Alternative hosts and model animals: The severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) pandemic may have originated in bats, but how it made its way into humans is unknown. Because of its zoonotic origins, SARS-CoV-2 is unlikely to exclusively infect humans, so it would be valuable to have an animal model for drug and vaccine development. Shi et al. tested ferrets, as well as livestock and companion animals of humans, for their susceptibility to SARS-CoV-2 (see the Perspective by Lakdawala and Menachery). The authors found that SARS-CoV-2 infects the upper respiratory tracts of ferrets but is poorly transmissible between individuals. In cats, the virus replicated in the nose and throat and caused inflammatory pathology deeper in the respiratory tract, and airborne transmission did occur between pairs of cats. Dogs appeared not to support viral replication well and had low susceptibility to the virus, and pigs, chickens, and ducks were not susceptible to SARS-CoV-2. Science , this issue p. 1016 ; see also p. 942

The unprecedented coronavirus disease 2019 (COVID-19) epidemic has created a worldwide public health emergency, and there is an urgent need to develop an effective vaccine to control this severe infectious disease. Here, we find that a single vaccination with a replication-defective human type 5 adenovirus encoding the SARS-CoV-2 spike protein (Ad5-nCoV) protect mice completely against mouse-adapted SARS-CoV-2 infection in the upper and lower respiratory tracts. Additionally, a single vaccination with Ad5-nCoV protects ferrets from wild-type SARS-CoV-2 infection in the upper respiratory tract. This study suggests that the mucosal vaccination may provide a desirable protective efficacy and this delivery mode is worth further investigation in human clinical trials.

Rabies virus (RABV) invades the central nervous system and nearly always causes fatal disease in humans. How RABV interacts with host neuron membrane receptors to become internalized and cause rabid symptoms is not yet fully understood. Here, we identified a novel receptor of RABV, which RABV uses to infect neurons. We found that metabotropic glutamate receptor subtype 2 (mGluR2), a member of the G protein-coupled receptor family that is abundant in the central nervous system, directly interacts with RABV glycoprotein to mediate virus entry. RABV infection was drastically decreased after mGluR2 siRNA knock-down in cells. Antibodies to mGluR2 blocked RABV infection in cells in vitro. Moreover, mGluR2 ectodomain soluble protein neutralized the infectivity of RABV cell-adapted strains and a street strain in cells (in vitro) and in mice (in vivo). We further found that RABV and mGluR2 are internalized into cells and transported to early and late endosomes together. These results suggest that mGluR2 is a functional cellular entry receptor for RABV. Our findings may open a door to explore and understand the neuropathogenesis of rabies. Rabies virus (RABV) invades the central nervous system and nearly always causes fatal disease in humans. How RABV interacts with host neuron membrane receptors to become internalized and cause rabid symptoms is not yet fully understood. Here, we identified metabotropic glutamate receptor subtype 2 (mGluR2) as a novel cellular RABV receptor for host cell entry. mGluR2 directly interacts with RABV G protein and both proteins are internalized together. Our findings may open a door to explore the fundamental molecular mechanisms for rabies neuropathogenesis.

The spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an important target for vaccine and drug development. However, the rapid emergence of variant strains with mutated S proteins has rendered many treatments ineffective. Cleavage of the S protein by host proteases is essential for viral infection. Here, we discovered that the S protein contains two previously unidentified Cathepsin L (CTSL) cleavage sites (CS-1 and CS-2). Both sites are highly conserved among all known SARS-CoV-2 variants. Our structural studies revealed that CTSL cleavage promoted S to adopt receptor-binding domain (RBD) “up” activated conformations, facilitating receptor-binding and membrane fusion. We confirmed that CTSL cleavage is essential during infection of all emerged SARS-CoV-2 variants (including the recently emerged Omicron variant) by pseudovirus (PsV) infection experiment. Furthermore, we found CTSL-specific inhibitors not only blocked infection of PsV/live virus in cells but also reduced live virus infection of ex vivo lung tissues of both human donors and human ACE2-transgenic mice. Finally, we showed that two CTSL-specific inhibitors exhibited excellent In vivo effects to prevent live virus infection in human ACE2-transgenic mice. Our work demonstrated that inhibition of CTSL cleavage of SARS-CoV-2 S protein is a promising approach for the development of future mutation-resistant therapy.