuidos, permitiendo preservar stocks de vacuna y distribuir las dosis necesarias a vacunatorios.

Candid#1 is the first live attenuated vaccine produced and registered in Argentina. Produced since 2003 at the INEVH to prevent Argentine hemorrhagic fever, it is obtained by harvesting supernatants of diploid cells infected with an attenuated strain of Junin virus and subsequent lyophilization. The stability of this vaccine is crucial to ensure its effectiveness. This study was aimed to evaluate the stability of Candid#1 by exposing it to different time and temperature conditions. Three vaccine batches produced in 2003 were analysed according to the following storage scheme: (a) reconstituted vaccine at 2 °C to 8°C for 8 days; (b) lyophilized vaccine at 2 °C to 8 °C for 6 months; (c) lyophilized vaccine at -18 °C to -20 °C for 10 years. The potency was assessed in Vero cell monolayers under agar. The results were: (a) reconstituted vaccine was stable between 2 °C and 8 °C for 8 days, (b) lyophilized vaccine was stable between 2 °C and 8 °C for 2 months, and (c) lyophilized vaccine was stable 9 years between -18 °C and -20 °C, keeping all its properties. These results allowed us to establish the following storage conditions and expiration times for Candid#1: (a) reconstituted: 12 hours between 2 °C and 8 °C, (b) lyophilized: 30 days between 2 °C and 8 °C and (c) lyophilized: 9 years between -18 °C and -20 °C. Based on our results, favorable changes were made in the conditions of transport, storage and distribution of the vaccine. Domestic freezers in strategically located centers were installed, allowing the preservation of vaccine stocks for distribution to secondary vaccination centers.

Encuesta poblacional sobre vacunación contra Fiebre Hemorrágica Argentina en zona endémica en la provincia de Santa Fe / Population survey on vaccination against Hemorrhagic Fever Argentina in endemic area in the province of Santa Fe

La fiebre Hemorrágica Argentina es una enfermedad viral aguda grave, de carácter sistémico, con duración de una a dos semanas, con cuadros clínicos de gravedad variable. Su agente transmisor es el virus Junín cuyo reservorio natural es el llamado ratón maicero y su zona endémica de distribución comprende sur de la provincia de Santa Fe, Córdoba, Noroeste de Buenos Aires y La Pampa, en Argentina. La primera medida preventiva para la enfermedad es la vacuna llamada Candid 1. Se realizó una encuesta poblacional para dimensionar en la zona de Venado Tuerto y localidades vecinas el alcance de la vacunación y estimar el conocimiento de la existencia de dicha vacuna, que no es de aplicación obligatoria.

Population survey on vaccination against Argentine Hemorrhagic fever in endemic area in the Province of Santa Fe. Argentine Hemorrhagic Fever is a serious systemic, acute viral disease, with a duration of one or two weeks and of variable gravity. Its transmitting agent is Junín Virus, whose natural reservoir is the corn mouse. Its endemic zone is the south of the province of Santa Fe, Cordoba, northwest of Buenos Aires and La Pampa; in Argentina. The first preventive measure for the disease is the vaccine called Candid 1. A population survey was carried out to measure the extent of vaccination and the knowledge of the vaccine, that is not of compulsory application.

Differential Immune Responses to New World and Old World Mammalian Arenaviruses.

Some New World (NW) and Old World (OW) mammalian arenaviruses are emerging, zoonotic viruses that can cause lethal hemorrhagic fever (HF) infections in humans. While these are closely related RNA viruses, the infected hosts appear to mount different types of immune responses against them. Lassa virus (LASV) infection, for example, results in suppressed immune function in progressive disease stage, whereas patients infected with Junín virus (JUNV) develop overt pro-inflammatory cytokine production. These viruses have also evolved different molecular strategies to evade host immune recognition and activation. This paper summarizes current progress in understanding the differential immune responses to pathogenic arenaviruses and how the information can be exploited toward the development of vaccines against them.

