Mice were either treated with 25mg/kg monoclonal antibody KL-AN-5E8 or CR9114 (sham) intraperitoneally one day prior to infection. epithelium and macrophages in the human lung. A proof-of-concept preclinical study showed treatment of these mice with a virus neutralizing antibody could block Andes orthohantavirus infection and dissemination. This pan-orthohantavirus model will facilitate progress in the fundamental understanding of pathogenesis and virus-host interactions for orthohantaviruses. Furthermore, it is an invaluable tool for preclinical evaluation of novel candidate pan-orthohantavirus intervention strategies. == Author summary == Orthohantaviruses are rodent-borne pathogens that can be transmitted from rodents to humans by inhalation of aerosolized virus-contaminated rodent excreta. While orthohantaviruses generally do not cause overt clinical signs in rodents, orthohantavirus infection can lead to severe disease with case fatality rates up to 40%. The pathogenesis of associated hemorrhagic fever with renal syndrome (HFRS) mainly in Europe and Asia and hantavirus cardiopulmonary syndrome (HCPS) in the Americas remains poorly understood. Particularly the understanding of the early steps of pathogenesis occurring in the human lungs is limited. In addition, assessment of the efficacy of cross-reactive anti-orthohantavirus antibodies is severely hampered by the limited availability ofin vivomodels that allow for replication of both HFRS- and HCPS-associated orthohantaviruses within the same animal model. Therefore, we present a human lung xenograft mouse model to study early events of orthohantavirus pathogenesis in the human lung. We demonstrated that multiple orthohantaviruses replicate inside the human lung xenografts, and characterized the tropism and host responses within these human lung xenografts. Also, as a proof-of-principle, we showed that the model can be utilized to assess the protective efficacy of an existing monoclonal antibody against Andes virus infection. Overall, this pan-orthohantavirus model allows for the study of orthohantavirus pathogenesis and will aid as a novel platform to test anti-orthohantavirus countermeasures. == Introduction == Orthohantaviruses are zoonotic viruses, which are naturally carried by rodents and can be transmitted to humans. Transmission primarily occurs via inhalation of aerosolized viruses present in rodent excreta, such as saliva, urine and feces. However, human-to-human transmission has been described for one of the orthohantavirus species, Andes orthohantavirus (ANDV) [1]. Upon initial infection in the human respiratory tract, these viruses can subsequently cause severe symptoms such as hantavirus cardiopulmonary syndrome (HCPS) and hemorrhagic fever with renal syndrome (HFRS). Although it is known from lethal HCPS infections in humans that pulmonary endothelial cells, epithelial cells and macrophages are infected during disease [2,3], there is a lack of understanding which cells of the respiratory tract are initially infected and which early events lead to systemic dissemination of orthohantaviruses to endothelial cells in different organs throughout Peucedanol the human body [4]. Knowledge on the early mechanisms of pathogenesis in the human lung is also currently limited due to scarce availability of acute clinical samples and relevant animal models that recapitulate infection in the human lung. Although orthohantaviruses enter the human body upon inhalation of virus particles, the role of respiratory epithelium during early stages of infection remains largely unexplored. The specific sites of initial infection and the molecular mechanisms that Peucedanol contribute to disease within the human respiratory tract remain unidentified. Currentin vitromodels are limited as they do not reflect the complexity of the human lung, which contains up Peucedanol to forty different cell types including but not limited to respiratory epithelial, endothelial, mesenchymal and smooth muscle cells [5]. Furthermore, a local microenvironment and circulation may be essential factors of the initial stages of pathogenesis of these predominantly endotheliotropic viruses. Although pathogenesis is poorly understood, a strong neutralizing antibody response is suggested to be an important factor for protection [6,7]. Recent advances have therefore been made to isolate neutralizing monoclonal antibodies targeting orthohantaviruses [811] and to characterize pan-orthohantavirus neutralizing human antibodies as potential therapeutics [12,13]. However, the ability to confirm the breadth of the neutralizing capacities of such antibodies is hampered by the lack of a pan-orthohantavirus Peucedanol preclinical animal model that allows replication and study of multiple orthohantaviruses in the same model. As a consequence, there are currently no HCPS and/or KIAA1819 HFRS vaccines or therapeutics approved by the United States Food and Drug Administration (FDA) or European Medicines Agency (EMA). Previous studies have attempted to develop relevant animal models to study human orthohantavirus infection. These studies were conducted in non-human primates (NHPs), (genetically-modified) laboratory mice, rats, hamsters and ferrets [1420]. However, only NHPs and (immunosuppressed) Syrian hamsters allow for.