Entry and Antibody-Mediated Immune Targeting of Zoonotic Arenaviruses

Context and challenges: Emerging zoonotic viruses can cross the species barrier from animals to humans and constitute a persistent and growing threat to global health. Among these, rodent-borne New World arenaviruses (NWAVs), which are endemic to South America, have been designated by the World Health Organization as 'Priority Pathogens' due to their ability to cause severe viral haemorrhagic fever (HF) with human case fatality rates reaching up to 25%. Although a live-attenuated vaccine for one NWAV, Junín virus (JUNV), has been made available to at-risk communities in Argentina (Candid-1), there are no internationally approved therapeutics for preventing or treating NWAV HF. The NWAV envelope-displayed glycoprotein complex (GP) is presented on the virus surface and facilitates entry of the virion into host-cells. The ability of the GP to interact with the human host-cell surface receptor, transferrin receptor 1 (hTfR1) during host-cell entry is a primary determinant of zoonosis. Despite the importance of this host-cell recognition event, the molecular determinants underlying GP recognition of both native and human TfR1 for genetically diverse HF-causing NW GP1s remain undefined. Further, while the NWAV GP is the target for neutralising antibodies, information about the epitopes that can be targeted to achieve virus neutralisation and protection following vaccination and infection remains limited. Such information is essential for guiding efforts to rationally design immunogens that protect (and cross-protect) against NWAV infection and would provide a fundamental template for evaluating and improving vaccine designs. Aims: Our Project has two primary Aims. Aim-1. We will engineer a recombinant NWAV GP ectodomain trimer exhibiting native-like functional and immunological properties. We will further combine high-resolution structural methods with biophysical and cellular assays to dissect the molecular specificity underlying TfR1-mediated entry of NW arenaviruses into human cells. Such information is essential for identifying amino acid signatures that dictate the zoonotic potential of NWAVs. Aim-2. We will reveal the mechanistic and structural basis for how the NWAV GP is targeted by neutralising antibodies. Using our unique access to human clinical samples from convalescent and vaccinated individuals, we will generate a library of monoclonal antibodies (mAbs) to identify disparate sites of immune vulnerability on the GP surface. We will further utilise state-of-the-art methods in cryoEM used in our laboratories, including electron microscopy with polyclonal epitope mapping (EMPEM), to gain a holistic understanding of the antigenic topography of the NWAV surface. Finally, we will generate and characterise neutralising antibodies against the GPs of emergent NWAVs for which there are currently no reported mAbs. Combined, this information will provide much-needed information about sites of vulnerability presented on the NWAV surface. This research has four primary applications and benefits: 1.     By determining the molecular specificity of arenavirus-host interactions, we will better understand the molecular-level code that determines whether existing and newly emerging NWAVs can zoonose. 2.     Increased knowledge about NWAV pathobiology arising from the Project will be essential for combating accidental or purposeful dissemination of NWAVs, thus increasing biosecurity. 3.     By harnessing molecular-level, mechanistic knowledge of antibody recognition, we will be better placed to develop broadly protective vaccines and therapeutic mAbs for use in NW arenavirus outbreaks. 4.   In an outbreak setting, our work will push forward state-of-the-art methodologies in structural biology and immunology, rendering us better placed to evaluate the immune response arising from infection and immunisation.