Characterization and Demonstration of the Value of a Lethal Mouse Model of Middle East Respiratory Syndrome Coronavirus Infection and Disease

Abstract

Characterized animal models are needed for studying the pathogenesis of and evaluating medical countermeasures for persisting Middle East respiratory syndrome-coronavirus (MERS-CoV) infections. Here, we further characterized a lethal transgenic mouse model of MERS-CoV infection and disease that globally expresses human CD26 (hCD26)/DPP4. The 50% infectious dose (ID 50 ) and lethal dose (LD 50 ) of virus were estimated to be <1 and 10 TCID 50 of MERS-CoV, respectively. Neutralizing antibody developed in the surviving mice from the ID 50 /LD 50 determinations, and all were fully immune to challenge with 100 LD 50 of MERS-CoV. The tissue distribution and histopathology in mice challenged with a potential working dose of 10 LD 50 of MERS-CoV were subsequently evaluated. In contrast to the overwhelming infection seen in the mice challenged with 10 5 LD 50 of MERS-CoV, we were able to recover infectious virus from these mice only infrequently, although quantitative reverse transcription-PCR (qRT-PCR) tests indicated early and persistent lung infection and delayed occurrence of brain infection. Persistent inflammatory infiltrates were seen in the lungs and brain stems at day 2 and day 6 after infection, respectively. While focal infiltrates were also noted in the liver, definite pathology was not seen in other tissues. Finally, using a receptor binding domain protein vaccine and a MERS-CoV fusion inhibitor, we demonstrated the value of this model for evaluating vaccines and antivirals against MERS. As outcomes of MERS-CoV infection in patients differ greatly, ranging from asymptomatic to overwhelming disease and death, having available both an infection model and a lethal model makes this transgenic mouse model relevant for advancing MERS research. IMPORTANCEFully characterized animal models are essential for studying pathogenesis and for preclinical screening of vaccines and drugs against MERS-CoV infection and disease. When given a high dose of MERS-CoV, our transgenic mice expressing hCD26/DPP4 viral receptor uniformly succumbed to death within 6 days, making it difficult to evaluate host responses to infection and disease. We further characterized this model by determining both the ID 50 and the LD 50 of MERS-CoV in order to establish both an infection model and a lethal model for MERS and followed this by investigating the antibody responses and immunity of the mice that survived MERS-CoV infection. Using the estimated LD 50 and ID 50 data, we dissected the kinetics of viral tissue distribution and pathology in mice challenged with 10 LD 50 of virus and utilized the model for preclinical evaluation of a vaccine and drug for treatment of MERS-CoV infection. This further-characterized transgenic mouse model will be useful for advancing MERS research.

Introduction of neutralizing immunogenicity index to the rational design of MERS coronavirus subunit vaccines

“…The wild type RBD vaccine was used as a control. The animal model for vaccine testing was the lethal transgenic mouse model expressing human DPP4 (hDPP4-Tg mice)4142. These mice were chosen for analysis because they are very susceptible to MERS-CoV and also because preventing disease in these mice is a stringent test of efficacy.…”

CD8 + T Cells and Macrophages Regulate Pathogenesis in a Mouse Model of Middle East Respiratory Syndrome

“…Experiments comparing viral RNA levels and depletion experiments during longer infection times will be analyzed in the future. Studies have shown that MERS-CoV is capable of spreading to other organs in infected mice when DPP4 is expressed under a strong ubiquitous promoter (23,25). The recent human case report suggests that MERS-CoV does not spread to any other organ during human infection (10), and we could find no evidence of MERS-CoV spread to the brain, kidney, or liver in C57B6/hDPP4 mice that were exposed to our highest dose of MERS-CoV and succumbed to fatal infection.…”

“…All three models of MERS-CoV infection in mice (22,25,26) have robust replication of MERS-CoV and, as such, have utility as a vehicle for testing of novel therapeutics or vaccines that inhibit MERS-CoV replication (25,26). However, they provide limited information about the natural pathogenesis of MERS-CoV infection in vivo (25).…”

“…T cells express DPP4, and DPP4 activity not accurately reproduce the authentic tissue-specific distribution and level of expression of endogenously expressed mDPP4 (reviewed in reference 24). Accordingly, this model is characterized by robust MERS-CoV replication and rapid lethal disease characterized by inflammation in the lung and brain (23,25). However, significant brain pathology has not been observed in MERS-CoV infection in humans (10).…”

“…However, they provide limited information about the natural pathogenesis of MERS-CoV infection in vivo (25).…”