Susceptibility of Well-Differentiated Airway Epithelial Cell Cultures from Domestic and Wild Animals to Severe Acute Respiratory Syndrome Coronavirus 2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally, and the number of worldwide cases continues to rise. The zoonotic origins of SARS-CoV-2 and its intermediate and potential spillback host reservoirs, besides humans, remain largely unknown. Because of ethical and experimental constraints and more important, to reduce and refine animal experimentation, we used our repository of well-differentiated airway epithelial cell (AEC) cultures from various domesticated and wildlife animal species to assess their susceptibility to SARS-CoV-2. We observed that SARS-CoV-2 replicated efficiently only in monkey and cat AEC culture models. Whole-genome sequencing of progeny viruses revealed no obvious signs of nucleotide transitions required for SARS-CoV-2 to productively infect monkey and cat AEC cultures. Our findings, together with previous reports of human-to-animal spillover events, warrant close surveillance to determine the potential role of cats, monkeys, and closely related species as spillback reservoirs for SARS-CoV-2.

Safe and effective two-in-one replicon-and-VLP minispike vaccine for COVID-19: Protection of mice after a single immunization.

Vaccines of outstanding efficiency, safety, and public acceptance are needed to halt the current SARS-CoV-2 pandemic. Concerns include potential side effects caused by the antigen itself and safety of viral DNA and RNA delivery vectors. The large SARS-CoV-2 spike (S) protein is the main target of current COVID-19 vaccine candidates but can induce non-neutralizing antibodies, which might cause vaccination-induced complications or enhancement of COVID-19 disease. Besides, encoding of a functional S in replication-competent virus vector vaccines may result in the emergence of viruses with altered or expanded tropism. Here, we have developed a safe single round rhabdovirus replicon vaccine platform for enhanced presentation of the S receptor-binding domain (RBD). Structure-guided design was employed to build a chimeric minispike comprising the globular RBD linked to a transmembrane stem-anchor sequence derived from rabies virus (RABV) glycoprotein (G). Vesicular stomatitis virus (VSV) and RABV replicons encoding the minispike not only allowed expression of the antigen at the cell surface but also incorporation into the envelope of secreted non-infectious particles, thus combining classic vector-driven antigen expression and particulate virus-like particle (VLP) presentation. A single dose of a prototype replicon vaccine complemented with VSV G, VSVΔG-minispike-eGFP (G), stimulated high titers of SARS-CoV-2 neutralizing antibodies in mice, equivalent to those found in COVID-19 patients, and protected transgenic K18-hACE2 mice from COVID-19-like disease. Homologous boost immunization further enhanced virus neutralizing activity. The results demonstrate that non-spreading rhabdovirus RNA replicons expressing minispike proteins represent effective and safe alternatives to vaccination approaches using replication-competent viruses and/or the entire S antigen.