Absence of an N-Linked Glycosylation Motif in the Glycoprotein of the Live-Attenuated Argentine Hemorrhagic Fever Vaccine, Candid #1, Results in Its Improper Processing, and Reduced Surface Expression.

Junin virus (JUNV), a highly pathogenic New World arenavirus, is the causative agent of Argentine hemorrhagic fever (AHF). The live-attenuated Candid #1 (Can) strain currently serves as a vaccine for at-risk populations. We have previously shown that the Can glycoprotein (GPC) gene is the primary gene responsible for attenuation in a guinea pig model of AHF. However, the mechanisms through which the GPC contributes to the attenuation of the Can strain remain unknown. A more complete understanding of the mechanisms underlying the attenuation and immunogenicity of the Can strain will potentially allow for the rational design of additional safe and novel vaccines. Here, we provide a detailed comparison of both RNA and protein expression profiles between both inter- and intra-segment chimeric JUNV recombinant clones expressing combinations of genes from the Can strain and the pathogenic Romero (Rom) strain. The recombinant viruses that express Can GPC, which were shown to be attenuated in guinea pigs, displayed different RNA levels and GPC processing patterns as determined by Northern and Western blot analyses, respectively. Analysis of recombinant viruses containing amino acid substitutions selected at different mouse brain passages during the generation of Can revealed that altered Can GPC processing was primarily due to the T168A substitution within G1, which eliminates an N-linked glycosylation motif. Incorporation of the T168A substitution in the Rom GPC resulted in a Can-like processing pattern of Rom GPC. In addition, JUNV GPCs containing T168A substitution were retained within the endoplasmic reticulum (ER) and displayed significantly lower cell surface expression than wild-type Rom GPC. Interestingly, the reversion A168T in Can GPC significantly increased GPC expression at the cell surface. Our results demonstrate that recombinant JUNV (rJUNV) expressing Can GPC display markedly different protein expression and elevated genomic RNA expression when compared to viruses expressing Rom GPC. Additionally, our findings indicate that the N-linked glycosylation motif at amino acid positions 166-168 is important for trafficking of JUNV GPC to the cell surface, and the elimination of this motif interferes with the GPC release from the ER.

The Ectodomain of Glycoprotein from the Candid#1 Vaccine Strain of Junin Virus Rendered Machupo Virus Partially Attenuated in Mice Lacking IFN-αß/γ Receptor.

Machupo virus (MACV), a New World arenavirus, is the etiological agent of Bolivian hemorrhagic fever (BHF). Junin virus (JUNV), a close relative, causes Argentine hemorrhagic fever (AHF). Previously, we reported that a recombinant, chimeric MACV (rMACV/Cd#1-GPC) expressing glycoprotein from the Candid#1 (Cd#1) vaccine strain of JUNV is completely attenuated in a murine model and protects animals from lethal challenge with MACV. A rMACV with a single F438I substitution in the transmembrane domain (TMD) of GPC, which is equivalent to the F427I attenuating mutation in Cd#1 GPC, was attenuated in a murine model but genetically unstable. In addition, the TMD mutation alone was not sufficient to fully attenuate JUNV, indicating that other domains of the GPC may also contribute to the attenuation. To investigate the requirement of different domains of Cd#1 GPC for successful attenuation of MACV, we rescued several rMACVs expressing the ectodomain of GPC from Cd#1 either alone (MCg1), along with the TMD F438I substitution (MCg2), or with the TMD of Cd#1 (MCg3). All rMACVs exhibited similar growth curves in cultured cells. In mice, the MCg1 displayed significant reduction in lethality as compared with rMACV. The MCg1 was detected in brains and spleens of MCg1-infected mice and the infection was associated with tissue inflammation. On the other hand, all animals survived MCg2 and MCg3 infection without detectable levels of virus in various organs while producing neutralizing antibody against Cd#1. Overall our data suggest the indispensable role of each GPC domain in the full attenuation and immunogenicity of rMACV/Cd#1 GPC.