Coelho R, Kehl S, Periolo N, Biondo E, Alonso D, Perez C, et al. (2025) Virological characterization of a new isolated strain of Andes virus involved in the recent person-to-person transmission outbreak reported in Argentina. PLoS Negl Trop Dis 19(6): e0013205. https://doi.org/10.1371/journal.pntd.0013205
https://www.cell.com/cms/10.1016/j.cell.2026.01.030/asset/19303c45-3f83-4144-ba0a-415a9aa8db40/main.assets/fx1.jpg
Introduction
Andes virus (ANDV), a rodent-borne New World hantavirus, causes hantavirus cardiopulmonary syndrome (HCPS) in humans, with case fatality rates reaching 40%.
1 Hantaviruses are classified into Old World hantaviruses (OWHs), which cause hemorrhagic fever with renal syndrome (HFRS), and New World hantaviruses (NWHs), which cause the more frequently fatal HCPS. Human infection occurs primarily through the inhalation of aerosolized rodent saliva and excreta, although
human-to-human transmission through close contact has been documented for ANDV.
2,3,4 Despite the public health threat posed by ANDV, there are no approved vaccines or therapeutics.
Like other viruses of the family
Hantaviridae, ANDV is an enveloped virus enclosing a tri-segmented, negative-strand RNA genome.
5,6 The medium (M) segment encodes a glycoprotein precursor (GPC), which is co-translationally cleaved by signal peptidase in the endoplasmic reticulum (ER) into
two glycoproteins, Gn and Gc.7 These proteins form a metastable heterodimer at neutral pH, which then oligomerizes into
tetramers that form a curved lattice structure critical for virion assembly and budding.
8,9 Hantavirus assembly predominantly occurs at the Golgi apparatus or plasma membrane.
10,11,12 Following egress, ANDV binds to its
primary receptor, protocadherin-1 (PCDH1), for entry.
13 Following endocytosis, the acidic endosomal environment triggers conformational changes in the glycoprotein complex.
14 This leads to the release of the class II
viral fusion protein, Gc, from the Gn–Gc complex,
15 allowing Gc to mediate the fusion of the viral and endosomal membranes as it transitions from the metastable prefusion conformation to the stable
postfusion conformation.5,6Gn and Gc are the only surface-exposed glycoproteins on hantavirus virions and serve as the primary targets of the neutralizing antibody response.
16,17 Antibodies that cross-neutralize multiple hantaviruses have been reported,
18,19 and survivors of hantavirus infection often retain long-lasting neutralizing antibody titers.
20 Moreover, neutralizing antibody titers are a strong correlate of protection for both HFRS and HCPS patients.
21,22,23 These observations have spurred
extensive vaccine development efforts aimed at eliciting robust, long-lasting, and broadly neutralizing immune responses directed toward the Gn and Gc antigens.
24,25 Notably, recombinant vesicular stomatitis viruses (rVSVs) expressing ANDV
26 or Sin Nombre virus (SNV) glycoproteins
27 have shown efficacy in animal models. Additionally, an ANDV M-segment-based DNA vaccine
28 has demonstrated protective effects. These approaches induced cross-neutralizing antibodies and protected hamsters and rhesus macaques against lethal challenge with ANDV and SNV, respectively.
In parallel, high-throughput isolation and characterization of monoclonal antibodies have advanced our understanding of the humoral immune response to hantavirus infection.
29,30,31 Structural studies using X-ray crystallography and cryo-electron tomography (cryo-ET) have provided insights into the molecular mechanisms of antibody-mediated neutralization.
30,32,33,34,35 However, high-resolution structural information of antibodies in complex with Gn–Gc in their tetrameric or lattice-associated forms remains scarce.
Structural studies of authentic ANDV virions have been constrained by
biosafety level 3 requirements.36 Nevertheless, significant insights have been obtained from studies of apathogenic hantaviruses, like Tula virus (TULV). In addition, investigations of OWHs, including Puumala virus (PUUV) and Hantaan virus (HTNV), have elucidated the organization of the glycoprotein lattices and the conformational arrangement of Gn and Gc.
9,15,37,38,39,40 A model of the ANDV glycoprotein tetramer and lattice was subsequently generated by docking crystal structures of the ANDV Gn base tetramer and a single-chain construct of the Gn head and Gc ectodomain heterodimer in its prefusion conformation into the cryo-ET map of TULV.
8 In this model, Gn resides centrally, mediating tetramerization, whereas Gc is positioned peripherally along the edge of each tetramer, mediating tetramer-tetramer interactions. However, differences in tetramer architecture between OWHs and NWHs complicate direct extrapolation to ANDV,
41 and the absence of high-resolution structures of the tetramers in their native membrane environment continues to impede a comprehensive molecular understanding of ANDV architecture, function, and antibody-mediated inhibition.
Here, we demonstrate that the addition of an eVLP tag
42 to the ANDV-GPC substantially enhances the production of ANDV-virus-like particles (VLPs). Purification of these VLPs enabled single-particle cryo-electron microscopy (cryo-EM) studies, allowing us to determine the structure of individual ANDV Gn–Gc tetramers to 2.35 Å resolution, as well as dimers of ANDV Gn–Gc tetramers in three related flexing conformations to 3.2, 3.4, and 3.4 Å resolution. Furthermore, we resolved the structure of the antigen-binding fragment (Fab) of ADI-65534,
43 an engineered pan-hantavirus antibody, in complex with ANDV tetramers and dimers of tetramers, unexpectedly demonstrating that the full-length immunoglobulin G (IgG) is unable to cross-link neighboring tetramers. These structures reveal the molecular basis of Gn–Gc tetramer organization, lattice formation, acid-induced membrane fusion, and antibody-mediated neutralization. Additionally, immunogenicity studies of ANDV-VLPs as a self-amplifying replicon RNA (repRNA) vaccine candidate revealed improved binding—but equivalent neutralizing—antibody titers, suggesting a need to further characterize determinants of repRNA-encoded ANDV glycoprotein immunogenicity.
