Machupo virus with mutations in the transmembrane domain and glycosylation sites is attenuated and immunogenic in animal models of Bolivian Hemorrhagic Fever

Several highly pathogenic mammarenaviruses cause severe hemorrhagic and neurologic disease in humans, for which vaccines and antivirals are limited or unavailable. New World (NW) mammarenavirus Machupo virus (MACV) infection causes Bolivian hemorrhagic fever in humans. We previously reported that the disruption of specific N-linked glycan sites on the glycoprotein (GPC) partially attenuate MACV in an IFN-αβ/γ receptor knockout mouse model. However, some capability to induce neurological pathology still remained. Highly pathogenic Junin virus (JUNV) is another NW arenavirus closely related to MACV. A F427I substitution in the GPC transmembrane domain (TMD) rendered JUNV attenuated in a lethal mouse model after intracranial inoculation. In this study, we rationally designed and rescued a MACV containing mutations at two glycosylation sites and the corresponding F438I substitution in GPC TMD. The MACV mutant is fully attenuated in IFN-αβ/γ receptor knockout mice and outbred guinea pigs. Furthermore, inoculation with this mutant MACV fully protected guinea pigs from wild-type MACV lethal challenge. Lastly, we found the GPC TMD F438I substitution greatly impaired MACV growth in neuronal cell lines of mouse and human origins. Our results highlight the critical roles of the glycans and the TMD on the GPC in arenavirus virulence, which informs the rational design of potential vaccine candidates for highly pathogenic arenaviruses.ImportanceFor arenaviruses, the only vaccine available is the live-attenuated Candid#1 vaccine, a JUNV vaccine approved in Argentina. We and others have found that the glycans on GPC and the F427 residue in the GPC TMD are important for virulence of JUNV. Nevertheless, mutating either of them is not sufficient for full and stable attenuation of JUNV. Using reverse genetics, we disrupted specific glycosylation sites on MACV GPC, and also introduced the corresponding F438I substitution in the GPC TMD. This MACV mutant is fully attenuated in two animal models and protects animals from lethal infection. Thus, our studies highlight the feasibility of rational attenuation of highly pathogenic arenaviruses for vaccine development. Another important finding from this study is that the F438I substitution in GPC TMD could substantially affect MACV replication in neurons. Future studies are warranted to elucidate the underlying mechanism and the implication of this mutation in arenavirus neural tropism.

Isolation of reconstructed functional ribonucleoprotein complexes of Machupo virus

Arenaviruses initiate infection by delivering a transcriptionally-competent ribonucleoprotein (RNP) complex into the cytosol of host cells. The arenavirus RNP consists of the large (L) RNA-dependent RNA polymerase (RdRP) bound to a nucleoprotein (NP)-encapsidated genomic RNA (vRNA) template. During transcription and replication, L must transiently displace RNA-bound NP to allow for template access into the RdRP active site. Concomitant with RNA replication new subunits of NP must be added to the nascent complementary RNAs (cRNA) as they emerge from the product exit channel of L. Interactions between L and NP thus play a central role in arenavirus gene expression. We developed an approach to purify recombinant functional RNPs from mammalian cells in culture using a synthetic vRNA, affinity-tagged L and NP. Negative-stain electron microscopy of purified RNPs revealed they adopt diverse and flexible structures, like RNPs of other Bunyavirales members. Monodisperse L-NP and trimeric ring-like NP complexes were also obtained in excess of flexible RNPs, suggesting that these heterodimeric structures self-assemble in the absence of suitable RNA templates. This work allows for further biochemical analysis of the interaction between arenavirus L and NP proteins and provides a framework for future high-resolution structural analyses of this replication-associated complex. IMPORTANCE Arenaviruses are rodent-borne pathogens that can cause severe disease in humans. All arenaviruses begin the infection cycle with delivery of the virus replication machinery into the cytoplasm of the host cell. This machinery consists of an RNA-dependent RNA polymerase – which copies the viral genome segments and synthesizes all four viral mRNAs – bound to the two nucleoprotein-encapsidated genomic RNAs. How this complex assembles remains a mystery. Our findings provide direct evidence for the formation of diverse intracellular arenavirus replication complexes using purification strategies for the polymerase, nucleoprotein, and genomic RNA of Machupo virus, which causes Bolivian hemorrhagic fever in humans. We demonstrate that the polymerase and nucleoprotein assemble into higher-order structures within cells, providing a model for the molecular events of arenavirus RNA synthesis. These findings provide a framework for probing the architectures and functions of the arenavirus replication machinery, and thus advancing antiviral strategies targeting this essential complex.

A high-throughput fluorescence polarization assay to discover inhibitors of arenavirus and coronavirus exoribonucleases

Viral exoribonucleases are uncommon in the world of RNA viruses. To date, this activity has been identified only in the Arenaviridae and the Coronaviridae families. These exoribonucleases play important but different roles in both families: for mammarenaviruses the exoribonuclease is involved in the suppression of the host immune response whereas for coronaviruses, exoribonuclease is both involved in a proofreading mechanism ensuring the genetic stability of viral genomes and participating to evasion of the host innate immunity. Because of their key roles, they constitute attractive targets for drug development. Here we present a high-throughput assay using fluorescence polarization to assess the viral exoribonuclease activity and its inhibition. We validate the assay using three different viral enzymes from SARS-CoV-2, lymphocytic choriomeningitis and Machupo viruses. The method is sensitive, robust, amenable to miniaturization (384 well plates) and allowed us to validate the proof-of-concept of the assay by screening a small focused compounds library (23 metal chelators). We also determined the IC50 of one inhibitor common to the three viruses.HighlightsArenaviridae and Coronaviridae viral families share an exoribonuclease activity of common evolutionary originArenaviridae and Coronaviridae exoribonuclease is an attractive target for drug developmentWe present a high-throughput assay in 384 well-plates for the screening of inhibitors using fluorescence polarizationWe validated the assay by screening of a focused library of 23 metal chelators against SARS-CoV-2, Lymphocytic Choriomeningitis virus and Machupo virus exoribonucleasesWe determined the IC50 by fluorescence polarization of one inhibitor common to the three viruses.

Validation of Сhoice of Laboratory Model for Preclinical Estimation of Medical Protectors Against Bolivian Hemorrhagic Fever

Th is review is dedicated to the peculiarities of pathogenesis of the experimental Bolivian hemorrhagic fever (BHF) – the disease, caused by Machupo virus (Arenaviridae family). Th e authors come to the conclusion that for carrying out preclinical researches of the medical means of protection (MMP) in vivo on small laboratory animals it is expedient to use guinea pigs, infected with a strain of Chicava or with a variant of Carvallo strain, adapted for these animals. Th e use of guinea pigs as small laboratory animals when studying pathogenesis of the disease caused by Machupo virus allows to carry out statistically reliable defi nition of quantitative indices of an experimental infection and to select medicines for the fi nal stage of preclinical assessment. As arenaviruses block the process of formation of interferon (IFN) in the infected organism, mice, defective by IFN formation, are the perspective animal models for the study of BHF pathogenesis and may be used for the study of attenuated variants of Machupo virus. Th e Javanese macaques (Macaca fascicularis) are the laboratory animals, modeling the pathogenetic manifestations of BHF in humans. Th ey can be used when carrying out the fi nal stages of preclinical assessment of means of medical protection

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

ABSTRACT 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.