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

Abstract

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 of 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.

Synthesis and Evaluation of [64Cu]Cu-NOTA-HFn for PET Imaging of Transferrin Receptor 1 Expression in Nasopharyngeal Carcinoma

“…The binding activity of HFn-FITC to C666-1 cells was confirmed by flow cytometric analysis (Figure d), which illustrated that HFn-FITC strongly bound to C666-1, demonstrating the ability of HFn to recognize C666-1 NPC cells. Besides, the binding could be inhibited by anti-CD71 as the binding site of the anti-CD71 we used is also located at the apical domain of CD71 and may partially overlap with the binding site of HFn to CD71 . The cell uptake assay indicated the specific cellular uptake of Cy5.5-HFn in vitro (Figure S3).…”

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

“…An aptamer targeting the apical domain of hTfR1 has also been described and found to be active in cell culture-based assays 58 . More recently, the murine antibody OKT9, also targeting the apical domain of hTfR1, was shown to inhibit pathogenic NWM entry in vitro 59 . The ch128.1/IgG1 mouse/human chimeric antibody, the OKT9 mouse antibody, the aptamer, and the Arenacept strategies all exploit the vulnerability of NWM reliance on hTfR1.…”

Recent developments on Junin virus, a causative agent for Argentine haemorrhagic fever

“…Nucleocapsid protein has the property to bind zinc and several other characteristics of the NP as found in other arenaviruses make it the richest virion protein. The cellular binding site for Clade B arenaviruses, which includes the Junin virus is transferrin receptor‐1 (TfR1) 40 . This receptor is crucial for viral replication and disease pathogenesis as it tends to make certain behavioural changes on macrophages, activated lymphocytes, and endothelial cells.…”

“…The cellular binding site for Clade B arenaviruses, which includes the Junin virus is transferrin receptor-1 (TfR1). 40 This receptor is crucial for viral replication and disease pathogenesis as it tends to make certain behavioural changes on macrophages, activated lymphocytes, and endothelial cells.…”