== In vivo treatment with anti-S antibodies one day before infection protects huDPP4 mice from MERS-CoV infection. DPP4, neutralizing antibody, mouse model == Abstract == Traditional approaches to antimicrobial drug development are poorly suited to combatting the emergence of novel pathogens. Additionally, the lack of small animal models for these infections hinders the in vivo testing of potential therapeutics. Here we demonstrate the use of the VelocImmune technology (a mouse that expresses human antibody-variable heavy chains and light chains) alongside the VelociGene technology (which allows for rapid engineering of the mouse genome) to quickly develop and evaluate antibodies against an emerging viral disease. Specifically, we show the rapid generation of fully human neutralizing antibodies against the recently emerged Middle East Respiratory Syndrome coronavirus (MERS-CoV) and development of a humanized mouse model for MERS-CoV infection, which was used to demonstrate the therapeutic efficacy of the isolated antibodies. The VelocImmune and VelociGene technologies are powerful platforms that can be used to rapidly respond to emerging epidemics. Middle East respiratory syndrome coronavirus (MERS-CoV) was first isolated in September 2012 in the Kingdom of Saudi Arabia (1). Since then, more than 1,100 NMDI14 cases and more than 422 deaths have been reported in the Middle East (Iran, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, United Arab Emirates, and Yemen), in Africa (Algeria, Egypt and Tunisia), in Europe (Austria, France, Germany, Greece, Italy, the Netherlands, and the United Kingdom), in Asia (Malaysia and Philippines), and in the United States of America (www.who.int/csr/disease/coronavirus_infections/archive_updates/en/) as of April 29, 2015. Clinical features of MERS-CoV infection in humans range from an asymptomatic infection to very severe pneumonia, with potential development of acute respiratory distress syndrome, shock, and multiorgan failure, resulting in death (2). MERS-CoV is a betacoronavirus related to the severe acute respiratory syndrome coronavirus (SARS-CoV). Both viruses cause severe respiratory tract infections and are associated with high mortality rates. Although human-to-human transmission of MERS-CoV has been reported (3), the rate of transmission appears to be low (4,5). Recent studies have suggested that dromedary camels are involved in the zoonotic transmission of MERS-CoV; analyses of camel sera indicate MERS-CoV seropositivity in camels throughout the Middle East and Africa, suggesting MERS-CoV maintenance in camel populations (68). The MERS-CoV virion is decorated with a class I transmembrane envelope protein named Spike (S). S protein forms a homo-trimer and mediates binding to host receptors, membrane fusion, and entry into susceptible cells (9); consistent with this, MERS-CoV NMDI14 S protein is a major target for neutralizing antibodies (10). The receptor for MERS-CoV was identified as dipeptidyl peptidase 4 (DDP4, also known as CD26) (11), a protein with diverse functions in glucose homeostasis, T-cell activation, neurotransmitter function, and modulation of cardiac signaling (12). DPP4 is expressed in a variety of cell types, NMDI14 including endothelial cells, hepatocytes, enterocytes, and cells of the renal glomeruli and proximal tubules (12). Moreover, DPP4 recognition is mediated by the receptor-binding doman (RBD, amino acids E367Y606), and the structural basis for this interaction was recently delineated (13,14). Currently, there are no approved treatments or vaccines to treat or prevent MERS-CoV infections. Type I IFN and ribavirin have been reported to ameliorate disease in infected macaques (15), and small molecules targeting diverse intracellular pathways have been shown to inhibit MERS-CoV in vitro (1618). Furthermore, experimental immunogens can elicit an antiMERS-CoV response (19,20). However, no MERS-CoV targeting therapeutic has been demonstrated to function in vivo, partly because of limited NMDI14 small animal models of infection (2123). MERS-CoV does not natively replicate in wild-type mice. Two mouse models have been developed. In the first, a modified adenovirus expressing huDPP4 is administered intranasally to mice leading to huDPP4 expression in all cells of the lung, not just those that natively express DPP4 (21). SEDC In this model, mice show transient huDPP4 expression and mild lung disease. In the second model (23), a transgenic mouse was produced that expresses huDPP4 in all cells of the body, which in not physiologically relevant. In this NMDI14 model, MERS-CoV infection leads to high levels of viral RNA and inflammation in the lungs, but also significant inflammation and viral RNA in the brains of infected mice. However, no previous reports have documented tropism of MERS-CoV to the brains of an infected.